M

Macrophage colony stimulating factor, 684 definition, 833 eye structure, 808 Macula densa cellular effect of NaCl, 355f characteristics, 337 Macular yellow, 824 Magnesium ion fluid compartment ionic composition, 6 kidney, 445-446 Magnocellular pathways characteristics, 574 function, 815 ganglion cell function, 808 Main sensory nucleus, 802 Male reproduction development, 729f germinal epithelium, 724-726 Leydig cells, 723-724 overview, 720 sexual differentiation, 728-730 testes, 720-722...

Conduction in Myelinated Axons

Clearly, there must be another means available by which axons can increase their propagation velocity without drastic changes in fiber diameter. You will note from the relationship for propagation velocity that by changing the membrane capacitance velocity can be affected directly without involving the square root relationship. It is possible to decrease the membrane capacitance simply by coating the axonal membrane with a thick insulating sheath. This is exactly the strategy used by the...

Calcium Balance

Calcium is the most abundant ion in the body but 99 of it is in the skeleton and does not participate in the regulation of the plasma Ca2+ concentration. Typical adults ingest about 600 to 1500 mg of calcium daily however, the gastrointestinal tract absorbs only 150-200 mg day. This rate of absorption is regulated largely by the most active metabolite of vitamin D3, 1,25-dihydroxycholecalciferol 1,25(OH)2D3 see Chapter 43 , in response to the demands for the maintenance of the normal ECF...

Protein

Dietary protein intake varies greatly among individuals of like background and among groups with different geographic, cultural, and economic foundations. Adult humans require 0.5-0.7 g of protein per kilogram of body weight per day to maintain nitrogen balance. Young children may require 4 g kg per day. In addition to dietary intake, protein is present in gastrointestinal secretions and the cells shed into the lumen of the digestive tract. This protein is handled in the same manner as dietary...

Insulin

Although neither GH nor T4 appears to be an important determinant of fetal growth, insulin may act as a growth-promoting hormone during the fetal period. Infants born of diabetic mothers are often larger than normal, especially when the diabetes is poorly controlled. Because glucose readily crosses the placenta, high concentrations of glucose in maternal blood increase fetal blood glucose and stimulate the fetal pancreas to secrete insulin. In the rare cases of congenital deficiency of insulin...

Info

Action potentials (continued) Na+, 78f Na+ and K+ concentrations, 85-86 Na+ and K+ conductance, 83f nerve, 72, 73-74, 76-78 nerve, sketch, 78f optic nerve, 72f plateau phase, calcium channel role, 180 propagation, basic principles, 89-90 repolarization, voltage-dependent potassium conductance role, 83-85 sciatic nerve, 792f sequence of steps, 90f skeletal muscle, shock response, 130f sodium hypothesis, 76-78 sound intensity, 845 tetraethylammonium, 85f threshold, 86 Activation gate, 180 Active...

Vectors Can Be Determined From The Limb Leads

As action potentials are conducted through the heart, the resulting dipoles are constantly changing in both magnitude and orientation. Because of the physical orientation of the limb leads, they are sensitive to the orientation of the dipoles generated by the heart. Consider a vertically oriented dipole whose positive pole points down toward the patient's foot. This would cause the pubis to be positively charged with respect to either shoulder. Thus, the pen would be deflected upward in leads...

Regulation Of Blood Flow

As discussed in Chapter 10, the flow of blood through a vascular bed depends on the pressure gradient across it and its resistance to flow. Because arterial and venous pressures are normally maintained within narrow limits, regulation in flow through an organ is achieved by changing the internal diameter of the major resistance vessels, that is, the arterioles. Vascular resistance within many organs is regulated by systems that are intrinsic to the organ, as well as by extrinsic influences,...

Distribution of Blood Flow

The distribution of pulmonary blood flow throughout the pulmonary vascular tree and to different parts of the lung is not uniform. This was first shown in humans with a technique measuring pulmonary blood flow at different heights in the erect human lung using an insoluble radioactive gas. A saline solution containing radioactive xenon was infused in a vein, so the gas would enter the lung in proportion to blood flow (similar to CO2 elimination from the blood). Radioactive counters were placed...

Potassium Transport By The Intestines

K+ is both absorbed and secreted by the intestines. The bulk of the K + that enters the intestinal tract, derived from salivary, gastric, pancreatic, and biliary secretions as well as dietary intake, is reabsorbed in the small intestine. The primary mechanism responsible is probably diffusion through paracellular pathways. Thus, the reabsorption of water, secondary to the active absorption of Na + and other solutes (see below), will tend to concentrate K + in the chyme. But, as noted earlier,...

Fuels

Fuel selection during exercise is determined by both the duration and intensity of exercise. A short sprint such as a 50-meter dash will be fueled entirely by muscle stores of glycogen and phosphocreatine. At the other extreme of a long trek, oxidation of free fatty acids is the most important fuel. Protein is not a major fuel for exercise, comprising less than 2 of the substrate during the first hour of exercise and rising to only 15 after five hours. Fats contribute about two-thirds of the...

Clinical Note

Sleep apnea is a group of conditions characterized by pauses or reductions in breathing during sleep that last 10 sec or more. In most patients this leads to arterial hypoxemia and CO2 retention. When hypoxic or hypercapnic stimuli reach a sufficiently high level, breathing efforts increase and this arouses or awakens the individual. Apneas and arousals can occur repeatedly and cause sleep fragmentation and excessive daytime sleepiness. Cognitive and neurological effects may result from...

