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The enzymes of receptor-enzymes are either protein kinases arrhythmia cough purchase generic terazosin from india, such as tyrosine kinase (fig. Because of the association of these receptors with enzymes, they are now grouped into a receptor family called catalytic receptors. Ligands for receptor-enzymes include the hormone insulin as well as many cytokines and growth factors. In contrast, most cytokine receptor proteins do not have intrinsic enzyme activity. Place the following terms in the correct order for a signal transduction pathway: (a) cell response, receptor, second messenger, ligand (b) amplifier enzyme, cell response, phosphorylated protein, protein kinase, second messenger 12. The processes controlled by these signal molecules have been known for years, but the control signals themselves were discovered only relatively recently. Calcium Is an Important Intracellular Signal Calcium ions are the most versatile ionic messengers (fig. Calcium enters the cell through Ca2+ channels that may be voltage-gated, ligand-gated, or mechanically gated. Release of Ca2+ into the cytosol (from any of the sources just mentioned) creates a Ca2+ signal, or Ca2+ "spark," that can be recorded using special Ca2+-imaging techniques (see Biotechnology box on calcium signals). The calcium ions combine with cytoplasmic calcium-binding proteins to exert various effects. Calcium binding alters enzyme or transporter activity or the gating of ion channels. For years, researchers knew of a short-lived signal molecule produced by the endothelial cells lining blood vessels. This molecule diffuses from the endothelium into adjacent smooth muscle cells, causing the muscle to relax and dilate the blood vessel. Other Ca2+binding proteins Calmodulin Intracellular fluid Alters protein activity Exocytosis Movement ConCePt CheCk 13. If a cell is going to move calcium ions from its cytosol to the extracellular fluid, will it use passive or active transport Hydrogen sulfide also acts in the cardiovascular CliniCal FoCuS From Dynamite to Medicine Who would have thought that a component of smog and a derivative of dynamite would turn out to be a biological messenger And since the 1860s, physicians have used nitroglycerin to relieve angina, heart pain that results from constricted blood vessels. Even today, heart patients carry little nitroglycerin tablets to slide under their tongues when angina strikes. Still, it took years of work to isolate nitric oxide, the short-lived gas that is the biologically active molecule derived from nitroglycerin. Calcium binds to other regulatory proteins and alters movement of contractile or cytoskeletal proteins such as microtubules. For example, Ca2+ binding to the regulatory protein troponin initiates muscle contraction in a skeletal muscle cell. For example, the release of insulin from pancreatic beta cells occurs in response to a calcium signal. Gases Are Ephemeral Signal Molecules Soluble gases are short-acting paracrine/autocrine signal molecules that act close to where they are produced. Garlic is a major dietary source of the sulfur-containing precursors, which may explain studies suggesting that eating garlic has protective effects on the heart. Scientists are trying to work backward through signal pathways to find the ligands that bind to these orphan receptors. It was from this type of research that investigators recognized the importance and universality of eicosanoids, lipid-derived paracrine signals that play important roles in many physiological processes. All eicosanoid signal molecules are derived from arachidonic acid, a 20-carbon fatty acid. Arachidonic acid itself may act directly as a second messenger, altering ion channel activity and intracellular enzymes. It may also be converted into one of several classes of eicosanoid paracrine signals. These lipid-soluble molecules can diffuse out of the cell and combine with receptors on neighboring cells to exert their action. There are two major groups of arachidonic acid-derived paracrine molecules to be aware of: 1. Leukotrienes are molecules produced by the action of the enzyme lipoxygenase on arachidonic acid leuko-, white + triene, a molecule with three double bonds between carbon atoms. For this reason, pharmaceutical companies have been actively developing drugs to block leukotriene synthesis or action. Aequorin, a protein complex isolated from jellyfish such as the Chrysaora fuscescens shown here, is one of the molecules that scientists use to monitor the presence of calcium ions. When aequorin combines with calcium, it releases light that can be measured by electronic detection systems. Since the first use of aequorin in 1967 researchers have been designing increasingly, sophisticated indicators that allow them to follow calcium signals in cells. Lipids called sphingolipids also act as extracellular signals to help regulate inflammation, cell adhesion and migration, and cell growth and death. Like the eicosanoids, sphingolipids combine with G protein-coupled receptors in the membranes of their target cells. Epinephrine and norepinephrine also compete with each other for receptor binding sites. The isoform has a higher binding affinity for norepinephrine, and the 2 isoform has a higher affinity for epinephrine. Either the ligand activates the receptor and elicits a response, or the ligand occupies the binding site and prevents the receptor from responding (fig. A competing ligand that binds and elicits a response is known as an agonist of the primary ligand.

