Visual Acuity and Sensitivity

Convergence Bipolar Ganglion

While reading or similarly viewing objects in daylight, each eye is oriented so that the image falls within a tiny area of the retina called the fovea centralis. The fovea is a pinhead-sized pit fovea pit within a yellow area of the retina called the macula lutea. The pit is formed as a result of the displacement of neural layers around the periphery therefore, light falls directly on photoreceptors in the center fig. 10.41 . Light falling on other areas, by contrast, must pass through several...

Pulse Pressure and Mean Arterial Pressure

Korotkoff Sounds

When someone takes a pulse, he or she palpates an artery for example, the radial artery and feels the expansion of the artery occur in response to the beating of the heart the pulse rate is thus a measure of the cardiac rate. The expansion of the artery with each pulse occurs as a result of the rise in blood pressure within the artery as the artery receives the volume of blood ejected by a stroke of the left ventricle. Since the pulse is produced by the rise in pressure from dia-stolic to...

Ventilation and Acid Base Balance

The Effect Bicarbonate Blood

The basic concepts and terminology relating to the acid-base balance of the blood were introduced in chapter 13. In brief review, acidosis refers to an arterial pH below 7.35, and alkalosis refers to an arterial pH above 7.45. There are two components of each respiratory and metabolic. The respiratory component refers to the carbon dioxide concentration of the blood, as measured by the PCO2. As implied by its name, the respiratory component is regulated by the respiratory system. The metabolic...

Carrier Mediated Transport

Molecules such as glucose are transported across plasma membranes by special protein carriers. Carrier-mediated transport in which the net movement is down a concentration gradient, and which is therefore passive, is called facilitated diffusion. Carrier-mediated transport that occurs against a concentration gradient, and which therefore requires metabolic energy, is called active transport. In order to sustain metabolism, cells must take up glucose, amino acids, and other organic molecules...

Spiral Organ Organ of Corti

Cochlear Duct Frequency

The sensory hair cells are located on the basilar membrane, with their hairs actually stereocilia projecting into the endolymph of the cochlear duct. These hair cells are arranged to form one row of inner cells, which extends the length of the basilar membrane, and multiple rows of outer hair cells three rows in the basal turn, four in the middle turn, and five in the apical turn of the cochlea fig. 10.21 . The stereocilia of the outer hair cells are embedded in a gelatinous tectorial membrane...

Pressure Changes During the Cardiac Cycle

Pressure Changes Cardiac Cycle

When the heart is in diastole, pressure in the systemic arteries averages about 80 mmHg millimeters of mercury . These events in the cardiac cycle then occur 1. As the ventricles begin their contraction, the intraventricular pressure rises, causing the AV valves to snap shut. At this time, the ventricles are neither being filled with blood because the AV valves are closed nor ejecting blood because the intraventricular pressure has not risen sufficiently to open the semilunar valves . This is...

Digestion and Absorption in the Stomach

Proteins are only partially digested in the stomach by the action of pepsin, while carbohydrates and fats are not digested at all by pepsin. Digestion of starch begins in the mouth with the action of salivary amylase and continues for a time when the food enters the stomach, but amylase soon becomes inactivated by the strong acidity of gastric juice. The complete digestion of food molecules occurs later, when chyme enters the small intestine. Therefore, people who have had partial gastric...

Inspiration and Expiration

Human Expiration

Between the bony portions of the rib cage are two layers of intercostal muscles the external intercostal muscles and the internal intercostal muscles fig. 16.14 . Between the costal cartilages, however, there is only one muscle layer, and its fibers are oriented in a manner similar to those of the internal inter-costals. These muscles are therefore called the interchondral part of the internal intercostals. Another name for them is the parasternal intercostals. An unforced, or quiet,...

Organs with Dual Innervation

Most visceral organs receive dual innervation they are innervated by both sympathetic and parasympathetic fibers. In this condition, the effects of the two divisions of the autonomic system may be antagonistic, complementary, or cooperative table 9.7 . The effects of sympathetic and parasympathetic innervation of the pacemaker region of the heart is the best example of the antagonism of these two systems. In this case, sympathetic and parasympathetic fibers innervate the same cells. Adrenergic...

Synergistic and Permissive Effects

When two or more hormones work together to produce a particular result, their effects are said to be synergistic. These effects may be additive or complementary. The action of epinephrine and norepinephrine on the heart is a good example of an additive effect. Each of these hormones separately produces an increase in cardiac rate acting together in the same concentrations, they stimulate an even greater increase in car- diac rate. The synergistic action of FSH and testosterone is an example of...

Endocrine Functions of the Placenta

Chorionic Villi And Intervillous Space

The placenta secretes both steroid hormones and protein hormones. The protein hormones include chorionic gonadotropin hCG and chorionic somatomammotropin hCS , both of which have actions similar to those of some anterior pituitary hormones table 20.7 . Chorionic gonadotropin has LH-like effects, as previously described it also has thyroid-stimulating ability, like pituitary TSH. Chorionic somatomammotropin likewise has actions that are similar to two pituitary hormones growth hormone and...

Twitch Summation and Tetanus

Maximale Tetanus Stimulatie

When the muscle is stimulated with a single electric shock of sufficient voltage, it quickly contracts and relaxes. This response is called a twitch. Increasing the stimulus voltage increases the strength of the twitch, up to a maximum. The strength of a muscle contraction can thus be graded, or varied an obvious requirement for the proper control of skeletal movements. If a second electric shock is delivered immediately after the first, it will produce a second twitch that may partially ride...

Chemical Classification of Hormones

Chemical Classes Hormones

Hormones secreted by different endocrine glands vary widely in chemical structure. All hormones, however, can be divided into a few chemical classes. 1. Amines. These are hormones derived from the amino acids tyrosine and tryptophan. They include the hormones secreted by the adrenal medulla, thyroid, and pineal glands. 2. Polypeptides and proteins. Polypeptide hormones generally contain less than 100 amino acids an example is antidiuretic hormone table 11.2 . Protein hormones are polypeptides...

