Growth Hormone Promotes Growth of Many Body Tissues

Growth hormone, also called somatotropic hormone or somatotropin, is a small protein molecule that contains 191 amino acids in a single chain and has a molecular weight of 22,005. It causes growth of almost all tissues of the body that are capable of growing. It promotes increased sizes of the cells and increased mitosis, with development of greater numbers of cells and specific differentiation of certain types of cells such as bone growth cells and early muscle cells. Figure 75-5 shows typical...

Innate Immunity

The human body has the ability to resist almost all types of organisms or toxins that tend to damage the tissues and organs. This capability is called immunity. Much of immunity is acquired immunity that does not develop until after the body is first attacked by a bacterium, virus, or toxin, often requiring weeks or months to develop the immunity. An additional portion of immunity results from general processes, rather than from processes directed at specific disease organisms. This is called...

Angiotensin II Increases Sodium and Water Reabsorption

Angiotensin II is perhaps the body's most powerful sodium-retaining hormone. As discussed in Chapter 19, angiotensin II formation increases in circumstances associated with low blood pressure and or low extracellular fluid volume, such as during hemorrhage or loss of salt and water from the body fluids. The increased formation of angiotensin II helps to return blood pressure and extracellular volume toward normal by increasing sodium and water reabsorption from the renal tubules through three...

Reabsorption and Secretion by the Renal Tubules

As the glomerular filtrate enters the renal tubules, it flows sequentially through the successive parts of ____ the tubule the proximal tubule, the loop o f Henle, the distal tubule, the collecting tubule, and, finally, the collecting duct before it is excreted as urine. Along this course, some substances are selectively reabsorbed from the tubules back into the blood, whereas others are secreted from the blood into the tubular lumen. Eventually, the urine that is formed and all the substances...

Depolarization Waves Versus Repolarization Waves

Figure 11-2 shows a single cardiac muscle fiber in four stages of depolarization and repolarization, the color red designating depolarization. During depolarization, the normal negative potential inside the fiber reverses and becomes slightly positive inside and negative outside. In Figure 11-2A, depolarization, demonstrated by red positive charges inside and red negative charges outside, is traveling from left to right. The first half of the fiber has already depolarized, while the remaining...

Info

Interstitial fluid and in the plasma is considered to be about equal. Referring again to Figure 25-2, one can see that the extracellular fluid, including the plasma and the interstitial fluid, contains large amounts of sodium and chloride ions, reasonably large amounts of bicarbonate ions, but only small quantities of potassium, calcium, magnesium, phosphate, and organic acid ions. The composition of extracellular fluid is carefully regulated by various mechanisms, but especially by the...

Clinical Abnormalities of the Cerebellum

An important feature of clinical cerebellar abnormalities is that destruction of small portions of the lateral cerebellar cortex seldom causes detectable abnormalities in motor function. In fact, several months after as much as one half of the lateral cerebellar cortex on one side of the brain has been removed, if the deep cere-bellar nuclei are not removed along with the cortex, the motor functions of the animal appear to be almost normal as long as the animal performs all movements slowly....

Sympathetic Nervous System Activation Increases Sodium Reabsorption

Activation of the sympathetic nervous system can decrease sodium and water excretion by constricting the renal arterioles, thereby reducing GFR. Sympathetic activation also increases sodium reabsorption in the proximal tubule, the thick ascending limb of the loop of Henle, and perhaps in more distal parts of the renal tubule. And finally, sympathetic nervous system stimulation increases renin release and angiotensin II formation, which adds to the overall effect to increase tubular reabsorption...

Pulmonary Edema

Pulmonary edema occurs in the same way that edema occurs elsewhere in the body. Any factor that causes the pulmonary interstitial fluid pressure to rise from the negative range into the positive range will cause rapid filling of the pulmonary interstitial spaces and alveoli with large amounts of free fluid. The most common causes of pulmonary edema are as follows 1. Left-sided heart failure or mitral valve disease, with consequent great increases in pulmonary venous pressure and pulmonary...

Cells as the Living Units of the Body

The basic living unit of the body is the cell. Each organ is an aggregate of many different cells held together by intercellular supporting structures. Each type of cell is specially adapted to perform one or a few particular functions. For instance, the red blood cells, numbering 25 trillion in each human being, transport oxygen from the lungs to the tissues. Although the red cells are the most abundant of any single type of cell in the body, there are about 75 trillion additional cells of...

Qpo

Excitation of the Rod When Rhodopsin Is Activated by Light Rhodopsin-retinal visual cycle in the rod, showing decomposition of rhodopsin during exposure to light and subsequent slow reformation of rhodopsin by the chemical processes. The Rod Receptor Potential Is Hyperpolarizing, Not Depolarizing. When the rod is exposed to light, the resulting receptor potential is different from the receptor potentials in almost all other sensory receptors. That is, excitation of the rod causes increased...

Chemical Structures of ADH and Oxytocin

Both oxytocin and ADH (vasopressin) are polypeptides, each containing nine amino acids. Their amino acid sequences are the following Vasopressin Oxytocin Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH2 Note that these two hormones are almost identical except that in vasopressin, phenylalanine and arginine replace isoleucine and leucine of the oxytocin molecule. The similarity of the molecules explains their partial functional similarities.

Jow

Measurement of Maximum Expiratory Flow In many respiratory diseases, particularly in asthma, the resistance to airflow becomes especially great during expiration, sometimes causing tremendous difficulty in breathing. This has led to the concept called maximum expiratory flow, which can be defined as follows When a person expires with great force, the expiratory airflow reaches a maximum flow beyond which the flow cannot be increased any more even with greatly increased additional force. This is...

