Circulatory Physiology

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the FORCE resisting the flow of blood through a vessel (usually from friction): Resistance to Flow (Peripheral Resistance) -
a measure of the "thickness" or "stickiness" of a fluid flowing through a pipe: viscosity -
viscosity -: water < V blood < V toothpaste
water flows easier than blood
the longer the vessel, the greater the drop in pressure due to friction: tube length -
smaller diameter = greater friction: tube diameter -
Relation Between Blood Flow, Pressure, Resistance: increased P -> increased flow
decreased P -> decreased flow
increased R (vasoconstriction) -> DECREASED flow
decreased R (vasodilation) -> INCREASED flow
Blood Pressure Near the Heart: Systemic Blood Pressure
HEART produces blood pressure by: pumping the blood
Blood pressure ? with distance from Heart: decreases
pressure in aorta (& major arteries) in middle of ventricular contraction (120 mm Hg in healthy adult): systolic arterial blood pressure -
pressure in aorta (& major arteries) during ventricular diastole, when semilunar valves are closed (80 mm Hg in healthy adult): diastolic arterial blood pressure -
the "average" blood pressure produced by the heart (93 mm Hg in healthy adult): mean arterial pressure (MAP) -
mean arterial pressure =: diastolic pressure + 1/3 pulse pressure
pulse pressure =: systolic pressure - diastolic pressure
blood pressure decreases throughout system: L ventricle -->120 mm Hg
arteries -->120 - 60 mm Hg
arterioles -->60 - 40 mm Hg
capillaries -->40 - 20 mm Hg
venous -->20 - 10 mm Hg
R atrium -->10 - 0 mm Hg
venous blood pressure is so low, other factors contribute to venous blood flow: venous return -
venous return breathing action of thorax "squeezes" blood back toward the heart: respiratory pump -
venous return contraction/relaxation of skeletal muscles "milk" blood up veins to heart: muscular pump -
endothelium derived factors strong vasoconstrictor: endothelin -
Cardiac Output =: stroke volume X heart rate

CO = SV (ml/beat) x HR (beats/min)

CO = 70 ml/beat x 60 beats/min = 4200 ml/min
Cardiac Output increased cardiac output ->: increased blood pressure
Cardiac Output increased stroke volume ->: increased blood pressure
Cardiac Output increased heart rate ->: increased blood pressure
Peripheral Resistance arteriole constriction --->: increased blood pressure
Peripheral Resistance resistance inversely proportional to the "fourth power" of the radius change: for every radius change, resistance is increased by a factor of 4
Regulation of Blood Pressure Nervous System Control: 1. control of arteriole diameter
2. directs blood flow to proper organs and tissues that need it
3. REFLEX PATHWAY:
REFLEX PATHWAY:: baroreceptors/chemoreceptors/brain -->
afferent nerve fibers -->
medulla (vasomotor center) -->
vasomotor (efferent) nerve fibers -->
smooth muscle of arterioles
Regulation of Blood Pressure Vasomotor Fibers to Smooth Muscle of Arterioles: sympathetic fibers that release norepinephrine (NE); cause vasoconstriction of arterioles
Regulation of Blood Pressure Vasomotor Center of the Medulla: 1. sympathetic neuron cell bodies in the medulla
2. receive input from baroreceptors, chemoreceptors, and brain
3. vasomotor tone - general constricted state of arterioles set by vasomotor center
Regulation of Blood Pressure Baroreceptors: 1. blood pressure receptors large arteries (carotid sinuses, aortic arch, neck/thorax arteries)
2. send blood pressure information to vasomotor center of medulla
Regulation of Blood Pressure Baroreceptors blood pressure receptors large arteries:: carotid sinuses, aortic arch, neck/thorax arteries
Regulation of Blood Pressure Baroreceptors send blood pressure information to vasomotor center of medulla (increased pressure): increased pressure -->
inhibits vasomotor center -->
vasodilation
Regulation of Blood Pressure Baroreceptors send blood pressure information to vasomotor center of medulla (decreased pressure): decreased pressure -->
stimulates vasomotor center ->
vasoconstriction
Regulation of Blood Pressure Chemoreceptors: 1. located in aortic arch and carotid arteries
carotid and aortic bodies

