Biochemical Interactions Of Actin And Myosin

The myosin molecule is an adenosine triphosphatase (ATPase), and adenosine triphosphate (ATP) is required for crossbridge cycling in intact muscle. Thus, muscle contraction requires energy expenditure. Actin and myosin can be extracted and purified. If purified striated muscle myosin is dissolved under the ionic conditions found in muscle cells, it exhibits a low level of ATPase activity. Upon addition of striated muscle actin, FIGURE 4 The events during a crossbridge cycle. First, activated...

Pivotal Role Of Calcium

Whether a muscle is contracting or relaxed depends on the level of cytosolic calcium available to interact with the regulatory proteins. In relaxed muscle, the level of free cytosolic calcium (calcium that is not bound to other structures such as sarcoplasmic reticulum, mitochondria, or nuclei) is low (< 10-7 M). Upon stimulation of the muscle, the calcium level increases into micromolar or higher ranges to initiate contraction. In striated muscle, calcium binds directly to troponin C of the...

Other Blood Volumerelated Mechanisms Involved In Blood Pressure Regulation

Although the kidneys play a dominant role in restoring blood pressure to normal values over the long term, there are other blood volume-related mechanisms that can contribute to arterial pressure regulation. Two notable mechanisms that become activated within minutes to hours after a pressure change and whose effects can last for days are (1) the capillary fluid shift mechanism and (2) the stressrelaxation mechanism. The former mechanism involves a role for capillary hydrostatic pressure in...

Acth

FIGURE 16 Hormonal interactions that regulate ACTH secretion by pituitary corticotropes. CRH, corticotropin releasing hormone AVP, arginine vasopressin AC, adenylyl cyclase PLC, phospholipase C ATP, adenosine triphosphate cAMP, cyclic adenosine monophosphate PKC, protein kinase C DAG, diacylglycerol IP3, inositol trisphosphate PKA, protein kinase A CREB, cyclic AMP response element binding protein AP-1, activator protein-1 POMC, pro-opiomelanocortin. in the anterior pituitary. These effects are...

Organization Of The Spinal Cord

To better understand somatotopic and modality-specific arrangements, it is helpful to review the general organization of the spinal cord (Figs. 1 and 2). Dorsal roots carrying sensory information and ventral roots transmitting motor signals occur in left and right pairs attached at 30 regular intervals along the spinal cord. Each point of attachment establishes a separate spinal segment. Rootlets from individual segments merge just distal to the dorsal root ganglia to form spinal nerves, which...

Blood Flow Velocities And Pressures In The Renal Vasculature

The glomerulus is a unique structure designed to produce rapid ultrafiltration of fluid from the plasma across the glomerular capillary endothelium and into FIGURE 1 Scanning electron micrograph showing a vascular cast of a glomerular capillary tuft and its associated afferent arteriole (AA) and efferent arteriole (EA). Within the glomerular tuft smaller capillaries are seen interconnecting larger loops. (Electron micrograph courtesy of Dr. Andrew P. Evan, Indiana University Medical Center,...

Additional Complexities

The conceptual approach to the sympathetic and parasympathetic divisions presented here is consistent with the presentation of this topic in most general textbooks and forms the basic foundation underlying much of autonomic pharmacology however, this foundation omits many basic mechanisms that function in autonomic ganglia. For example, traditionally, sympathetic ganglia have been thought to function primarily as relays in which neural information coming from the spinal cord via preganglionic...

Neural Integration In The Vasomotor Center

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

Body Fluid Compartments And Their Contacts With The Outside World

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

Synaptic Transmission In The Central Nervous System

The study of synaptic transmission in the central nervous system (CNS) is both an opportunity to learn more about the diversity and richness of mechanisms underlying this process and an opportunity to learn how some of the fundamental signaling properties of the nervous system, such as action potentials and synaptic potentials, work together to process information and generate behavior. One of the simplest behaviors controlled by the central nervous system is the knee-jerk or stretch reflex....

Interactions Of Responding Systems

Maintaining the integrity of the internal environment or successfully meeting an external challenge typically involves the coordinated interplay of several physiologic systems and the integration of multiple hormonal signals. Solutions to physiologic problems require integration of a large variety of simultaneous events that together may produce results that are greater or less than the simple algebraic sum of the individual hormonal responses. In the following section, we consider some of the...