Elevated Blood Glucose Concentration and Adrenal Diabetes

Both the increased rate of gluconeogenesis and the moderate reduction in the rate of glucose utilization by the cells cause the blood glucose concentrations to rise. The rise in blood glucose in turn stimulates secretion of insulin. The increased plasma levels of insulin, however, are not as effective in maintaining plasma glucose as they are under normal conditions. For reasons that are not entirely clear, high levels of glucocorticoid reduce the sensitivity of many tissues, especially...

Composition of Alveolar Air Its Relation to Atmospheric

Alveolar air does not have the same concentrations of gases as atmospheric air by any means, which can readily be seen by comparing the alveolar air composition in Table 39-1 with that of atmospheric air. There are several reasons for the differences. First, the alveolar air is only partially replaced by atmospheric air with each breath. Second, oxygen is constantly being absorbed into the pulmonary blood from the alveolar air. Third, carbon dioxide is constantly diffusing from the pulmonary...

Premotor Area

The premotor area, also shown in Figure 55-1, lies 1 to 3 centimeters anterior to the primary motor cortex, extending inferiorly into the sylvian fissure and superiorly into the longitudinal fissure, where it abuts the supplementary motor area, which has functions similar to those of the premotor area. The topographical organization of the premotor cortex is roughly the same as that of the primary motor cortex, with the mouth and face areas located most laterally as one moves upward, the hand,...

Ejection or Let Down Process in Milk Secretion Function of Oxytocin

Milk is secreted continuously into the alveoli of the breasts, but milk does not flow easily from the alveoli into the ductal system and, therefore, does not continually leak from the breast nipples. Instead, the milk must be ejected from the alveoli into the ducts before the baby can obtain it. This is caused by a combined neurogenic and hormonal reflex that involves the posterior pituitary hormone oxytocin, as follows. When the baby suckles, it receives virtually no milk for the first half...

Atp

Interconversions of the three major monosaccharides glucose, fructose, and galactose in liver cells. and phosphate, and the glucose can then be transported through the liver cell membrane back into the blood. Once again, it should be emphasized that usually more than 95 per cent of all the monosaccharides that circulate in the blood are the final conversion product, glucose. Transport of Glucose Through the Cell Membrane Before glucose can be used by the body's tissue cells, it must be...

Increased Blood Volume and Extracellular Fluid Volume Caused by Heart Diseases

In congestive heart failure, blood volume may increase 15 to 20 per cent, and extracellular fluid volume sometimes increases by 200 per cent or more. The reason for this can be understood by re-examination of Figure 29-12. Initially, heart failure reduces cardiac output and, consequently, decreases arterial pressure. This in turn activates multiple sodium-retaining systems, especially the renin-angiotensin, aldosterone, and sympathetic nervous systems. In addition, the low blood pressure itself...

Neurohormonal Control of Brain Activity

Aside from direct control of brain activity by specific transmission of nerve signals from the lower brain areas to the cortical regions of the brain, still another physiologic mechanism is very often used to control brain activity. This is to secrete excitatory or inhibitory neurotransmitter hormonal agents into the substance of the brain. These neurohormones often persist for minutes or hours and thereby provide long periods of control, rather than just instantaneous activation or inhibition....

Effect of Thyroid Hormone on Sexual Function For normal sexual function thyroid secretion needs to be

In men, lack of thyroid hormone is likely to cause loss of libido great excesses of the hormone, however, sometimes cause impotence. In women, lack of thyroid hormone often causes menorrhagia and polymenorrhea that is, respectively, excessive and frequent menstrual bleeding. Yet, strangely enough, in other women thyroid lack may cause irregular periods and occasionally even amenorrhea. A hypothyroid woman, like a man, is likely to have greatly decreased libido. To make the...

Substance10 In Physiology

Energy (in calories per osmole) 1400 log - Thus, in terms of calories, the amount of energy required to concentrate 1 osmole of substance 10-fold is about 1400 calories or to concentrate it 100-fold, 2800 calories. One can see that the energy expenditure for concentrating substances in cells or for removing substances from cells against a concentration gradient can be tremendous. Some cells, such as those lining the renal tubules and many glandular cells, expend as much as 90 per cent of their...

Functional Anatomy of the Cochlea

The cochlea is a system of coiled tubes, shown in Figure 52-1 and in cross section in Figures 52-2 and 52-3. It consists of three tubes coiled side by side (1) the scala vestibuli, (2) the scala media, and (3) the scala tympani. The scala vestibuli and scala media are separated from each other by Reissner's membrane (also called the vestibular membrane), shown in Figure 52-3 the scala tympani and scala media are separated from each other by the basilar membrane. On the surface of the basilar...

Layered Structure of the Primary Visual Cortex

Like almost all other portions of the cerebral cortex, the primary visual cortex has six distinct layers, as shown in Figure 51-4. Also, as is true for the other sensory systems, the geniculocalcarine fibers terminate mainly in layer IV. But this layer, too, is organized into subdivisions. The rapidly conducted signals from the Y retinal ganglion cells terminate in layer IVca, and from there they are relayed vertically both outward toward the cortical surface and inward toward deeper levels....

Automatic Regulation of Retinal Sensitivity Light and Dark Adaptation

Photochemistry of Color Vision by the Cones It was pointed out at the outset of this discussion that the photochemicals in the cones have almost exactly the same chemical composition as that of rhodopsin in the rods. The only difference is that the protein portions, or the opsins called photopsins in the cones are slightly different from the scotopsin of the rods. The retinal portion of all the visual pigments is exactly the same in the cones as in the rods. The color-sensitive pigments of the...

Respiratory Wave Outcome Of Cns Ischemic Pressure Control Mechanism

Baroreceptor fibers, pass through Hering's nerves and the vagus nerves into the vasomotor center of the brain stem. Each carotid or aortic body is supplied with an abundant blood flow through a small nutrient artery, so that the chemoreceptors are always in close contact with arterial blood. Whenever the arterial pressure falls below a critical level, the chemoreceptors become stimulated because diminished blood flow causes decreased oxygen as well as excess buildup of carbon dioxide and...

