Sympathetic System Often Responds by Mass Discharge In

Many instances, almost all portions of the sympathetic nervous system discharge simultaneously as a complete unit, a phenomenon called mass discharge. This frequently occurs when the hypothalamus is activated by fright or fear or severe pain. The result is a widespread reaction throughout the body called the alarm or stress response, which we shall discuss shortly. At other times, activation occurs in isolated portions of the sympathetic nervous system. The most important of these are the...

Absorption of Bicarbonate Ions in the Duodenum and Jejunum

Often large quantities of bicarbonate ions must be reabsorbed from the upper small intestine because large amounts of bicarbonate ions have been secreted into the duodenum in both pancreatic secretion and bile. The bicarbonate ion is absorbed in an indirect way as follows When sodium ions are absorbed, moderate amounts of hydrogen ions are secreted into the lumen of the gut in exchange for some of the sodium. These hydrogen ions in turn combine with the bicarbonate ions to form carbonic acid...

Physiologic Control of Glomerular Filtration and Renal Blood Flow

The determinants of GFR that are most variable and subject to physiologic control include the glomerular hydrostatic pressure and the glomerular capillary colloid osmotic pressure. These variables, in turn, are influenced by the sympathetic nervous system, hormones and autacoids (vasoactive substances that are released in the kidneys and act locally), and other feedback controls that are intrinsic to the kidneys. Sympathetic Nervous System Activation Decreases GFR Essentially all the blood...

Effects of Sympathetic and Parasympathetic Stimulation on Specific Organs

Two functions of the eyes are controlled by the autonomic nervous system. They are 1 the pupillary opening and 2 the focus of the lens. Sympathetic stimulation contracts the meridional fibers of the iris that dilate the pupil, whereas parasym-pathetic stimulation contracts the circular muscle of the iris to constrict the pupil. The parasympathetics that control the pupil are reflexly stimulated when excess light enters the eyes, which is explained in Chapter 51 this reflex reduces the...

Edema Excess Fluid in the Tissues

Edema refers to the presence of excess fluid in the body tissues. In most instances, edema occurs mainly in the extracellular fluid compartment, but it can involve intracellular fluid as well. Two conditions are especially prone to cause intracel-lular swelling (1) depression of the metabolic systems of the tissues, and (2) lack of adequate nutrition to the cells. For example, when blood flow to a tissue is decreased, the delivery of oxygen and nutrients is reduced. If the blood flow becomes...

Factors That Affect the Rate of Gas Diffusion Through the Respiratory Membrane

Referring to the earlier discussion of diffusion of gases in water, one can apply the same principles and mathematical formulas to diffusion of gases through the respiratory membrane. Thus, the factors that determine how rapidly a gas will pass through the membrane are (1) the thickness of the membrane, (2) the surface area of the membrane, (3) the diffusion coefficient of the gas in the substance of the membrane, and (4) the partial pressure difference of the gas between the two sides of the...

Function of Bile Salts in Fat Digestion and Absorption

The liver cells synthesize about 6 grams of bile salts daily. The precursor of the bile salts is cholesterol, which is either present in the diet or synthesized in the liver cells during the course of fat metabolism. The cholesterol is first converted to cholic acid or che-nodeoxycholic acid in about equal quantities. These acids in turn combine principally with glycine and to a lesser extent with taurine to form glyco- and tauro-conjugated bile acids. The salts of these acids, mainly sodium...

Flow of Electrical Currents in the Chest Around the Heart

The Fatty Liver Bible Ezra Protocol

Figure 11-5 shows the ventricular muscle lying within the chest. Even the lungs, although mostly filled with air, conduct electricity to a surprising extent, and fluids in other tissues surrounding the heart conduct electricity even more easily. Therefore, the heart is actually suspended in a conductive medium. When one portion of the ventricles depolarizes and therefore becomes electronegative with respect to the Flow of current in the chest around partially depolarized ventricles. Flow of...

Effect of Potassium and Calcium Ions on Heart Function

In the discussion of membrane potentials in Chapter 5, it was pointed out that potassium ions have a marked effect on membrane potentials, and in Chapter 6 it was noted that calcium ions play an especially important role in activating the muscle contractile process. Therefore, it is to be expected that the concentration of each of these two ions in the extracellular fluids should also have important effects on cardiac pumping. Effect of Potassium Ions. Excess potassium in the extracellular...

Factors That Stimulate or Inhibit Secretion of Growth Hormone

Glucose Inhibit Growth Hormone

Decreased blood glucose Decreased blood free fatty acids deficiency Trauma, stress, excitement Exercise Testosterone, estrogen Deep sleep ( stages II and IV) Growth hormone-releasing hormone Increased blood glucose Increased blood free fatty hormone (somatostatin) Growth hormone (exogenous) Somatomedins (insulin-like growth factors) Protein Carbohydrate Protein Protein deficiency treatment treatment treatment (kwashiorkor) (3 days) (3 days) (25 days) Protein Carbohydrate Protein Protein...

