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Chapter 21. Blood Vessels and Circulation. Blood Pressure and Cardiovascular regulation Exercise. arteries arterioles capillaries venules veins. carry blood away from heart thicker walls (smooth muscle) branch and get narrower bifurcation (tri-, rami-) smallest vessels

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Chapter 21

Blood Vessels

and Circulation


Blood Pressure and

Cardiovascular regulation

Exercise


arteries

arterioles

capillaries

venules

veins

carry blood away from heart

thicker walls (smooth muscle)

branch and get narrower

bifurcation (tri-, rami-)

smallest vessels

in networks (beds)

exchange with ECF

carry blood back to heart

thinner walls

small v. join to form larger veins

anastomosis


blood circuit

fig. 21-8


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.”


Controlling CO and bp

Autoregulation of blood flow

Neural mechanisms

Hormonal mechanisms

*

*


CO = HR x SV

neural mechanisms

(reflex control of

cardiovascular function)


Neural mechanisms

Reflex control of

cardiovascular function

baroreceptors

blood pressure

chemoreceptors

pH, [gases]

negative feedback loops


Neural mechanisms

Reflex control of

cardiovascular function

baroreceptors

monitor degree of stretch in walls of expandable organs

carotid sinuses

aortic sinuses

atrium


baroreceptors

if blood pressure climbs

  • decrease cardiac output

    • lower HR (ACh SA)

  • vasodilation

  • lowers peripheral resistance

  • reflex:

    reduce blood pressure


    baroreceptors

    if blood pressure falls

    • increase cardiac output

      • NE on heart

  • vasoconstriction

  • NE inc. peri. resistance

  • reflex:

    increase blood pressure


    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

    brief rise in bp

    pressure on lungs sends pulmonary blood to atria

    bp falls

    reduced venous return

    low CO

    reflexive vasoconstriction

    increase in heart rate


    baroreceptors

    Valsalva maneuver

    • release pressure

      expansion of vessels (bp6)

      (6return, 5aortic volume)

      4. restore normal

      blood return up

      CO is up

      BP is up


    graph of

    bp drop and

    HR increase

    during Valsalva


    to here 4/2/07

    Lec # 34



    Neural mechanisms

    Reflex control of

    cardiovascular function

    baroreceptors

    chemoreceptors


    Neural mechanisms

    chemoreceptors

    monitor pH (H+)

    [CO2]

    [O2]

    of blood and CSF

    sensory neurons in: carotid body

    aortic bodies

    (med. oblong.)


    Neural mechanisms

    chemoreceptors

    pH drops (H+5)

    or 5[CO2]

    or 6[O2]

    reflex stimulation of cardio-

    acceleratory centers (sym)

    stimulate vasomotor

    (vasoconstriction)


    Neural mechanisms

    chemoreceptors

    pH drops (H+5)

    or 5[CO2]

    or 6[O2]

    increase cardiac output

    peripheral vasoconstriction

    increase bp


    Neural mechanisms

    chemoreceptors

    pH drops (H+5)

    or 5[CO2]

    or 6[O2]

    receptors in medulla obl.

    stimulate respiratory centers

    more O2

    and more venous return


    Neural mechanisms

    chemoreceptors

    pH drops (H+5)

    or 5[CO2]

    or 6[O2]

    increased bp and resp.

    more O2 to cells



    CO = HR x SV

    hormonal control

    neural mechanisms

    NE, E

    ADH

    angiotensin II

    EPO

    natriuretic peptides

    all regulate

    blood volume


    ADH

    Antidiuretic hormone

    made in hypothalamus

    released from posterior pituitary gland

    in response to 6 blood volume

    vasoconstriction (5bp)

    H2O recovery in kidney


    angiotensin II

    fall in bp

    renin release from kidney

    angiotensinogen (from liver)

    angiotensin I

    angiotensin II

    renin

    ACE


    angiotensin II

    four functions:

    stimulates kidney to

    produce 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 volume

    reduce blood pressure


    natriuretic peptides

    increase Na+ excretion at kidney

    increase volume of urine produced

    reduce thirst

    block ADH, NE, E, aldosterone release

    stimulate peripheral vasodilation

    reduce blood volume

    and blood pressure




    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.”



    Summary

    hormones

    venous return

    filling time

    venous return

    preload

    contractility

    afterload

    Heart rate

    EDV

    ESV

    SV = EDV-ESV

    CO = HR x SV


    Exercise

    light

    slight sympathetic innervation

    slight increase in HR

    vasodilation

    get blood to tissues

    resistance drops

    more blood flows


    Exercise

    light

    increase in venous return

    muscle pumps


    muscle activity

    venous return

    fig. 21-6


    Exercise

    light

    increase in venous return

    muscle pumps

    increase respiratory pump

    cardiac output increases

    due to higher venous return


    Exercise

    heavy

    more sympathetic stimulation

    vasocontriction to “non-essentials”

    (most internal organs except brain)

    blood

    lungs

    skeletal

    muscle

    - heart -

    - heart -


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