anatomy and Physiology of Adrenal Glands PDF

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anatomy and physiology notes on the adrenal glands...

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Anatomy and Physiology of Adrenal glands

Gross Structure of the Adrenal Glands

The adrenal glands are on top of each kidney. Each gland has a cortex (outer region) and a medulla (inner region). The cortex secretes glucocorticoids such as cortisol, mineralocorticoids, and small amounts of androgens and estrogens responsible for some secondary sex characteristics. Glucocorticoids raise blood sugar levels by increasing gluconeogenesis (synthesis of glucose from amino acid). This action ensures glucose supplies for the body when it is under stress. Mineralocorticoids such as aldosterone promote sodium (salt) reabsorption by stimulating the kidneys to absorb more sodium from the blood.

The adrenal glands which are also called the suprarenal glands, are small, triangular glands located on top of both kidneys. An adrenal gland is made of two parts: the outer region is called the adrenal cortex and the inner region is called the adrenal medulla. Both parts of the adrenal glands -- the adrenal cortex and the adrenal medulla -- perform very separate functions.

The adrenal glands work interactively with the hypothalamus and pituitary gland in the following process: 

the hypothalamus produces corticotropin-releasing hormones, which stimulate the pituitary gland.

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the pituitary gland, in turn, produces corticotropin hormones, which stimulate the adrenal glands to produce corticosteroid hormones.

Internal Structure of the Adrenal Cortex

The outer covering (adrenal cortex) is derived from the fetal mesodermal ridge, a structure that also gives rise to the kidneys so that the juxtaposition of the two organs is not surprising. Within the adrenal cortex are three zones known as the outer (zona glomerulosa), the middle (zona fasciculata), and the inner (zona reticularis). Under the microscope the cells are rather typical endocrine cells; the distinction between zones is made by differing staining characteristics.

Adrenal Cortex Functions The adrenal cortex, the outer portion of the adrenal gland, secretes hormones that have an effect on the body's metabolism, on chemicals in the blood, and on certain body characteristics. The adrenal cortex secretes corticosteroids and other hormones directly into the bloodstream. The hormones produced by the adrenal cortex include: 

corticosteroid hormones

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hydrocortisone hormone - this hormone, also known as cortisol, controls the body's use of fats, proteins, and carbohydrates.

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corticosterone - this hormone, together with hydrocortisone hormones, suppresses inflammatory reactions in the body and also affects the immune system.

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aldosterone hormone - this hormone inhibits the level of sodium excreted into the urine, maintaining blood volume and blood pressure.

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androgenic steroids (androgen hormones) - these hormones have minimal effect on the development of male characteristics

Hormones Adrenocortical cells synthesize and secrete chemical derivatives (steroids) from cholesterol, the major animal sterol. While cholesterol can be synthesized in many body tissues, further differentiation into steroid hormones takes place only in the adrenal cortex and in its embryological cousins, the ovaries and the testes. Aldosterone The biologic effect of aldosterone, the principal mineralocorticoid, is to set in motion a set of reactions at the cell surface of all body tissues in order to enhance the uptake and retention of sodium in all cells and the extrusion of potassium from them. It also has a major impact on kidney function, to retain sodium within the circulation while increasing

the excretion of potassium into the urine. At the same time, aldosterone tends to decrease the acidity of body fluids. Cortisol Cortisol (hydrocortisone) is the major human glucocorticoid. It exerts multiple and varied effects. It also serves as a mineralocorticoid but is considerably less effective than aldosterone. Cortisol plays a major role in the body's response to stress. In fasting, for example, it sustains the blood sugar concentration by blocking the egress of glucose into all tissues other than the critically important brain and spinal cord, while it simultaneously increases the breakdown of protein from muscle and other organs and hastens the conversion of newly generated amino acids to glucose to replenish the supply constantly being consumed by the brain. Adrenal androgens Adrenal androgens are not as potent as testosterone, the major steroid secreted by the testis, but a number of them, including androstenedione, dehydroepiandrosterone (DHEA), and its sulfate (DHEAS) may be converted to stronger androgens such as testosterone. Although little androgen is secreted before puberty, the output increases dramatically at puberty so that the adrenal cortex makes a significant contribution, known as the adrenarche, to developmental changes in both sexes....