Physiological Actions Of Ovarian Steroid Hormones

As described above, intraovarian actions of estradiol and progesterone are intimately connected to ovulation and formation of the corpus luteum. In general, extra-ovarian actions of these hormones ensure that the ovum reaches its potential to develop into a new individual. Ovarian steroids act on the reproductive tract to prepare it for fulfilling its role in fertilization, implantation, and development of the embryo, and they induce changes elsewhere that equip the female physically and...

Airway Defense Mechanisms

The exchange surface area of the lung is the largest interface between the body and the environment. Therefore, the lungs have an important set of mechanisms to defend the body from foreign matter. The first line of defense is the upper airways, including the mouth and nose. A major function of the upper airways is to warm and humidify air entering the respiratory system, which prevents drying and cooling of the delicate epithelial barrier in the lungs. Complex air passages in the nose, called...

Morphology Of The Endocrine Pancreas

The 1 to 2 million islets of the human pancreas range in size from about 50-500 mm in diameter and contain from 50-300 endocrine cells. Collectively the islets comprise only 1-2 of the pancreatic mass. They are highly vascular, with each cell seemingly in direct contact with a capillary. Blood is supplied by the pancreatic artery and drains into the portal vein, which thus delivers the entire output of pancreatic hormones to the liver. The islets are also richly innervated with both sympathetic...

Limitations Of Pulmonary Gas Exchange

Gas exchange limitations in the lungs can reduce PO2 throughout the O2 cascade. Recall that limitations do not decrease resting Vo2, although they may limit maximal O2 consumption during exercise. Hypoxemia is defined as a decrease in blood PO2, and arterial hypoxemia, or decreased PaO2, indicates a limitation of pulmonary gas exchange. Gas exchange limitation does not imply a decrease in resting O2 consumption, because Po2 will adjust throughout the O2 cascade to maintain O2 consumption in a...

Physiology Of The Mineralocorticoids

Although several naturally occurring adrenal cortical hormones, including glucocorticoids, can produce mineralocorticoid effects, aldosterone is by far the most important mineralocorticoid physiologically. In its absence there is a progressive loss of sodium by the kidney, which results secondarily in a loss of extracellular fluid (see Chapter 29). Recall that the kidney adjusts the composition of the extracellular fluid by processes that involve formation of an ultrafiltrate of plasma followed...

Physiologic Effects Of Thyroid Hormones

Growth and Maturation Skeletal System One of the most striking effects of thyroid hormones is on bodily growth (see Chapter 44). Although fetal growth appears to be independent of the thyroid, growth of the neonate and attainment of normal adult stature require optimal amounts of thyroid hormone. Because stature or height is determined by the length of the skeleton, we might anticipate an effect of thyroid hormone on growth of bone. However, there is no evidence that T3 acts directly on...

Control Of Testicular Function

Physiological activity of the testis is governed by two pituitary gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (see Chapter 38). The same gonadotropic hormones are FIGURE 3 The formation of mammalian germ cells. Each primary spermatogonia ultimately gives rise to 64 sperm cells. Cytokinesis is incomplete in all but the earliest spermatogonial divisions, resulting in expanding clones of germ cells that remain joined by intercellular bridges. (From Fawcett...

Descending Motor Tracts In The Spinal Cord

Reflex activity generated from motor programs in the spinal cord represents the foundation of the motor hierarchy. These programs provide the basic plans by which movement can be achieved in a coordinated fashion. In addition, they facilitate the transfer of information about more complex movements and about volitional movement from brain to appropriate groups of lower motor neurons. Motor input to spinal cord levels is received in two major pathways (1) the ventromedial pathway, consisting of...

Key Points

Coordination of cortical motor commands is achieved by motor loop pathways that pass information from the cortex through the basal ganglia and thalamic nuclei and back to the cortex. The direct (excitatory) and indirect (inhibitory) pathways of the basal ganglia loop provide opposite, counterbalanced influences on activity of the motor cortex. The dopaminergic nigrostriatal pathway modulates activity in the direct and indirect pathways, maintaining a critical level of excitatory drive for...

Physiologic And Pathophysiologic Changes In Renal Blood Flow And Glomerular Filtration Rate

Although GFR and RPF are normally relatively constant, they can change from their normal set point when influenced by other signaling systems. Under normal conditions, the GFR is nearly maximal so that most of the normal physiologic changes occur in the direction of decreasing GFR. Presuming there are no changes in plasma protein concentration, this could be accomplished by changes in afferent or efferent arteriolar resistance, or in the ultrafiltration coefficient Kf. The effects of arteriolar...

Control Of Ventilation

The body contains several physiologic control systems to maintain arterial pH (pHa) within normal limits, to meet the oxygen demands of the tissues, to minimize the mechanical work of breathing, and to prevent lung injury by environmental agents. This means that limitations in lung function or gas exchange can be masked by the physiologic control systems acting to maintain homeostasis. Therefore, knowledge of the normal physiology of respiratory control is critical for understanding respiratory...

Impairments In Urinary Concentrating And Diluting Ability

Deficiencies in the ability of the kidney to regulate plasma osmolality by appropriately forming either dilute or concentrated urine may have several causes. There may be a defect in production or regulation of vasopressin release, an inability of the collecting duct to respond to vasopressin, or a failure to form a medullary osmolality gradient. Diabetes insipidus refers to high rates of production of dilute urine either because the posterior pituitary fails to release vasopressin or because...

