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Chitin (C 8 H 13 O 5 N) n (/ ˈ k aɪ t ɪ n / KY-tin) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. [1]
The role of the chitin and proteins in such structures is more than just holding the crystals together; the crystal structure itself is so affected as to prevent the propagation of cracks under stress, leading to remarkable strength. [10] The process of formation of such mineral-rich matrices is called biomineralization. [11]
Discarded exoskeleton of dragonfly nymph Exoskeleton of cicada attached to a Tridax procumbens (colloquially known as the tridax daisy)An exoskeleton (from Greek έξω éxō "outer" [1] and σκελετός skeletós "skeleton" [2] [3]) is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs ...
Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. [2] In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). [3] It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells.
The first, at a scale of 100 μm to 1 mm, is inside the compact bone where cylindrical units called osteons and small struts can be distinguished. [16] The second hierarchical structure, the ultrastructure, at a scale of 5 to 10 μm, is the actual structure of the osteons and small struts.
In mammals, B cells mature in the bone marrow and T cells mature in the thymus. [1] Central tolerance is not perfect, so peripheral tolerance exists as a secondary mechanism to ensure that T and B cells are not self-reactive once they leave primary lymphoid organs.
Softer shells are mostly protein. It may be fibrous or quite liquid. Some arthropod eggs do not actually have shells, rather, their outer covering is actually the outermost embryonic membrane, the choroid, which protects inner layers. This can be a complex structure, and it may have different layers, including an outermost layer called an ...
Special connective tissue consists of cartilage, bone, blood and lymph. [10] Other kinds of connective tissues include fibrous, elastic, and lymphoid connective tissues. [11] Fibroareolar tissue is a mix of fibrous and areolar tissue. [12] Fibromuscular tissue is made up of fibrous tissue and muscular tissue.