Blood Vessels and Pressure I&2

What does cardiac output depend on?

heart rate and stroke volume

How do you calculate cardiac output?

heart rate x stroke volume

what is stroke volume determined by?

the extent of venous return and by sympathetic activity

What is the difference between intrinsic and extrinsic control of cardiac output?

intrinsic is related to the extent of venous return, extrinsic is related to the extent of sympathetic stimulation of the heart

How is blood transported to all parts of the body?

a system of vessels

How does blood flow assist in maintaining homeostasis?

reconditioning organs receive blood flow in excess of their needs

What does blood flow through a vessel depend on?

the pressure gradient, vascular resistance

What is flow rate and the formula?

volume of blood passing through per unit of time

Flow rate of blood through a vessel = pressure gradient / resistance of blood vessels

pressure gradient

the difference in pressure between the beginning and end of a vessel

Resistance in blood flow

hindrance to blood flow through a vessel

viscosity in blood flow

friction developed between molecules of a fluid as they slide over each other during fluid flow

Poiseuille’s Law

integrates factors affecting flow rate through a vessel

What does the vascular tree consist of?

arteries, arterioles, capillaries, venules and veins

arteries function

transport blood from the heart to organs, pressure reservoir

arterioles function

control the amount of blood that flows through each organ

capillaries function

vessels where materials are exchanged between blood and tissue cells

veins function

return blood to the heart

avergae systolic / diastolic pressure

systolic ~ 120 mm Hg

diastolic ~ 80 mm Hg

What happens when the heart contracts versus relaxes?

contracts and empties, relaxes and fills

What is a sphygmomanometer?

used to measure bp by externally applying an inflatable cuff attached to a pressure gauge

What is the mean arterial pressure (MAP)?

main driving force for blood flow, average pressure driving blood forward into the tissues throughout the cardiac cycle

vasoconstriction

narrowing of a vessel

vasodilation

enlargement of a vessel

vascular tone

state of partial constriction of arteriolar smooth muscle

What is local control of arteriolar radius important for?

determining the distribution of cardiac output

What are the differences in flow to organs determined by?

differences in vascularization, differences in resistance offered by arterioles supplying each organ

active hyperemia

increase blood flow in response to enhanced tissue activity

What local metabolic changes influence arteriolar radius?

decreased O2, adenosine release, increases in CO2, acid, K, and osmolarity

Effect of endothelin

vasoconstriction

effect of nitric oxide (NO)

vasodilation

Effect of angiogenesis

vascular endothelial growth factor (VEGF) stimulates new vessel growth

effect of norepinephrine and epinephrine on arteriolar radius

vasoconstriction

effect of ADH on arteriolar radius

vasoconstriction, water balance

effect of angiotensin II on arteriolar radius

vasoconstriction, salt balance

What factors enhance diffusion across capillaries?

travel a short distance, narrow so rbc’s have to squeeze through, cells rarely farther than .1mm from a capillary

Key characteristics of capillaries

walls composed of single layer of endothelium, water filled capillary pores doe passage of small water-soluble substances, many are not open under resting conditions

role of precapillary sphincters

wisps of spiraling smooth muscle cells, stopcocks that control blood flow through the particular capillary that each one guards

What happens when demands for blood are low?

Veins can store extra blood in reserve because of their passive stretchiness

What is blood pressure regulated by?

controlling cardiac output, total peripheral resistance and blood volume

Short term vs long term control measures for bp

short term - alterations in cardiac output and total peripheral pressure

long term - adjusting total blood volume by restoring normal salt and water balance

What is the baroreceptor reflex?

a short term mechanism for regulating blood pressure, in aortic arch and carotid artery

Highest —> Lowest pressure of branches of the vascular tree

veins, arteries, capillaries, venules, artierioles

Arteries, arterioles, capillaries, venules, veins

What vessel type serves as a pressure reservoir?

arteries

What vessel type is considered to be the major resistance vessel?

arterioles

Which of the following are examples of local control factors of arteriole radius?

endohtelien (vasoconstrictor), ADH (vasoconstriction), norepin (vasoconstrictor), nitric oxide (vasodilator)

Endothelin (vasoconstrictor)

Nitric oxide (vasodilator)