Descending Motor Tracts In The Spinal Cord

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

Glucosefatty Acid Cycle

The self-regulating interplay between glucose and fatty acid metabolism is called the glucose-fatty acid cycle. This cycle constitutes an important biochemical mechanism for limiting glucose utilization when alternative substrate is available, and conversely limiting the consumption of stored fat when glucose is available. Fatty acids that are produced in adipose tissue in an ongoing cycle of lipolysis and reesterification may either escape from fat cells to become the free fatty acids, or they...

Pressures And Resistances In The Cardiovascular System

The resistance to blood flow differs at each level in the vasculature. Resistance in the aorta and the network of large conducting arteries is minimal because of their large radii. On the other hand, resistance is quite high in the arteriolar network because of the small radius of each vessel, even though there are many arterioles arranged in parallel. This illustrates the major importance of vessel radius. The capillaries offer much less resistance than the arterioles. Although the radius of...

Overview Of The Peripheral Nervous System

The peripheral nervous system arises from specialized cells (neural crest cells) located along the lateral edges of the neural plate (see Fig. 1). These cells bud off and become separated from the neural tube as it forms. Some groups of neural crest cells migrate to form a linear array of dorsal root ganglia located adjacent to the lateral borders of the spinal cord. These cells function as sensory

Mechanical Response Of Smooth Muscle In Vivo

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

The Heart Is An Example Of A Reciprocating Pump

The heart can be classified as a simple reciprocating pump. The mechanical principles of a reciprocating pump are illustrated in Fig. 1. The pumping chamber has a variable volume and input and output ports. A one-way valve in the input port is oriented such that it opens only when the pressure in the input chamber exceeds pressure within the pumping chamber. Another one-way valve in the output port opens only when pressure in the pumping chamber exceeds the pressure in the output chamber. In...

Other Neural Reflexes Involved With Blood Pressure Regulation

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

Mechanical Response Of Smooth Muscle In Vitro

FIGURE 10 (A) Length-force relationship for a smooth muscle. The solid line indicates active force, and the dashed line indicates passive force. Length is expressed as a fraction of optimal length (Lo). (B) Afterload-velocity relationship for a smooth muscle. Note that the general shapes of these relationships are the same as for skeletal muscle. FIGURE 10 (A) Length-force relationship for a smooth muscle. The solid line indicates active force, and the dashed line indicates passive force....

Cellular Circuits Of The Cerebellum

The cellular anatomy of the cerebellar cortex is a relatively simple, stereotyped arrangement with the same basic pattern repeating across all divisions (Fig. 4). One output neuron, the Purkinje cell, projects to cerebellar nuclei, and there are two inputs. Direct input is provided A. General motor loop of the cerebral cortex - basal ganglia B. General motor loop of the cerebral cortex - cerebellum to restricted area of cerebral cortex to restricted area of cerebral cortex to restricted area of...

Physiological Signals

Cells modify their activity in response to information received from their immediate environment, including such physical signals as light, heat, distortion of their surfaces by stretching or compression, and a vast array of chemical signals that may originate in the external environment or in other cells. Chemical signals are the most common form of information transfer that cells use to communicate with each other. Chemical signals may be simple substances such as ions, metabolites, or...

Clinical Note

Creatinine Balance and the Plasma Creatinine Concentration Consider the following hypothetical and idealized example to understand why a patient with reduced renal function remains in creatinine balance, but with a higher plasma creatinine concentration. An 80-kg patient has a normal metabolism and diet and produces 1.8 g of creatinine per day. He then undergoes a uninephrectomy to remove a renal carcinoma. Presume that after the unine-phrectomy the function of his remaining kidney is unchanged...

Localization Of Sound

Location of the source of sound plays a large role in central processing in the auditory system. Localization of sound along the vertical axis can be achieved using input from only one ear. The folds and bulges in the structure of the outer ear apparently produce reflections of sound waves as they enter the auditory canal. The lack of symmetry of the pinna allows for different echoing effects of sounds based on their angle of entry along a vertical plane. Sound entering the ear from below will...

The Olfactory Cortex

Mitral cells and tufted cells send central processes within the lateral olfactory tract to the primary olfactory cortex located on the inferior surface of the temporal lobe. The neurotransmitters utilized in this pathway appear to be excitatory neuropeptides and perhaps amino acids such as glutamate and aspartate. Mitral cells release cholecystokinin tufted cells release corticotropin-releasing hormone. This relatively simple sensory pathway is unusual in that it is the only sensory system...

