Innervation Of The Gastrointestinal Tract

The Tract Innervated Autonomically

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...

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...

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...

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...

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...

Endothelial Mechanisms

Endothelial cells contribute to the regulation of arterial blood pressure by regulating vascular tone through activation or inactivation of various circulating vasoactive substances, and by producing numerous agents that can act locally and or systemically to affect vascular tone. Nitric oxide (NO) is a potent vasodilator that is produced in endothelial cells via the oxidation of L-arginine by the enzyme NO synthase. Inhibitors of NO synthase elicit a reduction in blood flow to some tissues and...

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...

Treatment of the Failing Heart

Treatment of heart failure is directed to correction of the two major problems associated with failure venous congestion and reduced cardiac output. Systemic venous congestion can cause renal and liver damage as well as discomfort. The threat of pulmonary edema from pulmonary congestion has already been discussed. Diuretics and reduced salt intake can reduce the accumulated blood volume and venous congestion even though these treatments may actually lower the filling pressure of the heart and...

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...

Training Muscle

Endurance training at submaximal levels of VO2 increases the oxidative capacity of muscle without causing muscle hypertrophy. Muscle size does not change but there are increases in the number of mitochondria and enzymes for fatty acid oxidation, the citric acid cycle, and the electron transport chain. Capillary density and myoglobin also increase to enhance O2 transport. Muscles must be activated during training to undergo these changes, so higher levels of VO2 are necessary to train...

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....

Synaptic Transmission At The Neuromuscular Junction

The chemical synapse from which most of our information about synaptic transmission has been derived is the synaptic contact made by a spinal motor neuron with a skeletal muscle cell. Figure 2 is a schematic diagram of some of the general features of this synapse. The myelinated axon of a motor neuron whose cell body is located in the ventral horn of the spinal cord innervates a number of individual muscle fibers (Fig. 2A). At each muscle fiber, the axon branches further and forms a series of...

Structure Of The Voltagegated Na Channel

The principal structural and functional unit of the voltage-gated Na+ channel consists of a single polypep-tide chain exhibiting four homologous domains (I-IV, Fig. 14), with each domain having six hydrophobic FIGURE 12 Schematic diagram of the apparatus used for singlechannel recording. A micropipette is positioned to touch the surface of the membrane. A tight seal develops, and the current flowing through individual channels can be monitored. FIGURE 12 Schematic diagram of the apparatus used...

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...

Biochemical Interactions Of Actin And Myosin

Smooth muscle myosin is also an adenosine triphos-phatase (ATPase), and energy is required for muscle contraction. Like skeletal muscle myosin, pure smooth muscle myosin exhibits little ATPase activity. Unlike skeletal muscle myosin, smooth muscle myosin ATPase activity is not increased upon addition of actin alone, unless one set of the myosin light chains is phosphory-lated. In smooth muscle cells, adenosine triphosphate (ATP) hydrolysis due to the cycling of phosphorylated myosin...

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...

Circulatory Shock Is Progressive

After World War II, Carl Wiggers simulated hemor-rhagic shock in dogs by connecting a large bottle to the femoral artery of an anesthetized dog with a length of flexible tubing. If the bottle was suspended 136 cm above the heart, the dog's blood pressure (100 mm Hg) would be just enough to push blood up the tubing to the reservoir but little would enter. If the reservoir was lowered to 54 cm above the heart, blood quickly flowed out of the dog and into the reservoir. This continued until enough...

The Filtration Barrier

Graph Glomerular Capillary

As discussed earlier, the process of glomerular filtration produces an ultrafiltrate of plasma, that is, a fluid that has approximately the same composition as the blood plasma but virtually no protein. It is estimated that in humans much less than 1 of the plasma albumin that enters the kidney via the renal artery is filtered at the glomerulus, and this small amount of filtered protein is reabsorbed by the proximal nephron. Only trace amounts of the larger globulins are filtered and...

Info

Arise primarily from efferent arterioles of juxtamedullary nephrons (see Chapter 23, Fig. 2). The average blood pressure in the peritubular capillaries is only 15-20 mm Hg. This is considerably lower than in the capillaries of other organs because the two series resistances of the afferent and efferent arterioles have dropped it. This lower pressure means that the sum of the Starling forces favors the uptake of water and solutes that have been reabsorbed by the renal tubules, which is the...

