Pathways for blood and bone exchange
The long bones have nourishing arteries, metaphyseal arteries, and iliac arteries through the bone cortex into the bone. The blood supply of irregular bones, flat bones, and short bones also comes from the periosteum artery or nourishing arteries; the membrane blood vessels supply the outer 1/3 of the cortex. In part, the anastomotic network of arteries deep into the membrane branches out into the cortical bone. The above arteries are accompanied by veins. There are many branches of blood vessels in the cortex that enter the Haver's canal. The blood vessels in the Haver's canal and the blood in the bone marrow cavity exchange materials with the cells on the bone surface. Bone cells on the bone surface exchange non-stop material with each other through cytoplasmic processes and bone cells in the same bone structural unit, so that bone tissues (cells and matrix) carry out normal metabolic activities. When people are full, a lot of calcium is absorbed into the bloodstream through the intestines. Blood calcium must be maintained at a relatively constant level. Part of the excess calcium in the blood is excreted by the kidneys, and part of it is stored in the bone fluid and bone matrix by bone cells. When starving at night, the calcium in the bone matrix and bone fluid enters the blood through bone cells to maintain the stability of blood calcium. This exchange between bone and blood is rapid and is called the rapid regulation mechanism of blood calcium.