text stringlengths 1.02k 3.02k |
|---|
provides depth perception. 55.5 Some vertebrates use heat, electricity, or magnetism for orientation. Diversity of Sensory Experiences Vision is the primary sense used by all vertebrates that live in a light-filled environment, but visible light is by no means the only part of the electromagnetic spectrum that vertebr... |
depolarize the receptor at the base, causing the release of neurotransmitter and increased activity of sensory neurons. This allows sharks, for example, to detect the electrical fields generated by the muscle contrac- Pit Outer chamber Membrane Inner chamber FIGURE 55.25 “Seeing” heat. The depression between the nostr... |
ceptors and exteroceptors respond to stimuli that originate in the internal and external environments, respectively. 1. Can you name a sensory receptor that does not produce a membrane depolarization? • Introduction to sense organs • Receptors and sensations • Somatic senses 55.2 Mechanical and chemical receptors sense... |
. Some vertebrates can orient themselves using the earth’s magnetic field. 7. Why do rattlesnakes strike a moving lightbulb? 8. How do sharks detect their prey? Why don’t terrestrial vertebrates have this sense? 1124 Part XIV Regulating the Animal Body • Art Activity Human eye anatomy • Vision • Chemorecptors 56 The En... |
homeostasis of the body’s internal environment and control other body functions such as reproduction. Homeostasis is achieved through the actions of many regulatory mechanisms that involve all the organs of the body. Two systems, however, are devoted exclusively to the regulation of the body organs: the nervous system... |
to the way that hormones regulate their target cells. Such regulation is called paracrine. Another type of chemical messenger that is released into the environment is called a pheromone. These messengers aid in the communication between animals, not in the regulation within an animal. A comparison of the different typ... |
corticosteroids, secreted only by the adrenal cortex (the outer portion of the adrenal gland). The corticosteroids include cortisol, which regulates glucose balance, and aldosterone, which regulates salt balance. The amine hormones secreted by the adrenal medulla (the inner portion of the adrenal gland), known as cate... |
+), respectively. Any organ that secretes a hormone from a ductless gland is part of the endocrine system. Hormones may be any of a variety of different chemicals. Chapter 56 The Endocrine System 1127 Table 56.1 Principal Endocrine Glands and Their Hormones* Endocrine Gland and Hormone Target Tissue POSTERIOR LOBE OF P... |
the immune system. Other paracrine regulators are called growth factors, because they promote growth and cell division in specific organs. Examples include platelet-derived growth factor, epidermal growth factor, and the insulin-like growth factors that stimulate cell division and proliferation of their target cells. ... |
, adipose tissue Liver, adipose tissue Lowers blood glucose level; stimulates storage of glycogen in liver Peptide (51 amino acids) Raises blood glucose level; stimulates breakdown of glycogen in liver Peptide (29 amino acids) General Stimulates development of secondary sex characteristics in females Steroid Female rep... |
ib (Celebrex), inhibits cox-2 but not cox-1, a potentially great benefit to arthritis sufferers and others who must use pain relievers regularly. The neural and endocrine control systems are supplemented by paracrine regulators, including the prostaglandins, which perform many diverse functions. Chapter 56 The Endocrin... |
. 4 Protein synthesis is induced. 5 Protein is produced. 3 mRNA Chromosome Nucleus 5 Protein Interstitial fluid FIGURE 56.5 The mechanism of steroid hormone action. Steroid hormones are lipid-soluble and thus readily diffuse through the plasma membrane of cells. They bind to receptor proteins in either the cytoplasm or... |
iodothyronine T3 T4 Blood plasma T4 Thyroxine T4 Protein carrier T3 Receptor protein T3 Plasma membrane Interstitial fluid Nucleus mRNA FIGURE 56.6 The mechanism of thyroxine action. Thyroxine contains four iodines. When it enters the target cell, thyroxine is changed into triiodothyronine, with three iodines. This hor... |
). The cAMP second-messenger system was the first such system to be described. The β-adrenergic receptors are associated with membrane proteins called G proteins (see chapters 7 and 54). Each G protein is composed of three subunits, and the binding of epinephrine to its receptor causes one of the G protein subunits to ... |
