Control of Calcium Excretion by the Kidneys

Because calcium is both filtered and reabsorbed in the kidneys but not secreted, the rate of renal calcium excretion is calculated as Renal calcium excretion Calcium filtered - Calcium reabsorbed Only about 50 per cent of the plasma calcium is ionized, with the remainder being bound to the plasma proteins or complexed with anions such as phosphate. Therefore, only about 50 per cent of the plasma calcium can be filtered at the glomerulus. Normally, about 99 per cent of the filtered calcium is...

Info

Normal electrocardiograms recorded from the three augmented unipolar limb leads. Normal electrocardiograms recorded from the three augmented unipolar limb leads. electrical potential of the cardiac musculature immediately beneath the electrode. Therefore, relatively minute abnormalities in the ventricles, particularly in the anterior ventricular wall, can cause marked changes in the electrocardiograms recorded from individual chest leads. In leads V1 and V2, the QRS recordings of the normal...

Transport of Substances Through the Cell Membrane

1 Figure 4-1 gives the approximate concentrations of important electrolytes and other substances in the J ' extracellular fluid and intracellular fluid. Note that the extracellular fluid contains a large amount of sodium but only a small amount of potassium. Exactly the opposite is true of the intracellular fluid. Also, the extracellular fluid contains a large amount of chloride ions, whereas the intracellular fluid contains very little. But the concentrations of phosphates and proteins in the...

Interstitial Fluid Colloid Osmotic Pressure

Although the size of the usual capillary pore is smaller than the molecular sizes of the plasma proteins, this is not true of all the pores. Therefore, small amounts of plasma proteins do leak through the pores into the interstitial spaces. The total quantity of protein in the entire 12 liters of interstitial fluid of the body is slightly greater than the total quantity of protein in the plasma itself, but because this volume is four times the volume of plasma, the average protein concentration...

Prolonged QRS Complex Resulting from Purkinje System Blocks

When the Purkinje fibers are blocked, the cardiac impulse must then be conducted by the ventricular muscle instead of by way of the Purkinje system. This decreases the velocity of impulse conduction to about one third of normal. Therefore, if complete block of one of the bundle branches occurs, the duration of the QRS complex usually is increased to 0.14 second or greater. In general, a QRS complex is considered to be abnormally long when it lasts more than 0.09 second when it lasts more than...

Spread of the Action Potential to the Interior of the Muscle Fiber by Way of Transverse Tubules

The skeletal muscle fiber is so large that action potentials spreading along its surface membrane cause almost no current flow deep within the fiber. Yet, to cause maximum muscle contraction, current must penetrate deeply into the muscle fiber to the vicinity of the separate myofibrils. This is achieved by transmission of action potentials along transverse tubules (T tubules) that penetrate all the way through the muscle fiber from one side of the fiber to the other, as illustrated in Figure...

Figure 282

Formation of a dilute urine when antidiuretic hormone (ADH) levels are very low. Note that in the ascending loop of Henle, the tubular fluid becomes very dilute. In the distal tubules and collecting tubules, the tubular fluid is further diluted by the reabsorption of sodium chloride and the failure to reabsorb water when ADH levels are very low. The failure to reabsorb water and continued reabsorption of solutes lead to a large volume of dilute urine. (Numerical values are in milliosmoles per...

Measurement of Cardiac Output Using the Oxygen Fick Principle

The Fick principle is explained by Figure 20-18. This figure shows that 200 milliliters of oxygen are being absorbed from the lungs into the pulmonary blood each minute. It also shows that the blood entering the right heart has an oxygen concentration of 160 milliliters per liter of blood, whereas that leaving the left heart has an oxygen concentration of 200 milliliters per liter of blood. From these data, one can calculate that each liter of blood passing through the lungs absorbs 40...

Long Term Mechanisms for Arterial Pressure Regulation

Goal of this chapter has been to explain the role of the kidneys in long-term control of arterial pressure. To the far right in Figure 19-15 is shown the renal-blood volume pressure control mechanism (which is the same as the renal-body fluid pressure control mechanism), demonstrating that it takes a few hours to begin showing significant response. Yet it eventually develops a feedback gain for control of arterial pressure equal to infinity. This means that this mechanism can eventually return...

Transport of Oxygen in the Dissolved State

At the normal arterial Po2 of 95 mm Hg, about 0.29 milliliter of oxygen is dissolved in every 100 milliliters of water in the blood, and when the Po2 of the blood falls to the normal 40 mm Hg in the tissue capillaries, only 0.12 milliliter of oxygen remains dissolved. In other words, 0.17 milliliter of oxygen is normally transported in the dissolved state to the tissues by each 100 milliliters of arterial blood flow. This compares with almost 5 milliliters of oxygen transported by the red cell...

Sense of Taste

Taste is mainly a function of the taste buds in the mouth, but it is common experience that one's sense of smell also contributes strongly to taste perception. In addition, the texture of food, as detected by tactual senses of the mouth, and the presence of substances in the food that stimulate pain endings, such as pepper, greatly alter the taste experience. The importance of taste lies in the fact that it allows a person to select food in accord with desires and often in accord with the body...

Pain in Coronary Heart Disease

Normally, a person cannot feel his or her heart, but ischemic cardiac muscle often does cause pain sensa-tion sometimes severe pain. Exactly what causes this pain is not known, but it is believed that ischemia causes the muscle to release acidic substances, such as lactic acid, or other pain-promoting products, such as histamine, kinins, or cellular proteolytic enzymes, that are not removed rapidly enough by the slowly moving coronary blood flow. The high concentrations of these abnormal...