Gonadal Hormones

Awakening of the gonads at the onset of sexual maturation is accompanied by a dramatic acceleration of growth. The adolescent growth spurt, like other changes at puberty, is attributable to steroid hormones of the gonads and perhaps the adrenals. Because the development of pubic and axillary hair at the onset of puberty is a response to increased secretion of adrenal androgens, this initial stage of sexual maturation is called adrenarche. The physiological mechanisms that trigger increased...

Nad

FIGURE 17 Extraocular muscles and cranial nerves responsible for movements of right eye. (A) Extraocular muscles are controlled by three cranial nerves (III, IV, and VI). The levator palpebrae opens the eyelid and is innervated by cranial nerve III. (B) Horizontal gaze is controlled by paired contraction-relaxation of the medial rectus and lateral rectus muscles. (C) Vertical gaze is controlled by four muscles. Downward gaze is produced by inferior rectus and superior oblique muscles. Because...

General Features Of Energy Metabolism

In discussing how hormones regulate fuel metabolism, we consider first the characteristics of metabolic fuels and the intrinsic biochemical regulatory mechanisms on which hormonal control is superimposed. Glucose is readily oxidized by all cells. One gram yields about 4 Calories. The average 70-kg man requires approximately 2000 Calories per day and therefore would require a reserve supply of approximately 500 g of glucose to ensure sufficient substrate to survive 1 day of food deprivation. If...

Other Hormones Affecting Calcium Balance

In addition to the primary endocrine regulators of calcium balance discussed earlier, it is apparent that many other endocrine and paracrine factors influence calcium balance. Bone growth and remodeling involve a still incompletely understood interplay of local and circulating cytokines, growth factors and hormones including insulin-like growth factor-1, growth hormone (see Chapter 44), the cytokines interleukin 1 (see Chapter 40), interleukin 6, interleukin 11, TNFa, TGF , and doubtless many...

L

Opponent processing in the red - green system red-ON GC red-OFF GC green-ON GC green-OFF GC blue-ON GC active in short wavelengths blue-OFF GC active in long wavelengths red-ON GC red-OFF GC green-ON GC green-OFF GC FIGURE 16 Color-opponent receptive fields of ganglion cells and neurons in the blob regions of the V1 cortex. (A) Three types of cones contribute to blue yellow-opponent receptive fields in ganglion cells (GCs) and cells within blobs of cortical area V1. Excitatory input from...

Overall Regulation Of Blood Glucose Concentration

Despite vagaries in dietary input and large fluctuations in food consumption, the concentration of glucose in blood remains remarkably constant. Its concentration at any time is determined by the rate of input and the rate of removal by the various body tissues (Fig. 2).

Integrated Ventilatory Responses

Integrated ventilatory responses to changes in activity and the environment illustrate many important interactions between elements of the respiratory control system. Such interactions are typical in patients, and the physician needs to understand them to make an intelligent diagnosis and provide appropriate treatments. The most common stimulus to increase ventilation in healthy subjects is exercise. Relatively common problems in control of ventilation during sleep are described in the Clinical...

Clinical Note continued

The middle-aged working population, and can occur in 35-50 of some groups, such as diabetics, the morbidly obese, or the elderly (> 65 years of age). Snoring is a mild form of upper airway obstruction, where the soft palate vibrates during inspiration at 40-60 Hz and impedes airflow. Obstructive apneas can occur during all sleep stages, however, often they are longer and result in more severe hypoxemia during REM (rapid eye movement) sleep. REM sleep is also called active sleep and is the...

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...

Overview

The pituitary gland has usually been thought of as the ''master gland'' because its hormone secretions control the growth and activity of three other endocrine glands the thyroid, adrenals, and gonads. Because the secretory activity of the master gland is itself controlled by hormones that originate in either the brain or the target glands, it is perhaps better to think of the pituitary gland as the relay between the control centers in the central nervous system and the peripheral endocrine...

Roles Of Progesterone And Estrogens In Sustaining Pregnancy

As its name implies, progesterone is essential for maintaining all stages of pregnancy, and pharmacologic blockade of its actions at any time terminates the pregnancy. Progesterone sustains pregnancy by opposing the forces that conspire to increase uterine contractility and expel the fetus. One of these forces is physical stretch of the myometrium by the growing fetus. Stretch or FIGURE 8 Effects of estrogen on production of placental steroid hormones. By increasing uterine blood flow and...

Lactation

The mammary glands are specialized secretory structures derived from the skin. As the name implies, they are unique to mammals. The secretory portion of the mammary glands is arranged in lobules consisting of branched tubules, the lobuloalveolar ducts, from which multiple evaginations or alveoli emerge in an arrangement resembling a bunch of grapes. The alveoli consist of a single layer of secretory epithelial cells surrounded by a meshwork of contractile myoepithelial cells (Fig. 11) Many...