Pepsin and Hydrochloric Acid Secretion

Chief Cells Parietal Cells

The parietal cells secrete H , at a pH as low as 0.8, into the gastric lumen by primary active transport involving carriers that function as an ATPase . These carriers, known as H K ATPase pumps, transport H uphill against a million-to-one concentration gradient into the lumen of the stomach while they transport K in the opposite direction fig. 18.8 . At the same time, the parietal cell's basolateral membrane facing the blood in capillaries of the lamina propria take in Cl-against its...

Hormones That Use Second Messengers

Synaptic Transmission Retinoic Acid

Hormones that are catecholamines epinephrine and norepineph-rine , polypeptides, and glycoproteins cannot pass through the lipid barrier of the target cell's plasma membrane. Although some of these hormones may enter the cell by pinocytosis, most of their effects result from their binding to receptor proteins on the outer surface of the target cell membrane. Since they exert their effects without entering the target cells, the actions of these hormones must be mediated by other molecules within...

Chemoreceptors in the Medulla

Pco2 And Total Minute Volume

The chemoreceptors most sensitive to changes in the arterial PCO2 are located in the ventral area of the medulla oblongata, near the exit of the ninth and tenth cranial nerves. These chemoreceptor neurons are anatomically separate from, but synaptically communicate with, the neurons of the respiratory control center in the medulla. An increase in arterial PCO2 causes a rise in the H concentration of the blood as a result of increased carbonic acid concentrations. The H in the blood, however,...

Bone Deposition and Resorption

The skeleton, in addition to providing support for the body, serves as a large store of calcium and phosphate in the form of crystals called hydroxyapatite, which has the formula Cajo PO4 6 OH 2. The calcium phosphate in these hydroxyap-atite crystals is derived from the blood by the action of bone-forming cells, or osteoblasts. The osteoblasts secrete an organic matrix composed largely of collagen protein, which becomes hardened by deposits of hydroxyapatite. This process is called bone...

Red Blood Cell Antigens and Blood Typing

Anti Agglutinins Human Blood Types

There are certain molecules on the surfaces of all cells in the body that can be recognized as foreign by the immune system of another individual. These molecules are known as antigens. As part of the immune response, particular lymphocytes secrete a class of proteins called antibodies that bond in a specific fashion with antigens. The specificity of antibodies for antigens is analogous to the specificity of enzymes for their substrates, and of receptor proteins for neurotransmitters and...

Regulation of Blood Volume by the Kidneys

Photo Hypothalamus Thirst Mechanism

The formation of urine begins in the same manner as the formation of tissue fluid by filtration of plasma through capillary pores. These capillaries are known as glomeruli, and the filtrate they produce enters a system of tubules that transports and modifies the filtrate by mechanisms discussed in chapter 17 . The kidneys produce about 180 L per day of blood filtrate, but since there is only 5.5 L of blood in the body, it is clear that most of this filtrate must be returned to the vascular...

Tonic and Phasic Receptors Sensory Adaptation

Some receptors respond with a burst of activity when a stimulus is first applied, but then quickly decrease their firing rate adapt to the stimulus if the stimulus is maintained. Receptors with this response pattern are called phasic receptors. Receptors that produce a relatively constant rate of firing as long as the stimulus is maintained are known as tonic receptors fig. 10.1 . Phasic receptors alert us to changes in sensory stimuli and are in part responsible for the fact that we can cease...

Exchange of Fluid Between Capillaries and Tissues

Forces Acting Capillary

The distribution of extracellular fluid between the plasma and interstitial compartments is in a state of dynamic equilibrium. Tissue fluid is not normally a stagnant pond rather, it is a continuously circulating medium, formed from and returning to the vascular system. In this way, the tissue cells receive a continuously fresh supply of glucose and other plasma solutes that are filtered through tiny endothelial channels in the capillary walls. Filtration results from blood pressure within the...

Effects of Temperature and pH

Pepsine Amylase Trypsine

An increase in temperature will increase the rate of non-enzyme-catalyzed reactions. A similar relationship between temperature and reaction rate occurs in enzyme-catalyzed reactions. At a temperature of 0 C the reaction rate is immeasurably slow. As the temperature is raised above 0 C the reaction rate increases, but only up to a point. At a few degrees above body temperature which is 37 C the reaction rate reaches a plateau further increases in temperature actually decrease the rate of the...

Explain How Valves In Veins Breathing And Skeletal Muscle Contractions Help Venous Blood Return To The Heart

Skeletal Muscle Squeezing Vein

Most of the total blood volume is contained in the venous system. Unlike arteries, which provide resistance to the flow of blood from the heart, veins are able to expand as they accumulate additional amounts of blood. The average pressure in the veins is only 2 mmHg, compared to a much higher average arterial pressure of about 100 mmHg. These values, expressed in millimeters of mercury, represent the hydrostatic pressure that the blood exerts on the walls of the vessels. The low venous pressure...

Reciprocal Innervation and the Crossed Extensor Reflex

Reciprocal Innervation

In the knee-jerk and other stretch reflexes, the sensory neuron that stimulates the motor neuron of a muscle also stimulates interneu-rons within the spinal cord via collateral branches. These interneu-rons inhibit the motor neurons of antagonist muscles via inhibitory postsynaptic potentials IPSPs . This dual stimulatory and inhibitory activity is called reciprocal innervation fig. 12.29 . When a limb is flexed, for example, the antagonistic extensor muscles are passively stretched. Extension...

Transport of Lipids in the Blood

Bile Salts Emulsify Fat Droplets

Once the chylomicrons are in the blood, their triglyceride content is removed by the enzyme lipoprotein lipase, which is attached to the endothelium of blood vessels. This enzyme hydrolyzes triglycerides and thus provides free fatty acids and Step 1 Emulsification of fat droplets by bile salts Step 2 Hydrolysis of triglycerides in emulsified fat droplets into fatty acid and monoglycerides Step 3 Dissolving of fatty acids and monoglycerides into micelles to produce mixed micelles Figure 18.35...