set of cellular proteins, which cause the heart to beat faster and more forcefully. The IP3/Ca++ Second-Messenger System When epinephrine binds to α-adrenergic receptors, it doesn’t activate adenylyl cyclase and cause the production of cAMP. Instead, through a different type of G protein, it activates another membrane... |
When IP3 binds to its receptors on the endoplasmic reticulum, it stimulates the endoplasmic reticulum to release its stored Ca++. Calcium channels in the plasma membrane may also open, allowing Ca++ to diffuse into the cell from the extracellular fluid. Some of the Ca++ that has suddenly entered the cytoplasm then bin... |
Such second messengers include cyclic AMP (cAMP), inositol trisphosphate (IP3), and Ca++. In many cases, the second messengers activate previously inactive enzymes. Chapter 56 The Endocrine System 1133 56.3 The hypothalamus controls the secretions of the pituitary gland. The Posterior Pituitary Gland The pituitary gla... |
, which promotes water retention by the kidneys. This works as a negative feedback loop to correct the initial disturbance of homeostasis. Lowers blood volume and pressure Dehydration Osmotic concentration of blood increases Osmoreceptors – Negative feedback – Negative feedback ADH synthesized by neurosecretory cells i... |
terior Pituitary Gland The anterior pituitary, unlike the posterior pituitary, does not develop from a downgrowth of the brain; instead, it develops from a pouch of epithelial tissue that pinches off from the roof of the embryo’s mouth. Because it is epithelial tissue, the anterior pituitary is a complete gland—it prod... |
The major hormones of the anterior and posterior pituitary glands. Only a few of the actions of these hormones are shown. 1136 Part XIV Regulating the Animal Body 5. Follicle-stimulating hormone (FSH) is required for the development of ovarian follicles in females. In males, it is required for the development of sperm... |
are produced by the liver and secreted into the blood in response to stimulation by GH. The insulin-like growth factors then stimulate growth of the epiphyseal growth plates and thus elongation of the bones. When a person’s skeletal growth plates have converted from cartilage into bone, however, GH can no longer cause... |
, the hypothalamus controls production and secretion of the anterior pituitary hormones. This control is exerted hormonally rather than by means of nerve axons. Neurons in the hypothalamus secrete releasing hormones and inhibiting hormones into blood capillaries at the base of the hypothalamus (figure 56.13). These cap... |
of endocrine organs, such as the adrenal medulla and the pancreas, are not directly regulated by this control system. Second, the hypothalamus and the anterior pituitary gland are themselves partially controlled by the very hormones whose secretion they stimulate! In most cases this is an in- 1138 Part XIV Regulating ... |
, LH) TSH (Thyroid-stimulating hormone) Target glands (Thyroid, adrenal cortex, gonads) Thyroid gland Hormones Thyroxine FIGURE 56.14 Negative feedback inhibition. The hormones secreted by some endocrine glands feed back to inhibit the secretion of hypothalamic releasing hormones and anterior pituitary tropic hormones.... |
in this section TRH TSH Thyroxine TRH rises The Thyroid Gland –35 –30 –25 –20 –15 –10 –5 0 +5 +10 Premetamorphosis Days from emergence of forelimb Prometamorphosis Climax Reduced growth, rapid differentiation Rapid differentiation FIGURE 56.17 Thyroxine triggers metamorphosis in amphibians. In tadpoles at the premetam... |
proper levels of calcium (Ca++) in the blood. When the blood Ca++ concentration rises too high, calcitonin stimulates the uptake of Ca++ into bones, thus lowering its level in the blood. Although calcitonin may be important in the physiology of some vertebrates, its significance in normal human 1140 Part XIV Regulatin... |
cannot be allowed to continue uncorrected, because a significant fall in the blood Ca++ level can cause severe muscle spasms. A normal blood Ca++ is important for the functioning of muscles, including the heart, and for proper functioning of the nervous and endocrine systems. PTH stimulates the osteoclasts (bone cells... |
increased heart rate, increased blood pressure, dilation of the bronchioles, elevation in blood glucose, and reduced blood flow to the skin and digestive organs. The actions of epinephrine released as a hormone supplement those of norepinephrine released as a sympathetic nerve neurotransmitter. The Adrenal Cortex: Hom... |
to dangerous levels. Because of these essential functions performed by aldosterone, removal of the adrenal glands, or diseases that prevent aldosterone secretion, are invariably fatal without hormone therapy. The adrenal medulla is stimulated by sympathetic neurons to secrete epinephrine and norepinephrine during the ... |
