1.11: Lymphatic and Immune Systems
- Apply the rules of medical language to build, analyze, spell, pronounce, abbreviate, and define terms as they relate to the lymph and immune systems
- Identify meanings of key word components of the lymph and immune systems
- Categorize diagnostic, therapeutic, procedural or anatomic terms related to the lymph and immune systems
- Use terms related to the lymph and immune systems
- Use terms related to the diseases and disorders of the lymph and immune systems
Word Parts for the Lymphatic and Immune Systems
Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Lymphatic and Immune Systems.
Introduction to the Lymphatic and Immune Systems
The lymphatic system is a series of vessels, ducts, and trunks that remove interstitial fluid from the tissues and return it the blood. The lymphatic vessels are also used to transport dietary lipids and cells of the immune system . Cells of the immune system, lymphocytes, all come from the hematopoietic system of the bone marrow. Primary lymphoid organs, the bone marrow and thymus gland, are the locations where lymphocytes proliferate and mature. Secondary lymphoid organs are the site in which mature lymphocytes congregate to mount immune responses. Many immune system cells use the lymphatic and circulatory systems for transport throughout the body to search for and then protect against pathogens.
This chapter begins by describing the anatomy and physiology of the lymphatic system, whose immune functions lead us into a discussion of the body’s multifaceted defenses, which together make up the immune system. Since the lymphatic system shares organs with a number of other body systems, the pathology discussed near the end of this chapter mainly focuses on disorders of the immune system.
Anatomy and Physiology of the Lymphatic System
The lymphatic vessels begin as open-ended capillaries, which feed into larger and larger lymphatic vessels, and eventually empty into the bloodstream. Along the way, the lymph travels through the lymph nodes, which are commonly found near the groin, armpits, neck, chest, and abdomen. Humans have about 500–600 lymph nodes throughout the body (see Figure 11.1). Several organs and tissues that participate in immunity are also part of the lymphatic system.
Larger Lymphatic Vessels, Trunks, and Ducts
The lymphatic capillaries empty into larger lymphatic vessels, which are similar to veins in terms of their three-tunic structure and the presence of valves. These one-way valves are located fairly close to one another, and each one causes a bulge in the lymphatic vessel, giving the vessels a beaded appearance (see Figure 11.2).
In general, superficial lymphatics, follow the same routes as veins, whereas deep lymphatic vessels of the viscera generally follow the paths of arteries. The superficial and deep lymphatics eventually merge to form larger lymphatic structures known as lymphatic trunks . On the right side of the body, the right sides of the head, thorax, and right upper limb trunks drain lymph fluid into the right subclavian vein via the right lymphatic duct (see Figure 11.3). On the left side of the body, the trunks from the remaining portions of the body drain into the larger thoracic duct , which drains into the left subclavian vein. The thoracic duct itself begins just beneath the diaphragm in the cisterna chyli.
Primary Lymphoid Organs
The primary lymphoid organs are the bone marrow and thymus gland. The lymphoid organs are where lymphocytes mature, proliferate, and are selected, which enables them to attack pathogens without harming the cells of the body.
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Bone Marrow
- Recall that all blood cells, including lymphocytes, are formed in the red bone marrow. The B cell undergoes nearly all of its development in the red bone marrow, whereas the immature T cell, called a thymocyte , leaves the bone marrow and matures largely in the thymus gland .
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Thymus
- The thymus gland , where T cells mature, is a bilobed organ found in the space between the sternum and the aorta of the heart (see Figure 11.4). Connective tissue holds the lobes closely together but also separates them and forms a capsule .
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The loss of immune function with age is called immunosenescence. One major cause of age-related immune deficiencies is thymic involution.
- The shrinking of the thymus gland begins at birth at a rate of about three percent tissue loss per year. This shrinking continues until 35–45 years of age then the rate declines to about one percent loss per year for the rest of one’s life. At that pace, the total loss of thymic epithelial tissue and thymocytes would occur at about 120 years of age. So, in theory, 120 years could be the maximum life span.
Concept Check
- Do you remember what the suffix “-oid” means?
- Can you explain the term lymphoid ?
Secondary Lymphoid Organs
Lymphocytes develop and mature in the primary lymphoid organs, but they mount immune responses from the secondary lymphoid organs, which include the lymph nodes, spleen, and lymphoid nodules . A naïve lymphocyte is one that has left the primary organ, where it learned to function immunologically, and entered a secondary lymphoid organ where it waits to encounter an antigen against which it will mount a response.
Lymph Nodes
Lymph nodes function to remove debris and pathogens from the lymph, and are thus sometimes referred to as the “filters of the lymph” (see Figure 11.6). Any bacteria that infect the interstitial fluid are taken up by the lymphatic capillaries and transported to a regional lymph node. Dendritic cells and macrophages within this organ internalize and kill many of the pathogens that pass through, thereby removing them from the body. The lymph node is also the site of adaptive immune responses mediated by T cells, B cells, and accessory cells of the adaptive immune system.
Spleen
The spleen is a vascular organ that is somewhat fragile due to the absence of a capsule. It is about 12 cm long and is attached to the lateral border of the stomach. The spleen is sometimes called the “filter of the blood” because of its extensive vascularization and the presence of macrophages and dendritic cells that remove microbes and other materials from the blood, including dying red blood cells. The spleen also functions as the location of immune responses to blood-borne pathogens. (See Fig 11.6).
Lymphoid Nodules
The other lymphoid tissues, the lymphoid nodules , consist of a dense cluster of lymphocytes without a surrounding fibrous capsule. These nodules are located in the respiratory and digestive tracts, areas routinely exposed to environmental pathogens.
Tonsils are lymphoid nodules located along the inner surface of the pharynx and are important in developing immunity to oral pathogens (see Figure 11.7). The tonsil located at the back of the throat, the pharyngeal tonsil, is sometimes referred to as the adenoid when swollen. Such swelling is an indication of an active immune response to infection. Tonsils have deep grooves called crypts, which accumulate all sorts of materials taken into the body through eating and breathing and actually “encourage” pathogens to penetrate deep into the tonsillar tissues where they are eliminated. A major function of tonsils is to help children’s bodies recognize, destroy, and develop immunity to common environmental pathogens so that they will be protected in their later lives. Tonsils are often removed in children who have recurring throat infections since swollen palatine tonsils can interfere with breathing and/or swallowing.
Concept Check
Tonsils are named after their locations.
- Look at the figure above and determine which anatomical structure is closely associated with each set of tonsils and was therefore used to name the tonsils, for example, the lingual tonsils are named after the tongue (lingula).
- Can you tell which structures were used to name the palatine tonsils and the pharyngeal tonsils ?
Watch this video:
Media 11.2 Immune System, Part 1: Crash Course A&P #45 [Online video]. Copyright 2015 by CrashCourse .
Cells of the Innate Immune Response
Phagocytes: Macrophages and Neutrophils
A phagocyte is a cell that is able to surround and engulf a particle or cell, a process called phagocytosis . The phagocytes of the immune system engulf other particles or cells, either to clean an area of debris, old cells, or to kill pathogenic organisms such as bacteria. Macrophages, neutrophils, and dendritic cells are the major phagocytes of the immune system and are the body’s fast acting, front line immunological defense against organisms that have breached barrier defenses and have entered the body.
Macrophages not only participate in innate immune responses but have also evolved to cooperate with lymphocytes as part of the adaptive immune response. Macrophages exist in many tissues of the body, either freely roaming through connective tissues or fixed to reticular fibers within specific tissues such as lymph nodes. When pathogens breach the body’s barrier defenses, macrophages are the first line of defense.
A neutrophil is a phagocytic cell that is attracted via chemotaxis from the bloodstream to infected tissues. contains cytoplasmic granules, which in turn contain a variety of vasoactive mediators such as histamine. Whereas macrophages act like sentries, always on guard against infection, neutrophils can be thought of as military reinforcements that are called into a battle to hasten the destruction of the enemy.
