TYPES AND EXAMPLES OF CAPILLARIES

             CAPILLARY:(hair like)

It has two meanings:

1-pertaining to hair or resembling a hair.

2-any one of minute vessels that connect the arterioles and venules, forming a network in nearly all parts of the body.

Walls of capillaries:

The walls of the capillary act as semipermeable membranes for interchange of fluids, gases, nutrients, hormones, vitamins, minerals antibodies, etc., between the blood and tissue fluids. Their diameter varies from 7-9 m.

Types of capillaries;

a) Continuous capillaries:

 In these capillaries, no pores are seen. They are present at following sites:

*Skin.

*Connective tissue

*Skeletal and smooth muscle.

* Lungs.

*Brain.

b) Fenestrated capillaries:

These are those capillaries, the lining endothelial cells of which show characteristic pore system. They are seen at following sites:

*Renal glomeruli.

* Intestinal villi.

* Endocrine glands.

*Pancreas

Sinusoids of sinusoidal capillaries :

These are dilated capillaries and are lined by reticulo-endothelial cells.

Examples:

*Liver

*Spleen

* Parathyroid glands.

*Hypophysis cerebri.

*Carotid and Coccygeal bodies.

*Pancreas (Endocrine portion).

*Haemolymph nodes.

The sinusoids differ from capillaries in four respects :

>The lining is incomplete, irregular, and is formed by endothelial cells and reticuloendothelial cell

 >They are only surrounded by a fine network of reticulin fibres, and are often collapsed when they are empty of blood.

>The sinusoids connect the vessels of same type, i.e., venous vessels whereas a capillary is always a connecting link between arterial and venous vessel

>The sinusoids have a wider lumen (20 μm. or more

Some Interesting Examples of Capillaries~

•Erythrocytic capillaries: 

These are the capillaries of bone marrow of early life which seem to produce erythrocyte

•Meigs's capillaries: 

These are the capillaries of myocardium of the hear

• Secretory capillaries: 

These are extremely thin capillaries present between adjacent gland cell

•Arterial capillaries: 

These are minute capillaries, distal to the arterioles and carry oxygenated bloo

•Venous capillaries:

 These are minute capillaries proximal to venules which carry venous blood

•Lymphatic or lymph capillaries: These are the capillaries of lymphatic system. Their caliber is slightly greater than the capillaries of blood circulatory system

•Bile capillaries or cholangioles or Bile Canaliculi:

These are minute channels formed by apposition of cell membranes of hepatic cells and carry the bile.