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Human histology - Textbook (Seventh edition): Part 2

(BQ) Continued part 1, part 2 of the document Human histology - Textbook (Seventh edition) has contents: Nervous system, skin and its appendages, the cardiovascular system, the respiratory system, hepatobiliary system and pancreas, the urinary system,. and other contents. Invite you to refer. | Chapter The Cardiovascular System e cardiovascular system consists of the heart and blood vessels. e blood vessels that take blood from the heart to various tissues are called arteries. e smallest arteries are called arterioles. Arterioles open into a network of capillaries that pervade the tissues. Exchanges of various substances between the blood and the tissues take place through the walls of capillaries. In some situations capillaries are replaced by slightly di erent vessels called sinusoids. Blood from capillaries or from sinusoids is collected by small venules that join to form veins. e veins return blood to the heart. Blood vessels deliver nutrients oxygen and hormones to the cells of the body and remove metabolic base products and carbon dioxide from them. ENDOTHELIUM e inner surfaces of the heart and of all blood vessels are lined by attened endothelial cells also called endotheliocytes . On surface view the cells are polygonal and elongated along the length of the vessel. Cytoplasm is sparse. e cytoplasm contains endoplasmic reticulum and mitochondria. Micro laments and intermediate laments are also present and these provide mechanical support to the cell. Many endothelial cells show invaginations of cell membrane on both internal and external surfaces . Sometimes the inner and outer invaginations meet to form channels passing right across the cell seen typically in small arterioles . ese features are seen in situations where vessels are highly permeable. Adjoining endothelial cells are linked by tight junctions and also by gap junctions. Externally they are supported by a basal lamina. Functions of Endothelium Apart from providing a smooth internal lining to blood vessels and to the heart endothelial cells perform a number of other functions as follows Endothelial cells are sensitive to alterations in blood pressure blood ow and in oxygen tension in blood. ey secrete various substances that can produce vasodilation by in uencing the tone of muscle in .