Pregnancy and Lactation

In Chapters 80 and 81, the sexual functions of the male and female are described to the point of fertilization of the ovum. If the ovum becomes fertilized, a new sequence of events called gestation, or pregnancy, takes place, and the fertilized ovum eventually develops into a full-term fetus. The purpose of this chapter is to discuss the early stages of ovum development after fertilization and then to discuss the physiology of pregnancy. In Chapter 83, some special aspects of fetal and early...

I I I I I Ii

Retinal image Cortical stimulation Pattern of excitation that occurs in the visual cortex in response to a retinal image of a dark cross. of each line or border that is, whether it is vertical or horizontal or lies at some degree of inclination. This is believed to result from linear organizations of mutually inhibiting cells that excite second-order neurons when inhibition occurs all along a line of cells where there is a contrast edge. Thus, for each such orientation of a line, specific...

Diffusion of Gases Through Tissues

The gases that are of respiratory importance are all highly soluble in lipids and, consequently, are highly soluble in cell membranes. Because of this, the major limitation to the movement of gases in tissues is the rate at which the gases can diffuse through the tissue water instead of through the cell membranes. Therefore, diffusion of gases through the tissues, including through the respiratory membrane, is almost equal to the diffusion of gases in water, as given in the preceding list.

Figure 293

Mechanisms of potassium secretion and sodium reabsorption by the principal cells of the late distal and collecting tubules. and make up about 90 per cent of the epithelial cells in these regions. Figure 29-3 shows the basic cellular mechanisms of potassium secretion by the principal cells. Secretion of potassium from the blood into the tubular lumen is a two-step process, beginning with uptake from the interstitium into the cell by the sodium-potassium ATPase pump in the basolateral membrane of...

Sodium Excretion Is Precisely Matched to Intake Under Steady State Conditions

An important consideration in overall control of sodium excretion or excretion of any electrolyte, for that matter is that under steady-state conditions, excretion by the kidneys is determined by intake. To maintain life, a person must, over the long term, excrete almost precisely the amount of sodium ingested. Therefore, even with disturbances that cause major changes in kidney function, balance between intake and output of sodium usually is restored within a few days. If disturbances of...

Figure 372

Contraction and expansion of the thoracic cage during expiration and inspiration, demonstrating diaphragmatic contraction, function of the intercostal muscles, and elevation and depression of the rib cage. Figure 37-1 also shows the mechanism by which the external and internal intercostals act to cause inspiration and expiration. To the left, the ribs during expiration are angled downward, and the external intercostals are elongated forward and downward. As they contract, they pull the upper...

The Cardiac Cycle

The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle. Each cycle is initiated by spontaneous generation of an action potential in the sinus node, as explained in Chapter l0. This node is located in the superior lateral wall of the right atrium near the opening of the superior vena cava, and the action potential travels from here rapidly through both atria and then through the A-V bundle into the ventricles. Because of this...

Increase in Arterial Pressure During Muscle Exercise and Other Types of Stress

An important example of the ability of the nervous system to increase the arterial pressure is the increase in pressure that occurs during muscle exercise. During heavy exercise, the muscles require greatly increased blood flow. Part of this increase results from local vasodilation of the muscle vasculature caused by increased metabolism of the muscle cells, as explained in Chapter 17. Additional increase results from simultaneous elevation of arterial pressure caused by sympathetic stimulation...

G

The baroreceptors respond extremely rapidly to changes in arterial pressure in fact, the rate of impulse firing increases in the fraction of a second during each systole and decreases again during diastole. Furthermore, the baroreceptors respond much more to a rapidly changing pressure than to a stationary pressure. That is, if the mean arterial pressure is 150 mm Hg but at that moment is rising rapidly, the rate of impulse transmission may be as much as twice that when the pressure is...

Control of Overall Respiratory Center Activity

Up to this point, we have discussed the basic mechanisms for causing inspiration and expiration, but it is also important to know how the intensity of the respiratory control signals is increased or decreased to match the ventilatory needs of the body. For example, during heavy exercise, the rates of oxygen usage and carbon dioxide formation are often increased to as much as 20 times normal, requiring commensurate increases in pulmonary ventilation.The major purpose of the remainder of this...

Overview of Renal Potassium Excretion

Potassium excretion is determined by the sum of three renal processes (1) the rate of potassium filtration (GFR multiplied by the plasma potassium concentration), (2) the rate of potassium reabsorption by the tubules, and (3) the rate of potassium secretion by the tubules. The normal rate of potassium filtration is about 756 mEq day (GFR, 180 L day multiplied by plasma potassium, 4.2 mEq L) this rate of filtration is usually relatively constant because of the autoregula-tory mechanisms for GFR...

Visual Pathways

Figure 51-1 shows the principal visual pathways from the two retinas to the visual cortex. The visual nerve signals leave the retinas through the optic nerves. At the optic chiasm, the optic nerve fibers from the nasal halves of the retinas cross to the opposite sides, where they join the fibers from the opposite temporal retinas to form the optic tracts. The fibers of each optic tract then synapse in the dorsal lateral geniculate nucleus of the thalamus, and from there, geniculocalcarine...

Stomach Emptying

Stomach emptying is promoted by intense peristaltic contractions in the stomach antrum. At the same time, emptying is opposed by varying degrees of resistance to passage of chyme at the pylorus. Intense Antral Peristaltic Contractions During Stomach Emptying Pyloric Pump. Most of the time, the rhythmical stomach contractions are weak and function mainly to cause mixing of food and gastric secretions. However, for about 20 per cent of the time while food is in the stomach, the contractions...