Some General Characteristics Of Carriermediated Transport

The following features are so widely characteristic of carrier-mediated transport processes that they are generally considered sufficient and often necessary criteria for the implication of carriers in the transport of a given solute 1. Virtually all carriers appear to display a high degree of structural specificity with regard to the substances they will bind and transport. For example, the carriers responsible for the transport of glucose into animal cells are highly stereospecific they will...

Hierarchical Arrangement Of Motor Cortical Areas

Firing of MI upper motor neurons is associated with relatively simple motor commands more complex movements are linked to upper motor neurons in area MII (Fig. 2). Two separate somatotopic maps are present in MII The supplementary motor area (SMA) is located near the superior medial region of the cortex, and the premotor area (PMA) occupies a more lateral position. Pyramidal cells in these areas contribute to corticofugal pathways and are also heavily interconnected to MI. Both areas of MII...

Regulation Of Metabolism During Feeding And Fasting

Immediately after eating, metabolic activity is directed toward the processing and sequestration of energy-rich substrates that are absorbed by the intestines. This phase is dominated by insulin, which is secreted in response to three inputs to the beta cells. The cephalic, or psychological aspect of eating, stimulates insulin secretion through acetylcholine and vasoactive inhibitory peptide (VIP) released from vagal fibers that innervate islet cells. Food in the small intestine stimulates...

Salt And Water Reabsorption In The Proximal Tubule

Mass Flow Balance Proximal Tubule

As shown in the following sections, it is important to think of the transport of each substance along the nephron in terms of its rate of movement rather than by its concentration in the tubular fluid. The same considerations of mass balance that apply to the kidney as a whole also apply to the proximal tubule. In the case of the proximal tubule, the rate of input of substances is determined by the product of the glomerular filtration rate (GFR) and the concentration of the substance in the...

Metabolism Of Thyroid Hormones

Because T4 is bound much more tightly by plasma proteins then T3, a greater fraction of T3 is free to diffuse out of the vascular compartment and into cells where it can produce its biological effects or be degraded. Consequently, it is not surprising that the half-time for disappearance of an administered dose of 125I-labeled T3 is only one-sixth of that for T4, or that the lag time needed to observe effects of T3 is considerably shorter than that needed for T4. However, because of the binding...

Qqj

IC, see Inspiratory capacity ICCs, see Interstitial cells of Cajal ICF, see Intracellular fluid compartment Ideal alveolar-arterial pulmonary oxygen difference, 301 Ideal gas law, respiratory system, 263-264 IgA, see Immunoglobulin A IGFBPs, see Insulin-like growth factor- binding proteins IGF-I, see Insulin-like growth factor I IGF receptors, see Insulin-like growth factor receptors IL, see Interleukins Ileocecal sphincter relaxation, 480 Immune system defense mechanisms, 275 response and...

Secretory Processes In The Proximal Straight Tubule

Excretion Pah

The proximal tubule has an important function in secreting many substances that can be regarded as metabolic by-products or potential toxins. Given normal rates of production of some metabolic byproducts, the body requires a renal secretory process to maintain acceptable plasma concentrations. Renal secretory processes serve a more important role in excreting exogenous toxic substances that are ingested in the diet. Secretion of these substances results in an excretion rate that exceeds their...

Central Auditory Pathways

Auditory Pathway Action Potential Nerves

The central pathway of the auditory system contains a large number of relay nuclei within the brain stem (Fig. 6). Central fibers from primary sensory neurons in the spiral ganglia project along with vestibular fibers in cranial nerve VIII and synapse first within the dorsal and ventral cochlear nuclei located near the pontomedullary junction. Ascending fibers from these nuclei project to both the FIGURE 4 Structure and functional relationships of the basilar membrane. The cochlea is shown...

Pancreatic Secretion

Exchange Between And Ions

Pancreatic exocrine secretion consists of an aqueous or bicarbonate component and an enzymatic component. The aqueous component consists primarily of water and sodium bicarbonate and is produced by the cells lining the pancreatic ducts. The aqueous component neutralizes duodenal contents, preventing injury to the duodenal mucosa and bringing the contents within the pH range necessary for optimal enzymatic digestion of nutrients. The enzymatic or protein component is a low-volume secretion from...

Criteria for Active Transport of Ions

In a previous section we distinguished between passive (or downhill) and active (or uphill) transport of uncharged molecules. The sole criterion for this distinction is the relation between the direction of the net movement of the molecule and the direction of the concentration gradient. If an uncharged molecule moves or is transported from a region of higher concentration to one of lower concentration, the transport process is said to be passive (or downhill) because the flow is in the...

Hormonal Interactions During Exercise

During exercise, overall oxygen consumption may increase 10-15 times in a well-trained young athlete. The requirements for fuel are met by mobilization of reserves within muscle cells and from extramuscular fuel depots. Rapid uptake of glucose from blood can potentially deplete, or at least dangerously lower, glucose concentrations and hence jeopardize the brain unless some physiologic controls are operative. We can consider two forms of exercise short-term maximal effort, characterized by...

H

Activities are discussed in Chapter 35, which is concerned with the digestion and absorption of nutrients. Between meals, pancreatic enzymes are stored in zymogen granules that have migrated to an area near the apical membrane of the acinar cell. A secretory stimulus results in the fusion of the granule membrane with the apical membrane of the cell and the secretion of enzyme contents into the lumen. This process of exocytosis is the only step in the synthesis of the proteins, formation of...