Hypothalamic Releasing and Inhibitory Hormones That Control Secretion of the Anterior Pituitary Gland

Thyrotropin-releasing hormone (TRH) Gonadotropin-releasing hormone (GnRH) Corticotropin-releasing hormone (CRH) Growth hormone-releasing hormone (GHRH) (somatostatin) Prolactin-inhibiting hormone (PIH) Peptide of 3 amino acids Single chain of 10 amino acids Single chain of 41 amino acids Single chain of 44 amino acids Primary Action on Anterior Pituitary Stimulates secretion of TSH by thyrotropes Stimulates secretion of FSH and LH by gonadotropes Stimulates secretion of ACTH by corticotropes...

Daily Rate of Secretion of Thyroxine and Triiodothyronine

About 93 per cent of the thyroid hormone released from the thyroid gland is normally thyroxine and only 7 per cent is triiodothyronine. However, during the ensuing few days, about one half of the thyroxine is slowly deiodinated to form additional triiodothyro-nine. Therefore, the hormone finally delivered to and Monoiodotyrosine + Diiodotyrosine HO Monoiodotyrosine + Diiodotyrosine HO HO h- O k h CH2 CHNH2 COOH used by the tissues is mainly triiodothyronine, a total of about 35 micrograms of...

Fibrillation of the Ventricles After Myocardial Infarction

Many people who die of coronary occlusion die because of sudden ventricular fibrillation. The tendency to develop fibrillation is especially great after a large infarction, but fibrillation can sometimes occur after small occlusions as well. Indeed, some patients with chronic coronary insufficiency die suddenly from fibrillation without any acute infarction. There are two especially dangerous periods after coronary infarction during which fibrillation is most likely to occur. The first is...

Anterior

Paraventricular nucleus (Oxytocin release) (Water conservation) Medial preoptic area (Bladder contraction) (Decreased heart rate) (Decreased blood pressure) Posterior preoptic and anterior hypothalamic areas behavior. Let us discuss first the vegetative and endocrine control functions and then return to the behavioral functions of the hypothalamus to see how these operate together.

Current of Injury

Many different cardiac abnormalities, especially those that damage the heart muscle itself, often cause part of the heart to remain partially or totally depolarized all the time. When this occurs, current flows between the pathologically depolarized and the normally polarized areas even between heartbeats. This is called a current of injury. Note especially that the injured part of the heart is negative, because this is the part that is depolarized and emits negative charges into the...

Overview of the Circulation Medical Physics of Pressure Flow and Resistance

The function of the circulation is to service the needs of the body tissues to transport nutrients to the body tissues, to transport waste products away, to conduct hormones from one part of the body to another, and, in general, to maintain an appropriate environment in all the tissue fluids of the body for optimal survival and function of the cells. The rate of blood flow through most tissues is controlled in response to tissue need for nutrients. The heart and circulation in turn are...

Decreased Prothrombin Factor VII Factor IX and Factor X Caused by Vitamin K Deficiency

With few exceptions, almost all the blood-clotting factors are formed by the liver. Therefore, diseases of the liver such as hepatitis, cirrhosis, and acute yellow atrophy can sometimes depress the clotting system so greatly that the patient develops a severe tendency to bleed. Another cause of depressed formation of clotting factors by the liver is vitamin K deficiency. Vitamin K is necessary for liver formation of five of the important clotting factors prothrombin, Factor VII, Factor IX,...

Ways In Which The Norepinephrine Is Removed From The Secretory Site

Mechanisms of Transmitter Secretion and Subsequent Removal of the Transmitter at the Postganglionic Endings Secretion of Acetylcholine and Norepinephrine by Postganglionic Nerve Endings. A few of the postganglionic autonomic nerve endings, especially those of the parasympathetic nerves, are similar to but much smaller than those of the skeletal neuromuscular junction. However, many of the parasympathetic nerve fibers and almost all the sympathetic fibers merely touch the effector cells of the...

Negative Feedback Prevents Overactivity of Hormone Systems

Although the plasma concentrations of many hormones fluctuate in response to various stimuli that occur throughout the day, all hormones studied thus far appear to be closely controlled. In most instances, this control is exerted through negative feedback mechanisms that ensure a proper level of hormone activity at the target tissue. After a stimulus causes release of the hormone, conditions or products resulting from the action of the hormone tend to suppress its further release. In other...

Motor Functions of the Spinal Cord the Cord Reflexes

In this chapter, we discuss the control of muscle function by the spinal cord. Without the special neuronal circuits of the cord, even the most complex motor control systems in the brain could not cause any purposeful muscle movement. To give an example, there is no neuronal circuit anywhere in the brain that causes the specific to-and-fro movement of the legs that is required in walking. Instead, the circuits for these movements are in the cord, and the brain simply sends command signals to...

S4z

Artificial Climate in the Sealed CHAPTER 44 Physiology of Deep-Sea Diving and Other Hyperbaric Conditions 545 Effect of High Partial Pressures of Individual Gases on the Body 545 Oxygen Toxicity at High Pressures 546 Carbon Dioxide Toxicity at Great Depths Decompression of the Diver After Excess Exposure to High Pressure 547 Breathing Apparatus) Diving 549

Hormones That Act Mainly on the Genetic Machinery of the Cell

Steroid Hormones Increase Protein Synthesis Another means by which hormones act specifically, the steroid hormones secreted by the adrenal cortex, ovaries, and testes is to cause synthesis of proteins in the target cells. These proteins then function as enzymes, transport proteins, or structural proteins, which in turn provide other functions of the cells. The sequence of events in steroid function is essentially the following 1. The steroid hormone diffuses across the cell membrane and enters...

