Masao Hayashi, MD

IgD is present on the surface of many B cells acne 2009 dress proven 30 gm permethrin, but its functhe appropriate antigen gains entry to the body and binds with tion is uncertain acne lesions 30 gm permethrin purchase with visa. Plasma cell Note that this classification is based on different ways in which antibodies function skin care vietnam order generic permethrin line. Within each functional subclass are millions of different antibodies acne when pregnant buy 30 gm permethrin mastercard, each able to bind with a specific antigen only acne early sign of pregnancy generic 30 gm permethrin with mastercard. Characteristics of the arm regions of the Y determine the specificity of the antibody. Properties of the tail portion of the antibody determine the functional properties of the antibody (what the antibody does once it binds with antigen). It is able to bind only with the specific antigen that "fits" its antigen-binding sites (Fab) on the arm tips. The tail region (Fc) binds with particular mediators of antibodyinduced activities. Antibodies and immune responses Immunoglobulins cannot directly destroy foreign organisms or other unwanted materials on binding with antigens on their surfaces. Instead, antibodies exert their protective influence by Neutralization and agglutination Antibodies can physically hinder some antigens from exerting their detrimental effects. For example, by combining with bacterial toxins, antibodies can prevent these harmful chemicals from interacting with susceptible cells. Antibodies physically hinder antigens through neutralization or (a) agglutination and precipitation. Antibodies amplify innate immune responses by (b) activating the complement system, (c) enhancing phagocytosis by acting as opsonins, and (d) stimulating killer cells. Similarly, antibodies can bind with surface antigens on some types of viruses, preventing these viruses from entering cells, where they could exert their damaging effects. Sometimes multiple antibody molecules can cross-link numerous antigen molecules into chains or lattices of antigen- antibody complexes. The process in which foreign cells, such as bacteria or mismatched transfused red blood cells, bind together in such a clump is known as agglutination. When linked antigen-antibody complexes involve soluble antigens, such as tetanus toxin, the lattice can become so large that it precipitates out of solution. However, the tendency for certain antigens to agglutinate or precipitate on forming large complexes with antibodies specific for them is useful clinically and experimentally for detecting the presence of particular antigens or antibodies. Pregnancy diagnosis tests, for example, use this principle to detect, in urine, the presence of a hormone secreted soon after conception. In these ways, antibodies, although unable to directly destroy invading bacteria or other undesirable material, bring about destruction of the antigens to which they are specifically attached: specifically, by amplifying other nonspecific lethal defence mechanisms. At the same time they enhance the activity of these defence systems by the following methods: 1. When an appropriate antigen binds with an antibody, receptors on the tail portion of the antibody bind with and activate C1, the first component of the complement system. This sets off the cascade of events leading to formation of the membrane attack complex, which is specifically directed at the membrane of the invading cell that bears the antigen that initiated the activation process. Furthermore, various activated complement components enhance virtually every aspect of the inflammatory process. The same complement system is activated by an antigen-antibody complex regardless of the type of antigen. The tail portion of an antigen-bound IgG antibody binds with a receptor on the surface of a phagocyte and subsequently promotes phagocytosis of the antigencontaining victim attached to the antibody. Occasionally an overzealous antigen-antibody response inadvertently causes damage to normal cells as well as to invading foreign cells. Typically, antigen-antibody complexes, formed in response to foreign invaders, are removed by phagocytic cells after having revved up nonspecific defence strategies. If large numbers of these complexes are continuously produced, however, the phagocytes cannot clear away all the immune complexes formed. Antigen-antibody complexes that are not removed continue to activate the complement system, among other things. Excessive amounts of activated complement and other inflammatory agents may "spill over," damaging surrounding normal cells as well as the unwanted cells. Furthermore, destruction is not necessarily restricted to the initial site of inflammation. Such damage produced by immune complexes is referred to as an immune complex disease, which can be a complicating outcome of bacterial, viral, or parasitic infection. Yet each B cell is preprogrammed to respond to only one of these millions of different antigens. Other antigens cannot combine with the same B cell and induce it to secrete different antibodies. The astonishing implication is that each of us is equipped with millions of different preformed B lymphocytes, at least one for every possible antigen that we might ever encounter-including those specific for synthetic substances that do not exist in nature. The clonal selection theory proposes how a matching B cell responds to its antigen. Early researchers in immunological theory believed antibodies were "made to order" whenever a foreign antigen gained entry to the body. All offspring of a particular ancestral B lymphocyte form a family of identical cells, or a clone, that is committed to producing the same specific antibody. B cells remain dormant, not actually secreting their particular antibody product nor undergoing rapid division until (or unless) they come into contact with the appropriate antigen. Lymphocytes that have not yet been exposed to their specific antigen are known as naive lymphocytes. Here, they serve as receptor sites for binding with a specific kind of antigen, almost like advertisements for the kind of antibody the cell can produce. Selected clones Antigen binding causes the activated B-cell clone to multiply and differentiate into two cell types: plasma cells and memory cells. Most progeny are transformed into active plasma cells, which are prolific producers of customized antibodies that contain the same antigen-binding sites as the surface receptors. However, plasma cells switch to producing IgG antibodies, which are secreted rather than remaining membrane bound. In the blood, the secreted antibodies combine with the invading free antigen (not bound to lymphocytes), marking it for destruction by the complement system, phagocytic ingestion, or other means. B cell specific to antigen Plasma cells Not all the new B lymphocytes produced by the specifically activated clone differentiate into antibody-secreting plasma cells. A small proportion of them become memory cells, which do not participate in the current immune attack against the antigen, but instead remain dormant and expand the specific clone. If the person is ever re-exposed to the same antigen, these memory cells are primed and ready for even more immediate action than were the original lymphocytes in the clone. Those clones specific for antigens to which a person is never exposed remain dormant for life, whereas Binding of antigen and interaction with a helper T cell stimulates the matching B cells to those specific for antigens in the indidivide and expand the clone of selected cells. The different naive clones provide protection against unknown new pathogens, and the evolving populations of memory cells protect against the recurrence of infections Memory encountered in the past. A few new B-cell clones differentiate into