Feedback Effect of Thyroid Hormone to Decrease Anterior Pituitary Secretion of TSH

Increased thyroid hormone in the body fluids decreases secretion of TSH by the anterior pituitary. When the rate of thyroid hormone secretion rises to about 1.75 times normal, the rate of TSH secretion falls essentially to zero. Almost all this feedback depressant effect occurs even when the anterior pituitary has been separated from the hypothalamus. Therefore, as shown in Figure 76-7, it is probable that increased thyroid hormone inhibits anterior pituitary secretion of TSH mainly by a direct...

Figure 305

Cellular mechanisms for (1) active secretion of hydrogen ions into the renal tubule (2) tubular reabsorption of bicarbonate ions by combination with hydrogen ions to form carbonic acid, which dissociates to form carbon dioxide and water and (3) sodium ion reabsorption in exchange for hydrogen ions secreted. This pattern of hydrogen ion secretion occurs in the proximal tubule, the thick ascending segment of the loop of Henle, and the early distal tubule. process begins when CO2 either diffuses...

Figure 205

Experiment in a dog to demonstrate the importance of nervous maintenance of the arterial pressure as a prerequisite for cardiac output control. Note that with pressure control, the metabolic stimulant dinitrophenol increases cardiac output greatly without pressure control, the arterial pressure falls and the cardiac output rises very little. (Drawn from experiments by Dr. M. Banet.) However, after autonomic control of the nervous system had been blocked, none of the normal circulatory reflexes...

Figure 199

Renin-angiotensin vasoconstrictor mechanism for arterial pressure control. arterioles immediately proximal to the glomeruli. When the arterial pressure falls, intrinsic reactions in the kidneys themselves cause many of the prorenin molecules in the JG cells to split and release renin. Most of the renin enters the renal blood and then passes out of the kidneys to circulate throughout the entire body. However, small amounts of the renin do remain in the local fluids of the kidney and initiate...

Combination of Hemoglobin with Carbon Monoxide Displacement of Oxygen

Carbon monoxide combines with hemoglobin at the same point on the hemoglobin molecule as does oxygen it can therefore displace oxygen from the hemoglobin, thereby decreasing the oxygen carrying capacity of blood. Further, it binds with about 250 times as much tenacity as oxygen, which is demonstrated by the carbon monoxide-hemoglobin dissociation curve in Figure 40-12. This curve is almost identical to the oxygen-hemoglobin dissociation curve, except that the carbon monoxide partial pressures,...

Figure 167

Effect of Abnormal Imbalance of Forces at the Capillary Membrane If the mean capillary pressure rises above 17 mm Hg, the net force tending to cause filtration of fluid into the tissue spaces rises. Thus, a 20 mm Hg rise in mean capillary pressure causes an increase in net filtration pressure from 0.3 mm Hg to 20.3 mm Hg, which results in 68 times as much net filtration of fluid into the interstitial spaces as normally occurs. To prevent accumulation of excess fluid in these spaces would...

Nervous Regulation of the Circulation

As discussed in Chapter 17, adjustment of blood flow tissue by tissue is mainly the function of local tissue blood flow control mechanisms. We shall see in this chapter that nervous control of the circulation has more global functions, such as redistributing blood flow to different areas of the body, increasing or decreasing pumping activity by the heart, and, especially, providing very rapid control of systemic arterial pressure. The nervous system controls the circulation almost entirely...

Hmb

The 10 essential amino acids cannot be synthesized in sufficient quantities in the body these essential amino acids must be obtained, already formed, from food. by other linkages, often by hydrogen bonding between the CO and NH radicals of the peptides, as follows

Diffusion of Gases Through the Respiratory Membrane

Figure 39-7 shows the respiratory unit (also called respiratory lobule), which is composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli. There are about 300 million alveoli in the two lungs, and each alveolus has an average diameter of about 0.2 millimeter. The alveolar walls are extremely thin, and between the alveoli is an almost solid network of interconnecting capillaries, shown in Figure 39-8. Indeed, because of the extensiveness of the capillary...

Figure 653

Hydrolysis of neutral fat catalyzed by lipase. are digested to the final stage to form single amino acids these then pass on through to the other side of the enterocyte and thence into the blood. More than 99 per cent of the final protein digestive products that are absorbed are individual amino acids, with only rare absorption of peptides and very, very rare absorption of whole protein molecules. Even these very few absorbed molecules of whole protein can sometimes cause serious allergic or...

References

Gehlbach BK, Geppert E The pulmonary manifestations of left heart failure. Chest 125 669, 2004. Guazzi M Alveolar-capillary membrane dysfunction in heart failure evidence of a pathophysiologic role. Chest 124 1090, 2003. Guyton AC, Lindsey AW Effect of elevated left atrial pressure and decreased plasma protein concentration on the development of pulmonary edema. Circ Res 7 649,1959. Guyton AC, Parker JC, Taylor AE, et al Forces governing water movement in the lung. In Fishman AP, Renkin EM...

Cortical and Brain Stem Control of Motor Function

In this chapter, we discuss control of body movements by the cerebral cortex and brain stem. Most voluntary movements initiated by the cerebral cortex are achieved when the cortex activates patterns of function stored in lower brain areas the cord, brain stem, basal ganglia, and cerebellum. These lower centers, in turn, send specific control signals to the muscles. For a few types of movements, however, the cortex has almost a direct pathway to the anterior motor neurons of the cord, bypassing...

