Cardiac Output, Venous Return, and Their Regulation Flashcards
cardiac output
quantity of blood pumped into the aorta or into the pulmonary artery every minute by the heart and blood flowing through the circulation
venous return
Quantity of blood flowing from the vein to the atrium each minute.
t/f cardaic putput = venous return
true
Factors affecting cardiac output
Level of metabolism
Age
Size of the body
Exercise level
Cardiac index
Control of cardiac output by venous return Frank-Starling mechanism
increased quantity of blood flows into the heart = increased stretch of the walls of heart chambers = increased force of muscle contraction = emptying of the chambers
Bainbridge reflex, cardiac output by increasing heart rate, how does it work?
acts on the vasomotor center stimulating SNS and PNS increasing heart rate
this helps to pump blood from the heart
Increased amount of blood in the chambers causes stretching o and affects
sinus node in the right atrium affecting the rhythmicity of the heart
the venous return to the heart is the sum of
All the local blood flows through all the individual tissue segments of the peripheral circulation.
what regulates blood locally in the tissues?
metabolism
O2
t/f cardiac output is determineed by the sum of all factors that regulate blood flow
true
hyper-effective cardiac function is affected by
Nervous stimulation
hypertrophy
SNS stimulation
PSNS inhibition
hypo-effective cardiac function is affected by
Nervous inhibition
disease
valvular heart disease
hypertension (increased AP)
congenital heart disease
myocarditis
cardiac anoxia
myocardial damage due to toxins
Hypertrophy of heart occurs due to
Caused by increased workload = increase in mass and increase in contractile strength
what happens with AP during exercise?
nervous system increases AP to above normal
brain centers send info toperipheral muscles to increase activity
brain center send impulses to ciculatory syst. to increase heart rate, contractility and venous return to heart
Factors that affect venous return
right atrial pressure - backward force on veins to impede flow of blood from veins into atrium
mean systemic filling pressure- forces blood to heart
resistance blood flow- between peripheral vessels and the right atrium
Mean circulatory filling pressure (psf)
when there is no blood flow, the pressure everywhere in the circulation become equal. It is the mean pressure forcing blood into the heart.
how do youi measure Mean circulatory filling pressure (psf)?
stopping the heart’s pumping ability by shock or other means.
2 factors that determine the Mean circulatory filling pressure (psf)
Degree of sympathetic stimulation on the peripheral arteries and veins
Amount of blood in the circulation
if the SNS stimulation acts on Mean circulatory filling pressure (psf)
constricts all the systemic blood vessels, larger pulmonary vessels, and chambers of the heart, resulting in increased mean filling pressure
for venous return, the greater the system is filled
easier for blood to flow to the heart
for venous return, the lesser the system is filled
The more difficult it is for the blood to flow into the heart.
when the right atrial pressure = psf
There is not a pressure difference between the peripheral vessels and the right atrium = no longer any blood flow from the periphery to the right atrium
Greater the difference between psf and RAP
greater the venous return
pressure gradient for venous return is calculated
psf-RAP
when resistance in veins increases
venous return decreases
when arteriolar and artery resistance increases
blood accumulates in the arteries increasing the pressure, overcomes resistance and venous return goes back to normal
Blood tansfusion causes an increase in psf and a decrease in
resistance venous return
spinal anesthesia inhibits
SNS blocking transmission of nerve signals through the autonomic ganglia and cardiac output decreases
measuring cardiac output in animals
electromagentic or ultrasonic flowmeter
measuring cardiac output in humans (indirect method)
The oxygen Fick method
Indicator dilution method
During excercise, what 2 factors are important
Local tissue autoregulation
SNS enhancement
t/f during exercise all capillaries are open
true
the opening of dormant capillaries during excercise increases
surface area for nutrient and O2 exchange
control of blood flow through skeletal muscle is done
locally, chemical effects causing vasodilation of arterioles
local increase in muscle blood flow is caused by 2 factors
Reduction in oxygen to the muscle
release of vasodilator substances
vasodilator substances include
Adenosine
potassium ions
adenosine triphosphate (ATP)
lactic acid
CO2
arterial walls cannot maintain contraction during the absence of
O2
muscle blood flow control is don by the
SNS, vasoconstrictor and vasodilators
during excercise the SNS stimulates nerve endings and the adrenal medulla to secrete
nor- epi and epi
nor - epi attaches to what receptors and causes what effect
alfa receptors
vasoconstriction
epi attaches to what receptors and causes what effect
beta receptors
vasodilation
What are the 3 circulatory adjustments that occur during exercise
SNS stimulation
Increase in the arterial pressure
Increase in cardiac output
during excercise, the SNS exchange occurs in two ways
barin - muscle
muscle control center of brain - vasomotor control center
SNS discharge during exercise is expressed in 4 ways
heart stimulation = increase heart reate and streght contraction and loss of PNS inhibition
arterioles of peripheral circulation are contracted
arterioles in muscle exerting activity are vasodilated
muscle walls of veins contracted increasing
systemic filling pressure
venous return to heart
increasing cardiac output
Increase in AP during excercise occurs due to
vasoconstriction of arterioles not directly on the muscle
increased pumping activity of heart
increase in mean systemic filling pressure caused by venous contraction
t/f CO only increases to level of venous return during excercise
true
SNS contract veins during
exercise
t/f venous return is not dependent on mean systemic filling pressure during exercise
false
left coronary arteries supply
anterior and left lateral portions of the left ventricle.
Right coronary artery supplies
most of the right ventricle and the posterior part of the left ventricle.
Venous blood from the left ventricle retuns
to the right side of the heart by the coronary sinus
Venous blood from the right ventricle returns
to the heart via the anterior cardiac veins
Capillary blood flow falls to a low value during
systole due to the compression of the left ventricular muscle
Capillary blood flow rapidly during
Diastole, cardiac muscle relaxes and no longer obstructs blood flow
Control of coronary blood flow is regulated by
local arterial and arteriolar vasodilation in response to cardiac muscle’s need for nutrition.
A decrease in O2 concentration in the heart causes
vasodilator substances to be released from the muscle which dilates the arterioles
direct nervous control of coronary vessels is through
neurotransmitters released from the nerve terminals
PSNS - ACETYLCHOLINE - BETA - VASODILATION
SNS - NOR-EPI AND EPI - ALPHA - VASOCONSTRICTIO
INDIRECT NERVOUS CONTROL OF CORONARY VESSELS
secondary changes in coronary blood flow by increased or decreased activity of the heart
Under resting conditions, cardiac muscle uses what for energy?
fatty acids
Under anaerobic conditions or ischemia, the cardiac muscle uses
anaerobic glycolysis
