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109 Cards in this Set
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Describe the basic physiological process involved with muscle contraction
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1.An action potential travels along a motor nerve to its ending on muscle fibers, and the nerve secretes a small amount of the neurotransmitter substance acetylcholine.
2. The acetylcholine acts on a local area of the muscle membrane to open acetylcholine-gated channels, which allows sodium ions to flow into the muscle fiber. 3. The action potential travels along the muscle fiber membrane, causing the sarcoplasmic reticulum to release calcium ions into the myofibrils that have been stored in the reticulum. 4.The calcium ions initiate attractive forces between the actin and myosin filaments, causing them to slide together this is the contractile process. 5. After a fraction of a second, the calcium ions are pumped back into the sarcoplasmic reticulum, where they remain stored until a muscle action potential arrives, this removal of the calcium ions from the myofibrils causes muscle contraction to cease. |
5 steps
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Describe the differences between isometric and isotonic muscle contraction
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If a stimulated muscle is held so that it cannot shorten, it simply exerts tension. This is called an isometric ("same length") contraction. If the muscle is allowed to shorten, the contraction is called isotonic ("same tension").
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Describe the structures associated with the neuromuscular junction
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Each motor neuron connects to several skeletal muscle fibers to form a motor unit. The number of muscle fibers within the motor unit varies enormously, from a few, for fine motor control (e.g. the muscles of the eye), to several thousand for coarse actions (e.g. the thigh muscles). There is however only one neuromuscular junction on each skeletal muscle fiber, any others are eliminated during development. As the motor neuron enters a muscle, the axon divides into telodendria, the ends of which, the terminal buttons, synapse with the motor endplate. The two are separated by approximately 20nm, the junctional gap or synaptic cleft. It is here that release of the neurotransmitter acetylcholine occurs with consequent binding to the receptors on the motor endplate.
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How many neuromuscular junctions are on each skeletal muscle fiber
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1, any others are eliminated during development
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As the motor neuron enters a muscle, the axon divides into what?
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into telodendria, the ends of which, the terminal buttons, synapse with the motor endplate. The two are separated by approximately 20nm, the junctional gap or synaptic cleft. It is here that release of the neurotransmitter acetylcholine occurs with consequent binding to the receptors on the motor endplate
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Where does the neurotransmitter acetylcholine release occur?
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The synaptic cleft which occurs with consequent binding to the receptors on the motor endplate
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Describe the effects of acetylcholine in the neuromuscular junction
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When a nerve impulse reaches the Neuromuscular Junction, vesicles containing acetylcholine are released into the synaptic space. On the inside surface of the neural membrane are linear dense bars. To the side of each dense bar are voltage-gated calcium channels. When the action potential spreads over the terminal, these channels open, allowing calcium to diffuse into the terminal. The calcium ions are believed to exert an attractive influence on the acetylcholine vesicles, drawing them adjacent to the dense bars. Some of the vesicles fuse with the neural membrane and empty their acetylcholine into the synaptic space via the process of exocytosis.
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Describe the charge and time of the muscle action potential
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An ACTION POTENTIAL occurs if a membrane reaches threshold potential.
• Voltage-gated channels in the membrane for sodium and potassium ions undergo conformational changes. • The flow of sodium ions into the ICF reverses the membrane potential from -70 mV to +30mV. • The flow of potassium ions into the ECF restores the membrane potential to the resting state. • Action Potentials are all or none. |
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Describe the function of T-tubules in the spreading of a muscle action potential
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Action potential spreads into each cardiac muscle fiber along the Transverse Tubles, causing the longitudinal sarcoplasmic tubules to release calcium ions into the sarcoplasmic reticulum. These calcium ions catalyze the chemical reactions that promote the sliding of the actin and myosin filaments along one another to cause muscle contraction. This mechanism is also present in skeletal muscle.
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Myosin has what bound to its nucleotide binding pocket and what state is it in?
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Has ADP and inorganic phosphate bound to its nucleotide binding pocket and is in a ready state
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A lack of ATP to bind to myosin causes what?