Normal Bowel Rectosphincteric Reflex

FIGURE 12 Mass movement. (A) Colon before entry of barium sulfate. (B) Barium enters proximal ascending colon, showing haustra. (C) As more barium enters, the haustra disappear from a portion of the ascending and transverse colons, and a contraction begins in this area. (D) The contraction has moved a portion of the barium into the caudad transverse colon. (E) Haustra return. exposing them to absorptive surfaces. These contractions last from 12-60 seconds and generate intraluminal pressures...

Gastrointestinal Smooth Muscle

The smooth muscle cells in each part of the gastrointestinal (GI) tract have structural and functional differences. However, certain basic properties are common to all of these cells. Smooth muscle cells make up all of the contractile tissue of the GI tract with the exception of the pharynx, the upper one-third to one-half of the esophagus, and the external anal sphincter, which are striated muscle. Smooth muscle cells are smaller than skeletal muscle cells and are long, narrow, and spindle...

Respiratory Muscles

Ventilatory flow is driven by pressure differences between the alveoli and the atmosphere. In normal individuals at rest, active contraction of skeletal muscle generates this pressure difference during inspiration. In contrast, expiration at rest results from passive elastic recoil of the lungs. The diaphragm is the main muscle of inspiration and, therefore, the most important muscle for resting breathing. The diaphragm is innervated by the phrenic nerve, which originates from the third,...

Bile Secretion And Gall Bladder Function

Lecithin Cholesterol And Bile Salts

Bile is responsible for the principal digestive functions of the liver. The presence of bile in the small intestine is necessary for the digestion and absorption of lipids. The problem of the insolubility of fats in water is solved by the constituents of bile. The bile salts and other organic components of bile are responsible in part for emulsifying fat so that it can be digested by pancreatic lipase. The bile acids also take part in solubilizing the digestion products into micelles. Micellar...

Immune System Defense Mechanisms

The lung is similar to all other organs by containing lymphocytes (T and B cells) in the interstitium. These defense cells originate from the bone marrow and lymph nodes and respond to foreign invaders with cellular (acquired antibody) mechanisms. Dendritic cells present antigens to the lymphocytes. Considering that up to 1010 antigenic particles may reach the alveoli every day, the challenge for the pulmonary immune system is to process this foreign material and not overamplify an inflammatory...

Diffusion Of Electrolytes

The previous section dealt with the diffusion of uncharged particles, but many of the fundamental properties of the diffusional process described therein also apply to the diffusion of charged particles. In both instances, net flow due to diffusion is the result of random thermal movements, and the diffusion coefficients of the particles are inversely proportional to their molecular or hydrated ionic radii. However, because ions bear a net electrical charge, the diffusion of a salt such as...

Integrated Actions Of Metabolic Hormones

Metabolic fuels absorbed from the intestine are largely converted to storage forms in liver, adipocytes and muscle. It is fair to state that storage is virtually the exclusive province of insulin, which stimulates biochemical reactions that convert simple compounds to more complex storage forms and inhibits fuel mobilization. Hormones that mobilize fuel and defend the glucose concentration of the blood are called counter-regulatory and include glucagon, epinephrine, norepinephrine, cortisol,...

Water Reabsorption Driven By Solute Reabsorption

As described earlier, reabsorption of Na+ with its accompanying anions is driven by the Na+,K+-ATPase. This movement is also accompanied by the reabsorption of other solutes linked to Na+ reabsorption including glucose, amino acids, and other organic solutes. The net effect of the reabsorption of all of these solutes is to deplete the tubular lumen of solutes while adding them to the lateral intercellular spaces and interstitium. Therefore, the fluid in the proximal tubule should become...

Functional Anatomy Of The Kidney

Juxtamedullary Nephrons

A person's kidney is about the size of a clenched fist. When examined in cross section as shown in Fig. 1, the kidney is easily divided into two regions the cortex and the medulla. The blood, lymphatic, and neural supply of the kidney enter through the hilus together with the ureter, which carries the urine from the kidney to the bladder, where it is stored until emptied by micturition (urination). In the human kidney, the medulla terminates in several conical structures called papillae. The...

Salivary Secretion

The functions of saliva fall into three general categories digestion, lubrication, and protection. Saliva is produced in large volumes, relative to the weight of the salivary glands, by an active process. Unlike the process in the other gastrointestinal glands, the secretion of saliva is almost totally under neural control. Both branches of the autonomic nervous system stimulate salivary secretion, although the para-sympathetic system provides a much stronger input. The healthy adult secretes...

Autoregulation

As shown in Fig. 10, RBF and GFR remain relatively constant over a wide range of systemic blood pressures. To prevent changes in blood flow and GFR with changes in systemic blood pressure that occur normally during the day with changes in activity, the resistance to flow must change appropriately. As systemic blood pressure increases, total renal vascular resistance increases so that blood flow and GFR remain constant. Autoregulation, which is exhibited in the circulation of many organs, refers...

Movement Of Material Through The Esophagus

Peristalsis Movement

The obvious function of the esophagus is to serve as a conduit for and to propel swallowed material to FIGURE 4 Neural pathways involved in the regulation of pharyngeal and esophageal peristalsis. Vagal sensory input is relayed to the swallowing center in the medulla, where output to muscles is coordinated with respiration. Muscles of the pharynx and the striated esophagus are innervated via the nucleus ambiguus smooth muscles of the esophagus are innervated via the dorsal motor nucleus....

