Capillary

Capillaries ( capillaries ) are the smallest blood vessels in animals and humans. A distinction blood, lymph and air capillaries.

Blood capillaries

Blood capillaries are about 0.5 mm long and have a diameter of 5 to 10 microns. They form a fine network ( capillary, capillary rete ) in most organs and tissues of the body, which is fed by arterioles and venules drained via. The capillary density is different in the various tissues and corresponds approximately to the average metabolic activity. Only the cornea, the eye lens, horn structure, hyaline cartilage and epithelia are kapillarfrei. About the capillaries there is a continuing exchange of material. Nutrients are supplied to the tissue and the waste removed again. Capillaries are not visible with the naked eye. They were first discovered in 1661 by the Italian anatomist Marcello Malpighi in the frog lung.

The thin capillary walls are semi- permeable ( semipermeable ) and consist of a layer of endothelial cells, which sit a basal lamina, in the mostly pericytes are turned on. There are three building types of capillaries:

• Continuous capillaries have a closed endothelial layer and therefore allow only the passage of very small molecules.
• Fenestrated capillaries ( fenestrated capillaries) have been able to pass between the endothelial cells of small, 60-80 nm large pores through which smaller proteins. Fenestrated capillaries are found in endocrine glands, intestines, pancreas and kidney. In the glomeruli, the pores are the greatest.
• Sinusoids are dilated capillaries, which are also fenestrated and also comprise a fenestrated basal lamina. The pores of the sinusoids are about 30-40 microns in size and permit the passage of larger proteins and blood cells. Sinusoids are found in liver ( liver sinusoids → ), spleen, bone marrow, lymph nodes and adrenal medulla.

Lymph

Lymphatic capillaries are the initial portion of the lymphatic system of humans and many vertebrates. You start blindly and are embedded with Ankerfilamenten between the cells of the tissue. Lymphatic capillaries consist of a single layer of flat cells (endothelium ) that are connected to each other, but have gaps regarding the influence of the tissue fluid. These endothelial cells overlap with oak leaf -like protuberances. These are stitched with a cementing substance to each other, in between these large gaps arise. This can be added to the lymph even including cells such as bacteria or immune cells (leukocytes), foreign bodies, large molecular weight proteins such as albumin, antibodies, or fibrin. Its lumen (tube diameter) is therefore significantly greater than the blood capillaries (3-5 microns) with 30-50 microns. The lymphatic system is, for example, carry away debris and blood components for injuries in the situation. The lymph capillaries merge into larger lymph vessels, which supply the lymph fluid to lymph nodes. If lymph in the lymphatic system via the lymphatic capillaries, a, it is called lymph.

Air capillaries

Air capillaries ( Pneumocapillares ) are the air exchange tissue of the avian lung. They usually form a network of interacting tubes and surrounded by dense Blutkapillarnetzen. In contrast to the alveoli of mammals is not a blind -ending system, but an open tube system.