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Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]
Most famous parts of the brain highlighted in different colours. The human brain anatomical regions are ordered following standard neuroanatomy hierarchies. Functional, connective, and developmental regions are listed in parentheses where appropriate.
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for special senses such as vision, hearing and olfaction.
Major gyri and sulci on the lateral surface of the cortex Lobes of the brain. The cerebrum is the largest part of the brain and is divided into nearly symmetrical left and right hemispheres by a deep groove, the longitudinal fissure. [17] Asymmetry between the lobes is noted as a petalia. [18]
Diagram of different sized veins with differing component proportions. The three layers of the vein wall are the outer tunica externa, the middle tunica media and the inner tunica intima. There are also numerous valves present in many of the veins. The outer tunica externa, also known as the tunica adventitia is a sheath of thick connective ...
They are part of the circle of Willis, which provides backup circulation to the brain. In case one of the supply arteries is occluded, the circle of Willis provides interconnections between the anterior and the posterior cerebral circulation along the floor of the cerebral vault, providing blood to tissues that would otherwise become ischemic .
Most vessels of the microcirculation are lined by flattened cells of the endothelium and many of them are surrounded by contractile cells called pericytes.The endothelium provides a smooth surface for the flow of blood and regulates the movement of water and dissolved materials in the interstitial plasma between the blood and the tissues.
As the brain develops, by the fourth week of embryological development three swellings known as brain vesicles have formed within the embryo around the canal, near where the head will develop. The three primary brain vesicles represent different components of the central nervous system: the prosencephalon, mesencephalon and rhombencephalon ...