rete glucose into the blood. These antagonistic effects help to maintain homeostasis of the blood glucose concentration. That hormone is insulin, secreted by the beta (β) cells of the islets. Insulin was not isolated until 1922, when two young doctors working in a Toronto hospital succeeded where many others had not. O... |
be taken up by cells and used for energy. The β cells of the islets of Langerhans secrete insulin, and the α cells secrete glucagon. These two hormones have antagonistic actions on the blood glucose concentration; insulin lowers and glucagon raises blood glucose. Chapter 56 The Endocrine System 1143 Other Endocrine Gl... |
processes to a circadian rhythm (one that repeats every 24 hours). Through regulation by the SCN, the secretion of melatonin by the pineal gland is entrained to cycles of light and dark, decreasing during the day and increasing at night. This daily cycling of melatonin release regulates body cycles such as sleep/wake ... |
not produce large amounts of juvenile hormone. Neurosecretory cells Corpora allata Brain hormone Juvenile hormone Low amounts Prothoracic gland Molting hormone Larval molt Pupal molt Adult molt larger one. In one molt, a juvenile insect, or larvae, often undergoes a radical transformation to the adult. This process is... |
chemicals have been shown to interfere with reproductive hormones, thyroid hormones, and the immune system chemical messengers. These effects are not lethal, but may make individuals vulnerable in their environment. If they are having problems reproducing, maintaining the proper metabolic rate, or fighting off infecti... |
pituitary gland. • Axons from neurons in the hypothalamus enter the posterior pituitary, carrying ADH and oxytocin; the posterior pituitary stores these hormones and secretes them in response to neural activity. • The anterior pituitary produces and secretes a variety of hormones, many of which control other endocrine... |
agocytotic cells, and fever may all play a role in local inflammations. 57.2 Specific immune defenses require the recognition of antigens. The Immune Response: The Third Line of Defense. Lymphocytes target specific antigens for attack. Cells of the Specific Immune System. B cells and T cells serve different functions i... |
this year. Attempts to improve our defenses against infection are among the most active areas of scientific research today. 1147 57.1 Many of the body’s most effective defenses are nonspecific. Skin: The First Line of Defense The vertebrate is defended from infection the same way knights defended medieval cities. “Wal... |
new cells produced in the innermost layer of the epidermis, the stratum basale, which contains some of the most actively dividing cells in the vertebrate body. The cells formed in this layer migrate upward and enter a broad intermediate stratum spinosum layer. As they move upward they form the protein keratin, which m... |
and into the digestive tract. Occasionally, an infectious agent, called a pathogen, will enter the digestive and respiratory systems and the body will use defense mechanisms such as vomiting, diarrhea, coughing, and sneezing to expel the pathogens. The surface defenses of the body consist of the skin and the mucous me... |
are part of the structure of the liver, spleen, and bone marrow. In response to an infection, monocytes (an undifferentiated leukocyte) found in the blood squeeze through capillaries to enter the connective tissues. There, at the site of the infection, the monocytes are transformed into additional macrophages. Neutrop... |
burst. Aggregation of the complement proteins is also triggered by the binding of antibodies to invading microbes, as we will see in a later section. The proteins of the complement system can augment the effects of other body defenses. Some amplify the inflammatory response (discussed next) by stimulating histamine re... |
, most notably histamine and prostaglandins. These chemicals promote the dilation of local blood vessels, which increases the flow of blood to the site of infection or injury and causes the area to become red and warm. They also increase the permeability of capillaries in the area, producing the edema (tissue swelling)... |
vessels to dilate. Increased blood flow brings a wave of phagocytic cells, which attack and engulf invading bacteria. Chapter 57 The Immune System 1151 57.2 Specific immune defenses require the recognition of antigens. FIGURE 57.7 The birth of immunology. This famous painting shows Edward Jenner inoculating patients w... |
