Vascular Histology Flashcards
what are the three layers of a vessel
Trunca intima
Trunca media
Trunca adventitia
what are the three aspects of the Tunica intima
Endothelium: single layer of squamous epithelial cells
Basal lamina: thin extra cellular layer of collagen proteoglycans and glycoproteins
Subendotheliallayer: loose CT
-internal elastic membrane (sheet like layer fenestrated elastic material with in arteries and arterioles
Intima in veins contains valves
Characteristics of Tunica media
circumferentially arranged layers of smooth muscle
thick in arteries
external elastic membrane: layer of elastin that separates the tunica media and adventitia
varying elastin, reticular fibers, and proteoglycans
Characteristics of Tunica adventitia
Longitudinally arranged collagenous tissue with fewer elastin
merges with loose CT around vessels
thin in arterial system
thick in vein system
what two vessels are found in the tunica adventitia
Vasa vasorum: vessels that supply the tunica adventitia with blood
-found in large arteries and veins
Nervi vasorum: ANS input that controls contraction of vascular smooth muscle
Characteristics of large Arteries
has elastin that forms concentric sheets between the muscle cell layers
has no fibroblasts
strong pressure from systole will expand the arterial wall
lumen size reduces pressure and allows strong blood flow to continue during diastole
Characteristics of Medium arteries
More smooth muscle and less elastin than elastic arteries
has a prominent internal elastic membrane
a recognizable external elastic membrane
smooth muscle arranged in spiral fashion
relatively thick tunica adventitia
Characteristics of small arteries
have up to eight layers, will also have an internal elastic membrane
characteristics of arterioles
have 1-2 layers and internal elastic membrane may or may not be present
flow regulators for capillaries
sympathetic innervation to tunica media causes vasoconstriction
parasympathetic innervation to tunica media causes vasodilation
Characteristics of capillaries
smallest of all blood vessesl
- site of metabolic exchange
- diameter often smaller than an RBC
contain pericytes (perivascular contractile cells with branching cytoplasmic processes)
what is the function of the pericytes
promote stabillity of capillaries and postcapillary venules
controlled by NO via endothelial cells
Function of the endothelial cells of the vasculature
connected via cell to cell junctions to help alter permeabillity
support the basement membrane and prodce collagen
metabollically involoved in blood coagulation and thrombosis, local vasodilation and constriction
what are the three different capillaries
Continuous
Fenestrated
Discontinuous/sinusoidal
characteristics of Continuous capillaries
Most common
have tight occluding junctions sealing off the intercellular clefts
all molecular exchange must occur via diffusion or transcytosis
continuous basement membrane
located throughout the body (muscle, brain, peripheral nerves, exocrine glands)
characteristics of Fenestrated Capillaries
Located in organs where molecular exchange with the blood is important
have tight junctions, with fenestrations among the endothelial cells
allows greater exchange across the endothelium, but limited to size of macromolecule
continuous basement membrane
endocrine gland and sites of fluid/metabolite absorption (gallbladder, kidney)
characteristics of discontinuous/sinusodial capillaries
located where exchanges of macromolecules and cells (b/w tissue and blood) must openly occur
large fenestrations among endothelial cells
open exchange occurs and large cell movements allowed
partial discontinuous basal membrane
bone marrow, liver, spleen
what is the first branch off the arteriole to supply the capillary
Metarterioles
function of the precapillary sphincter
regulate blood through true capillaries
what is considered the true capillaries
branch from metarteriole that lack smooth muscle , may have pericytes
what is the thoroughfare channel
distal end of the metarteriole (lacks the smooth muscle )
will connect with the postcapillary venule
if precapillary sphincters are relaxed what is the status of the capillary bed? what about contracted
the capillary bed is well perfused for relaxed sphincftor
if they are contracted: the blood will shunt and move quickly through the thoroughfare channel
- prevents exchange within true capillaries
- forces blood to enter venous return more quickly
Diameter, charcteristics of Tunica intima, media, and adventitia for: Large artery
> 10mm
Intima: Endothelium, connective tissue, smooth muscle
media: smooth muscle, elastic lamellae
Adventitia: thinner than media, connective tissue and elastic fibers
Diameter, charcteristics of Tunica intima, media, and adventitia for: Medium artery
2-10mm
intima: Endothelium, connective tissue, smooth muscle, prominent internal elastic membrane
media: smooth muscle, collagen fibers, relatively little elastic tissues
adventitia: thinner than media, connective tissue, some elastic fibers
Diameter, charcteristics of Tunica intima, media, and adventitia for: small artery
- 1-2mm
intima: endothelium, connective tissue, smooth muscle, internal elastic membrane
media: smooth muscle (8 to 10 cell layers), collagen fibers
adventitia: thinner than media, connective tissue, some elastic fibers