Physiologic Effects Of Thyroid Hormones

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

Regulation Of Blood Flow

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

Chloride Absorption And Bicarbonate Secretion By The Intestinal Tract

Chloride Absorption

FIGURE 4 Cellular model for Cl absorption coupled to HCO secretion. The mechanisms responsible for H+ and Cl exit from the cell across the basolateral membrane are unclear. FIGURE 4 Cellular model for Cl absorption coupled to HCO secretion. The mechanisms responsible for H+ and Cl exit from the cell across the basolateral membrane are unclear. Chloride absorption by the small and large intestines involves both paracellular and transcellular routes. The active absorption of Na + by mechanisms a...

Ss

7th Cervical Spinal Cord

FIGURE 1 Organization and internal structure of the spinal cord. Pairs of spinal nerves leave the vertebral column through spaces between the vertebra. These nerves are classified by the region of the body they innervate cervical, thoracic, lumbar, or sacral. (A) Lateral and (B) dorsal views of the entire spinal cord. The spinal cord is shown in blue, and spinal neurons are in black. Note that the spinal cord is shorter than the vertebral column, leaving a space at the caudal end of the...

Calcitonin

Pka Hormone Secretion

Calcitonin is sometimes also called thyrocalcitonin to describe its origin in the parafollicular cells of the thyroid gland. These cells, which are also called C cells, occur singly or in clusters in or between thyroid follicles. They are larger and stain less densely than follicular cells in routine preparations (Fig. 12). Like other peptide hormone-secreting cells, they contain membrane-bound storage granules. Parafollicular cells arise embryologi-cally from neuroectodermal cells that migrate...

Venous Pressure Is Reciprocally Related To Arterial Pressure

Venous Capactiance

Venous return refers to the amount of blood flowing back to the heart per unit of time. At steady state, venous return and cardiac output must be equal. Because the atria lack valves, their contraction contributes little to diastolic filling and blood flows into the heart passively as a result of the pressure in the great veins. Thus, systemic venous pressure can be considered to be the filling pressure for the right ventricle. To develop a conceptual understanding of what affects venous...

Tpd

Biosynthesis, secretion, metabolism, 691 Ca2+ regulation, 680, 698f cells of origin, 691 physiologic actions, 691-693 in pig plasma, 694f secretion regulation, 693 Calcitonin gene related peptide characteristics, 691 mRNA splicing, 692f Calcitriol, see 1,25-Dihydroxycholecalciferol Calcitropic hormones hypercalcemic challenge response, 698 hypocalcemic challenge response, 698 Calcium in actin-myosin interactions, 138-139 excitation-contraction coupling, 182-183 parathyroid glands and hormone,...

Arterial Pressure

Arterial blood pressure increases during exercise, but the increase is much greater in isometric than in dynamic exercise. During isometric exercise, the blood vessels are clamped shut by sustained contractions, and resistance increases. This leads to anaerobic metabolism and strong stimulation of the muscle chemoreflex. Without the benefits of local vasodilation in isometric muscle contraction, the net effect is an increase total peripheral resistance and arterial pressure. During dynamic...

Cardiac Output34 35 45 24 1 8005

Distribution Cardiac Output

15 FIGURE 4 Distribution of cardiac output during rest and maximal exercise, when cardiac output increases from 5 to 25 L min. (Adapted from Powers, SK, Howley, ET., Exercise physiol., 1997.) 15 FIGURE 4 Distribution of cardiac output during rest and maximal exercise, when cardiac output increases from 5 to 25 L min. (Adapted from Powers, SK, Howley, ET., Exercise physiol., 1997.) vasoconstrict arterioles. Sympathetic activation of vasoconstrictor pathways occurs in response to a central...

The Emotional Reward Pathway

Papez Pathway

Experimental studies designed to localize specific circuits and identify underlying cellular mechanisms responsible for emotional perception and emotionally driven behavior are particularly challenging. By comparison, sensory and motor pathways are much more amenable to standard techniques of experimental examination. One obvious problem is that the emotional state of experimental animals is difficult to assess. One type of animal behavior experiment has shown that rats will repeatedly...