it had been weakened; the injected birds became only slightly ill and then recovered. Surprisingly, however, those 1152 Part XIV Regulating the Animal Body birds did not get sick when subsequently infected with fresh fowl cholera. They remained healthy even if given massive doses of active fowl cholera bacteria that d... |
ocytes. Leukocytes include neutrophils, eosinophils, basophils, and monocytes, all of which are phagocytic and are involved in the second line of defense, as well as two types of lymphocytes (T cells and B cells), which are not phagocytic but are critical to the specific immune response (table 57.1), the third line of ... |
response; detects infection and sounds the alarm, initiating both T cell and B cell responses Not involved in the immediate response to infection; mediates the maturation of other T cells in the thymus Detects and kills infected body cells; recruited by helper T cells Dampens the activity of T and B cells, scaling bac... |
us-nonself MHC protein recognition. T cells of the immune system will recognize a cell as self or nonself by the MHC proteins present on the cell surface. When a foreign particle, such as a virus, infects the body, it is taken in by cells and partially digested. Within the cells, the viral antigens are processed and mo... |
. (c) T cells can bind to antigens only after the antigens are processed and complexed with MHC proteins on the surface of an antigenpresenting cell. (c) Antigen-presenting cell 1154 Part XIV Regulating the Animal Body Cell Type B cell CD4+ T cell CD8+ T cell Macrophage Table 57.2 Key Cell Surface Proteins of the Immun... |
System 1155 57.3 T cells organize attacks against invading microbes. T cells: The Cell-Mediated Immune Response The cell-mediated immune response, carried out by T cells, protects the body from virus infection and cancer, killing abnormal or virus-infected body cells. Once a helper T cell that initiates this response ... |
stimulates the multiplication of cytotoxic T cells. In addition, proliferation of cytotoxic T cells is stimulated when a T cell with a receptor that fits the antigen displayed by an antigen-presenting cell binds to the antigen-MHC protein complex. Body cells that have been infected by the antigen are destroyed by the ... |
describe the proposed role of the immune system in fighting cancer. The production of human interferons by genetically engineered bacteria has made large amounts of these substances available for the experimental treatment of cancer. Thus far, interferons have proven to be a useful addition to the treatment of particu... |
on antigen-presenting cells, B cell receptors can bind to free, unprocessed anti- gens. When a B cell encounters an antigen, antigen particles will enter the B cell by endocytosis and get processed. Helper T cells that are able to recognize the specific antigen will bind to the antigen-MHC protein complex on the B cel... |
and mother’s milk. 5. IgE. This form of antibodies promotes the release of histamine and other agents that aid in attacking a pathogen. Unfortunately, they sometimes trigger a full-blown response when a harmless antigen enters the body producing allergic symptoms, such as those of hay fever. Each B cell has on its sur... |
mediated immune response Stimulate macrophages to congregate at site of infection Cause humoral immune response FIGURE 57.13 The many roles of helper T cells. Helper T cells, through their secretion of lymphokines and interaction with other cells of the immune system, participate in every aspect of the immune response.... |
form five classes of immunoglobulins: IgM, IgG, IgA, IgD, and IgE. We have already discussed the roles of IgM and IgG antibodies in the humoral immune response Light chain Constant region Variable region S-S bridges SS IgE antibodies bind to mast cells. The heavy-chain stems of the IgE antibody molecules insert into r... |
,000 different heavy chains and about 1200 different light chains (in mouse antibodies). Two other processes generate even more sequences. First, the DNA segments are often joined together with one or two nucleotides off-register, shifting the reading frame during gene transcription and so generating a totally differen... |
regions of the DNA code for different regions of the receptor structure (C, constant regions; J, joining regions; D, diversity regions; and V, variable regions) and are brought together to make a composite gene that codes for the receptor. Through different somatic rearrangements of these DNA segments, an enormous num... |
