Vascular Histology Flashcards
What are the 3 layers within the tunica intima?
endothelium = single layer of squamous epithelial cells
basal lamina = thin EC layer
subendothelial layer = loose areolar CT; interal elastic membrane
What makes up the tunica media?
How does it compare btw arteries and veins?
circumferentially arranged layers of smooth muscle; from internal elastic membrane to external elastic membrane; elastin reticular fibers, and proteoglycans
much thicker in arteries
What makes up the tunica adventitia?
How does it compare btw arteries and veins?
longitudinally arranged collagenous tissue w/ few elastic fibers; merges w/ loose CT surrounding vessels
thin in arteries; very thick in veins
What is the vasa vasorum?
vessels of tunica adventitia that supply blood to vascular walls themselves of large arteries and veins
What is the nervi vasorum?
ANS input that controls contraction of vascular smooth muscle
What distinguishes large arteries?
a ton of elastin in tunica media that forms lamellae btw muscle layers
No fibroblasts! (smooth muscle makes ECM)
What distinguishes medium arteries?
more smooth muscle and less elastin in tunica media than elastic arteries
*prominent internal elastic membrane seen and external elastic membrane is recognizable
tunica adventitia abt same thickness as tunica media
What distinguishes small arteries and arterioles?
number of smooth muscle layers
small = up to 8 layers w/ internal elastic membrane
arterioles = 1-2 layers, internal elastic mem may or may not be present
What is the site of metabolic exchange?
capillary beds
what are pericytes?
perivascular contractile cells in capillaries (instead of smooth muscle)
enclosed w/in BL continuous w/ endothelium
What controls perivascular contractile contraction?
Nitric Oxide
What controls the permeability of blood vessels?
number of cell-cell junctions btw endothelial cells in the tunica intima
What characterizes a continuous capillary?
complete basal lamina; a lot of junctions btw endothelial cells
no fenestrations
What characterizes a fenestrated capillary?
fenestrations w/in endothelial cells and in btw them –> allow things through
Basal lamina is still complete
What characterizes a discontinuous capillary?
discontinuous basal lamina
fenestrations in endocthelium
Where are fenestrated capillaries located?
endocrine glands and sites of fluid/metabolite absorption
Where are discontinuous capillaries located?
bone marrow, liver spleen
fenestrations are large enough to let an entire cell through!
What is a thoroughfare channel?
distal end of metarteriole
lacks smooth muscle
connects capillary to a postcapillary venule
What is a metarteriole?
first branch off of arteriole supplying tissues
What happens if precapillary sphincters contract?
bloodflow will shunt so it goes straight from metarteriole –> thoroughfare channel –> venule
skips capillary bed
What structures do capillaries lack?
tunica media and tunica adventitia
What distinguishes a small vein?
diameter less than 1 mm in diameter; continuous w/ muscular venules
all 3 tunics
media is 2-3 layers thick
What distinguishes a medium vein?
have a diameter of as much as 10 mm
these are most of named veins
What is the order into a small vein from a capillary?
postcapillary venule –> muscular venules –> small vein
What characterizes a postcapillary venule?
drain capillaries
no true tunica media
What characterizes a muscular venule?
1-2 layers smooth muscle in media
thin tunica adventitia
What characterizes medium veins?
always travel w/ muscular As
thicker tunica media and adventitia
valves
wall often folded
What is the thickest layer of a large vein?
tunica adventitia - contains longitudinal smooth muscle!
also has collagen, elastic fibers, and fibroblasts
How do you distinguish a large vein from a medium vein?
tunica adventitia on a large vein will be thicker and has longitudinal smooth muscles
What holds openings in lymphatic capillaries in place?
anchoring filaments btw endothelial cells
What characterizes lymphatic capillaries?
closed-ended tubes among capillary beds
one-way valves formed by endothelial cells overlapping
incomplete BL for more permeability
What characterizes lymphatic vessels?
have all vascular tunics and have valves
continuous tight jxns to prevent leakage
What is the order of lymph flow?
lymphatic capillaries –> lymphatic vessels –> trunks –> R lymphatic duct –> thoracic duct –> drain into brachiocephalic V.