Characteristics Of Gastrointestinal Peptides

The GI peptides regulate many different functions water and electrolyte secretion from the stomach, pancreas, liver, and gut enzyme secretion of the stomach and pancreas and contraction and relaxation of the smooth muscle of the stomach, small and large bowel, various sphincters, and gall bladder. These peptides also regulate the release of GI peptides and some other endocrines, such as insulin, glucagon, and calcitonin. Some GI peptides have trophic effects, regulating the growth of the...

Overview

Mammalian survival in a cold, hostile environment demands an uninterrupted supply of metabolic fuels to maintain body temperature, to escape from danger, and to grow and reproduce. A constant supply of glucose and other energy-rich metabolic fuels to the brain and other vital organs must be available at all times despite wide fluctuations in food intake and energy expenditure. Constant availability of metabolic fuel is achieved by storing excess carbohydrate, fat, and protein principally in...

Info

FIGURE 7 Ventilatory response to hypoxia plotted as a function of Pao2 ( Pao2 in these normal subjects). Nonisocapnic curve Paco2 decreases when hypoxia stimulates increases in ventilation. Normo-capnic curve Hypoxic ventilatory response is increased if Paco2 is held constant, by adding CO2 to inspired gas. Hypercapnic curve The ventilatory response to increased Paco2 and decreased Pao2 is greater than the sum of the individual stimuli, as explained in the text. (After Loeschke et al, Pflug...

Adaptation to a Hot Environment

When exposed acutely to a hot environment, the hypo-thalamic integrative center acts as described earlier to increase heat loss by causing vasodilation and sweating. Both mechanisms can increase heat output from the body as long as the ambient temperature is below the body core temperature however, when the ambient temperature is higher, the body is constantly gaining heat by radiation and conduction, and the only means of effecting a net heat loss to match the rate of heat production is by...

Excitation Originates Within The Heart Muscle Cells

Larynx Diagram

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

Nad

To motor neurons innervation extensor muscles FIGURE 5 Central vestibular pathways. (A) Position of the vestibular nuclei in a dorsal view of the brain with the cerebral cortex removed and the cerebellum rendered transparent. (B) Major connections of the vestibular nuclei. (Left) Superior and medial vestibular nuclei (light blue). The main input is from the semicircular canals. to the unopposed excitatory drive of the vestibular nucleus. Under the constant stimulation from motor neurons,...

Lhg

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

Endplate Potential

It is possible to study various aspects of chemical synaptic transmission in a reduced preparation. One can dissect a skeletal muscle cell (with its intact neural innervation) from an animal and place it in an experimental solution, where it can remain viable for long periods of time (Fig. 4). The postsynaptic muscle cell is impaled with a microelectrode to record potentials in the muscle cell, and the motor axon is stimulated to initiate action potentials in the axon. Figure 5A illustrates a...

The Organ Of Corti

Auditory hair cells are arranged within a structure called the organ of Corti that rests on the basilar as frequency of vibration in hertz (cycles per second.) Doubling the frequency raises the pitch one octave. (C) Pressure oscillations are plotted for these notes over a 7.8-ms interval. Because sound travels 340 m s in air, one can calculate the wavelength as wavelength (meters cycle) 340 m s frequency (Hz). Very low C is produced by a 64-Hz vibration, and only half a cycle occurs in 7.8 ms....

C

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

Regulation Of Cardiac Output

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

Key Points

Conscious movement is initiated by upper motor neurons in an area of the frontal cortex designated as MI. Pyramidal cells in the MI issue motor commands based on input from the adjacent motor association area designated as MII, as well as from prefrontal cortex, motor nuclei in the thalamus, and primary (SI) and association (SII) sensory cortex. The firing rate of an individual pyramidal cell correlates with the force of the resulting muscle contraction the average firing rate of a given...

Neurocrines

At first, all GI peptides were believed to originate from endocrine cells. Powerful cytochemical techniques for the localization of peptides, however, have shown that many were located in nerves throughout the mucosa and smooth muscle of the gut. Currently, three peptides are known to function physiologically in the gut as neurocrines (Table 4). Pancreatic bicarbonate secretion Pancreatic enzyme secretion Inhibits Gastric secretion Gastric emptying Stimulates a Parentheses indicate an item of...

