Term
| Why is it important that blood flow to each tissue is regulated to the minimal level that will supply the tissue's requirements? |
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Definition
-keeps the workload on the heart to a minimum
-prevents tissues from suffering from low oxygen |
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Term
| What is the difference between acute and long term control of blood flow? |
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Definition
| Acute control can change rapidly via local vasodilation or vasoconstriction or the arterioles, metaarteriols, and precapillary sphincters. Long term control is slow and changes over days, weeks, or months and is the result of changes in the size or number of blood vessels |
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Term
| What are the two basic theories for the regulation of local blood flow when either the rate of tissue metabolism changes or the availability of oxygen changes? |
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Definition
-the vasodilator theory
-the oxygen lack theory |
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Term
| What is the vasodilator theory? |
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Definition
| The vasodilator theory states that the greater the rate of metabolism, the greater the rate of formation of vasodilator substances in the tissue cells. The vasodilator substances then diffues through the tissues to the precapillary sphincters, metarteriols, and arterioles to cause relaxation of smooth muscle and dilation. |
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Term
| What are four vasodilator substances? |
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Definition
| Adenosine, carbon dioxide, potassium ions, hydrogen ions |
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Term
| What is the oxygen lack theory for local blood flow control? |
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Definition
| Oxygen is required as one of the metabolic nutrients to cause vascular muscle contraction. Therefore, the absence of adequate oxygen as a result of increase metabolism would result in the relaxation and dilation of blood vessels. |
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Term
| Define reactive hyperemia. |
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Definition
| Reactive hyperemia is the transient increase in organ blood flow that occurs following a brief period of ischemia, usually produced by temporary arterial occlusion. |
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Term
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Definition
| Active hyperemia is the increase in organ blood flow that is associated with increased metabolic activity of an organ or tissue. |
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Term
| What organs have the greatest degree of autoregulation? The least? |
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Definition
Greatest
-coronoary circulation
-cerebral circulation
-renal circulation
Very little autoregulation
-cutaneous ciruclation |
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Term
| How is nitric oxide formed? |
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Definition
| In endothelial cells nitric oxide synthase synthesizes nitric oxide from arginine and oxygen and reduction of inorganic nitrate. |
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Term
| How is nitric oxide activated? |
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Definition
| Shear stress on endothelial cells lining arteries and arterioles causes the release of NO. NO oxide then activates soluble guanylate cyclase in vascular smooth muscle cells resulting in conversion of cyclic guanosine triphosphate to cyclic guanosine monophosphate and activation of cGMP dependent protein kinase which results in blood vessels relaxation. |
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Term
| Why would it be useful for angiotensin II to stimulate the release of NO? |
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Definition
| Angiotensin II is a vasoconstrictor and release of NO would prevent excessive vasoconstriction. |
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Term
| What is released when blood vessels are damaged? |
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Definition
| Endothelin- a vasoconstrictor that is released when endothelial cells are damaged. |
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Term
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Definition
-Nitric oxide
-prostacyclin (PGL2)
-Prostaglandin E2 (PGE2) |
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Term
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Definition
-Angiotensin II
-PGF 2 alpha
-Thromboxanes
-Leukotrienes |
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Term
| T/F Average oxygen and metabolic need determine vascularity. |
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Definition
| False. Maximum need determines vascularity. |
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Term
| What are some examples of vascular growth factors? What do they do? |
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Definition
-vascular endothelial growth factor (VEGF)
-Fibroblast growth factor
-Angiogenin
-Angiogenic factors promote new vessel growth from existing vessels. |
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Term
| What is collateral circulation? |
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Definition
| Collateral circulation is the formation of new vascular channels around a blockage, allowing at least a partial resupply of blood to the affected area. |
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Term
| What are some secreted substances or hormones that conrol blood flow? |
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Definition
VASOCONSTRICTORS
-Norepinephrine
-epinephrine--through it can cause mild vasodialtion via beta adrenergic receptor
-agiontensin
-vasopressin
VASODILATORS
-bradykinin
-histamine |
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Term
| What is the effect of norepinephrine on blood vessels? |
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Definition
| Norepinephrine is a powerful vasocontricor (via alpha adrenergic receptors of the vascular smooth muscle) |
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Term
| What is released during sympathetic excitation? What effect does it have on blood vessels? |
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Definition
| Stimulation of the sympathetic system causes sympathetic nerve endings to release of norepinephrine which excites the heart and contracts the veins and arterioles. Sympathetic nerves in the adrenal medulla causing the release of norepinephrine and epinephrine which has the same excitatory effect on the heart and vasoconstriction of veins and arterioles. |
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Term
| What effect do calcium ions have on blood vessels? |
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Definition
| Calcium ions stimulate smooth muscle contraction=vasoconstriction |
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Term
| What ions lead to vasodilation? |
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Definition
-Potassium and magnesium via inhibition of smooth muscle contraction.
