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M2M Unit IV HM > Blood Vessels > Flashcards

Flashcards in Blood Vessels Deck (20):

Tunica intima

inner layer of vessel. layer of endothelial cells in intimate contact with blood + layer of & loose collagenous tissues containing intimal cells (in larger vessels)


Tunica media

Layer in middle of vessel (composed of collagen, elastic laminae, or smooth muscle)


Tunica adventitia

Outer supporting layer
Collagenous tissue.
Anchors blood vessel to nearby organs etc.
In larger vessels adventitia has blood vessels (vasa vasorum)


Vasa vasorum

Vessels of vessels.
Give O2 and nutrients to adventitia & outer parts of the tunica media



Has tunica adventitia outermost, inside this is tunica media (with elastic fibers and smooth muscle) and inside this is tunica intima (enothelial cells touching blood).
Large arteries: THICK media (lots of elastic layers)... these elastic layers decrease in # farther from heart.

Smooth muscle is in media all the way through arterioles. Imp. for bp/blood flow to capillaries.


What controls blood pressure?

The smooth muscle is arteries and arterioles! They permit expansion of vessels after contraction of heart.


Elastic arteries

Aorta and large arteries.
Intima has thin layer of endothelial cells PLUS underlying layer of collagen/elastic fibers (that has fibroblasts and myointimal cells.... similar to smooth muscle).

Tunica media: has multiple elastic layers! some collagenous fibers/smooth muscle cells sandwiched in between
Tunica adventitia: has vasa vasorum


Muscular arteries

Tunica intima: thin, endothelial + thin layer of connective tissue

Only 2 well-defined elastic layers (inner elastic lamina b/w intima and media and outer elastic lamina that defines boundary between media and adventitia)... vs. elastic arteries w/ many elastic layers

Tunica media: primarily composed of smooth muscle

Adventitia: comparatively thick, has collagen and elastin.


Small muscular arteries

Intima: endothelial cells + thin layer of collagenous

Have inner elastic lamina (but no outer) unlike muscular

Media: relatively LARGE amt. of smooth muscle (control vessel diameter)

Adventitia: same width as the media, usually merges with surrounding connective tissue



Intima: small layer of endothelial cells on thin basement membrane
Then 1-2 layers of smooth muscle cells
Outer collagenous tissue (blends with surrounding CT)

Gatekeepers to local capillary beds, can greatly restrict flow of blood


Meta-arterioles and arteriole-venule shunts

Connect larger arterioles and venules. Their vasoconstriction/dilation can direct blood through or permit bypass of capillary beds.



1-2 endothelial cells around lumen
NO muscle. Instead endothelial are surrounded by pericytes (unspecialized cells that give rise to smooth muscle in vessel growth/wound healing. Could be contractile).
Surrounded by collagen fibrils that connect capillary to adjacent CT.

This is where exchange happens!


2 main types of capillaries

Continuous: endothelial cells form uninterrupted lining, transfer across lining via pinocytosis

Fenestrated : pores/fenestrations in endothelial cells (may be covered by thin diaphragm), example is kidney glomerulus. Allow bulk flow of plasma past endothelial boundary.

(also discontinuous): wide pores that permit RBCs to pass.


Post-capillary venules

Capillaries empty into these. Similar structure, but larger diameter.
Slow flow. Leukocytes will diapedese through here.

Endothelium responds to vasoregulators (serotonin and histamine), so this area is sensitive to controlled permeability.

larger venules start to get 1-2 layers of smooth muscle in media (muscular venules) with thin layers of adventitia merging with CT.



more thin-walled than arteries. seen as collapsed. Bp is low.

Small veins: intimal layer endothelia, NO inner elastic lamina, media is smooth muscle, adventitia is collagenous and blends with surrounding CT

Medium veins: similar endothelial, muscle layers, with increasing thickness of adventitia (thickest layer)

Large veins: thin intima endothelial layer, media of inter-layered smooth muscle/collagen (5-7 layers), and SMALL amts of elastin, adventitia is thick and has vasa vasorum


How does circulation in veins occur?

Hydrostatic pressure, aided by smooth m. contraction. Compression of surrounding skeletal m.
Often have one-way flap valves to prevent back-flow.



Flow only one way, from tissues to empty into blood near IJ and SVC
Begin as nothing more than small spaces in CT, connect to larger spaces lined by very thin layer of squamos endothelium

Size of small veins they have single, thin endothelial layer

Can see lymphocytes, but RBCs absent. Inside will stain (unlike plasma)

larger lymphatics: loosely-defined CT structure outside the endothelium. Lots of flap valves.


Vascular patterns

Anastomoses: connections b/w arteries and veins
End arteries: supply section of tissue w/o alternate arterial blood flow
Portal systems: begin and end in capillary bed (hepatic portal)
Pampiniform plexus: concurrent arrangement b/w arteries and veins (heat exchange. spermatic cord).


Elastic layers are...

Present in arteries/arterioles, absent in capillaries and veins (although large veins have slight elasticity)


Smooth muscle is...

Seen in all except capillaries and smaller venules (they have pericytes, that are contractile, blood flow)