Lecture: Circulatory Physiology
I.
Factors Involved in Blood Circulation
A.
Blood Flow - the actual VOLUME of blood moving through a particular site (vessel or organ)
over a certain TIME period (liter/hour, ml/min)
B.
Blood Pressure - the FORCE exerted on the wall of a blood vessel by the blood contained within
(millimeters of Mercury; mm Hg)
blood pressure = the systemic arterial pressure of large vessels of the body (mm Hg)
C.
Resistance to Flow (Peripheral Resistance) - the FORCE resisting the flow of blood through a
vessel (usually from friction)
1.
viscosity - a measure of the "thickness" or "stickiness" of a fluid flowing through a pipe
a.
b.
D.
V water < V blood < V toothpaste
water flows easier than blood
2.
tube length - the longer the vessel, the greater the drop in pressure due to friction
3.
tube diameter - smaller diameter = greater friction
Relation Between Blood Flow, Pressure, Resistance
difference in blood pressure ( P)
Blood Flow (F) =
peripheral resistance (R)
a.
b.
c.
d.
II.
increased P -> increased flow
decreased P -> decreased flow
increased R (vasoconstriction) -> DECREASED flow
decreased R (vasodilation) -> INCREASED flow
Systemic Blood Pressure
A.
Blood Pressure Near the Heart
1.
2.
HEART produces blood pressure by pumping the blood
Blood pressure decreases with distance from Heart
3.
systolic arterial blood pressure - pressure in aorta (& major arteries) in middle of
ventricular contraction (120 mm Hg in healthy adult)
4.
diastolic arterial blood pressure - pressure in aorta (& major arteries) during ventricular
diastole, when semilunar valves are closed (80 mm Hg in healthy adult)
5.
mean arterial pressure (MAP) - the "average" blood pressure produced by the heart (93
mm Hg in healthy adult)
mean arterial pressure = diastolic pressure + 1/3 pulse pressure
**
6.
pulse pressure = systolic pressure - diastolic pressure
blood pressure decreases throughout system
L ventricle
arteries
arterioles
capillaries
venous
R atrium
7.
-->120 mm Hg
-->120 - 60 mm Hg
-->60 - 40 mm Hg
-->40 - 20 mm Hg
-->20 - 10 mm Hg
-->10 - 0 mm Hg
venous return - venous blood pressure is so low, other factors contribute to venous blood
flow
a. respiratory pump - breathing action of thorax "squeezes" blood back toward the heart
b. muscular pump - contraction/relaxation of skeletal muscles "milk" blood up veins to
heart
III.
Factors Affecting Blood Pressure
A.
Cardiac Output ( = stroke volume X heart rate)
CO
1.
2.
3.
B.
=
70 ml/beat x 60 beats/min = 4200 ml/min
increased cardiac output -> increased blood pressure
increased stroke volume -> increased blood pressure
increased heart rate -> increased blood pressure
arteriole constriction ---> increased blood pressure
resistance inversely proportional to the "fourth power" of the radius change
Blood Volume
1.
2.
3.
4.
IV.
SV (ml/beat) x HR (beats/min)
Peripheral Resistance
1.
2.
C.
=
hemorrhage - decrease in blood pressure
salt/fluid - increase in blood pressure
polycythemia - increase in blood viscosity
RBC anemia - decrease in blood viscosity
Regulation of Blood Pressure
A.
Nervous System Control
1.
control of arteriole diameter
2.
3.
directs blood flow to proper organs and tissues that need it
REFLEX PATHWAY:
baroreceptors/chemoreceptors/brain
afferent nerve fibers
medulla (vasomotor center)
vasomotor (efferent) nerve fibers
smooth muscle of arterioles
B.
Vasomotor Fibers to Smooth Muscle of Arterioles
1.
C.
sympathetic fibers that release norepinephrine (NE); cause vasoconstriction of arterioles
Vasomotor Center of the Medulla
1.
2.
3.
D.
sympathetic neuron cell bodies in the medulla
receive input from baroreceptors, chemoreceptors, and brain
vasomotor tone - general constricted state of arterioles set by vasomotor center
Baroreceptors
1.
2.
blood pressure receptors large arteries (carotid sinuses, aortic arch, neck/thorax arteries)
send blood pressure information to vasomotor center of medulla
increased pressure
inhibits vasomotor center
vasodilation
E.
F.
-->
-->
decreased pressure -->
stimulates vasomotor center ->
vasoconstriction
Chemoreceptors
1.
located in aortic arch and carotid arteries
a.
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
1.
G.
-->
-->
-->
-->
hypothalamus & cortex also effect vasomotor area
Chemical Controls of Blood Pressure
1.
hormones of adrenal medulla - "fight-or-flight" response to fear; release of
norepinephrine and epinephrine from adrenal medulla; causes vasoconstriction and
increased BP
2.
atrial natriuretic factor (ANF) - secreted by the atria of the heart, promotes general
decline in blood pressure kidney releasing more Na+ and water, reducing fluid volume
3.
antidiuretic hormone (ADH) - released by the hypothalamus, causes increase in blood
pressure by getting the kidneys to conserve water in the body; e.g. during hypotensive
situations
4.
endothelium derived factors
a.
b.