Atrioventricular Node and Delay of Impulse Conduction from the Atria to the Ventricles

The atrial conductive system is organized so that the cardiac impulse does not travel from the atria into the ventricles too rapidly this delay allows time for the atria to empty their blood into the ventricles before ventricular contraction begins. It is primarily the A-V node and its adjacent conductive fibers that delay this transmission into the ventricles. The A-V node is located in the posterior wall of the right atrium immediately behind the tricuspid valve, as shown in Figure 10-1. And...

Effects of Cortisol on Fat Metabolism

In much the same manner that cortisol promotes amino acid mobilization from muscle, it promotes mobilization of fatty acids from adipose tissue. This increases the concentration of free fatty acids in the plasma, which also increases their utilization for energy. Cortisol also seems to have a direct effect to enhance the oxidation of fatty acids in the cells. The mechanism by which cortisol promotes fatty acid mobilization is not completely understood. However, part...

Inflammation Role of Neutrophils and Macrophages

When tissue injury occurs, whether caused by bacteria, trauma, chemicals, heat, or any other phenomenon, multiple substances are released by the injured tissues Functional structures of the spleen. (Modified from Bloom W, Fawcett DW A Textbook of Histology, 10th ed. Philadelphia WB Saunders, 1975.) and cause dramatic secondary changes in the surrounding uninjured tissues. This entire complex of tissue changes is called inflammation. Inflammation is characterized by (1) vasodilation of the local...

Effects of Cortisol on Carbohydrate Metabolism

By far the best-known metabolic effect of cortisol and other glucocorticoids on metabolism is their ability to stimulate gluconeo-genesis (formation of carbohydrate from proteins and some other substances) by the liver, often increasing the rate of gluconeogenesis as much as 6- to 10-fold. This results mainly from two effects of cortisol. 1. Cortisol increases the enzymes required to convert amino acids into glucose in the liver cells. This results from the...

Types of Smooth Muscle

Smooth Muscle

The smooth muscle of each organ is distinctive from that of most other organs in several ways (1) physical dimensions, (2) organization into bundles or sheets, (3) response to different types of stimuli, (4) characteristics of innervation, and (5) function. Yet, for the sake of simplicity, smooth muscle can generally be divided into two major types, which are shown in Figure 8-1 multi-unit smooth muscle and unitary (or single-unit) smooth muscle. Multi-Unit Smooth Muscle. This type of smooth...

Types of Sensory Receptors and the Sensory Stimuli They Detect

Types Touch Receptors

Table 46-1 lists and classifies most of the body's sensory receptors. This table shows that there are five basic types of sensory receptors (1) mechanorecep-tors, which detect mechanical compression or stretching of the receptor or of tissues adjacent to the receptor (2) thermoreceptors, which detect changes in temperature, some receptors detecting cold and others warmth (3) nociceptors (pain receptors), which detect damage occurring in the tissues, whether physical damage or chemical damage...

Glucose Is Transported by a Sodium CoTransport Mechanism

In the absence of sodium transport through the intestinal membrane, virtually no glucose can be absorbed. The reason is that glucose absorption occurs in a co-transport mode with active transport of sodium. There are two stages in the transport of sodium through the intestinal membrane. First is active transport of sodium ions through the basolateral membranes of the intestinal epithelial cells into the blood, thereby depleting sodium inside the epithelial cells. Second, decrease of sodium...

Regulation of Cortisol Secretion by Adrenocorticotropic Hormone from the Pituitary Gland

Adrenocorticotropic Hormone

Unlike aldosterone secretion by the zona glomerulosa, which is controlled mainly by potassium and angiotensin acting directly on the adrenocortical cells, almost no stimuli have direct control effects on the adrenal cells that secrete cortisol. Instead, secretion of cortisol is controlled almost entirely by ACTH secreted by the anterior pituitary gland. This hormone, also called corticotropin or adrenocorticotropin, also enhances the production of adrenal...

Abdominal Muscle Contractions During Labor

Once uterine contractions become strong during labor, pain signals originate both from the uterus itself and from the birth canal. These signals, in addition to causing suffering, elicit neurogenic reflexes in the spinal cord to the abdominal muscles, causing intense contractions of these muscles. The abdominal contractions add greatly to the force that causes expulsion of the baby. The uterine contractions during labor begin mainly at the top of the uterine fundus and spread downward over the...

Chemical Structure and Synthesis of Hormones

There are three general classes of hormones 1. Proteins and polypeptides, including hormones secreted by the anterior and posterior pituitary gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many others (see Table 74-1). 2. Steroids secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone), the testes (testosterone), and the placenta (estrogen and progesterone). 3. Derivatives of the amino acid tyrosine,...