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A lack of ATP makes the release of actin impossible, resulting in the rigor state characteristic of rigor mortis
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Describe the function of Calcium ions with respect to muscle action potential propagation
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Calcium causes vesicles containing the neurotransmitter acetylcholine to fuse with the plasma membrane, releasing acetylcholine into the synaptic cleft between the motor neuron terminal and the motor end plate of the skeletal muscle fiber. The acetylcholine diffuses across the synapse and binds to and activates nicotinic acetylcholine receptor on the motor end plate. Activation of the nicotinic receptor opens its intrinsic sodium/potassium channel, causing sodium to rush in and potassium to trickle out. Because the channel is more permeable to sodium, the muscle fiber membrane becomes more positively charged, triggering an action potential. The action potential spreads through the muscle fiber's network of T-tubules, depolarizing the inner portion of the muscle fiber. The depolarization activates L-type voltage-dependent calcium channels (dihydropyridine receptors) in the T tubule membrane, which are in close proximity to calcium-release channels (ryanodine receptors) in the adjacent sarcoplasmic reticulum. Activated voltage-gated calcium channels physically interact with calcium-release channels to activate them, causing the sarcoplasmic reticulum to release calcium. The calcium binds to the troponin C present on the actin-containing thin filaments of the myofibrils. The troponin then allosterically modulates the tropomyosin. Normally the tropomyosin sterically obstructs binding sites for myosin on the thin filament; once calcium binds to the troponin C and causes an allosteric change in the troponin protein, troponin T allows tropomyosin to move, unblocking the binding sites. Myosin binds to the newly uncovered binding sites on the thin filament (binding to the thin filament is very tightly coupled to the release of inorganic phosphate). Myosin is now bound to actin in the strong binding state. The release of ADP and inorganic phosphate are tightly coupled to the power stroke (actin acts as a cofactor in the release of inorganic phosphate, expediting the release). This will pull the Z-bands towards each other, thus shortening the sarcomere and the I-band. ATP binds myosin, allowing it to release actin and be in the weak binding state . The myosin then hydrolyzes the ATP and uses the energy to move into the "cocked back" conformation.
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In general, evidence indicates that each skeletal muscle myosin head moves how far during each power stroke?
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10-12 nm each power stroke, however there is also evidence (in vitro) of variations (smaller and larger) that appear specific to the myosin isoform.
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ATP binding to myosin and myosin hydralyzing the ATP lasts how long?
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As long as ATP is available and calcium is present on thin filament.While those steps are occurring, calcium is actively pumped back into the sarcoplasmic reticulum. When calcium is no longer present on the thin filament, the tropomyosin changes conformation back to its previous state so as to block the binding sites again. The myosin ceases binding to the thin filament, and the contractions cease. The calcium ions leave the troponin molecule in order to maintain the calcium ion concentration in the sarcoplasm.
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The active pumping of calcium ions into the sarcoplasmic reticulum creates what?
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A deficiency in the fluid around the myofibrils. This causes the removal of calcium ions from the troponin. Thus the tropomyosin-troponin complex again covers the binding sites on the actin filaments and contraction ceases.
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What happens when an action potential originating in the CNS reaches an alpha motor neuron?
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An action potential originating in the CNS reaches an alpha motor neuron, which then transmits an action potential down its own axon. The action potential activates voltage-dependent calcium channels on the axon, and calcium rushes in.
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What are the different types of smooth muscle
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Smooth muscle can be divided into two major types: Multi-unit smooth muscle and Single unit smooth muscle.
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What is the most important charateristics of multi-unit smooth muscle
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The most important characteristics of multi-unit smooth muscle fibers are that each fiber can contract independently of the others and the control is exerted mainly by nerve signals. Examples include the smooth muscle fibers of the ciliary muscle of the eye, the iris of the eye, and the pilorector muscles that cause erection of the hairs when stimulated by the sympathetic nervous system.
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Describe single unit smooth muscle
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This type is also called unitary smooth muscle (visceral smooth muscle). A mass of hundreds to millions of muscle fibers contract together as a single unit. The cell membranes are joined by gap junctions so action potentials can travel from one fiber to the next and cause the muscle fibers to contract together. This type of muscle is found in the walls of the gut, bile ducts, ureters, uterus, and blood vessels.
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Describe the differences between striated and smooth muscle anatomy
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The muscle tissue of the GI tract is smooth muscle, except for that in the oral cavity (lips, tongue, palate) and upper esophagus. Unlike striated muscle, smooth muscle consists of individual cells, each cell with its own nucleus. Each smooth muscle cell (or "muscle fiber") is just a few microns in diameter but a couple hundred microns long. The nucleus is similarly elongated. Each striated fiber has so many nuclei that any random cross section typically displays at least one and often several, normally located around the periphery of the fiber.
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Describe the differences between striated and smooth muscle physiology
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The function of smooth muscle differs substantially from that of striated muscle. Neurotransmitter activation of smooth muscle is fairly diffuse (no discrete, well-defined neuromuscular junctions). The motor endings of autonomic axons, where neurotransmitter is released, are not closely associated with individual smooth muscle fibers. Electrical activation of smooth muscle is passed from cell to cell by gap junctions. Smooth muscle of the gut can generate intrinsic rhythmic contraction, independent from direct neural control. Input from the autonomic nervous system increases or decreases the level of this spontaneous activity. Because the cells that comprise smooth muscle fibers are typically packed closely together, individual cells are usually difficult to resolve, especially at low magnification. In contrast, individual striated muscle fibers are conspicuous as individual units. The appearance, or visual texture, of smooth muscle varies dramatically depending on the orientation of the fibers with respect to the plane of section.
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Describe the effect of Calcium ions on smooth muscle action potential generation/propagation.
