Blood pressure and Regulation

factors that contribute to movement of blood

• heart - primary source

• gravity

• skeletal muscle

• diaphragm movements

• elastic tissue in arteries

systolic blood pressure

max pressure exerted in arteries when blood ejects into them during systole

• contracting phase

diastolic blood pressure

min pressure within arteries when heart relaxes

pulse pressure

measure of strength of pressure wave

• systolic BP - diastolic BP

mean arterial pressure (MAP)

average pressure responsible for driving blood forward into tissue thruout cardiac cycle

• MAP = diastolic + 1/3(pulse pressure)

what happens to pressure wave when moving to capillaries

loss of energy due to friction = pulse pressure reduced to 0 when reach capillaries

why is MAP important

essential for efficient function and life

• low bp = dizziness, organ failure

• high bp = stroke, aneurysm

what determines MAP

• cardiac output (CO) - depends on stroke volume and heart rate

• resistance of peripheral circulation (TPR)

MAP proportional to CO x TPR

hypertension

high blood pressure

hypotension

low blood pressure

regulation when mean arterial pressure gets low

• increase cardiac output

• constrict aterioles close to capillaries = increases resistance = heart increases pressure

which nervous system effects blood pressure

autonomic

• SNS = raises

• PNS = lowers

cardiac output

volume of blood pumped by 1 ventricle in given time

• CO = heart rate x stroke volume

• avg 5 L/min

stroke volume

amount of blood pumped by 1 ventricle during contraction

• SV = end diastolic volume - end systolic volume

• avg at rest = 135ml - 65ml = 70ml

venous return

volume of blood flowing back into right atrium per minute

• determines how much blood we have in heart

end diastolic volume

volume in ventricle at end of diastole

• determined by venous return

end systolic volume

volume of blood in ventricle

what determines stroke volume

venous return and contractility of ventricles

what affects venous return

• respiratory pump - inhale decreases pressure near heart = draws blood up

• skeletal muscle pump - skeletal muscle contract = compress deep veins = push blood up

• blood volume

• neural control - veins have alpha-1 receptors

what happens when blood volume decreases

venous return decreases > end diastolic volume decreases > lower stroke volume> lower cardiac output > lower arterial mean pressure

frank-starling law

stretch-force relationship

• more blood in ventricle = stretches cardiac muscles closer to optimal length = stronger contraction force

modulation of stroke volume

by sympathetic nerves = causes myocytes to contract harder

what affects heart rate

changing rate of depolarisation of autorhythmic pacemaker cells - Ifunny current

how sympathetic modulates heart rate

changes ion permeability = depolarises = reach threshold sooner = faster heart rate

• by noradrenaline in Beta-1 receptors\

• increases action potentials = reduces conduction thru AV node

parasympathetic modulation of heart rate

changes ion permeability = hyperpolarises = longer to reach threshold = slower heart rate

• by muscarinic receptors (Ach)

• decreases action potentials = longer conduction thru AV node

how does control over cardiac output and total peripheral resistance differ

• TPR = fluctates based on needs of local tissue

• CO - autonomic system

when TPR adjusts ANS adjust CO to maintain constant arterial pressure

What happens to MAP when total peripheral resistance decreases

initially MAP decreases = SNS increase stroke volume and heart rate = increase cardiac output = MAP increases

what happens to MAP when standing

pooling of blood in legs = reduced venous return = reduced cardiac output = decreases MAP

• regulate by increasing heart rate and SNS causes vasoconstriction = push blood to heart

short-term blood pressure regulation

second to second - predominately neural thru baroreceptor reflex

baroreflex

baroreceptors on carotid sinus (blood to brain) and aortic arch (blood to body)

• when blood pressure increases = artery stretches = stimulates baroreceptors = sends signals to brain to adjust accordingly

how baroreflex controls blood pressure

change in blood pressure = baroreceptors detect change = sends info to medulla = corrrects changes thru SNS and ParaNS

• BP down = decreased baroreceptor signals = increases SNS and decrease ParaNS

what does parasympathetic control in heart

chronotopy/heart rate and AV conduction time

what does sympathetic control in heart

• ventricular contractility = change stroke volume thru beta-1 receptors

• diameter of vessels thru alpha-1 receptors = increase TPR to increase MAP and increase venous return by constricting veins

long term blood pressure regulation

changing blood volume thru CO and TPR

• CO thru regulating Na+ in extracelllular fluid via excretion in urine

• TPR changes due to thickening arterial wall and high levels of vasoconstrictive hormones

low pressure baroreceptors

in right atrium = monitor change in pressure due to changes in blood volume

overview of what determines mean arterial pressure

1. Blood volume - determined by fluid intake/outake > regulated by kidneys

2. cardiac output - determined by heart rate and stroke volume

3. resistance to blood flow - determined by arteriole diameter

4. distribution of blood between arterys and veins - determined by vein diamter

• stroke volume determined by heart contractility and end diastole volume

• end diastole volume determined by venous pressure = affects blood volume

• venous pressure determined by blood volume

• vessel diamter determined by venous pressure redistributing blood

how does blood volume influence venous return

increased blood volume in veins = increases pressure = stretches veins = recoils = pushes blood to heart