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The survival rate among the treated patients was so much higher that testing was halted so that members of the control group could also be given the experimental drug arrhythmia sounds buy 5 mg terazosin amex. In contrast, tests on some anticancer agents have shown that the experimental treatments were less effective in stopping the spread of cancer than were the standard treatments used by the controls. Was it ethical to undertreat patients in the experimental group by depriving them of the more effective current medical practice Most studies now are evaluated continually over the course of the study to minimize the possibility that subjects will be harmed by their participation. In 2002, a trial on hormone replacement therapy in postmenopausal women was halted early when investigators realized that women taking a pill containing two hormones were developing cardiovascular disease and breast cancer at a higher rate than women on placebo pills. On the other hand, the women receiving hormones also had lower rates of colon cancer and bone fractures. The investigators decided that the risks associated with taking the hormones exceeded the potential benefits, and they stopped the study. Many different aspects of experimental design can affect the validity and applicability of the results of these trials. For example, some trials are carried out for only a limited time on a limited number of people, such as studies conducted for the U. In several instances in the past few years, drugs approved as a result of such studies have later been withdrawn from the market when extended use of the drug uncovered adverse side effects, including deaths. Framingham is a prospective study prospectus, outlook, looking forward that recruited healthy people and has been following them for years to identify factors that contribute to the development of cardiovascular disease. This study has already made important contributions to healthcare, and it continues today with the adult children and grandchildren of the original participants. Additional study designs you may encounter in the literature include cross-sectional and retrospective studies. Cross-sectional studies survey a population for the prevalence of a disease or condition. Data from cross-sectional studies identify trends to be investigated further, such as whether age group or socioeconomic status is associated with a higher risk of developing the condition being surveyed. Retrospective studies retro, backward + spectare, to look match groups of people who all have a particular disease to a similar but healthy control group. The goal of these studies is to determine whether development of the disease can be associated with a particular variable. Often, the results of one or more published studies do not agree with the conclusions of other published studies. In some cases, the reason for the disagreement turns out to be a limitation of the experimental design, such as a small number of subjects who may not be representative of larger populations. In other cases, the disagreement may be due to small but potentially significant differences in the experimental designs of the different studies. One way scientists attempt to resolve contradictory results is to perform a meta-analysis of the data meta-, at a higher level. A meta-analysis combines all the data from a group of similar studies and uses sophisticated statistical techniques to extract significant trends or findings from the combined data. For example, multiple studies have been done to assess whether glucosamine and chondroitin, two dietary supplements, can improve degenerative joint disease. However, the individual studies had small numbers of subjects (<50) and used different dosing regimens. A meta-analysis using statistical methods is one way to compare the results from these studies. Since the 1970s, physiological research has increasingly augmented animal experimentation with techniques developed by cellular biologists and molecular geneticists. As we have come to understand the fundamentals of chemical signaling and communication in the body, we have unlocked the mysteries of many processes. In doing so, we also have come closer to being able to treat many diseases by correcting their cause rather than simply treating their symptoms. More and more, medicine is turning to therapies based on interventions at the molecular level. A classic example is the treatment of cystic fibrosis, an inherited disease in which the mucus of the lungs and digestive tract is unusually thick. For many years, patients with this condition had few treatment options, and most died at a young age. However, basic research into the mechanisms by which salt and water move across cell membranes provided clues to the underlying cause of cystic fibrosis: a defective protein in the membrane of certain cells. Once molecular geneticists found the gene that coded for that protein, the possibility of repairing the defective protein in cystic fibrosis patients became a reality. Without the basic research into how cells and tissues carry out their normal function, however, this treatment would never have been developed. As you read this book and learn what we currently know about how the human body works, keep in mind that many of the ideas presented in it reflect models that represent our current understanding and are subject to change. There are still many questions in physiology waiting for investigators to find the answers. Effects of glucosamine, chondroitin, or placebo in patients with osteoarthritis of hip or knee: network meta-analysis. There is no screening process comparable to peer review in journals, and the reader of a web page must decide how valid the information is. Web sites published by recognized universities and notfor-profit organizations are likely to have good information, but you should view an article about vitamins on the web page of a health food store with a skeptical eye unless the article cites published peer-reviewed research. However, unless a book has a recent publication date, it may not be the most upto-date source of information. Many students begin their quest for information on a subject by searching the Internet. Continued Answer and Commentary Including more words in a web search is the best way to narrow the results list.

