Flashcards in Vascular Histology Deck (44)
What are the 3 layers found in arteries and veins?
Tunica intima (inner most)
Tunica media (middle)
Tunica adventitia (outer most)
How are arteries and veins different?
arteries branch to decrease in diameter
veins merge to increase in diameter
Describe the layers of tunica intima
endothelium (simple squamous epithelial cells)
basal lamina (collagen, proteoglycans, glycoproteins)
subendothelial layer (loose CT) w/ internal elastic membrane
What is the internal elastic membrane?
found in the subendothelial layer of the tunica intima in ARTERIES & ARTERIOLES
fenestrated elastic material (many elastic fibers to add recoil properties to vessels)
How is the tunica intima different in veins from arteries?
tunica intima in veins contains valves
Describe the tunica media
part of layers that can contract to close off lumen
arranged layers of smooth muscle
extends from internal elastic membrane to external elastic membrane
What separates the tunica media & tunica adventitia?
layer of elastin
What is the tunica media composed of?
smooth m & varying amounts of elastin, reticular fibers & proteoglycans
Describe the tunica adventitia
longitudinal collagenous tissue w/ few elastic fibers
merges w/ loose CT surrounding the vessels (assoc w/ neurovasc bundles)
How is the tunica adventitia different in arteries & veins?
thin in arteries & thick in veins
How do the tunics receive blood & nervous innervation?
vasa vasorum & Nervi vasorum
What is the vasa vasorum?
vessels of the tunica adventitia that supply blood to vascular tunics (found in large arteries & veins)
What is the nervi vasorum?
ANS input that controls contraction of vascular smooth m (control of vascular tone)
Defining features of large arteries
lots of elastic fibers forming concentric sheets between muscle cell layers
NO fibroblasts (smooth m makes collagen, elastin & ECM)
Why do large arteries have lots of elastin?
strong pressure of blood pulsating during systole will expand arterial wall
large lumen size reduces pressure & allows strong blood flow to continue during diastole
What makes large arteries distinct on an image?
concentric sheets of elastin w/ in smooth m
tunica media makes up majority of wall
Defining features of medium (muscular) arteries
prominent internal elastic membrane (that lines the lumen) & external elastic membrane
smooth m cells arranged in SPIRAL fashion
thicker tunica adventitia
Defining features of small arteries
have up to 8 layers of smooth m & internal elastic membrane
Defining features of arterioles
only 1-2 layers of smooth m & internal elastic membrane is more variable
What is the role of arterioles?
flow regulators for capillary beds
where sympathetics act on tunica media to cause vasoconstriction & where parasympathetics act on tunica media to cause vasodilation
Defining features of capillaries
smallest blood vessels that form capillary beds
vessels surrounded by Pericytes
single layer of endothelial cells
What is the role of capillaries?
site of metabolic exchange
What are Pericytes?
perivascular contractile cells w/ branching cytoplasmic processes surrounding capillaries
controlled by NO from endothelial cells & promote stability of capillaries & post-cap venules
Where are endothelial cells found & what is their role?
single layer of cells forming innermost aspect of tunica intima
support basement membrane & produce collagen
involved in blood coagulation, thrombosis, local dilation & constriction
How do endothelial cells communicate?
via cell-cell junctions (# of junctions alter permeability)
connection between endothelial cells defines capillary bed function
What are the 3 types of capillaries?
Defining features of continuous capillaries
tight, occluding junctions to seal of intercellular clefts
continuous basement membrane & cells meet end-to-end
Where are continuous capillaries found?
How does exchange occur in these capillaries?
throughout body in muscle, brain, peripheral nerves, exocrine glands
all molecular exchange must occur via diffusion or transcytosis
Where are fenestrated capillaries found?
How does exchange occur?
organs where molecular exchange w/ blood is important (endocrine glands, kidney, gallbladder)
tight junctions w/ openings that allows greater exchange across endothelium (limited by size of molecule)