Phosphate Buffer System

Although the phosphate buffer system is not important as an extracellular fluid buffer, it plays a major role in buffering renal tubular fluid and intracellular fluids. The main elements of the phosphate buffer system are H2PO4- and HPO4 . When a strong acid such as HCl is added to a mixture of these two substances, the hydrogen is accepted by the base HPO4 and converted to H2PO4-. HCl + Na2HPO4 > NaH2PO4 + NaCl The result of this reaction is that the strong acid, HCl, is replaced by an...

Energy Metabolism Factors That Influence Energy Output

As discussed in Chapter 71, energy intake is balanced with energy output in healthy adults who maintain a stable body weight. About 45 per cent of daily energy intake is derived from carbohydrates, 40 per cent from fats, and 15 per cent from proteins in the average American diet. Energy output can also be partitioned into several measurable components, including energy used for (1) performing essential metabolic functions of the body (the basal metabolic rate) (2) performing various physical...

Effect of Local Tissue Factors and Hormones to Cause Smooth Muscle Contraction Without Action Potentials

Skeletal Muscle Pump

Probably half of all smooth muscle contraction is initiated by stimulatory factors acting directly on the smooth muscle contractile machinery and without action potentials. Two types of non-nervous and non-action potential stimulating factors often involved are 1 local tissue chemical factors and 2 various hormones. Smooth Muscle Contraction in Response to Local Tissue Chemical Factors. In Chapter 17, we discuss control of contraction of the arterioles, meta-arterioles, and pre-capillary...

Types of Pain and Their Qualities Fast Pain and Slow Pain

Pain has been classified into two major types fast pain and slow pain. Fast pain is felt within about 0.1 second after a pain stimulus is applied, whereas slow pain begins only after 1 second or more and then increases slowly over many seconds and sometimes even minutes. During the course of this chapter, we shall see that the conduction pathways for these two types of pain are different and that each of them has specific qualities. Fast pain is also described by many alternative names, such as...

Effects of Cortisol on Protein Metabolism

One of the principal effects of cortisol on the metabolic systems of the body is reduction of the protein stores in essentially all body cells except those of the liver. This is caused by both decreased protein synthesis and increased catabolism of protein already in the cells. Both these effects may result from decreased amino acid transport into extra-hepatic tissues, as discussed later this probably is not the major cause, because cortisol also depresses the...

Function of the Basal Ganglia in Executing Patterns of Motor Activity The Putamen Circuit

Basal Ganglia Circuitry

One of the principal roles of the basal ganglia in motor control is to function in association with the corti-cospinal system to control complex patterns of motor activity. An example is the writing of letters of the alphabet. When there is serious damage to the basal ganglia, the cortical system of motor control can no longer provide these patterns. Instead, one's writing becomes crude, as if one were learning for the first time how to write. Other patterns that require the basal ganglia are...

Prevention of Blood Coagulation Outside the Body

Although blood removed from the body and held in a glass test tube normally clots in about 6 minutes, blood collected in siliconized containers often does not clot for 1 hour or more. The reason for this delay is that preparing the surfaces of the containers with silicone prevents contact activation of platelets and Factor XII, the two principal factors that initiate the intrinsic clotting mechanism. Conversely, untreated glass containers allow contact activation of the platelets and Factor...

Acute Control of Local Blood Flow

Normal Cardiac Oxygen Saturation Dog

Effect of Tissue Metabolism on Local Blood Flow. Figure 17-1 shows the approximate quantitative acute effect on blood flow of increasing the rate of metabolism in a local tissue, such as in a skeletal muscle. Note that an increase in metabolism up to eight times normal increases the blood flow acutely about fourfold. Acute Local Blood Flow Regulation When Oxygen Availability Changes. One of the most necessary of the metabolic nutrients is oxygen. Whenever the availability of oxygen to the...

Some Special Characteristics of Synaptic Transmission

When excitatory synapses are repetitively stimulated at a rapid rate, the number of discharges by the postsynaptic neuron is at first very great, but the firing rate becomes progressively less in succeeding milliseconds or seconds. This is called fatigue of synaptic transmission. Fatigue is an exceedingly important characteristic of synaptic function because when areas of the nervous system become overexcited, fatigue causes them to lose this excess...

Some Hormones That Use the Phospholipase C Second Messenger System

Angiotensin II (vascular smooth muscle) Catecholamines (a receptors) Gonadotropin-releasing hormone (GnRH) Growth hormone-releasing hormone (GHRH) Oxytocin Thyroid-releasing hormone (TRH) Vasopressin (Vi receptor, vascular smooth muscle) reticulum, and the calcium ions then have their own second messenger effects, such as smooth muscle contraction and changes in cell secretion. DAG, the other lipid second messenger, activates the enzyme protein kinase C (PKC), which then phos-phorylates a large...