Motor Neurons For Head And Neck Muscles

Reflex Arc Diagram

Muscles of the head and neck are for the most part highly specialized, and each exhibits unique functional properties. Extraocular muscles are innervated by lower motor neurons in cranial nerves III (oculomotor), IV (trochlear), and VI (abducens), which originate from the brain stem. They are among the fastest muscles in the body and are continually active during awake hours as well as during certain segments of the sleep cycle, called rapid eye movement (REM) sleep. As described below, the...

Ionic Fluxes In The Cardiac Muscle Cells

Figure 7 summarizes some of the key changes in ion permeability that contribute to the cardiac action potential. The upper trace shows a typical cardiac action potential and the lower traces illustrate the changes in permeability to Na+, K+, and Ca2+. As a consequence of a depolarizing stimulus, a voltage-dependent increase in Na+ conductance occurs. A regenerative cycle is initiated, which tends to depolarize the cell toward the equilibrium potential of Na+. This regenerative increase in Na+...

Examples

A typical adult human ingests of 8-10 g about NaCl each day. There is no metabolic production of this inorganic compound, so for a steady state to be maintained (as is further discussed in Chapter 29) NaCl must be excreted (by the sum of urinary, sweat, and fecal routes) at the same rate of 8-10 g per day. 2. Water is typically ingested at a rate of 1-2 L day with about 150-250 mL day added from metabolism of various substrates such as glucose. Water loss, which occurs via the same routes as...

Coronal View Of Brain Showing Spinal Cord

Brain Coronal Cross Section Spinal Cord

Herpes zoster virus, commonly known as chicken pox, preferentially infects neurons of the peripheral nervous system, particularly dorsal root ganglion cells. Individuals infected with the virus during childhood usually display red, itchy spots on the skin for approximately 1 week and are symptom free thereafter. However, the virus may remain dormant, usually residing in a single dorsal root ganglion, and can become reactivated in some individuals decades later to produce a condition known as...

Regulation Of Thyroid Hormone Secretion

As already indicated, secretion of thyroid hormones depends on stimulation of thyroid follicular cells by TSH, which bears the primary responsibility for integrating thyroid function with bodily needs (Chapter 38). In the absence of TSH, thyroid cells are quiescent and atrophy, and, as we have seen, administration of TSH increases both synthesis and secretion of T4 and T3. Secretion of TSH by the pituitary gland is governed by positive input from the hypothalamic hormone thyrotropin-releasing...

Mqe

FIGURE 15 Synergistic effects of human growth hormone (hGH) and the synthetic glucocorticoid dexamethasone (Dex) on lipolysis as measured by the increase in glycerol release from rat adipocytes. Both hGH and Dex were effective when added individually, but when added together their effect was greater than the sum of their individual effects. (From Gorin et al., Endocrinology 1990 126 2973.) FIGURE 16 Push-pull mechanism. Epinephrine inhibits insulin secretion while promoting glucagon secretion....

Mechanical Response Of Smooth Muscle In Vivo

Most smooth muscles form, along with other tissues, the walls of hollow organs such as the gastrointestinal tract, the uterus, and the blood vessels. In these organs, smooth muscle contractions serve many purposes such as the movement of lumenal contents, the regulation of lumenal volume, and the alteration of the resistance to flow through the lumen. For some of these functions, contractions must be phasic to allow the lumens to refill between contractions. For others, contractions must be...

Alveolar Ventilation

Ventilation is the first step in the O2 cascade, and the level of alveolar ventilation (Va) is the most important physiologic factor determining arterial Po2 for any given inspired Po2 and level of O2 demand (Vo2) in healthy lungs. As described in Chapter 18, anatomic dead space reduces the fraction of the tidal volume that reaches the alveoli where Va is alveolar ventilation, fR is respiratory frequency, VT is tidal volume, and VD is anatomic dead space. Anatomic dead space can be measured...

Lcg Hormon Function

FABPs, see Fatty acid-binding protein Facial nerve, in taste, 858 Facilitated diffusion characteristics, 533 definition, 38 overview, 59 Facilitatory neurons, Aplysia short-term sensitization, 911 Fahraeus-Lindquist effect, 166 Fallopian tubes, 742 Fasciculus, dorsal spinal column, 801 Fastigial nucleus, spinocerebellum, 890 Fasting blood constituents, 672f IGF-I and GH effects, 712f leptin concentration, 676f metabolic hormones, 671f metabolism regulation, postprandial period, 669-671...

General Properties Of Sensory Receptors

Sensory information from the body reaches the nervous system piecemeal through a series of separate sensory pathways associated with specific sensory modalities. These pathways consist of sensory receptors and their projections to designated receiving areas in the cortex. A unified perception of our physical world emerges from the coordinated response of these primary receiving areas and secondary association areas. Separate pathways for the special senses of vision, hearing, taste, and...

Stanley G Schultz

The word diabetes derives from the Greek, Stapatvo, meaning passing through'' or too swift a passage of the matter that is drunk.'' It is used today to describe the condition of excessive production of urine or polyuria. As discussed earlier (Chapters 28 and 41), there are two forms of diabetes. One is diabetes insipidus, which results from impaired secretion or production of the antidiuretic hormone (ADH) due to injury to the hypothalamus or supraoptic nucleii. Diabetes insipidus can also,...

