1 Chapter 14 Cardiac Output, Blood Flow and Blood Pressure Adjusting the pumping mechanism on demand. Calculating Cardiac Output • Stroke volume – volume of blood ejected by each ventricle during each contraction. • Cardiac rate – Beats per minute • Cardiac output = Stroke volume X Cardiac Rate Fig. 14.5
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Calculating Cardiac Output - SUNY Geneseolewisj/phys./posts/Circulation...Circulatory Shock •Hypovolemic shock: –Circulatory shock that is due to low blood volume. –Decreased
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Chapter 14Cardiac Output, Blood Flow and
Blood Pressure
Adjusting the pumping mechanism ondemand.
Calculating Cardiac Output
• Stroke volume– volume of blood ejected by each ventricle
during each contraction.• Cardiac rate
– Beats per minute• Cardiac output
= Stroke volume X Cardiac Rate
Fig. 14.5
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Regulation of Cardiac Rate• Regulation of HR
(chronotropic effect):– Positive or negative
chronotropic effect.• Autonomic control:
– Major means by whichcardiac rate isregulated.
• Cardiac Control Center(medulla):– Coordinates activity of
autonomic innervation.Fig. 14.1
Figure not in book:see fig. 14.2
Chronotropic Effect• Norepinephrine
– From sympathetic nerve endings– Opens Na+ and Ca2+ channels–
• Epinephrine– From adrenal medulla– Opens Na+ and Ca2+ channels–
mm Hg.– Interstitial hydrostatic pressure = 1 mm Hg.
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Colloid Osmotic Pressure• Pressure exerted by plasma proteins or
interstitial proteins.• Oncotic pressure
– Difference between plasma osmotic pressure andinterstitial osmotic pressure
– Colloid osmotic pressure of the plasma = 25 mm Hg.– Colloid osmotic pressure of the interstitium= 0 mm Hg.
Determining fluid movement intoor out of the capillaries:
• (Pc +πi) - (Pi + πp)– Pc = hydrostatic pressure in the capillary– πi = colloid osmotic pressure in the interstitium– Pi = hydrostatic pressure of interstitium– πp = colloid osmotic pressure of blood plasma
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Edema• Excessive accumulation of tissue fluid.• Edema may result from:
– High arterial blood pressure.– Venous obstruction.– Leakage of plasma proteins into interstitial
fluid.– Myexedema.– Decreased plasma protein.– Obstruction of lymphatic drainage.
• Look at Table 14.2
Severe edema of elephantiasis
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• Formation of urine begins by filtration ofplasma through glomerular capillary pores.
• Volume of urine excreted can be varied bychanges in reabsorption of filtrate.
• Adjusted according to needs of body byaction of hormones.
Kidney Regulation of BloodVolume
• ADH:– Antidiuretic hormone.
• Produced by neuronsof hypothalamus.
• Released by posteriorpituitary whenosmoreceptors detectan increase in plasmaosmolality.
Fig. 14.11
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Aldosterone
• Mechanism to maintain blood volume andpressure through absorption and retention ofNa+ and Cl-.– Stimulates reabsorption of NaCl.– Increases H20 reabsorption.– Does not dilute osmolality.
Fig. 14.12
Angiotensin II– Powerful
vasoconstrictor.– Stimulates production
of aldosterone.– Stimulates thirst.
Stimulationof thirstcenters inhypothalamus
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ANF
• Atrial natriuretic factor.• Stretch of atria stimulates production of
ANF.– Antagonistic to aldosterone and angiotensin II.– Promotes Na+ and H20 excretion by the kidney.
Steady-state blood volume changes are the single most importantlong-term determinant of blood pressure!!!!
Fig not in book
Fig. 14.13
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Blood Flow = F• Hydrostatic pressure• Always from region of higher pressure to lower pressure.• Generated by contraction of heart.• Magnitude varies throughout system.• F = ΔP/R
– F = flow– ΔP = pressure difference (mmHg)– R = resistance to flow.
Figure Not inBook:SeeFig. 14.9
Resistance• Opposition to blood flow.• Resistance directly proportional to length of vessel
and to the viscosity of the blood.• Inversely proportional to 4th power of the radius of
the vessel.• R = _Ln_
r4
• L = length of the vessel• n = viscosity of blood• r = radius of the vessel
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Components contributing to resistance• R = (nL/r4) (8/π)– n = fluid viscosity– L = Length– r = inside radius of tube.– 8/ π = constant
• Usually viscosity and length does not change in bloodsystem.
• Major regulators of blood flow through an organ are:– Mean arterial pressure.– Vascular resistance to flow.