Intrapulmonary and Intrapleural Pressures

The visceral and parietal pleurae are normally flush against each other, so that the lungs are stuck to the chest wall in the same manner as two wet pieces of glass sticking to each other. The intrapleural space contains only a film of fluid secreted by the two membranes. The pleural cavity in a healthy person is thus potential rather than real it can become real only in abnormal situations when air enters the intrapleural space. Since the lungs normally remain in contact with the chest wall,...

Generator Receptor Potential

Pacinian Corpuscle Generator Potential

The electrical behavior of sensory nerve endings is similar to that of the dendrites of other neurons. In response to an environmental stimulus, the sensory endings produce local graded changes in the membrane potential. In most cases, these potential changes are depolarizations that are analogous to the excitatory postsynaptic potentials EPSPs described in chapter 7. In the sensory endings, however, these potential changes in response to environmental stimulation are called receptor, or...

Effects of Blood PO2 on Ventilation

Chemoreceptors Graph Pco2

Under normal conditions, blood Po2 affects breathing only indirectly, by influencing the chemoreceptor sensitivity to changes in PcO2- Chemoreceptor sensitivity to PCO gt 2 is augmented by a low PO2 so ventilation is increased at a high altitude, for example and is decreased by a high PO2. If the blood PO2 is raised by breathing 100 oxygen, therefore, the breath can be held longer because the response to increased PCO2 is blunted. When the blood PCO2 is held constant by experimental techniques,...

Significance of Blood PO and PCO2 Measurements

Blood Po2 And Pco2 Measurements

Since blood PO2 measurements are not directly affected by the oxygen in red blood cells, the PO2 does not provide a measurement of the total oxygen content of whole blood. It does, however, provide a good index of lung function. If the inspired air had a normal PO2 but the arterial PO2 was below normal, for example, you could conclude that gas exchange in the lungs was impaired. Measurements of arterial PO2 thus provide valuable information in treating people with pulmonary diseases, in...

Nitric Oxide and Carbon Monoxide as Neurotransmitters

Nitric oxide NO was the first gas to be identified as a neuro-transmitter. Produced by nitric oxide synthetase in the cells of many organs from the amino acid L-arginine, nitric oxide's actions are very different from those of the more familiar nitrous oxide N2O , or laughing gas, sometimes used as a mild anesthetic in dentistry. Nitric oxide has a number of different roles in the body. Within blood vessels, it acts as a local tissue regulator that causes the smooth muscles of those vessels to...

Control of the Autonomic Nervous System by Higher Brain Centers

Gehirnzentren

Visceral functions are largely regulated by autonomic reflexes. In most autonomic reflexes, sensory input is transmitted to brain centers that integrate this information and respond by modifying the activity of preganglionic autonomic neurons. The neural centers that directly control the activity of autonomic nerves are influenced by higher brain areas, as well as by sensory input. The medulla oblongata of the brain stem is the area that most directly controls the activity of the autonomic...

Negative Feedback Control of Calcium and Phosphate Balance

Low Plasma Ca2 Feedback

The secretion of parathyroid hormone is controlled by the plasma calcium concentrations. Its secretion is stimulated by low calcium concentrations and inhibited by high calcium concentrations. Since parathyroid hormone stimulates the final hy-droxylation step in the formation of 1,25-dihydroxyvitamin D3, a rise in parathyroid hormone results in an increase in production of 1,25-dihydroxyvitamin D3. Low blood calcium can thus be corrected by the effects of increased parathyroid hormone and...

Effects of Blood PCO2 and pH on Ventilation

Physiology Heart Vagus Carotid Sinus

Chemoreceptor input to the brain stem modifies the rate and depth of breathing so that, under normal conditions, arterial PCo2, pH, and Po2 remain relatively constant. If hypoventilation inadequate ventilation occurs, PCO2 quickly rises and pH falls. The fall in pH is due to the fact that carbon dioxide can combine Sensory nerve fibers in vagus nerve Sensory nerve fibers in vagus nerve Figure 16.26 Sensory input from the aortic and carotid bodies. The peripheral chemoreceptors aortic and...

Lung Volumes and Capacities

Lung Volumes And Capacities

An example of a spirogram is shown in figure 16.16, and the various lung volumes and capacities are defined in table 16.3. A lung capacity is equal to the sum of two or more lung volumes. During quiet breathing, for example, the amount of air expired in each breath is the tidal volume. The maximum amount of air that can be forcefully exhaled after a maximum inhalation is called the vital capacity, which is equal to the sum of the inspiratory reserve volume, tidal volume, and expiratory reserve...

Single Unit and Multiunit Smooth Muscles

Multi Unit Smooth Muscle

Smooth muscles are often grouped into two functional categories single-unit and multiunit fig. 12.35 . Single-unit smooth muscles have numerous gap junctions electrical synapses between adjacent cells that weld them together electrically they thus behave as a single unit, much like cardiac muscle. Most smooth muscles including those in the digestive tract and uterus are single-unit. Only some cells of single-unit smooth muscles receive autonomic innervation, but the ACh released by the axon can...

Erection Emission and Ejaculation

Bulbourethral Gland Inflammation

Erection, accompanied by increases in the length and width of the penis, is achieved as a result of blood flow into the erectile tissues of the penis. These erectile tissues include two paired structures the corpora cavernosa located on the dorsal side of the penis, and one unpaired corpus spongiosum on the ventral Seminal vesicle Ejaculatory duct Prostate Figure 20.21 The organs of the male reproductive system. The male organs are seen here in a sagittal view. side fig. 20.22 . The urethra...

Tyrosine Kinase Second Messenger System

Calmodulin Kinase Cascade

Insulin promotes glucose and amino acid transport and stimulates glycogen, fat, and protein synthesis in its target organs primarily the liver, skeletal muscles, and adipose tissue. These effects are achieved by means of a mechanism of action that is quite complex, and in some ways still incompletely understood. Nevertheless, it is known that insulin's mechanism of action bears similarities to the mechanism of action of other regulatory molecules known as growth factors. These growth factors,...

