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CV Regulatory Mechanisms

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imissyou419's version from 2017-01-31 17:58

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Question Answer
Purpose: (4)homeostasis.
1. ↑ blood supply to active tissues.
2. ↑/↓ heat loss from body.
3. maintain blood supply to vital organs.
4. maintain MAP
Local mechanisms autoregulation: individual vascular beds maintain a relatively constant blood flow when moderate changes occur in blood pressure, 2 theories as to how vascular beds do this
Myogenic theoryautoregulation occurs as a result of locally induced vasomotion due to a DIRECT SENSITIVITY of resistance vessels (arterioles) to pressure within their lumen
What type of effect is myogenic theorypositive so delicate capillaries do not get damaged (arterioles constrict to protect capillaries downstream)
What happens in myogenic when ↑ arterial pressure?↑ arterial pressure distends blood vessels (arteriole), stretch of VASCULAR SMOOTH MUSCLE (VSM), Open stretch activated non-selective cation channels, depolarize cell membrane which opens VG Ca2+ channels, CONTRACTION of VSM, vasoconstriction (↓ further in size than normal), ↑ resistance to blood flow, blood flow return to normal and capillary pressure maintained
What happens in myogenic when ↓ arterial pressure?↓ arterial pressure does not stretch, no depol, blood vessels relax and dilate (to try to ↑ blood flow)
Metabolic theoryautoregulation occurs as a result of locally induced vasomotion due to presence or absence of vasodilator metabolites (VDMs) in region of arterioles
vasodilator metabolites (VDMs)O2 (decrease),
[H+] or decrease in pH,
CO2,
temp,
[K+]o (AP of muscle cell, repolarization),
lactic acid,
[adenosine]o (from ATP breakdown)* EXCEPT IN KIDNEY WHERE IT CONSTRICTS
What happens in metabolic theory when ↑ atrial pressure?↑ atrial pressure, ↑ blood flow (initially), VDMs away, vessel constricts, ↑ resistance to blood flow, blood flow reduced to normal
What happens in metabolic theory when ↓ atrial pressure?↓ atrial pressure, ↓ blood flow (initially), VDMs build up, vessels dilate, ↑ blood flow back to normal
Active hyperemiaDuring exercise, ↑ metabolic activity of tissue, ↑ production of VDMs, vessels dilate, ↑ blood flow to active tissue
What is the strongest regulator of blood flow during exercise?VDMs
Reactive hyperemiaBrief ↑ blood flow following brief period of arterial occlusion. Tissue still metabolically active, VDMs build up so when restore blood flow, have sudden surge. Eventually, blood flow washes away VDMs
What are the 4 vasoconstrictor agents?epinephrine, angiotensin II, vasopressin, endothelins (ETs) - ↓ blood flow, ↑ MAP
What are the 6 vasodilator agents?epinephrine, Bradykinins, histamine, NO, prostagladins, ANF - ↑ blood flow, ↓ MAP
epinephrinesecreted by adrenal medulla (by SNS stimulation), exerts a vasoCONSTRICTING effect in MOST vascular beds by binding alpha1 adrenergic receptors in blood vessels (↓ blood flow to those areas);
causes mild vasoDILATION in skeletal, cardiac muscle, liver by binding to beta2 adrenergic receptor (get oxygen to those organs)
angiotensin IIpowerful vasoconstrictor formed in blood, causes ↑ MAP, production stimulated by ↓ bp and ↓ [Na+]
What do you use for someone with chronic high bp?ACE inhibitor because ACE converts Ang I -> II (and Ang II is a vasoconstrictor which brings bp up)
vasopressin (ADH)formed in hypothalamus, secreted by pituitary gland,
promotes WATER REABSORPTION in kidneys, high conc. produces vasoconstriction and therefore ↑ MAP
endothelins (ETs)proteins found in endothelial cells of most blood vessels (inner layer), very strong vasoconstrictors, can be released from endothelial cells when blood vessels are crushed (cause vasoconstriction and ↓ blood flow so not so much bleeding)
Bradykininsformed in blood and body fluids
Histaminereleased by tissue when damaged
NOreleased by endothelial cells and causes relaxation of smooth muscle in walls of blood vessels
How is nitroglycerin used to treat chest pain (angina pectoris)?it is converted to NO in the body, binds to NO receptor and increases cGMP which causes smooth muscle relaxation in the blood vessels therefore increasing blood flow into tissue
How does viagara work?prevent breakdown of cGMP (which causes smooth muscles to relaxation in blood vessels therefore increasing blood flow to tissue)
Prostalgladinsproduced by endothelial cells, causes relaxation of vascular smooth muscle
ANFpowerful vasodilator, released by atrial muscle when they are stretched
Neural controlmaintains normal MAP for proper perfusion of tissues throughout the body, RAPID adjustment of both CO and TPR (MAP = CO x TPR)
