BIO 245 Exam 2b
Compare arteries, veins, and capillaries. - ANS-Arteries: convey blood from heart to
capillaries, smaller than veins, retain shape, vessels with the highest blood pressure,
thickest vessels with the highest blood pressure, 3 types: elastic, muscular, and
arterioles
Veins: drains blood from capillaries and conveys blood to the heart, contains valves,
larger than arteries, collapses when not filled with blood, have the lowest blood
pressure, largest amt of blood in the body is found in systemic veins, defined by size
Capillaries: the smallest blood vessel with a narrow thin wall that supports the exchange
of materials between the blood and body tissues.
List the three types of capillaries and describe their characteristics. - ANS-Continuous
capillary: lining of endothelial cells is complete around lumen; basement membrane is
complete, intercellular clefts between endothelial cells; least leaky, most common type,
found in skin, muscles, lungs, CNS
Fenestrated Capillary: same as continuous capillary except also contains fenestrations;
somewhat "leaky" acts as a filter; found in most endocrine organs
Sinusoid: lining of endothelial cells is incomplete around the lumen, basement
membrane is incomplete or absent; most leaky, found in red bone marrow, liver, spleen,
some endocrine organs
Describe the structure of a capillary bed and explain how perfusion is regulated. -
ANS-Most beds follow a simple pathway where blood enters the capillary bed from an
arteriole and is drained by a venule
Blood enters the capillary bed from an arteriole through a metarteriole. The proximal
part is encircled by smooth muscle cells and the distal part forms the thoroughfare
channel which has no smooth muscle cells and leads to venule
True capillaries branch from the metarteriole and thoroughfare channel and make up
most of the bed; precapillary sphincters control blood flow through the true capillaries
perfusing the tissues when open
Compare simple and alternative circulatory pathways (anastomoses and portal
systems) of blood vessels. - ANS-Alternative pathways of circulation vary from the
simple pathway in the number of arteries, capillaries, or venules that serve an organ or
region
Anastomoses: Arteria: multiple arteries converge into a single body region
Arteriovenous (shunt) moves blood directly from artery to a vein bypassing the capillary
bed Venous: multiple veins collectively drain a single body region
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