Neurilemma and Myelin Sheath

Neurilemma

All axons in the PNS myelinated and unmyelinated are surrounded by a continuous, living sheath of Schwann cells, known as the neurilemma, or sheath of Schwann. The axons of the CNS, by contrast, lack a neurilemma Schwann cells are only found in the PNS . This is significant in terms of regeneration of damaged axons, as will be described shortly. Some axons in the PNS and CNS are surrounded by a myelin sheath. In the PNS, this insulating covering is formed by successive wrappings of the cell...

Circulatory Changes During Exercise

Circulatory Changes

While the vascular resistance in skeletal muscles decreases during exercise, the resistance to flow through the visceral organs and skin increases. This increased resistance occurs because of vasoconstriction stimulated by adrenergic sympathetic fibers, and it results in decreased rates of blood flow through these organs. During exercise, therefore, the blood flow to skeletal muscles increases because of three simultaneous changes 1 increased total blood flow cardiac output 2 metabolic...

Mechanism of Thyroid Hormone Action

Mechanisms Hormones Action

As previously discussed, the major hormone secreted by the thyroid gland is thyroxine, or tetraiodothyronine T4 . Like steroid hormones, thyroxine travels in the blood attached to carrier proteins primarily to thyroxine-binding globulin, or TBG . The thyroid also secretes a small amount of triiodothyronine, or T3. The carrier proteins have a higher affinity for T4 than for T3, however, and, as a result, the amount of unbound or free T3 in the plasma is about ten times greater than the amount of...

Regulation of Insulin and Glucagon Secretion

Insulin Release Glucagon

Insulin and glucagon secretion is largely regulated by the plasma concentrations of glucose and, to a lesser degree, of amino acids. The alpha and beta cells, therefore, act as both the sensors and effectors in this control system. Since the plasma concentration of glucose and amino acids rises during the absorption of a meal and falls during fasting, the secretion of insulin and glucagon likewise fluctuates between the absorptive and postabsorptive states. These changes in insulin and...

Responses to Adrenergic Stimulation

Adrenergic stimulation by epinephrine in the blood and by norepinephrine released from sympathetic nerve endings has both excitatory and inhibitory effects. The heart, dilatory muscles of the iris, and the smooth muscles of many blood vessels are stimulated to contract. The smooth muscles of the bronchioles and of some blood vessels, however, are inhibited from contracting adrenergic chemicals, therefore, cause these structures to dilate. Since excitatory and inhibitory effects can be produced...

Feedback Control of the Anterior Pituitary

In view of its secretion of releasing and inhibiting hormones, the hypothalamus might be considered the master gland. The chain of command, however, is not linear the hypothalamus and anterior pituitary are controlled by the effects of their own actions. In the endocrine system, to use an analogy, the general takes orders from the private. The hypothalamus and anterior pituitary are not master glands because their secretions are controlled by the target glands they regulate. Anterior pituitary...

Review Activities

Test Your Knowledge ofTerms and Facts 1. Which of these statements is false 2. a. Most of the total blood volume is contained in veins. b. Capillaries have a greater total surface area than any other type of vessel. c. Exchanges between blood and 3. tissue fluid occur across the walls d. Small arteries and arterioles present great resistance to blood flow. All arteries in the body contain oxygen-rich blood with the exception of The lub, or first heart sound, is b. the pulmonary semilunar valve....

Atrial Stretch Reflexes

In addition to the baroreceptor reflex, several other reflexes help to regulate blood pressure. The reflex control of ADH release by osmoreceptors in the hypothalamus and the control of an-giotensin II production and aldosterone secretion by the juxta- glomerular apparatus of the kidneys have been previously discussed. Antidiuretic hormone and aldosterone increase blood pressure by increasing blood volume, and angiotensin II stimulates vasoconstriction to cause an increase in blood pressure....

The Formed Elements of Blood

Blood Cells Needle

The formed elements of blood include two types of blood cells erythrocytes, or red blood cells, and leukocytes, or white blood cells. Erythrocytes are by far the more numerous of the two. A cubic millimeter of blood contains 5.1 million to 5.8 million erythrocytes in males and 4.3 million to 5.2 million erythrocytes in females. The same volume of blood, by contrast, contains only 5,000 to 9,000 leukocytes. Erythrocytes are flattened, biconcave discs, about 7 im in diameter and 2.2 im thick....

Effect of Exercise and High Altitude on Respiratory Function

Exercise And Arterial Blood Gases

The arterial blood gases and pH do not significantly change during moderate exercise because ventilation increases during exercise to keep pace with the increased metabolism. Adjustments are also made at high altitude in both the control of ventilation and the oxygen transport ability of the blood to permit adequate delivery of oxygen to the tissues. Figure 16.41 The effect of exercise on arterial blood gases and pH. Notice that there are no consistent or significant changes in these...

Length Tension Relationship

Length Tension Relationship

The strength of a muscle's contraction is influenced by a variety of factors. These include the number of fibers within the muscle that are stimulated to contract, the frequency of stimulation, the thickness of each muscle fiber thicker fibers have more myofibrils and thus can exert more power , and the initial length of the muscle fibers when they are at rest. There is an ideal resting length for striated muscle fibers. This is the length at which they can generate maximum force. When the...

Hormones That Bind to Nuclear Receptor Proteins

Hormones Receptors Target Cells

Unlike the water-soluble hormones, the lipophilic steroid and thyroid hormones do not travel dissolved in the aqueous portion of the plasma rather, they are transported to their target cells attached to plasma carrier proteins. These hormones must then dissociate from their carrier proteins in the blood in order to pass through the lipid component of the plasma membrane and enter the target cell, within which their receptor proteins are located fig 11.4 . The receptors for the lipophilic...

Glomerular Ultrafiltrate

Filtration Slits

The fluid that enters the glomerular capsule is called ultrafiltrate fig. 17.10 because it is formed under pressure the hydrostatic pressure of the blood. This process is similar to the formation of tissue fluid by other capillary beds in the body in response to Starling forces chapter 14 see fig. 14.9 . The force favoring filtration is opposed by a counterforce developed by the hydrostatic pressure of fluid in the glomerular capsule. Also, since the protein concentration of the tubular fluid...

