Blood Vessels: part 2 Flashcards


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1

Hemodynamics of Blood Flow: Blood flow

-Measured as ml/min
-Equivalent to cardiac output (CO) for entire vascular system

*Depends on Pressure Differences that drive blood flow and the Resistance to blood flow in specific blood vessels

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Hemodynamics of Blood Flow: Blood Pressure (BP)

-Force per unit area exerted on the wall of a blood vessel by the blood
-Expressed in mm Hg

-highest in aorta & falls progressively as the distance from L ventricle increases

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BP: The ____ _____ provides the driving force that keeps blood moving from higher to lower pressure areas

pressure gradient

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BP: measured as _____ _____ BP in large arteries near the heart

systemic arterial

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Aorta =
arterioles =
capillaries (venous end)=
right ventricle =

Aorta = 110 mmHg,
arterioles = 35 mmHg,
capillaries (venous end) 16 mmHg,
right ventricle = 0 mmHg

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Arterial Blood Pressure: Mean arterial pressure (MAP):

average BP in the arteries
propels the blood to the tissues

MAP = diastolic pressure + 1/3 pulse pressure
BP 110/70, MAP = 83 mmHg

*Pulse pressure and MAP both decline with increasing distance from the heart

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Factors Affecting MAP

Elasticity (compliance or distensibility) of arteries
Volume of blood forced into arteries

blood loss (>10% volume) causes drop in BP... Hemorrhage

Increased blood volume increases BP
...Water retention by kidneys

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Vascular Resistance

Opposition to flow due to friction between blood and vessel walls

*Generally encountered in the peripheral systemic circulation

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Vascular Resistance: sources of resistance

Blood viscosity – higher the viscosity, the higher the resistance (constant)

Total blood vessel length – longer the vessel, greater the resistance (constant)

Blood vessel diameter – smaller the lumen, the greater the resistance (variable)

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Venous Return

Blood flow back to the heart

Result of pressure generated by L ventricular contraction
Increased pressure in R atrium or R ventricle will decrease venous return

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factors that aid venous return

Skeletal muscle pump
Respiratory pump

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Velocity of Blood Flow: Inversely related to the cross-sectional area

Slowest where cross-sectional area is greatest
Slowest in the capillaries where there are many branches

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Velocity of Blood Flow: Circulation time

time it takes for a drop of blood to pass from the R atrium through systemic circulation to the foot and back to the R atrium – about 1 minute

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What Controls Blood Pressure

Cooperative effort of the heart, blood vessels, and kidneys, and supervised by the brain

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CV center in the brain =

medulla oblongata

-Regulates HR and SV

-Controls neural, hormonal, and local feedback systems that regulate BP and blood flow to specific tissues

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Neural Regulation of BP: Baroreceptors

pressure-sensitive sensory receptors

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Neural Regulation of BP: Baroreceptors: ____ reflex in the aorta

*aortic

Regulates systemic BP

Nerve impulses from baroreceptors here reach the CV center via sensory axon of the vagus (X) nerves

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Neural Regulation of BP: Baroreceptors: ____ ____ reflex of the ____ arteries

*carotid sinus; carotid

Regulate BP in the brain
Nerve impulses from baroreceptors here reach the CV center via sensory axons of the glossopharyngeal (IX) nerves

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Neural Regulation of BP: Baroreceptors: Chemoreceptors

sensory receptors that monitor chemical composition of blood

Detect changes in blood levels of oxygen, carbon dioxide, and H+ ions

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Hypoxia, acidosis, or hypercapnia stimulates chemoreceptors to send impulses to the CV center, which causes respiratory center to

adjust breathing rate

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Hormonal Regulation of BP: Renin-angotensin-aldosterone (RAA) system

When blood volume falls or blood flow to kidneys decreases, renin is secreted by kidneys into the bloodstream

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Renin and angiotensin-converting enzyme (ACE) act on their substrates to produce angiotensin II , which raises BP by:

Vasoconstriction (increasing vascular resistance)

Aldosterone secretion – increases blood volume

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Epinephrine and norepinephrine

Cause vasoconstriction of arterioles and veins in skin and abdominal organs and vasodilation of arterioles in cardiac and skeletal muscle

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Antidiuretic hormone (ADH)

produced by hypothalamus and released by the posterior pituitary

Acts on the kidneys to promote water reabsorption, thereby increasing blood volume and blood pressure

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Atrial natriuretic peptide (ANP)

Released by cells in the atria of the heart

Lowers BP by causing vasodilation and by promoting loss of salt and water in the urine, which reduces blood volume

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Autoregulation of BP: types of stimuli

Myogenic responses

Vasodilating and vasoconstricting chemicals

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Myogenic

Stretch of muscles

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Vasodilating and vasoconstricting chemicals

K+, H+, lactic acid, and adenosine – vasodilating
Thromoxane, A2, superoxide radicals, serotonin, and endothelins - vasoconstricting

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Pulse pressure

difference between the systolic and diastolic pressures; normally about 40 mmHg