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Action potentials occur in single-unit smooth muscle, such as visceral muscle in the same way that they occur in skeletal muscle. The can be elicited by electrical stimulation, stretch or the action of hormones and transmitter substances, or they may be the result of spontaneous generation in the muscle fiber itself.
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What are the two forms that action potentials of visceral smooth muscle occur?
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The action potentials of visceral smooth muscle occur in two forms: Spike potentials: typical spike action potentials occur in most types of single-unit muscle. Action potentials with plateaus. The onset of this type of action potential is similar to that of the typical spike potential. However, repolarization is delayed for several hundred milliseconds. The plateau accounts for the prolonged periods of contraction that occur in the ureter, the uterus under some conditions, and some types of vascular smooth muscle. Calcium ions are important for generating the smooth muscle action potential. Sodium participates little in generation of the action potential in most smooth muscle. Instead the flow of calcium ions to the interior of the fiber is mainly responsible for the action potential.
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Describe physiological concerns specific to cardiac muscle
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Concerns with auto-regulation, problems with ionic concentration in the blood and extra-cellular fluid. Extra-cellular calcium, too much can cause them to spasm which can cause ventricular fibrillation. Too much potassium causes them to become weak and less contraction off of each action potential. Increased body temp can hurt the heart by ramping too high, decreased body temp can slow the HR down.
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Describe the role of the atria, ventricles, and valves in each phase of the cardiac cycle.
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Phase I; Period of filling during which the left ventricular volume increases from the end-systolic volume to the end-diastolic volume or from 45 milliliters to 115 milliliters, an increase of 70 milliliters. Phae II: Period of isovolumic contraction during which the volume of ventricle remains at the end-diastolic volume but the intra-ventricular pressure increases to the level of the aortic diastolic pressure or 80 mm Hg. Phase III: Period of ejection during which the systolic pressure increases further because of additional ventricular contraction, and the ventricular volume decreases by 70 milliliters, which is the stroke volume. Phase IV: Period of isovolumic relaxation during which the ventricular volume remains at 45 milliliters but the intra-ventricular pressure decreases to its diastolic pressure level.
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Describe the five cardiac fraction/volume measurements
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Blood goes through from when it fills up
EDV End Diastolic volume 120 mL EDV SVO Stroke Volume Output 70 mL End Systolic Volume the remaining EDV-DVO=50 Ejection fraction SVO/EDV = 70/120 Cardiac Volume= HR x SV |
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Describe the Frank-Starling mechanism of cardiac pumping regulation.
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When venous return of blood increases, the heart muscle stretches more, which makes it pump with a greater force of contraction. Within physiological limits, the heart pumps all the blood that comes to it without allowing excess accumulation of blood in the veins. The extra stretch of the cardiac muscle during increased venous return, within limits, causes the actin and myosin filaments to interdigitate at a more optimal length of force generation. In addition, more stretch of the right atrial wall causes reflex increase in the heart rate of 10 to 20 per cent, which helps the heart pump more blood.
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Describe the roles of the A-V node, sinus node, A-V bundle, and the Purkinje fibers in the control of the cardiac cycle.
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The purkinje fibers lead from the A-V node, through the A-V bundle and into the ventricles. The A-V bundle lies just under the endocardium and receives the cardiac impulse first. The A-V bundle then divides into the left and right bundles. The following are characteristics of the Purkinje system. The action potentials travel at a velocity of 1.5 to 4.0m/sec. which is 6 times the velocity in cardiac muscle. The high permeability of the gap junctions at the intercalated discs between the Purkinje fiber cells likely causes the high velocity of transmission.
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Describe the effects of parasympathetic stimulation on cardiac function.
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Stimulation of parasympathetic nerves to the heart releases the neurotransmitter acetylcholine from the vagal nerve endings. Acetylcholine causes the following effects. The rate of sinus node discharge decreases. The excitability of the fibers between the atrial muscle and the A-V node decreases. The heart rate decreases to one-half normal under mild or moderate vagal stimulation, but strong stimulation can temporarily stop the heart beat.
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Describe the effects of sympathetic stimulation on cardiac function.
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Stimulation of the sympathetic nerves to the heart has the following three basic effects: the rate of sinus node discharge increases. The cardiac impulse conduction rate increases in all parts of the heart. The force of contraction increases in both atrial and ventricular muscle.
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Describe the basic components of an EKG
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The spread of the action potential in the heart initiates each heartbeat. The electrocardiogram is a recording of the voltage generated by the heart from the surface of the body during each heartbeat. The P wave is caused by spread of depolarization across the atria, which causes atrial contraction. Atrial pressure increases just after the P wave. The QRS waves appear as a result of ventricular depolarization about .16 sec after the onset of the P wave and this initiates ventricular contraction; then the ventricular pressure begins to increase. The ventricular T wave is caused by repolarization of the ventricle.
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Do tissues need more blood flow when they are active or at rest?
