Blood Vascular System Originally given by: Dr.Ahmed Altayeb Written by: Nightmare Made up 2 date + edited: Abo Malek Thankx for: Dr. Abdullah

Blood Vascular System The blood vascular system is lined by simple squamous epithelium called endothelium  Consists of tow parts: 1. The arterial system 2. The venous system In general, an artery has a thicker wall & a smaller lumen than the vein of similar size

Structure of blood vessels  Depending on the type of blood vessel the wall may consist of 3 layers called tunics:- 1.Tunica intima (innermost layer) 2.Tunica media (middle layer) 3.Tunica adventitia (outermost layer)

Tunica intima (innermost layer)  Consists of: Endothelium (simple squamous) Basal lamina. Subendothelial CT. May contain fenestrated internal elastic lamina. (separating T. intima from T. media.

Tunica media (middle layer)  Contains smooth muscles, elastic fibers, & collagen fibers.  May contain external elastic lamina. (depending on the type of blood vessel)  In large blood vessels the Tunica media has small vessels called vasa vasorum.

Tunica adventitia  Contains: Fibroelastic CT. In large blood vessels T. adventitia contains vasa vasorum.

1.The arterial system  Comprises the following vessels: Elastic arteries. Muscular arteries. Arterioles. Capillaries.

Elastic arteries  Example aorta & pulmonary trunk.  T. intima has internal elastic lamina.  T. media has fenestrated elastic membrane & few smooth muscle cells.  T. adventitia has loose CT & vasa vasorum.

endothelium

Muscular arteries  T. intima has prominent internal elastic lamina.  T. media contains more than 3 circular layers of smooth muscle & up to 40 layers in a large muscluar artery.  External elastic lamina is present only in large muscular arteries & absent in small arteries.  T. adventitia contains vasa vasorum

Arterioles  Arise from muscular arteries.  Internal elastic lamina present in large arterioles & absent in small arterioles.  T. media has 1-2 smooth muscle layers.  T. adventitia is thin.

Blood capillaries  Smallest blood vessels (diameter 10 um)  Arise from arterioles.  Tubes of endothelium (simple squamous epithelium) with basal lamina cell called pericytes.

Pericytes  Form gap junction with endothelial cells.  Contractile.  May differentiate into endothelial cells & smooth muscle cells.

Type of capillaries  Three types: 1. Continuous capillaries. 2. Fenestrated capillaries. 3. Sinusoidal capillaries.

continuous capillaries.  The endothelial cells are continuous without holes  Have tight junction.  Have continuous basal lamina.  Found in CNS, muscle, & CT.

Fenestrated capillaries  The endothelial cells have small openings called fenesrae (fenestrated endothelium)  Found in endocrine glands & intestine.  The basal lamina is continuous.

Sinusoidal capillaries  Larger than other types of capillaries (40 um)  Large fenestrate  Discontinuous basal lamina.  Found in liver & lymphoid organs.

The venous system  Comprise from the following vessels: Postcapillary venules. Small veins. Medium veins. Large veins

Postcapillary venules  Receive blood from the capillaries.  Tube of endothelium similar to capillaries but larger (20 um)

Small veins  Larger than venules.  Endothelium surrounded by a single layer of smooth muscles.

Medium veins  T. intima forms valves in the lumen.  No internal elastic lamina.  T. media has smooth muscle & collagen.  T. adventitia is very thick & contains few smooth muscle cells.

Large veins  Example are the vena cava & pulmonary veins.  T. intima has thick subendothelial CT.  T. media has few smooth muscle cells.  T. adventitia of the vena cava contains longitudinally arranged smooth muscles