Medical Physiology - Chapter 15, Guyton 12th ed.

all blood vessels are

distensible

the most distensible of all the vessels are _____

veins

what type of vessel has the ability to act as a storage reservoir for extra blood?

veins

vascular distensibility

vascular distensibility = increase in volume/(increase in pressure*original volume)

walls of arteries are ______ than the walls of veins

thicker and stronger

a given increase in pressure causes about ______ times as much increase in blood in a vein as in an artery of comparable size

8

pulmonary vein distensibilities

are similar to those of the systemic circulation

pulmonary artery distensibilities

about 6 times greater distensibility than systemic arteries

- operate at 1/6 pressure of systemic arteries

vascular compliance

the ability of a vessel to distend and increase volume with increasing transmural pressure

vascular compliance =

increase in volume ÷ increase in pressure

under same pressure and volume conditions, blood vessels with _____ compliance deform easier than _____ compliance blood vessels

higher, lower

compliance =

distensibility ∗ volume

sympathetic nervous system

involved in the stimulation of activities that prepare the body for action

- increasing heart rate

- increasing release of sugar from liver into blood

- fight or flight responses

parasympathetic nervous system

activates tranquil functions

- stimulating the secretion of saliva

- digestive enzymes into the stomach

pressure-volume curve

increase in vascular smooth muscle tone caused by sympathetic stimulation increases the pressure at each volume of the arteries or veins

sympathetic inhibition decreases the pressure at each volume

one of the principle methods the body uses to increase heart pumping is...

an increase in vascular tone throughout the systemic circulation causes large volumes of blood to shift into the heart

hemorrhage and sympathetic control

enhancement of sympathetic tone, especially in the veins, reduces the vessel sizes enough that the circulation continues to operate almost normally even when as much as 25% of the total blood volume has been lost = delayed compliance in reverse direction

delayed compliance

a mechanism by which circulation can accommodate extra blood when necessary

a vessel exposed to increased volume at first exhibits a large increase in pressure, but progressive delayed stretching of smooth muscle in the vessel wall allows the pressure to return back toward normal over a period of minutes to hours

stress relaxation

after immediate increased volume, the smooth muscle fibers of the vein begin to "creep" to longer lengths, and their tensions correspondingly decrease

distensibility

the ability to become stretched, dilated or enlarged

tissue blood flow is mainly _____ with little _____

continuous pulsation

pulse pressure

the difference between systolic pressure and diastolic pressure

two factors that affect pulse pressure

1. stroke volume output of heart

2. compliance (total distensibility) of arterial tree

the greater the stroke volume output:

(place up or down arrow)

amount of blood in that must be accommodated in arterial tree ___

pressure rise and fall during systole/diastole ___

pulse pressure ___

amount of blood that must be accommodated in arterial tree ⬆︎

pressure rise and fall during systole/diastole ⬆︎

pulse pressure ⬆︎

effect of arteriosclerosis on pulse pressure

pulse pressure doubles because arteries are hardened and noncompliant

aortic stenosis

diameter of aortic valve reduced

aortic pressure pulse ⬇︎

because of diminished flow outward through stenotic valve

patent ductus arteriosus

after birth, ductus arteriosus fails to close after birth

50% of blood is pumped by left ventricle back into pulmonary artery

causes diastolic P to fall very low before next HB

aortic regurgitation

aortic valve is absent or doesn't close

after each HB, blood in aorta flows back into left ventricle

causes aortic P to fall all the way to 0 between heartbeats

- incisura is absent because there are no valves to close

transmission of pressure pulse

1. heart ejects blood into aorta

2. rising P overcomes inertia of blood

3. wave of distention spreads further along aorta

velocity of pressure pulse transmission in aorta compared to distal arteries

slower transmission in aorta and faster transmission in less compliant distal arteries

why?

the greater the compliance of each vascular segment, the slower the elocity

in the aorta, the velocity of pressure pulse transmission is ___ the velocity of blood flow - why?

15x

the pressure pulse is simply a moving wave of pressure that involves little forward movement of blood volume

intensity of pulsation ___ as it travels through smaller arteries, arterioles, and especially in _____

⬇︎

capillaries

damping of pressure pulse is due to...

