Study Guide C
Which cells stimulate apoptosis in other cells? What two chemicals are involved in this process and what is the role of each?
(Perforin pokes a hole or "perforates" the cell membrane) NK (natural killer) cells, which are located within secondary lymphoid structures (e.g., lymph nodes), destroy a wide variety of unhealthy or unwanted cells through apoptosis. the types of cells eliminated by NK cells include virus-infected cells, bacteria-infected cells, tumor cells, and cells of transplanted tissue. NK cells patrol the body in an effort to detect unhealthy cells a process referred to as immune surveillance. NK cells make physical contact with unhealthy cells and destroy them by release of cytotoxic chemicals. these cytotoxic chemicals include perforin, which perforates (forms pores in) the plasma membrane of targeted cells, and granzymes, which then enter the cell through the transmembrane pore, initiating apoptosis. apoptosis is a form of cellular death in which the cell does not lyse (i.e., rupture), but rather "shrivels"; this helps limit the spread of the infectious agent. remember that NK cells destroy unhealthy cells by a combination of puncturing, followed by poisoning.
What are the four ways that the complement system mediates dense mechanisms?
(acronym O-ICE) These complement proteins mediate several important defense mechanisms including (a) increasing inflammation, (b) engaging in opsonization, (c) including cytolysis, and (d) causing elimination of immune complexes - inflammation. complement increases the inflammatory response through the activation of mast cells and basophils and by attracting neutrophils and macrophages - opsonization. is the binding of a protein (in this case, complement) to a portion of bacteria or other cell type to enhance phagocytosis. the binding protein is called an opsonin. the binding of complement makes it more likely that a substance is identified and engulfed by a phagocytic cell (e.g., macrophage). an opsonin functions as a red flag to indicate the tagged microbe - elimination of immune complexes. complement links immune (antigen-antibody) complexes to erythrocytes so that they may be transported in the blood to the liver and spleen. erythrocytes are stripped of these complexes by macrophages within these organs, and the erythrocytes then continue circulating in the blood. - cytolysis. various complement components (e.g., C5-C9) trigger direct killing of a target by forming a protein channel in the plasma membrane of a target cell called a membrane complex protein (MAC). the MAC protein channel compromises the cell's integrity, allowing an influx of fluid that causes lysis of the cell
What is a goiter? What typically causes a goiter? Why is this not common in the US?
- A goiter is the enlargement of the thyroid, typically due to an insufficient amount of dietary iodine. Although the pituitary releases more TSH in an effort to stimulate the thyroid, the lack of dietary iodine prevents the thyroid from producing the needed TH. - Goiter was a relatively common deformity in the United States until food processors began addition iodine to table salt. It still occurs in parts of the world where iodine is lacking in the diet, and as such, is referred to as endemic goiter.
What is complement? What is the naming convention for these proteins?
- Complement is a collective name for a group of proteins that aid in defense against pathogens - Individual complement proteins are generally identified with the letter "C" followed by a number (e.g., C1, C2)
What region produces mineral corticoids? What is the principal mineralcorticoid? Describe its effect.
- The zona glomerulosa is a thin, outer cortical layer composed of dense, spherical clusters of cells. these cells synthesize mineralocorticoids, a group of hormones that regulate the composition and concentration of electrolytes (ions) in body fluids. - the principal mineralocorticoid is aldosterone, which regulates the ratio of Na+ and K+ in our blood and body fluids by altering the amounts excreted by the kidney into the urine. aldosterone stimulates retention of both Na+ and water and the secretion of K+. thus, the Na+ blood concentration remains the same (because of retention of both Na+ and water), and K+ blood concentration decreases. severe imbalances in this ratio can result in death
What are the types of nonspecific internal defenses?
- most immune cells (e.g., macrophages, NK cells) - chemicals (e.g., interferon, complement) - physiologic responses (e.g., inflammation, fever)
What region primarily produces gonadocorticoids? What are the primary gonadocorticoids? Describe the general effect of thse hormones.