A monocyte is a circulating precursor cell that differentiates into either a macrophage or dendritic cell , which can be rapidly attracted to areas of infection by signal molecules of inflammation.
 If apoptosis is induced before the virus has the ability to synthesize and assemble all its components, no infectious virus will be released from the cell, thus preventing further infection.
Concept Check
Do you know the difference between these terms?
- Intercellular
- Intracellular
- Interstitial
Cytokines and Chemokines
A cytokine is signaling molecule that allows cells to communicate with each other over short distances. Cytokines are secreted into the intercellular space, and the action of the cytokine induces the receiving cell to change its physiology. A chemokine is a soluble chemical mediator similar to cytokines except that its function is to attract cells (chemotaxis) from longer distances.
Early Induced Proteins
Early induced proteins are those that are not constitutively present in the body, but are made as they are needed early during the innate immune response. Interferons are an example of early induced proteins. Cells infected with viruses secrete interferons that travel to adjacent cells and induce them to make antiviral proteins. Thus, even though the initial cell is sacrificed, the surrounding cells are protected.
Inflammatory Response
The hallmark of the innate immune response is inflammation . Stub a toe, cut a finger, or do any activity that causes tissue damage and inflammation will result, with its four characteristics: heat, redness, pain, and swelling (“loss of function” is sometimes mentioned as a fifth characteristic). It is important to note that inflammation does not have to be initiated by an infection, but can also be caused by tissue injuries. The release of damaged cellular contents into the site of injury is enough to stimulate the response, even in the absence of breaks in physical barriers that would allow pathogens to enter (by hitting your thumb with a hammer, for example). The inflammatory reaction brings in phagocytic cells to the damaged area to clear cellular debris and encourages the entry of clotting factors to set the stage for wound repair. Inflammation also facilitates the transport of antigen to lymph nodes by dendritic cells for the development of the adaptive immune response. (Fig. 11.8).
The above image summarizes the following events in the inflammatory response:
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- The released contents of injured cells stimulate the release of substances from mast cells including histamine, leukotrienes, and prostaglandins.
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- Histamine increases blood flow to the area by vasodilation, resulting in heat and redness . Histamine also increases the permeability of local capillaries, causing plasma to leak out and form interstitial fluid, resulting in swelling
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Leukotrienes
attract neutrophils from the blood by chemotaxis.
When local infections are severe, neutrophils are attracted to the sites of infections in large numbers, and as they phagocytose the pathogens and subsequently die, their accumulated cellular remains are visible as pus at the infection site.
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Leukotrienes
attract neutrophils from the blood by chemotaxis.
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- Prostaglandins cause vasodilation by relaxing vascular smooth muscle and are a major cause of the pain associated with inflammation. Nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen relieve pain by inhibiting prostaglandin production.
Concept Check
- Do you remember the suffix used to describe ‘inflammation’?
- Describe what causes the pain associated with inflammation.
Acute inflammation is a short-term innate immune response to an insult to the body. If the cause of the inflammation is not resolved, however, it can lead to chronic inflammation , which is associated with major tissue destruction and fibrosis.
Phase 3: Adaptive Immune Response
Watch this video:
Media 11.3 I mmune System, Part 2: Crash Course A&P #46 [Online video]. Copyright 2015 by CrashCourse .
Benefits of the Adaptive Immune Response
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Specificity
- The ability to specifically recognize and mount a response against almost any pathogen.
- Antigens, are recognized by receptors on the surface of B and T lymphocytes.
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Immunological Memory
- The first exposure to a pathogen is called a primary adaptive response.
- Symptoms of a first infection, called primary disease, are always relatively severe because it takes time for an initial adaptive immune response to a pathogen to become effective.
- Upon re-exposure to the same pathogen, a secondary adaptive immune response is generated, which is stronger and faster that the primary response, often eliminating the pathogen before it can cause damage or even symptoms.
- This secondary response is the basis of immunological memory , which gives us immunity.
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Self Recognition
- The ability to distinguish between self-antigens, those that are normally present in the body, and foreign antigens, those that might be on a potential pathogen.
- As T and B cells mature, there are mechanisms in place that prevent them from recognizing self-antigen, preventing a damaging immune response against the body. When these mechanisms fail, their breakdown leads to autoimmune diseases.
Lymphocytes: B Cells, T Cells, Plasma Cells
As stated above, lymphocytes are the primary cells of adaptive immune responses. These cells were introduced in the previous chapter and are summarized in the following table:
| CELL TYPE | DESCRIPTION AND DETAILS |
| Plasma Cell |
B cell (lymphocyte) that has been activated through exposure to an antigen and produces antibodies against that antigen (see the figure below)
There are 5 classes of antibodies (IgM, IgG, IgE, IgA, IgD), each functioning in different ways: IgM promotes chemotaxis, opsonization, and cell lysis, making it a very effective antibody against bacteria at early stages of a primary antibody response IgG is the one that crosses the placenta to protect the developing fetus from disease and exits the blood to the interstitial fluid to fight extracellular pathogens IgA is the only antibody to leave the interior of the body to protect body surfaces. IgA is also of importance to newborns, because this antibody is present in mother’s breast milk (colostrum), which serves to protect the infant IgE is associated with allergies and anaphylaxis |
| T Cell |
Different T cell types have the ability to either secrete soluble factors that communicate with other cells of the adaptive immune response or destroy cells infected with intracellular pathogen
|
| Memory Cell |
B cells and T cells formed during primary exposure to a pathogen (see the figure below)
Remain in the body for a long time after an infection and are able to mount a fast and effective immune response to a pathogen if it is encountered a second time, preventing the pathogen from causing disease |
Active Versus Passive Immunity
Immunity to pathogens, and the ability to control pathogen growth so that damage to the tissues of the body is limited, can be acquired by:
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The active development of an immune response in the infected individual.
or - The passive transfer of immune components from an immune individual to a non-immune one.
The downside to this passive immunity is the lack of the development of immunological memory. Once the antibodies are transferred, they are effective for only a limited time before they degrade.
| IMMUNITY | NATURAL | ARTIFICIAL |
|---|---|---|
| Active: resistance to pathogens acquired during an adaptive immune response | Result of memory cells formed during the adaptive immune response to a pathogen | Vaccine response. Through vaccination, one avoids the disease that results from the first exposure to the pathogen, yet reaps the benefits of protection from immunological memory. Vaccination was one of the major medical advances of the twentieth century and led to the eradication of smallpox and the control of many infectious diseases, including polio, measles, and whooping cough |
| Passive: transfer of antibodies from an immune person to a nonimmune person | Trans-placental antibodies from mother to fetus and maternal antibodies in breast milk protect newborn from infections | Immunoglobulin injections taken from animals previously exposed to a specific pathogen; a fast-acting method of temporarily protecting an individual who was possibly exposed to a pathogen |
Evasion of the Immune System by Pathogens
The immune system and pathogens are in a slow, evolutionary race to see who stays on top. Early childhood is a time when the body develops much of its immunological memory that protects it from diseases in adulthood. Pathogens have shown the ability, however, to evade the body’s immune responses, as described below.
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- Protective adaptations : It is important to keep in mind that although the immune system has evolved to be able to control many pathogens, pathogens themselves have evolved ways to evade the immune response. An example is in Mycobactrium tuberculosis , which has evolved a complex cell wall that is resistant to the digestive enzymes of the macrophages that ingest them, and thus persists in the host, causing the chronic disease tuberculosis.
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- Multiple strains : Bacteria sometimes evade immune responses because they exist in multiple strains, each having different surface antigens and requiring individual adaptive immune responses. One example is a small group of strains of S. aureus , called methicillin-resistant Staphylococcus aureus (MRSA) , which has become resistant to multiple antibiotics..
