Endocrine glands ovaries

Steroid hormones are produced by the adrenal cortex, testes, ovaries, and placenta. Synthesized from cholesterol, these hormones are lipid soluble therefore, they cross cell membranes readily and bind to receptors found intracellularly. However, because their lipid solubility renders them insoluble in blood, these hormones are transported in the blood bound to proteins. Furthermore, steroid hormones are not typically preformed and stored for future use within the endocrine gland. Because they are lipid soluble, they could diffuse out of the cells and physiological regulation of their release would not be possible. Finally, steroid hormones are absorbed easily by the gastrointestinal tract and therefore may be administered orally. 

Location of major endocrine glands in humans. The hypothalamus regulates the anterior pituitary, which regulates the hormonal secretions of the thyroid, adrenals, and gonads (ovary in the female and testis in the male). 

The hypothalamus-pituitary, thyroid, parathyroid, pancreas, adrenals, ovary, and testes are considered to be the principal endocrine glands producing hormones. A more complete list of the major endocrine hormones and their primary gland of origin is shown in Table 9.1. 

Figure 13.1 Major human endocrine glands (1) pineal gland, (2) pituitary gland, (3) thyroid gland, (4) thymus, (5) adrenal gland, (6) pancreas, (7) ovary and (8) testes.

There are several approaches to the study of metabolism. First, isolation of steroid metabolites from various steroid-forming tissues (testes, ovaries, placentae, adrenal glands) makes it possible to evaluate the usefulness of a particular endocrine gland in the production of steroids. Secondly, in vitro experiments are conducted by incubation with tissue preparations followed by isolation of the metabolities of steroids. Thirdly, in vivo experiments are carried out by isolation of steroids from biological fluids, mainly from animal and human blood and urine. This last method includes evaluation of the rates of secretion and metabolism of... 

In addition to Its structural role In membranes, discussed In Chapter 5, cholesterol Is the precursor for several Important bloactive molecules. They Include bile acids (see Figure 18-6), which are made In the liver and help emulsify dietary fats for digestion and absorption In the Intestines, steroid hormones produced by endocrine cells (e.g., adrenal gland, ovary, testes), and vitamin D produced In the skin and kidneys. Arthropods need cholesterol or other sterols to produce membranes and ecdysterold hormones, which control development however, they cannot make the precursor sterols themselves and must obtain these compounds In their diet. Another critical function of cholesterol Is Its covalent addition to Hedgehog protein, a key signaling molecule In embryonic development (Chapter 15). 

Although there were no specific anatomical lesions in the endocrine glands that corresponded to a diminished pituitary stimulus, the type of changes found in the ovaries, in the testicles, in the adrenals, and in the thyroids suggests an involution similar to that observed in cases of early... 

Hormones are the chemical messengers of the body they are secreted by the endocrine glands and regulate biological processes. Corticosteroids, described in the preceding section, are hormones produced by the adrenal glands. The sex glands— testes in males, ovaries in... 

All OCPs are polytropic, parenchymatous poisons, afflicting the central nervous system, liver, kidneys, the heart muscle, the stomach and intestines, and the endocrine system (mostly the adrenal glands, thyroid, and ovaries). Morphological changes in warm-blooded creatures poisoned by OCPs vary from insignificant disruptions in circulation and reversible dystrophy to focal necroses these effects depend on the organism, the dose of OCP, how long the OCP remains active, as well as on other factors [9, 39, 40, A47, A79]. 

The endocrine effects of the glucocorticoids variously involve the pituitary-adrenal axis, the ovaries and testes, the parathyroid glands, and the thyroid gland. 

The similarities between ecdysone synthesis in the insect prothoracic gland and the ovary are obvious and in each case synthesis is initiated in response to a hormone originating in the brain. Both bear a striking resemblance to the mammalian system where steroid hormone synthesis in the various endocrine tissues is initiated in response to the release of appropriate hormones from the anterior pituitary. 

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