- the innermost region of the cortex, the zona reticularis, is a narrow band of small, branching cells. they are capable of secreting minor amounts of sex hormones called gonadocorticoids. - the primary gonadocorticoids secreted are male sex hormones called androgens, thus serving as a secondary site for androgens in males and the primary site in females. Gonadocorticoids include dehydroepiandrosterone (DHEA), DHEA-sulfate, and androstenedione. the amount of androgen secreted by the adrenal cortex is small compared to that secreted by the gonads; however, adrenal gland tumors in a female can result in elevated levels of androgens and varying degrees of masculinization - elevated testosterone and masculinization
What region primarily produces glucocorticoids? What is the primary glucocorticoid?
- the zona fasciculata is the middle layer and largest region of the adrenal cortex. it is composed of parallel cords of lipid-rich cells that have a bubbly, almost pale appearance. this region synthesizes glucocorticoids. - the main glucocorticoids synthesized in this region are cortisol and corticosterone, which are released in response to ACTH.
Thyroid hormone: T3/T4 cycle
1. Stimulus: variable that influence the release of TRH from the hypothalamus: - blood levels of thyroid hormone (TH) - other stimuli, including cold weather, pregnancy, high altitude, and hypoglycemia 2. Receptor: the hypothalamus responds to various stimuli 3. Control center: the hypothalamus releases thyrotropin-releasing hormone (TRH) into the hypothalamo-hypophyseal portal system 4. in response to TRH, the anterior pituitary releases thyroid-stimulating hormone (TSH) 5. TSH stimulates the thyroid gland to release thyroid hormone (TH) into the blood 6. TH then acts on target cells (effectors) 6. Effects: effectors respond to increased levels of TH in the following ways: Amino acids -> all cells especially neurons (increased metabolic rate, increased glucose uptake) glucose -> all cells, especially neurons liver tissue liver tissue -> glucose (increase glycogenolysis and gluconeogenesis, decreased glycogenesis) adipose connective tissue -> glycerol fatty acids (increased lipolysis, decreased lipogenesis) lungs (increased breathing rate) heart (increased heart rate, increased force of contraction) lungs and heart responses help meet increased O2 demand for aerobic cellular respiration 7. Net effect: increased metabolic rate; nutrient release into blood 8. Negative feedback: TH levels increased, inhibiting release of TRH and TSH
Steps of cortisol regulation
1. Stimulus: variables that influence the release of CRH from the hypothalamus: - blood levels of cortisol - time of day - stress 2. receptor: hypothalamus responds to various stimuli 3. control center: the hypothalamus releases corticotropin-releasing hormone (CRH) into the hypothalamo-hypophyseal portal system 4. in response to CRH, the anterior pituitary releases adrenocorticotropic hormone (ACTH) 5. ACTH stimulates the adrenal cortex to release glucocorticoids (e.g., cortisol) into the blood 6. cortisol stimulates target cells (effectors 6. Effectors: effectors respond to cortisol in the following ways 7. Net effect: increase all nutrient levels in the blood 8. Negative feedback: cortisol levels increase, inhibiting release of CRH and ACTH
What are the steps of inflammation?
1. release of inflammatory and chemotactic factors 2. vascular changes (vasodilation of arterioles, increase in capillary permeability, display of CAMS) 3. recruitment of leukocytes (margination, diapedesis, chemotaxis) 4. delivery of plasma proteins
Define fever.
A fever is defined as an abnormal elevation of core body temperature (pyrexia) of at least 1 C (1.8 F) from the typically accepted core body temperature of 37 C (98.6 F)
What are the two types of immunity?
Adaptive immunity and innate immunity
What are bacteria?
Bacteria are microscopic, single-celled organisms composed of prokaryotic cells. these cells are fundamentally different from the cells of humans and other living organisms. prokaryotic cells are smaller in size, averaging between 1 and 2 micrometers (um), which is approximately the size of a mitochondrion. prokaryotic cells lack a nuclear envelope, and their cytoplasm and DNA are enclosed by both a plasma membrane and a cell wall (formed by complex carbohydrates cross-linked with peptides). some bacteria have an external, sticky polysaccharide capsule, which increases their virulence- the ability to cause serious illness. pathogenic bacteria may also have pili, which are hairlike structures that act like Velcro for attaching to body structures (e.g., E. Coli that cause urinary tract infections). additionally, some pathogenic bacteria cause disease by releasing enzymes or toxins that interfere with the function of cells; an example is the bacterium Clostridium tetani.
What are proinflammatory chemical-secreting cells?