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Tissues need more blood flow when they are active than when they are at rest-occasionally as much as 20 times more.
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What continuously monitors the tissue needs and controls the blood flow at the level required for the tissue activity?
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The micro-vessels of each tissue.
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What is the sum of all the local tissue blood flows?
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The cardiac output
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The blood flow to each tissue of the body is precisely controlled according to what?
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the tissue’s needs.
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What provides additional control of tissue blood flow?
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Nervous and hormonal mechanisms.
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In most instances, the arterial pressure is controlled independently of what?
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Local blood flow or cardiac output control.
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Describe the primary functions of the circulatory system
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After blood flows through a tissue, it immediately returns by way of the veins to the heart. The heart responds automatically to the inflow of the blood by pumping almost all of it immediately back into the arteries. In this sense, the heart responds to the demands of the tissues, although it often needs help in the form of nervous stimulation to make it pump the required amounts of blood flow. The circulatory system is provided with an extensive system for controlling arterial pressure. If arterial pressure falls below normal a barrage of nervous reflexes elicit a series of circulatory changes that elevate the pressure back toward normal, including increased force of heart pumping, contraction of large venous reservoirs to provide more blood to the heart, and constriction of most of the arterioles throughout the body. Over more prolonged periods of time, the kidneys play additional roles by secreting pressure-controlling hormones and by regulating blood volume.
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Describe the general functional anatomy of the circulatory system
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Right heart (right atrium, right ventricle), pulmonary arteries, lungs (oxygenated blood), pulmonary veins, left heart (left atrium, left ventricle), systemic arteries, tissues (deoxygenated blood), systemic veins, right heart.
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Describe the basic process and physical principles of blood flow
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Blood flow = blood velocity x cross-sectional area. Blood velocity represents the speed of a blood “particle” in the stream ( how far the particle moves in one minute). As cross-sectional area increases, blood velocity decreases, so that the product of the two does not change. It follows that velocity will be smallest where the area is the largest (in the capillaries).
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Where is blood flow slowest?
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Blood flow represents how many particles pass a given cross-section in one minute, it is measure in mL/min. Blood velocity is slowest in the capillaries. This follows b/c the blood flow is constant throughout the vascular tree, and the total cross-sectional area is largest in the capillaries. This slowing is important b/c capillaries are very short and if the blood didn’t slow down, there wouldn’t be enough time for exchange of O2 between blood and tissues to occur.
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Describe factors that determine/impact resistance to blood flow
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P= pressure, F=flow, R=resistance, therefore: change P=FXR and R=change P/F. Note that it is the difference in pressure between the two ends of the vessel that provides the driving force for flow, not the absolute pressure in the vessel. I.E. if the pressure at both ends of the vessel were 100 mmHG there would be no flow despite the presence of high pressure. In the pulmonary circulation, the pressure gradient is much lower than that in the system circulation, whereas the blood flow is the same as that in the system circulation: therefore, the total pulmonary vascular resistance is much lower than the systemic vascular resistance.
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Describe Poiseuille's Law.
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According to Poiseuilles, vascular resistance is directly proportional to the viscosity of the blood and the length of the blood vessel and inversely proportional to the radius of the vessel raised to the fourth power. Decreased radius of a blood vessel markedly increases the vascular resistance. Small vessels in the circulation have the greatest amount of resistance, whereas large vessels have little resistance to blood flow.
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Describe the effects of vascular distensibility on blood pressure/volume control.
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The distensibility of the arteries allows them to accommodate the pulsatile output of the heart and average out the pressure pulsations: this ability provides a continuous flow of blood through the very small blood vessels of the tissues. Veins are even more distensible than arteries, allowing them to store large quantities of blood that can be called into use when needed. On average, veins are about eight times as distensible as arteries in the systemic circulation. In the pulmonary circulation, the distensiblity of veins is similar to that of the systemic circulation. The lung’s arteries, however are more distensible than those of the systemic circulation.
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Describe the physical/physiological factors that effect arterial pressure.
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With each heartbeat there is a new surge of blood in the arteries. Were it not for the distensibility of the arterial system, blood flow through the tissues would occur only during cardiac systole, with no blood flowing during diastole. The combination of distensibility of the arteries and their resistance to flow reduces the pressure pulsations to almost none by the time the blood reaches the capillaries, allowing continuous rather than pulsatile flow through the tissues. In the young adult, the pressure at the height of each pulse, the systolic pressure (120 mmHg) and pressure at its lowest point, the diastolic pressure (80mmHG) The difference between these two pressures is about 40 mmHG is called the pulse pressure.
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What are the two most important factors that can increase pulse pressure?
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1: increased stroke volume 2: decreased arterial compliance
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When can decreased arterial compliance result?
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When the arteries “harden” with aging (arteriosclerosis).
