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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 Haversian canal contains the bone's blood supplies. The boundary of an osteon is the cement line. Each Haversian canal is surrounded by varying number (5-20) of concentrically arranged lamellae of bone matrix. Near the surface of the compact bone, the lamellae are arranged parallel to the surface; these are called circumferential lamellae.
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 dental canaliculi (sometimes called dentinal tubules) are the blood supply of a tooth. [4] Odontoblast process run in the canaliculi that transverse the dentin layer and are referred as dentinal tubules. [5] The number and size of the canaliculi decrease as the tubules move away from the pulp and toward the enamel or cementum.
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]
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The outer shell of the long bone is made of cortical bone also known as compact bone. [1] This is covered by a membrane of connective tissue called the periosteum.Beneath the cortical bone layer is a layer of spongy cancellous bone.
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