Tooth Enamel
Tooth EnamelThe layer of enamel over the tooth crown is a substance similar to bone. A section through enamel shows that, like bone, it is composed of crystals of calcium phosphate embedded in a ground substance. These crystals are built up into rods or prisms which make enamel the hardest substance in the body
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enamel
Added: October 15, 2007, 8:11 pm
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Three Kinds of Cartilage
Three Kinds of CartilageCartilage, unlike other types of connective tissue, has no blood vessels. It is tough but pliant because the ground substance between the cells contains combinations of proteins and sugars. Cartilage is described as hyaline, fibrous or elastic, depending on the density and type of fibers present in its composition. Hyaline, the most abundant type of cartilage, is clear and glassy, with few cells and fibers in the ground substance. Hyaline covers the ends of bones at the joints, and also forms the rings which keep the trachea open. Fibrocartilage is made up of tightly packed bundles of collagen fibers, making it resilient and able to withstand compression. Fibrocartilage lies, for example, between vertebrae. Elastic cartilage contains, in addition to collagen, fibers of the protein elastin. This makes it firm yet supple, giving support, for example, to the external ear and epiglottis.
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cartilage
Added: October 15, 2007, 8:11 pm
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The Structure of Bone
The Structure of BoneThis is the structure of bone. Spongy or cancellous bone form the center bulk of all our bones. Its honeycomb structure keeps bone light, in contrast to the heavier, compact bone, which gives it strength. Bone cells or osteocytes are contained in spaces called lacunae. The minute projections of bone cells trail into adjoining channels known as canaliculi. Tissue fluid, which fills the lacunae, allows the transfer of materials between bone cells and capillaries. Haversian systems, each about one-sixtieth of an inch wide, make up the structure of compact bone. Each system is formed by a series of rings called lamellae, which are deposits of mineral salts and collagen fibers. Haversian canals, which run through the center of each Haversian system, contain the blood and lymphatic vessels supplying the bone. Here arteries carrying oxygenated blood are shown in red. Veins carrying deoxygenated blood are shown in blue. The lymphatic vessels are shown in white. A section through the shaft of the femur, a long bone, shows a central mass of spongy bone surrounded by the branching tubular Haversian systems. Blood vessels on the bone surface reach into the center of each Haversian system supplying the bone cells.
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bone
Added: October 15, 2007, 8:12 pm
Runtime: 86.00 | Views: 11931 |
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Skin Color
Skin ColorSkin color is created by production of the pigment melanin from cells called melanocytes in the epidermis. All races have equal melanocyte numbers, but genetic differences control the amount of melanin injected into the cells which are produced in the germinative layer. Melanin production is stimulated by the ultraviolet rays of the sun. The melanin absorbs these harmful rays, and the skin becomes tanned and protected. Freckles appear when only some groups of melanocytes become active and produce melanin.
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skin
Added: October 15, 2007, 8:13 pm
Runtime: 33.00 | Views: 7280 |
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Antibody Mediated Immune Response
Stages in this process are:
antigen detection
activation of helper T cells
antibody production by B cells
Each stage is directed by a specific cell type.
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immuneresponse
Added: November 4, 2007, 11:01 pm
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