memory B cells, which respond to a later encounter with the same antigen. The B-cell clone specific to the antigen proliferates and differentiates into plasma cells and memory cells. Plasma cells secrete antibodies that bind with free antigen not attached to B cells. Memory cells expand the specific clone and are primed and ready for subsequent exposure to the same antigen. Meanwhile, symptoms characteristic of the particular microbial invasion persist until either the invader succumbs to the mounting specific immune attack against it or the infected person dies. Pasteur demonstrated that the disease-inducing capability of organisms could be greatly reduced (attenuated) so they could no longer produce disease but would still induce antibody formation when introduced into the body- the basic principle of modern vaccines. Pasteur isolated and heated anthrax bacteria, then injected these attenuated organisms into a group of healthy sheep. A few weeks later at a gathering of fellow scientists, Pasteur injected these vaccinated sheep as well as a group of unvaccinated sheep with fully potent anthrax bacteria. The result was dramatic-all the vaccinated sheep survived, but all the unvaccinated sheep died. Today, vaccinations work using the same principles as those used by Jenner and Pasteur, but we have developed other methods of delivering the foreign antigen. Inserting an inactivated vaccine consisting of virus particles that have been grown in culture and then killed. Using an attenuated vaccine consisting of live virus particles with low virulence 3. Nearly 2500 years ago, our ancestors were aware of the existence of immune protection. However, the ancients did not understand the basis of this protection, so they could not manipulate it to their advantage. Early attempts to deliberately acquire lifelong protection against smallpox, a dreaded disease that was highly infectious and frequently fatal (up to 40% of the sick died), consisted of intentionally exposing oneself by coming into direct contact with a person suffering from a milder form of the disease. The hope was to protect against a future fatal bout of smallpox by deliberately inducing a mild case of the disease. By the beginning of the 17th century, this technique had evolved into using a needle to extract small amounts of pus from active smallpox pustules (the fluid-filled bumps on the skin, which leave a characteristic depressed scar or pock mark after healing) and introducing this infectious material into healthy individuals. This inoculation process was done by applying the pus directly to slight cuts in the skin or by inhaling dried pus. Edward Jenner, an English physician, was the first to demonstrate that immunity against cowpox, a disease similar to but less serious than smallpox, could also protect humans against smallpox. Having observed that milkmaids who got cowpox seemed to be protected from smallpox, Jenner in 1796 inoculated a healthy boy with pus he had extracted from cowpox boils. After the boy recovered, Jenner (not being restricted by modern ethical standards of research on human subjects) deliberately inoculated him with what was considered a normally fatal dose of smallpox infectious material. Influenza vaccination for health-care workers who work with elderly people in institutions: A systematic review. Longterm protection against the same antigen, however, is primarily attributable to the memory cells. If the same antigen ever reappears, the long-lived memory cells launch a more rapid, more potent, and longer-lasting secondary response than occurred during the primary response. This swifter, more powerful immune attack is frequently adequate to prevent or minimize overt infection on subsequent exposures to the same microbe, forming the basis of long-term immunity against a specific disease. The original antigenic exposure that induces the formation of memory cells can occur through the person either actually having the disease or being vaccinated. Vaccination deliberately exposes the person to a pathogen that has been stripped of its disease-inducing capability but that can still induce antibody formation against itself. Relative antibody response (in logarithmic scale) 103 (1000) 102 (100) 101 (10) Relative antibody response (in logarithmic scale) 104 (10 000) in already-formed B cells. In this way, a huge antibody repertoire is possible using only a modest share of the genetic blueprint. Active and passive immunity the production of antibodies as a result of exposure to an antigen is referred to as active immunity against that antigen. The immediate "borrowed" immunity conferred upon receipt of preTime of subsequent exposure Time of first exposure to microbial antigen to microbial antigen formed antibodies is known as passive immunity. The primary response does not peak for a couple of weeks, whereas the secondary tains IgA antibodies that provide further protecresponse peaks in a week. The magnitude of the secondary response is 100 times greater than the tion for breastfed babies. Antibody-synthesizing ability does same each time a person is reinfected with a microbe that the not develop for about a month after birth. Typically, the adminiseach of us has the potential to actively produce antibodies, tered preformed antibodies have been harvested from another how is it possible for an individual to have such a tremendous source (often nonhuman) that has been exposed to an attenuated diversity of B lymphocytes, each capable of producing a form of the antigen. The different portion of the genetic code being used by each B-cell result may be a severe allergic reaction to the treatment, a condiclone), along with all the other genetic instructions used by tion known as serum sickness. Actually, only a relatively small number of gene fragments code for antibody synthesis, but during B-cell development these fragments are cut, reshuffled, and spliced Check Your Understanding 11. Describe the structure and function of the Fab and Fc regions genes are later even further diversified by somatic mutation of an antibody. List the means by which antibodies help to eliminate invading B cells are highly prone to mutations in the region that codes microbes. According to the clonal selection theory, draw a flow diagram Each different mutant cell in turn gives rise to a new clone. T cells account for approximately 50 to 70 percent of the total lymphocyte number in circulation. The T lymphocytes are equally as important in defence against most viral infections as B lymphocytes are and also play an important regulatory role in immune mechanisms. Unlike B cells, which secrete antibodies that can attack antigen at long distances, T cells do not secrete antibodies. Instead, they must directly contact their targets, a process known as cell-mediated immunity. T cells of the killer type release chemicals that destroy targeted cells that they contact, such as virus-infected cells and cancer cells. On its plasma membrane, each T cell bears unique receptor proteins called T-cell receptors, similar although not identical to the surface receptors on B cells. Immature lymphocytes acquire their T-cell receptors in the thymus during their differentiation into T cells. A delay of a few days generally follows exposure to the appropriate antigen before sensitized (activated) T cells are prepared to launch a cell-mediated immune attack. When exposed to a specific antigen combination, cells of the complementary T-cell clone proliferate and differentiate for several days, a process that yields large numbers of activated effector T cells that carry out various cell-mediated responses. Helper T cells are by far the most numerous T cells, making up 60­80 percent of circulating T cells. Primary responses tend to be initiated in the lymphoid tissues, where naive lymphocytes and antigen-presenting cells interact.