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- Antigen mutation: Because viruses’ surface molecules mutate continuously, viruses like influenza change enough each year that the flu vaccine for one year may not protect against the flu common to the next. New vaccine formulations must be derived for each flu season.
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- Genetic recombination: An example is the influenza virus, which contains gene segments that can recombine when two different viruses infect the same cell. Recombination between human and pig influenza viruses led to the 2010 H1N1 swine flu outbreak.
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- Immunosuppression : Pathogens, especially viruses, can produce immunosuppressive molecules that impair immune function.
Tissue Transplantation
Immunosuppressive drugs such as cyclosporine A have made transplants more successful, but tissue matching is still key. Family members, since they share a similar genetic background, are much more likely to share MHC molecules than unrelated individuals do.
One disease of transplantation occurs with bone marrow transplants, which are used to treat various diseases, including SCID and leukemia. Because the bone marrow cells being transplanted contain lymphocytes capable of mounting an immune response, and because the recipient’s immune response has been destroyed before receiving the transplant, the donor cells may attack the recipient tissues, causing graft-versus-host disease . Symptoms of this disease, which usually include a rash and damage to the liver and mucosa, are variable, and attempts have been made to moderate the disease by first removing mature T cells from the donor bone marrow before transplanting it.
Immune Responses Against Cancer
It is clear that with some cancers, like Kaposi’s sarcoma (see Figure 11.11), for example, that a healthy immune system does a good job at controlling them. This disease, which is caused by the human herpes virus, is almost never observed in individuals with strong immune systems. Other examples of cancers caused by viruses include liver cancer caused by the hepatitis B virus and cervical cancer caused by the human papilloma virus. As these last two viruses have vaccines available for them, getting vaccinated can help prevent these two types of cancer by stimulating the immune response.
On the other hand, as cancer cells are often able to divide and mutate rapidly, they may escape the immune response, just as certain pathogens such as HIV do.
There are three stages in the immune response to many cancers:
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- Elimination occurs when the immune response first develops toward tumor-specific antigens specific to the cancer and actively kills most cancer cells.
- Equilibrium is the period that follows, during which the remaining cancer cells are held in check.
- Escape of the immune response, and resulting disease, occurs because many cancers mutate and no longer express any specific antigens for the immune system to respond to.
This fact has led to extensive research in trying to develop ways to enhance the early immune response to completely eliminate the early cancer and thus prevent a later escape. One method that has shown some success is the use of cancer vaccines. These differ from other vaccines in that they are directed against the cells of one’s own body. Treated cancer cells are injected into cancer patients to enhance their anti-cancer immune response and thereby prolong survival. The immune system has the capability to detect these cancer cells and proliferate faster than the cancer cells do, thus overwhelming the cancer in a similar way as they do for viruses. Cancer vaccines are being developed for malignant melanoma and renal (kidney) cell carcinoma.
Immune Responses and Stress
In order to protect the entire body from infection, the immune system is required to interact with other organ systems, sometimes in complex ways. For example, hormones such as cortisol (naturally produced by the adrenal cortex) and prednisone (synthetic) are well known for their abilities to suppress T cell immune mechanisms, hence, their prominent use in medicine as long-term, anti-inflammatory drugs.
One well-established interaction of the immune, nervous, and endocrine systems is the effect of stress on immune health. In the human vertebrate evolutionary past, stress was associated with the fight-or-flight response, largely mediated by the central nervous system and the adrenal medulla. This stress was necessary for survival since fighting or fleeing usually resolved the problem in one way or another. It has been found that short-term stress diverts the body’s resources towards enhancing innate immune responses. This has the ability to act fast and would seem to help the body prepare better for possible infections associated with the trauma that may result from a fight-or-flight exchange.
On the other hand, there are no physical actions to resolve most modern day stresses, including short-term stressors like taking examinations and long-term stressors such as being unemployed or losing a spouse. The effect of stress can be felt by nearly every organ system, and the immune system is no exception (see Table 11.3) . Chronic stress, unlike short-term stress, may inhibit immune responses even in otherwise healthy adults. The suppression of both innate and adaptive immune responses is clearly associated with increases in some diseases.
| SYSTEM | STRESS-RELATED ILLNESS |
|---|---|
| Integumentary system | Acne, skin rashes, irritation |
| Nervous system | Headaches, depression, anxiety, irritability, loss of appetite, lack of motivation, reduced mental performance |
| Muscular and skeletal systems | Muscle and joint pain, neck and shoulder pain |
| Circulatory system | Increased heart rate, hypertension, increased probability of heart attacks |
| Digestive system | Indigestion, heartburn, stomach pain, nausea, diarrhea, constipation, weight gain or loss |
| Immune system | Depressed ability to fight infections |
| Male reproductive system | Lowered sperm production, impotence, reduced sexual desire |
| Female reproductive system | Irregular menstrual cycle, reduced sexual desire |
Anatomy Labeling Activity
Medical Terms not Easily Broken into Word Parts
Lymphatic and Immune System Abbreviations
Diseases and Disorders of the Lymphatic and Immune Systems
The immune response can be under-reactive or over-reactive, leading to a state of disease. The factors that maintain immunological homeostasis are complex and incompletely understood.
Underactive Immune System: Immunodeficiencies
Suppressed immunity can result from inherited genetic defects or by acquiring viruses (Betts, et al., 2021 ) .
Inherited Immunodeficiencies/SCID
While many inherited immunodeficiencies exist, the most serious is severe combined immunodeficiency disease (SCID) . This complex disease is caused by many different genetic defects which result in impaired B cell and T cell arms of the adaptive immune response. Children with this disease usually die of opportunistic infections within their first year of life unless they receive a bone marrow transplant. Such a procedure had not yet been perfected for David Vetter, the “boy in the bubble,” who was treated for SCID by having to live in a sterile plastic cocoon for the 12 years before his death from infection in 1984. One of the features that make bone marrow transplants work as well as they do is the proliferative capability of hematopoietic stem cells of the bone marrow. Only a small amount of bone marrow from a healthy donor is given intravenously to the recipient. It finds its own way to the bone where it populates it, eventually reconstituting the patient’s immune system, which is usually destroyed beforehand by treatment with radiation or chemotherapeutic drugs (Betts, et al., 2021 ) .
New treatments for SCID using gene therapy, inserting nondefective genes into cells taken from the patient and giving them back, have the advantage of not needing the tissue match required for standard transplants. Although not a standard treatment, this approach holds promise, especially for those in whom standard bone marrow transplantation has failed (Betts, et al., 2021 ) .
Acquired Immunodeficiency/HIV and AIDS
Although many viruses cause suppression of the immune system, only HIV wipes it out completely. HIV is transmitted through semen, vaginal fluids, and blood, and can be caught by risky sexual behaviors and the sharing of needles by intravenous drug users. There are sometimes, but not always, flu-like symptoms in the first 1 to 2 weeks after infection. The presence of anti-HIV antibodies indicates a positive HIV test. Because seroconversion takes different lengths of time in different individuals, multiple HIV tests are given months apart to confirm or eliminate the possibility of infection.
After seroconversion, the amount of virus circulating in the blood drops and stays at a low level for several years. During this time, the levels of CD4 T cells decline steadily, until at some point, the immune response is so weak that opportunistic disease and eventually death result.
Treatment for the disease consists of drugs that target virally encoded proteins that are necessary for viral replication but are absent from normal human cells. By targeting the virus itself and sparing the cells, this approach has been successful in significantly prolonging the lives of HIV-positive individuals (Betts, et al., 2021 ) .
