Specialized Tissues and Organs

A. Basic Concepts and Molecular Essentials 1900 D. Specialized Tissues and Organs... 

Arts. From only 20 amino acids and eight nitrogen bases, cells have been able to create extraordinarily large numbers of different proteins, nucleic acids, and other compounds necessary to carry out metabolism and the specific functions of specialized tissues and organs such as the brain, kidney,... 

General functions of the skin are outlined in Table 1. These functions include containment of tissues and organs, multifaceted protections, environmental sensing, and body temperature regulation. Some skin functions are inextricably entwined. For instance, containment and the barrier functions are to some extent inseparable. Active sweating is accompanied by increased peripheral blood flow, which in turn is tied in with greater nourishment of the cells of the skin as needed to promote their proliferation, differentiation, and specialization. 

The carbohydrate metabolic routes in various tissues of the organism discussed above differ in intensity, which is defined by metabolic features specific of each tissue and organ. However, from the standpoint of activity of the whole organism, certain specializations of the carbohydrate metabolic routes in individual tissues are profitably complementary. For example, strenuous muscular exertion requires energy which is initially supplied by the breakdown of glycogen to lactic acid. The latter compound is excreted into the blood to be supplied... 

Functional specialization of tissues and organs allows for greater efficiency than in single-celled organisms where all reactions and processes occur in close proximity. An analogy is to think of a typical university. It would not be conducive to learning... 

The potential contribution of stem cells to medical treatment lies in then-capability to differentiate and grow into normal, healthy cells. Using pluripotent stem cells, scientists are devising means to culture them in the laboratories and coax them to grow into various specialized cells. Rather than gene therapy, with stem cells we have the potential of cell therapy to repair our diseased tissues and organs. This will circumvent the lack of donor organs. Stem cells also provide the possibility for healthy cells to cure disabilities such as strokes, Parkinson s disease, and diabetes. 

The term blood-brain barrier (BBB) refers to the special obstacle that drugs encounter when trying to enter the brain from the circulatory system. The difference between the brain and other tissues and organs is that the capillaries in the brain do not have pores for the free flow of small molecules in the interstitial fluid of the brain. To enter the interstitial fluid, all molecules must cross a membrane. This design is a protective measure to defend the brain from unwanted and potentially hazardous xenobiotics. Traditionally, drugs that target the brain or central nervous system (CNS) cross the BBB by passive diffusion. Transport by carrier proteins across the BBB is becoming better understood but remains an area of active research. 

Vitamins and hormones are minor organic biomolecules, but both of them are required by animals for the maintenance of normal growth and health. They differ in that vitamins are not synthesized by animals and must be supplied in diets while hormones are secreted by specialized tissues and carried by the circulatory system to the target cells somewhere in the body to initiate/stimulate specific biochemical or physiological activities. Vitamins (Dyke, 1965) can be classified as water-soluble (B vitamins and vitamin C) or fat-soluble (vitamins A, D, E, and K) and act as cofactors for numerous enzyme catalyzed reactions or cellular processes. Hormones (Nornam and Litwack, 1997) can be classified structurally as follows ... 

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