Insulin and Glucagon Postabsorptive State

Formation Ketone Bodies

The plasma glucose concentration is maintained surprisingly constant during the fasting, or postabsorptive, state because of the secretion of glucose from the liver. This glucose is derived from the processes of glycogenolysis and gluconeogenesis, which are promoted by a high secretion of glucagon coupled with a low secretion of insulin. Glucagon stimulates and insulin suppresses the hydrolysis of liver glycogen, or glycogenolysis. Thus during times of fasting, when glucagon secretion is high...

Adrenergic and Cholinergic Synaptic Transmission

Epinephrine Norepinephrine

Acetylcholine ACh is the neurotransmitter of all preganglionic fibers both sympathetic and parasympathetic . Acetylcholine is also the transmitter released by most parasympathetic post- ganglionic fibers at their synapses with effector cells fig. 9.7 . Transmission at these synapses is thus said to be cholinergic. The neurotransmitter released by most postganglionic sympathetic nerve fibers is norepinephrine noradrenaline . Transmission at these synapses is thus said to be adrenergic. There are...

Extrinsic Regulation of Blood Flow

Renal Circulation

The term extrinsic regulation refers to control by the autonomic nervous system and endocrine system. Angiotensin II, for example, directly stimulates vascular smooth muscle to produce generalized vasoconstriction. Antidiuretic hormone ADH also has a vasoconstrictor effect at high concentrations this is why it is also called vasopressin. This vasopressor effect of ADH is not believed to be significant under physiological conditions in humans. Stimulation of the sympathoadrenal system produces...

The Loading and Unloading Reactions

Oxyhemoglobin Dissociation Curve

Deoxyhemoglobin and oxygen combine to form oxyhemoglo-bin this is called the loading reaction. Oxyhemoglobin, in turn, dissociates to yield deoxyhemoglobin and free oxygen molecules this is the unloading reaction. The loading reaction occurs in the lungs and the unloading reaction occurs in the systemic capillaries. Loading and unloading can thus be shown as a reversible reaction Deoxyhemoglobin O2 lt z gt Oxyhemoglobin tissues The extent to which the reaction will go in each direction depends...

Antagonistic Effectors

Most factors in the internal environment are controlled by several effectors, which often have antagonistic actions. Control by antagonistic effectors is sometimes described as push-pull, where the increasing activity of one effector is accompanied by decreasing activity of an antagonistic effector. This affords a finer degree of control than could be achieved by simply switching one effector on and off. Room temperature can be maintained for example, by simply turning an air conditioner on and...

Enterohepatic Circulation

Liver Gallbladder Portal Vein Intestines

In addition to the normal constituents of bile, a wide variety of exogenous compounds drugs are secreted by the liver into the bile ducts table 18.2 . The liver can thus clear the blood of particular compounds by removing them from the blood and excreting them into the intestine with the bile. Molecules that are cleared from the blood by secretion into the bile are eliminated in the feces this is analogous to renal clearance of blood through excretion in the urine chapter 17 . Many compounds...

Prohormones and Prehormones

Hormone molecules that affect the metabolism of target cells are often derived from less active parent, or precursor, molecules. In the case of polypeptide hormones, the precursor may be a longer chained prohormone that is cut and spliced together to make the hormone. Insulin, for example, is produced from proinsulin within the beta cells of the islets of Langerhans of the pancreas see fig. 3.25 . In some cases, the prohormone itself is derived from an even larger precursor molecule in the case...

Parasympathetic Division

Collateral Ganglia Location

The parasympathetic division is also known as the craniosacral division of the autonomic system. This is because its preganglionic fibers originate in the brain specifically, in the midbrain, medulla oblongata, and pons and in the second through fourth sacral levels of the spinal column. These pre-ganglionic parasympathetic fibers synapse in ganglia that are located next to or actually within the organs innervated. These parasympathetic ganglia, called terminal ganglia, supply the...

Structural Organization of the Brain

Central Canal Spinal Cord

The brain is composed of an enormous number of association neurons and accompanying neuroglia, arranged in regions and subdivisions.These neurons receive sensory information, direct the activity of motor neurons, and perform such higher brain functions as learning and memory. The central nervous system CNS , consisting of the brain and spinal cord fig. 8.1 , receives input from sensory neurons and directs the activity of motor neurons that innervate muscles and glands. The association neurons...

Pancreatic Islets Islets of Langerhans

Pancreatic Islets Alpha Cells

On a microscopic level, the most conspicuous cells in the islets are the alpha and beta cells fig. 11.30 . The alpha cells secrete the hormone glucagon, and the beta cells secrete insulin. Alpha cells secrete glucagon in response to a fall in blood glucose concentrations. Glucagon stimulates the liver to Figure 11.29 The actions of parathyroid hormone and the control of its secretion. An increased level of parathyroid hormone causes the bones to release calcium and the kidneys to conserve...

Intrinsic Regulation of Blood Flow

Intrinsic, or built-in, mechanisms within individual organs provide a localized regulation of vascular resistance and blood flow. Intrinsic mechanisms are classified as myogenic or metabolic. Some organs, the brain and kidneys in particular, utilize these intrinsic mechanisms to maintain relatively constant flow rates despite wide fluctuations in blood pressure. This ability is termed autoregulation. If the arterial blood pressure and flow through an organ are inadequate if the organ is...

Coupled Reactions Oxidation Reduction

When an atom or a molecule gains electrons, it is said to become reduced when it loses electrons, it is said to become oxidized. Reduction and oxidation are always coupled reactions an atom or a molecule cannot become oxidized unless it donates electrons to another, which therefore becomes reduced. The atom or molecule that donates electrons to another is a reducing agent, and the one that accepts electrons from another is an oxidizing agent. It is important to understand that a particular atom...