Adrenal Cortex

In all species thus far studied, the adrenal cortex is essential for maintenance of life. Insufficiency of adrenal cortical hormones (Addison's disease) produced by pathologic destruction or surgical removal of the adrenal cortices results in death within 1-2 weeks unless replacement therapy is instituted. Virtually every organ system goes awry with adrenal cortical insufficiency, but the most likely cause of death appears to be circulatory collapse secondary to sodium depletion. When food...

Metabolism

Adenosine triphosphate (ATP) provides the energy for muscle contraction, just as for other cellular functions. ATP can be generated most efficiently by oxidative phosphorylation, but it can also be generated by anaerobic glycolysis. Anaerobic glycolysis uses glucose or glycogen stores in muscle to generate ATP and is useful at the immediate onset of exercise and for short periods of time. The major muscle store of high-energy phosphate necessary to generate ATP from adenosine diphosphate (ADP)...

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...

Coordination Of Cellular Activity With Changing Demands Of The Internal And External Environment

Cells perceive a variety of chemical and physical factors as indicators of environmental change and respond to them in coordinated and characteristic ways. The final response, or output, of any specific cell and the signals, or inputs, to which it responds are determined by its particular differentiated state. Thus, a pancreatic beta cell perceives glucose and secretes insulin, a muscle cell perceives acetylcholine and contracts, and a retinal cell perceives light and stops releasing inhibitory...

Djh

FIGURE 11 Anti-mullerian hormone (AMH) signaling pathway. AMH binds to its specific primary receptor (I) which then forms a heterodimer with and phosphorylates the secondary signal transducing subunit (II). The activated receptor complex then catalyzes phosphor-ylation ofSmad proteins on serine and threonine residues, causing them to bind Smad 4, which carries them into the nucleus, where transcription of specific genes results in expression of an apoptotic program and resorption of the...

S

Characteristics, 833-835 function, 831 structure, 836f Sacral segment, spinal cord, 799 Saline solution, infusion in proximal tubule, inorganic composition, 500-501 ion concentrations, 500f Na+ K+-ATPase, 501 organic composition, 501 overview, 498 production, 497 transport mechanisms, 501f Salivary glands anatomy and innervation, 499-500 ducts, 499 regulation, 502f secretion regulation, 502 Salivon ion and water flux, 501f schematic diagram, 499f Salt 375-378 taste overview, 857 Salt-sensitive...

The Oculomotor System

The oculomotor system is comprised of the intrinsic and extrinsic muscles of the eye along with motor nuclei and higher cortical centers that serve to control the position of the eye as well as the shape of the lens and the size of the pupil. The main purpose of the system is to aid in vision by keeping the visual target focused on the fovea, the area ofcentral retina that has the highest visual acuity. Diplopia (double vision), blurred vision, or loss of depth perception can occur as a result...

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...

Regulation Of Testicular Function

Testicular function, as we have seen, depends on stimulation by two pituitary hormones, FSH and LH. Without them, the testes lose spermatogenic and steroi-dogenic capacities and either atrophy or fail to develop. Secretion of these hormones by the pituitary gland is driven by the central nervous system through its secretion of the gonadotropin-releasing hormone (GnRH), which reaches the pituitary by way of the hypophysial portal blood vessels (see Chapter 38). Separation of the pituitary gland...

Dvy

Q carrier Q) carrier Na+-K+ ATPase FIGURE 18 Cellular models of Na+-coupled co-transport (A) and countertransport (B). Q carrier Q) carrier Na+-K+ ATPase FIGURE 18 Cellular models of Na+-coupled co-transport (A) and countertransport (B). gradient in turn provides the energy for many Na+-coupled secondary active co- and countertransport processes. (The terms symport and antiport are sometimes employed to describe co- and countertransport processes, respectively.) THE PUMP-LEAK MODEL, THE ORIGIN...

Central Gustatory Pathways

Taste receptors synapse with dendritic elements of the primary afferent neurons of the gustatory pathway, causing the neurons to fire in response to appropriate stimuli above threshold levels. These afferent fibers represent the peripheral projection of the primary sensory neurons of the gustatory pathway, and they arise from cell bodies within three cranial nerve ganglia (Fig. 7). Afferent fibers within the facial nerve (cranial nerve VII) arise from the geniculate ganglia and innervate the...