Digestion of Triglycerides by Pancreatic Lipase By far the

Most important enzyme for digestion of the triglycerides is pancreatic lipase, present in enormous quantities in pancreatic juice, enough to digest within 1 minute all triglycerides that it can reach. In addition, the enterocytes of the small intestine contain still more lipase, known as enteric lipase, but this is usually not needed. End Products of Fat Digestion. Most of the triglycerides of the diet are split by pancreatic lipase into (Bile + Agitation) Fat--- Emulsified fat

Hydrolysis of Disaccharides and Small Glucose Polymers into Monosaccharides by Intestinal Epithelial Enzymes

Enterocytes lining the villi of the small intestine contain four enzymes (lactase, sucrase, maltase, and a-dextrinase), which are capable of splitting the disac-charides lactose, sucrose, and maltose, plus other small glucose polymers, into their constituent monosaccha-rides.These enzymes are located in the enterocytes covering the intestinal microvilli brush border, so that the disaccharides are digested as they come in contact with these enterocytes. Lactose splits into a molecule of...

Work of Breathing

We have already pointed out that during normal quiet breathing, all respiratory muscle contraction occurs during inspiration expiration is almost entirely a passive process caused by elastic recoil of the lungs and chest cage. Thus, under resting conditions, the respiratory muscles normally perform work to cause inspiration but not to cause expiration. The work of inspiration can be divided into three fractions (1) that required to expand the lungs against the lung and chest elastic forces,...

Diq

Changes in the average direction of the electrical potential from the heart. The so-called vectorcardiogram depicts these changes at different times during the cardiac cycle, as shown in Figure 12-10. In the large vectorcardiogram of Figure 12-10, point 5 is the zero reference point, and this point is the negative end of all the successive vectors. While the heart muscle is polarized between heartbeats, the positive end of the vector remains at the zero point because there is no vectorial...

Nadh

This reaction will not occur without intermediation of the specific dehydrogenase or without the availability of NAD+ to act as a hydrogen carrier. Both the free hydrogen ion and the hydrogen bound with NAD+ subsequently enter into multiple oxidative chemical reactions that form tremendous quantities of ATP, as discussed later. The remaining four hydrogen atoms released during the breakdown of glucose the four released during the citric acid cycle between the succinic and fumaric acid stages...

Physiologic Anatomy of the Sympathetic Nervous System

Figure 60-1 shows the general organization of the peripheral portions of the sympathetic nervous system. Shown specifically in the figure are (1) one of the two paravertebral sympathetic chains of ganglia that are interconnected with the spinal nerves on the side of the vertebral column, (2) two prevertebral ganglia (the celiac and hypogastric), and (3) nerves extending from the ganglia to the different internal organs. The sympathetic nerve fibers originate in the spinal cord along with spinal...

Vestibular Mechanisms for Stabilizing the Eyes

When a person changes his or her direction of movement rapidly or even leans the head sideways, forward, or backward, it would be impossible to maintain a stable image on the retinas unless the person had some automatic control mechanism to stabilize the direction of the eyes' gaze. In addition, the eyes would be of little use in detecting an image unless they remained fixed on each object long enough to gain a clear image. Fortunately, each time the head is suddenly rotated, signals from the...

Figure 583

Multiple centers in the brain stem, the neurons of which secrete different transmitter substances (specified in parentheses). These neurons send control signals upward into the diencephalon and cerebrum and downward into the spinal cord. JCingulate cortex Caudate nucleus

Figure 158

Changes in systolic, diastolic, and mean arterial pressures with age. The shaded areas show the approximate normal ranges. by millisecond over a period of time. It is not equal to the average of systolic and diastolic pressure because the arterial pressure remains nearer to diastolic pressure than to systolic pressure during the greater part of the cardiac cycle. Therefore, the mean arterial pressure is determined about 60 per cent by the diastolic pressure and 40 per cent by the systolic...

Hemophilia

Hemophilia is a bleeding disease that occurs almost exclusively in males. In 85 per cent of cases, it is caused by an abnormality or deficiency of Factor VIII this type of hemophilia is called hemophilia A or classic hemophilia. About 1 of every 10,000 males in the United States has classic hemophilia. In the other 15 per cent of hemophilia patients, the bleeding tendency is caused by deficiency of Factor IX. Both of these factors are transmitted genetically by way of the female chromosome....

Low Output Cardiac Failure Cardiogenic Shock

In many instances after acute heart attacks and often after prolonged periods of slow progressive cardiac deterioration, the heart becomes incapable of pumping even the minimal amount of blood flow required to keep the body alive. Consequently, all the body tissues begin to suffer and even to deteriorate, often leading to death within a few hours to a few days. The picture then is one of circulatory shock, as explained in Chapter 24. Even the cardiovascular system suffers from lack of...

Increased Voltage in the Standard Bipolar Limb Leads

Normally, the voltages in the three standard bipolar limb leads, as measured from the peak of the R wave to the bottom of the S wave, vary between 0.5 and 2.0 millivolts, with lead III usually recording the lowest voltage and lead II the highest. However, these relations are not invariable, even for the normal heart. In general, when the sum of the voltages of all the QRS complexes of the three standard leads is greater than 4 millivolts, the patient is considered to have a highvoltage...

Figure 752

Metabolic functions of the anterior pituitary hormones. ACH, adrenal corticosteroid hormones. anterior pituitary gland. With special stains attached to high-affinity antibodies that bind with the distinctive hormones, at least five cell types can be differentiated (Figure 75-3). Table 75-1 provides a summary of these cell types, the hormones they produce, and their physiological actions. These five cell types are 1. Somatotropes human growth hormone (hGH) (ACTH) hormone (TSH) 4. Gonadotropes...

Distribution of Extracellular Fluid Between the Interstitial Spaces and Vascular System

From Figure 29-12 it is apparent that blood volume and extracellular fluid volume are usually controlled in parallel with each other. Ingested fluid initially goes into the blood, but it rapidly becomes distributed between the interstitial spaces and the plasma. Therefore, blood volume and extracellular fluid volume usually are controlled simultaneously. There are circumstances, however, in which the distribution of extracellular fluid between the interstitial spaces and blood can vary greatly....