P

Because of inability of damaged tubules to secrete PAH into the tubular fluid. The calculation of RPF can be demonstrated by the following example Assume that the plasma concentration of PAH is 0.01 mg ml, urine concentration is 5.85 mg ml, and urine flow rate is 1 ml min. PAH clearance can be calculated from the rate of urinary PAH excretion (5.85 mg ml x 1 ml min) divided by the plasma PAH concentration (0.01 mg ml).Thus, clearance of PAH calculates to be 585 ml min. If the extraction ratio...

Milk Composition and the Metabolic Drain on the Mother Caused by Lactation

Table 82-1 lists the contents of human milk and cow's milk. The concentration of lactose in human milk is about 50 per cent greater than in cow's milk, but the concentration of protein in cow's milk is ordinarily two or more times greater than in human milk. Finally, only one third as much ash, which contains calcium and other minerals, is found in human milk compared with cow's milk. At the height of lactation in the human mother, 1.5 liters of milk may be formed each day (and even more if the...

Figure 742

Synthesis and secretion of peptide hormones. The stimulus for hormone secretion often involves changes in intracellular calcium or changes in cyclic adenosine monophosphate (cAMP) in the cell. They are lipid soluble and consist of three cyclohexyl rings and one cyclopentyl ring combined into a single structure (Figure 74-3). Although there is usually very little hormone storage in steroid-producing endocrine cells, large stores of cholesterol esters in cytoplasm vacuoles can be rapidly...

Effect of Slow Conduction of the Depolarization Wave on the Characteristics of the T Wave

Referring back to Figure 12-14, note that the QRS complex is considerably prolonged. The reason for this prolongation is delayed conduction in the left ventricle resulting from left bundle branch block. This causes the left ventricle to become depolarized about 0.08 second after depolarization of the right ventricle, which gives a strong mean QRS vector to the left. However, the refractory periods of the right and left ventricular muscle masses are not greatly different from each other....

Diffusion of Oxygen from the Alveoli to the Pulmonary Capillary Blood

The top part of Figure 40-1 shows a pulmonary alveolus adjacent to a pulmonary capillary, demonstrating diffusion of oxygen molecules between the alveolar air and the pulmonary blood. The Po2 of the gaseous oxygen in the alveolus averages 104 mm Hg, whereas the Po2 of the venous blood entering the pulmonary capillary at its arterial end averages only 40 mm Hg because a large amount of oxygen was removed from this blood as it passed through the peripheral tissues. Therefore, the initial pressure...

Blood Volume of the Lungs

The blood volume of the lungs is about 450 milliliters, about 9 per cent of the total blood volume of the entire circulatory system. Approximately 70 milliliters of this pulmonary blood volume is in the pulmonary capillaries, and the remainder is divided about equally between the pulmonary arteries and the veins. Lungs as a Blood Reservoir. Under various physiological and pathological conditions, the quantity of blood in the lungs can vary from as little as one half normal up to twice normal....

Basic Properties

The principal constituents of proteins are amino acids, 20 of which are present in the body proteins in significant quantities. Figure 69-1 shows the chemical formulas of these 20 amino acids, demonstrating that they all have two features in common each amino acid has an acidic group ( COOH) and a nitrogen atom attached to the molecule, usually represented by the amino group ( NH2). Peptide Linkages and Peptide Chains. In proteins, the amino acids are aggregated into long chains by means of...

Special Features of Cardiac Muscle Metabolism

The basic principles of cellular metabolism, discussed in Chapters 67 through 72, apply to cardiac muscle the same as for other tissues, but there are some quantitative differences. Most important, under resting conditions, cardiac muscle normally consumes fatty acids to supply most of its energy instead of carbohydrates (about 70 per cent of the energy is derived from fatty acids). However, as is also true of other tissues, under anaerobic or ischemic conditions, cardiac metabolism must call...

Determination of Loudness

Loudness is determined by the auditory system in at least three ways. First, as the sound becomes louder, the amplitude of vibration of the basilar membrane and hair cells also increases, so that the hair cells excite the nerve endings at more rapid rates. Second, as the amplitude of vibration increases, it causes more and more of the hair cells on the fringes of the resonating portion of the basilar membrane to become stimulated, thus causing spatial summation of impulses that is, transmission...

Regulation of Glandular Secretion by Hormones In the

Stomach and intestine, several different gastrointestinal hormones help regulate the volume and character of the secretions. These hormones are liberated from the gastrointestinal mucosa in response to the presence of food in the lumen of the gut. The hormones then are absorbed into the blood and carried to the glands, where they stimulate secretion. This type of stimulation is particularly valuable to increase the output of gastric juice and pancreatic juice when food enters the stomach or...

Bicarbonate Buffer System

The bicarbonate buffer system consists of a water solution that contains two ingredients (1) a weak acid, H2CO3, and (2) a bicarbonate salt, such as NaHCO3. H2CO3 is formed in the body by the reaction of CO2 with H2O. This reaction is slow, and exceedingly small amounts of H2CO3 are formed unless the enzyme carbonic anhydrase is present. This enzyme is especially abundant in the walls of the lung alveoli, where CO2 is released carbonic anhydrase is also present in the epithelial cells of the...

C

Establishment of resting membrane potentials in nerve fibers under three conditions A, when the membrane potential is caused entirely by potassium diffusion alone B, when the membrane potential is caused by diffusion of both sodium and potassium ions and C, when the membrane potential is caused by diffusion of both sodium and potassium ions plus pumping of both these ions by the Na+-K+ pump. Figure 5-5 shows the important factors in the establishment of the normal resting membrane potential of...