Shock Is Caused by an Inadequate Cardiac Output

Action Potential Pain Flow Chart

The beginning student often erroneously believes that the heart is the sole determinant of cardiac output. In Chapter 14, we learned that the peripheral circulation also plays an important governing role in the circulation. The peripheral circulation controls the filling pressure of the heart as well as its afterload, two major determinants of the stroke volume. This interaction between the heart and the periphery is vividly illustrated by the shock syndrome. In its simplest form, circulatory...

Voltage Dependent Release of Neurotransmitter

One of the most interesting aspects of synaptic transmission is the mechanism by which an action potential in the presynaptic terminal triggers the release of the chemical transmitter substance. One possibility is that transmitter release is due to some aspect of the sequence of permeability changes underlying the action potential in the presynaptic terminal. The action potential is associated with a slight influx of Na+ and a slight efflux of K+. Perhaps in some way either the small influx of...

Development Of Brain Vesicles

The closed lumen of the neural tube is altered in shape as a result of enlargement of the three brain vesicles, particularly the telencephalon. As the cerebral hemispheres of the telencephalon increase in size, two lateral expansions of the lumen form the first and second (lateral) ventricles, connected to each other and to the third ventricle by a thin, Y-shaped midline channel called the foramen of Monro. Continued posterior and inferior expansion of the hemispheres eventually forces the...

Transport In The Thin And Thick Ascending Limb

When the tubular fluid turns the bend at the tip of the loop of Henle, it enters the thin ascending limb of the loop of Henle. At this point, the epithelial transport properties change dramatically. Both the thin and the thick regions of the ascending limb of the loop of Henle are water impermeable because of the absence of aquaporin water channels, and there is no significant transepithelial water flow. On the other hand, these regions avidly reabsorb NaCl and can remove 20-25 of the filtered...

Clinical Note

Lesions and Motor Reflex Abnormalities Specific lesions within the neuronal components of the somatic motor system can cause characteristic abnormalities in motor reflexes. Flaccid paralysis usually denotes the loss of peripheral nerve innervation. Without input from alpha motor neurons of the spinal cord, there is no voluntary movement of the muscle and no resistance to passive movement. No reflexes can be elicited, and atrophy of the muscle will be observed. Unlike components of the central...

Transmission Across Synapses

Transmission across synapses in the ANS is mediated by chemicals known as neurotransmitters. These chemicals are synthesized within the nerves and in most instances are stored in synaptic vesicles in the nerve endings. Upon activation of the nerve, nerve action potentials invade the nerve ending, causing the release of a portion of the stored neurotransmitter. Once released, the neurotransmitter binds to specific receptors located on postsynaptic structures. Only those cells that possess...

Overview Of Sensory Pathways

It is apparent from the descriptions given earlier that specific areas of brain, spinal cord, or peripheral nervous tissue are assigned specific functional roles based on their relative position with the nervous system (Fig. 5). A general rule for neurons might be stated, Where you are is what you are.'' However, the nervous system should not be viewed as a series of isolated modules with specified duties rather, it more correctly resembles A. Cross sections of the nervous system FIGURE 5...

Ovarian Hormones

The principal hormones secreted by the ovary are estrogens (estradiol-17fi and estrone) and progesterone. These hormones are steroids and are derived from cholesterol by the series of reactions depicted in Fig. 6. Their biosynthesis is intricately interwoven with the events of the ovarian cycle. In addition, the ovary produces a large number of biologically active peptides, most of which act within the ovary as paracrine growth factors, but at least two, inhibin and relaxin, are produced in...

Female Reproductive Tract

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...

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...

Excitation Of The Muscle Cell

All muscle cells have resting membrane potentials in the range of 70 to 90 mV. As in nerve, this potential is due to the presence of ionic concentration gradients (with K+ being greater intracellularly and Na+ greater extracellularly) and to the resting membrane being much more permeable to K+ than to Na+. Muscle cells are excitable due to the presence of voltage-dependent ion channels in their cell membranes. However, the type of channels present, the manner in which channels are activated,...

The Olfactory Bulb

Odorant receptors and associated second-messenger systems are primarily localized within the ciliary tufts of olfactory neurons. The tufts extend from the surface of the epithelial plate and are immersed in mucous. The cell body, located in deeper epithelial layers, has a single nonmyelinated axon that must pass through small holes in the cribriform plate before synapsing on the olfactory bulb located just above the level of the eyes (Fig. 3). These are among the smallest (therefore, slowest...

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...