Immediate Hypersensitivity

Wheel And Flare Allergy Skin Test

Immediate hypersensitivity can produce allergic rhinitis chronic runny or stuffy nose conjunctivitis red eyes allergic asthma atopic dermatitis urticaria, or hives and other symptoms. These symptoms result from the immune response to the allergen. In people who are not allergic, the allergen stimulates one type of helper T lymphocyte, the TH1 cells, to secrete interferon-y and inter-leukin-2. In people who are allergic, dendritic cells stimulate the other type of helper T lymphocytes, the TH2...

Renal Clearance of Inulin Measurement of GFR

Inulin Clearance

If a substance is neither reabsorbed nor secreted by the tubules, the amount excreted in the urine per minute will be equal to the amount that is filtered out of the glomeruli per minute. There does not seem to be a single substance produced by the body, however, that is not reabsorbed or secreted to some degree. Plants such as artichokes, dahlias, onions, and garlic, fortunately, do produce such a compound. This compound, a polymer of the monosaccharide fructose, is inulin. Once injected into...

Slow and Fast Twitch Fibers

Muscle Fiber Type Average Couch Potato

Skeletal muscle fibers can be divided on the basis of their contraction speed time required to reach maximum tension into slow-twitch, or type I, fibers, and fast-twitch, or type II, fibers. These differences are associated with different myosin ATPase isoenzymes, which can also be designated as slow and fast. The two fiber types can be distinguished by their ATPase isoenzyme when they are appropriately stained fig. 12.23 . The extraocular muscles that position the eyes, for example, have a...

Examples of Autocrine Regulation

Many autocrine regulatory molecules are also known as cy-tokines, particularly if they regulate different cells of the immune system, and as growth factors if they promote growth and cell division in any organ. This distinction is somewhat blurred, however, because some cytokines may also function as growth factors. Cytokines produced by lymphocytes the type of white blood cell involved in specific immunity see chapter 15 are also known as lymphokines, and the specific molecules involved are...

Organs without Dual Innervation

Although most organs are innervated by both sympathetic and parasympathetic nerves, some including the adrenal medulla, ar-rector pili muscles, sweat glands, and most blood vessels receive only sympathetic innervation. In these cases, regulation is achieved by increases or decreases in the tone firing rate of the sympathetic fibers. Constriction of cutaneous blood vessels, for example, is produced by increased sympathetic activity that stimulates alpha-adrenergic receptors, and vasodilation...

Phases of the Menstrual Cycle Cyclic Changes in the Ovaries

The duration of the menstrual cycle is typically about 28 days. Since it is a cycle, there is no beginning or end, and the changes that occur are generally gradual. It is convenient, however, to call the first day of menstruation day one of the cycle, because the flow of menstrual blood is the most apparent of the changes that occur. It is also convenient to divide the cycle into phases based on changes that occur in the ovary and in the endometrium. The ovaries are in the follicular phase from...

Monoamines as Neurotransmitters

A variety of chemicals in the CNS function as neurotransmitters. Among these are the monoamines,a chemical family that includes dopamine,norepinephrine,and serotonin. Although these molecules have similar mechanisms of action, they are used by different neurons for different functions. The regulatory molecules epinephrine, norepinephrine, dopamine, and serotonin are in the chemical family known as monoamines. Serotonin is derived from the amino acid tryptophan. Epinephrine, norepinephrine, and...

Development of Accessory Sex Organs and External Genitalia

Labia Majora And Labia Minora Disease

In addition to testes and ovaries, various internal accessory sex organs are needed for reproductive function. Most of these are derived from two systems of embryonic ducts. Male accessory organs are derived from the wolffian mesonephric ducts, and female accessory organs are derived from the mullerian paramesonephric ducts fig. 20.5 . Interestingly, the two duct systems are present in both male and female embryos between day 25 and day 50, and so embryos of both sexes have the potential to...

Parathyroid Hormone and Calcitonin

Calcitonin Osteoporosis

Whenever the plasma concentration of Ca2 begins to fall, the parathyroid glands are stimulated to secrete increased amounts of parathyroid hormone PTH , which acts to raise the blood Ca2 back to normal levels. As might be predicted from this action of PTH, people who have their parathyroid glands removed as may occur accidentally during surgical removal of the thyroid will experience hypocalcemia. This can cause severe muscle tetany, for reasons previously discussed, and serves as a dramatic...

Cardiac Cycle and Heart Sounds

Cardiac Cycle Diastole And Systole

The two atria fill with blood and then contract simultaneously. This is followed by simultaneous contraction of both ventricles, which sends blood through the pulmonary and systemic circulations. Contraction of the ventricles closes the AV valves and opens the semilunar valves relaxation of the ventricles causes the semilunar valves to close. The closing of first the AV valves and then the semilunar valves produces the lub-dub sounds heard with a stethoscope. The cardiac cycle refers to the...

Structure of Skeletal Muscles

Skeletal Muscle Fiber Structure

The fibrous connective tissue proteins within the tendons extend around the muscle in an irregular arrangement, forming a sheath known as the epimysium epi above my muscle . Connective tissue from this outer sheath extends into the body of the muscle, subdividing it into columns, or fascicles these are the strings in stringy meat . Each of these fascicles is thus surrounded by its own connective tissue sheath, which is known as the perimysium peri around . Dissection of a muscle fascicle under...

Diseases of the Thyroid

Hyperthyroid Appetite

Thyroid-stimulating hormone TSH from the anterior pituitary stimulates the thyroid to secrete thyroxine however, it also exerts a trophic growth-stimulating effect on the thyroid. This trophic effect is evident in people who develop an iodine-deficiency endemic goiter, or abnormal growth of Monoiodotyrosine MIT Diiodotyrosine DIT Figure 11.23 The production and storage of thyroid hormones. Iodide is actively transported into the follicular cells. In the colloid, it is converted into iodine and...