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The thoracic cavity is bounded by the spine and ribs on top and sides heart attack in women terazosin 5 mg otc, with the muscular diaphragm forming the floor. The thorax contains the heart, which is enclosed in a membranous pericardial sac peri-, around + cardium, heart, and the two lungs, enclosed in separate pleural sacs. A tissue lining called the peritoneum lines the abdomen and surrounds the organs within it (stomach, intestines, liver, pancreas, gallbladder, and spleen). The kidneys lie outside the abdominal cavity, between the peritoneum and the muscles and bones of the back, just above waist level. The pelvis contains reproductive organs, the urinary bladder, and the terminal portion of the large intestine. In addition to the body cavities, there are several discrete fluid-filled anatomical compartments. The blood-filled vessels and heart of the circulatory system form one compartment. Our eyes are hollow fluid-filled spheres subdivided into two compartments, the aqueous and vitreous humors. George Papanicolaou has saved the lives of millions of women by popularizing the Pap test, a screening method that detects the early signs of cervical cancer. In the past 50 years, deaths from cervical cancer have dropped dramatically in countries that routinely use the Pap test. In contrast, cervical cancer is a leading cause of death in regions where Pap test screening is not routine, such as Africa and Central America. The results will determine whether she needs to undergo further testing for cervical cancer. The Lumens of Some Organs Are Outside the Body All hollow organs, such as heart, lungs, blood vessels, and intestines, create another set of compartments within the body. Cell Heart Loose connective tissue Seen magnified, the pericardial membrane is a layer of flattened cells supported by connective tissue. An interesting illustration of this distinction between the internal environment and the external environment in a lumen involves the bacterium Escherichia coli. This organism normally lives and reproduces inside the large intestine, an internalized compartment whose lumen is continuous with the external environment. Biological memBranes the word membrane membrana, a skin has two meanings in biology. Before the invention of microscopes in the sixteenth century, a membrane always described a tissue that lined a cavity or separated two compartments. Even today, we speak of mucous membranes in the mouth and vagina, the peritoneal membrane that lines the inside of the abdomen, the pleural membrane that covers the surface of the lungs, and the pericardial membrane that surrounds the heart. By the 1890s, scientists had concluded that the outer surface of cells, the cell membrane, was a thin layer of lipids that separated the aqueous fluids of the interior and outside environment. We now know that cell membranes consist of microscopic double layers, or bilayers, of phospholipids with protein molecules inserted in them. One source of confusion is that tissue membranes are often depicted in book illustrations as a single line, leading students to think of them as if they were similar in structure to the cell membrane. In this section, you will learn more about the phospholipid membranes that create compartments for cells. The extracellular fluid subdivides further into plasma, the fluid portion of the blood, and interstitial fluid inter-, between + stare, to stand, which surrounds most cells of the body. The Cell Membrane Separates Cell from Environment There are two synonyms for the term cell membrane: plasma membrane and plasmalemma. We will use the term cell membrane in this book rather than plasma membrane or plasmalemma to avoid confusion with the term blood plasma. The cell membrane is a physical barrier that separates intracellular fluid inside the cell from the surrounding extracellular fluid. The cell membrane controls the entry of ions and nutrients into the cell, the elimination of cellular wastes, and the release of products from the cell. The cell membrane contains proteins that enable the cell to recognize and respond to molecules or to changes in its external environment. Membrane proteins also create specialized junctions between adjacent cells or between cells and the extracellular matrix extra-, outside, which is extracellular material that is synthesized and secreted by the cells. Cancerous cells that originate in one tissue can escape from that tissue and spread to other organs through the circulatory system and the lymph vessels, a process known as metastasis. Membrane Lipids Create a Hydrophobic Barrier Three main types of lipids make up the cell membrane: phospholipids, sphingolipids, and cholesterol. Phospholipids are made of a glycerol backbone with two fatty acid chains extending to one side and a phosphate group extending to the other [p. When placed in an aqueous solution, phospholipids orient themselves so that the polar heads of the molecules interact with the water molecules while the nonpolar fatty acid tails "hide" by putting the polar heads between themselves and the water. Micelles are small droplets with a single layer of phospholipids arranged so that the interior of the micelle is filled with hydrophobic fatty acid tails. Micelles are important in the digestion and absorption of fats in the digestive tract. This arrangement leaves a hollow center with an aqueous core that can be filled with water-soluble molecules. Biologists think that a liposome-like structure was the precursor of the first living cell. Today, liposomes are being used as a medium to deliver drugs and cosmetics through the skin. Phospholipids are the major lipid of membranes, but some membranes also have significant amounts of sphingolipids. Sphingolipids also have fatty acid tails, but their heads may be either phospholipids or glycolipids.

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Magruder also mentions pain in his shin bones heart attack kurt terazosin 1 mg fast delivery, muscle weakness, stomach upset, and a vague feeling of depression. AdRenAl GlucocoRticoids the paired adrenal glands sit on top of the kidneys like little caps (fiG. Each adrenal gland, like the pituitary gland, is two embryologically distinct tissues that merged during fiG. This complex organ secretes multiple hormones, both neurohormones and classic hormones. The adrenal medulla occupies a little over a quarter of the inner mass and is composed of modified sympathetic ganglia that secrete catecholamines (mostly epinephrine) to mediate rapid responses in fight-or-flight situations [p. The adrenal cortex forms the outer three-quarters of the gland and secretes a variety of steroid hormones. Region Capsule Capsule Zona glomerulosa Aldosterone Secretes Adrenal cortex secretes steroid hormones. Zona fasciculata Glucocorticoids Zona reticularis Adrenal medulla Sex hormones Adrenal medulla secretes catecholamines. Catecholamines (b) Synthesis pathways for steroid hormones All steroid hormones are synthesized from cholesterol. The blank boxes represent intermediate compounds whose names have been omitted for simplicity. Each step is catalyzed by an enzyme, but only two enzymes are shown in the figure. A baby is born with a genetic mutation that results in a deficiency of the enzyme 21-hydroxylase. Based on the role of this enzyme in the pathway illustrated, what symptoms might you predict in the baby The inner zona reticularis secretes mostly androgens, the sex hormones dominant in men. The middle zona fasciculata secretes mostly glucocorticoids, named for their ability to increase plasma glucose concentrations. All steroid hormones begin with cholesterol, which is modified by multiple enzymes to end up as aldosterone, glucocorticoids, or sex steroids (androgens as well as estrogens and progesterone, the dominant sex hormones in females). The pathways are the same in the adrenal cortex, gonads, and placenta, but what differs from tissue to tissue is the distribution of enzymes that catalyze the different reactions. For example, the enzyme that makes aldosterone is found in only one of the three adrenal cortex zones. This chapter opened with the story of baseball player Mark McGwire and his controversial use of the supplement androstenedione. The close structural similarity among steroid hormones means that the binding sites on their receptors are also similar, leading to crossover effects when one steroid binds to the receptor for a related molecule. By inactivating cortisol, renal cells normally prevent crossover effects from cortisol. However, crossover activity and the structural similarities of steroid hormones mean that in many endocrine disorders, patients may experience symptoms related to more than one hormone. Adrenal catecholamines, particularly epinephrine, are responsible for rapid metabolic responses needed in fight-or-flight situations. Elevated plasma Ca2+ can affect the function of excitable tissues, such as muscles and neurons. The condition is usually discovered during blood work performed for a routine health evaluation. Animals whose adrenal glands have been removed die if exposed to any significant environmental stress. The most important metabolic effect of cortisol is its protective effect against hypoglycemia. When blood glucose decreases, the normal response is secretion of pancreatic glucagon, which promotes gluconeogenesis and glycogen breakdown [p. In the absence of cortisol, however, glucagon is unable to respond adequately to a hypoglycemic challenge. Cortisol receptors are found in every tissue of the body, but for many targets we do not fully understand the physiological actions of cortisol. However, we can speculate on these actions based on tissue responses to high levels (pharmacological doses) of cortisol administered for therapeutic reasons or associated with hypersecretion. Some glucose produced in the liver is released into the blood, and the rest is stored as glycogen. Cortisol causes the breakdown of skeletal muscle proteins to provide a substrate for gluconeogenesis. Cortisol enhances lipolysis so that fatty acids are available to peripheral tissues for energy use. Cortisol decreases intestinal Ca 2+ absorption and increases renal Ca2+ excretion, resulting in net Ca2+ loss from the body. In addition, cortisol is catabolic in bone tissue, causing net breakdown of calcified bone matrix. As a result, people who take therapeutic cortisol for extended periods have a higherthan-normal incidence of broken bones. States of cortisol excess or deficiency cause mood changes as well as memory and learning alterations. For this reason, it is essential that patients taking steroids taper their dose gradually, giving the pituitary and adrenal glands a chance to recover, rather than stopping the drug abruptly. The illegal use of anabolic steroids by bodybuilders and athletes periodically receives much attention.