The Muscle Spindle

The driving force on lower motor neurons comes from three major sources (1) sensory pathways from the spinal cord and brain stem that trigger reflex actions, (2) interneurons within the spinal cord that interconnect synergistic and antagonistic motor neuron pools, and (3) upper motor neurons in the motor cortex and other motor areas in the brain that provide complex motor commands. One of the major sensory inputs to the lower motor neuron is derived from specialized end organs located within...

Ho

FIGURE 6 Biosynthesis of ovarian hormones. Cleavage of the cholesterol side chain by P450scc between carbons 21 and 22 gives rise to 21-carbon progestins. Removal of carbons 20 and 21 by the two-step reaction catalyzed by P450c17 (17a hydroxylase lyase) produces the 19-carbon androgen series. Aromatization of ring A catalyzed by P450cyp19 (aromatase) eliminates carbon 19 and yields 18-carbon estrogens. 3pHSD, 3p hydroxyster-oid dehydrogenase 17pHSD, 17p hydroxysteroid dehydrogenase.

Other Neural Reflexes Involved With Blood Pressure Regulation

Although the baroreceptor reflex is the primary moment-to-moment controller of aortic pressure, other 0 50 100 150 200 250 Mean Arterial Pressure (mm Hg) FIGURE 6 Variations in mean arterial pressure over a 24-hr period in a normal dog before and several weeks after baroreceptor denervation. (Modified from Guyton AC, Hall JE. Textbook of medical physiology, 9th ed. Philadelphia WB Saunders, 1996.) mechanisms exist that come into play under periods of extreme cardiovascular stress. These are...

Avb

GABA, see Gamma aminobutyric acid Gag reflex, 806 Galactose, 534, 534f Gall bladder bile concentration, 526-527 bile expulsion, 527-528 bile secretion, overview, 520-521 filling, 526 Gall stones characteristics, 527 during pregnancy, 966 Gametes, 758-759 Gamma aminobutyric acid inhibitory postsynaptic potentials, 116 olfactory bulb, 852 rhythmic breathing, 318 Gamma loop system, 867, 869-870 Gamma motor neurons, 869f, 870 Ganglion cells cortex blob region, 825f function, 807 receptive field...

Glomerular Filtration

Afferent Efferent Rpf Gfr

The high hydrostatic pressure of the blood in the glomerular capillaries is responsible for a net driving force favoring ultrafiltration from the glomerular capillaries. In the young male adult, the glomerular filtration rate GFR averages about 130 mL min, which amounts to a whopping 187 L day. The high rate of glomerular filtration means that as plasma flows through the kidneys at a rate of 670 mL min, 130 mL min, or 20 , is filtered. This 20 represents what is referred to as the filtration...

The Visual Cortex

Cells within the six ocular dominance layers of the lateral geniculate project to distinct ocular dominance stripes or columns within Brodmann's area 17 also called area VI of the primary visual cortex see Fig. 11 . Pairs of adjacent ocular dominance columns one with ipsilat-eral projections from the lateral geniculate nucleus LGN , and the other with contralateral projections receive information about the same point in visual space. Adjacent pairs are collectively designated as a hyper-column....

Specialized Features Of Rod And Cone Photoreceptors

The two types of retinal photoreceptor cells, rods and cones, are not evenly distributed across the retina Fig. 3 . Cones are concentrated in the foveal region, whereas rods are absent. Several of the cellular characteristics of cones make them particularly suited for high-acuity vision. Because of the tightly packed arrangement of foveal cones, the foveal region is capable of high-resolution finegrained responses. In addition, the outer segment, which contains most of the visual pigment of the...

Ionic Mechanisms Underlying The Endplate Potential

How does ACh produce the permeability change responsible for the EPP In the early 1950s, Bernard Katz and his colleagues proposed that the binding of ACh with receptors on the postjunctional membrane led to a simultaneous increase in Na and K permeabilities. If a membrane is permeable only to Na and K , then the Goldman-Hodgkin-Katz GHK equation is applicable where a PNa PK. If a 1 and the K and Na concentrations on the inside and outside of the cell are substituted into the equation, a...

Emotions Related To Autonomic Nervous System Function

Strong emotional feelings are often associated with most autonomic responses. Coordinated parasympa-thetic responses evoke a vegetative state that generates an overall relaxed, pleasurable feeling. They are often linked to eating behavior and can be triggered by food-related sensory stimuli, such as seeing or smelling appetizing food. The opposite is true for coordinated responses from the sympathetic division of the ANS. In this case, sympathetic pathways coordinate protective responses,...

Xvf

FIGURE 8 Three sets of mechanical g and electrical mV tracings from the caudad region of the stomach. A Slow-wave depolarization of insufficient magnitude to cause contraction. B Increased depolarization results in contraction. C Electrical slow wave with multiple spike potentials and extended plateau produces a vigorous and extended contraction. Although digestive events and the resulting neural and hormonal input to the stomach are not necessary for slow waves to occur, they markedly affect...

Sound Transmission Through The Middle And Inner Ears

Sound waves enter the auditory canal after being funneled and reflected by components of the external ear, or pinna Fig. 2 . The canal extends 2.5 cm into the skull and ends at the tympanic membrane eardrum , which forms the boundary between the outer and middle ears. The middle ear is an air-filled cavity containing three small bones, the ossicles, which are connected in series to the tympanic membrane. Sound waves in the auditory canal cause the tympanic membrane to vibrate and thus transmit...