Figure 376

Diagram showing respiratory excursions during normal breathing and during maximal inspiration and maximal expiration. expiring to the maximum extent (about 4600 milliliters). 4. The total lung capacity is the maximum volume to which the lungs can be expanded with the greatest possible effort (about 5800 milliliters) it is equal to the vital capacity plus the residual volume. All pulmonary volumes and capacities are about 20 to 25 per cent less in women than in men, and they are greater in large...

Moderate Fluid Retention in Cardiac Failure Can Be Beneficial

Many cardiologists formerly considered fluid retention always to have a detrimental effect in cardiac failure. But it is now known that a moderate increase in body fluid and blood volume is an important factor in helping to compensate for the diminished pumping ability of the heart by increasing the venous return. The increased blood volume increases venous return in two ways First, it increases the mean systemic filling pressure, which increases the pressure gradient for causing venous flow of...

Visual Acuity

Theoretically, light from a distant point source, when focused on the retina, should be infinitely small. However, because the lens system of the eye is never perfect, such a retinal spot ordinarily has a total diameter of about 11 micrometers, even with maximal resolution of the normal eye optical system. The spot is brightest in its center and shades off gradually toward the edges, as shown by the two-point images in Figure 49-16. The average diameter of the cones in the fovea of the retina...

Physiology of Treatment in Shock

If a person is in shock caused by hemorrhage, the best possible therapy is usually transfusion of whole blood. If the shock is caused by plasma loss, the best therapy is administration of plasma when dehydration is the cause, administration of an appropriate electrolyte solution can correct the shock. Whole blood is not always available, such as under battlefield conditions. Plasma can usually substitute adequately for whole blood because it increases the blood...

Oif

By HCO3-, which is then converted into dissolved CO2, decreasing the ratio of HCO3- to CO2 and decreasing the pH of the extracellular fluid. Buffer Power Is Determined by the Amount and Relative Concentrations of the Buffer Components. From the titration curve in Figure 30-1, several points are apparent. First, the pH of the system is the same as the pK when each of the components (HCO3- and CO2) constitutes 50 per cent of the total concentration of the buffer system. Second, the buffer system...

Cardiac Reserve

The maximum percentage that the cardiac output can increase above normal is called the cardiac reserve. Thus, in the healthy young adult, the cardiac reserve is 300 to 400 per cent. In athletically trained persons, it is occasionally 500 to 600 per cent. But in heart failure, there is no cardiac reserve. As an example of normal reserve, during severe exercise the cardiac output of a healthy young adult can rise to about five times normal this is an increase above normal of 400 per cent that is,...

Puberty and Menarche

Puberty means the onset of adult sexual life, and menarche means the beginning of the cycle of Total rates of secretion of gonadotropic hormones throughout the sexual lives of female and male human beings, showing an especially abrupt increase in gonadotropic hormones at menopause in the female. menstruation. The period of puberty is caused by a gradual increase in gonadotropic hormone secretion by the pituitary, beginning in about the eighth year of life, as shown in Figure 81-9, and usually...

Specific Areas in the Hypothalamus Control Secretion of Specific Hypothalamic Releasing and Inhibitory Hormones All or

Most of the hypothalamic hormones are secreted at nerve endings in the median eminence before being transported to the anterior pituitary gland. Electrical stimulation of this region excites these nerve endings and, therefore, causes release of essentially all the hypothalamic hormones. However, the neuronal cell bodies that give rise to these median eminence nerve endings are located in other discrete areas of the hypothalamus or in closely related areas of the basal brain. The specific loci...

Cuz

Macula densa feedback mechanism for autoregulation of glomerular hydrostatic pressure and glomerular filtration rate (GFR) during decreased renal arterial pressure. Blockade of Angiotensin II Formation Further Reduces GFR During Renal Hypoperfusion. As discussed earlier, a preferential constrictor action of angiotensin II on efferent arteri-oles helps prevent serious reductions in glomerular hydrostatic pressure and GFR when renal perfusion pressure falls below normal. The administration of...

Excretion of Excess Hydrogen Ions and Generation of New Bicarbonate by the Ammonia Buffer System

A second buffer system in the tubular fluid that is even more important quantitatively than the phosphate buffer system is composed of ammonia (NH3) and the ammonium ion (NH4+). Ammonium ion is synthesized from glutamine, which comes mainly from the metabolism of amino acids in the liver. The glutamine delivered to the kidneys is transported into the epithelial cells of the proximal tubules, thick ascending limb of the loop of Henle, and distal tubules (Figure 30-8). Once inside the cell, each...

Transport of Carbon Dioxide in the Blood

Transport of carbon dioxide by the blood is not nearly as problematical as transport of oxygen is, because even in the most abnormal conditions, carbon dioxide can usually be transported in far greater quantities than oxygen can be. However, the amount of carbon dioxide in the blood has a lot to do with the acid-base balance of the body fluids, which is discussed in Chapter 30. Under normal resting conditions, an average of 4 milliliters of carbon dioxide is transported from the tissues to the...

Theoretical Function of the Hippocampus in Learning

Hippocampus originated as part of the olfactory cortex. In many lower animals, this cortex plays essential roles in determining whether the animal will eat a particular food, whether the smell of a particular object suggests danger, or whether the odor is sexually inviting, thus making decisions that are of life-or-death importance.Very early in evolutionary development of the brain, the hippocampus presumably became a critical decision-making neuronal mechanism, determining the importance of...

