Animal Physiology Exam 2 Review: Example Questions

Ex). Explain the forces affecting bulk flow across a capillary wall and how these processes ultimately regulate blood pressure. Key Words: *Bulk flow, plasma, interstitial fluid, capillary, fluid distribution.*

*Bulk flow* is used by small, lipid-insoluble solutes in water to cross the the capillary wall. The movement of materials across the wall is dependent on pressure and is bi-directional depending on the net filtration pressure derived from the four Starling forces that modulate capillary dynamics. - bulk flow in this form essentially makes the so-called closed circulatory system into an open system, creating a cell-bathing fluid analogous to hemolymph. - bulk flow occurs because of differences in the hydrostatic and colloid osmotic pressures between the plasma and interstitial fluid. - bulk flow plays only a minor role in the exchange of individual solutes between blood and tissues because the quantity of solutes moved across the capillary wall by bulk flow is small compared to the much larger transfer of solutes by direct diffusion.

Ex). Describe the processes involved in cross-bridge cycling during muscle contraction. Key Words: *Sarcomere, myofibrils, sarcoplasmic reticulum, T-tubule system, Ca++, troponin, tropomyosin, ATP.*

*Cross-Bridge* Excited: 1). Muscle fiber is excited and Ca^2+ is released. 2). Released Ca^2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site. 3). Cross-bridge binding occurs. 4). Binding of actin and myosin cross bridge triggers power stroke that pulls thin filament inward during contraction. Cross-Bridge Activity: 1) Binding: Myosin cross bridge binds to actin molecule. 2). Power Stroke: cross bridge bends, pulling thing myofilament inward. 3) Detachment: cross bridge detaches at end of power stroke and returns to original conformation. 4). Binding: cross bridge binds to more distal actin molecules; cycle repeats. *Sarcomere* - the functional unit of skeletal muscle; the area between two Z lines within a myofibril. *Sarcoplasmic reticulum* - a fine meshwork of interconnected tubules that surrounds a muscle fiber's myofibrils; contains expanded lateral sacs, which store calcium that is released into the cytosol in response to a local action potential. *T-tubule system* - a perpendicular infolding of the surface membrane of a muscle fiber; rapidly spread surface electric activity into the central portions of the muscle fiber. *Troponin* - one of the regulatory proteins found in the thin filaments of muscle fibers *Tropomyosin* - one of the regulatory proteins found in the thin filaments of muscle fibers.

Ex).Explain the homeostatic mechanism that regulates red blood cell production in mammals. Key Words: *Hemopoietic tissue, EPO, Erythrocytes.*

*Hemopoietic tissue* - such as bone marrow continuously replace worn-out erythrocytes. - Erthropoiesis in mammals and probably other vertebrates is controlled by erythropoietin from the kidneys. *EPO (erythropoietin)* - a hormone produced primarily by the kidneys. It plays a key role in the production of red blood cells (RBCs), which carry oxygen from the lungs to the rest of the body. This test measures the amount of erythropoietin in the blood. *Erythrocytes* - a red blood cell that (in humans) is typically a biconcave disc without a nucleus. Erythrocytes contain the pigment hemoglobin, which imparts the red color to blood, and transport oxygen and carbon dioxide to and from the tissues. Erythropoietin (Epo) is a glycoprotein hormone produced in the kidney that acts on erythroid progenitor cells in the bone marrow. A negative feedback system, in which tissue oxygenation controls EPO production and EPO controls red blood cell (RBC) production, provides homeostasis in oxygen delivery to body tissues.

