3.7 Blood Flow and pressure

what is blood flow (F)?

volume of blood flowing through a vessel, organ, or entire circulation per minute (mL/min)

difference between blood flow and cardiac output?

blood flow of entire circulation is cardiac output whereas blood flow is through vessel, organ, or entire circulation

what is blood pressure (P)?

force per unit area exerted by blood on vessel wall

• measured in mm Hg

• usually in reference to systemic arterial pressure in large arteries near heart (aorta and major branches

what is pressure gradient (deltaP)?

the difference in blood pressure between two point in circulation, allows blood to move from hight to low pressure

what is resistance?

opposition to flow from friction between blood and vessel wall

what circulation structure does most resistance take place in?

arterioles

what is total peripheral resistance (TPR)?

used to describe resistance of entire systemic circulation

what is the relationship between all these factors?

F =detaP/TPR

what three factors determine resistance?

blood viscosity

total blood vessel length

blood vessel diameter (most important)

what is laminar flow?

uneven flow of fluid moving through a tube due to friction along walls of tube

how does fluid closest to walls move?

move slower due to friction

how does more central fluid flow?

moves faster

what happens to fluid when decrease diameter of vessel?

increases resistance as higher proportion of fluid in contact with wall

what is turbulent flow?

irregular fluid motion which replaces laminar flow when blood encounters abrupt change in diameter or protrusions of vessel wall (like with plaque or thrombus)

arterial pressure is what in elastic and muscular arteries?

PULSATILE

what are the systolic, diastolic, and pulse pressure of arteries?

normal systolic pressure = 120 mm Hg

normal diastolic = 80 mm Hg

pulse pressure = systolic - diastolic pressure = 40 mm Hg

what is mean arterial pressure (MAP)?

describes overall arterial pressure despite initial pulsatile flucturation

MAP equation?

MAP = diastolic pressure + pulse pressure/3

recap question i think: where does greatest resistance occur?

arterioles

what happens to pulse pressure as vessels become less elastic?

pulse pressure decreases so nonpulsatile flow in capillaries!!

pressure of capillaries range?

range from 35-17 mm Hg and pressure continues to decline in veins

blood pressure by time reaches right atrium?

about 0 mm Hg

what factors affect blood pressure?

cardiac output CO and total peripheral resistance TPR establish blood pressure

relationship between flow and pressure and resistance?

F = deltaP/TPR

relationship between flow, cardiac output, HR, and stroke volume?

F = CO = HR x SV

how to find value for pressure?

deltaP = aortic mean arterial pressure MAP - right atrial MAP is 0

cardiac output equations?

CO = MAP/TPR or MAP = CO x TPR

what is another major factor for blood pressure?

blood volume which is largely regulated by kidneys

what/where are neural controls which are short term regulation of blood pressure located?

cardiac centers including cardioacceleeratory and cardioinhibitory and vasomotor center in the medulla oblongata of brainstem

what does the cardioacceleratory center stimulation do?

sympathetic stimulation which increases HR and contractility which increases cardiac output

what does cardioinhibitory center stimulation do?

parasympathetic stimulation which decreases HR and contractility which decreases cardiac output

what does vasomotor center stimulation do?

sympathetic stimulation which increases vasoconstriction which increase TPR

what do baroreceptors do?

detect pressure changes in aorta and carotid sinus through stretch

when stretched (high MAP), what signal does that send?

signals relatyed to inhibit cardioacceleratory and vasomotor centers and stimulate cardioinhibitory center

what are the factors altered in short-term regulation of blood pressure?

TPR and CO

how are TPR and CO short-term regulated?

achieved through hormones

what do epinephrine and norepinephrine from adrenal glands do?

increase vasoconstriction and CO which increases MAP

what does angiotensin II do?

increase vasoconstriction which increases MAP

what does antidiuretic hormone ADH do?

increases vasoconstriction which increase blood volume (water retention) and increases MAP

what does atrial natriuretic peptide ANP do?

increase vasodilation and reduce blood volume (salt and water excretion) which decreases MAP

what mechanisms do long-term regulation of blood pressure?

direct and indirect renal mechanisms regulate blood volume

what do direct renal mechanisms do?

pressure-related adjustments in filtration and reabsorption during urine formation

what does indirect renal mechanisms (renin-angiotensin-aldosterone system) do?

low blood pressure stimulates hormones and enzymes to increase blood volume

what does angiotensin II stimulate?

adrenal glands to release aldosterone

posterior pituitary to release ADH

thirst center in hypothalamus so increase water consumption

vasoconstriction which increase TPR

what does autoregulation of blood flow do?

are intrinsic controls of local blood flow depending on tissue needs

autoregulation: metabolic controls?

paracrine factors released by endothelial cells to regulate vasoconstriction/dilation

autoregulation: what is released by metabolic controls?

nitrous oxide released in high pressure so vasodilates

endothelins which are released in low pressure and vasoconstricts

autoregulation: what are myogenic controls?

smooth muscle in arterioles directly responds to fluctuations in systemic BP, providing appropriate flow to capillaries downstream

autoregulation: what happens under myogenic controls under high and low pressure?

high pressure causes vessel wall to stretch leading to vasoconstriction which decreases blood flow

low presure causes lack of stretch so leads to vasodilation which increases blood flow