Lymphatic Drainage System

All of the fluid and protein that normally accumulate in the interstitial compartment as a consequence of capillary filtration are efficiently removed and carried back to the bloodstream via the lymphatic system. It is estimated that for a 70-kg man, the lymphatics return nearly 3 L of fluid and approximately 120 g of protein to the bloodstream every 24 hr. Because the recycling of plasma proteins is essential for maintenance of the normal oncotic pressure gradient between plasma and...

Integrated Actions Of Metabolic Hormones

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

An Accessory Pathway Can Shorten The Pr Interval

Occasionally, a muscle bridge exists between the atria and ventricles as a congenital defect. This is termed an accessory pathway which can activate the ventricles before the signal can traverse the AV node. In this case the PR interval will be abnormally short (less than 0.12 sec). This condition, termed Wolff-Parkinson-White syndrome, puts the patient at risk because he or she now lacks the long refractory period of the AV node. Should an atrial arrhythmia such as atrial fibrillation or...

Morphology

The human thyroid gland is located at the base of the neck and wraps around the trachea just below the cricoid cartilage (Fig. 1). The two large lateral lobes that comprise the bulk of the gland lie on either side of the trachea and are connected by a thin isthmus. A third structure, the pyramidal lobe, which may be a remnant of the embryonic thyroglossal duct, is sometimes also seen as a finger-like projection extending headward from the isthmus. The thyroid gland in the normal human being...

Uzi

Telencephalon cerebral cortex basal ganglia Diencephalon thalamus pineal hypothalamus FIGURE 2 Growth and folding of the rostral portion of the neural tube. Human embryos at the three-vesicle stage at about 28 days (A) and the five-vesicle stage at about 38 days (B). Dorsal views of the unfolded embryos show the expansion of the neural tissue during development. Lateral views of the embryos show the three bends or flexures that occur as the embryo develops. The organization of the adult brain...

Hormonal Interactions During Exercise

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

Gastrointestinal Smooth Muscle

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

The Golgi Tendon Organ

The second type of specialized sensory receptor found in muscle tissue is the Golgi tendon organ. Its function is to signal the amount of tension generated by muscle contraction. The end organ is composed of braided collagen fibers within a capsule approximately 1 mm in length and 0.1 mm in diameter (Fig. 3). It is innervated by a free nerve ending classified as Ib, slightly smaller than Ia fibers of the muscle spindle. Golgi tendon organs are located at junctions between muscles and their...

Secretory Processes In The Proximal Straight Tubule

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

Absolute and Relative Refractory Periods

The absolute refractory period refers to that period of time after the initiation of one action potential when it is impossible to initiate another action potential no matter what the stimulus intensity used. The relative refractory period refers to that period of time after the initiation of one action potential when it is possible to initiate another action potential but only with a stimulus intensity greater than that used to produce the first action potential. At least part of the relative...

Yes

FIGURE 17 Mechanisms inhibiting gastric acid secretion. Blanks indicate actions that either do not occur or are not significant physiologically. FIGURE 17 Mechanisms inhibiting gastric acid secretion. Blanks indicate actions that either do not occur or are not significant physiologically. additional enzyme from pepsinogen. At an intragastric pH of 2 or less, the conversion of pepsinogen to pepsin is almost instantaneous. Pepsin begins the digestion of protein by splitting interior peptide...

Olfactory Receptors

Small, paired patches of olfactory epithelium, each approximately 2 cm2 in size, are located within the uppermost levels of the nasal cavities (Fig. 1). They are arranged in a horizontal line just below the level of the eyes. Three major cell types are present olfactory receptor neurons, supporting or sustentacular cells, and basal cells, which are the stem cells for production of new receptor cells. Interspersed among the cells of the olfactory epithelium are Bowman's glands, which produce a...

Motor Neurons For Head And Neck Muscles

Neuronal Circuit Patterns

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

Mechanism Of Thyroid Hormone Action

As must already be obvious, virtually all cells appear to require optimal amounts of thyroid hormone for normal operation, even though different aspects of cellular function may be affected in different cells. Thyroid hormones are quite hydrophobic and may either diffuse across the cell membrane or enter target cells by a carrier-mediated transport process. T3 formed within the target cell by deiodination of T4 appears to mix freely with T3 taken up from the plasma and to enter the nucleus,...