Ex). Describe the unique anatomy of the portal system connecting the hypothalamus to the anterior pituitary and explain its functional significance. Key Words: *Hypothalamus, anterior pituitary, hypothalamic-hypophysial portal system, hypophysiotrophic hormones.*

*Hypothalamus* - the vertebrate brain region located beneath the thalamus that is concerned with regulating many aspects of the internal fluid environment, such as water and salt balance and food intake; serves as an important link between the autonomic nervous system and endocrine system. *Anterior Pituitary* - the nonneural endocrine portion of the vertebrate pituitary gland, having three parts with variable representation in various species; pars tuberalis, pars intermedia, and pard distalis; stores and secretes 6 different hormones: GH, TSH, ACTH, FSH, LH, and prolactin. The secretion of each anterior pituitary hormone is stimulated or inhibited by hypothalamic *hypophysiotropic hormones* - (vertebrate hormones secretes by the hypothalamus that regulate the secretion of anterior pituitary hormones.) Depending on their actions, these hormones are called releasing hormones or inhibiting hormones: thyrotropin-releasing hormone (TRH). *Hypothalamic-hypophyseal portal system* - the vascular connection between the hypothalamus and anterior pituitary gland used for the pickup and delivery of hypophysiotropic hormones.

Ex). Explain how insulin and glucagon signaling modulate blood glucose levels. Key Words: *Insulin, glucagon, GLUT-4, glucose.*

*Insulin* promotes the conversion of of glucose into glycogen ( a storage polymer) within vertebrate liver cells by stimulating one particular hepatic enzyme, whereas another hormone, *glucagon*, by activating a different set of hepatic enzymes, enhances the degradation of glycogen into glucose within liver cells. The second factor complicating fuel metabolism is that the vertebrate brain normally depends on the delivery of adequate blood glucose at its sole source of energy. Insulin decreases concentration of blood glucose by promoting the cell's uptake of glucose from the blood for use and storage, while simultaneously blocking the two mechanisms by which the liver releases glucose into the blood. *Glucose* transport between the blood and cells is accomplished by means of plasma membrane carries known as *glucose transporters (GLUT)*. *GLUT4* - the glucose transporter that is responsible for the majority of glucose uptake by most cells of the body; the only type of glucose transporter that responds to insulin. Insulin lower blood amino acid levels and enhances protein synthesis through several effects: 1). Promotion of the active transport of anima acids from the blood into muscles and other tissues. This effect lowers the circulating amino acid level and provides the building blocks from protein synthesis with the cells. 2). Enhancing the rate of amino acid incorporation into protein by stimulating the cell' protein-synthesizing machinery. 3). Inhibition of protein degradation. - Glucagon raises blood glucose and insulin decreases blood glucose, the changes in secretion of these pancreatic hormones in response to deviation in blood glucose work together homeostatically to restore blood glucose levels to normal. FIGURE 7-26

Ex). Describe how the lymphatic system functions to reclaim fluid lost from capillary bulk flow and to fight against infections. Key Words: *Initial lymphatic, lymph, lymph node, skeletal muscle pumping, one-way valves.*

*Lymphatic system* - consists of an extensive network of one-way vessels for returning the remaining interstitial fluid to the blood. *Initial Lymphatics* - small, blind-ended terminal lymph vessels that permeate almost every tissue of the body. - the endothetial cells forming the walls of initial lymphatics slightly overlap like shingles on a roof, with their overlapping edges being free instead of attached to the surrounding cells. *Lymph nodes* - the lymph percolates through lymph nodes located en route within the lymphatic system. - passage of this fluid through the lymph nodes is an important aspect of immune defenses against disease. *Skeletal Muscle Pumps* - this external venous compression decreases venous capacity and increase venous pressures in effect squeezing fluid contained in the veins forward toward the heart. This pumping action, is one way extra blood stored in the veins is returned to the heart during locomotory activity.