Basophil and mast cell
Which cell type releases calcitonin?
Calcitonin is synthesized and released from the parafollicular cells of the thyroid gland
Describe the effects of calcitonin on its primary targets.
Calcitonin primarily inhibits osteoclast activity within bone tissue (which decreases the breakdown of bone tissue) and stimulates the kidneys to increase the loss of calcium in the urine. the net effect of calcitonin is a reduction in blood calcium levels. calcitonin seems to have the greatest effect in the bones of growing children, where there is the greatest turnover of bone.
You do not needed to differentiate between the different types of cytokines, but you should recognize each category in table 22.2 as a cytokine.
Categories= interleukin (IL), tumor necrosis factor (TNF), colony-stimulating factor (CSF), interferon (IFN)
Which cells stimulate inflammation? What is histamine? What is heparin?
Chemical secreting cells that enhance inflammation include both basophils and mast cells. basophils circulate in the blood and mast cells reside in connective tissue of the skin, mucosal linings, and various internal organs. substances secreted by basophils and mast cells increase fluid movement from the blood to an injured tissue. they also serve as chemotaxic chemicals, which are molecules that attract immune cells as part of the inflammatory response. basophils and mast cells release granules during the inflammatory response. these granules contain various substances, including histamine, which increases both vasodilation and capillary permeability, and heparin, an anticoagulant. They also release eicosanoids from their plasma membrane which increase inflammation.
What causes cytolysis?
Collectively, these complement proteins form a protein pore in a microbe's plasma membrane to cause cytolysis by an influx of fluid
What increases inflammation?
Complement increases inflammation through the activation of various cells (mast cells, basophil, neutrophil, macrophage, which all lead to inflammation)
What eliminates immune complexes?
Complement links immune (antigen-antibody) complexes with erythrocytes which are later stripped of these complexes by macrophages within the liver and spleen
What causes opsonization?
Complement serves as an opsin ("red flag") by binding to pathogen (e.g., bacteria) to enhance phagocytosis of the pathogen
Generally, cortisol moves nutrients such as glucose, fatty acids, and amino acids into the blood. Why?
Cortisol accounts for 95% of the glucocorticoid activity. Cortisol is transported within the blood by carrier proteins. Cortisol circulates the blood, and small amounts become unbound from their carrier protein and exit the blood - an attempt to resist stress and help repair injured or damaged tissues
What is the hypothalamic-pituitary adrenal axis?
Cortisol and corticosterone are released from the adrenal cortex as a result of the integrated activities of the hypothalamus and anterior pituitary. this physiologic relationship is referred to as the hypothalamic-pituitary-adrenal axis.
What are cytokines?
Cytokines are small, soluble proteins produced and released by cells to regulate and facilitate immune system activity.
What are parasite destroying cells?
Eosinophils
Which cells destroy parasites?
Eosinophils target multicellular parasites, attacking the organisms' surfaces. Mechanisms of destruction include degranulation and release of enzymes and other substances (e.g., reactive oxygen-containing compounds, neurotoxins) from the eosinophils that are lethal to the parasite. like NK cells, eosinophils can release proteins that form a transmembrane pore to destroy cells. however, eosinophils function against cells of a multicellular organism. eosinophils can participate in the immune response associated with allergy -antibody complexes
Where are dendritic cells housed? What is their function?
Epithelial layers of the skin and mucosal membranes. Dendritic cells are also located in the skin and mucosal membranes, and they are typically derived from monocytes. These cells in the epidermis of the skin are more specifically called epidermal dendritic cells. Dendritic cells engulf pathogens in the skin and mucosal membranes and subsequently migrate to a lymph node through lymph vessels that drain the tissue.
What is hyperthyroidism and what are its symptoms?
