Free Download Endocrinology

        Endocrinology (from Greek, endo, "within"; krīnō, "to separate"; and  -logia) is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions called hormones, the integration of developmental events such as proliferation, growth, and differentiation (including histogenesis and organogenesis) and the coordination of metabolism, respiration, excretion, movement, reproduction, and sensory perception depend on chemical cues, substances synthesized and secreted by specialized cells.

       Endocrinology is concerned with the study of the biosynthesis, storage, chemistry, and physiological function of hormones and with the cells of the endocrine glands and tissues that secrete them.

The endocrine system consists of several glands, all and in different parts of the body, that secrete hormones directly into the blood rather than into a duct system. Hormones have many different functions and modes of action; one hormone may have several effects on different target organs, and, conversely, one target organ may be affected by more than one hormone.

       The study of endocrinology began in China.^[1] The Chinese were isolating sex and pituitary hormones from human urine and using them for medicinal purposes by 200 BC.^[1]  In medieval Persia, Avicenna (980-1037) provided a detailed account on diabetes mellitus in The Canon of Medicine (c. 1025), "describing the abnormal appetite and the collapse of sexual functions and he documented the sweet taste of diabetic urine.

        Avicenna recognized a primary and secondary diabetes. He also described diabetic gangrene, and treated diabetes using a mixture of lupine, trigonella (fenugreek), and zedoary seed, which produces a considerable reduction in the excretion of sugar, a treatment which is still prescribed in modern times. Avicenna also "described diabetes insipidus very precisely for the first time", though it was later Johann Peter Frank (1745–1821) who first differentiated between diabetes mellitus and diabetes insipidus.^[5]

In the original 1902 definition by Bayliss and Starling, they specified that, to be classified as a hormone, a chemical must be produced by an organ, be released (in small amounts) into the blood, and be transported by the blood to a distant organ to exert its specific function. This definition holds for most "classical" hormones, but there are also paracrine mechanisms (chemical communication between cells within a tissue or organ), autocrine signals (a chemical that acts on the same cell), and intracrine signals (a chemical that acts within the same cell).[2] A neuroendocrine signal is a "classical" hormone that is released into the blood by a neurosecretory neuron (neuroendocrinology).

Classification of Hormones

According to Griffin and Ojeda  three are different classes of hormone based on their chemical composition:^[3]


Amines

Amines, such as norepinephrine, epinephrine, and dopamine, are derived from single amino acids, in this case tyrosine. Thyroidhormones such as 3,5,3’-triiodothyronine (T3) and 3,5,3’,5’-tetraiodothyronine (thyroxine, T4).

Peptide and protein

Peptide hormones and protein hormones consist of three (in the case of thyrotropin-releasing hormone) to more than 200 (in the case of follicle-stimulating hormone) amino acid residues and can have molecular weights as large as 30,000. All hormones secreted by the pituitary gland are peptide hormones, as are leptin from adipocytes and insulin from pancreas.

Steroi
Steroid hormones are converted from their parent compound, cholesterol. Mammalian steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestagens.

General Function of Hormones

Hormones act by binding to specific receptors in the target organ. As Baulieu notes, a receptor has at least two basic constituents:
a recognition site, to which the hormone binds
an effector site, which precipitates the modification of cellular function.

References

1. Temple, Robert (2007) [1986]. The genius of China: 3,000 years of science, discovery & invention (3rd ed.). London: Andre Deutsch. pp. 141–145.
2. Nussey, S; Whitehead, S. (2001). Endocrinology: An Integrated Approach. Oxford: Bios Scientific Publ.. ISBN 1-85996-252-1.

3.  Ojeda, S. R.; Griffin, J. B. (2000). Textbook of endocrine physiology (4th ed.). Oxford [Oxfordshire]: Oxford University Press. ISBN 0-19-513541-5.
5. Nabipour, I. (2003). "Clinical Endocrinology in the Islamic Civilization in Iran".International Journal of Endocrinology and Metabolism 1: 43–45 [44–5].

(Courtesy:  http://en.wikipedia.org )

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