Adenylate Cyclase Cyclic AMP Second Messenger System

Adenylyl Cyclase Protein Kinase

Cyclic adenosine monophosphate abbreviated cAMP was the first second messenger to be discovered and is the best understood. When epinephrine and norepinephrine bind to their P-adrenergic receptors chapter 9 , the effects of these hormones are due to cAMP production within the target cells. It was later discovered that the effects of many but not all polypeptide and glycoprotein hormones are also mediated by cAMP. When one of these hormones binds to its receptor protein, it causes the...

Gross Structure of the Urinary System

Gross Structure Human Kidney

The paired kidneys lie on either side of the vertebral column below the diaphragm and liver. Each adult kidney weighs about 160 g and is about 11 cm 4 in. long and 5 to 7 cm 2 to 3 in. wide about the size of a fist. Urine produced in the kidneys is drained into a cavity known as the renal pelvis basin , and then it is channeled from each kidney via long ducts the ureters to the urinary bladder fig. 17.1 . Figure 17.1 The organs of the urinary system. The urinary system of a female is shown that...

Digestion and Absorption of Proteins

Polypeptide Chain Digestion

Protein digestion begins in the stomach with the action of pepsin. Some amino acids are liberated in the stomach, but the major products of pepsin digestion are short-chain polypeptides. Figure 18.32 The action of pancreatic amylase. Pancreatic amylase digests starch into maltose, maltriose, and short oligosaccharides containing branch points in the chain of glucose molecules. Pepsin digestion helps to produce a more homogenous chyme, but it is not essential for the complete digestion of...

Digestion and Absorption of Carbohydrates Lipids and Proteins

Polysaccharides and polypeptides are hydrolyzed into their subunits. These subunits enter the epithelial cells of the intestinal villi and are secreted into blood capillaries. Fat is emulsified by the action of bile salts, hydrolyzed into fatty acids and monoglycerides,and absorbed into the intestinal epithelial cells. Once inside the cells, triglycerides are resynthesized and combined with proteins to form particles that are secreted into the lymphatic fluid. The caloric energy value of food...

Endocrine Functions of the Testes

Human Physiology Endorphin

Testosterone is by far the major androgen secreted by the adult testis. This hormone and its derivatives the 5a-reduced androgens are responsible for initiation and maintenance of the body changes associated with puberty in males. Androgens are sometimes called anabolic steroids because they stimulate the growth of muscles and other structures table 20.4 . Increased testosterone secretion during puberty is also required for growth of the accessory sex organs primarily the seminal vesicles and...

Structure of the Respiratory System

Larynx And Carina

Gas exchange in the lungs occurs across an estimated 300 million tiny 0.25 to 0.50 mm in diameter air sacs, known as alveoli. Their enormous number provides a large surface area 60 to 80 square meters, or about 760 square feet for diffusion of gases. The diffusion rate is further increased by the fact that each alveolus is only one cell-layer thick, so that the total air-blood barrier is only two cells across an alveolar cell and a capillary endothelial cell , or about 2 im. This is an average...

Paracrine Regulation of Blood Flow

Paracrine regulators, as described in chapter 11, are molecules produced by one tissue that help to regulate another tissue of the same organ. Blood vessels are particularly subject to paracrine regulation. Specifically, the endothelium of the tunica interna produces a number of paracrine regulators that cause the smooth muscle of the tunica media to either relax or contract. The endothelium produces several molecules that promote smooth muscle relaxation, including nitric oxide, bradykinin,...

Carbon Dioxide Transport and Acid Base Balance

Carbon dioxide is transported in the blood primarily in the form of bicarbonate HCO3- ,which is released when carbonic acid dissociates. Bicarbonate can buffer H , and thus helps to maintain a normal arterial pH. Hypoventilation raises, and hyperventilation lowers, the carbonic acid concentration of the blood. Carbon dioxide is carried by the blood in three forms 1 as dissolved CO2 carbon dioxide is about twenty-one times more soluble than oxygen in water, and about one-tenth of the total blood...

Energy Requirements of Skeletal Muscles

Skeletal muscles generate ATP through aerobic and anaerobic respiration and through the use of phosphate groups donated by creatine phosphate.The aerobic and anaerobic abilities of skeletal muscle fibers differ according to muscle fiber type, which are described according to their speed of contraction, color,and major mode of energy metabolism. Skeletal muscles at rest obtain most of their energy from the aerobic respiration of fatty acids. During exercise, muscle glycogen and blood glucose are...

Neural Control of Skeletal Muscles

Skeletal muscles contain stretch receptors called muscle spindles that stimulate the production of impulses in sensory neurons when a muscle is stretched.These sensory neurons can synapse with alpha motoneurons, which stimulate the muscle to contract in response to the stretch. Other motor neurons, called gamma motoneurons, stimulate the tightening of the spindles and thus increase their sensitivity. Motor neurons in the spinal cord, or lower motor neurons often shortened to motoneurons , are...

Electrical Activity of the Heart

Human Heart Conduction System

If the heart of a frog is removed from the body and all neural innervations are severed, it will still continue to beat as long as the myocardial cells remain alive. The automatic nature of the heartbeat is referred to as automaticity. As a result of experiments with isolated myocardial cells and clinical experience with patients who have specific heart disorders, many regions within the heart have been shown to be capable of originating action potentials and functioning as pacemakers. In a...

Killer Helper and Suppressor T Lymphocytes

The killer, or cytotoxic, T lymphocytes can be identified in the laboratory by a surface molecule called CD8. Their function is to destroy body cells that harbor foreign molecules. These are usually molecules from an invading microorganism, but they can also be molecules produced by the cell's genome because of a malignant transformation, or they may simply be body molecules that had never been presented before to the immune system. In contrast to the action of B lymphocytes, which kill at a...

Physical Aspects of Ventilation

Pleura Visceral

The movement of air into and out of the lungs occurs as a result of pressure differences induced by changes in lung volumes. Ventilation is thus influenced by the physical properties of the lungs, including their compliance, elasticity, and surface tension. Movement of air, from higher to lower pressure, between the conducting zone and the terminal bronchioles occurs as a result of the pressure difference between the two ends of the airways. Air flow through bronchioles, like blood flow through...