Overactive Immune System: Hypersensitivities and Autoimmune Diseases
Hypersensitivities
Over-reactive immune responses include the hypersensitivities: allergies and inflammatory responses to nonpathogenic environmental substances (Betts, et al., 2021 ) . The table below compares different hypersensitivities.
| TYPE OF HYPERSENSITIVITY | DETAILS AND EXPLANATION |
| Type I |
|
| Type II |
|
| Type III |
|
| Type IV |
|
Autoimmune Responses
The worst cases of the immune system over-reacting are autoimmune diseases in which the immune systems begin to attack cells of the patient’s own body, causing chronic inflammation and significant damage. The trigger for these diseases is often unknown, although environmental and genetic factors are likely involved. Treatments are usually based on resolving the symptoms using immunosuppressive and anti-inflammatory drugs. Figure 11.12 below provides two examples of autoimmune diseases: rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) (Betts, et al., 2021 ) .
Overall, there are more than 80 different autoimmune diseases, which are a significant health problem in the elderly. Table 14.5 below lists several of the most common autoimmune diseases, the antigens that are targeted (autoantigen or “self” antigen), and the resulting tissue damage (Betts, et al., 2021 ) .
| DISEASE | AUTOANTIGEN | SYMPTOMS |
|---|---|---|
| Celiac disease | Tissue transglutaminase | Damage to small intestine |
| Diabetes mellitus type I | Beta cells of pancreas | Low insulin production; inability to regulate serum glucose |
| Graves’ disease | Thyroid-stimulating hormone receptor (antibody blocks receptor) | Hyperthyroidism |
| Hashimoto’s thyroiditis | Thyroid-stimulating hormone receptor (antibody mimics hormone and stimulates receptor) | Hypothyroidism |
| Lupus erythematosus | Nuclear DNA and proteins | Damage of many body systems |
| Myasthenia gravis | Acetylcholine receptor in neuromuscular junctions | Debilitating muscle weakness |
| Rheumatoid arthritis | Joint capsule antigens | Chronic inflammation of joints |
Lymphoma
Lymphoma was briefly discussed in the previous chapter.
Medical Terms in Context
Medical Specialties and Procedures Related to the Lymphatic and Immune Systems
Clinical Immunology/Allergy is a medical specialty that diagnoses and treats diseases of the immune system (American Academy of Allergy Asthma and Immunology, 2021). For more information, please visit the ‘ About Careers in Allergy/Immunology ‘ page from the American Academy of Allergy Asthma and Immunology.
Skin testing (for allergies) is done by a clinical immunologist/allergist to identify allergens in Type I hypersensitivity. In skin testing, allergen extracts are injected into the epidermis, and a positive result of the wheal and flare response usually occurs within 30 minutes. The soft center is due to fluid leaking from the blood vessels and the redness is caused by the increased blood flow to the area that results from the dilation of local blood vessels at the site (Betts, et al., 2021 ) .
Test Yourself
References
American Academy of Allergy Asthma and Immunology . (2021). About Careers in Allergy/Immunology . https://www.aaaai.org/Professional-Education/careers-in-a-i
[CrashCourse]. (2015, November 30). Lymphatic system: Crash course A&P #44 [Video]. YouTube. https://youtu.be/I7orwMgTQ5I
[CrashCourse]. (2015, December 8). Immune system, part 1: Crash course A&P #45 [Video]. YouTube. https://youtu.be/GIJK3dwCWCw
[CrashCourse]. (2015, December 14). I mmune system, part 2: Crash course A&P #46 [Video]. YouTube. https://youtu.be/2DFN4IBZ3rI
Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax ), by Betts, et al. and is used under a a CC BY 4.0 international license . Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .


10.2: The Cell Cycle
Skills to Develop
- Describe the three stages of interphase
- Discuss the behavior of chromosomes during karyokinesis
- Explain how the cytoplasmic content is divided during cytokinesis
- Define the quiescent G 0 phase
The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produces two identical (clone) cells. The cell cycle has two major phases: interphase and the mitotic phase (Figure \(\PageIndex{1}\)). During interphase , the cell grows and DNA is replicated. During the mitotic phase , the replicated DNA and cytoplasmic contents are separated, and the cell divides.
Interphase
During interphase, the cell undergoes normal growth processes while also preparing for cell division. In order for a cell to move from interphase into the mitotic phase, many internal and external conditions must be met. The three stages of interphase are called G 1 , S, and G 2 .
G 1 Phase (First Gap)
The first stage of interphase is called the G 1 phase (first gap) because, from a microscopic aspect, little change is visible. However, during the G 1 stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus.
S Phase (Synthesis of DNA)
Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration. In the S phase , DNA replication can proceed through the mechanisms that result in the formation of identical pairs of DNA molecules—sister chromatids—that are firmly attached to the centromeric region. The centrosome is duplicated during the S phase. The two centrosomes will give rise to the mitotic spindle , the apparatus that orchestrates the movement of chromosomes during mitosis. At the center of each animal cell, the centrosomes of animal cells are associated with a pair of rod-like objects, the centrioles , which are at right angles to each other. Centrioles help organize cell division. Centrioles are not present in the centrosomes of other eukaryotic species, such as plants and most fungi.
G 2 Phase (Second Gap)
In the G 2 phase , the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation. Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase. There may be additional cell growth during G 2 . The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis.
The Mitotic Phase
The mitotic phase is a multistep process during which the duplicated chromosomes are aligned, separated, and move into two new, identical daughter cells. The first portion of the mitotic phase is called karyokinesis , or nuclear division. The second portion of the mitotic phase, called cytokinesis, is the physical separation of the cytoplasmic components into the two daughter cells.
Karyokinesis (Mitosis)
Karyokinesis, also known as mitosis , is divided into a series of phases—prophase, prometaphase, metaphase, anaphase, and telophase—that result in the division of the cell nucleus (Figure \(\PageIndex{2}\)). Karyokinesis is also called mitosis.
Exercise \(\PageIndex{1}\)
Which of the following is the correct order of events in mitosis?
- Sister chromatids line up at the metaphase plate. The kinetochore becomes attached to the mitotic spindle. The nucleus reforms and the cell divides. Cohesin proteins break down and the sister chromatids separate.
- The kinetochore becomes attached to the mitotic spindle. Cohesin proteins break down and the sister chromatids separate. Sister chromatids line up at the metaphase plate. The nucleus reforms and the cell divides.
- The kinetochore becomes attached to the cohesin proteins. Sister chromatids line up at the metaphase plate. The kinetochore breaks down and the sister chromatids separate. The nucleus reforms and the cell divides.
- The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins break down and the sister chromatids separate. The nucleus reforms and the cell divides.
- Answer
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D. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins break down and the sister chromatids separate. The nucleus reforms and the cell divides.
During prophase , the “first phase,” the nuclear envelope starts to dissociate into small vesicles, and the membranous organelles (such as the Golgi complex or Golgi apparatus, and endoplasmic reticulum), fragment and disperse toward the periphery of the cell. The nucleolus disappears (disperses). The centrosomes begin to move to opposite poles of the cell. Microtubules that will form the mitotic spindle extend between the centrosomes, pushing them farther apart as the microtubule fibers lengthen. The sister chromatids begin to coil more tightly with the aid of condensin proteins and become visible under a light microscope.
During prometaphase , the “first change phase,” many processes that were begun in prophase continue to advance. The remnants of the nuclear envelope fragment. The mitotic spindle continues to develop as more microtubules assemble and stretch across the length of the former nuclear area. Chromosomes become more condensed and discrete. Each sister chromatid develops a protein structure called a kinetochore in the centromeric region (Figure \(\PageIndex{3}\)). The proteins of the kinetochore attract and bind mitotic spindle microtubules. As the spindle microtubules extend from the centrosomes, some of these microtubules come into contact with and firmly bind to the kinetochores. Once a mitotic fiber attaches to a chromosome, the chromosome will be oriented until the kinetochores of sister chromatids face the opposite poles. Eventually, all the sister chromatids will be attached via their kinetochores to microtubules from opposing poles. Spindle microtubules that do not engage the chromosomes are called polar microtubules. These microtubules overlap each other midway between the two poles and contribute to cell elongation. Astral microtubules are located near the poles, aid in spindle orientation, and are required for the regulation of mitosis.
