Term
| Explain the extrinsic regulation of cardiac rate and contractility: |
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Definition
The strength of ventricular contraction depends on the activity of the sympathoadreanal system. Norepinephrine and epinephrine produce an increase in contraction strength, a positive inotropic effect (due to an increase in the amount of Ca2+ available to the sarcomeres). Cardiac output is thus affected in two ways by the sympathoadrenal system; 1) through a positive inotropic effect on contractility and 2) through a positive chronotropic effect on cardiac rate. Parasympathetic stimulation to the SA node has a negative chronotropic effect, which causes increased EDV, which increases contraction strength (Frank-Starling law). This increases stroke volume, but not enough to compensate for slower cardiac rate. Thus, cardiac output is decreased when the heart beats slower. |
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Term
| Explain the relationship between venous return and stroke volume: |
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Definition
| The EDV and thus the stroke volume (directly related) are controlled by factors tha affect venous return. These factors are dependent on: 1) Blood volume and venous pressure 2) Vasoconstriction caused by sympathetic tone 3) Skeletal muscle pumps 4) Intrathoracic pressure drop during inhalation. |
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Term
| Explain the Frank-Starling law of the heart: |
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Definition
| States that ventricular contraction varies directly with EDV. As EDV increases, myocardium is stretched more, causing greater contraction and stroke volume. the relationship between EDV, contraction strength and stroke volume is an intrinsic property of heart muscle. ex. 1) Rise in peripheral resistance causes decrease in stroke volume of the ventricle, so 2) more blood remains in the ventricle and the EDV is graeter for the next cycle; as a result 3) the ventricle is stretched to a greater degree in the next cycle and contracts more strongly to eject more blood. |
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Term
| Explain the forces that act in capillaries: |
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Definition
| Filtration results from hydrostatic pressure exerted against the capillary wall. Net filtration pressure is equal to the hydrostatic pressure of the blood in the capillaries minus the hydrostatic pressure of the tissue fluid outside the capillaries. Proteins in plasma is restricted from filtering out of capillaries into interstitial fluid, so the osmotic pressure exerted by plasma proteins called colloid osmotic pressure is greater than that of interstitial fluid. The difference between the two is oncotic pressure. Since colloid pressure is so low, the oncotic pressure is essentially equal to the colloid pressure of plasma. Since water moves by osmosis into the solution of lower to the solution of higher osmotic pressure, the oncotic pressure favors the movement of water into the capillaries. Thesea re all opposing forces that affect the distribution of fluid across the capillary, known as Starling forces. |
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Term
| How can edema be produced: |
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Definition
| High arterial blood pressure, venous obstruction, leakage of plasma proteins into interstitial fluid, myxedema, decreased plasma protein concentration, obstruction of lymphatic drainage. |
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Term
| Explain how the kidneys regulate blood volume: |
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Definition
| The kidneys filter plasma through the capillary pores (glomeruli) and the plasma then becomes filtrate. The kidneys produce 180L of blood filtrate per day, but since there is only 5.5L of blood in the body. most is returned and recycled. Only 1.5L of urine is excreted daily, 99-98% of the amount filtered is reabsorbed back. If 99% is reabsorbed, 1% must be excreted. Decreasing the reabsorbtion from 99 to 98% would double the volume of urine excreted (an increase to 2% of the amount filtered). This would mean that doubling urine volume from 1-2L would result in an additional loss of 1L blood volume. This is because the percentage of filtrate reabsorbed, thus urine volume and blood volume- is adjusted according to the needs of the body and by the action of specific hormones on the kidneys. |
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Term
| Explain the hormonal regulation of how the kidneys regulate blood volume: |
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Definition
ADH- reatains fluid, increased blood pressure; released by posterior pituitary when osmoreceptors detect high osmolality (salt). From excess salt intake of dehydration, causes thirst, stimulates H2O reabsorbtion from urine. ADH release stimulated by aldosterone.
Aldosterone- retains salt, fluid, increased blood pressure; released by adrenal cortex, helps maintain blood volume and pressure through reabsorbtion and retention of salt and water from urine. release is stimulated by salt deprivation, low blood volume and low blood pressure.