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Also hypertension organization buy discount terazosin on-line, if the fluid lost is hyposmotic to the body (as is the case in excessive sweating), the solutes left behind in the body raise osmolarity, potentially disrupting cell function. Salt and water balance is a subtle process that we are only peripherally aware of, like breathing and the beating of the heart. Notice that the only means by which water normally enters the body from the external environment is by absorption through the digestive tract. Unlike some animals, we cannot absorb significant amounts of water directly through our skin. Most water is lost from the body in the urine, which has a daily volume of about 1. This water loss, called insensible because we are not normally aware of it, occurs across the skin surface and through exhalation of humidified air. Even though the human epidermis is modified with an outer layer of keratin to reduce evaporative water loss in a terrestrial environment [p. Although urine is normally the major route of water loss, in certain situations other routes of water loss can become significant. Another way in which water is lost is through diarrhea, a condition that can pose a major threat to the maintenance of water balance, particularly in infants. The main point to remember is that the kidneys can remove excess fluid by excreting it in the urine, but the kidneys cannot replace lost volume. The mug represents the body, and its hollow handle represents the kidneys, where body fluid filters into the nephrons. The volume that leaves can be regulated, as indicated by the little gates at the bottom of the handle. The normal range for fluid volume in the mug lies between the dashed line and the open top. Lauren reported that to avoid getting dehydrated in the warm weather, she had drunk large quantities of water in addition to sports gel and sports drinks containing carbohydrates and electrolytes. Q1: Name the two major body fluid compartments and give the major ions in each compartment. If a small volume is lost from the mug, fluid still flows through the handle, but fluid loss from the handle is turned off to prevent additional fluid loss. Translating this model to the body underscores the fact that the kidneys cannot replenish lost water: All they can do is conserve it. And as shown in the mug model, if fluid loss is severe and volume falls below the dashed line, fluid no longer flows into the handle, just as a major fall in blood volume and blood pressure shuts down renal filtration. The Renal Medulla Creates Concentrated Urine the concentration, or osmolarity, of urine is a measure of how much water is excreted by the kidneys. When maintenance of homeostasis requires eliminating excess water, the kidneys produce copious amounts of dilute urine with an osmolarity as low as 50 mOsM. Removal of excess water in urine is known as diuresis diourein, to pass in urine. In contrast, if the kidneys need to conserve water, the urine becomes quite concentrated. The kidneys control urine concentration by varying the amounts of water and Na+ reabsorbed in the distal nephron (distal tubule and collecting duct). To produce dilute urine, the kidney must reabsorb solute without allowing water to follow by osmosis. This means that the apical tubule cell membranes and cell junctions must not be permeable to water. On the other hand, if urine is to become concentrated, the nephron must be able to reabsorb water but leave solute in the tubule lumen. Mechanistically, it seems simple enough to create an epithelium that transports solutes but is impermeable to water (dilute urine)-simply remove all water pores on the apical cell membrane. At one time, scientists speculated that water was actively transported on carriers, just as Na+ and other ions are. However, once scientists developed micropuncture techniques for sampling fluid inside kidney tubules, they discovered that water is reabsorbed by osmosis through water pores (aquaporins). The mechanism for absorbing water without solute turned out to be simple: make the collecting duct cells and interstitial fluid surrounding them more concentrated than the fluid flowing into the tubule. Then, if the tubule cells have water pores, water can be absorbed from the lumen without first reabsorbing solute. Through an unusual arrangement of blood vessels and renal tubules, which we discuss later, the renal medulla maintains a high osmotic concentration in its cells and interstitial fluid. This high medullary interstitial osmolarity allows urine to be concentrated as it flows through the collecting duct. Fluid passing through the descending limb of the loop loses water to the interstitium. Tubule fluid at the bottom of the loop will be of the same osmolarity as in the medulla. The cells in the thick portion of the ascending limb of the loop have apical surfaces (facing the tubule lumen) that are impermeable to water. The reabsorption of solute without water decreases the concentration of the tubule fluid. Fluid leaving the loop of Henle therefore is hyposmotic, with an osmolarity of around 100 mOsM. Once hyposmotic fluid leaves the loop of Henle, it passes into the distal nephron. When the apical membrane of distal nephron cells is not permeable to water, water cannot leave the tubule, and the filtrate remains dilute.

