Circulatory system 5

What is cardiac output?

the efficiency and work of the heart as a pump measured.

The volume of blood the heart pumps out each minute

What is the equation for cardiac output?

CO=SV x HR

What is stroke volume?

volume of blood ejected by the left ventricle with each heartbeat

Why is cardiac output adjusted?

to meet the bodys physiological and metabolic needs

How is cardiac output adjusted?

changes in SV and HR

What determines HR?

autonomic tone on the heart, SNS and PNS

What determines SV?

preload, afterload, cardiac contractility

Does cardiac output change when we exercise?

Yes- distribution changes and blood flow increases.

What is preload?

workload on the heart before contraction begins. Equal to end-diastolic volume/pressure

What is end-diastolic pressure/volume?

volume of blood or pressure in ventricle prior to contraction

What is the Frank-Starling law of the heart?

SV is directly proportional to preload.

What is afterload?

load against which the heart must contract in order to eject blood into the aorta.

The pressure the heart must generate in order to eject blood into the aorta

What is afterload determined by?

systemic or total peripheral resistance.

What is the pattern between SV and afterload/TPR?

inversely proportional

What is contractility?

Ability of the heart to change its force of contraction without changing resting muscle length

What does contractility depend on?

availability of Ca++ to participate in contractile process

What is the pattern between SV and contractility and why?

directly proportional.

increased Ca++— increased actin-myosin bridge— increased contractility— higher SV

What is systolic blood pressure?

force exerted by blood on arterial walls during systole.

What is diastolic BP?

force exerted by blood on arterial walls during diastole.

How do we find pulse pressure?

systolic BP- diastolic BP

What is mean arterial BP?

average pressure responsible for driving blood forward into tissues.

What is the calculation for mean BP?

diastolic BP + (1/3 x pulse pressure)

What is calculation for BP?

CO x TPR

What is total peripheral resistance determined by?

sympathetic tone, circulating hormones and local hormones.

Why is mean BP highly regulated and kept in narrow range?

BP must be high enough to perfuse organs and tissues, must not be so high to strain heart and damage vessels.

What are the 2 mechanisms of homeostatic BP control?

short term via baroreceptors, long term via kidneys

What are short term control adjustments?

alterations in CO and TPR, mediated via autonomic nervous system, within seconds

What are long term control adjustments?

require minutes to days, renal mechanisms to change total blood volume.