the same pathogen, the immune system is ready. As a result of the first infection, there is now a large clone of lymphocytes that can recognize that pathogen (figure 57.19). This more effective response, elicited by subsequent exposures to an antigen, is called a secondary immune response. Memory cells can survive for... |
bind to infected cells and kill them. 2 Viruses and viral proteins on infected cells stimulate macrophages. 9 Other B cells become antibodyproducing factories. 8 Some B cells become memory cells. Cytotoxic T cell B cell Macrophage 7 Activated B cells multiply. 5 Interleukin-2 activates B cells and cytotoxic T cells. I... |
-B antibodies in their plasma. If type A blood is mixed on a glass slide with serum from a person with type B blood, the anti-A antibodies in the serum will cause the type A red blood cells to clump together, or agglutinate (figure 57.21). These tests allow the blood types to be matched prior to transfusions, so that a... |
) hybrids Selection of hybrid cells Hybridoma cell Assay for antibody B lymphocytes from spleen Reclone positive hybrids Monoclonal antibody Mass culture growth Monoclonal antibody Freeze hybridoma for future use FIGURE 57.22 The production of monoclonal antibodies. These antibodies are produced by cells that arise fro... |
clinical tests (such as pregnancy testing), the monoclonal antibodies are bound to particles of latex, which agglutinate in the presence of the antigen. chapter 59) as the antigen. When these particles are mixed with a sample that contains this hormone antigen from a pregnant woman, the antigen-antibody reaction causes... |
chnikoff was awarded the 1908 Nobel Prize in Physiology or Medicine, along with Paul Ehrlich for his work on the other major part of the immune defense, the antibody or humoral immune response. The invertebrate immune response shares several elements with the vertebrate one. Phagocytes. All animals possess phagocytic c... |
tag invading microorganisms, enhancing phagocytosis. The genes encoding vertebrate antibodies are part of a very ancient gene family, the immunoglobulin superfamily. Proteins in Sponge Starfish Tunicate Lamprey Shark Fish Frog Snake Bird Human Lymphocytes separate into populations of T and B cells First lymphocytes ap... |
based on mobile phagocytic cells. Chapter 57 The Immune System 1167 57.6 The immune system can be defeated. T Cell Destruction: AIDS One mechanism for defeating the vertebrate immune system is to attack the immune mechanism itself. Helper T cells and inducer T cells are CD4+ T cells. Therefore, any pathogen that inact... |
, as it is transmitted from one individual to another through the transfer of internal body fluids, typically in semen and in blood during transfusions. Not all individuals exposed to HIV (as judged by anti-HIV antibodies in their blood) have yet acquired the disease. Until recently, the only effective treatment for sl... |
of what constitutes an AIDS case. Source: Data from U.S. Centers for Disease Control and Prevention, Atlanta, GA. come available that acts to inhibit protease, an enzyme needed for viral assembly. Treatments that include a combination of reverse transcriptase inhibitors and protease inhibitors (p. 672) appear to lower... |
evolution by natural selection at work. We usually think of evolution as requiring thousands of years to occur, and not in the time frame of weeks. However, evolution can occur whenever mutations are passed on to offspring that provide an organism with a competitive advantage. In the case of viruses, bacteria, and oth... |
vaccination triggers an immune response against the pathogen, and the bloodstream of the vaccinated person contains B cells which will remember and quickly destroy the pathogen in future infections. However, for some diseases, vaccination is nearly impossible because of antigen shifting; the pathogens change over time... |
chemicals Granule IgE receptor B cell Allergen Mast cell FIGURE 57.29 An allergic reaction. This is an immediate hypersensitivity response, in which B cells secrete antibodies of the IgE class. These antibodies attach to the plasma membranes of mast cells, which secrete histamine in response to antigen-antibody bindin... |
histamine may cause anaphylactic shock, an uncontrolled fall in blood pressure. In delayed hypersensitivity, symptoms take a longer time (hours to days) to develop than in immediate hypersensitivity. This may be due to the fact that immediate hypersensitivity is mediated by antibodies, whereas delayed hypersensitivity... |
immunity by prior exposure to a pathogen; passive immunity is produced by the transfer of antibodies from one individual to another. 5. How do IgM and IgG antibodies differ in triggering destruction of infected cells? 6. How does the clonal selection model help to explain active immunity? 7. How are lymphocytes able t... |