Excessive production of TH and it causes increased metabolic rate, weight loss, hyperactivity, and heat intolerance hyperthyroidism results from excessive production of TH and is characterized by increased metabolic rate, weight loss, hyperactivity, and heat tolerance. although there are a number of causes of hyperthyroidism, the more common ones are (a) ingestion of T4 (weight control clinics sometimes use TH to increase metabolic activity); (b) excessive stimulation of the thyroid by the pituitary gland; and (c) loss of feedback control by the thyroid. this last condition, called Graves disease, is an autoimmune disorder involving the formation of autoantibodies that mimic TSH hormone. the antibodies bind to TSH receptors on the follicular cells of the thyroid, causing an abnormally high level of TH release. Graves disease includes all the symptoms of hyperthyroidism plus protruding and bulging eyeballs known as exophthalmos. hyperthyroidism is treated by removing the thyroid gland, either by surgery or by intravenous injections of radioactive iodine (I-131). in the procedure for treating hyperthyroidism, the thyroid gland cells are destroyed as the organ sequesters the I-131, but other organs are not damaged because they do not store iodine as does the thyroid. patients whose thyroid glands have been removed or destroyed must take daily hormone supplements.
Why is a mild fever beneficial?
Fever actually has numerous benefits. A fever inhibits replication of bacteria and viruses, promotes interferon activity, increases activity of lymphocytes, and accelerates tissue repair. most recently, it has been demonstrated that a fever also increases CAMS on the endothelium of capillaries in lymph nodes, resulting in additional immune cells migrating out of the blood and into the lymphoid tissue. thus, it is not necessary (and may be detrimental) to treat a mild fever. most physicians recommend letting a fever "run its course" and give fever-reducing medication only if the fever becomes very high or if the patient is in significant discomfort from the fever
What else can cause disease?
Fungi, protozoans, parasites, and prions
What is hypothyroidism and what are its symptoms?
Hypothyroidism results from decreased production of TH. It is characterized by low metabolic rate, lethargy, a feeling of being cold, weight gain (in some patients), and photophobia (the disdain and avoidance of light)
Why is an increase in lymph helpful?
Increased hydrostatic pressure exerted by the interstitial fluid causes additional fluid uptake by lymphatic capillaries. The newly formed lymph carries with it unwanted substances that include infectious agents, dead cells, and cellular debris. the contents of lymph can then be monitored as it passes through a series of lymph nodes. you may find it helpful to think of the inflammatory response as "washing" the infected or injured area.
Explain the feedback loop that regulates TH levels
Increased thyroid hormone inhibits both the release of TRH from the hypothalamus and the release of TSH from the anterior pituitary T3 and T4 are transported within the blood bound by carrier proteins (e.g., thyroxine-binding globulin (TBG), albumin). At any given time, a small percentage of T3 and T4 becomes unbound from the carrier proteins and then exit from the blood. the amount of TRH released from the hypothalamus and TSH from the anterior pituitary is regulated by negative feedback. increased thyroid hormone inhibits both the release of TRH from the hypothalamus and the release of TSH from the anterior pituitary. Other stimuli (in addition to blood levels of thyroid hormone) influence the release of TRH from the hypothalamus. these stimuli include cold weather, pregnancy, high altitude, hypoglycemia, and in children, decreased body temperature
Describe the effects of TH on important targets organs/tissues.
Increases protein synthesis, stimulates synthesis of sodium-potassium pumps in neurons, raises temperature, increases glucose uptake A cellular transport system (carrier-mediated endocytosis) moves TH into target cells, while it binds to intracellular receptors. T3 is the most active form of TH. Most cells, however, have an enzyme to remove one iodine to convert T4 to T3. This increases a cell's response to thyroid hormone because a much greater amount of T4 (~90%) than T3 (~10%) is produced and released from the thyroid gland. TH is a lipid-soluble hormone that interacts with target cells of effectors to (a) increase metabolism and (b) cause release of nutrients into the blood (steps 6 and 7). TH specifically stimulates the synthesis of sodium-potassium (Na+/K+) pumps in neurons, and the action of these additional ion pumps generates heat. the rise in temperature is referred to as the calorigenic effect. increased amino acid uptake by cells provides the structural building blocks for these processes. TH also stimulates all cells to increase their glucose uptake. concomitant with this increase is buildup in the number of cellular respiration enzymes within mitochondria because additional ATP is needed to support the higher metabolic rate
Why is a high fever dangerous?
Individuals should seek ways to decrease a fever when a fever is intermediate or high-grade or if a low-grade fever persists (i.e., a fever that lasts longer than 4 to 7 days). High-grade fevers are potentially dangerous because of the changes in metabolic pathways and denaturation of body proteins. seizures may occur at sustained body temperature above 102 F (although generally they occur at much higher temperatures), irreversible brain damage may occur at body temperatures that are sustained at greater than 106 F, and convulsions and death are likely when body temperature reaches 108 F.
