Physiology 12.13.12 Circulation through Individual Tissue Beds Flashcards
Is sympathetic tone always present in coronary circulatino
yes
What changes the flow to heart
local metabolites produced by working msucle
Blood flow is proportional to what
Rate of work
Is flow slowed or increased during contraction of heart
slowed
What is ht mL/min of coronary blood flow at rest
250 mL/min
What % of coronary blood flow supplies left heart? right heart?
80% left heart
remainder ot right heart
What % of CO is coronary blood flow at rest
5%
Where do the major coronary arteries arise form?
Aorta distal to aortic valve
and provide virtually all the arterial blood supply
Describe the venous drainage of the myocardium
Coronary capillary blood flows via venules to veins that reach epicardial surface of heart and parallel teh arterial supply back to Coronary sinus
How do most of hte left ventricular capillary blood reach the right atrium
by wa of coronary sinus
small portion (of right ventricle capillaries) reaches right atirum by way ANTERIOR CARDIAC VEIN
What are thesbian veins
how inconsequential amt of blodo reaches cardiac ventricels direclty
What are factors that influence coronary blood flow
Aortic Pressure during Diastole
Extravascular Compression (squeezing of vessels during systole)
Sympathetic effects
Metabolic Factors
Coronary BF and Aortic P
Aortic P provides DF for BF through coronary arteries
During Diastole, flow is direclty proportional to aortic pressure
Severe hypothension (shock) and Coronary BF
Low aortic P may limit coronary BF
Increase in mean aortic P during exercise
increased ocronary BF
Extravascualr compression (squeezing) of myocardial vessels
occurs during cardiac systole
Compression reduces vascular diameter –> Increase vascular resistance –> decreases flow
What can happen during isovolumentric contraction of left ventricle
Extravascular compression is so great that flow in the left coronary artery may reverse momentarily
When is extravascular compression a problem
with sustained hypertension
Elevated afterload on LV increases ventriuclar work and O2 demand while also increasing extravascular compression
Combo increses the need for blood flow and restricts it as well
During conditions with reduced BF to heart (coronary occlusion or hypotension) is damage more likely to the inner (endocardial) wall of ventricle or outer (epicardial) wall
Inner Endocardial Wall
b/c extravascular compression is more significant
Does extravascular copression disturb coronary flow in right ventricle
not as much bc myocardial pressure is not nearly as reat
Total flow in right coronary artery is actually greater during systole than diastole b/c of greater driving pressure during systole
Sympathetic effect on coronary blood flow
Stimulation of sympathetic nerves to heart increases BF indirectly
In normal circumstances, sympathetic stimulation increases coronary BF by increasing HR and contractility whih increases Cardiac worka nd Myocardial O2 consumption
The resuling decerase in tissue O2 increases coronary BF by METABOLIC REGULATION
What happens if inotropic and chornotorpic effects of smpahteric stimulation are inhibited by beta adrenergi blocker
symp stimu decreases BF suggestion that alpha adrenergic vasoconstriction of cornoary vessels has occurred
What metabolites are implicated in metabolic mechainism which O2 demands triggers coronary vasodilation
H+ lactic acid Co2 Adenosine Endothelial derived relaxing factor (NO) K+
The more oxygen consumed, the more coronary blood flow
What happens during progressive ischemia (causing hypoxia) of myocardial tissue
stiualtes growth of colalteral vessels allowign more blood (O2) to reach ischemic area
Severe ischemia of cardiac tissue gives rise to chest pain (angina pectorsi)
What can releive angina
adminitstration of nitrites (nitroglycerin or ayl nitrite)
Gives rise to NO, acts as systemic vasodialtors, esp dilating coronary arterioles – .decreaseing afterload against whcih LV works
THis decreases myocardial O2 deman ,relieves myocardial ypoxia and angina
What is the O2 consumption in the non-exercising invididual
8-10 ml/min/100g of heart
Even at rest the herat is owrking
How much does O2 consumption increase during exercise
How does this affect coronary BF
It increases 5x during exercise
The increased delivery of O2 during exercise must be met by increasing coronary BF
Work formula
Work = Pressure x Volume
Aortic Pressure is the P against
What is the work of the heart when SV is 120 mL agasint MEP of 90 mm Hg, or a SV of 60 mL agasints MAP of 180 mmHG
Same!