Regulation of Food Intake and Energy Storage

Hypothalamus Food Intake Regulation

Stability of the body's total mass and composition over long periods requires that energy intake match energy expenditure. As discussed in Chapter 72, only about 27 per cent of the energy ingested normally reaches the functional systems of the cells, and much of this is eventually converted to heat, which is generated as a result of protein metabolism, muscle activity, and activities of the various organs and tissues of the body. Excess energy intake is stored mainly as fat, whereas a deficit...

Detection and Transmission of Tactile Sensations

Iggo Dome Receptor

Interrelations Among the Tactile Sensations of Touch, Pressure, and Vibration. Although touch, pressure, and vibration are frequently classified as separate sensations, they are all detected by the same types of receptors. There are three principal differences among them 1 touch sensation generally results from stimulation of tactile receptors in the skin or in tissues immediately beneath the skin 2 pressure sensation generally results from deformation of deeper tissues and 3 vibration...

Growth Hormone Has Several Metabolic Effects

Effects Growth Hormone Cellebrities

Aside from its general effect in causing growth, growth hormone has multiple specific metabolic effects, Comparison of weight gain of a rat injected daily with growth hormone with that of a normal littermate. including (1) increased rate of protein synthesis in most cells of the body (2) increased mobilization of fatty acids from adipose tissue, increased free fatty acids in the blood, and increased use of fatty acids for energy and (3) decreased rate of glucose utilization throughout the body....

Clearance of Hormones from the Blood

Two factors can increase or decrease the concentration of a hormone in the blood. One of these is the rate of hormone secretion into the blood. The second is the rate of removal of the hormone from the blood, which is called the metabolic clearance rate. This is usually expressed in terms of the number of milliliters of plasma cleared of the hormone per minute. To calculate this clearance rate, one measures (1) the rate of disappearance of the hormone from the plasma per minute and (2) the...

Diagonal Stepping of All Four Limbs Mark Time Reflex If

Mark Time Reflex

A well-healed spinal animal (with spinal transection in the neck above the forelimb area of the cord) is held up from the floor and its legs are allowed to dangle, as shown in Figure 54-12, the stretch on the limbs occasionally elicits stepping reflexes that involve all four limbs. In general, stepping occurs diagonally between the forelimbs and hindlimbs. This diagonal response is another manifestation of reciprocal innervation, this Diagonal stepping movements exhibited by a spinal animal...

Mechanism of Blood Coagulation

More than 50 important substances that cause or affect blood coagulation have been found in the blood and in the tissues some that promote coagulation, called procoagulants, and others that inhibit coagulation, called anticoagulants. Whether blood will coagulate depends on the balance between these two groups of substances. In the blood stream, the anticoagulants normally predominate, so that the blood does not coagulate while it is circulating in the blood vessels. But when a...

Inanition Anorexia and Cachexia

Inanition is the opposite of obesity and is characterized by extreme weight loss. It can be caused by inadequate availability of food or by pathophysiologic conditions that greatly decrease the desire for food, including psy-chogenic disturbances, hypothalamic abnormalities, and factors released from peripheral tissues. In many instances, especially in those with serious diseases such as cancer, the reduced desire for food may be associated with increased energy expenditure, causing serious...

Coordination of Body Functions by Chemical Messengers

Secondary Endocrine Tissues

The multiple activities of the cells, tissues, and organs of the body are coordinated by the interplay of several types of chemical messenger systems 1. Neurotransmitters are released by axon terminals of neurons into the synaptic junctions and act locally to control nerve cell functions. 2. Endocrine hormones are released by glands or specialized cells into the circulating blood and influence the function of cells at another location in the body. 3. Neuroendocrine hormones are secreted by...

Thyroid Hormones Increase Active Transport of Ions Through

Activator Inhibitor

One of the enzymes that increases its activity in response to thyroid hormone is Na -K -ATPase. This in turn increases the rate of transport of both sodium and potassium ions through the cell membranes of some tissues. Because this process uses energy and increases the amount of heat produced in the body, it has been suggested that this might be one of the mechanisms by which thyroid hormone increases the body's metabolic rate. In fact, thyroid hormone also causes the cell...

Regulation of Aldosterone Secretion

The regulation of aldosterone secretion is so deeply intertwined with the regulation of extracellular fluid electrolyte concentrations, extracellular fluid volume, blood volume, arterial pressure, and many special aspects of renal function that it is difficult to discuss the regulation of aldosterone secretion independently of all these other factors. This subject is presented in detail in Chapters 28 and 29, to which the reader is referred. However, it is important to list here some of the...