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Describe the physical/physiological factors that effect venous pressure
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Because blood from systemic veins flows into the right atrium, anything that affects the right atrial pressure usually affects venous pressure everywhere in the body. Right atrial pressure is regulated by a balance between the ability of the heart to pump blood out of the right atrium and a tendency of blood to flow from the peripheral vessels back to the right atrium.
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What is normal right atrial pressure and what can it rise to?
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The normal right atrial pressure is about 0 mm HG but it can rise to as high as 20-30 mmHg under abnormal conditions such as heart failure or after transfusion.
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Describe components of the microcirculatory anatomy
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Blood enters the capillaries through an arteriole and leaves through a venule. Blood from the arteriole passes into a series of metarterioles, which have structures into a series of metarterioles, which have structures midway between those of arterioles and capillaries. Arterioles are highly muscular and play a major role in controlling blood flow to the tissues. The metarterioles do not have a continuous smooth muscle coat, but smooth muscle fibers encircle the vessel at intermittent points called pre-capillary sphincters. Contraction of the muscle in these sphincters can open and close the entrance to the capillary.
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Describe the mechanism for blood flow through the capillaries
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In many tissues, blood flow through capillaries is not continuous but, instead, turns on and off every few seconds (vasomotion). The cause of this intermittence is contraction of the metarterioles and pre-capillary sphincters, which are influenced mainly by oxygen and waste products of tissue metabolism. When oxygen concentrations of the tissue are reduced (due to increased oxygen utilization) the periods of blood flow occur more often and last longer, thereby allowing the blood to carry increased quantities of oxygen and other nutrients to the tissues.
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Describe the physiology of nutrient exchange in the capillaries.
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Diffusion is the most important means for transferring substances between plasma and interstitial fluid. As blood traverses the capillary, tremendous numbers of water molecules and dissolved substances diffuse back and forth through the capillary wall, providing continual mixture of the interstitial fluid and plasma.
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How do lipid soluble substances diffuse into the celss during nutrient exchange in the capillaries?
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Lipid-soluble substances, such as O2 and CO2, can diffuse directly through the cell membranes without having to go through the pores.
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How do water soluble substances diffuse into the celss during nutrient exchange in the capillaries?
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Water-soluble substances, such a s glucose and electrolytes, diffuse only through intercellular pores in the capillary membrane.
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Describe the composition of the Interstitium and Interstitial Fluid.
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About 1/6th of the body consists of spaces between cells, which collectively are called the interstitium. The fluid in these spaces in the insterstitial fluid. The interstitium has two major types of solid structures: 1: collagen fiber bundles and 2: proteoglycan filaments. The collagen provides most of the tensional strength of the tissues, whereas the proteoglycan filaments, composed mainly of hyaluronic acid, are very thin and form a filler of fine reticular filaments, often describes as a “brush pile.”
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Define
Major structures of the interstitium What does collagen do |
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What are the primary factors that affect the rate of diffusion across the capillary walls are as follows?
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1: The pore size in the capillary.
2: The molecular size of the diffusing substance. 3: The concentration difference of the substance between two sides of the membrane. |
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Describe the forces/pressures that determine the distribution of fluid across the capillary membrane.
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Four forces determine fluid filtration through the capillary membrane.
1: Capillary hydrostatic pressure (Pc) which forces fluid outward through the capillary membrane. 2: Interstitial fluid hydrostatic pressure (Pif), which forces fluid inward through the capillary membrane when the Pif is positive, but outward into the intersititium when the Pif is negative. 3: Plasma colloid osmotic pressure (IIp) which tends to cause osmosis of the fluid inward through the capillary membrane 4: Intersitial fluid colloid osmotic pressure (IIif), which tends to cause osmosis of fluid outward through the capillary membrane. |
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Describe the basic anatomy of the lymphatic system
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Almost all tissues of the body have lymphatic channels. Most of the lymph from the lower part of the body flows up the thoracic duct and empties into the venous system at the juncture of the left interior jugular vein and subclavian vein. Lymph from the left side of the head, left arm, and parts of the chest region also enters the thoracic duct before it empties into the veins. Lymph from the right side of the neck and head, right arm, and parts of the thorax enter the right lymph duct, which then empties into the venous system at the juncture of the right sublavian vein and internal jugular vein.
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What does the lymphatic system do?
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The lymphatic system carries fluid from tissue spaces into the blood. Importantly, the lymphatics also carry away proteins and large particulate matter from the tissue spaces, neither of which can be removed through absorption directly into the blood capillary.
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Describe the purpose/function of the lymphatic system
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Lymph is derived from interstitial fluid. As lymph first flows from the tissue, it has almost the same composition as the interstitial fluid. In many tissues the protein concentration averages about 2gm/dl.
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In addition to carrying fluid and protein from the interstitial spaces to the circulation, the lymphatic system is one of the major routes for what?
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Absorption of nutrients from the gastrointestinal tract.
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Describe factors that acutely control local blood flow.