Response Response Endocrine integrating center Output signal #2: hormone Target 165 168 181 182 186 188 191 Response 6 skin care questionnaire 30 gm permethrin purchase otc. Electrical signal that passes through neuron skin care 20s generic permethrin 30 gm with amex, then chemical neurotransmitters that carry the signal from cell to cell acne with pus generic 30 gm permethrin mastercard. Specificity Neural control is very specific because each neuron has a specific target cell or cells to which it sends its message acne solutions cheap permethrin 30 gm amex. Anatomically skin care clinique generic 30 gm permethrin visa, we can isolate a neuron and trace it from its origin to where it terminates on its target. Endocrine control is more general because the chemical messenger is released into the blood and can reach virtually every cell in the body. Nature of the Signal the nervous system uses both electrical and chemical signals to send information throughout the body. Electrical signals travel long distances through neurons, releasing chemical signals (neurotransmitters) that diffuse across the small gap between the neuron and its target. In a limited number of instances, electrical signals pass directly from cell to cell through gap junctions. The endocrine system uses only chemical signals: hormones secreted into the blood by endocrine glands or cells. In a neuroendocrine pathway, a neuron creates an electrical signal, but the chemical released by the neuron is a neurohormone that goes into the blood for general distribution. The electrical signals of the nervous system cover great distances very rapidly, with speeds of up to 120 m/sec. Their distribution through the circulatory system and diffusion from capillary to receptors take considerably longer than signals through neurons. In target tissues, the response may take minutes to hours before it can be measured. A mouse ventures out of his hole and sees a cat ready to pounce on him and eat him. If his brain and feet were only 5 micrometers (5 mm = 1/200 millimeter) apart, it would take a chemical signal 20 milliseconds (msec) to diffuse across the space and the mouse could escape. If the brain and feet were 50 mm (1/20 millimeter) apart, diffusion would take 2 seconds and the mouse might get caught. The moral of this tale is that reflexes requiring a speedy response are mediated by the nervous system because they are so much more rapid. The neurotransmitter released by a neuron combines with a receptor on the target cell and initiates a response. The response is usually very brief, however, because the neurotransmitter is rapidly removed from the vicinity of the receptor by various mechanisms. To get a sustained response, multiple repeating signals must be sent through the neuron. Most of the ongoing, long-term functions of the body, such as metabolism and reproduction, fall under the control of the endocrine system. Coding for Stimulus Intensity As a stimulus increases in intensity, control systems must have a mechanism for conveying this information to the integrating center. The signal strength from any one neuron is constant in magnitude and therefore cannot reflect stimulus intensity. In the endocrine system, stimulus intensity is reflected by the amount of hormone released: the stronger the stimulus, the more hormone is released. The endocrine cell acts as both sensor and integrating center so there is no input pathway. The endocrine cell itself monitors the regulated variable and is programmed to initiate a response when the variable goes out of an acceptable range. The output pathway is the hormone, and the target is any cell having the appropriate hormone receptor. An example of a simple endocrine reflex is secretion of the hormone insulin in response to changes in blood glucose level. Any target cell in the body that has insulin receptors responds to the hormone and initiates processes that take glucose out of the blood. The removal of the stimulus acts in a negative feedback manner: the response loop shuts off when blood glucose levels fall below a certain concentration. The neural reflex is represented in its simplest form by the knee jerk (or patellar tendon) reflex. A signal travels through an afferent sensory neuron to the spinal cord (the integrating center). If the blow is strong enough (exceeds threshold), a signal travels from the spinal cord through an efferent neuron to the muscles of the thigh (the target or effector). In response, the muscles contract, causing the lower leg to kick outward (the knee jerk). Q7: What do you think happens to insulin secretion when blood glucose levels fall An electrical signal in the efferent neuron triggers the release of the neurohormone oxytocin from the brain into the circulation. Oxytocin is carried to the breast, where it causes contraction of smooth muscles in the breast (the target), resulting in the ejection of milk. During a meal, the presence of food in the stomach stretches the wall of the digestive tract and sends input signals to the brain. The brain in turn sends excitatory output signals to the beta cells, telling them to release insulin. These signals take place even before the food has been absorbed and blood glucose levels have gone up (a feedforward reflex [p. This pathway therefore has two integrating centers (the brain and the beta cells). This pattern is typical of some hormones released by the anterior pituitary, an endocrine gland located just below the brain (see Chapter 7 for details). In the three complex pathways shown, the brain is the first integrating center and the neurohormone is the first output pathway. The second endocrine gland in the pathway (E2) is the third integrating center, and its hormone is the third output pathway. In this running problem, you learned about glucose homeostasis and how it is maintained by insulin and glucagon. The disease diabetes mellitus is an indication that glucose homeostasis has been disrupted. Check your understanding of this running problem by comparing your answers to the information in the summary table. With careful attention to his diet and with a regular exercise program, he has been able to keep his blood glucose levels under control. Diabetes is a growing epidemic in the United States, with more than 29 million diabetics in the United States in 2016 (about 9% of the population). Even scarier is the estimate that another 86 million people are considered "prediabetic" -at significant risk of becoming diabetic. Question Q1: In which type of diabetes is the signal pathway for insulin more likely to be defective Facts Insulin is a peptide hormone that uses membrane receptors linked to second messengers to transmit its signal to cells. People with type 1 diabetes lack insulin; people with type 2 diabetes have normal-toelevated insulin levels. Integration and Analysis Normal or high insulin levels suggest that the problem is not with amount of insulin but with the action of the insulin at the cell. The problem in type 2 diabetes could be a defective signal transduction mechanism. Would you expect to find its receptor on the cell surface or in the cytoplasm of the target cells Q3: In which form of diabetes are the insulin receptors more likely to be up-regulated Continued Integration and Analysis Proteins are lipophobic so protein hormones like insulin have cell surface receptors. Stimulus: increase in blood glucose levels; sensor: beta cells of the pancreas that sense the change; integrating center: beta cells; output signal: insulin; targets: any tissues of the body that respond to insulin; responses: cellular uptake and use of