Cellular Mechanism of Cortisol Action

Cortisol, like other steroid hormones, exerts its effects by first interacting with intracellular receptors in target cells. Because cortisol is lipid soluble, it can easily diffuse through the cell membrane. Once inside the cell, cortisol binds with its protein receptor in the cytoplasm, and the hormone-receptor complex then interacts with specific regulatory DNA sequences, called glucocorti-coid response elements, to induce or repress gene transcription. Other proteins in the cell, called...

Thermostat Resetting In Physiology

Fever, which means a body temperature above the usual range of normal, can be caused by abnormalities in the brain itself or by toxic substances that affect the temperature-regulating centers. Some causes of fever and also of subnormal body temperatures are presented in Figure 73-10.They include bacterial diseases, Body temperatures under different conditions. Redrawn from DuBois EF Fever. Springfield, IL Charles C Thomas, 1948. brain tumors, and environmental conditions that may terminate in...

Blood Reservoir Function of the Veins

As pointed out in Chapter 14, more than 60 per cent of all the blood in the circulatory system is usually in the veins. For this reason and also because the veins are so compliant, it is said that the venous system serves as a blood reservoir for the circulation. When blood is lost from the body and the arterial pressure begins to fall, nervous signals are elicited from the carotid sinuses and other pressure-sensitive areas of the circulation, as discussed in Chapter 18. These in turn elicit...

The Interstitium and Interstitial Fluid

About one sixth of the total volume of the body consists of spaces between cells, which collectively are called the interstitium. The fluid in these spaces is the interstitial fluid. The structure of the interstitium is shown in Figure 16-4. It contains two major types of solid structures (1) collagen fiber bundles and (2) proteoglycan filaments. The collagen fiber bundles extend long distances in the interstitium. They are extremely strong and therefore provide most of the tensional strength...

Abnormalities of Growth Hormone Secretion

This term means decreased secretion of all the anterior pituitary hormones. The decrease in secretion may be congenital (present from birth), or it may occur suddenly or slowly at any time during life, most often resulting from a pituitary tumor that destroys the pituitary gland. Dwarfism. Most instances of dwarfism result from generalized deficiency of anterior pituitary secretion (panhy-popituitarism) during childhood. In general, all the physical parts of the body develop...

Sympathetic and Parasympathetic Tone

Normally, the sympathetic and parasympathetic systems are continually active, and the basal rates of activity are known, respectively, as sympathetic tone and parasympathetic tone. The value of tone is that it allows a single nervous system both to increase and to decrease the activity of a stimulated organ. For instance, sympathetic tone normally keeps almost all the systemic arterioles constricted to about one half their maximum diameter. By increasing the degree of sympathetic stimulation...

Countercurrent Exchange in the Vasa Recta Preserves Hyperosmolarity of the Renal Medulla

State The Role Vasa Recta

Blood flow must be provided to the renal medulla to supply the metabolic needs of the cells in this part of the kidney. Without a special medullary blood flow system, the solutes pumped into the renal medulla by the countercurrent multiplier system would be rapidly dissipated. There are two special features of the renal medullary blood flow that contribute to the preservation of the high solute concentrations 1. The medullary blood flow is low, accounting for less than 5 per cent of the total...

Taste Preference and Control of the Diet

Taste preference simply means that an animal will choose certain types of food in preference to others, and the animal automatically uses this to help control the type of diet it eats. Furthermore, its taste preferences often change in accord with the body's need for certain specific substances. The following experiments demonstrate this ability of animals to choose food in accord with the needs of their bodies. First, adrenalectomized, salt-depleted animals automatically select drinking water...

Cell Divisions During Spermatogenesis

Cross Sectional Seminiferous Tubules

Modified from Bloom V, Fawcett DW Textbook of Histology, 10th ed. Philadelphia WB Saunders Co, 1975. B, Internal structure of the testis and relation of the testis to the epididymis. Redrawn from Guyton AC Anatomy and Physiology. Philadelphia Saunders College Publishing, 1985. A, Cross section of a seminiferous tubule. B, Stages in the development of sperm from spermatogonia. A, Cross section of a seminiferous tubule. B, Stages in the development of sperm from...

Cerebral Cortex Intellectual Functions of the Brain Learning and Memory

It is ironic that of all the parts of the brain, we know least about the functions of the cerebral cortex, even though it is by far the largest portion of the nervous system. But we do know the effects of damage or specific stimulation in various portions of the cortex. In the first part of this chapter, the facts known about cortical function are discussed then basic theories of neuronal mechanisms involved in thought processes, memory, analysis of sensory information, and so forth are...

Reward and Punishment Function of the Limbic System

From the discussion thus far, it is already clear that several limbic structures are particularly concerned with the affective nature of sensory sensations that is, whether the sensations are pleasant or unpleasant. These affective qualities are also called reward or punishment, or satisfaction or aversion. Electrical stimulation of certain limbic areas pleases or satisfies the animal, whereas electrical stimulation of other regions causes terror, pain, fear, defense, escape reactions, and all...