Blood Volume

Blood contains both extracellular fluid (the fluid in plasma) and intracellular fluid (the fluid in the red blood cells). However, blood is considered to be a separate fluid compartment because it is contained in a chamber of its own, the circulatory system. The blood volume is especially important in the control of cardiovascular dynamics. The average blood volume of adults is about 7 per cent of body weight, or about 5 liters. About 60 per cent of the blood is plasma and 40 per cent is red...

Synthesis and Secretion of the Thyroid Metabolic Hormones

About 93 per cent of the metabolically active hormones secreted by the thyroid gland is thyroxine, and 7 per cent triiodothyronine. However, almost all the thy-roxine is eventually converted to triiodothyronine in the tissues, so that both are functionally important. The functions of these two hormones are qualitatively the same, but they differ in rapidity and intensity of action. Triiodothy-ronine is about four times as potent as thyroxine, but it is present in the blood in much smaller...

Control of Pupillary Diameter

Stimulation of the parasympathetic nerves also excites the pupillary sphincter muscle, thereby decreasing the pupillary aperture this is called miosis. Conversely, stimulation of the sympathetic nerves excites the radial fibers of the iris and causes pupillary dilation, called mydriasis. Pupillary Light Reflex. When light is shone into the eyes, the pupils constrict, a reaction called the pupillary light reflex. The neuronal pathway for this reflex is demonstrated by the upper two black traces...

Renal Interstitial Hydrostatic and Colloid Osmotic Pressures

Ultimately, changes in peritubular capillary physical forces influence tubular reabsorption by changing the physical forces in the renal interstitium surrounding the tubules. For example, a decrease in the reabsorp-tive force across the peritubular capillary membranes, caused by either increased peritubular capillary hydrostatic pressure or decreased peritubular capillary colloid osmotic pressure, reduces the uptake of fluid and solutes from the interstitium into the peritubular capillaries....

Some Hormones That Use the Adenylyl CyclasecAMP Second Messenger System

Adrenocorticotropic hormone (ACTH) Angiotensin II (epithelial cells) Calcitonin Catecholamines ( receptors) Corticotropin-releasing hormone (CRH) Follicle-stimulating hormone (FSH) Glucagon Human chorionic gonadotropin (HCG) Luteinizing hormone (LH) Parathyroid hormone (PTH) Secretin Somatostatin Thyroid-stimulating hormone (TSH) Vasopressin (V2 receptor, epithelial cells) cAMP is not the only second messenger used by the different hormones. Two other especially important ones are (1) calcium...

Basilar Membrane and Resonance in the Cochlea

Basilar membrane is a fibrous membrane that separates the scala media from the scala tympani. It contains 20,000 to 30,000 basilar fibers that project from the bony center of the cochlea, the modiolus, toward the outer wall. These fibers are stiff, elastic, reedlike structures that are fixed at their basal ends in the central bony structure of the cochlea (the modi-olus) but are not fixed at their distal ends, except that the distal ends are embedded in the loose basilar membrane. Because the...

Figure 418

To transmit at the same time collateral impulses into the brain stem to excite the respiratory center. This is analogous to the stimulation of the vasomotor center of the brain stem during exercise that causes a simultaneous increase in arterial pressure. Actually, when a person begins to exercise, a large share of the total increase in ventilation begins immediately on initiation of the exercise, before any blood chemicals have had time to change. It is likely that most of the increase in...

Pituitary Gland and Its Relation to the Hypothalamus

Pituitary Gland Two Distinct Parts-The Anterior and Posterior Lobes. The pituitary gland (Figure 75-1), also called the hypophysis, is a small gland about 1 centimeter in diameter and 0.5 to 1 gram in weight that lies in the sella turcica, a bony cavity at the base of the brain, and is connected to the hypothalamus by the pituitary (or hypophysial) stalk. Physiologically, the pituitary gland is divisible into two distinct portions the anterior pituitary, also known as the adenohypophysis, and...

Absorption and Secretion of Electrolytes and Water

Mucosa of the large intestine, like that of the small intestine, has a high capability for active absorption of sodium, and the electrical potential gradient created by absorption of the sodium causes chloride absorption as well. The tight junctions between the epithelial cells of the large intestinal epithelium are much tighter than those of the small intestine. This prevents significant amounts of back-diffusion of ions through these junctions, thus allowing the large intestinal mucosa to...

Implantation of the Blastocyst in the Uterus

After reaching the uterus, the developing blastocyst usually remains in the uterine cavity an additional 1 to 3 days before it implants in the endometrium thus, implantation ordinarily occurs on about the fifth to seventh day after ovulation. Before implantation, the blastocyst obtains its nutrition from the uterine endometrial secretions, called uterine milk. Implantation results from the action of trophoblast cells that develop over the surface of the blastocyst. These cells secrete...

Figure 5612

Caudate circuit through the basal ganglia for cognitive planning of sequential and parallel motor patterns to achieve specific conscious goals. ventroanterior and ventrolateral thalamus, and finally back to the prefrontal, premotor, and supplementary motor areas of the cerebral cortex, but with almost none of the returning signals passing directly to the primary motor cortex. Instead, the returning signals go to those accessory motor regions in the premotor and supplementary motor areas that...

Regulation of Stomach Emptying

The rate at which the stomach empties is regulated by signals from both the stomach and the duodenum. However, the duodenum provides by far the more potent of the signals, controlling the emptying of chyme into the duodenum at a rate no greater than the rate at which the chyme can be digested and absorbed in the small intestine. Gastric Factors That Promote Emptying Effect of Gastric Food Volume on Rate of Emptying. Increased food volume in the stomach promotes increased emptying from the...

