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...

Info

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...

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...

Carbon Dioxide

Blood-CO2 equilibrium (or dissociation) curves are nonlinear, but they have a different shape and position than O2-blood equilibrium curves. Figure 4 shows how blood holds more CO2 than O2 and this is, in part, because CO2 is carried by blood in three forms (see later discussion). Also, the blood CO2 equilibrium curve is steeper than the O2 curve. This results in a smaller range of PCO2 values in the body, compared with the range of Po2 values, although the differences between arterial and...

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

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

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...

Salivary Secretion

The functions of saliva fall into three general categories digestion, lubrication, and protection. Saliva is produced in large volumes, relative to the weight of the salivary glands, by an active process. Unlike the process in the other gastrointestinal glands, the secretion of saliva is almost totally under neural control. Both branches of the autonomic nervous system stimulate salivary secretion, although the para-sympathetic system provides a much stronger input. The healthy adult secretes...

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

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

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

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

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...

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...

Clinical Note

Alzheimer's disease was first described by the German physician Alois Alzheimer in 1907. The disease is associated with a progressive decline in cognitive function (i.e., dementia), in general, and a specific impairment in the ability to retrieve old memories (retrograde amnesia) and form new memories (anterograde amnesia). Approximately 4 million individuals in the United States have Alzheimer's disease, and it has been estimated that the cost due to treatment and care of these individuals...

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

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...

General Properties Of Sensory Receptors

Sensory information from the body reaches the nervous system piecemeal through a series of separate sensory pathways associated with specific sensory modalities. These pathways consist of sensory receptors and their projections to designated receiving areas in the cortex. A unified perception of our physical world emerges from the coordinated response of these primary receiving areas and secondary association areas. Separate pathways for the special senses of vision, hearing, taste, and...

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

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

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

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...

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...

Diffusion

Pulmonary Gas Diffusion Images

Diffusion of O2 from alveoli to pulmonary capillary blood is the next step in the O2 cascade after alveolar ventilation. However, it is important to note that blood leaving the pulmonary capillaries is in equilibrium with alveolar gas in healthy lungs under normal resting conditions. Hence, the small decrease between Pao2 and Pao2 shown in Fig. 1 is not caused by diffusion, but by ventilation-perfusion mismatching in healthy lungs under normal conditions see Ventilation-Perfusion Mismatching...

Limitations Of Pulmonary Gas Exchange

Mixed Venous Blood Sample

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...

Overview Of The Cardiovascular System

Column Mercury Column Water

Conceptually, it is useful to subdivide the cardiovascular system into the following four functional components blood, vessels, heart, and its associated control systems. As shown in Fig. 1, blood circulates within a closed series of vessels consisting of a systemic and a pulmonary circuit that are in series with each other. The blood functions as the carrier for transporting substances to and from the various tissues. Although simple diffusion can be an effective transporter of material, it is...

Epithelial Characteristics Of The Nephron

All nephron segments, from the glomerulus to the ducts of Bellini, consist of epithelial cells that are joined in a continuous layer by specialized structures called junctional complexes, as illustrated in Fig. 1. Although some epithelia consist of multiple cell layers, a single cell layer forms the epithelium of the nephron. On the basal side of all epithelia a continuous basement membrane composed of collagen, laminin, and other extracellular matrix proteins provides structural support that...

Active And Passive Solute Transport

Passive Active Solute Transport

Up until this point, solute reabsorption in the proximal tubule has been discussed in general terms as FIGURE 8 Effect of reduced plasma colloid osmotic pressure and increased interstitial fluid pressure on the permeability properties of the junctional complexes. It has been proposed that an increase in interstitial fluid pressure may be associated with an increased permeability of the junctional complexes between proximal tubule cells that would enable backflux diffusion of Na , Cl, HCO, and...

Physical and Chemical Principles in Respiratory Physiology

Quantitative descriptions of gas exchange depend on relatively simple applications of the principle of conservation of mass or mass balance and the ideal gas law using the symbols defined in Table 1. The symbols may appear complicated at first, but they are based on a few simple conventions. Primary variables are symbolized with a capital letter, and a dot over the variable indicates the first derivative with respect to time e.g., Q blood flow, or quantity of blood per unit time in liters per...

Eiq

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,...

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, and the...

Cardiovascular And Tissue Oxygen Transport

The cardiovascular system is responsible for transporting O2 to metabolizing tissues after it has diffused into pulmonary capillary blood. The heart pumps 02-rich arterial blood to the tissues, where O2 leaves the systemic capillaries and moves to the mitochondria through tissue gas exchange. The heart also pumps O2-poor venous blood back to the lungs, where it is reoxygenated. The magnitude of the Po2 decrease between arterial and venous blood see Fig. 1 depends on both the cardiovascular O2...

Physiological Actions Of Ovarian Steroid Hormones

Menstrual Physiology

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...

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...

Prolonged Refractory Periods Prevent The Heart From Being Tetanized

The fast sodium channels trigger action potentials in contractile and Purkinje cells. They have actually two gates that control passage of Na through the channel. The activation gate normally blocks the channel. Because it is voltage-gated it opens only when the membrane potential reaches threshold creating phase 0. Shortly after the activation gate opens a second part of the molecule, the inactivation gate closes the channel, causing phase 0 to end. The inactivation gate is voltage sensitive...

Nonrespiratory Functions Of The Lung

Mucociliary Transport

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...

Iontophoresis of Acetylcholine

Another prediction of the ACh hypothesis is that it should be possible to mimic the release of ACh from the presynaptic terminal by artificially applying some ACh to the vicinity of the neuromuscular junction. A simple technique called iontophoresis is available to precisely deliver very small amounts of ACh to restricted regions of a cell. The technique is illustrated in Fig. 9. One intracellular microelectrode is used to record the membrane potential. Another extracellular microelec-trode is...

Bernsteins Hypothesis for the Resting Potential

In 1902, Julius Bernstein proposed the first satisfactory hypothesis for generation of the resting potential. Bernstein knew that the inside of cells have high K and low Na concentrations and that the extracellular fluid has low K and high Na concentrations. In addition, there appeared to be large negatively charged molecules, presumably proteins, to which the cell was impermeable. Bernstein also knew a critical piece of information that cells were highly permeable to K but not very permeable...

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...

Alveolar Ventilation

Ventilation is the first step in the O2 cascade, and the level of alveolar ventilation Va is the most important physiologic factor determining arterial Po2 for any given inspired Po2 and level of O2 demand Vo2 in healthy lungs. As described in Chapter 18, anatomic dead space reduces the fraction of the tidal volume that reaches the alveoli where Va is alveolar ventilation, fR is respiratory frequency, Vt is tidal volume, and Vd is anatomic dead space. Anatomic dead space can be measured with...

Glomerular Filtration

Glomerular Filtration Hydrostatic

The high hydrostatic pressure of the blood in the glomerular capillaries is responsible for a net driving force favoring ultrafiltration from the glomerular capillaries. In the young male adult, the glomerular filtration rate GFR averages about 130 mL min, which amounts to a whopping 187 L day. The high rate of glomerular filtration means that as plasma flows through the kidneys at a rate of 670 mL min, 130 mL min, or 20 , is filtered. This 20 represents what is referred to as the filtration...