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Full Version: Physiologicoanatomical Peculiarities of the Endocrine System
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The major chemical regulators of the body are the internal secretions and their secreting cells, which are collectively known as the endocrine system.

Ordinarily the endocrine system of the newborn is adequately developed, but its functions are immature. For example, the posterior lobe of the pituitary gland produces limited quantities of antidiuretic hormone (ADH), or vasopression, which inhibits diuresis. This renders the neonate highly susceptible to dehydration.

The effect of maternal sex hormones is particularly evident in the newborn because it causes miniature puberty. The labia are hypertrophied, and the breasts may be engorged and secrete milk during the first few days of life. Female newborns sometimes have pseudo-menstruation from the sudden drop in the levels of progesterone and estrogen.

The endocrine system is adequately developed at birth, but its functions are immature, The interrelatedness of all the endocrine organs has a major effect on the function of any one gland. The lack of homeostatic control because of various functional deficiencies renders the infant especially vulnerable to imbalances in fluid and electrolytes, glucose concentration, and amino acid metabolism.

For example, corticotrophin (ACTH) is produced in limited quantities during infancy. ACTH acts on the adrenal cortices to produce their hormones, particularly the glucocorticoids and aldosterone. Because the feedback mechanism between ACTH and the adrenal cortex is immature during infancy, there is much less tolerance for stressful conditions, which affect fluid and electrolytes and the metabolism of fats, and carbohydrates. In addition, although the islets of Langerhans produce insulin and glucagons during fetal life and early infancy, blood sugar levels tend to remain labile, particularly under conditions of stress.

The function of the endocrine system is:

• To secrete intracellularly synthesized hormones into the circulation
• To serve as pacemaker substances for metabolic processes
• Together with the closely related but more rapidly reacting nervous system
• To serve to integrate the various physiologic functions of the organism in adjusting to external and internal environmental demands.

Endocrine substances even in extremely small concentrations are effective in modifying metabolism, behavior and development. The endocrine system consists of three components:

1. The cell, which sends a chemical message by means of a hormone
2. the target cells, or end organs, which receive the chemical message
3. the environment through which the chemical is transported (blood, lymph, extracellular fluids) from the site of synthesis to the sites of cellular action.

Some hormones, such as acetylcholine, have specific local effects: others are secreted by specific endocrine glands and then transported by the fluids to create their effects on target tissues at locations distant from the secreting glands. Some of the general hormones, such as thyroid hormone and growth hormone, affect most cells of the body, whereas the effect of others, such as the tropic hormones, is chiefly restricted to some specific tissues.