During metaphase , the “change phase,” all the chromosomes are aligned in a plane called the metaphase plate , or the equatorial plane, midway between the two poles of the cell. The sister chromatids are still tightly attached to each other by cohesin proteins. At this time, the chromosomes are maximally condensed.
During anaphase , the “upward phase,” the cohesin proteins degrade, and the sister chromatids separate at the centromere. Each chromatid, now called a chromosome, is pulled rapidly toward the centrosome to which its microtubule is attached. The cell becomes visibly elongated (oval shaped) as the polar microtubules slide against each other at the metaphase plate where they overlap.
During telophase , the “distance phase,” the chromosomes reach the opposite poles and begin to decondense (unravel), relaxing into a chromatin configuration. The mitotic spindles are depolymerized into tubulin monomers that will be used to assemble cytoskeletal components for each daughter cell. Nuclear envelopes form around the chromosomes, and nucleosomes appear within the nuclear area.
Cytokinesis
Cytokinesis , or “cell motion,” is the second main stage of the mitotic phase during which cell division is completed via the physical separation of the cytoplasmic components into two daughter cells. Division is not complete until the cell components have been apportioned and completely separated into the two daughter cells. Although the stages of mitosis are similar for most eukaryotes, the process of cytokinesis is quite different for eukaryotes that have cell walls, such as plant cells.
In cells such as animal cells that lack cell walls, cytokinesis follows the onset of anaphase. A contractile ring composed of actin filaments forms just inside the plasma membrane at the former metaphase plate. The actin filaments pull the equator of the cell inward, forming a fissure. This fissure, or “crack,” is called the cleavage furrow . The furrow deepens as the actin ring contracts, and eventually the membrane is cleaved in two (Figure \(\PageIndex{4}\)).
In plant cells, a new cell wall must form between the daughter cells. During interphase, the Golgi apparatus accumulates enzymes, structural proteins, and glucose molecules prior to breaking into vesicles and dispersing throughout the dividing cell. During telophase, these Golgi vesicles are transported on microtubules to form a phragmoplast (a vesicular structure) at the metaphase plate. There, the vesicles fuse and coalesce from the center toward the cell walls; this structure is called a cell plate . As more vesicles fuse, the cell plate enlarges until it merges with the cell walls at the periphery of the cell. Enzymes use the glucose that has accumulated between the membrane layers to build a new cell wall. The Golgi membranes become parts of the plasma membrane on either side of the new cell wall (Figure \(\PageIndex{4}\)).
G 0 Phase
Not all cells adhere to the classic cell cycle pattern in which a newly formed daughter cell immediately enters the preparatory phases of interphase, closely followed by the mitotic phase. Cells in G 0 phase are not actively preparing to divide. The cell is in a quiescent (inactive) stage that occurs when cells exit the cell cycle. Some cells enter G 0 temporarily until an external signal triggers the onset of G 1 . Other cells that never or rarely divide, such as mature cardiac muscle and nerve cells, remain in G 0 permanently.
Scientific Method Connection: Determine the Time Spent in Cell Cycle Stages
Problem: How long does a cell spend in interphase compared to each stage of mitosis?
Background: A prepared microscope slide of blastula cross-sections will show cells arrested in various stages of the cell cycle. It is not visually possible to separate the stages of interphase from each other, but the mitotic stages are readily identifiable. If 100 cells are examined, the number of cells in each identifiable cell cycle stage will give an estimate of the time it takes for the cell to complete that stage.
Problem Statement: Given the events included in all of interphase and those that take place in each stage of mitosis, estimate the length of each stage based on a 24-hour cell cycle. Before proceeding, state your hypothesis.
Test your hypothesis: Test your hypothesis by doing the following:
- Place a fixed and stained microscope slide of whitefish blastula cross-sections under the scanning objective of a light microscope.
- Locate and focus on one of the sections using the scanning objective of your microscope. Notice that the section is a circle composed of dozens of closely packed individual cells.
- Switch to the low-power objective and refocus. With this objective, individual cells are visible.
- Switch to the high-power objective and slowly move the slide left to right, and up and down to view all the cells in the section (Figure \(\PageIndex{5}\)). As you scan, you will notice that most of the cells are not undergoing mitosis but are in the interphase period of the cell cycle.
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Practice identifying the various stages of the cell cycle, using the drawings of the stages as a guide (Figure \(\PageIndex{2}\)).
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Once you are confident about your identification, begin to record the stage of each cell you encounter as you scan left to right, and top to bottom across the blastula section.
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Keep a tally of your observations and stop when you reach 100 cells identified.
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The larger the sample size (total number of cells counted), the more accurate the results. If possible, gather and record group data prior to calculating percentages and making estimates.
Record your observations: Make a table similar to the Table \(\PageIndex{1}\) in which you record your observations.
Table \(\PageIndex{1}\): Results of cell stage identification.
| Phase or Stage | Individual Totals | Group Totals | Percent |
|---|---|---|---|
| Interphase | |||
| Prophase | |||
| Metaphase | |||
| Anaphase | |||
| Telophase | |||
| Cytokinesis | |||
| Totals | 100 | 100 | 100 percent |
Analyze your data/report your results: To find the length of time whitefish blastula cells spend in each stage, multiply the percent (recorded as a decimal) by 24 hours. Make a table similar to the Table \(\PageIndex{2}\) to illustrate your data.
Table \(\PageIndex{2}\): Estimate of cell stage length.
| Phase or Stage | Percent (as Decimal) | Time in Hours |
|---|---|---|
| Interphase | ||
| Prophase | ||
| Metaphase | ||
| Anaphase | ||
| Telophase | ||
| Cytokinesis |
Draw a conclusion: Did your results support your estimated times? Were any of the outcomes unexpected? If so, discuss which events in that stage might contribute to the calculated time.
Summary
The cell cycle is an orderly sequence of events. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages. In eukaryotes, the cell cycle consists of a long preparatory period, called interphase. Interphase is divided into G 1 , S, and G 2 phases. The mitotic phase begins with karyokinesis (mitosis), which consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase. The final stage of the mitotic phase is cytokinesis, during which the cytoplasmic components of the daughter cells are separated either by an actin ring (animal cells) or by cell plate formation (plant cells).
Glossary
- anaphase
- stage of mitosis during which sister chromatids are separated from each other
- cell cycle
- ordered series of events involving cell growth and cell division that produces two new daughter cells
- cell plate
- structure formed during plant cell cytokinesis by Golgi vesicles, forming a temporary structure (phragmoplast) and fusing at the metaphase plate; ultimately leads to the formation of cell walls that separate the two daughter cells
- centriole
- rod-like structure constructed of microtubules at the center of each animal cell centrosome
- cleavage furrow
- constriction formed by an actin ring during cytokinesis in animal cells that leads to cytoplasmic division
- condensin
- proteins that help sister chromatids coil during prophase
- cytokinesis
- division of the cytoplasm following mitosis that forms two daughter cells.
- G 0 phase
- distinct from the G 1 phase of interphase; a cell in G 0 is not preparing to divide
- G 1 phase
- (also, first gap) first phase of interphase centered on cell growth during mitosis
- G 2 phase
- (also, second gap) third phase of interphase during which the cell undergoes final preparations for mitosis
- interphase
- period of the cell cycle leading up to mitosis; includes G 1 , S, and G 2 phases (the interim period between two consecutive cell divisions
- karyokinesis
- mitotic nuclear division
- kinetochore
- protein structure associated with the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase
- metaphase plate
- equatorial plane midway between the two poles of a cell where the chromosomes align during metaphase
- metaphase
- stage of mitosis during which chromosomes are aligned at the metaphase plate
- mitosis
- (also, karyokinesis) period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase
- mitotic phase
- period of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis
- mitotic spindle
- apparatus composed of microtubules that orchestrates the movement of chromosomes during mitosis
- prometaphase
- stage of mitosis during which the nuclear membrane breaks down and mitotic spindle fibers attach to kinetochores
- prophase
- stage of mitosis during which chromosomes condense and the mitotic spindle begins to form
- quiescent
- refers to a cell that is performing normal cell functions and has not initiated preparations for cell division
- S phase
- second, or synthesis, stage of interphase during which DNA replication occurs
- telophase
- stage of mitosis during which chromosomes arrive at opposite poles, decondense, and are surrounded by a new nuclear envelope


6: Metabolism and Cellular Respiration
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- 6.1: Introduction
- Virtually every task performed by living organisms requires energy. Energy is needed to perform heavy labor and exercise, but humans also use a great deal of energy while thinking, and even during sleep. In fact, the living cells of every organism constantly use energy. Nutrients and other molecules are imported, metabolized (broken down) and possibly synthesized into new molecules, modified if needed, transported around the cell, and may be distributed to the entire organism.