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Signal Processing Begins in the Retina We now move from the cellular mechanism of light transduction to the processing of light signals by the retina and brain blood pressure medication problems cheap generic terazosin uk, the third and final step in our vision pathway. Depending on location in the retina, as many as 15 to 45 photoreceptors may converge on one bipolar neuron. Multiple bipolar neurons in turn innervate a single ganglion cell, so that the information from hundreds of millions of retinal photoreceptors is condensed down to a mere 1 million axons leaving the eye in each optic nerve. Convergence is minimal in the fovea, where some photoreceptors have a 1:1 relationship with their bipolar neurons, and greatest at the outer edges of the retina. Bipolar cells are either activated or inhibited by light, depending on their type. Ganglion cells respond most strongly when there is good contrast of light intensity between the center and the surround. Visual Field Type On-center, off-surround Bright light onto center Field Is On-Center/Off-Surround Field Is Off-Center/On-Surround Ganglion cell is excited by light in the center of the visual field. Off-center, on-surround Bright light onto surround Bright light onto surround Both field types Diffuse light on both center and surround Ganglion cell responds weakly. Amacrine cells modulate information flowing between bipolar cells and ganglion cells. By using different glutamate receptors, one stimulus (light) creates two different responses with a single neurotransmitter. Whether glutamate is excitatory or inhibitory depends on the type of glutamate receptor on the bipolar neuron. Bipolar cell signal processing is also modified by input from the horizontal and amacrine cells. Objects seen by both eyes fall within the binocular zone and are perceived in three dimensions. Objects seen with only one eye fall outside the binocular zone and are perceived in only two dimensions. Left visual field Binocular zone Ganglion cells Bipolar cells synapse with ganglion cells, the next neurons in the pathway. We know more about ganglion cells because they lie on the surface of the retina, where their axons are the most accessible to researchers. Extensive studies have been done in which researchers stimulated the retina with carefully placed light and evaluated the response of the ganglion cells. These areas, known as visual fields, are similar to receptive fields in the somatic sensory system [p. Only a few photoreceptors are associated with each ganglion cell, and so visual acuity is greatest in these areas. This organization allows each ganglion cell to use contrast between the center and its surround to interpret visual information. Strong contrast between the center and surround elicits a strong excitatory response (a series of action potentials) or a strong inhibitory response (no action potentials) from the ganglion cell. If light is brightest in the off-surround region of the field, the on-center/off-surround field ganglion cell is inhibited and stops firing action potentials. Right visual field Optic chiasm Optic nerve Optic tract Lateral geniculate body (thalamus) Visual cortex What happens if light is uniform across a visual field Thus, the retina uses contrast rather than absolute light intensity to recognize objects in the environment. One advantage of using contrast is that it allows better detection of weak stimuli. The Eye and Vision 377 Scientists have now identified multiple types of ganglion cells in the primate retina. The two predominant types, which account for 80% of retinal ganglion cells, are M cells and P cells. Large magnocellular ganglion cells, or M cells, are more sensitive to information about movement. Smaller parvocellular ganglion cells, or P cells, are more sensitive to signals that pertain to form and fine detail, such as the texture of objects in the visual field. A recently discovered subtype of ganglion cell, the melanopsin retinal ganglion cell, apparently also acts as a photoreceptor to relay information about light cycles to the suprachiasmatic nucleus, which controls circadian rhythms [p. At this point, some nerve fibers from each eye cross to the other side of the brain for processing. The two eyes have slightly different views of objects in this region, and the brain processes and integrates the two views to create threedimensional representations of the objects. Our sense of depth Processing beyond the retina Once action potentials leave perception-that is, whether one object is in front of or behind another-depends on binocular vision. Objects that fall within the visual field of only one eye are in the monocular zone and are viewed in two dimensions. Most axons, however, project to the lateral geniculate body of the thalamus, where the optic fibers synapse onto neurons leading to the visual cortex in the occipital lobe.

