Ch 20 Flashcards
what is the difference between arteries, veins and capillaries
Arteries: carry blood away from heart
Veins: carry blood back to heart
Capillaries: connect smallest arteries to smallest veins
what are the three layers of the walls of arteries and veins
tunica interna,
tunica media,
tunica externa
describe the tunica interna
lines the blood vessel and is exposed to blood
Endothelium: simple squamous epithelium overlying basement membrane and sparse layer of loose connective tissue
- Acts as a selectively permeable barrier
- Secretes chemicals that stimulate dilation or constriction of the vessel
describe the tunica media
middle layer
consists of smooth muscle, collagen, and elastic tissue
strengthens vessels and prevents blood pressure from ruptureing them
regulated diameter of blood vessel
tunica externa (tunica adventitia)
what is the vasa vansorum
outermost layer
consists of loose connective tissue that often merges with that of neighboring blood vessles, nervous or other organs
anchors the vessel and provides passage for small nerves and lymphatic vessels
vasa vansorum: small vessles that supply blood to outer part of large vessels
what are arteries called
resistance vessels because of their strong resilient tissue structure
how are arteries classified and what are the different arteries
they are classified by size and consist of
- conducting arteries (elastic or large)
- distributing artereies (muscular or medium)
- resistance arteries (small)
- metaerterioles
what do conducting (elastic or large) arteries do
Biggest arteries
Aorta, common carotid, subclavian, pulmonary trunk, and common iliac arteries
Have a layer of elastic tissue, internal elastic lamina, at the border between interna and media
External elastic lamina at the border between media and externa
Expand during systole, recoil during diastole
Expansion takes pressure off smaller downstream vessels
Recoil maintains pressure during relaxation and keeps blood flowing
what are distributing arteries (muscular or medium)
Distributes blood to specific organs
Brachial, femoral, renal, and splenic arteries
Smooth muscle layers constitute three-fourths of wall thickness
Resistance (small) arteries
Arterioles: smallest arteries
Control amount of blood to various organs
Thicker tunica media in proportion to their lumen than large arteries and very little tunica externa
what are metarterioles
In some places, short vessels that link arterioles to capillaries
Muscle cells form a precapillary sphincter around entrance to capillary
Constriction of these sphincters reduces blood flow through their capillaries
Diverts blood to other tissues
what is an aneurysm
weak point in artery or heart wall
Forms a thin-walled, bulging sac that pulsates with each heartbeat and may rupture at any time
Dissecting aneurysm: blood accumulates between tunics of artery and separates them, usually because of degeneration of the tunica media
Most common sites: abdominal aorta, renal arteries, and arterial circle at base of brain
Can cause pain by putting pressure on other structures
Can rupture causing hemorrhage
what can cause an anuerysm
Result from congenital weakness of blood vessels, trauma, or bacterial infections
Most common cause is atherosclerosis and hypertension
what are capillaries
what are they composed of
what are they absent in
exchange vessels: site where gases, nutrients, wastes, and hormones pass between the blood and tissue fluid
The “business end” of the cardiovascular system
Composed of endothelium and basal lamina
Absent or scarce in tendons, ligaments, epithelia, cornea, and lens of the eye
what are the three capillary types and how do you distinguish between them
Three capillary types distinguished by ease with which substances pass through their walls (permeability):
continuous capillaries,
fenestrated capillaries,
sinusoids
Describe continuous capillaries
occur in most tissues
Endothelial cells have tight junctions forming a continuous tube with intercellular clefts
Allow passage of solutes such as glucose
Pericytes wrap around the capillaries and contain the same contractile protein as muscle
Contract and regulate blood flow
describe fenestrated capillaries
kidneys, small intestine
Organs that require rapid absorption or filtration
Endothelial cells riddled with holes called filtration pores (fenestrations)
Spanned by very thin glycoprotein layer
Allow passage of only small molecules
describe sinusoids
discontinuous capillaries:
liver, bone marrow, spleen
Irregular blood-filled spaces with large fenestrations
Allow proteins (albumin), clotting factors, and new blood cells to enter the circulation
describe capillary beds
are networks of 10-100 capillaries
Usually supplied by a single arteriole or metarteriole
At distal end, capillaries transition to venules
describe veins
Greater capacity for blood containment than arteries
Thinner walls, flaccid, less muscular and elastic tissue
Collapse when empty, expand easily
Have steady blood flow
Merge to form larger veins
Subjected to relatively low blood pressure
what are the three (4) types of veins
postcapillary venules
medium veins
venous sinuses
large veins
describe post capillary venules
smallest veins
Even more porous than capillaries so also exchange fluid with surrounding tissues
Tunica interna with a few fibroblasts and no muscle fibers
Most leukocytes emigrate from the bloodstream through venule walls
describe medium veins
- what are the layers of it in proportion to eachother
- what disrupts part of this function
- what helps propel blood back to heart
-
—up to 10 mm in diameter
Thin tunica media and thick tunica externa
Tunica interna forms venous valves
Varicose veins result in part from the failure of these valves
Skeletal muscle pump propels venous blood back toward the heart
what are things that can create issues with veins
Hereditary weakness, obesity, and pregnancy also promote problems