References

Albert R, Spiro S, Jett J Comprehensive Respiratory Medicine. Philadelphia Mosby, 2002. Dempsey JA, Wagner PD Exercise-induced arterial hypoxemia. J Appl Physiol 87 1997,1999. Geers C, Gros G Carbon dioxide transport and carbonic anhydrase in blood and muscle. Physiol Rev 80 681, 2000. Henry RP, Swenson ER The distribution and physiological significance of carbonic anhydrase in vertebrate gas exchange organs. Respir Physiol 121 1, 2000. Jones AM, Koppo K, Burnley M Effects of prior exercise on...

Formation of Carbohydrates from Proteins and Fats Gluconeogenesis

When the body's stores of carbohydrates decrease below normal, moderate quantities of glucose can be formed from amino acids and the glycerol portion of fat. This process is called gluconeogenesis. Gluconeogenesis is especially important in preventing an excessive reduction in the blood glucose concentration during fasting. Glucose is the primary substrate for energy in tissues such as the brain and the red blood cells, and adequate amounts of glucose must be present in the blood for several...

Functions of the Amygdala

The amygdala is a complex of multiple small nuclei located immediately beneath the cerebral cortex of the medial anterior pole of each temporal lobe. It has abundant bidirectional connections with the hypothalamus as well as with other areas of the limbic system. In lower animals,the amygdala is concerned to a great extent with olfactory stimuli and their interrelations with the limbic brain. Indeed, it is pointed out in Chapter 53 that one of the major divisions of the olfactory tract...

Stimulation of Gastric Acid Secretion

Parietal Cells of the Oxyntic Glands Are the Only Cells That Secrete Hydrochloric Acid. The parietal cells, located deep in the oxyntic glands of the main body of the stomach, are the only cells that secrete hydrochloric acid. As noted earlier in the chapter, the acidity of the fluid secreted by these cells can be very great, with pH as low as 0.8. However, secretion of this acid is under continuous control by both endocrine and nervous signals. Furthermore, the parietal cells operate in close...

B

Membrane change in such a way that the entire pit invaginates inward, and the fibrillar proteins surrounding the invaginating pit cause its borders to close over the attached proteins as well as over a small amount of extracellular fluid. Immediately thereafter, the invaginated portion of the membrane breaks away from the surface of the cell, forming a pinocytotic vesicle inside the cytoplasm of the cell. What causes the cell membrane to go through the necessary contortions to form pinocytotic...

Mechanisms of Blood Flow Control

Local blood flow control can be divided into two phases (1) acute control and (2) long-term control. Acute control is achieved by rapid changes in local vasodilation or vasoconstriction of the arterioles, metarterioles, and precapillary sphincters, occurring within seconds to minutes to provide very rapid maintenance of appropriate local tissue blood flow. Long-term control, however, means slow, controlled changes in flow over a period of days, weeks, or even months. In general, these long-term...

Unit Xi

Motor and Integrative Neurophysiology CHAPTER 54 Motor Functions of the Spinal Cord the Cord Reflexes 673 Organization of the Spinal Cord for Motor Muscle Sensory Receptors Muscle Spindles and Golgi Tendon Organs And Their Roles in Muscle Control 675 Receptor Function of the Muscle Spindle 675 Role of the Muscle Spindle in Voluntary Clinical Applications of the Stretch Function of the Muscle Spindles and Golgi Tendon Organs in Conjunction with Motor Control from Higher...

Thyroxine and Triiodothyronine Are Bound to Plasma Proteins

On entering the blood, over 99 per cent of the thyroxine and triiodothyronine combines immediately with several of the plasma proteins, all of which are synthesized by the liver. They combine mainly with thyroxine-binding globulin and much less so with thyroxine-binding prealbumin and albumin. Thyroxine and Triiodothyronine Are Released Slowly to Tissue Cells. Because of high affinity of the plasma-binding proteins for the thyroid hormones, these substances in particular, thyroxine are released...

Physiologic Anatomy of the Parasympathetic Nervous System

The parasympathetic nervous system is shown in Figure 60-3, demonstrating that parasympathetic fibers leave the central nervous system through cranial nerves III, VII, IX, and X additional parasympathetic fibers leave the lowermost part of the spinal cord through the second and third sacral spinal nerves and occasionally the first and fourth sacral nerves. About 75 per cent of all parasympathetic nerve fibers are in the vagus nerves (cranial nerve X), passing to the entire thoracic and...

Depolarization of the Atria The P Wave

Depolarization of the atria begins in the sinus node and spreads in all directions over the atria. Therefore, the point of original electronegativity in the atria is about at the point of entry of the superior vena cava where the sinus node lies, and the direction of initial depolarization is denoted by the black vector in Figure 12-9. Furthermore, the vector remains generally in this direction throughout the process of normal atrial depolarization. Because this direction is generally in the...

Secretions of the Large Intestine

The mucosa of the large intestine, like that of the small intestine, has many crypts of Lieberkuhn however, unlike the small intestine, there are no villi. The epithelial cells contain almost no enzymes. Instead, they consist mainly of mucous cells that secrete only mucus. The great preponderance of secretion in the large intestine is mucus. This mucus contains moderate amounts of bicarbonate ions secreted by a few non-mucus-secreting epithelial cells. The rate of secretion of...

Smw

Development of atherosclerotic plaque. A, Attachment of a monocyte to an adhesion molecule on a damaged endothelial cell of an artery. The monocyte then migrates through the endothelium into the intimal layer of the arterial wall and is transformed into a macrophage. The macrophage then ingests and oxidizes lipoprotein molecules, becoming a macrophage foam cell. The foam cells release substances that cause inflammation and growth of the intimal layer. B, Additional accumulation of macrophages...