Polypeptides as Neurotransmitters

Many polypeptides of various sizes are found in the synapses of the brain. These are often called neuropeptides and are believed to function as neurotransmitters. Interestingly, some of the polypeptides that function as hormones secreted by the small intestine and other endocrine glands are also produced in the brain and may function there as neurotransmitters table 7.8 . For example, cholecystokinin CCK , which is secreted as a hormone from the small intestine, is also released from neurons...

Test Your Knowledge ofTerms and I

Which of these statements about hypothalamic-releasing hormones is true a. They are secreted into capillaries in the median eminence. b. They are transported by portal veins to the anterior pituitary. c. They stimulate the secretion of specific hormones from the anterior pituitary. 2. The hormone primarily responsible for setting the basal metabolic rate and for promoting the maturation of the brain is 3. Which of these statements about the a. It is not innervated by nerve fibers. c. The...

Hypothalamus and Pituitary Gland

Posterior Hypothalamus Shivering

The hypothalamus is the most inferior portion of the dien-cephalon. Located below the thalamus, it forms the floor and part of the lateral walls of the third ventricle. This small but extremely important brain region contains neural centers for hunger and thirst and for the regulation of body temperature and hormone secretion from the pituitary gland fig. 8.17 . In addition, centers in the hypothalamus contribute to the regulation of sleep, wakefulness, sexual arousal and performance, and such...

Bile Production and Secretion

The liver produces and secretes 250 to 1,500 ml of bile per day. The major constituents of bile are bile pigment bilirubin , bile salts, phospholipids mainly lecithin , cholesterol, and inorganic ions. Bile pigment, or bilirubin, is produced in the spleen, liver, and bone marrow as a derivative of the heme groups minus the iron from hemoglobin fig. 18.23 . The free bilirubin is not very water-soluble, and thus most is carried in the blood attached to albumin proteins. This protein-bound...

Destruction of T Lymphocytes

Macrophage Cell

The activated T lymphocytes must be destroyed after the infection has been cleared. This occurs because T cells produce a surface receptor called FAS. Production of FAS increases during the infection and, after a few days, the activated T lymphocytes begin to produce another surface molecule called FAS ligand. The binding of FAS to FAS ligand, on the same or on different cells, triggers the apoptosis cell suicide of the lymphocytes. R- Glucocorticoids such as hydrocortisone secreted by SP I t...

Cleavage and Blastocyst Formation

Image Blastocyst And Trophoblast

At about 30 to 36 hours after fertilization, the zygote divides by mitosis a process called cleavage into two smaller cells. The rate of cleavage is thereafter accelerated. A second cleavage, which occurs about 40 hours after fertilization, produces four cells. A third cleavage about 50 to 60 hours after fertilization produces a ball of eight cells called a morula mulberry . This very early embryo enters the uterus 3 days after ovulation has occurred fig. 20.43 . Continued cleavage produces a...

Introduction to Physiology

Human physiology is the study of how the human body functions, with emphasis on specific cause-and-effect mechanisms. Knowledge of these mechanisms has been obtained experimentally through applications of the scientific method. Physiology from the Greek physis nature logos study is the study of biological function of how the body works, from cell to tissue, tissue to organ, organ to system, and of how the organism as a whole accomplishes particular tasks essential for life. In the study of...

Test Yourself Before You Continue

Glucose Metabolism Feeding And Fasting

Describe how the secretions of insulin and glucagon change during periods of absorption and periods of fasting. How are these changes in hormone secretion produced 2. Explain how the synthesis of fat in adipose cells is regulated by insulin. Also, explain how fat metabolism is regulated by insulin and glucagon during periods of absorption and fasting. 3. Define the following terms glycogenolysis, gluconeogenesis, and ketogenesis. How do insulin and glucagon affect each of these processes...

Structure of Proteins

Van Der Waals Bond Protein

Proteins consist of long chains of subunits called amino acids. As the name implies, each amino acid contains an amino group NH2 on one end of the molecule and a carboxyl group COOH on another end. There are about twenty different amino acids, each with a distinct structure and chemical properties, that are used to build proteins. The differences between the amino acids are due to differences in their functional groups. R is the abbreviation for functional group in the general formula for an...

Regeneration of a Cut Axon

When an axon in a peripheral nerve is cut, the distal portion of the axon that was severed from the cell body degenerates and is phagocytosed by Schwann cells. The Schwann cells, surrounded by the basement membrane, then form a regeneration tube fig. 7.9 as the part of the axon that is connected to the cell body begins to grow and exhibit amoeboid movement. The Schwann cells of the regeneration tube are believed to secrete chemicals that attract the growing axon tip, and the regeneration tube...

Ligand Operated Channels

Nicotinic Receptor

This is the most direct mechanism by which chemically regulated gates can be opened. In this case, the ion channel runs through the receptor itself. The ion channel is opened by the binding of the receptor to the neurotransmitter ligand. Such is the case when ACh binds to its nicotinic ACh receptor. This receptor consists of five polypeptide subunits that enclose the ion channel. Two of these subunits contain ACh-binding sites, and the channel opens when both sites bind to ACh fig. 7.23 . The...

Labor and Parturition

Parturition

Powerful contractions of the uterus are needed to expel the fetus in the sequence of events called labor. These uterine contractions are known to be stimulated by two agents 1 oxytocin, a polypeptide hormone produced in the hypothalamus and released by the posterior pituitary and also produced by the uterus itself , and 2 prostaglandins, a class of cyclic fatty acids with paracrine functions produced within the uterus. The particular prostaglandins PGs involved are PGF2a and PGE2. Labor can...

Hepatic Portal System

The products of digestion that are absorbed into blood capillaries in the intestine do not directly enter the general circulation. Instead, this blood is delivered first to the liver. Capillaries in the digestive tract drain into the hepatic portal vein, which carries this blood to capillaries in the liver. It is not until the blood has passed through this second capillary bed that it enters the general circulation through the hepatic vein that drains the liver. The term portal system is used...