Effect of Arterial Pressure on Urine Output The Pressure Natriuresis and Pressure Diuresis Mechanisms

Even small increases in arterial pressure often cause marked increases in urinary excretion of sodium and water, phenomena that are referred to as pressure natriuresis and pressure diuresis. Because of the autoregulatory mechanisms described in Chapter 26, increasing the arterial pressure between the limits of 75 and 160 mm Hg usually has only a small effect on renal blood flow and GFR. The slight increase in GFR that does occur contributes in part to the effect of increased arterial pressure...

Major Levels of Central Nervous System Function

The human nervous system has inherited special functional capabilities from each stage of human evolutionary development. From this heritage, three major levels of the central nervous system have specific functional characteristics (1) the spinal cord level, (2) the lower brain or subcortical level, and (3) the higher brain or cortical level. We often think of the spinal cord as being only a conduit for signals from the periphery of the body to the brain, or in the opposite direction from the...

Pain Suppression Analgesia System in the Brain and Spinal Cord

Brain Stem Spinal Cord

The degree to which a person reacts to pain varies tremendously. This results partly from a capability of the brain itself to suppress input of pain signals to the nervous system by activating a pain control system, called an analgesia system. The analgesia system is shown in Figure 48-4. It consists of three major components (1) The periaqueductal gray and periventricular areas of the mesencephalon and upper pons surround the aqueduct of Sylvius and portions of the third and fourth ventricles....

Dynamic Stretch Reflex and Static Stretch Reflexes

Stretch reflex can be divided into two components the dynamic stretch reflex and the static stretch reflex. The dynamic stretch reflex is elicited by the potent dynamic signal transmitted from the primary sensory endings of the muscle spindles, caused by rapid stretch or unstretch. That is, when a muscle is suddenly stretched or unstretched, a strong signal is transmitted to the spinal cord this causes an instantaneous strong reflex contraction (or decrease in contraction) of the same muscle...

Transmission and Processing of Signals in Neuronal Pools

Facilitation Neuronal Pools

The central nervous system is composed of thousands to millions of neuronal pools some of these contain few neurons, while others have vast numbers. For instance, the entire cerebral cortex could be considered to be a single large neuronal pool. Other neuronal pools include the different basal ganglia and the specific nuclei in the thalamus, cerebellum, mesen-cephalon, pons, and medulla. Also, the entire dorsal gray matter of the spinal cord could be considered one long pool of neurons. Each...

Clinical Applications of the Stretch Reflex

Almost every time a clinician performs a physical examination on a patient, he or she elicits multiple stretch reflexes. The purpose is to determine how much background excitation, or tone, the brain is sending to the spinal cord. This reflex is elicited as follows. Knee Jerk and Other Muscle Jerks. Clinically, a method used to determine the sensitivity of the stretch reflexes is to elicit the knee jerk and other muscle jerks. The knee jerk can be elicited by simply striking the patellar tendon...

Muscles That Cause Lung Expansion and Contraction

The lungs can be expanded and contracted in two ways (1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity, and (2) by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of the chest cavity. Figure 37-1 shows these two methods. Normal quiet breathing is accomplished almost entirely by the first method, that is, by movement of the diaphragm. During inspiration, contraction of the diaphragm pulls the lower surfaces of...

Human Chorionic Somatomammotropin

A more recently discovered placental hormone is called human chorionic somatomammotropin. It is a protein with a molecular weight of about 38,000, and it begins to be secreted by the placenta at about the fifth week of pregnancy. Secretion of this hormone increases progressively throughout the remainder of pregnancy in direct proportion to the weight of the placenta. Although the functions of chorionic somatomammotropin are uncertain, it is secreted in quantities several times greater than all...

Liver Secretion of Cholesterol and Gallstone Formation

Cilia Respiratory Tract

Bile salts are formed in the hepatic cells from cholesterol in the blood plasma. In the process of secreting the bile salts, about 1 to 2 grams of cholesterol are removed from the blood plasma and secreted into the bile each day. Cholesterol is almost completely insoluble in pure water, but the bile salts and lecithin in bile combine physically with the cholesterol to form ultramicroscopic micelles in the form of a colloidal solution, as explained in more detail in Chapter 65. When the bile...

Obligatory Urine Volume

The maximal concentrating ability of the kidney dictates how much urine volume must be excreted each day to rid the body of waste products of metabolism and ions that are ingested. A normal 70-kilogram human must excrete about 600 milliosmoles of solute each day. If maximal urine concentrating ability is 1200 mOsm L, the minimal volume of urine that must be excreted, called the obligatory urine volume, can be calculated as This minimal loss of volume in the urine contributes to dehydration,...