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The kidneys keep concentrations of key ions within a normal range by balancing dietary intake with urinary loss arteria yahoo discount terazosin 5 mg buy on-line. Sodium (Na+) is the major ion involved in the regulation of extracellular fluid volume and osmolarity. The kidneys play a significant role in pH homeostasis, but they do not correct pH disturbances as rapidly as the lungs do. The kidneys remove metabolic waste products and xenobiotics, or foreign substances, such as drugs and environmental toxins. A metabolite of hemoglobin called urobilinogen gives urine its characteristic yellow color. Examples of foreign substances that the kidneys actively remove include the artificial sweetener saccharin and the anion benzoate, part of the preservative potassium benzoate, which you ingest each time you drink a diet soft drink. Although the kidneys are not endocrine glands, they play important roles in three endocrine pathways. Kidney cells synthesize erythropoietin, the cytokine/hormone that regulates red blood cell synthesis [p. They also release renin, an enzyme that regulates the production of hormones involved in sodium balance and blood Functions oF the Kidneys If you ask people on the street, "What is the most important function of the kidney When the pain began, Michael thought he had a mild sprain or perhaps the beginnings of arthritis. On hearing his symptoms and looking at the toe, the doctor seemed to know instantly what was wrong. Finally, renal enzymes help convert vitamin D3 into a hormone that regulates Ca2+ balance. The kidneys, like many other organs in the body, have a tremendous reserve capacity. By most estimates, you must lose nearly three-fourths of your kidney function before homeostasis begins to be affected. Many people function perfectly normally with only one kidney, including the one person in 1000 born with only one kidney (the other fails to develop during gestation) or those people who donate a kidney for transplantation. What happens to the resting membrane potential of a neuron if extracellular K+ levels decrease What happens to the force of cardiac contraction if plasma Ca2+ levels decrease substantially Although they are below the diaphragm, they are technically outside the abdominal cavity, sandwiched between the membranous peritoneum, which lines the abdomen, and the bones and muscles of the back. Because of their location behind the peritoneal cavity, the kidneys are sometimes described as being retroperitoneal retro-, behind. The renal blood vessels, nerves, lymphatics, and ureters all emerge from this surface. Renal arteries, which branch off the abdominal aorta, supply blood to the kidneys. The study of kidney function is called renal physiology, from the Latin word renes, meaning "kidneys. The layers are formed by the organized arrangement of microscopic tubules called nephrons. Urine production begins when water and solutes move from plasma into the hollow tubules (nephrons) that make up the bulk of the paired kidneys. The modified fluid, now called urine, leaves the kidney and passes into a hollow tube called a ureter. The bladder expands and fills with urine until, in a reflex called micturition or urination, the bladder contracts and expels urine through a single tube, the urethra. In females, the urethral opening is found anterior to the openings of the vagina and anus. These crystals trigger an inflammatory reaction and cause periodic attacks of excruciating pain. Urine leaving the nephrons flows into the renal pelvis prior to passing through the ureter into the bladder. Nephrons Urinary System (a) Urinary system Cortex Medulla Kidney Renal pelvis Ureter Ureter Urinary bladder Urethra (d) Renal arteries take blood to the cortex. Capsule (b) the kidneys are located retroperitoneally at the level of the lower ribs. Inferior vena cava Diaphragm Aorta Renal artery Left adrenal gland Left kidney Renal vein Right kidney Renal artery Renal vein Ureter (e) Afferent arterioles and glomeruli are all found in the cortex. Arcuate artery Arcuate vein Cortical nephron Juxtamedullary nephron Glomerulus Afferent arterioles Peritoneum (cut) Urinary bladder Rectum (cut) Structure of the Nephron (f) Some nephrons dip deep into the medulla. Juxtaglomerular apparatus Nephrons Afferent arteriole Glomerulus (capillaries) Peritubular capillaries (h) Juxtamedullary nephron with vasa recta Peritubular capillaries Glomerulus the medulla contains loops of Henle and collecting ducts. At this point, the arrangement of blood vessels forms a portal system, one of three in the body [p. Recall that a portal system consists of two capillary beds in series (one after the other). In the renal portal system, blood flows from renal arteries into an afferent arteriole. Finally, peritubular capillaries converge to form venules and small veins, sending blood out of the kidney through the renal vein. The function of the renal portal system is to filter fluid out of the blood and into the lumen of the nephron at the glomerular capillaries, then to reabsorb fluid from the tubule lumen back into the blood at the peritubular capillaries.