2. monitor OXYGEN and pH levels of the blood
low OXYGEN or low pH -------> increase blood pressure, return blood to lungs quickly
Higher Brain Centers Control on BP: hypothalamus & cortex also effect vasomotor area
Chemical Controls of Blood Pressure: 1. hormones of adrenal medulla -
2. atrial natriuretic factor (ANF) -
3. antidiuretic hormone (ADH) -
4. endothelium derived factors
5. alcohol -
"fight-or-flight" response to fear; release of norepinephrine and epinephrine from adrenal medulla; causes vasoconstriction and increased BP: hormones of adrenal medulla -
secreted by the atria of the heart, promotes general decline in blood pressure kidney releasing more Na+ and water, reducing fluid volume: atrial natriuretic factor (ANF) -
endothelium derived factors endothelium derived relaxing factor: vasodilation -
Chemical Controls of Blood Pressure causes vasodilation: alcohol -
released by the hypothalamus, causes increase in blood pressure by getting the kidneys to conserve water in the body; e.g. during hypotensive situations: antidiuretic hormone (ADH) -
Renal (Kidney) Regulation of Blood Pressure fluid loss through urine: direct regulation -

a. low pressure/volume --> conserve water
b. high pressure/volume --> release more water
Renal (Kidney) Regulation of Blood Pressure renin-angiotensin mechanism: low blood pressure -->
release of renin -->
formation of angiotensin II--> vasoconstriction
release of aldosterone --> Na+/water reabsorption (by kidney)
blood pressure, pulse, respiratory rate, and body temperature: vital signs -
the actual VOLUME of blood moving through a particular site (vessel or organ) over a certain TIME period (liter/hour, ml/min): Blood Flow -
the FORCE exerted on the wall of a blood vessel by the blood contained within (millimeters of Mercury; mm Hg): Blood Pressure -
blood pressure =: the systemic arterial pressure of large vessels of the body (mm Hg)
auscultory method of blood pressure measurement: 1. Â“sphygmomanometerÂ” wrapped around upper arm
2. inflate above systolic pressure of brachial a.
3. pressure released, first sounds - systolic pr.
4. disappearance of sounds - diastolic pr.
below normal blood pressure, < 100/60: Hypotension
Hypotension factors -: age, physical conditioning, illness
generally in elderly, drop in blood pressure during postural changes: orthostatic hypotension -
ongoing low blood pressure: chronic hypotension -
chronic hypotension -: 1. low blood protein levels (nutrition)
2. AddisonÂ’s disease (adrenal cortex malfunction)
3. hypothyroidism
4. also sign of various types of cancer
above normal blood pressure at rest, > 140/90: Hypertension
Hypertension factors -: weight, exercise, emotions, stress
ongoing high blood pressure: chronic hypertension -
chronic hypertension -: 1. prevalent in obese and elderly
2. leads to heart disease, renal failure, stroke
3. also leads to more arteriosclerosis
4. primary hypertension - unidentified source
primary hypertension - unidentified source: 1. high Na+, cholesterol, fat levels
2. clear genetic component (in families)
3. diuretics - promote water removal
4. NE blockers - slow vasoconstriction
secondary hypertension - identifiable disorder: i. kidney disorders
ii. endocrine (hormone) disorders
iii. arteriosclerosis
Blood Flow in the Body General Features: 1. delivery of oxygen and removal of carbon dioxide
2. gas exchange in the lungs
3. absorption and delivery of nutrients from GI tract
4. processing/waste removal in the kidneys
normal blood flow at rest: abdominal organs 24%
skeletal muscle 20%
kidneys 20%
BRAIN 13%
heart 4%
other 15%
Velocity of Blood Flow velocity directly related to:: TOTAL cross-sectional area of the vessel(s)
Velocity of Blood Flow: aorta 40-50 cm/s (FASTEST)
arteries 20-40 cm/s
arterioles 1-20 cm/s
capillaries 0.1-1 cm/s (SLOWEST)
Local Regulation of Blood Flow regulation of blood flow by altering arteriole diameter: autoregulation -
autoregulation - regulation of blood flow by altering arteriole diameter: 1. oxygen and carbon dioxide levels
2. prostaglandins, histamines, kinins
3. needy areas --> more blood flow
change in flow through arteriole in response to stretch of smooth muscle: myogenic response -
increase in blood flow to area where an occlusion has occurred: reactive hyperemia -
results from prolonged lack of oxygen/nutrients to an area (eg. heart): increased vasculature -
Blood Flow to Skeletal Muscles increased blood flow to muscles during heavy activity: active (exercise) hyperemia -
active (exercise) hyperemia - increased blood flow to muscles during heavy activity: 1. decreased oxygen and increased lactic acid
2. visceral organ blood flow is decreased
Blood Flow to The Brain: 1. MUST maintain constant blood flow (750 ml/min)
2. sensitive to low pH and high carbon dioxide
3. blood pressure tightly regulated in the brain
a. fainting -> below 60 mm Hg
b. edema (brain swelling) -> above 180 mm Hg
Blood Flow to The Skin intimately involved in temperature regulation: increased body temperature ->
hypothalamic inhibition of vasomotor area ->
vasodilation of vessels in skin ->
increased blood flow ->
sweating ->
(bradykinin -> more vasodilation)

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