glucose. An increase in blood glucose concentration stimulates insulin release; therefore, a decrease in blood glucose should decrease insulin release. In this example, the response (lower blood glucose) offsets the stimulus (increased blood glucose), so a negative feedback loop is operating. Up-regulation of receptors usually occurs if a signal molecule is present in unusually low concentrations [p. The stimulus for insulin release is an Q7: What do you think happens to the rate increase in blood glucose levels. In negaof insulin secretion when blood glucose tive feedback, the response offsets the levels fall The sensors, integrating centers, and targets of physiological control systems are described in the context of reflex control pathways, which vary from simple to complex. Functional control systems require efficient communication that uses various combinations of chemical and electrical signals. Those signals that cannot enter the cell must use membrane receptor proteins and signal transduction to transfer their information into the cell. The interaction of signal molecules with protein receptors illustrates another fundamental theme of physiology, molecular interactions. When they are open, chemical and electrical signals pass directly from one cell to the next. The activity of paracrine and autocrine signal molecules is limited by diffusion distance. Chemical signals bind to receptors and change intracellular signal molecules that direct the response. Lipophilic signal molecules enter the cell and combine with cytoplasmic or nuclear receptors. Lipophobic signal molecules and some lipophilic molecules combine with membrane receptors. Signal transduction pathways use membrane receptor proteins and intracellular second messenger molecules to translate signal information into an intracellular response. G proteins linked to amplifier enzymes are the most prevalent signal transduction system. Cells exposed to abnormally high concentrations of a signal for a sustained period of time attempt to bring their response back to normal through down-regulation or by desensitization. Up-regulation is the opposite of down-regulation and involves increasing the number of receptors for a signal. Cells have mechanisms for terminating signal pathways, such as removing the signal molecule or breaking down the receptor-ligand complex. Many diseases have been linked to defects in various aspects of signal pathways, such as missing or defective receptors. Calcium is an important signal molecule that binds to calmodulin to alter enzyme activity. The arachidonic acid cascade creates lipid signal molecules, such as leukotrienes, prostaglandins, and thromboxanes. Walter Cannon first stated four basic postulates of homeostasis: (1) the nervous system plays an important role in maintaining homeostasis. In reflex control pathways, an integrating center makes the decision to respond to a change. A chemical or electrical signal to the target cell or tissue then initiates the response. Long-distance reflex pathways involve the nervous and endocrine systems and cytokines. Neural control is faster and more specific than endocrine control but is usually of shorter duration. Endocrine control is less specific and slower to start but is longer lasting and is usually amplified. Many reflex pathways are complex combinations of neural and endocrine control mechanisms. Which two body systems maintain homeostasis by monitoring and responding to changes in the environment In a signal transduction pathway, the signal ligand, also called the first messenger, binds to a(n), which activates and changes intracellular. An enzyme known as protein kinase adds the functional group to its substrate, by transferring it from a(n) molecule. In a negative feedback loop, the response moves the system in the (same/opposite) direction as the stimulus moves it. Now identify the integrating center for examples (a), (c), and (d) in question 17. You are sitting quietly at your desk, studying, when you become aware of the bitterly cold winds blowing outside at 30 mph, and you begin to feel a little chilly. While you are strolling through the shopping district, the aroma of cinnamon sticky buns reaches you. When she exposes the airways to the neurotransmitter acetylcholine, the smooth muscle contracts. Which chemical messenger is secreted in higher concentrations: acetylcholine or epinephrine Arrange the following terms in the order of a reflex and give an anatomical example of each step when applicable: input signal, integrating center, output signal, response, sensor, stimulus, target. Compare and contrast the advantages and disadvantages of neural versus endocrine control mechanisms. In a signal cascade for rhodopsin, a photoreceptor molecule, one rhodopsin activates 1,000 molecules of transducin, the next molecule in the signal cascade. David was placed on insulin injections, a treatment he would continue for the rest of his life.

Major Approaches the goal is not to find a replacement for whole blood but to duplicate its O2 -carrying capacity acne 2004 buy cheap permethrin 30 gm on-line. The biggest need for blood transfusions is to replace acute blood loss in accident victims skin care 0-1 years buy permethrin 30 gm line, surgical patients acne 404 nuke permethrin 30 gm order free shipping, and wounded soldiers acne 24 cheap 30 gm permethrin with amex. Problematically acne natural treatment discount 30 gm permethrin visa, red blood cells are the whole-blood component that requires refrigeration, has a short shelf life, and bears the markers for the various blood types. Some have reached the stage of clinical trials, but no products have yet reached the market, although they are getting close. Haemoglobin Products By far the greatest number of research efforts has focused on manipulating the structure of haemoglobin so that it can be effectively and safely administered as a substitute for whole-blood transfusions. A cross-binding reagent has been developed that keeps haemoglobin molecules intact when they are outside the confines of red blood cells, thereby surmounting one major obstacle to administering free haemoglobin. Instead of the blood being discarded, its haemoglobin is extracted, purified, sterilized, and chemically stabilized. However, this strategy relies on the continued practice of collecting human blood donations. Bovine haemoglobin is readily available from slaughterhouses, is cheap, and can be treated for administration to humans. A big concern with these products is the potential of introducing into humans unknown disease-causing microbes that might be lurking in the bovine products. A potential candidate as a blood substitute is genetically engineered haemoglobin that bypasses the ongoing need for human donors or the risk of spreading disease from cows to humans. Genetic engineers can insert the gene for human haemoglobin into bacteria, which act as a factory to produce the desired haemoglobin product. A drawback for genetically engineered haemoglobin is the high cost involved in operating the facilities. By changing surgical practices, the medical community has reduced the need for transfusions. The necessity of matching blood types for transfusions is a major reason for waste at blood banks. Therefore, a blood bank may be discarding stocks of one blood type that has gone unused while facing a serious shortage of another type. Their administration can cause flu-like symptoms, and because of poor excretion, they may be retained and accumulate in the body. Tactics to Reduce Need for Donated Blood Other tactics besides blood substitutes aimed toward