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For example pulse pressure definition medical 5 mg terazosin with visa, as noted in the Running Problem, emphysema is a disease in which elastin fibers normally found in lung tissue are destroyed. Destruction of elastin results in lungs that exhibit high compliance and stretch easily during inspiration. However, these lungs also have decreased elastance, so they do not recoil to their resting position during expiration. To understand the importance of elastic recoil to expiration, think of an inflated balloon and an inflated plastic bag. Its elastic walls squeeze on the air inside the balloon, thereby increasing the internal air pressure. When the neck of the balloon is opened to the atmosphere, elastic recoil causes air to flow out of the balloon. The inflated plastic bag, on the other hand, is like the lung of an individual with emphysema. If the inflated plastic bag is opened to the atmosphere, most of the air remains inside the bag. Patients with emphysema contract their expiratory muscles (active expiration) to force out air that is not leaving from elastic recoil. However, if the particles cannot be digested or if they accumulate in large numbers, an inflammatory process ensues. However, studies comparing the work required to expand airfilled and saline-filled lungs showed that air-filled lungs are much harder to inflate. From this result, researchers concluded that lung tissue itself contributes less to resistance than once thought. Some other property of the normal air-filled lung, a property not present in the saline-filled lung, must create most of the resistance to stretch. At any airfluid interface, the surface of the fluid is under tension, like a thin membrane being stretched. When the fluid is water, surface tension arises because of the hydrogen bonds between water molecules. Alveolar surface tension is similar to the surface tension that exists in a spherical bubble, even though alveoli are not perfect spheres. The surface tension created by the thin film of fluid is directed toward the center of the bubble and creates pressure in the interior of the bubble. It states that the pressure (P) inside a bubble formed by a fluid film is a function of two factors: the surface tension of the fluid (T) and the radius of the bubble (r). This relationship is expressed by the equation P = 2T>r 17 Restrictive Lung disease A decrease in lung compliance affects ventilation because more work must be expended to stretch a stiff lung. Pathological conditions in which compliance is reduced are called restrictive lung diseases. In these conditions, the energy expenditure required to stretch less-compliant lungs can far exceed the normal work of breathing. Two common causes of decreased compliance are inelastic scar tissue formed in fibrotic lung diseases, and inadequate alveolar production of surfactant, a chemical that facilitates lung expansion. Pulmonary fibrosis is characterized by the development of stiff, fibrous scar tissue that restricts lung inflation. Other forms of fibrotic lung disease result from chronic inhalation of fine particulate matter, such as asbestos and silicon, that escapes the mucus lining the airways and reaches the alveoli. In physiology, we can equate the bubble to a fluid-lined alveolus (although alveoli are not perfect spheres). If the surface tension (T) of the fluid were the same in small and large alveoli, small alveoli would have higher inwardly directed pressure than larger alveoli, and increased resistance to stretch. Surfactants ("surface active agents") are molecules that disrupt cohesive forces between water molecules by substituting themselves for water at the surface. For example, that product you add to your dishwasher to aid in the rinse cycle 576 chapTeR 17 Mechanics of Breathing FiG. In the lungs, smaller alveoli have more surfactant, which equalizes the pressure between large and small alveoli. Law of LaPlace P = 2T/r P = pressure T = surface tension r = radius According to the law of LaPlace, if two bubbles have the same surface tension, the smaller bubble will have higher pressure. In the lungs, surfactant decreases surface tension of the alveolar fluid and thereby decreases resistance of the lung to stretch. Lower surface tension helps equalize the pressure among alveoli of different sizes and makes it easier to inflate the smaller alveoli. With lower surface tension, the work needed to expand the alveoli with each breath is greatly reduced. Normally, surfactant synthesis begins about the 25th week of fetal development under the influence of various hormones. Production usually reaches adequate levels by the 34th week (about 6 weeks before normal delivery). These infants must use a tremendous amount of energy to expand their collapsed lungs with each breath. Amniotic fluid can be sampled to assess whether or not the fetal lungs are producing adequate amounts of surfactant. The current treatment also includes artificial ventilation that forces air into the lungs (positive-pressure ventilation) and keeps the alveoli open. Elastin is destroyed by elastase, an enzyme released by alveolar macrophages, which must work overtime in smokers to rid the lungs of irritants. Their alveoli have lost elastic recoil, which makes expiration-normally a passive process-require conscious effort. Airway Diameter Determines Airway Resistance the other factor besides compliance that influences the work of breathing is the resistance of the respiratory system to air flow. Resistance in the respiratory system is similar in many ways to resistance in the cardiovascular system [p.

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The flaps are slightly thickened at the edge and connect on the ventricular side to collagenous tendons prehypertension medicine order terazosin american express, the chordae tendineae (fig. The opposite ends of the chordae are tethered to mound-like extensions of ventricular muscle known as the papillary muscles papilla, nipple. The chordae tendineae prevent the valve from being pushed back into the atrium, just as the struts on an umbrella keep the umbrella from turning inside out in a high wind. Occasionally, the chordae fail, and the valve is pushed back into the atrium during ventricular contraction, an abnormal condition known as prolapse. The valve between the left atrium and left ventricle has only two flaps and is called the bicuspid valve. The bicuspid is also called the mitral valve because of its resemblance to the tall headdress, known as a miter, worn by popes and bishops. The aortic valve is between the left ventricle and the aorta, and the pulmonary valve lies between the right ventricle and the pulmonary trunk. Each semilunar valve has three cuplike leaflets that snap closed when blood attempting to flow back into Cardiac Muscle Cells Contract without Innervation the bulk of the heart is composed of cardiac muscle cells, or myocardium. Most cardiac muscle is contractile, but about 1% of the myocardial cells are specialized to generate action potentials spontaneously. These cells account for a unique property of the heart: its ability to contract without any outside signal. As mentioned in the introduction to this chapter, records tell us of Spanish explorers in the New World witnessing human sacrifices in which hearts torn from the chests of living victims continued to beat for minutes. The heart can contract without a connection to other parts of the body because the signal for contraction is myogenic, originating within the heart muscle itself. The signal for myocardial contraction comes not from the nervous system but from specialized myocardial cells known as autorhythmic cells. The autorhythmic cells are also called pacemakers because they set the rate of the heartbeat. Myocardial autorhythmic cells are anatomically distinct from contractile cells: autorhythmic cells are smaller and contain few contractile fibers. Because they do not have organized sarcomeres, autorhythmic cells do not contribute to the contractile force of the heart. Contractile cells are typical striated muscle, however, with contractile fibers organized into sarcomeres [p. Cardiac muscle differs in significant ways from skeletal muscle and shares some properties with smooth muscle: 1. Cardiac muscle fibers are much smaller than skeletal muscle fibers and usually have a single nucleus per fiber. The cell junctions, known as intercalated disks inter-, between + calare, to proclaim, consist of interdigitated membranes. Desmosomes are strong connections that tie adjacent cells together, allowing force created in one cell to be transferred to the adjacent cell. Gap junctions in the intercalated disks electrically connect cardiac muscle cells to one another. They allow waves of depolarization to spread rapidly from cell to cell, so that all the heart muscle cells contract almost simultaneously. The t-tubules of myocardial cells are larger than those of skeletal muscle, and they branch inside the myocardial cells. Myocardial sarcoplasmic reticulum is smaller than that of skeletal muscle, reflecting the fact that cardiac muscle depends in part on extracellular Ca2+ to initiate contraction. Mitochondria occupy about one-third the cell volume of a cardiac contractile fiber, a reflection of the high energy demand of Cardiac Muscle and the Heart 473 fig. When heart muscle cells die, they release various enzymes such as creatine kinase that serve as markers of a heart attack. Intercalated disk (sectioned) Nucleus 460 463 473 479 490 492 496 Intercalated disk Mitochondria Cardiac muscle cell Contractile fibers these cells. During periods of increased activity, the heart uses almost all the oxygen brought to it by the coronary arteries. As a result, the only way to get more oxygen to exercising heart muscle is to increase the blood flow. Reduced myocardial blood flow from narrowing of a coronary vessel by a clot or fatty deposit can damage or even kill myocardial cells. An action potential that enters a contractile cell moves across the sarcolemma and into the t-tubules 1, where it opens voltage-gated L-type Ca2+ channels in the cell membrane 2. Ca2+ enters the cell through these channels, moving down its electrochemical gradient. Calcium entry opens ryanodine receptor Ca2+ release channels (RyR) in the sarcoplasmic reticulum 3. When the RyR channels open, stored Ca2+ flows out of the sarcoplasmic reticulum and into the cytosol 4, creating a Ca2+ "spark" that can be seen using special biochemical methods [p. Calcium released from the sarcoplasmic reticulum provides about 90% of the Ca2+ needed for muscle contraction, with the remaining 10% entering the cell from the extracellular fluid. Calcium diffuses through the cytosol to the contractile elements, where the ions bind to troponin and initiate the cycle of crossbridge formation and movement 6. Contraction takes place by the same type of sliding filament movement that occurs in skeletal muscle [p.