Gastric Motility

Activity of the smooth muscle of the stomach carries out three principal functions 1 The muscle relaxes to accommodate large volumes ingested during a meal 2 contractions mix ingested material with gastric juice, facilitating digestion, solubilizing some constituents, and reducing the size of the particles and 3 contractions propel material into the duodenum at a rate regulated to provide optimal time for intestinal digestion and absorption. Structure and Innervation of the Stomach Unlike the...

Vitamin Dendocrine System

A derivative of vitamin D3,1,25-dihydroxycholecalcif-erol 1,25 OH 2D3 , is indispensable for maintaining adequate concentrations of calcium in the extracellular fluid and adequate mineralization of bone matrix. Vitamin D deficiency leads to inadequate calcification of bone matrix and severe softening of the skeleton, called osteomalacia, and may result in bone deformities and fractures. Osteomalacia in children is called rickets and may produce permanent deformities of the weight-bearing bones...

Lipids

The daily dietary intake of fat varies from below 25 g, or less than 12 of caloric intake found among rice-eating Asian cultures , to as much as 140-160 g, or 40 of the caloric intake found among some individuals in Western meat-eating cultures . The difference is due primarily to the increased intake, in the latter group, of saturated fatty acids found in red meat and dairy products. The intake of unsaturated fatty acids is approximately the same in both groups. Among those substances...

Lh

FIGURE 11 Ovarian-pituitary interactions at different phases of the menstrual cycle. Solid arrows, stimulation dashed arrows, inhibition. Note that the frequency of the GnRH pulse generator slows in the luteal phase, and that the amplitude may increase at midcycle. the luteinization process. Conversely, the gradual loss of sensitivity of luteal cells to LH accounts for the decrease in progesterone and estrogen secretion during the latter part of the luteal phase. Thus, one of the unique...

Henderson Hasselbalch Equation

The Henderson-Hasselbalch equation describes the relationship between Pco2 pH, and HCO3- in human blood as follows where HCO- is the bicarbonate concentration in millimoles per liter, and 0.03 PCO2 is the total dissolved CO2 concentration, also in millimoles per liter 0.03 mmol L per mm Hg is the solubility of CO2 in water . As described in Chapter 31, the Henderson-Hasselbalch equation is based on the chemical equilibrium between carbonic acid and its dissociation products The dissociation...

Active And Passive Solute Transport

Up until this point, solute reabsorption in the proximal tubule has been discussed in general terms as FIGURE 8 Effect of reduced plasma colloid osmotic pressure and increased interstitial fluid pressure on the permeability properties of the junctional complexes. It has been proposed that an increase in interstitial fluid pressure may be associated with an increased permeability of the junctional complexes between proximal tubule cells that would enable backflux diffusion of Na , Cl-, HCO , and...

Regulation Of Cardiac Output

Any change in cardiac output must be the result of a change in either the vascular or the cardiac function curves. Neural, endocrine, and other regulatory mechanisms constantly change cardiac output to meet the body's metabolic needs by altering those curves. Often, simultaneous changes in several parameters work in concert or in opposition. For example, a decrease in blood volume may have little or no effect on mean circulatory filling pressure if the decreased blood volume is accompanied by...

Gibbsdonnan Equilibrium Ion Pumps And Maintenance Of Cell Volume

So far we have considered three of the functions that are fulfilled by the operation of Na -K pumps. First, they are responsible for the high K and low Na concentrations characteristic of the intracellular fluid of higher animals. A number of enzymes involved in intermediary metabolism and protein synthesis appear to require relatively high concentrations of K for optimal activity and are inhibited by high concentrations of Na the activities of these enzymes would be markedly impaired if the...

Development And Maintenance Of Medullary Hyperosmolality

Thus far, this chapter has discussed the effects of the hyperosmotic medullary interstitium on the abstraction of water from the thin descending limb and from the medullary collecting duct in the presence of vasopressin. How does this medullary hyperosmolality develop, and how is it maintained in the face of plasma flow through the medulla In any other tissue, one would expect that the constant blood flow, as well as the constant water entry from the thin descending limb of the loop of Henle...

Paracrines

Paracrines are synthesized in and released from endocrine cells in the same fashion as hormones. However, the amounts released do not reach the general circulation in concentrations sufficient to produce effects. Instead, paracrines act on cells in their immediate vicinity, reaching them by simple diffusion or perhaps movement through capillaries before being diluted in the general circulation. One can assess the biologic significance of a hormone by correlating its plasma levels with its...

Excitation Originates Within The Heart Muscle Cells

Cardiac muscle, like skeletal muscle, is a striated muscle and much of the mechanism of contraction is similar between the two muscle types. The electrophy-siology of the two muscles differs dramatically, however. In skeletal muscle an action potential in the synaptic terminal of a motor neuron coming from the central nervous system releases a transmitter substance, acetylcholine, which triggers a very brief action potential on the muscle cell, causing it to contract. Skeletal muscle contracts...

Goldmanhodgkinkatz Equation

The Goldman equation is also known as the Goldman-Hodgkin-Katz GHK equation because Hodgkin and Katz applied it to biologic membranes. As has already been seen in Chapter 3, the GHK equation can be used to determine the potential developed across a membrane permeable to Na and K . Thus, where Vm is the membrane potential in millivolts and a is equal to the ratio of the Na and K permeabilities PNa PK . This equation looks rather complex at first, but it can be simplified by examining two extreme...