5.
H.
endothelin - strong vasoconstrictor
endothelium derived relaxing factor - vasodilation
alcohol - causes vasodilation
Renal (Kidney) Regulation
1.
direct regulation - fluid loss through urine
a.
b.
2.
low pressure/volume --> conserve water
high pressure/volume --> release more water
renin-angiotensin mechanism
low blood pressure -->
release of renin -->
formation of angiotensin II--> vasoconstriction
release of aldosterone --> Na+/water reabsorption (by kidney)
V.
Variations in Blood Pressure
A.
Measuring Blood Pressure
1.
vital signs - blood pressure, pulse, respiratory rate, and body temperature
2.
auscultory method of blood pressure measurement
a.
b.
c.
d.
B.
“sphygmomanometer” wrapped around upper arm
inflate above systolic pressure of brachial a.
pressure released, first sounds - systolic pr.
disappearance of sounds - diastolic pr.
Hypotension (below normal blood pressure, < 100/60)
1.
factors - age, physical conditioning, illness
2.
orthostatic hypotension - generally in elderly, drop in blood pressure during postural
changes
3.
chronic hypotension - ongoing low blood pressure
a.
b.
c.
d.
low blood protein levels (nutrition)
Addison’s disease (adrenal cortex malfunction)
hypothyroidism
also sign of various types of cancer
C.
Hypertension (above normal blood pressure at rest, > 140/90)
1.
2.
factors - weight, exercise, emotions, stress
chronic hypertension - ongoing high blood pressure
a.
b.
c.
d.
prevalent in obese and elderly
leads to heart disease, renal failure, stroke
also leads to more arteriosclerosis
primary hypertension - unidentified source
i.
ii.
iii.
iv.
e.
secondary hypertension - identifiable disorder
i.
ii.
iii.
VI.
high Na+, cholesterol, fat levels
clear genetic component (in families)
diuretics - promote water removal
NE blockers - slow vasoconstriction
kidney disorders
endocrine (hormone) disorders
arteriosclerosis
Blood Flow in the Body
A.
General Features
1.
2.
3.
4.
5.
B.
delivery of oxygen and removal of carbon dioxide
gas exchange in the lungs
absorption and delivery of nutrients from GI tract
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
1.
velocity directly related to the TOTAL cross-sectional area of the vessel(s)
FASTEST
SLOWEST
C.
aorta
arteries
arterioles
capillaries
40-50 cm/s
20-40 cm/s
1-20 cm/s
0.1-1 cm/s
Local Regulation of Blood Flow
1.
autoregulation - regulation of blood flow by altering arteriole diameter
a.
b.
c.
D.
2.
myogenic response - change in flow through arteriole in response to stretch of smooth
muscle
3.
reactive hyperemia - increase in blood flow to area where an occlusion has occurred
4.
increased vasculature - results from prolonged lack of oxygen/nutrients to an area (eg.
heart)
Blood Flow to Skeletal Muscles
1.
active (exercise) hyperemia - increased blood flow to muscles during heavy activity
a.
b.
E.
decreased oxygen and increased lactic acid
visceral organ blood flow is decreased
Blood Flow to The Brain
1.
2.
3.
F.
oxygen and carbon dioxide levels
prostaglandins, histamines, kinins
needy areas --> more blood flow
MUST maintain constant blood flow (750 ml/min)
sensitive to low pH and high carbon dioxide
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
1.
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)
G.
Blood Flow to the Lungs
1.
2.
H.
Blood Flow to the Heart
1.
2.
VII.
short pathway from heart, less pressure required
low oxygen level --> vasoconstriction
blood to coronary arteries during diastole
vasodilation from ADP and carbon dioxide
Blood Flow in the Capillaries
A.
B.
C.
Exchange of Gases and Nutrients
1.
diffusion - all molecules move DOWN the concentration gradient (from HIGH to LOW)
into or out of the blood
2.
oxygen/nutrients
carbon dioxide/ wastes
(blood
(body cells
------> body cells)
------> blood)
Fluid Movements
1.
hydrostatic pressure - force from the capillary wall on the blood itself
a.
filtration pressure - the pressure forcing fluid and solutes through capillary clefts
2.
3.
osmotic pressure - force driving fluid in the direction of HIGHER solute concentration
movement out:
Hydrostatic pressure > Osmotic difference
movement in :
Hydrostatic pressure < Osmotic difference
4.
normal fluid movement 1.5 ml/min in the entire body
Circulatory Shock
1.
circulatory shock - blood pressure gets so low that blood will not flow adequately
2.
hypovolemic shock - circulatory shock resulting from loss of fluid (bleeding, diarrhea,
burn)
a.
heart rate increases rapidly
b.
general vasoconstriction of vessels
3.
vascular shock - extreme vasodilation causes sudden drop in blood pressure
a. snake and spider bites with NE blockers
b.
septicemia - bacterial infection
4.
cardiogenic shock - heart is unable to provide sufficient blood pressure