What are infectious agents?
Infectious agents are organisms that cause damage, or possibly death, to the host organism that they invade. infectious agents that cause harm to the host are said to be pathogenic. the five major categories of infectious agents that cause disease in humans are bacteria, viruses, fungi, protozoans, and multicellular parasites
What are the cardinal signs of inflammation and what is the cause of each?
Inflammation typically is accompanied by certain cardinal signs (i.e., major representative characteristics) that include the following: - redness, due to increased blood low - heat, due to increased blood flow and increased metabolic activity within the area - swelling, resulting from increase in fluid loss from capillaries into the interstitial space - pain, which is caused by stimulation of pain receptors from compression due to accumulation of interstitial fluid, and chemical irritation by kinins, prostaglandins, and substances released by microbes - loss of function (which may occur in more severe cases of inflammation due to pain and swelling)
What is inflammation?
Inflammation, or the inflammatory response, is an immediate, local, nonspecific event that occurs in vascularized tissue against a variety of injury-causing stimuli. inflammation can occur in many instances, such as in response to a scratch of your skin, a bee sting, overuse of a body structure (e.g., pitching arm), or proteolytic enzymes released by fungi
Compare and contrast innate and adaptive immunity.
Innate immunity - Some defense mechanisms of the immune system protect us against numerous different substances, and because we are born with these defenses, this type of immunity is referred to as innate immunity. The components that provide innate immunity include the barriers of the skin and mucosal membranes that prevent entry, as well as nonspecific internal defenses that include all immune cells except for T-lymphocytes and B-lymphocytes, selected chemicals (e..g, interferon), and physiologic processes (e.g., inflammation). These structures and mechanisms associated with innate immunity do not require previous exposure to a foreign substance, and they respond immediately to any potentially harmful agent adaptive immunity - other defense mechanisms of the immune system include the actions of T-lymphocytes and B-lymphocytes exclusively. each lymphocyte, whether a T-lymphocyte or B-lymphocyte, responds to a specific foreign substance (or antigen) to which we are exposed during our lifetime. for example, one lymphocyte may respond to the virus that causes chicken pox, but this same lymphocyte does not respond if it encounters the bacterium that causes strep throat. - this type of immunity provided by our lymphocytes is referred to as adaptive immunity (also called acquired immunity or specific immunity). lymphocytes provide a powerful means of eliminating foreign substances. however, although the process begins immediately, the development of adaptive immunity against foreign substances typically takes several days to be effective.
What are the two categories of immunity?
Innate immunity and adaptive immunity
What hormones are released by the adrenal medulla? What are their effects?
It releases the catecholamines epinephrine and norepinephrine. the stimulus for the release of these hormones is activation by the sympathetic division. approximately 80% of the hormone released is epinephrine and 20% is norepinephrine. Both hormones circulate within the blood and help prolong the fight-or-flight response, which is caused by the activation of the sympathetic division.
What are pyrogens? What do they target?
It results from release of fever-inducing molecules called pyrogens that are released from either infectious agents (e.g., bacteria) or immune cells in response to infection, trauma, drug reactions, and brain tumors
What are leukocytes? Where are they formed?
Leukocytes (white blood cells) are specialized cells of our immune system. they are cells that help defend our body against pathogens. they are formed in the red bone marrow prior to circulating in the blood
What are apoptosis-initiating cells?
NK cells
Is the immune system a true organ system? Why or why not?
No. The immune system is not composed of organs (e.g., lungs of the respiratory system.) instead, numerous types of cells (including specialized cells called immune cells), secreted molecules (including cytokines), and plasma proteins (e.g., antibodies) are functionally integrated to form our immune system
What are some important consequences of inflammation?
One of the most important consequences produced by the inflammatory response is a net movement of additional lymph fluid from the blood through the infected or injured area and then into the lymph. increased fluid, immune cells, and protein leave the capillaries and then enter the interstitial space of the tissue; this fluid and cellular/protein mix collectively is referred to as exudate. exudate delivers immune cells and substances needed to eliminate the injurious agent and promotes healing
Which cells are phagocytes? Describe the process of phagocytosis.