Extracellular Fluid Compartment

All the fluids outside the cells are collectively called the extracellular fluid. Together these fluids account for about 20 per cent of the body weight, or about 14 liters in a normal 70-kilogram adult. The two largest compartments of the extracellular fluid are the interstitial fluid, which makes up more than three fourths of the extracellular fluid, and the plasma, which makes up almost one fourth of the extracellular fluid, or about 3 liters. The plasma is the noncellular part of the blood...

Figure 148

Principles of three types of electronic transducers for recording rapidly changing blood pressures (explained in the text). In Figure 14-8A, a simple metal plate is placed a few hundredths of a centimeter above the membrane.When the membrane bulges, the membrane comes closer to the plate, which increases the electrical capacitance between these two, and this change in capacitance can be recorded using an appropriate electronic system. In Figure 14-85, a small iron slug rests on the membrane,...

Figure 141

Distribution of blood (in percentage of total blood) in the different parts of the circulatory system. in major segments of the circulation. For instance, about 84 per cent of the entire blood volume of the body is in the systemic circulation, and 16 per cent in heart and lungs. Of the 84 per cent in the systemic circulation, 64 per cent is in the veins, 13 per cent in the arteries, and 7 per cent in the systemic arterioles and capillaries. The heart contains 7 per cent of the blood, and the...

Medullary Collecting Duct

Although the medullary collecting ducts reabsorb less than 10 per cent of the filtered water and sodium, they are the final site for processing the urine and, therefore, play an extremely important role in determining the final urine output of water and solutes. The epithelial cells of the collecting ducts are nearly cuboidal in shape with smooth surfaces and relatively Cellular ultrastructure and transport characteristics of the medullary collecting duct. The medullary collecting ducts...

Muscle Stretch Reflex

The simplest manifestation of muscle spindle function is the muscle stretch reflex. Whenever a muscle is stretched suddenly, excitation of the spindles causes Neuronal circuit of the stretch reflex. Neuronal circuit of the stretch reflex. reflex contraction of the large skeletal muscle fibers of the stretched muscle and also of closely allied synergistic muscles. Neuronal Circuitry of the Stretch Reflex. Figure 54-4 demonstrates the basic circuit of the muscle spindle stretch reflex, showing a...

Digestion of Carbohydrates in the Small Intestine

Pancreatic secretion, like saliva, contains a large quantity of a-amylase that is almost identical in its function with the a-amylase of saliva but is several times as powerful. Therefore, within 15 to 30 minutes after the chyme empties from the stomach into the duodenum and mixes with pancreatic juice, virtually all the carbohydrates will have become digested. In general, the carbohydrates are almost totally converted into maltose and or other very small...

Physiologic Anatomy of the Coronary Blood Supply

Figure 21-3 shows the heart and its coronary blood supply. Note that the main coronary arteries lie on the surface of the heart and smaller arteries then penetrate from the surface into the cardiac muscle mass. It is almost entirely through these arteries that the heart receives its nutritive blood supply. Only the inner 1 10 millimeter of the endocardial surface can obtain significant nutrition directly from the blood inside the cardiac chambers, so that this source of muscle nutrition is...

Motor Cortex Level

The motor cortex system provides most of the activating motor signals to the spinal cord. It functions partly by issuing sequential and parallel commands that set into motion various cord patterns of motor action. It can also change the intensities of the different patterns or modify their timing or other characteristics. When needed, the corticospinal system can bypass the cord patterns, replacing them with higherlevel patterns from the brain stem or cerebral cortex. The cortical patterns...

Figure 381

Pressure pulse contours in the right ventricle, pulmonary artery, and aorta. normal human being, the diastolic pulmonary arterial pressure is about 8 mm Hg, and the mean pulmonary arterial pressure is 15 mm Hg. Pulmonary Capillary Pressure. The mean pulmonary capillary pressure, as diagrammed in Figure 38-2, is about 7 mm Hg. The importance of this low capillary pressure is discussed in detail later in the chapter in relation to fluid exchange functions of the pulmonary capillaries. Left Atrial...

Antidiuretic Hormone Controls Urine Concentration

There is a powerful feedback system for regulating plasma osmolarity and sodium concentration that operates by altering renal excretion of water independently of the rate of solute excretion. A primary effector of this feedback is antidiuretic hormone (ADH), also called vasopressin. When osmolarity of the body fluids increases above normal (that is, the solutes in the body fluids become too concentrated), the posterior pituitary gland secretes more ADH, which increases the permeability of the...

Dog

Before a sperm can enter the ovum, it must first penetrate the multiple layers of granulosa cells attached to the outside of the ovum (the corona radiata) and then bind to and penetrate the zona pellucida surrounding the ovum itself. The mechanisms used by the sperm for these purposes are presented in Chapter 80. Once a sperm has entered the ovum (which is still in the secondary oocyte stage of development), the oocyte divides again to form the mature ovum plus a second polar body that is...

I

Aa aa5 aa3 aa9 aa2 aa13 aa20 Chemical events in the formation of a protein molecule. process in which ATP combines with the amino acid to form an adenosine monophosphate complex with the amino acid, giving up two high-energy phosphate bonds in the process. (2) The activated amino acid, having an excess of energy, then combines with its specific transfer RNA to form an amino acid-tRNA complex and, at the same time, releases the adenosine monophosphate. (3) The transfer RNA carrying the amino...

What Is the Role of the Nervous System in Controlling Cardiac Output

Importance of the Nervous System in Maintaining the Arterial Pressure When the Venous Return and Cardiac Output Increase Figure 20-5 shows an important difference in cardiac output control with and without a functioning auto-nomic nervous system. The solid curves demonstrate the effect in the normal dog of intense dilation of the peripheral blood vessels caused by administering the drug dinitrophenol, which increased the metabolism of virtually all tissues of the body about fourfold. Note that...

