Transcript Cardiovascular System: Blood Vessels and Circulation

Cardiovascular System: Blood
Vessels and Circulation
A Presentation
Structure and Function
• The vital functions of the cardiovascular
system occur at the capillary level
• Chemical and gaseous exchange between
the blood and interstitial fluid occurs
across capillary walls.
– Tissues relay on capillary diffusion for
nutrients and oxygen and to remove
metabolic waste.
Structure of vessel walls
• Three layers
– Tunica intima or innermost layer. Includes a
lining of endothelium and a connective tissue
layer.
– Tunica media or middle layer. Contains
smooth muscle tissue and collagen and
elastic fibers.
– Tunica externa forms sheath of connective
tissue around the vessel.
Arteries
• Elastic: large, able to absorb the pressure
changes of the cardiac cycle, contain
many elastic fibers that stretch and return
to original dimension. Examples: aorta,
pulmonary trunk
• Muscular arteries: medium sized distribute
blood to skeletal muscles and internal
organs. Not as elastic. Example: external
carotid arteries.
• Arterioles: small (30u), diameter of muscle
layer very thin.
Capillaries
• Only vessels that permit exchange
between blood and interstitial fluid.
• Walls are thin(no tunica externa or tunica
media)
• Small diameter slows blood flow
• Permits water, small solutes and lipidsoluble materials to pass.
• Interconnect to form capillary bed.
Veins collect blood and return it
to the heart
• Venules: smallest
• Veins have relatively thin walls.
• In medium veins contain valves that
prevent the backflow of blood due to low
pressure and gravity
• Stretching and distortion of these valves
cause varicose veins.
Pressure and resistance
determine blood flow and affect
rates of capillary exchange
• Highest pressure at the base of the aorta
• Resistance opposes movement of blood.
– Sources include
• Vascular resistance
• Viscosity
• turbulence
Pressures within the systemic
circuit
• Highest in the aorta and lowest at the vena
cava
• Arterial pressure rises during ventricular
systole and falls during ventricular
diastole.
• 120/80 reflects the separate systolic and
diastolic pressures.
• Read the Clinical Note page 435.
Forces Acting Across Capillary
Walls
Venous pressure
• Pressure is only 1/10th of the arterial
system at the beginning.
• When standing two factors help venous
return
– Muscular compression of skeletal muscles
– Respiratory pump: inhalation causes both the
vena cava and rt. atria to expand and fill.
Cardiovascular Regulation
• Involves
– Autoregulation
– Neural mechanisms
– Endocrine mechanisms
Pulmonary Circuit
• Deoxgenated blood enters the lungs in
arteries
• Oxygenated blood leaves the lungs in
veins.
Systemic Circuit
• Oxygenated blood from the left ventricle
goes to tissues other than the lungs’
exchange surfaces.
• Deoxygenated blood returns to the right
atrium.
Fetal Circulation
• Embryonic lungs are collapsed and
nonfunctional
• All nutritional and respiratory needs are
provided by diffusion across the placenta.
• Umbilical arteries carry deoxygenated
blood from fetus to placenta
• Umbilical veins returns oxygenated blood
from placenta to fetus.
• Veins bypass developing liver through
ductus venosus.
• Foramen ovale in fetal heart and ductus
arteriosus between pulmonary and aortic
trunks by pass collasped lungs.
• At birth lungs expand and smooth muscles
in ductus arteriosus contract closing
connection. Increased pressure in L atrium
closes foramen ovale.
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Aging
Decreased hematocrit
Blockage of peripheral veins
Pooling of blood in the veins
Reduction in max. cardiac output
Changes in heart conduction
Reduction in elasticity of cardiac skeleton
Progressive atheroschlerosis
Replacement of damaged heart muscle by
scar tissue.
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