Chapter 21

Blood Vesselsand

Circulation

Blood Pressure andCardiovascular regulation

Exercise

arteries

arterioles

capillaries

venules

veins

carry blood away from heartthicker walls (smooth muscle)branch and get narrower

bifurcation (tri-, rami-)

smallest vesselsin networks (beds)exchange with ECF

carry blood back to heartthinner wallssmall v. join to form larger veins

anastomosis

fig. 21-8

blood circuit

100 keys (pg. 725)

“It is blood flow that’s the goal, and total peripheral blood flow is equal to cardiac output. Blood pressure is needed to overcome friction and elastic forces and sustain blood flow. If blood pressure is too low, vessels collapse, blood flow stops, and tissue die; if blood pressure is too high, vessel walls stiffen and capillary beds may rupture.”

100 keys (pg. 732)

“Cardiac output cannot increase indefinitely, and blood flow to active versus inactive tissues must be differentially controlled. This is accomplished by a combination of autoregulation, neural regulation and hormone release.”

Autoregulation of blood flow

Neural mechanisms

Hormonal mechanisms

Controlling CO and bp

*

*

CO = HR x SV

(reflex control of cardiovascular function)

neural mechanisms

Neural mechanisms

baroreceptorsblood pressure

chemoreceptorspH, [gases]

Reflex control of cardiovascular function

negative feedback loops

Neural mechanisms

baroreceptors

Reflex control of cardiovascular function

monitor degree of stretch in walls of expandable organs

carotid sinusesaortic sinusesatrium

baroreceptors

if blood pressure climbs

decrease cardiac outputlower HR (ACh SA)

vasodilationlowers peripheral resistance

reduce blood pressure

reflex:

baroreceptors

if blood pressure falls

increase cardiac outputNE on heart

vasoconstrictionNE inc. peri. resistance

increase blood pressure

reflex:

baroreceptors

atrial reflex

stretching the atrium(more blood returning)

will stimulate cardiac output(more blood leaving)

baroreceptors

Valsalva maneuver

exhale forcefully

close glottis

baroreceptors

Valsalva maneuver

1. brief rise in bppressure on lungs sends pulmonary blood to atria

2. bp fallsreduced venous returnlow COreflexive vasoconstrictionincrease in heart rate

baroreceptors

Valsalva maneuver

3. release pressureexpansion of vessels (bp)

(return, aortic volume)

4. restore normalblood return upCO is upBP is up

graph ofbp drop and HR increase

during Valsalva

to here 4/2/07Lec # 34

fig. 21-14

Neural mechanisms

baroreceptors

chemoreceptors

Reflex control of cardiovascular function

Neural mechanisms

chemoreceptors

monitor pH (H+)[CO2][O2]

of blood and CSF

sensory neurons in: carotid bodyaortic bodies(med. oblong.)

Neural mechanisms

chemoreceptors

pH drops (H+)or [CO2]or [O2]

reflex stimulation of cardio-acceleratory centers (sym)

stimulate vasomotor(vasoconstriction)

Neural mechanisms

chemoreceptors

pH drops (H+)or [CO2]or [O2]

increase cardiac outputperipheral vasoconstriction

increase bp

Neural mechanisms

chemoreceptors

pH drops (H+)or [CO2]or [O2]

receptors in medulla obl.

stimulate respiratory centers

more O2and more venous return

Neural mechanisms

chemoreceptors

pH drops (H+)or [CO2]or [O2]

increased bp and resp.

more O2 to cells

fig. 21-15 here

CO = HR x SV

neural mechanismshormonal control

NE, E

ADHangiotensin IIEPOnatriuretic peptides

all regulateblood volume

ADH

Antidiuretic hormone

made in hypothalamusreleased from posterior pituitary glandin response to blood volume

vasoconstriction (bp)H2O recovery in kidney

angiotensin II

fall in bprenin release from kidney

angiotensinogen (from liver)

angiotensin I

angiotensin II

renin

ACE

angiotensin II

four functions:

stimulates kidney toproduce aldosterone

stimulates secretion of ADH

stimulates thirst

stimulates CO and vasconstriction

(bp)

EPO

erythropoietin

released from kidneys

low bp

low O2 levels

stimulates bone marrow to make more RBC’s

natriuretic peptides

natrium = sodium (Na)

atrial natriuretic peptide (ANP)brain natriuretic peptide (BNP)

released in response to stretching

reduce blood volumereduce blood pressure

natriuretic peptides

increase Na+ excretion at kidneyincrease volume of urine producedreduce thirstblock ADH, NE, E, aldosterone releasestimulate peripheral vasodilation

reduce blood volume and blood pressure

fig 21-16a

response to decrease in bp

fig 21-16b

response - increase in bp

100 keys (pg. 732)

“Cardiac output cannot increase indefinitely, and blood flow to active versus inactive tissues must be differentially controlled. This is accomplished by a combination of autoregulation, neural regulation and hormone release.”

fig. 20-23

Summary

Heart rate

EDV

ESV

SV = EDV-ESV

hormonesvenous return

filling timevenous return

preloadcontractilityafterload

CO = HR x SV

Exercise

light

slight sympathetic innervationslight increase in HR

vasodilationget blood to tissuesresistance dropsmore blood flows

Exercise

light

increase in venous returnmuscle pumps

fig. 21-6

muscle activityvenous return

Exercise

light

increase in venous returnmuscle pumpsincrease respiratory pump

cardiac output increasesdue to higher venous return

skeletalmuscle

Exercise

heavy

more sympathetic stimulation

vasocontriction to “non-essentials”(most internal organs except brain)

bloodlungs - heart - - heart -