Excretion

From the tubules, so that the urinary excretion rate is essentially zero. Many of the ions in the plasma, such as sodium, chloride, and bicarbonate, are also highly reabsorbed, but their rates of reabsorption and urinary excretion are variable, depending on the needs of the body. Certain waste products, such as urea and creati-nine, conversely, are poorly reabsorbed from the tubules and excreted in relatively large amounts. Therefore, by controlling the rate at which they reabsorb different...

T

------- CO,- ------------ 2 I The base portion of these molecules reacts quickly with H+ to remove it from solution they are, therefore, typical bases. For similar reasons, the term alkalosis refers to excess removal of H+ from the body fluids, in contrast to the excess addition of H+, which is referred to as acidosis. Strong and Weak Acids and Bases. A strong acid is one that rapidly dissociates and releases especially large amounts of H+ in solution. An example is HCl. Weak acids have less...

Most Daily Variation in Potassium Excretion Is Caused by Changes in Potassium Secretion in Distal and Collecting

The most important sites for regulating potassium excretion are the principal cells of the late distal tubules and cortical collecting tubules. In these tubular segments, potassium can at times be reabsorbed or at other times be secreted, depending on the needs of the body.With a normal potassium intake of 100 mEq day, the kidneys must excrete about 92 mEq day (the remaining 8 milliequivalents are lost in the feces). About one third (3l mEq day) of this amount of potassium is secreted...

Figure 223

Progressive changes in mean aortic pressure, peripheral tissue capillary pressure, and right atrial pressure as the cardiac output falls from normal to zero. of 13 mm Hg. Thus, severe acute cardiac failure often causes a fall in peripheral capillary pressure rather than a rise. Therefore, animal experiments, as well as experience in humans, show that acute cardiac failure almost never causes immediate development of peripheral edema. Long-Term Fluid Retention by the Kidneys The Cause of...

Figure 411

Organization of the respiratory center. potentials. Instead, in normal respiration, it begins weakly and increases steadily in a ramp manner for about 2 seconds. Then it ceases abruptly for approximately the next 3 seconds, which turns off the excitation of the diaphragm and allows elastic recoil of the lungs and the chest wall to cause expiration. Next, the inspiratory signal begins again for another cycle this cycle repeats again and again, with expiration occurring in between. Thus, the...

N

Postulated mechanism for sodium co-transport of glucose. Postulated mechanism for sodium co-transport of glucose. Other important co-transport mechanisms in at least some cells include co-transport of chloride ions, iodine ions, iron ions, and urate ions. Sodium Counter-Transport of Calcium and Hydrogen Ions Two especially important counter-transport mechanisms (transport in a direction opposite to the primary ion) are sodium-calcium counter-transport and sodium-hydrogen counter-transport....

Heart Muscle The Heart as a Pump and Function of the Heart Valves

With this chapter we begin discussion of the heart and circulatory system. The heart, shown in Figure 9-1, is actually two separate pumps a right heart that pumps blood through the lungs, and a left heart that pumps blood through the peripheral organs. In turn, each of these hearts is a pulsatile two-chamber pump composed of an atrium and a ventricle. Each atrium is a weak primer pump for the ventricle, helping to move blood into the ventricle. The ventricles then supply the main pumping force...

Changes in Voltage of the Resting Membrane Potential In

Addition to the slow waves and spike potentials, the baseline voltage level of the smooth muscle resting membrane potential also can change. Under normal conditions, the resting membrane potential averages about -56 millivolts, but multiple factors can change this level. When the potential becomes less negative, which is called depolarization of the membrane, the muscle fibers become more excitable.When the potential becomes more negative, which is called hyperpo-larization, the fibers become...

Endocrinology and Reproduction

Pituitary Hormones and Their Control by the Hypothalamus 78. Insulin, Glucagon, and Diabetes Mellitus 79. Parathyroid Hormone, Calcitonin, Calcium and Phosphate Metabolism, Vitamin D, Bone, and Teeth 80. Reproductive and Hormonal Functions of the Male 81. Female Physiology Before Pregnancy and the Female Hormones

Muscle Action Potential

Almost everything discussed in Chapter 5 regarding initiation and conduction of action potentials in nerve fibers applies equally to skeletal muscle fibers, except for quantitative differences. Some of the quantitative aspects of muscle potentials are the following 1. Resting membrane potential about -80 to -90 millivolts in skeletal fibers the same as in large myelinated nerve fibers. 2. Duration of action potential 1 to 5 milliseconds in skeletal muscle about five times as long as in large...

L

Interdigitate with the myosin filaments. The Z disc, which itself is composed of filamentous proteins different from the actin and myosin filaments, passes crosswise across the myofibril and also crosswise from myofibril to myofibril, attaching the myofibrils to one another all the way across the muscle fiber. Therefore, the entire muscle fiber has light and dark bands, as do the individual myofibrils.These bands give skeletal and cardiac muscle their striated appearance. The portion of the...

Dynamics of Mitral Stenosis and Mitral Regurgitation

In mitral stenosis, blood flow from the left atrium into the left ventricle is impeded, and in mitral regurgitation, much of the blood that has flowed into the left ventricle during diastole leaks back into the left atrium during systole rather than being pumped into the aorta. Therefore, either of these conditions reduces net movement of blood from the left atrium into the left ventricle. Pulmonary Edema in Mitral Valvular Disease. The buildup of blood in the left atrium causes progressive...