Ganglion Cells and Optic Nerve Fibers

Each retina contains about 100 million rods and 3 million cones yet the number of ganglion cells is only about 1.6 million. Thus, an average of 60 rods and 2 cones converge on each ganglion cell and the optic nerve fiber leading from the ganglion cell to the brain. However, major differences exist between the peripheral retina and the central retina. As one approaches the fovea, fewer rods and cones converge on each optic fiber, and the rods and cones also become more slender. These effects...

Differences Between the Myenteric and Submucosal Plexuses

The myenteric plexus consists mostly of a linear chain of many interconnecting neurons that extends the entire length of the gastrointestinal tract. A section of this chain is shown in Figure 62-4. Because the myenteric plexus extends all the way along the intestinal wall and because it lies between the longitudinal and circular layers of intestinal smooth muscle, it is concerned mainly with controlling muscle activity along the length of the gut. When this plexus is stimulated, its principal...

Regulation of Pepsinogen Secretion

Regulation of pepsinogen secretion by the peptic cells in the oxyntic glands is much less complex than regulation of acid secretion it occurs in response to two types of signals (1) stimulation of the peptic cells by acetylcholine released from the vagus nerves or from the gastric enteric nervous plexus, and (2) stimulation of peptic cell secretion in response to acid in the stomach. The acid probably does not stimulate the peptic cells directly but instead elicits additional enteric nervous...

Function of the Ileocecal Valve

A principal function of the ileocecal valve is to prevent backflow of fecal contents from the colon into the small intestine. As shown in Figure 63-4, the ileocecal valve itself protrudes into the lumen of the cecum and therefore is forcefully closed when excess pressure builds up in the cecum and tries to push cecal contents backward against the valve lips. The valve usually can resist reverse pressure of at least 50 to 60 centimeters of water. In addition, the wall of the ileum for several...

Concentration in Extracellular Fluid

Extracellular fluid potassium concentration normally is regulated precisely at about 4.2mEq L, seldom rising or falling more than 0.3 mEq L. This precise control is necessary because many cell functions are very sensitive to changes in extracellular fluid potassium concentration. For instance, an increase in plasma potassium concentration of only 3 to 4 mEq L can cause cardiac arrhythmias, and higher concentrations can lead to cardiac arrest or fibrillation. A special difficulty in regulating...

Metabolic Rate

The metabolism of the body simply means all the chemical reactions in all the cells of the body, and the metabolic rate is normally expressed in terms of the rate of heat liberation during chemical reactions. Heat Is the End Product of Almost All the Energy Released in the Body. In discussing many of the metabolic reactions in the preceding chapters, we noted that not all the energy in foods is transferred to ATP instead, a large portion of this energy becomes heat. On average, 35 per cent of...

Control of Accommodation Focusing the Eyes

The accommodation mechanism that is, the mechanism that focuses the lens system of the eye is essential for a high degree of visual acuity. Accommodation results from contraction or relaxation of the eye ciliary muscle. Contraction causes increased refractive power of the lens, as explained in Chapter 49, and relaxation causes decreased power. How does a person adjust accommodation to keep the eyes in focus all the time Accommodation of the lens is regulated by a negative feedback mechanism...

Effect of Tranquilizers on the Reward or Punishment Centers

Administration of a tranquilizer, such as chlorpro-mazine, usually inhibits both the reward and the punishment centers, thereby decreasing the affective reactivity of the animal. Therefore, it is presumed that tranquilizers function in psychotic states by suppressing many of the important behavioral areas of the hypothalamus and its associated regions of the limbic brain. Importance of Reward or Punishment in Learning and Memory Habituation Versus Reinforcement Animal experiments have shown...

Thoughts Consciousness and Memory

Our most difficult problem in discussing consciousness, thoughts, memory, and learning is that we do not know the neural mechanisms of a thought and we know little about the mechanisms of memory. We know that destruction of large portions of the cerebral cortex does not prevent a person from having thoughts, but it does reduce the depth of the thoughts and also the degree of awareness of the surroundings. Each thought certainly involves simultaneous signals in many portions of the cerebral...

Somatic Sensations II Pain Headache and Thermal Sensations

Many, if not most, ailments of the body cause pain. Furthermore, the ability to diagnose different diseases depends to a great extent on a physician's knowledge of the different qualities of pain. For these reasons, the first part of this chapter is devoted mainly to pain and to the physiologic bases of some associated clinical phenomena. Pain Is a Protective Mechanism. Pain occurs whenever any tissues are being damaged, and it causes the individual to react to remove the pain stimulus. Even...

Hydrogen Ion Concentration Is Precisely Regulated

Precise H+ regulation is essential because the activities of almost all enzyme systems in the body are influenced by H+ concentration. Therefore, changes in hydrogen concentration alter virtually all cell and body functions. Compared with other ions, the H+ concentration of the body fluids normally is kept at a low level. For example, the concentration of sodium in extracellular fluid (142 mEq L) is about 3.5 million times as great as the normal concentration of H+, which averages only 0.00004...

F

The life cycle of a cell is the period from cell reproduction to the next cell reproduction. When mammalian cells are not inhibited and are reproducing as rapidly as they can, this life cycle may be as little as 10 to 30 hours. It is terminated by a series of distinct physical events called mitosis that cause division of the cell into two new daughter cells. The events of mitosis are shown in Figure 3-13 and are described later. The actual stage of mitosis, however,...

Medullary Pontine and Mesencephalic Control of the Autonomic Nervous System

Many neuronal areas in the brain stem reticular substance and along the course of the tractus solitarius of the medulla, pons, and mesencephalon, as well as in many special nuclei (Figure 60-5), control different autonomic functions such as arterial pressure, heart rate, glandular secretion in the gastrointestinal tract, gastrointestinal peristalsis, and degree of contraction of the urinary bladder. Control of each of these is discussed at appropriate points in this text. Suffice it to point...

