Vascular Histology Flashcards
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?
Continuous capillary
Fenestrated capillary
Discontinuous capillary
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)
Where are discontinuous capillaries found?
How does exchange occur?
where exchange of marcomolecules & cells must occur openly (bone marrow, liver, spleen)
open exchange occurs b/c larger openings among endothelial cells (leaky & non-selective)
Describe flow of blood into & out of capillary bed
metarterioles branch off supplying arteriole & send blood into true capillaries
gas exchange occurs in true capillaries
blood leaves thru thoroughfare channel (distal end of metarteriole lacking smooth m)
blood continues to flow into postcapillary venule
How do capillaries differ from metarterioles?
capillaries do NOT have smooth m
How is blood flow thru capillary beds regulated?
via sphincters of smooth m @ arterial end (on metarterioles)
occurs differentially based on metabolic demand (sphincters shunt blood flow to different areas)
How do veins differ from arteries?
veins have thinner walls & lumen is larger which often collapses
Defining features of venules
post-capillary venules do NOT have tunica media
muscular venules have some smooth m in tunica media & thin tunic adventitia
Defining features of small veins
have all 3 layers of tunics
tunica media is 2-3 layers & thicker tunica adventitia (endothelium is continuous w/ 2-3 layers of smooth m)
Defining features of medium veins
thicker tunica media & adventitia, some elastic fibers
contain valves, travel w/ muscular arteries
Defining features of large veins
tunica adventitia is thickest layer of vessel wall (blends w/ thin tunica media)
has collagen, elastic fibers & fibroblasts
longitudinal smooth m cells
Role of lymphatic vessels
circulate lymph thru most parts of body in 1 direction & return it to venous supply
collects fluid that leaks out @ capillary bed due to pressure gradient & returns to blood volume
can clean fluid to prevent infection
Defining features of lymphatic capillaries
close-ended tubes found among capillary beds w/ overlapping endothelial cells (1 way valves)
incomplete basal lamina to increase permeability
How are endothelial cells of lymphatic capillaries connected?
openings held in place by ANCHORING FILAMENTS (so can collect as much fluid as possible)
Defining features of lymphatic vessels
have all vascular tunics & possess valves for 1 way flow
walls increase in thickness & cells connected via tight junctions
What are afferent & efferent lymphatic vessels?
afferent lead into lymph node & efferent exit lymph node
Describe flow of lymph
lymphatic capillaries lymphatic vessels lymphatic trunks R lymphatic duct Thoracic duct Brachiocephalic v