Epithelial Characteristics Of The Nephron

Interstitium

All nephron segments, from the glomerulus to the ducts of Bellini, consist of epithelial cells that are joined in a continuous layer by specialized structures called junctional complexes, as illustrated in Fig. 1. Although some epithelia consist of multiple cell layers, a single cell layer forms the epithelium of the nephron. On the basal side of all epithelia a continuous basement membrane composed of collagen, laminin, and other extracellular matrix proteins provides structural support that...

Bernsteins Hypothesis for the Resting Potential

Bernstein Hypothesis

In 1902, Julius Bernstein proposed the first satisfactory hypothesis for generation of the resting potential. Bernstein knew that the inside of cells have high K and low Na concentrations and that the extracellular fluid has low K and high Na concentrations. In addition, there appeared to be large negatively charged molecules, presumably proteins, to which the cell was impermeable. Bernstein also knew a critical piece of information that cells were highly permeable to K but not very permeable...

Measures of Airway Resistance

Intrapleural Pressure Lung Volume

The physical principles just described can be used to predict the main site of airway resistance in the bronchial tree, and this can be verified on experiments with isolated lungs or models of lungs. Figure 7 shows that the main site of airway resistance is the large airways, even though radius has a dominant influence on resistance cf. Poiseuille's law . This is because the small cross-sectional area in the upper airway branches results in high velocities and turbulent flow. Small airways...

Prolonged Refractory Periods Prevent The Heart From Being Tetanized

The fast sodium channels trigger action potentials in contractile and Purkinje cells. They have actually two gates that control passage of Na through the channel. The activation gate normally blocks the channel. Because it is voltage-gated it opens only when the membrane potential reaches threshold creating phase 0. Shortly after the activation gate opens a second part of the molecule, the inactivation gate closes the channel, causing phase 0 to end. The inactivation gate is voltage sensitive...

Neural Integration In The Vasomotor Center

The vasomotor center is located in the reticular substance of the medulla and a portion of the pons. Its anatomy and functional organization is complex and still not completely understood however, it is considered to have at least four important functional areas 1 the vasoconstrictor region often referred to as C-l , which is located in the upper medulla and lower pons, sends fibers into the spinal cord where they activate sympathetic vasoconstrictor neurons 2 the vasodilator region often...

D

FIGURE 6 Balance of the hydrostatic Pc and Pif and oncotic wp and wif pressures acting A across a normal capillary and B after an acute 10 mm Hg elevation in capillary hydrostatic pressure. Note that capillary fluid filtration rate Jv and lymph flow increase almost 20-fold in response to the elevated capillary pressure. oncotic pressures, as well as the elevated lymph flow. These compensatory responses that prevent excessive fluid accumulation in the interstitium are called the safety factors...

Cerebral Circulation

Under resting conditions, blood flow to the brain is about 50 mL min per 100 g, accounting for about 15 of cardiac output. O2 consumption by the human brain averages about 3.5 mL min per 100 g. Gray matter has a very high rate of oxidative metabolism and its flow rate is up to six times higher than that of white matter. The brain, particularly gray matter, is exquisitely sensitive to hypoxia and consciousness is lost in humans after as little as 10 min of ischemia, with irreversible cell damage...

Intracellular Receptors

Steroid Receptors With Response Element

To reach intracellular receptors, agonists must get across the plasma membrane. The steroid hormones and vitamin D see Chapters 40, 43, and 45-47 are derivatives of cholesterol and readily diffuse through the lipid bilayer of the plasma membrane because they are highly lipid soluble. Similarly, the thyroid hormones see Chapter 39 , which are a-amino acids, have large nonpolar constituents and penetrate cell membranes both by diffusion and to some extent by carrier-mediated transport. Retinoic...

Gorter And Grendel Bilayer Of Lipids Model

Gorter Und Grendel

FIGURE 1 A Monolayer formed by phospholipids at an air-water interface. B A phospholipid bilayer separating two aqueous compartments. C A bimolecular lipoprotein membrane. layer Fig. 1A of olive oil on water have not significantly improved on Franklin's estimate. In 1925, Gorter and Grendel, stimulated by the findings of Franklin and Overton, performed a series of studies that had a major impact on all subsequent thinking dealing with membrane structure. These investigators extracted the lipids...

Body Fluid Compartments And Their Contacts With The Outside World

Transcellular Space Fluid Compartments

The total body water TBW in higher animals is distributed among three major compartments the blood plasma, the interstitial fluid ISF , and the intracellular fluid ICF . The plasma is separated from the ISF compartment by highly permeable capillaries together, plasma and ISF constitute the extracellular fluid ECF compartment. This compartment is separated from the ICF compartment by cell membranes, which in most instances, as discussed in Chapter 3, are highly permeable to water but very...

Historical Perspectives The Dawning of Membrane Biology

The first suggestion of the existence of biological membranes is generally attributed to the botanist Carl Wilhelm Nageli 1817-1891 , who became a pioneer in the application of microscopic techniques to the study of cell detail through his attempts to relate structure and function. In his classic work Primordialschlauch, published in 1855, he pointed out that the region immediately adjacent to the inner surfaces of the walls of plant cells appeared to differ from the underlying protoplasm and...