reducing the need for donated blood include the following: As this list of strategies attests, considerable progress has been made toward developing a safe, effective alternative to wholeblood transfusions. Yet after more than three decades of intense effort, considerable challenges remain, and no ideal solution has been found. Normal haematocrit values for males and females are 42 percent and 38 percent, respectively. One negative aspect of increased haematocrit is a reduced ability of the heart to circulate the blood (because of increased friction), thereby decreasing the timely delivery of oxygen to the tissues. Primary polycythaemia is caused by a tumour-like condition of the bone marrow in which erythropoiesis proceeds at an excessive, uncontrolled rate instead of being subject to the normal erythropoietin regulatory mechanism. It occurs normally in people living at high altitudes, where less oxygen is available in the atmospheric air, or people in whom O2 delivery to the tissues is impaired by chronic lung disease or cardiac failure. The red cell count in secondary polycythaemia is usually lower than that in primary polycythaemia, typically averaging 6­8 million cells/mm3. A normal number of erythrocytes is simply concentrated in a smaller plasma volume. Relative polycythaemia frequently occurs in weight-class sports, such as boxing, wrestling, judo, and rowing. In high school or university wrestling, average weekly body weight fluctuations commonly exceed 2. There have been reports of athletes decreasing body weight by 5 kg in less than five hours, all via dehydration. Typically, dehydration methods include diuretics, saunas, rubber suits, and running. The physiological effects of dehydration include reductions in plasma volume, cardiac output, peripheral blood flow (muscle and skin), sweating, thermoregulatory ability, and rate of stomach emptying. However, once rehydration takes place via the consumption of fluids, primarily water, these negative physiological changes are reversed as the body moves toward homeostasis. Describe the anatomic features of erythrocytes that contribute to the efficiency with which they transport oxygen. The cells destined to become leukocytes eventually differentiate into various committed cell lines and proliferate under the influence of appropriate stimulating factors. Granulocytes and monocytes are produced only in the bone marrow, which releases these mature leukocytes into the blood. Lymphocytes are originally derived from precursor cells in the bone marrow, but most new lymphocytes are actually produced by lymphocytes already in the lymphoid tissues (lymphocytecontaining), such as the lymph nodes and tonsils. The total number of leukocytes normally ranges from 5 million to 10 million cells per millilitre of blood, with an average of 7 million cells/mL-expressed as an average white blood cell count of 7000/mm3 (Table 10-2). Leukocytes are the least numerous of the blood cells (about 1 white blood cell for every 700 red blood cells), not because fewer are produced but because they are merely in transit while in the blood. Normally, about two-thirds of the circulating leukocytes are granulocytes, Defence agents To carry out their functions, leukocytes largely use a "seek out and attack" strategy; that is, they go to sites of invasion or tissue damage. Unlike erythrocytes, which are of uniform structure, identical function, and constant number, leukocytes vary in structure, function, and number. There are five different types of circulating leukocytes-neutrophils, eosinophils, basophils, monocytes, and lymphocytes-each with a characteristic structure and function. Neutrophils, eosinophils, and basophils are categorized as polymorphonuclear granulocytes (polymorphonuclear means "many-shaped nucleus"; granulocyte means "granule-containing cell"). Their nuclei are segmented into several lobes of varying shapes, and their cytoplasm contains an abundance of membrane-enclosed granules. Monocytes and lymphocytes are known as mononuclear agranulocytes (mononuclear means "single nucleus"; agranulocyte means "cell lacking granules"). Monocytes are the larger of the two view is a blood smear under low magnification showing a singular leukocyte in the centre. All the blood cell types ultimately originate from the same undifferentiated pluripotent stem cells in the red bone marrow. However, the total number of white cells and the percentage of each type may vary considerably to meet changing defence needs. Depending on the type and extent of assault the body is combating, different types of leukocytes are selectively produced at varying rates. Chemical messengers arising from invaded or damaged tissues or from activated leukocytes themselves govern the rates of production of the various leukocytes. Specific hormones analogous to erythropoietin direct the differentiation and proliferation of each cell type. Some of these hormones have been identified and can be produced in the laboratory; an example is granulocyte colony­ stimulating factor, which stimulates increased replication and release of granulocytes, especially neutrophils, from the bone marrow. Neutrophils are the first defenders against bacterial invasion, are very important in inflammatory responses, and act as scavengers to clean up debris. Because an elevated neutrophil count is highly indicative of bacterial infection, it is appropriate to initiate antibiotic therapy long before the true causative agent is actually known. They are quite similar structurally and functionally to mast cells, which never circulate in the blood, but instead are dispersed in connective tissue throughout the body. Researchers have shown that basophils arise from the bone marrow, whereas mast cells are derived from precursor cells in connective tissue. Both basophils and mast cells synthesize and store histamine and heparin: powerful chemical substances that can be released on appropriate stimulation. Histamine release is important in allergic reactions, whereas heparin speeds up removal of fat particles from the blood after a fatty meal. Heparin can also prevent clotting (coagulation) of blood samples drawn for clinical analysis and is used extensively as an anticoagulant drug, but whether it plays a physiological role in clot prevention is still debated. Once released into the blood from the bone marrow, a granulocyte usually stays in transit in the blood for less than a day before leaving the blood vessels to enter the tissues, where it survives another three to four days unless it dies sooner in the line of duty. By comparison, the functions and lifespans of the agranulocytes are as follows: · Monocytes-major function: phagocytosis, antigen presentation, cytokine production, and cytotoxicity. They emerge from the bone marrow while still immature, and circulate for only a day or two before settling down in various tissues throughout the body. At their new residences, monocytes mature and greatly enlarge, becoming the large tissue phagocytes known as macrophages (macro means "large"; phage means "eater"). A phagocytic cell can ingest only a limited amount of foreign material before it succumbs. B lymphocytes (B cells) produce antibodies, which circulate in the blood and are responsible for antibody-mediated, or humoural, immunity. An antibody binds with and marks for destruction (by phagocytosis or other means) the specific kinds of foreign matter, such as bacteria, that induced production of the antibody. T lymphocytes (T cells) do not produce antibodies; instead, they directly destroy their specific target cells by releasing chemicals that punch