PHTH 8109 Exam 2: Cardiovascular Physiology Part 2 (Clinical Plugs)

Response to Exercise: Central Command

a series of responses directed by cerebral motor cortex initiated by anticipation of exercise

Central Command ANS Response

increased sympathetic outflow to heart and vessels, decreased parasympathetic outflow to heart

What is the cause of the autonomic response of central command?

increased CO, increased venous return, selective vasoconstriction

Why does CO increase during central command?

increase sympathetic activation & decrease parasympathetic activation; beta-1 adrenoreceptor activation increases SV and HR

What does increased CO ensure?

more O2 and nutrients get delivered to the exercising skeletal muscle

What are the 2 effects on the veins that cause an increase in venous return during exercise?

- contraction of skeletal muscle squeezes veins

- venoconstriction due to sympathetic activation

Where is selective arteriolar vasoconstriction seen?

splanchnic regions, kidney, inactive muscles

What causes selective arteriolar vasoconstriction?

alpha-1 receptors that shunt blood away from organs toward working muscles

Where is vasodilation seen?

in exercising skeletal muscle

Why does vasodilation occur?

local metabolic effects override sympathetic vasoconstricting effects

T or F: sympathetic vasoconstriction does not affect coronary and cerebral blood flow

true

Why does sympathetic vasoconstriction does not affect coronary and cerebral blood flow?

because we still want heart and brain to receive some blood flow

What happens in cutaneous circulation during the central command?

first vasoconstrict, then selective inhibition of cutaneous vasoconstriction to allow for heat loss

Local Responses to Exercises

local control of blood flow in exercising skeletal muscle controlled by active hyperemia

How does active hyperemia control local blood flow?

increase skeletal muscle metabolic rate -> production of vasodilator metabolites -> directly vasodilate arterioles of the muscle

Response to Hemorrhage

loss of large quantity of blood causes rapid decrease in arterial pressure -> compensatory cardiovascular responses attempt to restore normal pressure

Initiating Event of a Hemorrhage

loss of blood and decreased blood volume

What happens to MAP, CO, and RA pressure when blood volume decreases?

decrease

Why does MAP decrease when blood volume decreases during hemorrhage?

decreased pressure

Why does CO decrease when blood volume decreases during hemorrhage?

no volume

Why does RA pressure decrease when blood volume decreases during hemorrhage?

no venous return because no volume

Compensatory Mechanisms in a Hemorrhage

- baroreceptor reflex

- RAAS

- capillary absorption

- O2 chemoreceptor sympathetic activation

Compensatory changes favor _____ of fluid into capillaries

absorption

Response to Hemorrhage in Capillaries

increase sympathetic outflow to vessels and increased angiotensin II -> arteriolar vasoconstriction -> decrease capillary hydrostatic pressure

Response of Chemoreceptors to Hemorrhage (if complete loss of blood)

if hypoxic: increase facilitation by chemoreceptors; decreased PaO2 -> increased sympathetic outflow

If a person stands too quickly, they may experience brief _____

orthostatic hypotension

Where does blood pool when a person goes from supine to standing?

in veins of the lower extremities

How does blood pooling affect venous return to the heart?

decrease

What happens to CO and MAP when venous return decreases?

decrease

What happens when MAP is decreased?

activation of baroreceptors and baroreceptor reflex

Blood pooling ____ capillary ____ pressure in the veins of the LE

increases; hydrostatic

When capillary hydrostatic pressure in the veins of the LE increases, what happens with filtration?

increases

What is the cause of dependent edema?

net movement of fluid into interstitial space