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Vascular System
Dr. Samar AskerDr. Samar Asker
ArteriesLarge Arteries: aorta
caries blood from the heart.
Medium-sized arteries: cary blood to organs
Small Arteries (arterioles):regulate blood flow to capillaries.
General Structure of Blood Vessels
T.Intima
T.Media
T.Adventitia
Large arteriesAorta
Tunica intima 10%
simple squamous epithelium
Subendothelial C.T. rich in elastic fiber.
Undifferentiated Internal elastic lamina.
Tunica Media70%:
Fenestrated elastic membrane (40-70 layer)
Smooth muscle in()
Collagen fibers.
Tunica adventitia 20%:
Loose CT rich in elastic fibers.
Contain vasa vasora which is a small blood vessels that supply the outer part of T. media & T. adventitia
10%
70%
20%
Medium sized artery Medium sized vein
Wall
Lumen
Flow of Blood
Thick wall.
Narrow lumen. Not contain blood after death.No valve in the lumen.
It has a rapid flow of arterial blood.
Thin wall.
Wide lumen usually contains blood after death.
Valve present.
It has a slow flow of venous blood.
Medium sized artery Medium sized vein
T. Intima
Thick.
Folded due to internal elastic lamina.
Thin.
Not Folded.
Medium sized artery Medium sized vein
T. Media
Adventitia
Thick.Some elastic membrane.External elastic lamina may be present
Thin and contain elastic fibers.
Thin.Formed of few smooth
muscle fibers.No external elastic lamina.
ThickerNo elastic fibers
Larry M. Frolich, Ph.D.,Human Anatomy
Peripheral circulationArterioles give plexus of
capillaries to supply tissues
The Blood capillaries
Narrow vessels formed by rolling of an endothelial cell Length: 0.25- 1mmDiameter: 8 μm.
1 layer of endothelial cells Resting on basement membraneWhich split to enclose pericytes
Types of capillaries
Continuous capillaries:Continuous endothelium
(no pores)
Continuous basement membrane
Sites: C. T., bone, brain , skin
and exocrine glands.
Fenestrated or visceral:Endothelium has pores closed by membrane or diaphragms except renal capillariesSite:
Intestine Endocrine glands. Glomerular capillary of kidney,
Sinusoidal capillaries:Dilated irregular capillaries,
(5-40) m.Fenestrated endothelium have
pores without diaphragms.
The basement membrane either non continuous or absent.
Macrophages extend pseudo-podia inside () the endothelial cells to engulf any foreign body.
Sites :In bone marrow:-
Carry blood cells, to the circulation.
In spleen:
Carry stored blood cells
to circulation & filter the
blood.
liver: carry
plasma proteins to
bloodIn endocrine
glands: carry hormones to blood.