Position Senses

The position senses are frequently also called proprioceptive senses. They can be divided into two subtypes (1) static position sense, which means conscious perception of the orientation of the different parts of the body with respect to one another, and (2) rate of movement sense, also called kinesthesia or dynamic proprioception. Position Sensory Receptors. Knowledge of position, both static and dynamic, depends on knowing the degrees of angulation of all joints in all planes and their rates...

Relation of Stimulus Rate to Degree of Sympathetic and Parasympathetic Effect

A special difference between the autonomic nervous system and the skeletal nervous system is that only a low frequency of stimulation is required for full activation of autonomic effectors. In general, only one nerve impulse every few seconds suffices to maintain normal sympathetic or parasympathetic effect, and full activation occurs when the nerve fibers discharge 10 to 20 times per second. This compares with full activation in the skeletal nervous system at 50 to 500 or more impulses per...

Activating Driving Systems of the Brain

Without continuous transmission of nerve signals from the lower brain into the cerebrum, the cerebrum becomes useless. In fact, severe compression of the brain stem at the juncture between the mesencephalon and cerebrum, as sometimes results from a pineal tumor, often causes the person to go into unremitting coma lasting for the remainder of his or her life. Nerve signals in the brain stem activate the cerebral part of the brain in two ways (1) by directly stimulating a background level of...

Blood Flow Through the Lungs and Its Distribution

The blood flow through the lungs is essentially equal to the cardiac output. Therefore, the factors that control cardiac output mainly peripheral factors, as discussed in Chapter 20 also control pulmonary blood flow. Under most conditions, the pulmonary vessels act as passive, distensible tubes that enlarge with increasing pressure and narrow with decreasing pressure. For adequate aeration of the blood to occur, it is important for the blood to be distributed to those segments of the lungs...

Placenta

Fetal capillaries Intervillous space Fetal capillaries Intervillous space Above, Organization of the mature placenta. Below, Relation of the fetal blood in the villus capillaries to the mother's blood in the intervillous spaces. (Modified from Gray H, Goss CM Anatomy of the Human Body, 25th ed. Philadelphia Lea & Febiger, 1948 and from Arey LB Developmental Anatomy A Textbook and Laboratory Manual of Embryology, 7th ed. Philadelphia WB Saunders, 1974.) which fetal capillaries grow. Thus, the...

Mastication Chewing

The teeth are admirably designed for chewing, the anterior teeth (incisors) providing a strong cutting action and the posterior teeth (molars), a grinding action. All the jaw muscles working together can close the teeth with a force as great as 55 pounds on the incisors and 200 pounds on the molars. Most of the muscles of chewing are innervated by the motor branch of the fifth cranial nerve, and the chewing process is controlled by nuclei in the brain stem. Stimulation of specific reticular...

Respiratory Center

The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem, as shown in Figure 41-1. It is divided into three major collections of neurons (1) a dorsal respiratory group, located in the dorsal portion of the medulla, which mainly causes inspiration (2) a ventral respiratory group, located in the ventrolateral part of the medulla, which mainly causes expiration and (3) the pneumotaxic center, located dorsally in the...

Coronary Ischemia as a Cause of Injury Potential

Insufficient blood flow to the cardiac muscle depresses the metabolism of the muscle for three reasons (1) lack of oxygen, (2) excess accumulation of carbon dioxide, and (3) lack of sufficient food nutrients. Consequently, repolarization of the muscle membrane cannot occur in areas of severe myocardial ischemia. Often the heart muscle does not die because the blood flow is sufficient to maintain life of the muscle even though it is not sufficient to cause repolarization of the membranes. As...

Chemical Forms in Which Carbon Dioxide Is Transported

To begin the process of carbon dioxide transport, carbon dioxide diffuses out of the tissue cells in the dissolved molecular carbon dioxide form. On entering the tissue capillaries, the carbon dioxide initiates a host of almost instantaneous physical and chemical reactions, shown in Figure 40-13, which are essential for carbon dioxide transport. Transport of Carbon Dioxide in the Dissolved State. A small portion of the carbon dioxide is transported in the dissolved state to the lungs. Recall...

Adp

Primary Active Transport and Secondary Active Transport. Active transport is divided into two types according to the source of the energy used to cause the transport primary active transport and secondary active transport. In primary active transport, the energy is derived directly from breakdown of adenosine triphosphate (ATP) or of some other high-energy phosphate compound. In secondary active transport, the energy is derived secondarily from energy that has been stored in the form of ionic...

Cholinergic and Adrenergic Fibers Secretion of Acetylcholine or Norepinephrine

The sympathetic and parasympathetic nerve fibers secrete mainly one or the other of two synaptic transmitter substances, acetylcholine or norepinephrine. Those fibers that secrete acetylcholine are said to be cholinergic. Those that secrete norepinephrine are said to be adrenergic, a term derived from adrenalin, which is an alternate name for epinephrine. All preganglionic neurons are cholinergic in both the sympathetic and the parasympathetic nervous systems. Acetylcholine or...

Buffering of Hydrogen Ions in the Body Fluids

A buffer is any substance that can reversibly bind H+. The general form of the buffering reaction is In this example, a free H+ combines with the buffer to form a weak acid (H buffer) that can either remain as an unassociated molecule or dissociate back to buffer and H+. When the H+ concentration increases, the reaction is forced to the right, and more H+ binds to the buffer, as long as buffer is available. Conversely, when the H+ concentration decreases, the reaction shifts toward the left,...

Jke

Idiopathic nontoxic colloid goiter, 941 Idiopathic thrombocytopenia, 465 Iggo dome receptors, 586, 586f Ileocecal sphincter, 774, 788, 788f Ileocecal valve, 788, 788f Ileum, bicarbonate secretion in, 815 Immune complexes, in glomerulonephritis, 405-406 Immune hypersensitivity, 449-450. See also Allergy. Immune tolerance, 448 Immunity acquired (adaptive), 439-449 antigens in, 440, 441f cell-mediated (T-cell), 440, 441f, 446-448, 446f-448f humoral (B-cell), 440, 441f, 443-446, 443f-445f. See also...