Metabolic Functions of the Liver

The liver is a large, chemically reactant pool of cells that have a high rate of metabolism, sharing substrates and energy from one metabolic system to another, processing and synthesizing multiple substances that are transported to other areas of the body, and performing myriad other metabolic functions. For these reasons, a major share of the entire discipline of biochemistry is devoted to the metabolic reactions in the liver. But here, let us summarize those metabolic functions that are...

Energy System Used In Various Sport Such As Phosphagen System Almist Entirely

Muscle Glycogen Replenishment

When comparing the same systems for endurance, the relative values are the following Phosphagen system 8 to 10 seconds Glycogen-lactic acid system 1.3 to 1.6 minutes Aerobic system Unlimited time (as long as Thus, one can readily see that the phosphagen system is the one used by the muscle for power surges of a few seconds, and the aerobic system is required for prolonged athletic activity. In between is the glycogen-lactic acid system, which is especially important for giving extra power...

Physical Structure of the Cell

Internal Organelles The Human Body

The cell is not merely a bag of fluid, enzymes, and chemicals it also contains highly organized physical structures, called intracellular organelles. The physical nature of each organelle is as important as the cell's chemical constituents for cell function. For instance, without one of the organelles, the mitochondria, more than 95 per cent of the cell's energy release from nutrients would cease immediately. The most important organelles and other structures of the cell are shown in Figure...

Stages of Recovery from Acute Myocardial Infarction

The upper left part of Figure 21-8 shows the effects of acute coronary occlusion in a patient with a small area Top, Small and large areas of coronary ischemia. Bottom, Stages of recovery from myocardial infarction. Top, Small and large areas of coronary ischemia. Bottom, Stages of recovery from myocardial infarction. of muscle ischemia to the right is shown a heart with a large area of ischemia. When the area of ischemia is small, little or no death of the muscle cells may occur, but part of...

Hormone Secretion Transport and Clearance from the Blood

Onset of Hormone Secretion After a Stimulus, and Duration of Action of Different Hormones. Some hormones, such as norepinephrine and epinephrine, are secreted within seconds after the gland is stimulated, and they may develop full action within another few seconds to minutes the actions of other hormones, such as thyroxine or growth hormone, may require months for full effect. Thus, each of the different hormones has its own characteristic onset and duration of action each tailored to perform...

Increased Blood Volume Caused by Increased Capacity of Circulation

Any condition that increases vascular capacity will also cause the blood volume to increase to fill this extra capacity. An increase in vascular capacity initially reduces mean circulatory filling pressure (see Figure 29-12), which leads to decreased cardiac output and decreased arterial pressure. The fall in pressure causes salt and water retention by the kidneys until the blood volume increases sufficiently to fill the extra capacity. For example, in pregnancy the increased vascular capacity...

Untreated Diabetes Mellitus And Respiratory Quotient

Carbohydrate Fuel Value per 100 Grams (Calories) 60.0 240 68.2 396 11.2 50 8.1 41 4.0 23 0.5 194 cent of the weight.Therefore, the fat of one pat of butter mixed with an entire helping of potato sometimes contains as much energy as the potato itself. Average Daily Requirement for Protein Is 30 to 50 Grams. Twenty to 30 grams of the body proteins are degraded and used to produce other body chemicals daily. Therefore, all cells must continue to form new proteins to take the place of those that...

Regulation of Energy Release from Triglycerides

Carbohydrates Are Preferred over Fats for Energy When Excess Carbohydrates Are Available. When excess quantities of carbohydrates are available in the body, carbohydrates are used preferentially over triglycerides for energy. There are several reasons for this fat-sparing effect of carbohydrates. One of the most important is the fol-lowing The fats in adipose tissue cells are present in two forms stored triglycerides and small quantities of free fatty acids. They are in constant equilibrium...

Hormonal Regulation of Protein Metabolism

Growth Hormone Increases the Synthesis of Cellular Proteins. Growth hormone causes the tissue proteins to increase. The precise mechanism by which this occurs is not known, but it is believed to result mainly from increased transport of amino acids through the cell membranes or acceleration of the DNA and RNA transcription and translation processes for protein synthesis. Insulin Is Necessary for Protein Synthesis. Total lack of insulin reduces protein synthesis to almost zero. The mechanism by...

Reason Why The Extracellular Fluid Can Be Measured Directly

From Guyton AC, Hall JE Human Physiology and Mechanisms of Disease, 6th ed. Philadelphia WB Saunders, 1997. From Guyton AC, Hall JE Human Physiology and Mechanisms of Disease, 6th ed. Philadelphia WB Saunders, 1997. principle can be used to calculate total body water (Table 25-3). Another substance that has been used to measure total body water is antipyrine, which is very lipid soluble and can rapidly penetrate cell membranes and distribute itself uniformly throughout the intracel-lular and...

