Venule – What Do You Know About Venule?
A venule is a small blood vessel, which functions in the microcirculation. It helps in movement of the blood that is low in the oxygen content back to the veins (the larger blood vessels) from the capillary beds. Venule can be called as a ‘little vein’. It can also be said that it carries deoxygenated blood back to the heart from the body. The blood in the veins and the venule appears darker due to the presence of the deoxygenated form of hemoglobin. This type of hemoglobin is called as deoxyhemoglobin. In simple terms it can be regarded as one of the several types of blood vessel (veins, arteries and capillaries).
It consists of an endothelial tube. This tube is found enclosed in a variable amount of elastic and collagenous tissue. It has some connective tissue in its wall, unlike capillary. Several venules unite together forming a vein. The walls have three layers –
- An inner endothelium: It is composed of squamous endothelial cells. These cells act as a membrane.
- A middle layer: This layer is made up of elastic tissue and muscle. Since the middle layer is developed poorly, so it makes the walls of the venules thinner than the arterioles.
High endothelial venules are also present which share much similarities with the regular venules. The high endothelial venules are a special type of venule. The endothelium present in these is composed of simple cuboidal cells. These cells allow the re-entrance of the Lymphocytes into the bloodstream. Anastomosis (a network of streams, where they branch out and reconnect) of capillaries is possible along with the involvement of the beta form of semi-red blood cells and the white blood cells.