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An increased tissue metabolic rate increases local blood flow. In many tissues, such as skeletal muscle, increases in metabolism up to eight times normal acutely increase the blood flow about fourfold. Initially, the rise in flow is less than that of the metabolism, but once the metabolism increases sufficiently to remove most of the nutrients from the blood a further rise in metabolism can occur only with a concomitant increase in blood flow to supply the required nutrients.
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Describe factors that are long term controls of local blood flow.
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Changes in tissue vacularity contribute to longer term regulation of blood flow. If the metabolism of a tissue is increased for prolonged periods of time, the physical size of the vessels in a tissue increases; under some conditions, the number of blood vessels also increases.
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What does angiogenesis occur mainly in response from?
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Angiogenesis occurs mainly in response to the presence of angiogenic factors released from
1: ischemic tissues 2 tissues that are growing rapidly 3 tissues that have excessively high metabolic rates |
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What is one of the major factors that stimulate increased vascularity?
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Low O2 concentraion in the tissues. Animals that live at high altitudes, have increased vascularity. Like wise, chicks hatched at low O2 levels have up to twice as much vascular conductivity as in normal fetal chicks.
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Describe the effects of various hormones on the regulation of circulation.
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Several hormones are secreted into the circulation and tx’d in the blood throughout the entire body. Some of the hormones that have important effects on circulatory function:
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Name and describe some hormones that are vasoconstrictors
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Norepinephrine and epinephrine: released by the adrenal medulla, act as vasocontrictors in many tissues by stimulation adrenergic receptors.
AngitensisnII is a powerful vasoconstrictor that is usually formed in response to volume deletion or decreased blood pressure. Vasopressin(anti-diuretic hormone) is one of the most powerful vasoconstrictors in the body. It is formed in the hypothalamus and tx’d to the posterior pituitary, where it is released in response to decreased blood volume, as occurs with hemorrhage, or increased plasma osmolarity, as occurs with dehydration. Endothelin is a powerful vasoconstrictor released by endothelial cells in response to damage to these cells. After severe blood vessel damage, endothelin release and subsequent vasoconstriction may help prevent excessive bleeding from the vasculature. |
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Name and describe some hormones that are vasodialators
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Prostaglandins are formed in almost every tissue in the body. These substances have important intracellular effects, but some of them are released in the circulation, especially prostacyclin and prostaglandins of the Eseries, which are vasodilators.
Bradykinin: formed in the blood and in tissue fluids, is a powerful vasodilator that also increases capillary permeability. For this reason, increased levels of bradykinin may cause marked edema as well as increased blood flow in some tissues. Histamine: a powerful vasodilator, is released into the tissues when they become damaged or inflamed., Many ions and chemical factors can either dilate or constrict local blood vessels. Their specific effects are as follows: |
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Describe the effects of ionic concentration on the regulation of blood flow.
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Increased calcium ion concentration causes vasoconstriction.
Increased potassium ion concentration causes vasodilation. Increased magnesium ion concentration causes vasodilation. Increased sodium ion concentration casues vasodilation. Increase osmolarity of the blood caused by increased guantitieds of glucose or other nonvasoactive substances causes vasodilation. Increased hydrogen ion concentration causes vasodilation. Increased CO2 concentration causes vasodilation in most tissues and marked vasodilation in the brain. |
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What are the two components for the autonomic nervous system and what do they contribute to?
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The sympathetic nervous system, which is most important for controlling the circulation, and the parasympathetic nervous system, which contributes to the regulation of heart function.
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Describe autonomic nervous system regulation of the circulatory system.
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Sympathetic nerves innervate the blood vessels and heart. Sympathetic vasomotor fibers exit the spinal cord through all of the thoracic and first two lumbar nerves. They pass into the sympathetic chain then go via two routes to the circulation. Sympathetic stimulation of the small arteries and arterioles increases the vascular resistance and decreases the rate of blood flow through the tissues. Innervation of large vessels, especially the veins makes it possible for sympathetic stimulation to decrease the volume of the vessels. Sympathetic fibers also go to the heart and stimulate its activity, increasing both the rate and strength of pumping. Parasympathetic stimulation decreases heart rate and heart muscle contractility.
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What are the two routes the sympathetic vasomotor fibers go into the circulation?
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1: through specific sympathetic nerves that innervate mainly the vasculature of the internal viscera and heart; and
2: through spinal nerves that innervate mainly the vasculature of the periphereal areas. |
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What blood vessels are innervated by sympathetic nerve fibers
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Almost all the blood vessels, except the capillaries.
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What is the main role of the parasympathetic system?
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Althought the parasympathetic system plays an important role in controlling many other autonomic functions of the body its main role in controlling the circulation is to decrease the heart rate markedly and slightly decrease heart muscle contractility.
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The arterial baroreceptor reflex is initiated by what?
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This reflex is initiated by stretch receptors, called baroreceptors, that are located in the walls of large systemic arteries, particularly in the walls of the carotid sinus and aortic arch.