The Endocrine System

Chapter 2 considered the general issue of chemical communication between cells. This section focuses on the classic endocrine glands and their hormones. A hormone is a chemical substance that is released into the blood in small amounts and that, after delivery by the circulation, elicits a typical physiologic response in other cells. An endocrine gland is a group of cells that produce and secrete a hormone. Endocrine glands are also called ductless glands to distinguish them from exocrine...

Www Barnard

Arachnoid Granulations

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...

Uth

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,...

Dyw

E, see Epinephrine EA, see Efferent arteriole Eardrum, see Tympanic membrane Eccentric hypertrophy definition, 945 heart structure, 945f E-C coupling, see Excitation-contraction coupling ECF volume, see Extracellular fluid volume ECG, see Electrocardiogram ECL cells, see Enterochromaffin-like cells Ectopic focus, in premature heart characteristics, 235, 243, 260 definition, 243 in exercise, 937 extracellular fluid volume, 425, 426 in heart failure, 942-943 lung fluid balance, 273 overview,...

Sound Amplification And Attenuation

The elaborate system of fluid-filled membrane ducts within the cochlea serves to amplify sound vibrations and to provide maximum acuity while at the same time protecting receptor cells from potential damage from high-intensity sounds. The tips of the stereocilia are embedded in a gelatinous meshwork called the tectoral membrane, which is connected to the reticular lamina at one end and to a bony protuberance called the modiolus at the other end (see Fig. 5). This arrangement produces a shearing...

The Gamma Loop System

The muscle spindle not only serves as a feedback system to the alpha motor neuron, but has within it a separate feedback system of its own called the gamma loop system. This system operates to maintain tension on the intrafusal muscle fibers. To provide information about static or changing muscle length, the annulospiral ring must be under some minimal amount of tension otherwise, the stretch-sensitive channels remain closed, and no action potentials are generated. A correction for this...

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

Morphology

The adrenal glands are bilateral structures situated above the kidneys. They are comprised of an outer region or cortex, which normally makes up more than three-quarters of the adrenal mass, and an inner region or medulla (Fig. 1). The medulla is a modified sympathetic ganglion that, in response to signals reaching it through cholinergic, preganglionic fibers, releases either or both of its two hormones, epinephrine and norepi-nephrine, into adrenal venous blood. The cortex arises from...

M

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

Conduction in Myelinated Axons

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

Calcium Balance

Calcium Nephron

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

Protein

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

Insulin

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

Vectors Can Be Determined From The Limb Leads

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

Regulation Of Blood Flow

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

Distribution of Blood Flow

Distribution Lung Blood Circulation

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

Potassium Transport By The Intestines

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

Fuels

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

Physiological Actions Of Ovarian Steroid Hormones

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

Airway Defense Mechanisms

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

Morphology Of The Endocrine Pancreas

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

Limitations Of Pulmonary Gas Exchange

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

Physiology Of The Mineralocorticoids

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

Physiologic Effects Of Thyroid Hormones

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

Control Of Testicular Function

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

Descending Motor Tracts In The Spinal Cord

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

Key Points

Substantia Nigra Pars Reticulata Mouse

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

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

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

Control Of Ventilation

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

Impairments In Urinary Concentrating And Diluting Ability

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

Some General Characteristics Of Carriermediated Transport

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

Hierarchical Arrangement Of Motor Cortical Areas

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

Regulation Of Metabolism During Feeding And Fasting

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

Salt And Water Reabsorption In The Proximal Tubule

Mass Flow Balance Proximal Tubule

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

Metabolism Of Thyroid Hormones

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

Qqj

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

Secretory Processes In The Proximal Straight Tubule

Excretion Pah

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

Central Auditory Pathways

Auditory Pathway Action Potential Nerves

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

Pancreatic Secretion

Exchange Between And Ions

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

Criteria for Active Transport of Ions

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

Hormonal Interactions During Exercise

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

Chylomicron Exocytosis Mechanism

Chylomicron Formation

Neutral Neutral, aromatic, aliphatic Abnormalities of Protein Assimilation Decreases in the amounts (or absence) of proteolytic enzymes occur in cases of pancreatic insufficiency as might develop in patients with pancreatitis or cystic fibrosis. Such decreases in the amounts of active enzymes may impair protein digestion to the point at which absorption is decreased and nitrogen is lost in the stool. The congenital absence of trypsin alone can also result in protein malabsorption. Trypsin is...

Schematic Drawing Of An Acinar Cell

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

Normal Bowel Rectosphincteric Reflex

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

Gastrointestinal Smooth Muscle

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