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.