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Angiogenesis
The growth of new blood vessels
Blood Vessels
Form a closed system of tubes that carry blood away from the heart, transport it to the tissues of the body and then return it to the heart
Arteries
carry blood from the heart to the tissues
Arterioles
small arteries that connect and deliver blood to capillaries
capillaries
the site of substance exchange between blood and body tissues
Venules
connect capillaries to larger veins
veins
convey blood from tissues back to the heart
Vaso vasorum
small blood vessels that supply blood to the cells of the walls of the arteries and veins
Three layers of an artery
tunica interna
tunica media
tunica externa
Tunica interna
simple squamous epithelium known as endothelium
basement membrane
internal elastic lamina
Tunica media
circular smooth muscle and elastic fibers
tunica externa
elastic and collagen fibers
Elasticity
allows arteries to accept blood under great pressure from the contraction of ventricles and to send it on through the system
Contractility
allows arteries to increase or decrease lumen size and to limit bleeding from wounds
Sympathetic innervation
vascular smooth muscle is innervated by sympathetic nervous system
increase in stimulation causes muscle contraction or vasoconstriction
decrease in stimulation or presence of certain chemicals (K+, H+, nitric oxide, lactic acid) causes vasodilation
Elastic arteries
large arteries with more elastic fibers and less smooth muscle
function as a pressure reservoir
Muscular arteries
medium sized arteries with more muscle than elastic fibers in tunica media
capable of greater vasoconstriction and vasodilation to adjust rate of flow
Types of capillaries
continuous capillaries
fenestrated capillaries
sinusoids
Continuous capillaries
intercellular clefts are gaps between neighboring cells
skeletal and smooth, connective tissue in lungs
Fenestrated capillaries
plasma membranes have many holes
kidneys, small intestine, choroid plexuses, ciliary process and endocrine glands
Sinusoids
very large fenestrations
incomplete basement membrane
liver, bone marrow, spleen, anterior pituitary and parathyroid gland
Varicose veins
twisted, dilated superficial veins
caused by leaky venous valves
allow backflow and pooling of blood
Anastomoses
union of two or more arteries supplying the same body region
Are there more veins or arteries in the body?
Veins
Capillary exchange
movement of materials in and out of a capillary
Bulk flow
movement of large amounts of dissolves or suspended material in same direction
important for regulating volumes of blood and interstitial fluid
Edema
an abnormal increase in interstitial fluid if filtration exceeds reabsorption
results in excess filtration
results in inadequate reabsorption
Blood pressure
pressure exerted on the walls of a blood vessel
What factors affect blood pressure?
cardiac output
blood volume
viscosity
resistance
elasticity of arteries
Resistance
opposition of blood flow as a result of friction between blood and the walls of blood vessels
depends on the diameter of blood vessels, blood viscosity, and total blood vessel length
Systemic vascular resistance
all of the vascular resistance offered by systemic blood vessels
most resistance is in arterioles, capillaries, and venules due to their small diameters
Blood flow
the volume that flows through any tissue in a given period of time
Velocity of blood flow
speed of blood flow in cm/sec is inversely related to cross-sectional area
blood flow becomes faster when vessels merge to form veins
Venous return
volume of blood flowing back to the heart from the systemic veins
Skeletal muscle pump
contraction of muscles and presence of valves
Respiratory pump
decreased thoracic pressure and increased abdominal pressure during inhalation, moves blood into thoracic veins and the right atrium
Note
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