holes in the victim cells, a process called cell-mediated immunity. The target cells of T cells include body cells invaded by viruses and cancer cells. During this period, most of them continually recycle among the lymphoid tissues, lymph, and blood, spending only a few hours at a time in the blood. Therefore, only a small part of the total lymphocytes are in transit in the blood at any given moment. The bone marrow can greatly slow down or even stop production of white blood cells when it is exposed to certain toxic chemical agents (such as benzene and anticancer drugs) or to excessive radiation. The only defence still available when the bone marrow fails is the immune capabilities of the lymphocytes produced by the lymphoid organs. In infectious mononucleosis, not only does the number of lymphocytes (but not other leukocytes) in the blood increase, but also many of the lymphocytes are atypical in structure. This condition, which is caused by the Epstein-Barr virus, is characterized by pronounced fatigue, a mild sore throat, and low-grade fever. Another devastating consequence of leukaemia is displacement of the other blood cell lines in the bone marrow. This results in anaemia due to a reduction in erythropoiesis and in internal bleeding caused by a deficit of platelets. Platelets play a critical role in preventing bleeding from the myriad tiny breaks that normally occur in small blood vessel walls. Consequently, overwhelming infections and haemorrhage are the most common causes of death in leukemic patients. In the next section we examine the role of platelets in detail to show how they normally minimize the threat of haemorrhage. An average of 250 million platelets are normally present in each millilitre of blood (range of 150 000 to 350 000 / m3). Megakaryocytes are derived from the same undifferentiated stem cells that give rise to the erythrocytic and leukocytic cell lines. Platelets are essentially detached vesicles containing pieces of megakaryocyte cytoplasm wrapped in plasma membrane. Platelets remain functional for an average of 10 days, at which time they are removed from circulation by the tissue macrophages, especially those in the spleen and liver, and are replaced by newly released platelets from the bone marrow. The hormone thrombopoietin, produced by the liver, increases the number of megakaryocytes in the bone marrow and stimulates each megakaryocyte to produce more platelets. The factors that control thrombopoietin secretion and regulate the platelet level are currently under investigation. These stored platelets can be released from the spleen into the circulating blood as needed. However, they have organelles and cytosolic enzyme systems that generate energy and synthesize secretory products, which they store in numerous granules dispersed throughout the cytosol. Furthermore, platelets contain high concentrations of actin and myosin, which enable them to contract. Their secretory and contractile abilities are important in haemostasis, the topic we now examine. Haemostasis Haemostasis is the arrest of bleeding from a broken blood vessel-that is, the stopping of haemorrhage (haemo means "blood"; stasis means "standing"). The small capillaries, arterioles, and venules are often ruptured by minor traumas of everyday life; such traumas are the most common source of bleeding, although we often are not even aware that any damage has taken place. Bleeding from a severed artery is more profuse and therefore more dangerous than venous bleeding, because the outward driving pressure is greater in the arteries. First-aid measures for a severed artery include applying to the wound external pressure that is greater than the arterial blood pressure to temporarily halt the bleeding until the torn vessel can be surgically closed. If the accompanying drop in venous pressure is not enough to stop the bleeding, mild external compression is usually adequate. Haemostasis involves three major steps: (1) vascular spasm, (2) formation of a platelet plug, and (3) blood coagulation (clotting). They obviously play a major part in forming a platelet plug, but they also contribute significantly to the other two steps. The underlying mechanism is unclear but is thought to be an intrinsic response triggered by a paracrine released locally from the inner lining (endothelium) of the injured vessel. This constriction, or vascular spasm, slows blood flow through the defect and thus minimizes blood loss. Also, as the opposing endothelial surfaces of the vessel are pressed together by this initial vascular spasm, they become sticky and adhere to each other, further sealing off the damaged vessel. These physical measures alone cannot completely prevent further blood loss, but they minimize blood flow through the break in the vessel until the other haemostatic measures can actually plug up the hole. Collagen Outer connective tissue layer Smooth muscle Subendothelial connective tissue © 2016 Cengage 1 Platelets adhere to and are activated by exposed collagen at the site of vessel injury. Platelets are prevented from aggregating at the adjacent normal vessel lining by the release of prostacyclin and nitric oxide from the undamaged endothelial cells.

However acne era coat order permethrin master card, if a H 2 O deficit exists relative to the solute load skin care products cheap permethrin 30 gm on-line, the body fluids are too concentrated or are hypertonic acne 40 year old woman purchase permethrin master card, having an osmolarity greater than 300 mOsm/L skin care md buy generic permethrin 30 gm online. Recall that the driving force for H 2 O reabsorption throughout the entire length of the tubules is an osmotic gradient between the tubular lumen and the surrounding interstitial fluid acne 37 weeks pregnant buy generic permethrin on line. Therefore, given these osmotic considerations, you would expect that the kidneys could not excrete urine more or less concentrated than the body fluids. Indeed, this would be the case if the interstitial fluid surrounding the tubules in the kidneys were identical in osmolarity to the remaining body fluids. Water reabsorption would proceed only until the tubular fluid equilibrated osmotically with the interstitial fluid, and the body would have no way to eliminate excess H 2 O when the body fluids were hypotonic or to conserve H 2 O in the presence of hypertonicity. Fortunately, a large vertical osmotic gradient is uniquely maintained in the interstitial fluid of the medulla of each kidney. The kidneys and urine of varying concentrations Having considered how the kidneys deal with a variety of solutes in the plasma, we now examine renal handling of plasma H 2 O. Schematic representation of the kidney rotated 90 degrees from its normal position in an upright person for better visualization of the vertical osmotic gradient in the renal medulla. The osmolarity of the interstitial fluid throughout the renal cortex is otonic at 300 mOsm/L, but the osmolarity of the interstitial fluid in the renal medulla increases progressively from 300 mOsm/L at the boundary with the cortex to a maximum of 1200 mOsm/L at the junction with the renal pelvis. Conversely, the kidneys can put out a small volume of concentrated urine (down to 0. Unique anatomic arrangements and complex functional interactions between the various nephron components in the renal medulla establish and use the vertical osmotic gradient. Also, the vasa recta of juxtamedullary nephrons follow the same deep hairpin loop as the long loop of Henle. Flow in both the long loops of Henle and the vasa recta is considered countercurrent, because the flow