Phagocytic cells include neutrophils, macrophages, and dendritic cells, which engulf unwanted substances such as infectious agents and cellular debris through phagocytosis. the processes following phagocytosis are as follows: (1) the vesicle formed during phagocytosis that contains the unwanted substance (a phagosome) merges with a lysosome to form a phagolysosome. (2) within the phagolysosome, digestive enzymes contributed from the lysosome chemically digest the unwanted substances. (3) degraded residues of the engulfed substances are then released from the cell by exocytosis. destruction of bacteria and viruses by neutrophils and macrophages is facilitated by the production of reactive oxygen- containing molecules (e.g., nitric acid, hydrogen peroxide, superoxide); the release of these molecules is called a respiratory burst (or oxidative burst) phagocytosis and the subsequent destruction of microbes are highly effective in protecting us. in fact, most microbes that enter the body are engulfed and destroyed by phagocytic cells. participation in phagocytosis, however, is fatal for neutrophils, which die soon after engulfing microbes. dead neutrophils become the major component of the pus that is produced during some infections. macrophages and dendritic cells, in comparison, continue to function following phagocytosis. they serve an additional role, which is to present fragments of the microbe on their cell surface to T-lymphocytes. this process, called antigen presentation, is necessary for initiating adaptive immunity.
What is adaptive immunity?
Provided by lymphocytes that are activated to replicate and respond when stimulated by a specific antigen
What is innate immunity?
Provided by multiple components that protect against a wide array of substances
What is the first step of inflammation?
Release of chemicals. Damaged cells of injured tissue, macrophages, dendritic cells, basophils, mast cells, and infectious organisms release numerous chemicals that promote inflammation (e.g., histamine, leukotrienes, TNFs, chemotactic factors)
Where are macrophages housed?
Remember that these are "big eaters" that engulf pathogens. Select organs. Macrophages, which are derived from monocytes that have exited the blood, are also housed in select organs. Some of these cells are specifically named based on their location, such as alveolar macrophages of the lungs and microglia of the brain. macrophages may be permanent residents, referred to as fixed macrophages, or migrates through tissues and are called wandering macrophages
Where are mast cells housed?
Remember that these cells can stimulate an inflammatory response. Connective tissue. Mast cells (cells similar to basophils within the blood) are located within the connective tissue throughout the body, typically in close proximity to small blood vessels. they are especially abundant in the dermis of the skin and the mucosal linings of the respiratory, gastrointestinal, urinary, and reproductive tracts. however, they are also housed in connective tissue of organs, such as the endomysium that ensheathes muscle fibers.
Where are B lymphocytes and T lymphocytes housed?
Secondary lymphoid structures. T-lymphocytes and B-lymphocytes are housed in secondary lymphoid structures of lymph nodes, the spleen, tonsils, lymphoid nodules, and mucosa-associated lymphoid tissue (MALT)
What are the two types of innate immunity?
Skin and mucosal membranes (prevent entry) and nonspecific internal defenses
What are the two types of adaptive immunity?
T-lymphocytes and B-lymphocytes
What are the three regions of the adrenal cortex?
The adrenal cortex is partitioned into three separate regions: the outer zona glomularosa, the middle zona fasciculata, and the inner zona reticularis
Describe the shape and location of the adrenal glands
The adrenal glands, are suprarenal glands, are paired, pyramid-shaped endocrine glands anchored on the superior surface of each kidney
What are the two regions of the adrenal gland? Where is each located?
The adrenal glands, like the hypothalamus and pituitary gland, are composed of both nervous tissue and endocrine tissue. the inner portion of each gland, called the adrenal medulla, is composed of nervous tissue. the outer portion, called the adrenal cortex, is composed of endocrine tissue.
What is the first line of defense against pathogens?
The body has many anatomic structures, various secretions, and specific physiologic mechanisms that are typically effective in either preventing the entry of these organisms or preventing the entry of these organisms or eliminating them from the body skin and mucosal membranes
Describe the role of the hypothalamus and anterior pituitary in the regulation of cortisol levels. Explain the negative feedback mechanism.