Cholinergic system stimulating PNS fibers to heartstimulate PNS fibers to heart, release Ach onto Muscarinic receptors, ↓ HR and force of contraction (SV), ↓ CO, ↓ MAP
Cholinergic system stimulate sympathetic cholinergic vasodilator fibers to periphery tissues (skeletal muscle)release Ach, dilate blood vessels (arterioles), ↓ TPR, ↓ MAP
Adrenergic stimulating SNS fibers to heartstimulate SNS fibers to heart, release NE onto B1 receptors, ↑ HR and force of contraction (SV), ↑ CO, ↑ MAP
Adrenergic stimulation of preganglionic nerves to adrenal medullaRelease Ach onto adrenal gland, secretion of E (80%), NE (20%), bind to B1 receptors, ↑ HR and force of contraction (SV), ↑ CO, ↑ MAP
Adrenergic stimulating SNS vasoconstrictor fibers to most peripheral blood vesselsrelease NE onto blood vessels attaching to alpha1 adrenergic receptors, vasoconstrictor, ↑ TPR, ↑ MAP (does not affect CO because not affecting HR or SV with peripheral blood vessels)
What blocks the vasoconstricting effects of SNS in active tissue?VDMs
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Question Answer
Baroreceptor reflex, what are the 2 things it relies on?homeostatic mechanism for maintaing MAP, relies on 1. mechanoreceptors/high pressure baroreceptors, 2. CV control centre in medulla
High pressure baroreceptors locationin walls (tunica externa) of aortic arch and carotid sinus (swelling of internal carotid artery), monitor changes in arterial pressure and relay info to CV centre
Low pressure receptorsNOT INVOLVED IN BARORECEPTOR REFLEX;
Located in right atrium, detects fullness of circulation, helps regulate BLOOD VOLUME (b/c higher blood volume = higher MAP)
↑ Blood volume causes↓ ADH, renin, Ang II, ↑ ANF (vasodilator) through stretching of atrial muscle
↓ Blood volume causesrelease of ADH (↓ urine output + vasoconstrict), renin release -> formation of Ang II (vasoconstrict) -> stimulate thirst and aldosterone release
Cardiovascular centre, location + 3 structureslocated in medulla of brainstem, 1. solitary tract nucleus (NTS), 2. vagal centre (cardio-inhibitory area), vasomotor centre
↑ BP baroreceptor reflex↑ BP, stretch mechanoreceptor (stretch walls), ↑ firing rate through afferents to ACTIVATE/EXCITE NTS, NTS ACTIVATE Vagal centre (↑ vagal traffick to heart, Ach release - ↓ HR, ↓ CO, ↓ MAP) && NTS ACTIVATE INHIBITORY INTERNEURON TO Vasomotor centre (↓ sympathetic outflow to heart - ↓ HR & contraction so ↓ CO, ↓ MAP & blood vessels so ↓ constriction = dilation, ↓ resistance so ↓ MAP)
↓ BP baroreceptor reflex↓ BP, ↓ firing rate of AP to NTS, less activation of vagal centre by NTS && less activation of inhibitory neuron to vasomotor centre therefore vasomotor centre activated (↑ sympathetic outflow to heart & blood vessels)
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Question Answer
CV regulation during emotional stress (Hint: 6 - 3 exceptions, PNS and SNS, veins, splanchnic)1. ↑ activity of sympathetic cholinergic fibers to muscle arterioles -> dilation,
2. ↑ activity of sympathetic cholinergic fibers to sweat glands -> sweating.
3. ↑ activity of sympathetic fibers to adrenal medulla -> E will dilate muscle arterioles and constrict other kidney and splanchnic arterioles, E will ↑ HR and SV.
4. ↓ activity of vagal nerve and ↑ activity of sympathetic postganglionic fibers (NE) to heart -> ↑ HR and contractility.
5. ↑ sympathetic outflow to capacitance vessels -> constriction -> ↑ EDV by ↑ venous return.
6. ↑ sympathetic outflow to renal and splachnic resistance vessels -> constriction
CV regulation during exercise (local)resistance vessels dilate in active muscles due to vasodilator metabolites (very powerful mechanism), VDMs block sympathetic vasoconstrictor effects on muscle vessels
CV regulation during exercise (mechanical Hint: muscle pump)muscle pump returns blood from lower limbs to central circulation (↑ venous return, ↑ EDV, ↑ SV, ↑ CO, ↑ MAP)
CV regulation during exercise (nervous system Hint: SNS, PNS, temp)↑sympathetic outflow to heart & systemic blood vessels (↑ HR (tachycardia), ↑ contractility, ↑ CO, ↑ MAP, constriction of resistance vessels in kidney and intestines and intestinal veins),
↓ vagal flow to heart;
↑ temp so temp-sensitive cells in hypothalamus are activated -> inhibit sympathetic outflow to skin vessels (inhibit the vasoconstriction) and stimulate cholinergic fibers to sweat glands therefore dilation of skin vessels and sweating
CV regulation during exercise (humoral)if exercise severe, cholinergic fibers to adrenal medulla activated, E released into blood stream -> ↑ HR and contractility, constricts veins and arterioles, dilates blood vessels in skeletal muscle
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