CASE 3 Flashcards
Blood vessels
three major types
- arteries
- capillaries
- veins
Arterioles
smallest branch of arteries, which feed into the capillary beds of body organs and tissues
venules
blood drains from the capillaries into the venules, smallest veins
wall has three layers (tunics)
- tunica intima
- tunica media
- tunica externa
the vessel lumen
central blood-containing space
tunica intima
- closest to lumen
- contains endothelium
- minimizes friction as blood moves through the lumen
tunica media
- middle tunic
- mostly smooth muscle and sheets of elastin
- can cause vasoconstriction of vasodilation, maintain blood pressure and circulation
tunica externa
- loosely woven collagen fibers, protect and strengthen and anchor it to surrounding structures
- contains nerve fibers, lymphatic vessels (and elastic fibers in bigger vessels)
vasa vasorum
- tunica externa of bigger vessels contain the vasa vasorum
- system of tiny blood vessels
- nourish the tunica externa
Three types of arteries
- Elastic arteries
- Muscular arteries
- Arterioles
Elastic arteries
- thick-walled near the heart
- also called conducting arteries
- inactive in vasoconstriction
- expand and recoil as the heart ejects blood
- blood flows continuously
muscular arteries
- elastic arteries turn into muscular arteries
- deliver blood to specific organs, also called distributing arteries
- thickest tunica media
- active in vasoconstriction and less capable of stretching
arterioles
- very small ones contain one layer of smooth muscle cells
- constrict: tissues served are largely bypassed
- dilate: blood flow into the local capillaries increases dramatically
Three types of capillaries
- continuous capillaries
- fenestrated capillaries
- sinusoid capillaries
Capillaries
- smallest blood vessels
- thin layer of tunica intima
pericytes
- smooth muscle- like cells that stabilize the capillary wall and help control capillary permeability
continuous capillaries
- abundant in skin and muscle
- their endothelial cells are joined by tight junctions
- gaps of unjoined membrane: intercellular clefts, allow limited passage of fluids and small solutes
fenestrated capillaries
- endothelial cells are riddles with oval pores, fenestrations
- more permeable to fluids and small solutes
- they are found wherever active capillary absorption on filtration occurs
sinusoid capillaries
- most leaky capillaries
- found in liver, bone marrow, spleen and adrenal medulla
- fewer tight junctions, larger intercellular clefts
- allow blood cells to go out of the membrane
capillary beds
capillaries work in networks called capillary beds.
- consist of two types of vessels
1. vascular shunt
2. true capillaries
microcirculation
flow of blood from arteriole to venule, through capillary beds
vascular shunt
directly connects arteriole and venule at opposite ends of the bed
a. metarteriole: from terminal arteriole to middle of capillary bed
b. thoroughfare channel: from the middle of the capillary bed to the postcapillary venule
true capillaries
- exchange vessels
- branch of the metarteriole and return to the thoroughfare channel.
- precapillary sphincter, a cuff of smooth muscle fibers, acts as a valve to regulate blood flow into the capillary
Venous system
- carry blood from capillary beds to heart
- diameter increases and walls thicken along the way