Regulation of Sweat Production

The loss of heat by evaporation is regulated by controlling the rate of sweat production by the eccrine sweat glands. These glands are innervated by sympathetic cholinergic nerves, the firing of which can be stimulated by circulating epinephrine and norepinephrine. The latter hormones produce the sweating associated with stress and anxiety. The rate of sweat production can vary from 0 to about 1.5 L hr in an individual who is not acclimatized and is exercising in a hot environment. When the air...

The Vestibulocerebellum

The vestibulocerebellum represents a second functional division of the cerebellum. Also called the archicerebel-lum, it is considered the phylogenetically oldest portion of the cerebellum, and it encompasses a relatively small proportion of the main structure. It resides in the floc-culonodular lobe, separated from the body of the cerebellum by the posterolateral fissure. This division is involved in a relatively simple motor loop formed by reciprocal innervation with vestibular nuclei. The...

Oxx

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

Dlh Mi

Renal Tubular Acidosis Types

Descending limb of the loop of Henle (DLH) by the osmotic gradient and there is some urea diffusion from the medullary interstitium into the DLH. NaCl diffuses passively down its concentration gradient from the thin ascending limb of the loop of Henle into the medullary interstitium, leaving water and urea behind because they are impermeable. Thus, the tubular fluid flowing to the thick ascending limb (TAL) has the same urea concentration as at the tip of the medulla, but the NaCl concentration...

Rif

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

Transport In The Distal Convolution And Collecting Duct

As discussed in Chapter 23 (see Fig. 5 in that chapter), the distal convolution, i.e., the portion of the nephron between the macula densa and the beginning of the cortical collecting duct, consists of the distal convoluted tubule and the connecting tubule. The initial portion of the distal convolution is a very short continuation of the thick ascending limb, which is followed by the abrupt appearance of distal tubule cells (DCT cells), which have highly amplified basolateral membranes, as well...

Pancreatic Secretion

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

Po4j

Activation of protein kinase A accounts for most of the cellular actions of cAMP (upper portion of the figure). Inactive protein kinase consists of two catalytic units (C), each of which is bound to a dimer of regulatory units (R). When two molecules of cyclic AMP bind to each regulatory unit, active catalytic subunits are released. Phosphorylation of enzymes, ion channels, and transcription factors of the CREB family activates or inactivates these proteins. Cyclic...

Integration Of Simultaneous Signals

As must already be quite obvious, binding of a signal molecule to its receptor sets in motion intracellular signaling pathways that are both intricate and complex. Cells express receptors for multiple signaling molecules and are simultaneously bombarded with excitatory, inhibitory, or a conflicting mixture of excitatory and inhibitory inputs from different agents whose signaling pathways may run in parallel, intersect, coincide, diverge, and perhaps intersect again before influencing the final...

Clinical Note continued

Have revealed some important insights about the exact causes of hypoxemia in certain lung diseases, as well as how they respond to treatment. Diffuse interstitial pulmonary fibrosis is a thickening of the alveolar walls with collagen and scarring in the interstitium. As expected, fibrosis decreases the diffusing capacity (Dlco) experiments hypox-emia in patients with fibrosis at rest can be explained by Va Q heterogeneity. Uneven scarring of the lungs results in local changes in compliance and...

Parturition

Hormone And Parturition

Pregnancy in the human lasts about 40 weeks. The process of birth, or parturition, is the expulsion of a viable baby from the uterus at the end of pregnancy and is the culmination of all the processes discussed in this and the previous two chapters. Studying the phenomenon of parturition has revealed a surprising array of strategies that have been adopted by different species, regulate parturition. Humans and the great apes have evolved mechanisms that appear to be unique, and the scarcity of...

Oxygen In Blood

Normal O2 concentration in arterial blood (Cao2) is about 20 mL dL. (The usual units for O2 and CO2 concentration in blood are mL dL, also called volume 1 mL dL 0.45 mmol L.) However, only 0.3 mL dL is physically dissolved gas normal arterial Po2 (PaO2) is 100 mm Hg and the physical solubility of O2 in blood is 0.003 mL (dL mm Hg) at 37 C. If arterial blood contained only dissolved O2, then cardiac output would have to be 100 L min to deliver enough O2 to the tissues for a normal metabolic rate...

