9-18b Cardiac Physiology II Flashcards
Biomedical
What is flow equal to?
Change in pressure / Resistance
How does Ohm’s Law apply to pressure in the cardiovascular system?
Q = delta P / R CO = BP / TPR (total peripheral resistance in the system)
What are the greatest source of resistance to flow
in the cardiovascular system?
Arterioles
What portion of circulation has a high pressure gradient? Low pressure gradient?
Systemic = high Pulmonary = low
T or F: The flow of blood through the pulmonary circuit equals the flow through systemic
T
If one vessel is divided into 100 vessels, and each have the same resistance (20), and flow is 5 L/min, what is the flow through each of the branches?
5 L/min / 100 = 0.05 L/min
If the R in one of the 100 vessels increases 10 fold, but the flow through the whole sys. is 5 L/min, what happens to flow through the one branch? What will happen to pressure?
Flow decreases through the branch by a factor of 10.
Pressure will increase slightly
What are the mechanisms that control arterial smooth m. contraction?
Local Mechanisms: Tissue Metabolites, Myogenic, and Endothelial factors
Distant Mechanisms: Neural (SNS) Constriction and Humoral factors
What are tissue metabolites?
byproducts of tissue metabolism cause vasodilation of arterioles of the active m.
What are myogenic mechanisms?
the vessels inside the vascular wall have a degree of control over their contraction
dilation and constriction
What are endothelial factors?
Endothelial cells line the vessels and are metabolically active that can either constrict or dilate
What is active hyperemia?
It is an increase in organ blood flow as a response to exercise
blood flow increases proportionally to the metabolic activity
What are the mechanisms that allow blood flow to increase locally?
Accumulation of tissue metabolites cause vasodilation (K+, phosphate, adenosine, etc.) via active hyperemia, reactive hyperemia, endothelium contribution, and autoregulation
What is reactive hyperemia?
Period of arrested blood flow followed by release of pressure and spike in blood flow
Via metabolite accumulation
How does endothelium contribute to a local increase in blood flow?
Shear of blood flow against vessel wall causes release of vasodilator substances from the endothelium and vasodilation
What is a locally controlled myogenic mechanism?
Autoregulation
Intrinsic property of vascular smooth m. that allows the vessel to change diameter to maintain constant flow despite changes in BP
What controls the vasculature’s blood flow distantly?
Blood vessels are innervated by SNS via NE NT acting on alpha 1 receptors to cause vasoconstriction
SNS also stimulates the adrenal cortex to release epinephrine into the bloodstream “circulating catecholamines”
The kidneys also release hormones that regulate vessel contraction and resistance (for long-term maintenance of BP)
What are the sensors that detect a change in pressure?
Baroreceptors detect a degree of stretch at the aortic arch and the carotid body (rel. to BP)
How does the Baroreceptor Reflex move through the body?
Sensors: detect change in pressure (Baroreceptors)
Processor: develops response (brain)
Effector: carries out response
If the baroreceptor reflex signals for arterial pressure to decrease, the Response is to:
What is the goal?
Increase CO via PNS withdrawal (^ HR), increase SNS (^HR, ^SV), ^TPR via SNS-mediated vasoconstriction to ^ venous return
Goal is equilibrium
Short-term management of BP
What is VO2 in terms of the cardiovascular system?
VO2 = CO* a-vO2 diff (arterial oxygen content - venous oxygen content; O2 delivered to tissues)
What is an increase in HR due to?
Parasympathetic withdraw (lower activity of Vagus nerve)
SNS stimulation of SA node: (Direct stimulation, circulating catecholamines)
What is an increase in SV during exercise due to?
Increased preload
Positive inotropic effects (SNS stimulation)
Increased contractility
What drives changes in the redistribution of CO in the vasculature?
LE muscle pump (m. contraction squeezes veins and pushes blood up and valves prevent backflow)
What drives changes in the redistribution of CO in the vasculature?
peripheral/LE muscle pump (m. contraction squeezes veins and pushes blood up and valves prevent backflow)
respiratory m. pump: inhale decreases intrathoracic pressure and causes pressure in thorax to be less than the pressure in abdomen, pumps blood flow in; exhalation causes the inverse (thoracic pressure ^ and abdominal decreases) and allows blood to flow from the peripheral m. pumps into the abdomen (high to low pressure)
What controls the redistribution of blood flow (CO) during exercise?
sympathetically mediated vasoconstriction (arteriole) lessens visceral blood flow
locally-mediated vasodilation (arteriole) due to the release of vasodilator metabolites from active m., vessel endothelium increase blood flow to the muscles
Where does blood flow during rest? During exercise?
Rest: largely viscera blood flow
exercise: decrease in viscera blood flow, increase in muscle blood flow
What does exercise do to the a-vO2 difference?
arteriole O2 content stay the sam
venous O2 content depletes (more O2 is extracted and goes to m. b/c HGB has less of an affinity)
What two mechanisms cause depleted vO2 in blood during exercise?
Bohr effect: lower pH and higher PCO2; affinity of HGB to O2 lessens (right shift on curve) and allows more unloading of O2 to m.
increased blood flow to skeletal m. causes increase in SA for gas to exchange (recruiting capillaries that were not sustaining high levels of blood flow previously)
increase pressure gradient b/w capillary and mitochondria
What happens to BP during exercise? (MAP)
Qrest = 5 L/min > Qex = 25 L/min change in BP from 100 mmHg to 110 mmHg TPR = change in P/Q TPRrest = 100/5 = 20 TPRex = 110/25 = 4.4
although CO increased 5 fold, the decrease in TPR keeps MAP low