The hypothalamus releases corticotropin-releasing hormone (CRH), which is transported through the hypothalamo-hypophyseal portal system to the anterior pituitary (steps 1-3). CRH binds to receptors of the anterior pituitary (corticotropic cells) and stimulates the release of adrenocorticotropic hormone (ACTH) into general circulation (step 4). ACTH then binds to receptors within adrenal cortex cells (zona fasciculata) and stimulates the release of glucocorticoids including cortisol and corticosterone (step 5).
Explain how TH release is regulated and the role of the hypothalamus and anterior pituitary
The hypothalamus releases thyrotropin-releasing hormone (TRH) which enters the hypothalamo-hypophyseal portal system (steps 1-3). TRH binds to receptors in cells of the anterior pituitary (thyrotropic cells) and stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH) into the general circulation (step 4). TSH binds to receptors of the follicular cells of the thyroid glands and stimulates the release of thyroid hormone (TH)
What is colloid and what is its function? What element is needed to produce thyroid hormone?
The lumen (interstitial space) of each thyroid follicle houses a viscous, protein-rich fluid termed colloid. Precursors to thyroid hormone are stored in it. Iodine molecules must be combined with the thyroglobulin in the colloid to produce hormone precursors, which are TGB molecules that contain immature thyroid hormone within their structure.
How do mucous membranes create a barrier to pathogens?
The mucous membranes also form a physical, chemical, and biological barrier, but these membranes function to prevent entry at the openings of the body. the epithelium and underlying connective tissues of mucous membranes help us to block microbes from entering the body through our respiratory, gastrointestional (GI), urinary, and reproductive tracts. these membranes provide mucin (protein) that when released and hydrates forms mucus, a viscous fluid that also contains antimicrobial substances (e.g., lysozyme, defensins, IgA). Additionally, each tract has specific physiologic mechanism that help to protect it.
How does the respiratory organ system create barriers to pathogens?
The respiratory tract has cilia that sweep mucus with trapped microbes upward from the lungs to be expectorated (spit out) or swallowed and the coughing and sneezing reflexes, which remove microbes with blasts of exhaled air.
In what ways does the skin form a barrier to pathogens?
The skin forms a physical, chemical, and biological barrier that plays a significant role in preventing entry of pathogens at the body's surface if the skin is intact. the keratinized stratified squamous epithelium of the epidermis, as well as the areolar connective tissue and dense irregular connective tissue of the dermis provides a formidable barrier to prevent entry of most microbes. one specific substance within the areolar connective tissue of the dermis is a gel-like mucopolysaccharide called hyaluronic acid, which slows the migration of microbes that have penetrated the epidermis- much as a sticky fly paper traps flies. secretions of exocrine glands of the skin help inhibit microbial growth. these secretions include those of sweat glands (which contain antimicrobial lysozyme, defensins, and dermcidin) and sebaceous glands (which contain lactate and fatty acids that contribute to a low skin pH). the importance of skin in protecting us from pathogens can be appreciated when we consider that when the skin is compromised by a serious burn, one of the major causes of death is a fatal infection
What stimulates the release of calcitonin?
The stimulus for calcitonin release from parafollicular cells is a high blood calcium level; it is also secreted in response to stress from exercise
Describe the histological appearance of the thyroid gland. What are the two hormones produced by the thyroid gland and what cells produce each? Label the cells in the image.
The thyroid gland at the histological level is composed primarily of numerous microscopic, spherical structures called thyroid follicles. the wall of each follicle is formed by simple cuboidal epithelial cells, called follicular cells, which surround a central lumen. The follicular cells produce and later release thyroid hormone (TH) by first synthesizing a glycoprotein called thyroglobulin (TGB) and secreting it by exocytosis into the colloid-filled lumen. in brief, iodine molecules must be combined with the thyroglobulin in the colloid to produce hormone precursors, which are TGB molecules that contain immature thyroid hormone within their structure. the precursors are stored in the colloid until the secretion of the thyroid hormone is needed. when the thyroid gland is stimulated to secrete thyroid hormone, some of the colloid with thyroid hormone precursors is internalized by endocytosis into a follicular cell. it is transported to a lysosome, where an enzyme releases the immature thyroid hormone molecules from the precursor in preparation for its secretion from the follicular cells. parafollicular cells, also known as C-cells are the less numerous endocrine cells in the thyroid gland, and are located within the follicular cells. parafollicular cells synthesize and release the hormone calcitonin
Describe the function of cytokines.