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In the arterial baroreceptor reflex control system signals from the carotid sinus receptors are transmitted through what to what?
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Signals from the carotid sinus receptors are transmitted through Herring’s nerve to the glossopharyngeal nerve and then to the tractus solitarius in the meduallary area of the brain stem.
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In the arterial baroreceptor reflex control system signals from the aortic arch are transmitted through what to what?
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Signals from the aortic arch are transmitted through the vagus nerves to the same area of the medulla.
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Describe the physiology of the arterial baroreceptor reflex control system.
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Increased pressure in blood vessels containing baroreceptros causes increased impulse firing. Baro-receptor signals enter the traactus solitarius, inhibit the vasoconstrictor center of the medulla, and excite the vagal center. The net effects are inhibition of sympathetic activity and stimulation of parasympathetic activity, which cause 1, vasodilation of veins and arterioles, and 2:decreased heart rate and strength of heart contraction.
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What is closely associated with the baroreceptor control system?
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Closely associated with the baroreceptor control system is a chemoreceptor reflex
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How does the chemoreceptor reflex operate?
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Operates in much the same way as the baroreceptor reflex, except that chemoreceptors, instead of stretch receptors, initial the response.
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The chemoreceptors are sensitive to what?
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The chemoreceptors are sensitive to oxygen lack, carbon dioxide excess or hydrogen ion excess.
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There are the chemoreceptors located?
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They are located in two carotid bodies, one of which lies in the bifurcation of each common carotid artery, and in several aortic bodies adjacent to the aorta.
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How do the chemoreceptors work?
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Whenever the arterial pressure falls below a critical level, the chemoreceptors become stimulated b/c of diminished blood flow to the bodies and the resulting diminished availability of O2 and excess buildup of CO2 and hydrogen ions that are not removed by the slow blood flow. Signals tx’d from the chemoreceptors into the vasomotor center excite the vasomotor center which in turn elevates the arterial pressure.
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Describe the function of the cardiopulmonary reflex in arterial pressure regulation.
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Both atria and pulmonary arteries have in their walls stretch receptors called cardiopulmonary receptors or low pressure receptors that are similar to the baroreceptor stretch receptors of the systemic arteries. These low-pressure receptors play an important role in minimizing arterial pressure changes in response to blood volume changes. Although the low-pressure receptors do not directly detect systemic arterial pressure, they detect increases in pressure in the heart and pulmonary circulation caused by changes in volume and the elicit reflexes that parallel the baroreceptor reflexes to make the total reflex system more potent for controlling arterial pressure.
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What helps regulate arterial pressure?
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Cardiopulmonary reflexes
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What is the renal-body fluid feedback system
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The most important mechanism for the long-term control of blood pressure is linked to control of the circulatory volume by the kidneys.
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Describe the mechanism of the renal-body fluid system of blood volume/pressure regulation
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When arterial pressure rises too high, the kidneys excrete increased quantities of sodium (pressure natiuresis) and water (pressure diuresis). As a result of the increased renal excretion, the extra-cellular fluid volume and blood volume both decrease until blood pressure returns to normal and the kidneys excrete normal amounts of sodium and water.
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What happens to the kidneys when the arterial pressure falls too low?
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Conversely, when the arterial pressure falls too low, the kidneys reduce their rate of sodium and water excretion, over a period of hours to days, if the person drinks enough water and eats enough salt to increase the blood volume, the arterial pressure returns to its previous level.
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Is the renal-body fluid system of blood volume/pressure regulation slow or fast to act?
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This mechanism for blood pressure control is slow to act, sometimes requiring several days, weeks or longer to come to equilibrium; therefore, it is not of major importance in the acute control of arterial pressure. However, it is by far the most potent of all long-term arterial pressure controllers.
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Describe the mechanism of the renin-angiotensin system of blood volume/pressure regulation
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In addition to its capability of controlling arterial pressure through changes in extra-cellular fluid volume, the kidneys control pressure through the rennin-angiotensin system. When the arterial pressure falls to low, the kidneys release a protein enzyme, renin, that activates renin-angiotensin system and helps increase the arterial pressure in several ways, thus helping correct for the initial fall of pressure.
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What is cardiac output controlled by when the changes in cardiac strength is absent?
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In the absence of changes in cardiac strength, cardiac output is controlled by factors that affect venous return.
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What is one of the most important regulators of venous return?
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One of the most important regulators of venous return is metabolism of the tissues.
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Describe factors which effect coronary vessel output and venous return
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An increase in the tissue metabolic rate results in local vaso-dilation, which causes a decrease in total peripheral resistance and thus an increase in venous return. This greater venous return causes an increase in diastolic filling pressure in the ventricles, which in turn results in a greater force of contraction by the ventricles. This mechanism for increasing cardiac pumping ability is called the Frank-Starling law of the heart.
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What does the Frank-Sterling law of the heart state?
