HHP 2400: Chapter 14

Cardiac output

volume of blood ejected by each ventricle each minute

determined by stroke volume

End Diastolic Volume (EDV)

blood in ventricle after complete filling

increased by venous return

Stroke volume

EDV - ESV, measured in mL/beat

determined by EDV (venous return, Frank Starling Law of Heart/preload), total peripheral resistance (afterload), sympathetic activity

End Systolic Volume (ESV)

blood left after ventricle contracts

What factors influence stroke volume?

pressure difference between arteries and veins

sympathetic nerve activity to stimulate smooth muscle contraction and lower compliance

skeletal muscle pumps

blood volume (lower if dehydrated)

body position

Afterload

resistance to blood flow

if increased, stroke volume decreases

How is stroke volume affected by the sympathetic nervous system?

increases, increased contractility

norepinephrine opens more Ca2+ channels

What is heart rate determined by?

altering balance of parasympathetic and sympathetic influence on SA node

Ejection fraction

fraction of blood pumped out with each heart beat

SV/EDV x 100

normal 50 - 65%

Body fluid compartments

intracellular = water, extracellular = interstitial (in between cells), blood (plasma)

Fluid distribution

osmotic forces control movement of water between interstitial spaces and blood

high blood volume = low urine volume

Fluid exchange between capillaries and tissues

hydrostatic pressure blood, hydrostatic pressure interstitium, osmotic (oncotic) pressure blood, osmotic pressure interstitium

Starling Forces

movement of fluid out of capillaries at arteriole end (positive #, net filtration) and into capillaries at venule end (net absorption)

return of fluids on venous end not 100% (some remains in interstitial space to enter lymphatic capillaries and return to venous system)

Kidney blood volume regulation - ADH

secreted by posterior pituitary, responds to low blood volume/increased blood osmolarity, increases water retention

Kidney blood volume regulation - Aldosterone

secreted by adrenal cortex in response to low blood pressure and blood flow to kidneys

increases blood pressure by vasoconstriction

regulated by Renin-angiotensin aldosterone system

increases reabsorption of Na+

Atrial Natriuretic Peptide (ANP)

produced by atria of heart when stretched

promotes salt and water excretion in urine in response to increased blood volume

inhibits ADH secretion, aldosterone antagonist

Pressure

force exerted by blood

Blood flow

directly proportional to pressure gradient, flow high to low pressure

Resistance

difficulty of blood to flow at given pressure difference

determinants: blood viscosity (thickness), vessel length, vessel radius

Blood flow equation

F = deltaP (pressure gradient)/R (resistance of blood vessels)

Blood pressure

force exerted by blood against vessel wall

depends on volume of blood vessel contains, compliance of vessel walls (stretchability)

Systolic pressure

maximal arterial pressure, average = 120

Diastolic pressure

minimum arterial pressure when blood draining downstream into vessels, average = 80

Pulse pressure

difference between systolic and diastolic pressure (SBP - DBP)

Mean arterial pressure

average pressure driving blood forward into tissues during cardiac cycle (1/3 PP + DBP)

primary determinants: cardiac output, total peripheral resistance

MAP = cardiac output x total peripheral resistance

Where is the greatest change in systemic circulation pressure?

small arteries and arterioles T

Total Peripheral Resistance (TPR)

sum of all vascular resistance in systemic circulation

regulated by arterioles (major resistance vesels, MAP determination)

contain smooth muscle (vasoconstriction/vasodilation)

control by intrinsic and extrinsic factors

Extrinsic regulation

sympathetic nervous system (epinephrine)

hormones (angiotensin 2, vasopressin/ADH)

Vasoconstriction sends _____ APs, vasodilation sends _____ APs

more ; less

Intrinsic regulation

promotes constant blood flow, autoregulation

ex: active hyperemia, nitric oxide

How is mean arterial pressure maintained short term?

baroreceptors at aortic arch and carotid sinus, fire proportional to blood pressure

How is mean arterial pressure maintained long term?

adjustment of total blood volume (takes minutes to days), restoring normal salt and water balance through mechanisms regulating urine output

Hypertension

blood pressure elevated above normal values

primary = due to cardiovascular system, secondary = due to another disorder

potential causes: defects in kidney salt management, excessive salt intake, diets low in K+/Ca2+, excess vasopressin

Hypotension

blood pressure below 100/60 mmHg

too little blood to fill vessels or heart to weak to drive blood

orthostatic (plural): change in position causes diziness

Circulatory shock

when blood pressure falls so low adequate blood flow to tissues can no longer be maintained

Congestive heart failure

cardiac output not enough to maintain blood flow body needs

secondary to myocardial infraction

congestive = increase in fluid retention

Acute effects of exercise on cardiovascular system

cardiac output increases b/c injecting more blood from heart into body tissues

stroke volume and heart rate increase

Where does blood increase to during exercise?

heart, skin, skeletal muscle

Chronic effects of exercise on cardiovascular system

cardiac output increases due to left ventricle thickening, making heart muscle stronger

stroke volume increases, heart rate decreases