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Physiology - CH 21 - Blood Vessels & Circulation


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What are the three layers of a artery/vein wall?
tunica intima
tunica media
tunica externa
What is the tunica intima?
Is the innermost layer
the endothelial lining
connective tissue layer
Internal Elastic Membrane
In arteries, is a layer of elastic fibers in outer margin of tunica intima
What is tunica media?
Is the middle layer
Contains concentric sheets of smooth muscle in loose connective tissue
Binds to inner and outer layers
External elastic membrane of the tunica media:
separates tunica media from tunica externa
What is tunica externa?
Is outer layer
Contains connective tissue sheath
Anchors vessel to adjacent tissues
In arteries:
contain collagen
elastic fibers
In veins:
contain elastic fibers
smooth muscle cells
What are vaso vasorum?
Small arteries and veins
In walls of large arteries and veins
Supply cells of tunica media and tunica externa
Arteries vs. Veins
Arteries and veins run side-by-side
Arteries have thicker walls and higher blood pressure
Artery has small, round lumen
Vein has a large, flat lumen
Vein lining contracts, artery lining does not
Artery lining folds
Arteries more elastic
Veins have valves
What are the resistance vessels?
What is an aneurysm?
A bulge in an arterial wall
Is caused by weak spot in elastic fibers

Pressure may rupture vessel
What is capillary structure?
Endothelial tube, inside thin basal lamina
No tunica media
No tunica externa
Diameter is similar to red blood cell
What are the two types of capillaries?
Continuous capillaries
Fenestrated capillaries (allow passage of larger particles)
What are vein valves?
Folds of tunica intima
Prevent blood from flowing backward
Compression pushes blood toward heart
How does capillary exchange occur?
Diffusion, Filtration, reabsorption
What are the four functions of blood and lymph cycle?
Ensures constant plasma and interstitial fluid communication

Accelerates distribution of nutrients, hormones, and dissolves gases through tissues

Transports insoluble lipids and tissue proteins that can’t cross capillary walls

Flushes bacterial toxins and chemicals to immune system tissues
What are three regulatory systems for cardiac output and blood pressure?
Autoregulation: causes immediate, localized homeostatic adjustments

Neural mechanisms: respond quickly to changes at specific sites

Endocrine mechanisms: direct long-term changes
What are three effects of light exercise?
Extensive vasodilation occurs: increasing circulation

Venous return increases: with muscle contractions

Cardiac output rises: due to rise in venous return causes gradual increase in cardiac output to about double resting level
And due to atrial stretching
What are five effects of heavy exercise?
Activates sympathetic nervous system

Cardiac output increases to maximum: about 4 times resting level

Restricts blood flow to “nonessential” organs (e.g., digestive system)

Redirects blood flow to skeletal muscles, lungs, and heart

Blood supply to brain is unaffected
What three systems have seperate blood flow?
What are the three unpaired branches of abdominal aorta?
Celiac trunk, divides into:
left gastric artery
splenic artery
common hepatic artery

Superior mesenteric artery

Left mesenteric artery
What are the five paired branches of abdominal aorta?
Inferior phrenic arteries
Suprarenal arteries
Renal arteries
Gonadal arteries
Lumbar arteries
What are the two fetal circulatory bipasses?
Foramen ovale:
interatrial opening
covered by valve-like flap
directs blood from right to left atrium

Ductus arteriosus:
short vessel
connects pulmonary and aortic trunks

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