1. resistance of blood movement in vessels

2. compliance of vessels

why does resistance dampen the pressure pulse?

a small amount of blood must flow forward at the pulse wave front in order to distend the next segment of vessel

⬆︎resistance = more difficult for this to occur

Korotkoff sounds

when blood pressure cuff is inflated so that the pressure is great enough to close the brachial artery during part of the arterial pressure cycle, a sound is heard with each pulsation

- caused by blood jetting through partly occluded vessel and by vibrations of vessel wall

to determine BP via cuff

1. when cuff P > arterial systolic P ➜ brachial artery = collapsed and no Korotkoff sounds are heard

2. when cuff P is reduced to < arterial systolic P ➜ blood slips through brachial artery and Korotkoff sounds are heard in antecubital artery

3. when cuff P reduces to near diastolic P Korotkoff sounds become muffled

4. as cuff P falls further, Korotkoff sounds disappear

as one ages, there is a _____ _____ in BP - why?

progressive increase

results from aging effects on BP control mechanisms

what organ is responsible for long-term BP control?

kidneys

why does a slight increase in systolic pressure occur after age 60?

hardening of the arteries; decrease in distensibility

- often result of atherosclerosis

mean arterial pressure

average of arterial pressures measured millisecond by millisecond over a period of time

NOT SAME AS SUM OF SYSTOLIC AND DIASTOLIC DIVIDED BY 2

- at normal heart rates, a greater fraction of cardiac cycle is spent in diastole

- mean arterial pressure is 60% diastolic and 40% systolic, so it is closer to diastolic pressure

venous pump

peripheral veins can propel blood forward by means of a venous pump

why is the pressure in the right atrium called the central venous pressure?

blood from all systemic veins flows into the right atrium of the heart

right atrial pressure is regulated by

1. ability of heart to pump blood out of RA and RV into lungs

2. the tendency for blood to flow from peripheral veins to RA

if heart is pumping strongly, then

right atrial pressure decreases

if the heart is weak, then

right atrial pressure is elevated

increase in venous return increases right atrial pressure due to

1. ⬆︎ blood volume

2. ⬆︎ large vessel tone throughout body with resultant ⬆︎ in peripheral pressures

3. dilation of arterioles, which ⬇︎peripheral resistance and allows rapid flow of blood from arteries into the veins

the normal right atrial pressure =

0 mmHg

which is equal to atmospheric pressure around the body

after severe hemorrhage

blood flow from periphery ⬇︎

so right atrial pressure ⬇︎

resistance to flow of large veins

almost 0

- pressure in neck veins falls so low that pressure on outside of neck causes these veins to collapse

- veins in abdomen are always partially collapsed, which causes some resistance to blood flow

when right atrial pressure is above 0 mmHg, what happens?

blood begins to back up in the large veins, thus veins enlarge and even collapse points will open up

- this additional increase causes peripheral venous pressure to rise in limbs and elsewhere

when interabdominal pressure rises, what must happen?

pressure in the veins must rise ABOVE abdominal pressure before abdominal veins will open and allow blood flow from the legs to the heart

gravitational pressure

pressure resulting from weight of water

pressure of veins in feet when standing still = ____ - what is this an example of?

+90 mmHg

gravitational pressure

can the veins inside the skull collapse - why?

NO

the skull acts as a noncollapsible chamber

can gravitational pressure affect arteries?

yes

mean arterial P in feet is 190 mmHg

mean arterial P at heart = 100 mmHg

standing still

how does the venous pump work?

1. move legs = tighten muscles➔compress veins➔squeeze blood out of veins

2. valves arranged along veins to direct flow only toward heart

what happens to the venous pump if a person stops moving legs?

1. pump stops working

2. capillary P ⬆︎ and fluid leaks from circulatory system into tissue spaces = edema in legs and blood volume ⬇︎

venous valve incompetence

valves can be destroyed when veins have been overstretched by excess venous pressure lasting weeks or months

- leads to varicose veins

clinical estimation of venous P

can be estimated by degree of distention of peripheral veins - especially neck

direct measurement of venous P

insert needle into vein and connect to P recorder

reference level for pressure measurement

a point in the circulatory system at which gravitational pressure factors caused by changes in body position of a healthy person do not affect P measurement - near tricuspid valve

more than ___ of all blood is in the veins

60%

the venous system serves as a _____ _____ (2) for the circulation

blood reservoir

when blood is lost from body, arterial P ⬇︎, then what happens?

1. nerve signals elicited from carotid sinuses

2. nerve signals from brain and spinal cord through sympathetic nerves to veins

3. veins constrict to take up the slack from the lost blood

how much blood can be lost without affecting the normal function of the circulation?

20%

besides veins, what are the other specific blood reservoirs?

spleen

liver

large abdominal veins

venous plexus beneath the skin

heart and lungs

during sympathetic stimulation, what happens to the heart?

it shrinks

blood storage areas of the spleen

1. venous sinuses

2. red pulp - concentrated RBC can be expelled in to circulation upon sympathetic nervous system excitation

3. white pulp - houses white blood cells

how does the spleen clean blood?

1. RBC pass through splenic pulp before entering sinuses undergo squeezing

2. fragile cells cannot withstand trauma - destroyed and digested to help form new RBC

reticuloendothelial cells

phagocytic, located in spleen

function as cleaning system of blood