The third group of hormones are those derived either from tyrosine or from tryptophan. All adrenal and gonadal steroids have the same basic ring structure ( Box 1.4) and despite superficial 2D structural similarity, the side chains and spatial orientation generate specificity. The steroid hormones, which include vitamin D and those secreted by the adrenal cortex and gonads, are derived from cholesterol. Other hormones include those derived from tryptophan (serotonin and melatonin, Boxes 7.33 and 8.12) and those derived from fatty acids (eicosanoids, Box 8.8). Disturbances in feedback loops are clinically important and their significance in diagnosis is pivotal.Ĭhemical structures of the three major classes of human hormones. The integration of feedback loops involving several hormones may be complex. Feedback loops may involve the hypothalamo-pituitary axis that detects changes in the concentration of hormones secreted by peripheral endocrine glands or a single gland may both sense and respond to changes in a controlled variable. The secretion of hormones is subject to negative feedback control, and there are several ways by which this is achieved ( Box 1.2). Hormones act in concert and thus, an abnormality in a controlled variable, such as blood glucose concentration may result from defects in the control of any one of several hormones. The roles several hormones play in one function is exemplified by the control of blood glucose which involves the pancreatic peptide insulin and its counter regulatory hormone, glucagon, as well as cortisol, growth hormone and epinephrine. For example, thyroid hormone is essential in development as well as many aspects of homeostasis and metabolism, whilst glucocorticoids, such as cortisol, are important both in growth and nutrient supply and are also modulators of immune function. A single hormone may affect more than one of these functions and each function may be controlled by several hormones. Their functions can be broadly grouped into several categories: reproduction and sexual differentiation development and growth maintenance of the internal environment and regulation of metabolism and nutrient supply. Classification by structure of the major human hormones*.
0 kommentar(er)
