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Flashcards in Vascular Histology Deck (44)
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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)