Ex). Explain the mechanism behind pain signaling and how our analgesic pathway functions. Key Words: *Nociception, polymodal nociceptors, fast and slow pathways, substance P, glutamate, endogenous opiates.*

*Pain aka Nociception* - is primarily a protective mechanism meant to bring to awareness (or the higher brain centers) the fact that tissue damage is occurring or is about to occur. *Polymodal nociceptors* - respond equally to all kinds of damaging stimuli, including irritating chemicals released from injured tissues. (One of three other categories of pain; mechanical and thermal nociceptors). (do not have specialized receptor organs). Pain in mammals can occur in two phases: *Fast Pathway* - a quick response to direct damage. *Slow Pathway* - a slower prolonged, chemical response to inflammation and cell contents released by damage. There are multiple structures that are involved in mammalian pain processing. *Substance P* - a neurotransmitter that activates ascending pathways that transmit nociceptive signals to higher levels for further processing. *Glutamate* - a (major excitatory) neurotransmitter that in pain afferents acts on two different plasma membrane receptors: - Glutamate binds with AMPA receptors: results in the generation of action potentials in the dorsal horn cells transmitting the pain message to higher centers. - Glutamate bind with NMDA receptors: leads to CA^2+ entry into these neurons. Ca^2+ initiates second messenger systems that make the dorsal horn cells more excitable than usual. DORSAL HORN - located at the back of spinal cord the central grey matter forms two arms; contain the cell bodies of sensory neurons. Two arms located at the front of the spinal cord, central grey matter are called ventral horns. They contain the cell bodies of motor neurons. *Endogenous Opiates* - Morphine like substances, the endorphins, enkephalins, and dynorphin, which are important in the body's natural analgesic system. *Analgesic system* - in addition to the chain of neurons from peripheral nociceptors to higher CNS structures for pain perception, the mammalian CNS also contains a built in pain suppressing or analgesic system that suppresses transmission in the pain pathways as they enter the spinal cord. (relief from pain). FIGURE 6-46

Ex). Describe the initial phases of hemostasis that leads to the formation of a platelet plug, and how the plug is localized. Key Words: *Platelets, ADP, endothelial cells, collagen, nitric oxide.*

*Platelets* - specialized cell fragment in mammalian blood that participates in hemostasis by forming a plug at a vessel defect. - serves in the clotting mechanism. Hemostasis - is the arrest of bleeding; bleeding occurs when there is a rupture in a vessel or hemocoel wall, and the pressure inside is greater than the pressure outside. Hemostasis includes three steps that occur in a rapid sequence: (1) vascular spasm, or vasoconstriction, a brief and intense contraction of blood vessels; (2) formation of a platelet plug; and (3) blood clotting or coagulation, which reinforces the platelet plug with fibrin mesh that acts as a glue to hold the clot together. Once blood flow has ceased, tissue repair can begin. *Platelet plug* - is rapidly built up at the defect site in a positive-feedback fashion. The actin-myosin protein complex with the aggregated platelets contracts to compact and strengthen what was originally a fairly loose plug. - ADP and other chemicals released by the activated platelets stimulate the release of prostacyclin and nitric oxide. from the adjacent endothelium. Both chemical inhibit platelet aggregation thus the platelet plug is limited to the defect and does not spread to normal tissue. Platelets aggreagate at a vessel defect through a positive-feedback mechanism involving the release of adenosine diphosphate (ADP) and thromboxane A2 from platelets, which stick to exposed collagen at the site of injury. Platelets are prevented from aggregating at the adjacent normal vessel lining by the release of prostacyclin and nitric oxide from the undamaged endothelial cells.

Ex). Describe the process by which the stretch reflex works in a skeletal muscle group (patellar tendon reflex for example). Key Words: *Spindle apparatus, motor units, recruitment, tetanus.*

*Spindle apparatus* - are stretch receptors within the body of a muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. ... The muscle spindle has both sensory and motor components. *Motor units* - one motor neuron plus all the muscle fibers it innervates. *Motor unit recruitment* - for stronger and stronger contractions, more and more motor units are recruited, or stimulated. *Tetanus* - when a muscle fiber is stimulated so rapidly that it does not have a change to relax at all between stimuli, it s a smooth sustained contraction of maximal strength. - a tetanic contraction is usually three to four times stronger than a single twitch. The stretch reflex can be a monosynaptic reflex which provides automatic regulation of skeletal muscle length, whereby the signal entering the spinal cord arises from a change in muscle length or velocity. When a muscle lengthens, the muscle spindle is stretched and its nerve activity increases. FIGURE 8-16