Does icreasing Aortic Pressure or SV demand more O2 ?
but Elevating aortic P increases O2 demand more than increasing SV
How much O2 does Right heart require vs left heart. Why
Right heart only needs 1/5 O2 supply b/c PULMONARY ARTERY SYSTOLIC P is only 1/5 Aortic Systolic Pressure
Right heart only does 1/5 of the work since same CO
What hpapens when heart adapts to increased afterload
Ventricular Dialtion! common adaptiation in cardiac failure
What are the advantages of cardiac dilation
increases resting length (increased preload) which helps maintain SV
D
Disadvantage of cardiac dialtion
Dilation increases its radius –> will Law of LaPlace, tension in ventricular wall required to generate pressure increases with radisu of the herat
Tension agasint which heart must contract increases with dilation
What substrates are utilized by heart (and %) postprandial (after a meal)
glucose (40%) and 60% from non-carb (amino acids)
As interval after eating …source
more from amino acids, less from carbs
After prolonged fasting or strenuous exercise , heart sues
increases lasma concentration of KETONE BODIEs, whicha re used by heart (
When inadequate O2 is delivared to myocardium, heart produces
lactic acid from glycogen breakdwn to support aerobic carb metabolism until O2 lack wont allow further metabolism of lactic acid
Hypoxic (ischemic) heart
dependent on ATP generated from anaerobci metbolism for energy
How does blood enter skin
skin arterioles can pass through skin capillaries or arteriovenous anastomoses taht direclty connect arteries to veins, byapssign capillaries
What is the normal BF rate to skin ? when temp increas?
temp is comfortable from 3-5 mL/100g skin
Incresase to 150 mL/100g in hot atomstoshere
What controls BF to skin? Which R?
sympathetic NS
Adrenergic vasoconsttrictor through alpha-1 receptor
Do skin arterioles/BF increases or decreases durign heat?
Dilate during heat,
Constrict during cold
What happens when extreminiteis expose to severe cole
strong vasoconstriction
as hadns and feet reach near freezing, some vasodaltion occurs by relaxation of arteriovenous anastomoses
Vasodilation at expense of lowering core body T
Sympathetic cholinergic fibers. What is Bradykinin?
induce sweating
Sweat contains Bradykinin- local VASODILATOR
What are other vasodilators released during skin injury
Histamine, ATP, substance P, bradykinin
What receptors are in arterioles of skletal muscle beds
mostly Beta-2; respond to epineprhine and dilate
How much CO do sk muscle receive at rest?
20-25% but b/c large portion of body weight
Max exercise, how much CO input
90%
How much CO does BF to CNS receive
cerebral vessels receive nearly 15% of CO although CNS only accts for 2% of body weight
Which metabolites creastes increased local production of vasodilators (adenosine, lactic acid, H, CO2 and K) taht reduce cerebral arteriorlar resisteance
Adenosine, Lactic Acid H CO2 K
Can BF into brain exceed outflow?
NO!
What happens to BF in brain when flashes of light shined on retinea
Increased blood flow to, and metabolism within ,visual cortex
Consequently, flow is decreased in other brain areas
Large arteries leading to brain are innervated by
SNS but they exhibit myogenic autoregulatio thus brain blood flow is nearly constatn over range of arterial pressures
What is “Cushing’s Reflex”
Hypothalamic response to cerebral ischemia that consists of and increase in sympathetic tone that increases heart rate, arterial BP, and total periphearl resistance
What is the barorR reflex
incresing vagal tone and iminishes HR
REsulting combo of hypertensin, bardycardia, and increased pulse pressure seen in response to increased intracranial pressure a rereferred to as Cushing’s reflex
How much blood CO (%) does sphlancnic bed receive
255
What arteries supply splanchnic circuatio
celiac,
superior mesenteric
inferior mesenteric arteries to GI tract, spleen ,pancreas, and liver
Portal vein tranpsorts venous blood at low P to the liver
What innerveates teh splanchnic circualtion
Vagus nerve
predominates during digestion
Can be overcome by sympathetic sysstem whci reduces splanchnic BF`
What happens to Instestinal ciculation during hemorrhage or intesnse exercise
BF to intensine severely reduced by alpha-mediated vasoconstriction
BF divereted frm Splanchnic bed to central venous system for use by othe rtissues
What happens when BF to intestinal mucosa is esp low (hemorrhagic shock)
celsl at tipi of villus may become severely hypoxic, even to point of causing necrosis
more permeabl to bacteria and organisms
How much CO doe liver receive
25%
3/4 deliered by protal vein
1/4 delivered by hepatic artery
Bloodf rom hepatic artery and protal vein mix in liver then flows peripherally between hepatic cells and collects in venules – >coalesce into hepatic veins that feed into inferior vena cava
What is pressure in liver vessels compared to inferior vena cava
Pressure is only slightly above that of hte inferior vena cava and right atrium
What happens to hepatic when cardiac failture
Central Venous PRessure may exceed hepatic capilalry pressures
Elevation in hydrostatic P in hepatic interstitium causes exudation of fluid thorgh permeable liver capsule and into bdominal cavity abdominal edema or ascites)
What happens to hepatic when cardiac failture
Central Venous PRessure may exceed hepatic capilalry pressures
Elevation in hydrostatic P in hepatic interstitium causes exudation of fluid thorgh permeable liver capsule and into bdominal cavity abdominal edema or ascites)
How much blood volume in liver. what happens when alpha-adrenergenc innervation
15% BV.
Vasoconstriction and reduction in hepatic BF
CO of kindey
only 1% of body weight ,but receive 20% CO