-anions acetate and citrate also cause mild degrees of vasodilation
-carbon dioxide-moderate vasodilation in most tissues, but marked vasodilation in the brain
-hydrogen ions caases dilation of arteriols |
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Term
| What effect does a decrease in hydrogen ion concentration have on blood vessels? |
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Definition
| A decrease in hydrogen ion concentration leads to a causes arteriolar constriction. |
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Term
| How is blood flow to specific organs and tissues mainly controlled? (Local or nervous system control) |
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Definition
| Mainly local control mechanisms |
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Term
| The nervous system controls what functions of circulation? |
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Definition
Global functions including
- redistributing blood flow to different areas of the body
- increasing or decreasing pumping activity by the heart
-providing very rapid control of systemic arterial pressure |
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Term
| What parts of the circulatory system does the sympathetic nervous system innervate? |
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Definition
-precapillary sphincters
-metarterioles
more dense innvervation of
-small arteries
-arterioles
-veins |
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Term
| What vessels are not innervated? |
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Definition
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Term
| What area of the brain is responsible for regulating sympathetic and parasympathetic nervous system control of the circulatory system? |
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Definition
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Term
| What areas of the brain are particularly important for stimulating cardiovascular responses to emotion and stress? |
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Definition
| the hypothalamus and higher centers of the brain which modify the activity of the medullary centers |
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Term
| What are the impulses called that normally maintain a partial state of contraction in blood vessels? |
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Definition
| Sympathetic vasoconstrictor tone |
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Term
| What are the three changes that the nervous system induces simultaneously to increase arterial pressure? |
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Definition
-constriction of most arterioles systemic circulation
-veins are constricted
-heart is directly stimulated by autonomic nervous system |
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Term
| What is the most rapid of all our responses for arterial pressure control? |
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Definition
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Term
| If baroreceptors are stretched, what effect do the signals have once they enter the tractus solitarius of the medulla? |
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Definition
| Secondary signals will inhibit the vasoconstrictor center of the medulla and excite the vagal parasympathetic center. The net effects are vasodilation of the veins and arterioles throughout the peripheral circulatory system and decreased heart rate and strength of contraction. |
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Term
| Where is there a high concentration or baroreceptors? |
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Definition
| Baroreceptors are abundant in the wall of each internal carotid artery, specifically the carotid sinus, and in the wall of the aortic arch. |
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Term
| How is pressure maintained when a person transitions from laying down to standing? |
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Definition
| The baroreceptors maintain blood pressure by detecting the drop in pressure upon standing. They elicit an immediate reflex which results in a strong sympathetic discharge throughout the body, keeping blood pressure stable |
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Term
| Where are the chemoreceptors that control arterial pressure located? |
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Definition
In chemoreceptor organs:
-carotid bodies
-aortic bodies |
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Term
| When are the chemoreceptors most active in controlling arterial pressure? |
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Definition
| The chemoreceptor reflex is not a powerful arterial pressure controller until the arterial pressure falls below 80 mmHg |
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Term
| What role do the kidney play when arterial pressure is high? |
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Definition
| When the atria are stretched atrial natriuretic peptide (ANP) is secreated and antidiuretic hormone secretion is inhibitied from the hypothalamus. This causes afferent arteriols to the kidneys dilate, increasing sodium and water excretion. |
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Term
| Most of the body's control of blood pressure occurs through receptors that are located in peripheral ciruclation. What is the exception to this and what is the mechanism by which it works? |
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Definition
| The central nervous system can also directly respond to cerebral ischemia via the central nervous system ischemic response. Failure of blood flowing to the vasomotor center of the brain stem results in increased levels of CO2 which stimulates vasocontricotr and cardioaccelerator neurons in the vasomotor center. |
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Term
| What is the last ditch effort to prevent atrial pressure from falling? When is it activated? |
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Definition
| The central nervous system ischemic response is the last ditch stand and is activated when arterial pressure falls below 60mmHg and is particularly active at 15 to 20 mmHg. |
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Term
| What is the cushing reaction? |
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Definition
| The Cushing reaction if a CNS ischemic response that results from increased pressure of the cerebrospinal fluid. When cerebrospinal fluid pressure is greater than arterial pressure it will cut off blood supply to the brain resulting in activation of the CNS ischemic response. When arterial pressure is increased above cerebrospinal pressure blood flow is reestablished. |
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