Ex). Explain how the tapetum allows for enhanced nocturnal vision. Key Words: *Tapetum lucidum., riboflavin*

*Tapetum Lucidum is a layer of reflecting material the enhances the ability of many animal species to locate and detect distinct objects.* - It is able to enhance light detections in dim lit situations. The tapetum of certain animals, like cats and lemurs, contain *riboflavin* which can absorb light in the shorter wavelengths (blue, 450 nm) and then emit fluorescent light at a longer wavelength (520nm) more closely approximating the maximal sensitivity of rhodopsin in the rod photoreceptors. - This shift in wavelength would brighten to appearance of a blue-black background and enhance the contrast between objects in the environment and the background.

Ex). Explain how tip links function during stimulation of hair cells in a neuromast organ or in the mammalian inner ear? Key Words: *Hair cells, neuromast organ, tip links, stereocilia*

*Tip links* are cell adhesion molecules (CAM) that link the tips of *stereocilia* in adjacent rows. - Stereocilia are microvillar processes that are the actual sensory transducers that protrude from the sensory hair cells into a jellylike substance (at the base of the dome). The stereocilia of each hair cell are organized into rows of graded height tanging from short to tall in a staircase pattern. In *neuromasts (consists of a cluster of pear-shaped sensory cells surrounded by long, slender supporting cells. The sense hairs on top of the sensory cells project into a jellylike substance (the cupula) that bends in response to water displacement)* as well as all the inner-ear senses of reptiles, birds, and mammals, hair cells normally send out continuous bursts of nerve impulses when they are at rest. This is because the mechanically gated channels in the ciliary tips are partly open. When a force causes the cilia to bend (by pressure waves, sound waves, or gravity) towards the tallest stereocilum, the tip links stretch, tugging open the cation channels to which they are attached. When more cation channels are pulled open, more positive ions enter the hair cell, depolarizing it. When a force moves the cilia in the opposite direction, the hair bundle bends away from the tallest stereocilium, slackening the tip links and closing all the channels. As a result, ion entry ceases, hyperpolarizing the hair cell.

Ex). Explain how the suprachiasmatic nucleus and the pineal gland function to synchronize biological rhythms with environmental stimuli. Key Words: *Tropic hormones, prepro-/prohormones, peripheral activation, suprachiasmatic nucleus, pineal gland, melatonin.*

*Tropic Hormones* - a hormone that has a primary function the regulation of hormone secretion by another endocrine gland. tropic means "causing to turn" or "attracting"). *Preprohormones*- large precursor proteins, are synthesized by ribosomes on the rough endoplasmic reticulum. The preprohormoes then mitigate to the Golgi complex in memebrane-enclosed vesicles that pinch off from the smooth endoplasmic reticulum. *Prohormones* - during their journey through the endoplasmic reticulum and golgi complex, the large preprohormone precursor moecules are pruned first to prophormones and finally to active hormones. *Suprachiasmatic Nucleus* - a cluster of nerve cell bodies in the hypothalamus that serves as the master biological clock, acting as the pacemaker that establishes many of the mammalian body's circadian rhythm. *Pineal gland* - a small endocrine gland located in the center of the vertebrate brain that secretes the hormone melatonin. *Melatonin* - an indoleamine hormone derived from the amino acid tryptophan. - One of melatonin's most widely accepted roles is helping to keep the vertebrate body's inherent circadian rhythms in synchrony with the light-dark cycle.