Changes In Gt Balance

The three systemic mechanisms for regulating Na+ excretion just discussed (changes in GFR, plasma aldosterone levels, and circulating natriuretic factors) may not be responsible for the rapid changes in sodium excretion in response to sudden alterations in ECF volume. Changes in GFR hold promise as potential modulators of Na+ excretion, but they are extremely difficult to demonstrate. Aldosterone appears to be an appropriate hormone for the day-to-day regulation of Na+ excretion over a...

Examples

Toilet Space Requirements

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

Metabolism Of Thyroid Hormones

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

Diffusion Of Electrolytes

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

Bile Secretion And Gall Bladder Function

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

Movement Of Material Through The Esophagus

Decorticate Decerebrate Posturing

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

Functional Anatomy Of The Kidney

Medicl Physiology Terms Diagram Dolphin

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

Regional Blood Flow

Blood flow is redistributed during exercise away from vegetative organs and toward actively exercising muscles by both intrinsic (local) and extrinsic (reflex) mechanisms. In isometric exercise, muscle blood flow may actually decrease with compression of arteries and veins in contracted muscles. In contrast, active hyperemia, or an increase in blood flow, occurs in muscles during dynamic exercise. Arterioles dilate in exercising muscles in direct response to local metabolic changes (decreased...

Right Heart And Left Heart Pump As One Unit

In our analysis we have considered systemic venous pressure to be the filling pressure of the heart. Systemic venous pressure is, of course, the filling pressure only for the right heart. In actuality, the output of the left heart will have to equal the output of the right heart since they are in series. If the left heart's output were to lag behind that of the right, blood would accumulate in the pulmonary veins and raise filling pressure to the left heart. The increase in stroke volume would...

Jej

Key D, direct effect I, indirect effect. aGrowth hormone promotes protein synthesis and hence decreases availability of amino acids for ureogenesis. Key D, direct effect I, indirect effect. aGrowth hormone promotes protein synthesis and hence decreases availability of amino acids for ureogenesis. FIGURE 6 Normal glucose tolerance following ingestion of 100 g of glucose in a subject with a growth hormone-secreting pituitary tumor is accompanied by an exaggerated increase in plasma insulin...

Functional Anatomy Of The Microcirculation

Figure 1 illustrates an extensive capillary network and its associated structures (arterioles and venules) that constitute the microcirculation. Blood enters the microcirculation through arterioles, which are surrounded by a thick, continuous layer of smooth muscle. Contraction of smooth muscle reduces the internal diameter of this microvessel and consequently increases the resistance to blood flow in the entire vascular bed. This feature makes the arteriole the major resistance element in the...

The Muscle Spindle

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

Tfr

FIGURE 10 Model for the absorption of iron by the small intestine. TFR, transferrin receptor. in the form of bone, and calcium ions are essential as second messengers and metabolic regulators as well as for the excitation process of skeletal and cardiac muscle. Calcium absorption is regulated by vitamin D and parathyroid hormone and is matched to the dietary intake, urinary excretion, and plasma levels of the ion. The regulation of calcium homeostasis and the mechanisms involved are covered in...

Salt And Water Reabsorption In The Proximal Tubule

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

P

Pcr, see Plasma creatinine concentration Pacemaker cells autonomic nerve modulation, 185-186 heart rate control, 185 Pacesetter potentials, gastric motility, 487 Pacinian corpuscles characteristics, 789, 793f location, 790 PAG, see Periaqueductal gray matter PAH, see Para-aminohippurate Pain neuronal pathways, 804f referred pain, 796, 796f regulation, 794 sensory receptors, 790 Pain-gating mechanism, 794 Pain receptors, 793-795 Paired helical filaments, in Alzheimer's disease, 917...

Large Intestinal Motility

Approximately 7-10 L of ingested or secreted water enters the small intestine during a 24-hr period. Of this amount, about 600 mL reach the colon. The motility patterns of the large intestine are organized so that all but about 100 mL are absorbed. The remaining fecal material is then stored until it can be evacuated conveniently. Structure and Innervation of the Large Intestine Beginning from the ileocecal junction, the large intestine is anatomically divided into the cecum the ascending,...

Autoregulation

Autoregulation Examples

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

Overview Of The Gustatory System

The elemental role of the gustatory system is to distinguish between food and potential toxins. Two components are required to accomplish this task (1) a detection system of receptor cells capable of responding to the great diversity of substances in the environment that might be ingested, and (2) neuronal pathways that refer taste information to appropriate cortical structures in order to elicit pleasant or unpleasant sensations. Pleasing sensations associated with food are necessary to...

