Question

After reviewing, the arteries and veins structure, discuss the function of each one of them, then debate with your fellow students the location, structure, and the function of each type of the blood capillaries.

Answer 1

Three layers of blood vessels are :-

From inner to outside

1) Tunica intima :- It is the innermost layer which is composed of single layer of epithelial cells. They line the lumen of the vessel.

2) Tunica media :-

It is the thicker layer made up of mostly smooth muscles and elastin tissues. They differ in different types of vessel.

3) Tunica adventitia :-

This layer is composed of fibrous tissue and is the outermost layer. This layer function to provide protection.

Arteries: They Have thick Tunica media and all three layers are well differentiated.

- Lumen is smaller compared to the wall thickness.

- They mostly carry oxygenated to periphery.

- Due to thick Tunica media, they regulate the blood pressure

Veins :- They Have thin Tunica media and all three layers are not well differentiated.

- Lumen is larger compared to the wall thickness.

- They mostly carry deoxygenated towards the heart.

- Due to larger lumen, they carry most of the blood at a given instant. Hence they are called capacitance vessels.

Types of Capillaries

There are three main types of capillaries:-

1) Continuous Capillaries :

- Endothelial cells linings are uninterrupted.

- This only allows small molecules like water and ions to diffuse through tight junctions. This leave gaps of unjoined membrane called intercellular clefts.

The basement membrane is also uninterrupted.

These are present at arteriovenous junction.

They are also present in the lungs

2) Fenestrated capillaries :-

- Fenestrated capillaries have pores in the endothelial cells (60-80 nanometers in diameter) that are spanned by a diaphragm of radially-oriented fibrils.

- They allow small molecules and limited amounts of protein to diffuse.

- They are present in the Bowmens capsule of the nephron.

3) Sinusoidal Capillaries :

- Sinusoidal capillaries are a special type of fenestrated capillaries that have larger openings (30–40 μm in diameter) in the endothelium.

- They have interrupted basement membrane.

- These types of blood vessels allow red and white blood cells (7.5μm–25μm diameter) and various serum proteins to pass using a process aided by a discontinuous basal lamina.

- Sinusoid blood vessels are primarily located in the bone marrow, lymph nodes, and adrenal gland.