Ex). Explain how light interacts with a photoreceptor to generate an action potential in an ??? Key Words: *Rhodopsin, cGMP, cone convergence, outer segment Na+ channels, on-center ganglion cell depolarization.*

A generic review of the process is as follows: A photon of light strikes the retinal molecule within the opsin protein in the outer segment of the photoreceptor. The retinal changes its shape after absorbing the light energy (photoisomerization). As a result of isomeratization, several proteins are activated including phosphodiesterase. Phosphodiesterase hydrolyzes cGMP and therefore decreases the intracellular concentration of cGMP in the outer segment of the photoreceptor. Na+ channels in the outer segment are gated by cGMP, where cGMP binding to the intracellular side of these channel proteins keeps them open. When the photon absorption causes decreased cGMP levels, the gates are no longer kept open and start to close. When these cGMP-gated Na+ channels close, sodium stops entering the cell, and the whole cell begins to hyperpolarize. This hyperpolarization spreads to the synaptic terminal. When the synaptic terminal membrane becomes hyperpolarized, the voltage gated calcium channels close. When voltage gated calcium channels close, calcium influx into the synaptic terminal is reduced/stops and exocytosis of synaptic vesicles also stops (or is greatly reduced). The above processes result in little to no neurotransmitter release from the photoreceptor onto the ganglion cell. In the case of on-center ganglion cells, they are inhibited by the photoreceptor neurotransmitter release. When this neurotransmitter release stops, on-center ganglion cells depolarize and send action potentials to the CNS.

Ex). Describe how auto rhythmic pacemaker cells govern the contractions of the mammalian heart so that blood moves from atria to the ventricles appropriately. Key Words: *SA node, AV node, bundle of His, purkinje fibers, AV valves, semilunar valves, cardiac muscle cell refractory period.*

An action potential initiated at the SA node first spreads throughout both atria. Its spreads is facilitated by two specialized atrial conduction pathways, the interatrial and internodal pathways. The AV node is the only point where an action potential can spread from the atria to the ventricles. From the AV node, the action potential spread rapidly throughout the ventricles, hastened by a specialized ventricular conduction system consisting of the bundle of His and Purkinje Fibers. *SA Node (sinoatrial node)* - a small, specialized region in the right atrial wall in reptiles (including birds) and mammals. *AV Node (atrioventricular node)* - a small bundle of specialized cardiac muscle cells located at the base of the right atrium near the septum, just above the junction of the atria and ventricles.

Ex). Explain how intrinsic and extrinsic factors function together to ensure adequate perfusion of essential tissues during fight or flight. Key Words: *Local (intrinsic) factors, active hyperemia, nitric oxide, extrinsic controls. sympathetic stimulation.*

Both autonomic systems affect heart rates, but sympathetic also boosts stroke volume, the amount of blood pumped out by each ventricle during each beat. Actually there are two types of controls that influence stroke volume: - *intrinsic* control related to the extent of venous return which increase during activity - *extrinsic* control from sympathetic stimulation; allows an animals "higher" regulatory systems to control blood flow for the good of the entire body for both functions of flow distribution and arterial blood-pressure regulation. Both factors increase stroke volume by increasing the strength of contraction of the heart. *Local Intrinsic Factors* 1). Decreased O2 2). Increases CO2 3). Increased Acid 4). Increased K+ 5). Increase osmolarity 6). Adenosine Release *Active hyperemia* - a response caused by triggering relaxation of the nearby arteriolar smooth muscle, all these factors increase blood flow to the particular area; this brings in more O2 and nutrients and remove metabolic wastes at a higher rate.

Ex). Compare and contrast the different muscle fiber types with respect to primary source of ATP and physical characteristics. Key Words: *Fiber types (fast/slow; oxidative/glycolytic), phosphogens, characteristics of each, metabolism, fuels, myoglobin.*

Fast vs Slow Fibers: - fast fibers have higher myosin ATPase (ATP splitting) activity than slow fibers because of different myosin isoforms. Oxidative vs Glycolytic: - oxidative fibers are richly supplied with capillaries and also have a high myoglobin content; more resistant to fatigue. Fast and slow oxidative fibers both contain an abundance of mitochondria, the organelles that house the enzymes involved in the oxidative-phosphorylation pathway. - fast fibers specialized for glycolysis contain few mitochondria but have a high content of glycolytic enzymes instead; contain an abundance of store glycogen; they need relatively less O2 to function, they receive only a meager capillary supply compared with the oxidative fibers; they contain very little myoglobin and therefore are pale in color. *Phosphogens* - known as macroergic compounds, are high energy storage compounds, also known as high-energy phosphate compounds, chiefly found in muscular tissue in animals. TABLE 8-2