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That, within limits, an increase in the volume of blood returning to the heart stretches the cardiac muscle a greater amount, and the heart contracts with greater force and pumps out all the excess venous return.
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Describe the muscular blood flow regulating systems during exercise
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Rise in blood flow is necessary to deliver extra nutrients to the exercising muscle and carry away the byproducts of muscular contraction. During skeletal muscle contraction, the muscle blood flow drops markedly, but it rises rapidly between contractions. Vasodilator factors increase skeletal muscle blood flow during exercise. Muscle contraction increases the metabolic rate of the tissue, which in turn reduces oxygen concentration in the tissues; the decreased oxygen concentration causes blood vessels to vaso-dilate.
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Exercising skeletal muscle releases what vasodilator factors?
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Adenosine, potassium ions hydrogen ions, lactic acid and CO2
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Describe the cardiovascular changes that occur during exercise
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Deliver more nutrients and remove greater amounts of metabolic by-products from exercising muscle. The cardio-vascular changes that occur during exercise include the following:
Massive sympathetic discharge (increase heart rate and strength) Decreased parasympathetic impulses (increase heart rate) Local vaso-dilation in exercising muscle (venoconstriction) Increased mean systemic filling pressure (venoconstriction and arteriolar constriction) Increased venous return and cardiac output Increased mean arterial pressure |
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What is the resting coronary blood flow and what can it increase to during exercise?
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The resting coronary blood flow is about 225 ml/min and can increase by 3 to 4 fold during exercise.
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Describe the effects of exercise on coronary circulation
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The coronary flow is delivered to the cardiac muscle primarily through the left coronary artery, which supplies most of the left ventricle, and the right coronary artery, which supplies the right ventricle and part of the posterior part of the left ventricle. Like skeletal muscle, the flow into the cardiac muscle decreases during muscle contraction, which in the heart coincides with systole. Flow particularly decreases a large amount in the subendocardial vessels b/c they lie in the mid-portion of the heart muscle. The surface vessels, the epicardial vessels, experience a much smaller decrease in flow during systole
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Describe the factors that lead to ischemic heart disease
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Atherosclerosis is the primary cause of ischemic heart disease. People who eat excessive quantities of fat or cholesterol and are overweight have a high risk of developing atherosclerosis.
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Why does cardiac output decrese after myocardial infarction?
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Decreased cardiac output: occurs after myocardial infarction b/c the mass of cardiac tissue that contracts normally is decreased.
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What is systolic stretch?
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Further weakening of the heart may occur as some of the ischemic muscle bulges outward during the high intraventricular pressure of systole
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Describe the factors that lead to heart failure
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Systolic stretch, cardiogenic shock, pulmonary edema, ventricular fibrillation, cardiac rupture
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What is cardiogenic shock?
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If a large portion of the heart is damaged, cardiac output may decline to very low levels, which can reduce arterial pressure. The decreased pressure, in turn, reduces coronary flow and further weakens the heart. This vicious cycle of events is called cardiogenic shock.
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What are the stages of development of atherosclerosis?
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1. Large quantities of cholesterol are deposited underneath the endothelium in arteries throughout the body including coronary arteries.
2. Later, these areas are invaded by fibrous tissue. 3. This change is followed by a necrotic stage. 4. Calcification occurs. 5. The final result is the development of atherosclerotic vessel. The plaques’s rough surface initiates formation of blood clots. 6. The blood clot is called a thrombus and can partially or fully occlude the coronary vessels. 7. Sometimes the clot breaks away and flows down stream this is an embolism. 8. A thrombus or embolism can totally block blood flow to an area of the heart, which causes death or myocardial tissue. 9. The final result is a myocardial infarction. |
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What is pulmonary edema?
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Pulmonary edema: if the left side of the heart is damaged severely, blood backs up into the pulmonary system and causes pulmonary edema. Pulmonary capillary pressure increases in this condition, which can cause leakage of fluid into the pulmonary interstitium. This edema prevents proper oxygenation of blood and can lead to death.
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What is ventricular fibrillation
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Ventricular fibrillation: or uncoordinated contraction of the ventricle, usually occurs within 10 minutes of a myocardial infarction.
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What are the factors that increase the tendency of the heart to fibrillate?
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-Increased extracellular potassium concentration due to loss of potassium from ischemic cardiac muscle.
-current of injury from the infracted area -increased irritability of cardiac muscle due to sympathetic reflexes after a myocardial infarction -circus movements, which occur b/c dilation of the heart after a myocardial infarction causes and increased pathway length for impulse conduction in the heart . |
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What is cardiac rupture?
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Cardiac Rupture: is another cause of death after a myocardial infarction. If systolic stretch is severe after an infarction, the area sometimes ruptures and causes rapid blood loss into the pericardial area. Cardiac tamponade results, which causes marked decreases in cardiac output b/c of the inability of the heart to fill properly during diastole.
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