in the two closely adjacent limbs of the loop moves in opposite directions. Also running through the medulla in the descending direction only, on their way to the renal pelvis, are the collecting ducts that serve both types of nephrons. Collectively, this entire functional organization is known as the medullary countercurrent system. A typical urine chart is set up on an eight-step scale, with the colour of urine ranging from a very light yellow (well hydrated) to a very dark yellow (severe dehydration). Other factors, such as the removal of excess B vitamins from the bloodstream, may cause a yellowing of the urine. If blood is present in the urine (haematuria), there may be damage to the kidney, and immediate medical attention is required. Dark-coloured (melanuria) urine may be caused by a melanoma (a malignant tumour of melanocytes). Reddish urine is associated with porphyria, which is a disorder of certain enzymes associated with heme and its biochemical pathway. Milky white urine is a condition called chyluria, caused by the presence of chyle that consists of lymph fluid and fats. As a result, by the end of the proximal tubule about 65 percent of the filtrate has been reabsorbed, but the 35 percent remaining in the tubular lumen still has the same osmolarity as the body fluids. The additional 15 percent of the filtered H 2 O is obligatorily reabsorbed from the loop of Henle during the establishment and maintenance of the vertical osmotic gradient, thereby altering the osmolarity of the tubular fluid. The descending limb (1) is highly permeable to H 2 O, and (2) does not actively extrude Na1-that is, does not reabsorb Na1. Therefore, salt leaves the tubular fluid without H 2 O osmotically following along. Even though the flow of fluids is continuous through the loop of Henle, we will see what happens by going step by step, much like making an animated film run so slowly that each frame can be viewed. When the ascending limb pump starts actively extruding salt, the medullary interstitial fluid becomes hypertonic. Water cannot follow osmotically from the ascending limb, because this limb is impermeable to H 2O. However, net diffusion of H 2O does occur from the descending limb into the interstitial fluid. The tubular fluid entering the descending limb from the proximal tubule is otonic. Because the descending limb is highly permeable to H 2O, net diffusion of H 2O occurs by osmosis out of the descending limb into the more concentrated interstitial fluid. The passive movement of H 2O out of the descending limb continues until the osmolarities of the fluid in the descending limb and interstitial fluid become equilibrated. Thus, the tubular fluid entering the loop of Henle immediately starts to become more concentrated as it loses H 2O. At the bottom of the loop, a comparable mass of 400 mOsm/L fluid from the descending limb moves forward around the tip into the ascending limb, placing it opposite a 400 mOsm/L region in the descending limb. Note that the 200 mOsm/L concentration difference has been lost at both the top and the bottom of the loop. Note, however, that the concentration of tubular fluid is progressively increasing in the descending limb and progressively decreasing in the ascending limb. Because the interstitial fluid always achieves equilibrium with the descending limb, an incremental vertical concentration gradient, ranging from 300 to 1200 mOsm/L, is likewise established in the medullary interstitial fluid. In contrast, the concentration of the tubular fluid progressively decreases in the ascending limb because salt is pumped out, but H 2O is unable to follow. In fact, the tubular fluid even becomes hypotonic before it leaves the ascending limb to enter the distal tubule at a concentration of 100 mOsm/L- one-third the normal concentration of body fluids. Even though the ascending limb pump can generate a gradient of only 200 mOsm/L, this effect is multiplied into a large vertical gradient because of the countercurrent flow within the loop. This concentrating mechanism accomplished by the loop of Henle is known as countercurrent multiplication. We have artificially described countercurrent multiplication in a stop-and-flow, stepwise fashion to facilitate understanding. It is important to realize that once the incremental medullary gradient is established, it stays constant. This is due to the continuous flow of fluid, the ongoing ascending limb active transport, and the accompanying descending limb passive fluxes. If you consider only what happens to the tubular fluid as it flows through the loop of Henle, the whole process seems an exercise in futility. The isotonic fluid that enters the loop becomes progressively more concentrated as it flows down the descending limb, achieving a maximum concentration of 1200 mOsm/L, only to become progressively more dilute as it flows up the ascending limb, finally leaving the loop at a minimum concentration of 100 mOsm/L. What is the point of concentrating the fluid fourfold and then turning around and diluting it until it leaves at one-third the concentration at which it entered First, it establishes a vertical osmotic gradient in the medullary interstitial fluid. This gradient, in turn, is used by the collecting ducts to concentrate the tubular fluid so that a urine more concentrated than normal body fluids can be excreted. Second, the fact that the fluid is hypotonic as it enters the distal parts of the tubule enables the kidneys to excrete a urine more dilute than normal body fluids. And third, it allows for the overall volume of urine to be significantly reduced, which also allows the body to conserve both salt and water. This is more than 13 times the amount of plasma H 2 O in the entire circulatory system. The fluid leaving the loop of Henle enters the distal tubule at 100 mOsm/L, so it is hypotonic to the surrounding isotonic (300 mOsm/L) interstitial fluid of the renal cortex, through which the distal tubule passes. The distal tubule then empties into the collecting duct, which is bathed by progressively increasing concentrations (300­1200 mOsm/L) of surrounding interstitial fluid as it descends through the medulla. For H 2 O absorption to occur across a segment of the tubule, two criteria must be met: (1) an osmotic gradient must exist across the tubule, and (2) the tubular segment must be permeable to H 2 O. Unlike the proximal tubule, where the aquaporins are present and open, the distal and collecting tubules are impermeable to H 2 O except in the presence of vasopressin-also known as antidiuretic hormone (anti means "against"; diuretic means "increased urine output")3 -which increases their permeability to H 2 O. Vasopressin is produced by several specific neuronal cell bodies in the hypothalamus part of the brain, then stored in the posterior pituitary gland, which is attached to the hypothalamus by a thin stalk. The hypothalamus controls release of vasopressin from the posterior pituitary into the blood. Vasopressin reaches the basolateral membrane of the tubular cells lining the distal and collecting tubules through the circulatory system. The H 2 O channels in the basolateral membrane are always present, so this membrane is always permeable to H 2 O. By permitting more H 2 O to permeate from the lumen into the tubular cells, the additional vasopressin-regulated luminal channels increase H 2 O reabsorption from the filtrate into the interstitial fluid. The tubular response to vasopressin is graded: the more vasopressin present, the more luminal water channels are inserted, and the greater the permeability of the distal and collecting tubules