ption and secretion to produce urine. Transport Processes in the Mammalian Nephron. The nephron tubules of birds and mammals have loops of Henle, which function to draw water out of the tubule and back into the blood. Ammonia, Urea, and Uric Acid. The breakdown of protein and nucleic acids yields nitrogen, which is exc... |
to set point Perturbing factor Stimulus Deviation from set point Negative feedback loop completed – Effector Causes changes to compensate for deviation Sensor Constantly monitors conditions Integrating center Compares conditions to set point FIGURE 58.2 A generalized diagram of a negative feedback loop. Negative feedb... |
temperature (figure 58.3). One can think of the effectors as “defending” the set points of the body against deviations. Because the activity of the effectors is influenced by the effects they produce, and because this regulation is in a negative, or reverse, direction, this type of control system is known as a negativ... |
initial challenge to homeostasis. Vertebrates other than mammals and birds are ectothermic; their body temperatures are more or less dependent on the environmental temperature. However, to the extent that it is possible, many ectothermic vertebrates attempt to maintain some degree of temperature homeostasis. Certain l... |
hinx moth, contract their thoracic muscles to warm up for flight. Stops insulin secretion Negative feedback loop – Eating Blood glucose Islets of Langerhans Insulin Cellular uptake of glucose Blood glucose FIGURE 58.5 The negative feedback control of blood glucose. The rise in blood glucose concentration following a me... |
to a spark that ignites an explosion. They do not help to maintain homeostasis. Nevertheless, such systems are important components of some physiological mechanisms. For example, positive feedback occurs in blood clotting, where one clotting factor activates another in a cascade that leads quickly to the formation of ... |
homeostasis. Such exchanges of water and electrolytes between the body and the external environment occur across specialized epithelial cells and, in most vertebrates, through a filtration process in the kidneys. Most vertebrates maintain homeostasis in regard to the total solute concentration of their extracellular f... |
Part XIV Regulating the Animal Body Most marine invertebrates are osmoconformers; the osmolality of their body fluids is the same as that of seawater (although the concentrations of particular solutes, such as magnesium ion, are not equal). Because the extracellular fluids are isotonic to seawater, there is no osmotic... |
help them retain water. Marine invertebrates are isotonic with their environment, but most vertebrates are either hypertonic or hypotonic to their environment and thus tend to gain or lose water. Physiological mechanisms help most vertebrates to maintain a constant blood osmolality and constant concentrations of indiv... |
ules that open both to the inside and to the outside of the body. In the earthworm, these tubules are known as metanephridia (figure 58.10). The metanephridia obtain fluid from the body cavity through a process of filtration into funnelshaped structures called nephrostomes. The term filtration is used because the fluid... |
as the annelid shown here, have metanephridia. These consist of tubules that receive a filtrate of coelomic fluid, which enters the funnel-like nephrostomes. Salt can be reabsorbed from these tubules, and the fluid that remains, urine, is released from pores into the external environment. Air sac Malpighian tubules Re... |
excretion. Insects create an excretory fluid by secreting K+ into tubules, which draws water osmotically. The vertebrate kidney produces a filtrate that enters tubules and is modified to become urine. Chapter 58 Maintaining the Internal Environment 1181 Evolution of the Vertebrate Kidney The kidney is a complex organ ... |
animals seem to have evolved first in the sea, marine bony fish (teleosts) probably evolved from freshwater ancestors, as was mentioned in chapter 48. They faced significant new problems in making the transition to the sea because their body fluids are hypotonic to the surrounding seawater. Consequently, water tends t... |
e cartilaginous fish have evolved to tolerate the high urea concentrations. Chapter 58 Maintaining the Internal Environment 1183 Amphibians and Reptiles The first terrestrial vertebrates were the amphibians, and the amphibian kidney is identical to that of freshwater fish. This is not surprising, because amphibians spe... |