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- 6.2: Energy and Metabolism
- Cells perform the functions of life through various chemical reactions. A cell’s metabolism refers to the combination of chemical reactions that take place within it. Catabolic reactions break down complex chemicals into simpler ones and are associated with energy release. Anabolic processes build complex molecules out of simpler ones and require energy. In studying energy, the term system refers to the matter and environment involved in energy transfers.
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- 6.3: Glycolysis
- ATP functions as the energy currency for cells. It allows cells to store energy briefly and transport it within itself to support endergonic chemical reactions. The structure of ATP is that of an RNA nucleotide with three phosphate groups attached. As ATP is used for energy, a phosphate group is detached, and ADP is produced. Energy derived from glucose catabolism is used to recharge ADP into ATP. Glycolysis is the first pathway used in the breakdown of glucose to extract energy.
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- 6.4: Citric Acid Cycle and Oxidative Phosphorylation
- The citric acid cycle is a series of chemical reactions that removes high-energy electrons and uses them in the electron transport chain to generate ATP. One molecule of ATP (or an equivalent) is produced per each turn of the cycle. The electron transport chain is the portion of aerobic respiration that uses free oxygen as the final electron acceptor for electrons removed from the intermediate compounds in glucose catabolism.
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- 6.5: Fermentation
- If NADH cannot be metabolized through aerobic respiration, another electron acceptor is used. Most organisms will use some form of fermentation to accomplish the regeneration of NAD+, ensuring the continuation of glycolysis. The regeneration of NAD+ in fermentation is not accompanied by ATP production; therefore, the potential for NADH to produce ATP using an electron transport chain is not utilized.
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- 6.6: Connections to Other Metabolic Pathways
- Metabolic pathways should be thought of as porous—that is, substances enter from other pathways, and other substances leave for other pathways. These pathways are not closed systems. Many of the products in a particular pathway are reactants in other pathways.
Thumbnail: Group of people running on a stadium trach in a V-formation. (CC0 License; Steven Lelham , via Unsplash )


4: Further Applications of Trigonometry
In this chapter, we will explore applications of trigonometry that will enable us to solve many different kinds of problems, including finding the height of a tree. We extend topics we introduced in Trigonometric Functions and investigate applications more deeply and meaningfully.
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- 4.1: Prelude to Further Applications of Trigonometry
- The world’s largest tree by volume, named General Sherman, stands 274.9 feet tall and resides in Northern California. Just how do scientists know its true height? A common way to measure the height involves determining the angle of elevation, which is formed by the tree and the ground at a point some distance away from the base of the tree. This method is much more practical than climbing the tree and dropping a very long tape measure.
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- 4.2: Non-right Triangles - Law of Sines
- In this section, we will find out how to solve problems involving non-right triangles. The Law of Sines can be used to solve oblique triangles. According to the Law of Sines, the ratio of the measurement of one of the angles to the length of its opposite side equals the other two ratios of angle measure to opposite side. There are three possible cases: ASA, AAS, SSA. Depending on the information given, we can choose the appropriate equation to find the requested solution.
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- 4.3: Non-right Triangles - Law of Cosines
- Unfortunately, while the Law of Sines enables us to address many non-right triangle cases, it does not help us with triangles where the known angle is between two known sides, a SAS (side-angle-side) triangle, or when all three sides are known, but no angles are known, a SSS (side-side-side) triangle. In this section, we will investigate another tool for solving oblique triangles described by these last two cases.
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- 4.4: Polar Coordinates
- When we think about plotting points in the plane, we usually think of rectangular coordinates (x,y) in the Cartesian coordinate plane. However, there are other ways of writing a coordinate pair and other types of grid systems. In this section, we introduce to polar coordinates, which are points labeled (r,θ) and plotted on a polar grid. The polar grid is represented as a series of concentric circles radiating out from the pole, or the origin of the coordinate plane.
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- 4.5: Polar Coordinates - Graphs
- polar equation describes a relationship between rr and θ on a polar grid. It is easier to graph polar equations if we can test the equations for symmetry. There are three symmetry tests that indicate whether the graph of a polar equation will exhibit symmetry. If an equation fails a symmetry test, the graph may or may not exhibit symmetry.
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- 4.6: Polar Form of Complex Numbers
- In this section, we will focus on the mechanics of working with complex numbers: translation of complex numbers from polar form to rectangular form and vice versa, interpretation of complex numbers in the scheme of applications, and application of De Moivre’s Theorem.
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- 4.7: Parametric Equations
- We begin this section with a look at the basic components of parametric equations and what it means to parameterize a curve. Then we will learn how to eliminate the parameter, translate the equations of a curve defined parametrically into rectangular equations, and find the parametric equations for curves defined by rectangular equations.
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- 4.9: Vectors
- Ground speed refers to the speed of a plane relative to the ground. Airspeed refers to the speed a plane can travel relative to its surrounding air mass. These two quantities are not the same because of the effect of wind. In an earlier section, we used triangles to solve a similar problem involving the movement of boats. Later in this section, we will find the airplane’s ground speed and bearing, while investigating another approach to problems of this type.


2.4.4: Structural Rules
We also need a few rules that allow us to rearrange sentences in the left and right side of a sequent. Since the logical rules require that the sentences in the premise which the rule acts upon stand either to the far left or to the far right, we need an “exchange” rule that allows us to move sentences to the right position. It’s also important sometimes to be able to combine two identical sentences into one, and to add a sentence on either side.
Weakening
Contraction
Exchange
A series of weakening, contraction, and exchange inferences will often be indicated by double inference lines.
The following rule, called “cut,” is not strictly speaking necessary, but makes it a lot easier to reuse and combine derivations.


12.3: Gender as a Social Justice Issue
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- Krischa Esquivel, Emily Elam, Jennifer Paris, & Maricela Tafoya
- College of the Canyons
The social impacts of imposing gender roles on children become evident very early in life and usually follow the child as they continue their development. It is most observable when they interact with other members of their age group. A child's peers serve as both an archetype and a sounding board for the proper way to express themselves.
Children are especially apt at noticing when one of their peers violates their established gender role. As Fagot (1990) found, children had a pronounced response when one of their peers violated their established gender role. Same-sex peers acted as the distributors of both rewards for proper gender role behavior and punishments for improper gender role behavior. Boys who preferred to play with dolls rather than trucks were five to six times more likely to be harassed by their peers than those who conformed to the norm. Girls who preferred to play firefighter rather than nurse were ignored rather than criticized. Most importantly, Fagot's study shows the effect of gender segregation on children; boys tended to respond more readily to feedback from other boys while girls likewise responded to feedback from other girls. By surrounding themselves with members of the same sex, children are placing themselves in a situation where they more readily accept and conform to accepted gender roles. A study by Bandura and Bussey shows that kids want to be like others of their sex. They begin labeling objects as "for girls" or "for boys" and conform to what is expected of them. [153]
The attitudes and expectations surrounding gender roles are not typically based on any inherent or natural gender differences, but on gender stereotypes, or oversimplified notions about the attitudes, traits, and behavior patterns of males and females. Gender stereotypes form the basis of sexism, or the prejudiced beliefs that value males over females. [154] This is problematic for all children, but especially those that do not conform to gender roles and/or who are gender diverse.