Ex). Explain how electromotility in outer hair cells can enhance the response of inner hair cells to sound waves. Key Words: *Tectorial membrane, basilar membrane, electromotility, cochlear amplifier.*

In outer hair cells, they activate and rapidly elongate in responses to membrane potential known as *electromotility*. - These changes in length are believed to amplify or accentuate the motion of the *Basilar membrane* (forms the floor of the cochlear duct). The hair cells are are arranged in four parallel rows along the length of the basilar membrane: one row of inner hair cells and three rows of outer hair cells. Protruding form the surface of each hair cell are about 100 stereocilia which are mechanically embedded in the *tectorial membrane* (an awning like projection overhanging the organ of Corti throughout its length). *Cochlear Amplifier* is essentially a positive feedback loop within the cochlea that amplifies the traveling wave. Thus, vibrations within the organ of Corti are sensed and then force is generated in synchrony to increase the vibration ORGAN OF CORTI - the sense organ of hearing within the vertebrate inner ear that contains hair cells whose hairs are bent in response to sound waves, setting up action potentials in the auditory nerve.

Ex). Describe thyroid hormone synthesis and function as well as the processes that regulate production. Key Words: *TRH, TSH, iodine, thyroglobulin, colloid, thyroid hormone, Na+/K+, ATPase.*

The follicular cells of vertebrates produce two iodine-containing hormones derived from the amino acid tyrosine: T4 and T3. These two hormones, together referred to as *thyroid hormone* are important regulators of development and overall basal metabolic rate. The basic ingredients for thyroid hormone synthesis are tyrosine and iodine, both of which must be taken up from the blood by the follicular cells. Tyrosine, an amino acid, is synthesized in sufficient amounts by the body, so it is not an essential dietary requirement. By contrast, the iodine needed for thyroid hormone synthesis must be obtained from dietary intake. Dietary iodine (I) is reduced to iodide (I-) prior to absorption by the small intestine. Overall Process: 1). Tyrosine-containing Tg produced within the thyroid follicular cells by the endoplasmic reticulum/Golgi complex is transported by exocytosis into the colloid. 2). Iodide is carried by secondary active transport from the blood into the colloid by symporters in the basolateral membrane of the follicular cells. 3). In the follicular cell, the iodide is oxidized to active form by TPO at the limunal membrane. 4). The active iodide exits the cell through a luminal channel to enter the colloid. 5a). Catalyzed by TPO (thyroperoxidase), attachment of one iodide to tyrosine within the Tg molecules yields MIT. 5b). Attachment of two iodides to tyrosine yields DIT. 6a). Coupling of one MIT and one DIT yields T3. 6b). Coupling of two DITS yields T4. 7). On appropriate stimulation, the thyroid follicular cells engulf a portion of Tg-containing colloid by phagocytosis. 8). Lysosomes attack the engulfed vesicle and split the iodinated products from Tg. 9a). T3 and T4 diffuse into the blood (secretion). 9b). MIT and DIT are deiodinated and the freed iodide is recycled for synthesizing more hormone.

Ex). Explain the retinal adaptations that allow mammals to generate sharp images. Key Words: *Fovea, rods, cones, ganglion cells, and their axons*

The retinal visual pathway extends from the photoreceptor cells (*rod and cones*, whose light-sensitive ends face the choroid away from the incoming light) to the bipolar cells to the *ganglion cells*. - the horizontal and amacrine cells act locally for retinal processing of visual input. Light must pass through the ganglion and bipolar layers before reaching the photoreceptors in all areas of the retina except the fovea. *Fovea - a small depression in the retina of the eye where visual acuity is highest.* The bipolar and ganglion cell layers are pulled aside so the light strikes the photoreceptors directly. This feature, coupled with the fact that only *cones (which have greater acuity or discriminative ability than do rods*) are found here, makes the fovea point of greatest visual acuity (most distinct vision.