Atrial natriuretic peptide (ANP)- lose fluid, lowered blood pressure; expanded blood volume is detected by stretch receptors in left atrium and causes release of ANP. ANP inhibits aldosterone, promote salt and water excretion to lower blood volume, promotes vasodilation. ANP, together with decreased ADH, acts in a negative feedback system to lower blood volume. |
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Term
| Describe the factors that affect blood flow through vessels: |
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Definition
| Vascular resistance- vasodilation decreases resistance and increases blood flow, vasoconstriction increases resistance and decreases blood flow. Flow rate is inversely proportional to resistance. Resistance is directly proportional to length of vessel and viscosity of blood. Resistance is inversely proportional to 4th power of radius, diameter of vessel is very important for controlling resistance and blood flow. Mean arterial pressure and vascular resistance are the two major factors regulating blood flow. MAP = CO*VR. Blood is shunted from one organ to another by degree of constriction of their arterioles. |
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Term
| Explain the regulation of total peripheral resistance: |
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Definition
| Extrinsic regulation of vascular resistance is provided mainly by the sympathetic nervous system, which stimulates vasoconstriction of arterioles in the viscera and skin. Intrinsic control of vascular resistance allows organs to autoregulate their blood flow rates. Myogenic regulation occurs when vessels constrict or dilate as a direct response to a rise or fall in blood pressure; metabolic regulation occurs when vessels dilate in response to the local chemical environment within the organ. |
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Term
| Explain the mechanisms that regulate blood flow to the heart and skeletal muscles: |
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Definition
| During exercise, when the heart's metabolism rises, intrinsic metabolic mechanisms stimulate vasodilation of the coronary vessels, and thus increase coronary blood flow. Just prior to and at the start of exercise, blood flow through the skeletal muscles increases because of vasodilation caused by the activity of cholinergic sympathetic nerve fibers. During exercise, intrinsic metabolic vasodilation occurs. |
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Term
| Describe the circulatory changes that occur during exercise: |
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Definition
| Cardiac output can increase by a factor of 4, 5 or more during exercise, and the heart and skeletal muscles receive an increased proportion of higher total blood flow. a) The cardiac rate increases because of lower activity of the vagus nerve and higher activity of sympathetic nerves. b) Venous return is greater because of higher activity of the skeletal muscle pumps and increased breathing. c) Increased contractility of the heart, combined with a decrease in total peripheral resistance can result in higher stroke volume. |
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Term
| Explain how blood flow to the brain is regulated: |
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Definition
| It is regulated both myogenically and metabolically; cerebral vessels constrict as systemic blood pressure rises too high, and dilates when blood pressure is too low. Metabolic products cause local vessles to dilate and supply more active areas with blood. |
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Term
| Explain how blood flow to the skin is regulated: |
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Definition
| The skin contains unique arteriovenous anastomoses that can shunt the blood away from surface capillary loops. The activity of sympathetic nerve fibers causes constriction of cutaneous arterioles. As a thermoregulatory response, cutaneous blood flow and blood flow through surface capillary loops increase when body temperature rises. |
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Term
| Describe how blood pressure is regulated: |
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Definition
| Baroreceptors in the aortic arch and carotid sinuses affect the cardiac rate and the total peripheral resistance via the sympathetic nervous system. The baroreceptor reflex causes pressure to be maintained when an upright posture is assumed. This reflex can cause a lowered pressure when the carotid sinuses are massaged. Other mechanisms that affect blood volume help to regulate blood pressure. |
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Term
| Describe how blood pressure is measured: |
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Definition
| Blood pressure is commonly measured indirectly by auscultation of the brachial artery when a pressure cuff is inflated and deflated. The first sound of Korotkoff is caused by turbulent blood flow through a consttricion in the artery, and occurs when the cuff pressure equals the systolic pressure. The last sound of Korotkoff is heard when the cuff pressure equals the diastolic blood pressure. The mean arterial pressure represents the driving force for blood flow throug the arterial system. |
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Term
| Describe the causes and dangers of hypertension: |
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Definition
| Hypertension (high blood pressure) is classified as primary or secondary. Primary hypertension, or essential hypertension may result from the interaction of numerous mechanisms that raise the blood volume, cardiac output, and/or peripheral resistance. Secondary hypertension is the direct result of known diseases. It is dangerous because it increases the afterload, making ventricular ejection difficult, causing the heart to work harder, which pathologically changes the heart's structure and function which can lead to congestive heart failure. Also, it can damage cerebral blood vessels leading to stroke, and can contribute to development of atherosclerosis. |
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Term
| Describe the causes and dangers of circulatory shock: |
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Definition
| Circulatory shock occurs when delivery of oxygen to the organs of the body is inadequate. In hypovalemic shock, low blood volume causes low blood pressure, which may progress to an irreversible state. The fall in blood volume and pressure stimulates various reflexes that produce a rise in cardiac rate, a shift of fluid from the tissues into the vascular system, a decrease in urine volume and vasoconstriction. |
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