Structure and function of blood vessels

What are the 3 basic layers of different blood vessels?

• Tunica interna (intima)

• Tunica media

• Tunica externa (adventitia)

What are the 3 main tissue layers that make up the wall of a blood vessle?

• Epithelial inner lining

• middle layer of smooth muscle

• Connective tissue outer covering

Components of Tunica Interna

• Endothelium lining lumen

• Basement membrane

• Internal elastic lamina

How is the structure of the tunica media linked to its function?

Smooth muscle and connective tissue allows for vasoconstriction/dilation = regulation of peripheral blood pressure

Structure of tunica externa

Elastic and collagen fibres containing numerous blood vessels and nerves to supply vessel tissue

Vasa vasorium

The small vessels that supply blood to vessel tissues

What is compliance?

Ability of the walls of the blood vessels to stetch/ expand easily without tearing in response to small increases in pressure.

What are the two different kinds of arteries?

• Elastic

• Muscular

What characterises elastic arteries?

• Well defined internal and external elastic lamina

• thick tunica media

Which arteries in the body are elastic arteries?

• Aorta and pulmonary trunk

• and the main branches of the aorta (brachiocephalic, subclavian, common carotid, common iliac)

Function of elastic arteries?

CONDUCTING ARTERIES

Act as a pressure reservoir = store mechanical energy

• recoil converts stored kinetic energy into the blood, pushing it onward whilst ventricles are relaxing

Characteristics of muscular arteries?

• Much thicker muscular tunica media

• Well defined internal elastic lamina

• Tunica externa < tunica media = permitting change in diameter but bot elastic recoil

What is the main function of muscular arteries?

Vasoconstriction/ Vasodilation

DISTRIBUTING ARTERIES

Example of muscular arteries?

• brachial artery

• radial artery

What is the advantage of anastomoses?

They provide collateral supply of circulation - alternative routes for blood flow to maintain circulation and prevent necrosis.

What is the structure of an arteriole?

• Thin tunica intima (with fenestrated internal elastic lamina)

• 2 layers of smooth muscle

What is a metarteriole?

Terminal end of arteriole - forming the metarteriole-capillary junction

Precapillary sphincter

The sphincter at the metarteriole-capillary junction

• monitors blood flow into the capillary

What is resistance?

The opposing force of blood flow due to friction between blood vessel walls and blood

What effect does decreasing the diameter of blood vessels have on resistance?

It causes an increase in resistance

How is the structure of capillaries suited to their function?

• Capillaries lack tunica media and externa - only have endothelial cells and basement membrane = one cell thick for exchange

• Extensive branching = large SA for exchange

• Small lumen = only one cell can pass through at once

Kinds of capillaries?

• Continuous

• Fenestrated

• Sinusoids

Rank capillaries in terms of leakiness

Continuous<fenestrated<sinusoids

What is the name of venules immediately following capillaires?

Post capillary venules

What is the structure of muscular venules?

• 1-2 layers of circularly arranged smooth muscle

• Endothelium and basement membrane

• sparse tunica externa

Structure of vein

• Endothelium and basement membrane BUT no internal elastic lamina

• contains valves and much larger lumen

• Much thinner tunica media than arteries

• tunica externa = thickest of 3 layers

Where is the majority of blood volume at rest?

64% is in systemic veins/ venules

• functions as blood reserve/ reservoirs