Free Radicals and Antioxidants

The electrons in an atom are located in orbitals, with each orbital containing a maximum of two electrons. When an orbital has an unpaired electron, the molecule containing the unpaired electron is called a free radical. Free radicals are highly reactive in the body, oxidizing removing an electron from other Table 19.4 Estimated Safe and Adequate Daily Dietary Intakes of Selected Vitamins and Minerals1 Table 19.4 Estimated Safe and Adequate Daily Dietary Intakes of Selected Vitamins and...

Immune Complex Diseases

The term immune complexes refers to antigen-antibody combinations that are free rather than attached to bacterial or other cells. The formation of such complexes activates complement proteins and promotes inflammation. This inflammation is normally self-limiting because the immune complexes are removed by phagocytic cells. When large numbers of immune complexes are continuously formed, however, the inflammation may be prolonged. Also, the dispersion of immune complexes to other sites can lead...

An antigen that does not normally circulate in the blood may become exposed to the immune system

Thyroglobulin protein that is normally trapped within the thyroid follicles, for example, can stimulate the production of autoantibodies that cause the destruction of the thyroid this occurs in Hashimoto's thyroiditis. Similarly, autoantibodies developed against lens protein in a damaged eye may cause the destruction of a healthy eye in sympathetic ophthalmia . 2. A self-antigen that is otherwise tolerated may be altered by combining with a foreign hapten. The disease thrombocytopenia low...

Regulation of Contraction

Tropomyosin And Troponin

When the cross bridges attach to actin, they undergo power strokes and cause muscle contraction. In order for a muscle to relax, therefore, the attachment of myosin cross bridges to actin must be prevented. The regulation of cross-bridge attachment to actin is a function of two proteins that are associated with actin in the thin filaments. The actin filament or F-actin is a polymer formed of 300 to 400 globular subunits G-actin , arranged in a double row and twisted to form a helix fig. 12.13 ....

Implantation of the Blastocyst and Formation of the Placenta

Chorion Frondosum

If fertilization does not take place, the corpus luteum begins to decrease its secretion of steroids about 10 days after ovulation. This withdrawal of steroids, as previously described, causes necrosis and sloughing of the endometrium following day 28 of the cycle. If fertilization and implantation have occurred, however, these events must obviously be prevented to maintain the pregnancy. Figure 20.46 The secretion of human chorionic gonadotropin hCG . This hormone is secreted by trophoblast...

Nystagmus and Vertigo

When a person first begins to spin, the inertia of endolymph within the semicircular ducts causes the cupula to bend in the opposite direction. As the spin continues, however, the inertia of the endolymph is overcome and the cupula straightens. At this time, the endolymph and the cupula are moving in the same direction and at the same speed. If movement is suddenly stopped, the greater inertia of the endolymph causes it to continue moving in the previous direction of spin and to bend the cupula...