Conduction of Sound from the Tympanic Membrane to the Cochlea

Figure 52-1 shows the tympanic membrane commonly called the eardrum and the ossicles, which conduct sound from the tympanic membrane through the middle ear to the cochlea the inner ear . Attached to the tympanic membrane is the handle of the malleus. The malleus is bound to the incus by minute ligaments, so that whenever the malleus moves, the incus moves with it. The opposite end of the incus articulates with the stem of the stapes, and the faceplate of the stapes lies against the membranous...

Hormonal Control of Tubular Reabsorption

Precise regulation of body fluid volumes and solute concentrations requires the kidneys to excrete different solutes and water at variable rates, sometimes independently of one another. For example, when potassium intake is increased, the kidneys must excrete more potassium while maintaining normal excretion of sodium and other electrolytes. Likewise, when sodium intake is changed, the kidneys must appropriately adjust urinary sodium excretion without major changes in excretion of other...

Central Nervous System Synapses

200 300 Synaptic Cleft

Every medical student is aware that information is transmitted in the central nervous system mainly in the form of nerve action potentials, called simply nerve impulses, through a succession of neurons, one after another. However, in addition, each impulse 1 may be blocked in its transmission from one neuron to the next, 2 may be changed from a single impulse into repetitive impulses, or 3 may be integrated with impulses from other neurons to cause highly intricate patterns of impulses in...

Synthesis and Secretion of Adrenocortical Hormones

Adrenal Cortex Secretes

The Adrenal Cortex Has Three Distinct Layers. Figure 77-1 shows that the adrenal cortex is composed of three relatively distinct layers 1. The zona glomerulosa, a thin layer of cells that lies just underneath the capsule, constitutes about 15 per cent of the adrenal cortex. These cells are the only ones in the adrenal gland capable of secreting significant amounts of aldosterone because they contain the enzyme aldosterone synthase, which is necessary for synthesis of aldosterone. The secretion...

General Design of the Nervous System

Somatosensory Axis Nervous System

Central Nervous System Neuron The Basic Functional Unit The central nervous system contains more than 100 billion neurons. Figure 45-1 shows a typical neuron of a type found in the brain motor cortex. Incoming signals enter this neuron through synapses located mostly on the neuronal dendrites, but also on the cell body. For different types of neurons, there may be only a few hundred or as many as 200,000 such synaptic connections from input fibers. Conversely, the output signal travels by way...

Adjustments of the Infant to Extrauterine Life

Fetal Circulation

The most obvious effect of birth on the baby is loss of the placental connection with the mother and, therefore, loss of this means of metabolic support. One of the most important immediate adjustments required of the infant is to begin breathing. Cause of Breathing at Birth. After normal delivery from a mother who has not been depressed by anesthetics, the child ordinarily begins to breathe within seconds and has a normal respiratory rhythm within less than 1 minute after birth. The promptness...

Functional Organization of the Human Body and Control of the Internal Environment

The goal of physiology is to explain the physical and chemical factors that are responsible for the origin, development, and progression of life. Each type of life, from the simple virus to the largest tree or the complicated human being, has its own functional characteristics. Therefore, the vast field of physiology can be divided into viral physiology, bacterial physiology, cellular physiology, plant physiology, human physiology, and many more subdivisions. Human Physiology. In human...

Physiology of Deep Sea Diving and Other Hyperbaric Conditions

When human beings descend beneath the sea, the pressure around them increases tremendously. To keep the lungs from collapsing, air must be supplied at very high pressure to keep them inflated. This exposes the blood in the lungs also to extremely high alveolar gas pressure, a condition called hyper-barism. Beyond certain limits, these high pressures can cause tremendous alterations in body physiology and can be lethal. Relationship of Pressure to Sea Depth. A column of seawater 33 feet deep...

Effects of Low Oxygen Pressure on the Body

Barometric Pressures at Different Altitudes. Table 43-1 gives the approximate barometric and oxygen pressures at different altitudes, showing that at sea level, the barometric pressure is 760 mm Hg at 10,000 feet, only 523 mm Hg and at 50,000 feet, 87 mm Hg. This decrease in barometric pressure is the basic cause of all the hypoxia problems in high-altitude physiology because, as the barometric pressure decreases, the atmospheric oxygen partial pressure decreases proportionately, remaining at...

Multiple Functions of the Kidneys in Homeostasis

Most people are familiar with one important function of the kidneys to rid the body of waste materials that are either ingested or produced by metabolism. A second function that is especially critical is to control the volume and composition of the body fluids. For water and virtually all electrolytes in the body, the balance between intake (due to ingestion or metabolic production) and output (due to excretion or metabolic consumption) is maintained in large part by the kidneys. This...