Lecture #10: Internal Circulation in Mammals
I. INTRODUCTORY
REMARKS
1. Diffusion is not enough, a circulatory system
is necessary.
2. Gastrovascular cavities are simple, but
adequate for simple multicellular organisms.
3. Open and closed circulatory systems: (Fig. 42.2)
a. open system:
(1) it has blood and interstitial fluid together
(hemolymph).
(2) hemolymph is pumped by a neurogenic heart.
(3) it oozes through sinuses in response to heart
beat and body movements.
b. closed system:
(1) vascular blood is in a separate, closed
compartment.
(2) blood is pumped by a myogenic heart.
(3) blood cells are forced through small
capillaries by hydrostatic pressure.
4. Evolution of circulatory schemes of vertebrates. (Fig. 42.3)
II. CARDIOVASCULAR SYSTEMS OF
VERTEBRATES
1. An overview of the mammalian cardiovascular
system. (atria, ventricles, arteries, arterioles, capillaries, venules, veins) (Fig. 42.4)
2. Pulmonary circuit versus systemic circuit.
3. Properties of the heart: (Fig. 42.5)
a. left ventricle has more muscle (it has
thicker wall).
b. systole versus diastole.
c. atrioventricular valve versus semilunar
valves.
d. stroke volume, pulse rate, and cardiac
output (in volume/min: 5.25L/min).
4. Excitation of the heart: SA node, AV
node, AV bundle, Purkinje fibers (Fig. 42.7)
5. Control of the heart: sympathetic vs parasympathetic,
and hormones (adrenalin).
6. Body temperature and the heart: 1°C
can increase the rate 10-20 beats.
7. Exercise increases rate by increasing the venus return. (cardiac output can increase 5-fold)
II. OTHER CHARACTERISTICS OF THE VASCULAR SYSTEM
1. Arteries and veins have connective
tissue, smooth muscle, and endothelium. (See Fig. 42.8)
2. Velocity of blood slows as total
cross-sectional area of capillaries increases. (blood travels 30 cm/sec when it
first leaves the heart) (But, Fig. 42.10 says 48 cm/sec) (Fig. 42.10)
3. Pressure of blood decreases, mainly
due to peripheral resistance of arterioles.
a. pressure is dependent on (1) cardiac
output and (2) peripheral resistance.
b. physical or emotional stress can raise BP by
triggering neuronal and hormonal responses that increase CO and PR.
4. Measurement of blood pressure (Fig. 42.11)
5. Microcirculation and blood
distribution:
a. the organs most heavily supplied are the
brain, kidneys, liver, and heart.
b. after a meal, intestinal arterioles
dilate (specific dynamic action).
c. during strenuous exercise, blood is
diverted from GI tract to skeletal muscles.
d. distribution of blood is largely
dependent on precapillary sphincters. (Fig. 42.12)
e. at any given time, only 5-10% of body
capillaries have blood flowing. (Fig. 42.12)
6. Capillary exchange is based on hydrostatic
pressure vs osmotic pressure (Fig. 42.13)
7. Lymph is like interstitial fluid, but
flows thru lymph nodes to veins in shoulders.