The Nigrostriatal Pathway

A third neuronal component associated with basal ganglia feedback loops is called the nigrostriatalpathway (Fig. 4). It projects from the substantia nigra to the caudate and putamen, and its effects are mediated by the neurotransmitter dopamine. In essence, dopamine facilitates the motor loop in two ways. First, it provides tonic, excitatory drive to the direct (stimulatory) pathway through the neostriatum, and, second, it inhibits the indirect (inhibitory) pathway. The additive effects of this...

Systolic Pressurevolume Area Predicts The Oxygen Consumption Of The Heart

Virtually all of the heart's energy is derived from oxidative metabolism. Substrate is primarily fatty acids and to a much lesser extent carbohydrates. As a result, a linear relationship exists between the heart's energy production and its oxygen consumption. Because most of the heart's energy expenditure goes into mechanical work, it is not surprising that there is a close correlation between the oxygen consumption of the heart and its mechanical activity. Figure 13 reveals this relationship....

Physiology Of The Anterior Pituitary Gland

There are six anterior pituitary hormones whose physiologic importance is clearly established. They include the hormones that govern the function of the thyroid and adrenal glands, the gonads, the mammary glands, and bodily growth. They have been called trophic or tropic from the Greek trophos, meaning to nourish,'' or tropic, meaning to turn toward.'' Both terms are generally accepted. We thus have, for example, thyro-trophin, or thyrotropin, which is also more accurately called...

Female Reproductive Tract

Mammalian Ovary

The adult human ovaries are paired, flattened ellipsoid structures that measure about 5 cm in their longest dimension. They lie within the pelvic area of the abdominal cavity attached to the broad ligaments that extend from either side of the uterus by peritoneal folds called the mesovaria. Both the gamete-producing and hormone-producing functions of the ovary take place in the outer or cortical portion. It is within the ovarian cortex that the precursors of the female gametes, the oocytes, are...

Extracellular Recording From a Single Axon

Extracellular Recordings Depolarization

To introduce the principles of extracellular recording, it is useful to begin with the simplest case the extracellular recording of activity from a single nerve axon. Figure 5 illustrates both the general strategy and typical results. Two metal electrodes, A and B, are placed in close proximity to an isolated nerve axon. They do not impale the axon but are very near its outside surface. The electrodes are connected to a suitable electronic amplifier that is designed so that the voltage...

Testing Bernsteins Hypothesis

How would one go about testing Bernstein's hypothesis If the membrane potential Vm is equal to the K equilibrium potential EK , one should be able to substitute the known outside and inside concentrations of K into the Nernst equation and determine the equilibrium potential EK , which should equal the measured membrane potential Vm . Furthermore, because of the logarithmic relationship in the Nernst equation, if the outside K concentration is artificially manipulated by a factor of 10, then the...

Estimation of Venous Pressure

Systemic venous pressure is relatively easy to estimate by observing the filling of the jugular veins. The external jugular veins in the neck can be visualized where they run from the clavicle to the angle of the jaw. The clavicle is 10 to 15 cm above the heart, and normally the venous pressure is not enough to support that large a column of blood. As a result, the jugular veins in the neck of a healthy person should be collapsed in the upright posture. As venous pressure rises, the jugular...

The Semicircular Canals

The relative position of the kinocilium establishes the functional polarity of the hair cell namely, which direction of movement excites the cell and which inhibits the cell. Directional sensitivity of each of the individual vestibular organs is determined by the specific orientation of hair cells within the organ and the overall shape of the organ. In the semicircular canals, hair cells are clustered in a thickened zone of epithelium, the ampullary crest. A gelatinous, diaphragm-like mass, the...

Innervation Of The Gastrointestinal Tract

Esophagus Enteric Neurons

Extrinsic innervation of the GI tract is provided by both the parasympathetic and sympathetic systems. Together with the enteric or intrinsic nervous system, they make up the autonomic nervous system. The innervation of the GI tract is referred to as autonomic because we are unaware of its activities and have no conscious control over the functions it regulates. Down to the level of the transverse colon, parasym-pathetic innervation to the GI tract is supplied by the vagus nerve. The pelvic...