Zarkos, 61 years: When a neuron is at its resting membrane potential, the activation gate of the Na+ channel closes and no Na+ can move through the channel (fig. In the following sections, we look in more detail at the important processes of filtration, reabsorption, secretion, and excretion. The choroid plexus is selective about which substances it transports into the ventricles, and, as a result, the composition of cerebrospinal fluid is different from that of the plasma.

Aila, 25 years: As we have come to understand the fundamentals of chemical signaling and communication in the body, we have unlocked the mysteries of many processes. To keep the spindle functioning normally, gamma motor neurons innervating the contractile ends of the muscle spindle also fire at the same time (fig. For example, a drug might target adrenergic 1- receptors rather than all adrenergic and receptors.

Folleck, 60 years: Stem cells in the basal layer of the olfactory epithelium are continuously dividing to create new neurons. General ProPerties of sensory systems All sensory pathways have certain elements in common. From which special sense do you think the transplantation was carried out and why

Uruk, 26 years: They hoped to find a molecule that could compete with penicillin for the organic anion transporter responsible for secretion. The frontal view shown here is similar to the sectional view obtained using modern diagnostic imaging techniques. In most adult hemoglobin, there are two alpha chains and two beta chains as shown.

Kafa, 44 years: Lateral inhibition, which increases the contrast between activated receptive fields and their inactive neighbors, is another way of isolating the location of a stimulus. Sphingolipids also have fatty acid tails, but their heads may be either phospholipids or glycolipids. Many nerves are large enough to be seen with the naked eye and have been given anatomical names.

Jens, 23 years: As a result, people who take therapeutic cortisol for extended periods have a higherthan-normal incidence of broken bones. Carriers have lower-than-normal levels of the enzyme, but this amount is enough to prevent excessive accumulation of gangliosides in cells. Overall, the body is electrically neutral: for every cation, there is a matching anion.

Rufus, 37 years: This calculation provides a quick estimate of how much fluid needs to be replaced. After many washings the elastic waistband is easy to stretch (high compliance) but lacking in elastance, making it impossible for the shorts to stay up around your waist. The arterioles constrict, increasing their resistance to blood flow and diverting blood to lower-resistance blood vessels in the interior of the body.

Ramirez, 43 years: Think of how much information humans needed to remember in centuries past, when books were scare and most history was passed down by word of mouth. The Distal Nephron Controls Acid Excretion the distal nephron plays a significant role in the fine regulation of acid-base balance. American Heart Association, Heart Disease and Stroke Statistics-2006 Update, A Report From the American Heart Association Statistics Committee and Stroke Statistics Subcommittee 15 Blood flow and the control of Blood Pressure the Blood Vessels 503 lo 15.

Porgan, 63 years: However, in a series of classic experiments, Oskar Minkowski at the University of Strasbourg (Germany) pinpointed the relationship between diabetes and the pancreas. Because red blood cells contain no mitochondria, they cannot carry out aerobic metabolism. The neural control of breathing is one of the few "black boxes" left in systems-level physiology.

Torn, 57 years: Note that when the hydrogen is part of the intact carbonic acid molecule, it does not contribute to acidity. The movement of water across a membrane in response to a concentration gradient is called osmosis. Review Questions 677 (c) respiratory acidosis and metabolic acidosis, including causes and compensations (d) water reabsorption in proximal tubule, distal tubule, and ascending limb of the loop of Henle (e) respiratory alkalosis and metabolic alkalosis, including causes and compensations 30.

Ugrasal, 51 years: Pain signals from the skin are more common than pain from internal organs, and the brain associates activation of the pathway with pain in the skin. Decreases in blood pressure and blood volume are less powerful stimuli for vasopressin release. The reflex pathway in which muscle stretch initiates a contraction response is known as a stretch reflex.