Let’s look a bit more at gender roles and learn how programs can promote equity based on gender and acceptance of all children’s gender identity.
What Can Programs Do
Children need a safe and nurturing environment to explore gender and gender expression. It’s important for all children to feel good about who they are and what they can do.
Sometimes we unintentionally expect and encourage particular behaviors and traits based on a child’s gender. For example, adults tend to comment on a girl’s appearance, saying things like “Aren’t you adorable?” or “What a pretty dress!”
On the other hand, comments about boys tend to center on their performance with a focus on abilities, such as “You’re such a good climber!” or “You’re so smart.” As an adult supporting healthy development, you can develop a habit of commenting on who they are as individuals.
You can foster self-esteem in children of any gender by giving all children positive feedback about their unique skills and qualities. For example, you might say to a child, “I noticed how kind you were to your friend when she fell down” or “You were very helpful with clean-up today—you are such a great helper” or “You were such a strong runner on the playground today.” [155]
Bias against Boys in Early Childhood Education Programs
There is an overall goodness-of-fit between girls and early childhood education programs. The early childhood education field reflects a female cultural orientation as “almost all early childhood teachers are women [and] most women seem to prefer behaviors and activities more often attributed to girls than boys.” [156] They also respond to the behavior of boys and girls differently. With girls, teachers tend to overlook behavior that is not appropriate, but with boys they tend to overlook behavior that is appropriate. The results in girls are seemingly more “good” than they may really be. By the same token, the teacher’s patterns of response imply that boys are more “bad” than they may really be. [157]
There is research that shows that early childhood education programs are not serving boys as well as they are girls. Here are some data showing less favorable outcomes for boys:
- While they represent 54% of the preschool population, boys make up 79% of those suspended once, and 82% of those suspended more than once
- Boys are almost five times more likely to be expelled from preschool
- 61% of kindergartners held back are boys [158]
There are differences from gender, both cultural and physical (such as hormonal influences on brain development) that result in boys and girls having different needs. This includes:
- In general, boys’ brains and overall nervous systems develop more slowly than girls’.
- Boys being more physically active, engaging in more rough-and-tumble play, and showing more aggression than girls
- Boys tend to take up more space during both indoor and outdoor activities
- Boys tend to learn well through movement and hands-on activities, while struggling more than girls with memory and language (which results in more challenges with verbal instructions, literacy activities, and tore learning that many early childhood classrooms feature heavily) [159]
What Programs Can Do to Better Serve Boys
Programs can:
- Focus on true developmentally appropriate practices for each and every child; treat each child differently and recognize that developmental variability is natural.
- Have an environment and a curriculum that is play-based, hands-on, and whole-body that addresses the whole child.
- Don’t use threats of withholding something a child enjoys as an incentive to complete a task that they do not enjoy or struggle with.
- Provide many opportunities for children to be successful.
- Destigmatize men in caregiving roles and increase the number of men in early childhood programs.
- Make programs more boy-friendly, including
- Provide a woodworking center
- Rework the dramatic play center to include props to support the common themes of boys’ play (construction, community service workers, sports, etc)
- Make sure books that feature heroes, monsters, vehicles, messy activities, etc. are included in the classroom
- Have large blocks of time for outdoor activities every day [160]
Train staff on the unique needs of boys and how to meet these needs. This should include “instruction in woodwork, math and science projects, and typically ‘male’ experiences, since many women are uncomfortable or unfamiliar engaging in these activities.” [161]
Create a Learning Environment that Encourages Healthy Gender Development
Children make sense of the world through imagination and play, by observing, imitating, asking questions, and relating to other children and adults (Vygotsky & Cole, 1978). Here are a few ways you can support these ways of learning:
- Offer a wide range of toys, books, and games that expose children to diverse gender roles. For example, choose activities that show males as caregivers or nurturers or females in traditionally masculine roles, such as firefighters or construction workers.
- Provide dramatic play props that give children the freedom to explore and develop their own sense of gender and gender roles. Recognize that this may feel uncomfortable for some providers, teachers, home visitors, and families. Be ready to have conversations to address the value of this kind of play.
- Avoid assumptions that girls or boys are not interested in an activity that may be typically associated with one gender or the other. For example, invite girls to use dump trucks in the sand table and boys to take care of baby dolls.
- Use inclusive phrases to address your class as a whole, like “Good morning, everyone” instead of “Good morning, boys and girls.” Avoid dividing the class into “boys vs. girls” or “boys on one side, girls on the other” or any other actions that force a child to self-identify as one gender or another. This gives children a sense that they are valued as humans, regardless of their gender. It also helps all children feel included, regardless of whether they identify with a particular gender.
- Develop classroom messages that emphasize gender-neutral language, like “All children can . . .” rather than “Boys don’t . . .” or “Girls don’t . . .” Home visitors can encourage families to use similar messages.
- Help children expand their possibilities—academically, artistically, and emotionally. Use books that celebrate diversity and a variety of choices so that children can see that there are many ways to be a child or an adult. Display images around the room that show people in a wide variety of roles to inspire children to be who they want to be. [162]
Demonstrate Support for Children’s Gender Expression
Almost all children show interest in a wide range of activities, including those that some would associate with one gender or the other. Children’s choices of toys, games, and activities may involve exploration of male and female genders. They may express their own emerging gender identity through their appearance, choice of name or nickname, social relationships, and imitation of adults. Show support for each child’s gender expressions by encouraging all children to make their own choices about how to express themselves.
Regardless of whether they are boys or girls, children may act in ways that others categorize as feminine or masculine: they may be assertive, aggressive, dependent, sensitive, demonstrative, or gentle (Giles & Heyman, 2005).
Research has shown that when girls and boys act assertively, girls tend to be criticized as “bossy,” while boys are more likely to be praised for being leaders (Martin & Halverson, 1981; Theimer, Killen, & Stangorm, 2001; Martin & Ruble, 2004, 2009). To avoid this kind of unintentional gender stereotyping, try to describe rather than label behavior. “I see you have a strong idea, and you need your friends to help with it. Could you let them choose what they want to do?” [164]
What Programs Can Do to Support Gender-Diverse Children
From the available research, gender is something we are born with. When children identify with a specific gender that is different from the gender assigned at birth (based on physical biology) or who do not identify with either gender, it’s important that they receive gender affirmative care. [165] Some of the American Academy of Pediatrics tips for families can be adapted for early childhood educators:
- Respond in an affirming, supportive way to how children disclose their gender identity to you.
- Accept and love the child as they are.

- Include books and materials in your classroom that represent gender diverse people.
- Be supportive of the ways the child expresses themself.
- Be on the lookout for danger signs that may indicate a need for mental health support.
- Educate yourself about this form of diversity, just like you do other forms.
It is important to recognize that families will also go through a process of understanding and (hopefully) accepting the child’s identity, thoughts, and feelings. [166]
Engage in Discussions about Healthy Gender Development
Different perceptions among adults, whether staff or families, of gender development can be used as a basis for discussion. Some staff and families may feel uncomfortable with a child’s play when it explores a gender role the adult does not associate with that child’s biological sex. It can be helpful to remember that play is the way that children explore and make meaning of their world. Be prepared to have conversations that honor a range of feelings, make space for questions, address concerns, discuss varied points of view, and offer resources.
You can also offer a developmental perspective on why it’s important to let children explore different gender roles—once you have a sense that families seem open to this. For example, you could start by saying, “I understand that seeing Isaac playing house and wearing an apron in the kitchen makes you feel uncomfortable. Can you tell me a little more about that?”
