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Active transport is used to move most substances between the blood vessels and the osteocytes. [1] Haversian canals are contained within osteons, which are typically arranged along the long axis of the bone in parallel to the surface. The canals and the surrounding lamellae (8-15) form the functional unit, called a Haversian system, or osteon.
The nutrient canal (foramen) is directed away from the growing end of bone. The growing ends of bones in upper limb are upper end of humerus and lower ends of radius and ulna. In lower limb, the lower end of femur and upper end of tibia are the growing ends. [1] The nutrient arteries along with nutrient veins pass through this canal.
The nutrient artery (arteria nutricia, or central artery), usually accompanied by one or two nutrient veins, enters the bone through the nutrient foramen, runs obliquely through the cortex, sends branches upward and downward to the bone marrow, which ramify in the endosteum–the vascular membrane lining the medullary cavity–and give twigs to the adjoining canals.
The externa, alternatively known as the tunica adventitia, is composed of collagen fibers and elastic tissue—with the largest arteries containing vasa vasorum, small blood vessels that supply the walls of large blood vessels. [3] Most of the layers have a clear boundary between them, however the tunica externa has a boundary that is ill-defined.
When blood vessels connect to form a region of diffuse vascular supply, it is called an anastomosis. Anastomoses provide alternative routes for blood to flow through in case of blockages. Veins can have valves that prevent the backflow of the blood that was being pumped against gravity by the surrounding muscles. [8]
A long bone is one that is cylindrical in shape, being longer than it is wide. However, the term describes the shape of a bone, not its size, which is relative. Long bones are found in the arms (humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the fingers (metacarpals, phalanges) and toes (metatarsals, phalanges).
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Venous vasa vasorae, that originate within the vessel wall of the artery but then drain into the main lumen or branches of concomitant vein. [1] Depending on the type of vasa vasorum, it penetrates the vessel wall starting at the intimal layer (vasa vasorum interna) or the adventitial layer (vasa vasorum externa). Due to higher radial and ...