These soluble proteins (a) serve as a means of communication between the cells; (b) control the development and behavior of immune cells; (c) regulate the inflammatory response; and (d) function as weapons to destroy cells. cytokines have also recently been shown to influence other, non-immune cells such as those of the nervous systme.
List two factors that influence the amount of CRH released.
Time of day: there are daily fluctuations in the release of cortisol. in a normal sleep wake cycle, peak levels of cortisol correspond to the late stages of a normal sleep cycle. about half of all cortisol release occurs when you are asleep, with cortisol levels peaking right before waking in the morning. this rhythm of release is regulated by light and dark cycles detected by the retina as nerve signals are relayed to the hypothalamus. (There is significant variation in normal levels of cortisol in individuals) Stress. both emotional stress (e.g., anger, anxiety, feat) and physical stress (e.g., fever, trauma, intense exercise) increase the release of cortisol. the influence of chronic stress in triggering increased cortisol levels in the blood is the reason that cortisol has been given the nickname "the stress hormone"
What are the two forms of thyroid hormone?
Triiodothyronine (T3) and tetraiodothyronine (T4) (thyroxine)
How does the urinary tract create barriers to pathogens?
Urine "flushes" microbes from the urinary tract
What are viruses?
Viruses are not cells. Viruses are much smaller than a bacterial cell at about one-hundredth of a micrometer, and they are composed of DNA or RNA within a protein capsid, or shell. the protein capsid of some viruses may also be enclosed within a membrane. viruses are obligate intracellular parasites; that is, they must enter a cell to replicate by binding to a structure within the plasma membrane of a host cell. (for example, SARS-CoV-2, the virus that causes COVID-19, has a spike protein within its membrane that binds with a cell's ACE receptor in its plasma membrane; allowing the virus to enter to any cell that has an ACE receptor). the process of viral reproduction includes directing the infected cell to synthesize copies of both the vital DNA or RNA molecule and its capsid protein. new viral particles are then formed within the infected cells and released from them to enter the surrounding cells. a virus, or the immune system's response to it, ultimately kills the cell it invades. viruses cause different disease depending upon the type of cell they infect. examples of viral disease include the common cold, chicken pox, Ebola, COVID-19, and HIV.
What is a membrane attack complex (MAC)?
a formed protein channel in the plasma membrane of a target cell, compromises the cells integrity allowing an influx of fluid that causes lysis of the cell
How does the reproductive tract create barriers to pathogens?
acidic secretions inhibit microbial growth within the vagina of the female reproductive tract
What are B-lymphocytes responsible for?
antibody-mediated immunity - plasma cells (synthesize and release antibodies)
What are T-lymphocytes responsible for?
cell-mediated immunity
What is the fourth step of inflammation?
delivery of plasma proteins
What do interferons do?
interferons are released from a cell and stimulate neighboring cells to destroy viral DNA and RNA
What are phagocytic cells?
neutrophil, macrophage, and dendritic cells
What is the third step of inflammation?
recruitment of immune cells
How does the GI tract create barriers to pathogens?
secretions associated with the gastrointestinal (GI) tract also function to protect us from microbes: the viscous saliva (with lysozyme and IgA) within the mouth trapes microbes, acid within the stomach creates a very low pH that destroys most microbes and toxins that are ingested, and defecation and vomiting eliminate microbes before they can enter the body from the GI tract.
Describe the shape and location of the thyroid gland. Why does it appear so red?
the thyroid gland is a butterfly-shaped gland located immediately inferior to the thyroid cartilage of the larynx (voice box) and anterior to the trachea. this gland is composed of left and right lobes, which are connected at the anterior midline by a narrow isthmus. Both lobes of the thyroid gland are highly vascularized, giving the gland an intense reddish coloration. the entire gland is enclosed within a connective tissue capsule
What is the hypothalamic-pituitary-thyroid axis?
thyroid hormone is released from the thyroid gland as a result of the integrated activities of the hypothalamus and anterior pituitary. this physiologic relationship is referred to as the hypothalamic-pituitary thyroid axis
What is the second step of inflammation?
vasodilation of arterioles (this increases blood flow) and increased permeability of capillaries (this allows fluid and white blood cells to exit the capillary)