After you’ve listened, you may decide that it would be helpful to offer some developmental information by saying, for example, “We see this kind of play as a way for Isaac to explore the world around him, try on different ideas, and mirror what he sees family members, community members, or media characters doing.” [167]
Understand Developmentally Appropriate Curiosity about Bodies
Curiosity about people’s bodies is natural for children as they begin to notice differences and think of themselves as a boy or girl. Yet some exploration is not appropriate in an early childhood development program. If questions come up in the bathroom or if children want to learn about their friends’ bodies, let them know that most children have questions about their bodies and the differences between girls’ and boys’ bodies. That way they won’t feel ashamed when you remind them that their bodies are private.
If children demonstrate this kind of natural curiosity in your setting, you can share your observations with the children’s families and ask them if they want to talk more about it. Families may react differently, depending on their comfort level with you and this topic, and on what they’ve discussed with their children at home.
When your relationship with a family is strong and trusting, you might say, “I know this can be uncomfortable to talk about, but I wanted to share an observation I made today. I noticed your child and a friend were talking about their different body parts on the way to the bathroom. I’m wondering if you’ve seen the same kind of curiosity at home and if you’ve talked about it?” If they haven’t, ask if they’d like some ideas about how to answer their children’s questions when they do come up. Offer resources if they are interested in learning more. [168]
Note: if a teacher is ever suspicious of any type of abuse, they should always speak with a supervisor and parents.
Understanding Differences Between Gender and Sexual Orientation
Gender expression, gender identity and sexual orientation are not the same. Gender identity is about who you feel you are as a person. Sexual orientation is about the gender of the people you are sexually attracted to. A young child’s expression of gender-related preferences (in friends, activities, clothing choices, hairstyle, etc.) does not necessarily predict what their gender identity or sexual orientation will be later in life (American Psychological Association, 2015).
The age at which gender identity becomes established varies. Gender identity for some children may be fairly firm when they are as young as two or three years old (AAP, 2015; Balwin & Moses, 1996; Gender Spectrum, 2012; Zosuls et al., 2009). For others it may be fluid until adolescence and occasionally later.
The age at which an individual becomes aware of their sexual orientation, that is, their feelings of attraction for one gender or the other or both, also varies. Such feelings may emerge during childhood, adolescence, or later in life (Campo-Arias, 2010; Gender Spectrum, 2012).
If families or staff members have questions or are concerned about a child’s gender expression, assure them that you and your program are available for ongoing discussions. Family acceptance of a child’s gender identity is a critical factor in the child’s development (AAP, 2015; Gender Spectrum, 2012; Ryan et al, 2010). Whatever a child’s emerging gender identity, one very important message that caring adults can give to young children is that they are healthy, good human beings. Be prepared to share resources that can help family members learn more about gender in young children. [169]
Handling Gender Bias in the Classroom
Since young children learn by observing our words and actions, consider these strategies when dealing with children’s feelings about their own and each other’s gender expression:
- Share ideas with other providers about how to stop hurtful, gender-related teasing and redirect children to positive activities.
- Practice what you want to say and do. See the examples following this list for interacting with children and adults.
- Know your educational goals and how they are connected to social-emotional well-being in children.
- Help children choose kindness.
- Use instances of teasing as opportunities to help all the children understand other’s feelings and their own.
- Help them understand how their words might make their friends feel.
- Help them to learn to say “I’m sorry” and to show that they really mean it.
- Talk one-on-one with children who have teased another child. They are often confused about the hurt they cause and may be frightened by their own actions. They need to understand that hurting other children is not allowed. But they also need to know that you have confidence that they can learn to control themselves. Be sure to let them know that you are ready to forgive them once they have made a sincere apology.
- Help children to become resilient. Help those who are hurt by teasing to find simple responses to put a stop to it and affirm their positive feelings about themselves.
When you hear children making comments similar to the following ones (in italics), you might consider these responses:
“You can’t play in the kitchen area. You’re a boy!”
- “We can all learn together how to make a recipe and clean up the kitchen.”
- “I’m going to play in the kitchen with any of the children who like to play there.”
“Why does Diego always want to dress like a girl?”
- “There are lots of different ways that boys can dress and lots of different ways that girls can dress.”
- “Clothes are clothes. He likes to wear the clothes that he feels comfortable in.”
“Why does she always play with the boys?”
- “Those are the games that she likes to play, just as there are different games that you like to play.”
- “She can play with whoever she wants to, just like you.”
“You’re a girl!” (said in an insulting tone to a child who identifies as a boy).
- “It’s not okay to call someone a ‘girl’ to make them feel bad.”
“Boys are better at sports than girls.”
- “Some boys and girls are good at sports, and some are not. All children have different things that they are good at.”
When an early childhood educator shares questions similar to the ones below (in italics), you might consider these responses:
“Mercedes uses a boy’s name when they play pretend. Her grandmother said not to let her do that. I can’t go against the grandmother.”
- “Let’s talk this over with her grandmother and learn more about her views on this, why this is important to her, and what she would suggest. We can share our observation that Mercedes seems to know she disapproves, yet still really seems intent on using a boy’s name right now in her pretend play. Maybe then we could share with her our view of this kind of play as a way to use creativity to learn about one’s self and other people. She may still disagree, but getting this dialogue going would be a good start.”
“Zach’s dad makes fun of him when he sees him playing with girls. Zach now gets nervous whenever his father comes to pick him up. What can I say to the dad?”
- “Zach enjoys playing with the other children in our program. We encourage the boys and girls to play together to learn from each other.”
“One of the other teachers punishes Taylor when she acts like a boy. What should I do?”
- “I noticed that you scolded Taylor when she acted like a boy. Can we talk more about why you did that? You might remember that our educational approach encourages all children to play pretend. We believe creativity is a part of learning and development.”
Sometimes families ask about other children. For example, a family member might say, ‘I heard that Diego calls himself Isabella now, and he wears dresses every day. Why would his family let him do that?’” How can I answer this question and discourage gossip?
- “Well, normally I would not discuss details about another child, but in this case I have talked with Diego’s dad about this and how he would like us to address these types of questions as they come up. Isabella identifies as a girl and uses female pronouns, such as “she” and “her.” As early educators, we know some children are very clear at young ages that their gender expression is not the one they were assigned at birth based on their biology. Isabella’s family loves her, and they are trying to do what is best for her— just as you are doing for your child.”
When an early childhood educator wants to talk with a child’s family about gender-related teasing, similar to the example below (in italics), you might consider this response:
“A child called a boy a ‘“girl”’ at school today. It seemed intended as an insult. What can I say?”
- “Your child usually gets along so well with the other children. So when your child called a boy a ‘girl,’ as if that were a bad thing, we wanted to be sure to talk this over with you. Your son is such a leader, and we know he can be a positive one. We want to make sure that the children know that the words ‘girl’ and ‘boy’ aren’t insults, and that this is a safe and secure environment for all of them. Do you have some ideas about how we can work with your son as we work with all the children on this?” [170]
Simple Messages You Can Share with All Children
An essential part of children’s school readiness is developing self-confidence and resilience. Research shows that, even in early learning settings, boys and girls perform less well when they have negative concepts about their gender. Comments like “Girls can’t throw!” or “Boys always get into trouble!” can make them doubt their natural abilities (Hartley & Sutton, 2013; Del Rio & Strasser, 2013; Wolter, Braun, & Hannover, 2015).
Early learning environments are important places to teach children language and behavior that helps them all feel good about who they are and how to recover from the hurts they may cause each other.
Look for opportunities to help children practice positive language they can use with each other. Here are some examples that you can use to create your own:
- “Boys and girls can be good at sports/ writing/sitting still.”
- “Girls and boys can be friends with each other.”
- “Everybody can play in the kitchen/tool area/swing set.”
- “Running games are for everyone.”
- “Hair is hair. That is how she/he likes it.”
- “Boys and girls can wear what they like at our school.”
- “Colors are colors. There aren’t boy colors or girl colors. All children like different colors.” [171]