to H 2 O. The channels are retrieved when vasopressin secretion decreases and 3 Even though textbooks traditionally have tended to use the name antidiuretic hormone for this hormone, especially when discussing its actions on the kidney, investigators in the field now prefer vasopressin. Secretion in response to reduced plasma volume is activated by pressure receptors in the veins, atria, and carotids. Secretion in response to increases in plasma osmotic pressure is mediated by osmoreceptors in the hypothalamus. Many factors can reduce the secretion of vasopressin from the posterior pituitary gland, including the consumption of caffeine. The resulting decrease in water reabsorption by the kidneys may lead to a higher urinary production. Thus, caffeine causes the body to lose more water and may lead to dehydration if it is consumed excessively. After the obligatory H 2 O reabsorption from the proximal tubule (65% of the filtered H 2 O) and loop of Henle (15% of the filtered H 2 O), 20 percent of the filtered H 2 O remains in the lumen to enter the distal and collecting tubules for variable reabsorption that is under hormonal control. Consequently, the tubular fluid loses more H 2 O by osmosis Distal tubular cell and becomes further concentrated, only to move farther forward and be exposed to an even higher interstitial fluid osmolarity and lose even more H 2 O, and so on. As a result of this extensive H2O Increases permeability of vasopressin-promoted reabsorption of H 2 O in luminal membrane to H2O the late segments of the tubule, a small volume H2O by inserting new water channels of urine concentrated up to 1200 mOsm/L can Water be excreted. The reab1 Blood-borne vasopressin binds with its receptor sites on the basolateral membrane sorbed H 2 O entering the medullary interstitial of a distal or collecting tubule cell. Water exits the cell through a different water channel permanently positioned at the a minimum volume of H 2 O must be basolateral border. Accordingly, H 2 O permevolume of urine required to excrete these wastes is 500 mL/day ability is reduced when vasopressin secretion decreases. Vasopressin influences H 2 O permeability only in the distal (600 mOsm of waste / day 4 1200 mOsm / L of urine 5 0. Ultimately, this leads to the secretion of tubular cells until the tubular fluid reaches a maximum concenvasopressin (antidiuretic hormone) to enhance water reabtration of 300 mOsm/L by the end of the distal tubule. From proximal tubule 300 300 Loop of Henle 600 300 300 Filtrate has concentration of 100 mOsm as it enters distal and collecting tubules 300 300 H2O NaCl 400 100 H2O 300 Clinical Connections Continued Distal tubule 300 300 Cortex Medulla H2O 600 H2O 600 Collecting duct 600 600 H2O NaCl 900 H2O NaCl 900 900 700 1000 900 H2O 1200 900 1200 1200 1200 Concentration of urine may be up to 1200 mOsm/litre as it leaves collecting tubule Vasopressin present: distal and collecting tubules permeable to H2O (a) In the face of a water deficit From proximal tubule 300 300 Loop of Henle 600 300 300 H2O 600 300 NaCl 400 100 Small volume of concentrated urine excreted; reabsorbed H2O picked up by peritubular capillaries and conserved for body of 1200 mOsm/L, his urine was as concentrated as possible. Staying hydrated by drinking lots of water decreases vasopressin secretion and allows the urine to dilute so that precipitation does not occur. The pain associated with kidney stones is not caused by the presence of stones within the kidneys themselves. As stones enter the urinary tract, the smooth muscle of the ureter contracts in attempt to move the stones forward. The ureter lining can also tear, resulting in bleeding, which gives a pink hue to the urine. Under these circumstances, no vasopressin is secreted, so the distal and collecting tubules remain impermeable to H 2 O. In other words, none of the H 2 O remaining in the tubules can leave the lumen to be reabsorbed, even though the tubular fluid is less concentrated than the surrounding interstitial fluid. Therefore, in the absence of vasopressin, the 20 percent of the filtered fluid that reaches the distal tubule is not reabsorbed. The net result is a large volume of dilute urine, which helps rid the body of excess H 2 O. Urine osmolarity may be as low as 100 mOsm/L, the same as in the fluid entering the distal tubule. Urine flow may be increased up to 25 mL/min in the absence of vasopressin, compared with the normal urine production of 1 mL/min. The ability to produce urine less concentrated than the body fluids depends on the fact that the tubular fluid is hypotonic as it enters the distal part of the nephron. This dilution is accomplished in the ascending limb when NaCl is actively extruded, but H 2 O cannot follow. Therefore, the loop of Henle, by simultaneously establishing the medullary osmotic gradient and diluting the tubular fluid before it enters the distal segments, plays a key role in allowing the kidneys to excrete urine that ranges in concentration from 100 to 1200 mOsm/L. Countercurrent exchange within the vasa recta the vasa recta supply the renal medulla with blood to nourish its tissues and also to transport the water reabsorbed by the loops of Henle and collecting ducts back to the general circulation. Another key contribution of the vasa recta is to support the countercurrent multiplier mechanism, which produces a high concentration of solutes in the interstitial fluid. It accomplishes this due to the following important characteristics: (1) the hairpin (U-shape) construction of the vasa recta loops back through the concentration gradient; (2) the blood flow in the vasa recta is opposite that of the fluid movement through the loop of Henle; (3) the vasa recta lie in close proximity to the loop of Henle; (4) the two arms of the vasa recta lie in close proximity to each other; and (5) the vasa recta are highly permeable (NaCl and H 2 O). These characteristics allow the rapid exchange of fluid and solutes (H 2 O and NaCl) in the two parallel streams and thereby maintain a large concentration difference between the two ends of the vasa recta. As blood passes down the descending limb of the vasa recta, it equilibrates with the progressively increasing concentration of the surrounding interstitial fluid. It picks up Na1 and Cl2 (NaCl) and some urea, and loses H 2 O until it is very hypertonic (1200 mOsm/L) by the bottom of the loop. Then, as blood flows up the ascending limb, NaCl diffuses back out into the interstitium, and H 2 O reenters the vasa recta because the surrounding interstitial fluid has progressively decreasing concentrations; the passive exchange allows the blood leaving the vasa recta to be isotonic (~300­320 mOsm/L). This passive exchange of solutes and H 2 O between the two limbs of the vasa recta and the interstitial fluid is known as countercurrent exchange. Unlike countercurrent multiplication, it does not establish the concentration gradient. Because blood enters and leaves the medulla at the same osmolarity as a result of countercurrent exchange, the medullary tissue is nourished with blood, yet the incremental gradient of hypertonicity in the medulla is preserved. If the blood supply to the renal medulla flowed straight through from the cortex to the inner medulla, the blood would be isotonic on entering but very hypertonic on exiting, having picked up salt and lost water as it equilibrated with the surrounding interstitial fluid at each incremental horizontal level. However, the actual shape of the vasa recta mimics the loop of Henle, but the blood flow is reversed.

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