Hard tissue are lightweight yet strong and hard, and serve multiple functions. Mineralized osseous tissue or bone tissue, is of two types – cortical and cancellous and gives it rigidity and a coral-like three-dimensional internal structure. Other types of tissue found in bones include marrow, endosteum, periosteum, nerves, blood vessels and cartilage. Bone is an active tissue composed of different cells. Osteoblasts are involved in the creation and mineralisation of bone; osteocytes and osteoclasts are involved in the reabsorption of bone tissue. The mineralised matrix of bone tissue has an organic component mainly of collagen and an inorganic component of bone mineral
Blood lipids to release stored fatty acids into the blood as free fatty acids, in order to supply e.g. muscle cells with energy. In any case, also the fatty acids secreted from cells are anew taken up by other cells in the body, until entering fatty acid metabolism. The fate of cholesterol in the blood is highly determined by its constitution of lipoproteins, where some types favour transport towards body tissues and others towards the liver for excretion into the intestines. The 1987 report of National Cholesterol Education Program, Adult Treatment Panels suggest the total blood cholesterol level should be: <200 mg/dl