als and birds are the only vertebrates able to produce urine with a higher osmotic concentration than their body fluids. This allows these vertebrates to excrete their waste products in a small volume of water, so that more water can be retained in the body. Human kidneys can produce urine that is as much as 4.2 times ... |
FIGURE 58.15 The kangaroo rat, Dipodomys panamintensis. This mammal has very efficient kidneys that can concentrate urine to a high degree by reabsorbing water, thereby minimizing water loss from the body. This feature is extremely important to the kangaroo rat’s survival in dry or desert habitats. Salt glands Salt se... |
organs of the urinary system. (b) A sectioned kidney, revealing the internal structure. (c) The position of nephrons in the mammalian kidney. Cortical nephrons are located predominantly in the renal cortex, while juxtamedullary nephrons have long loops that extend deep into the renal medulla. (b) 1186 Part XIV Regulat... |
aries that surround the tubules. This is the only location in the body where two capillary beds occur in series. The glomerulus is drained by an arteriole and this second arteriole delivers blood to a second capillary bed, the peritubular capillaries. As described later, the peritubular capillaries are needed for the p... |
Indeed, the presence of glucose in the urine is diagnostic of diabetes mellitus. The secretion of foreign molecules and particular waste products of the body involves the transport of these molecules across the membranes of the blood capillaries and kidney tubules into the filtrate. This process is similar to reabsorp... |
were not reabsorbed back into the blood. It is clearly impossible to produce this much urine, yet water is only able to pass through a cell membrane by osmosis, and osmosis is not possible between two isotonic solutions. Therefore, some mechanism is needed to create an osmotic gradient between the glomerular filtrate ... |
not permeable to water. As Na+ exits, the fluid within the ascending limb becomes increasingly dilute (hypotonic) as it enters the cortex, while the surrounding tissue becomes increasingly concentrated (hypertonic). Distal tubule Na+ Cl– H2O 300 600 ) Cortex Outer medulla Inner medulla 1200 Collecting duct H2O Na+ Cl–... |
le in the renal medulla. Because fluid flows in opposite directions in the two limbs of the loop, the action of the loop of Henle in creating a hypertonic renal medulla is known as the countercurrent multiplier system. The high solute concentration of the renal medulla is primarily the result of NaCl accumulation by th... |
the balance of electrolytes in the blood by reabsorption and secretion. For example, the kidneys reabsorb K+ in the proximal tubule and then secrete an amount of K+ needed to maintain homeostasis into the distal convoluted tubule (figure 58.21). The kidneys also maintain acid-base balance by excreting H+ into the urin... |
ous wastes build up as the embryo grows within the egg. The formation of uric acid, while a lengthy process that requires considerable energy, produces a compound that crystallizes and precipitates. As a precipitate, it is unable to affect the embryo’s development even though it is still inside the egg. Mammals also pr... |
primarily by hormones (see chapter 56). Antidiuretic Hormone Dehydration Increased osmolality of plasma — Negative feedback Osmoreceptors in hypothalamus Thirst Posterior pituitary gland Increased ADH secretion Increased water intake Increased reabsorption of water FIGURE 58.23 Antidiuretic hormone stimulates the reab... |
, the blood osmolality also falls. This drop in osmolality inhibits ADH secretion, causing more water to remain in the collecting duct for excretion in the urine. As a result, the blood volume and blood pressure decrease. A decrease in extracellular Na+ also causes more water to be drawn into cells by osmosis, partiall... |
imal convoluted tubule Adrenal cortex Angiotensinogen 4 Angiotensin II 5 6 Aldosterone Increased NaCl and H2O reabsorption 8 Kidney 7 tion of Na+ is followed by Cl– and by water, so aldosterone has the net effect of promoting the retention of both salt and water. It thereby helps to maintain blood volume and pressure. ... |
the reabsorption of water and the excretion of a hypertonic urine. Aldosterone promotes the reabsorption of NaCl and water across the distal convoluted tubule, as well as the secretion of K+ into the tubule. ANH decreases NaCl reabsorption. Chapter 58 Maintaining the Internal Environment 1193 Chapter 58 Summary www.mh... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.