States of Brain Activity Sleep Brain Waves Epilepsy Psychoses

All of us are aware of the many different states of brain activity, including sleep, wakefulness, extreme excitement, and even different levels of mood such as exhilaration, depression, and fear. All these states result from different activating or inhibiting forces generated usually within the brain itself. In Chapter 58, we began a partial discussion of this subject when we described different systems that are capable of activating large portions of the brain. In this chapter, we present...

Tga

Circus movement, showing annihilation of the impulse in the short pathway and continued propagation of the impulse in the long pathway. A, Initiation of fibrillation in a heart when patches of refractory musculature are present. B, Continued propagation of fibrillatory impulses in the fibrillating ventricle. portions. This state of events is depicted in heart A by many lighter patches, which represent excitable cardiac muscle, and dark patches, which represent still refractory muscle. Now,...

Vascularity Is Determined by Maximum Blood Flow Need

An especially valuable characteristic of long-term vascular control is that vascularity is determined mainly by the maximum level of blood flow need rather than by average need. For instance, during heavy exercise the need for whole body blood flow often increases to six to eight times the resting blood flow. This great excess of flow may not be required for more than a few minutes each day. Nevertheless, even this short need can cause enough VEGF to be formed by the muscles to...

Transport of the Fertilized Ovum in the Fallopian Tube

After fertilization has occurred, an additional 3 to 5 days is normally required for transport of the fertilized ovum through the remainder of the fallopian tube into the cavity of the uterus (Figure 82-2). This transport is effected mainly by a feeble fluid current in the tube resulting from epithelial secretion plus action of the ciliated epithelium that lines the tube the cilia always beat toward the uterus. Weak contractions of the fallopian tube may also aid the ovum passage. The fallopian...

Figure 225

Progressive changes in cardiac output and right atrial pressure during different stages of cardiac failure. circulation. The two curves passing through Point A are (1) the normal cardiac output curve and (2) the normal venous return curve. As pointed out in Chapter 20, there is only one point on each of these two curves at which the circulatory system can operate. This point is where the two curves cross at point A. Therefore, the normal state of the circulation is a cardiac output and venous...

Decreased Voltage of the Electrocardiogram

Decreased Voltage Caused by Cardiac Myopathies. One of the most common causes of decreased voltage of the QRS complex is a series of old myocardial artery infarctions with resultant diminished muscle mass. This also causes the depolarization wave to move through the ventricles slowly and prevents major portions of the heart from becoming massively depolarized all at once. Consequently, this condition causes some prolongation of the QRS complex along with the decreased voltage. Figure 12-16...

Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids

Once oxygen has diffused from the alveoli into the pulmonary blood, it is transported to the peripheral tissue capillaries almost entirely in combination with hemoglobin. The presence of hemoglobin in the red blood cells allows the blood to transport 30 to 100 times as much oxygen as could be transported in the form of dissolved oxygen in the water of the blood. In the body's tissue cells, oxygen reacts with various foodstuffs to form large quantities of carbon dioxide. This carbon dioxide...

Water Soluble Non LipidSoluble Substances Diffuse Only Through Intercellular Pores in the Capillary Membrane

Many substances needed by the tissues are soluble in water but cannot pass through the lipid membranes of the endothelial cells such substances include water molecules themselves, sodium ions, chloride ions, and glucose. Despite the fact that not more than 1 1000 of the surface area of the capillaries is represented by the intercellular clefts between the endothelial cells, the velocity of thermal molecular motion in the clefts is so great that even this small area is sufficient to allow...

Estimating Plasma Osmolarity from Plasma Sodium Concentration

In most clinical laboratories, plasma osmolarity is not routinely measured. However, because sodium and its associated anions account for about 94 per cent of the solute in the extracellular compartment, plasma osmo-larity (Posm) can be roughly approximated as Posm 2.1 x Plasma sodium concentration For instance, with a plasma sodium concentration of 142 mEq L, the plasma osmolarity would be estimated from the formula above to be about 298 mOsm L. To be more exact, especially in conditions...

Incoming Fiber Pathways to the Motor Cortex

The functions of the motor cortex are controlled mainly by nerve signals from the somatosensory system but also, to some degree, from other sensory systems such as hearing and vision. Once the sensory information is received, the motor cortex operates in association with the basal ganglia and cerebellum to excite an appropriate course of motor action. The more important incoming fiber pathways to the motor cortex are the following 1. Subcortical fibers from adjacent regions of the cerebral...

Centrifugal Signals from the Central Nervous System to Lower Auditory Centers

Retrograde pathways have been demonstrated at each level of the auditory nervous system from the cortex to the cochlea in the ear itself. The final pathway is mainly from the superior olivary nucleus to the sound-receptor hair cells in the organ of Corti. These retrograde fibers are inhibitory. Indeed, direct stimulation of discrete points in the olivary nucleus has been shown to inhibit specific areas of the organ of Corti, reducing their sound sensitivities 15 to 20 decibels. One can readily...

Neuromuscular Junctions of Smooth Muscle

Physiologic Anatomy of Smooth Muscle Neuromuscular Junctions. Neuromuscular junctions of the highly structured type found on skeletal muscle fibers do not occur in smooth muscle. Instead, the autonomic nerve fibers that innervate smooth muscle generally branch diffusely on top of a sheet of muscle fibers, as shown in Figure 8-3. In most instances, these fibers do not make direct contact with the smooth muscle fiber cell membranes but instead form so-called diffuse junctions that secrete their...