ICL 3.3: Cardiac Physiology, Vascular Physiology & Autoregulation Flashcards
what is the purpose of homeostasis?
to provide adequate blood to the tissues
ex. during exercise the blood flow to skeletal muscles increases while GI decreases!
what are the 3 primary mechanisms through which homeostasis is achieved?
- autoregulation
- neural and endocrine mechanisms
- organ-specific regulations
what branch of the nervous system controls peripheral blood flow?
peripheral blood flow is under dual regulation of the CNS anddddd local!
whereas the heart is mainly just under CNS regulation
what is autoregulation?
maintenance of a constant blood flow to an organ in the face of changing arterial pressure/resistance
if you change the BP to double, the blood flow will not change! this is due to autoregulation!
this mechanisms is mainly driven by local factors –> so it’s based on the intrinsic ability of the organ and isn’t based on neural or hormonal effects!
which organs have strong autoregulation? weak? non?
STRONG
- kidney
- brain
- coronary
WEAK
- skeletal muscle
- splanchnic circulation
NONE
1. cutaneous circulation
how is autoregulation achieved?
CO = P/TPR
P = CO X TPR
= HR X SV X TPR
= HR X (EDV-ESV) X TPR
short term regulation of MAP principally involves the sympathetic nervous system and the regulation of HR and TPR
if you increase the perfusion pressure, you will have an increase in flow! if you decrease perfusion pressure, you will have a decrease in flow!
however, when there’s autoregulation, if there is a decrease in perfusion pressure, the autoregulation will maintain constant flow by decreasing resistance via vasodilation of the arterioles
arterioles are the major resistance controlling vessels!!
what is perfusion pressure?
the pressure difference between the arterial and venous pressure of an organ/tissue
what is the myogenic hypothesis?
increased perfusion pressure = increased blood flow and also increased stretch of arteriolar smooth muscle
this stretch is followed by a reflux that causes increased constriction of the arterioles and increased resistance which then causes a decrease in flow aka negative feedback! this is autoregulation and ultimately keeps the blood flow consistent even though perfusion pressure increased
again, if you decrease perfusion pressure then blood flow decreases and there is less stretch of the arterioles –> this causes vasodilation, decreased resistance and ultimately increased flow!
CO = P/TPR
what is reactive hyperemia-increased blood flow?
reactive increased blood flow that happens during ischemia
if you put on a tourniquet you cause an ischemia in your lower arm – when you take it off you expect it to go back to steady state immediately, there is a huge increase in blood flow in the lower arm! this transient increase in blood flow is called reactive hyperemia!
so it’s increased flow in response to a prior decrease in blood flow and it’s controlled by metabolites
this is totally controlled by the autoregulation mechanism
what is active hyperemia-increased blood flow?
when you’re exercising there’s an increasing demand for blood flow so more blood is flowing but it’s over a longer period of time
when you exercise you have lactic acid production which decreases pH and is a vasodilator and facilitates blood flow –> so there’s CNS activation increasing heart contractility and metabolic control decreasing pH
this is controlled by autoregulation and SNS control so we don’t talk about it as much in terms of autoregulation since it’s a mix
what is the metabolic hypothesis?
the blood flow is connected to the metabolic state of the tissue
hypoxia leads to vasodilation everywhere except for in the lungs where it’s a vasoconstriction
adenosine, NO, CO2, H and K lead to vasodilation
which natural molecules in the blood cause vasodilation?
- low O2
- adenosine
- NO
- CO2
- H+
- K+
which vasoactive compounds are vasoconstrictors?
- angiotensin II
2. vasopressin (ADH)
what are the 2 classes of receptors that help regulate blood flow?
- baroreceptors
2. chemoreceptors
what are baroreceptors?
clusters of nerve ending in blood vessel wall that respond to stretch that is exerted by the blood pressure
when we increase pressure on arterial wall there’s a natural reflex vasoconstriction