jueves, 5 de mayo de 2011

Adrenal glands

Adrenal Glands
An adrenal gland is located above each of the kidneys, as shown in Figure. Each adrenal gland is separated into two structures, the adrenal medulla, which is the center of the gland, and the adrenal cortex, which is the outer layer. The medulla and the cortex work as two separate endocrine glands.
Adrenal medulla
It is the core of the adrenal gland, and is surrounded by the adrenal cortex. Secretion of hormones from the medulla is controlled by the sympathetic nervous system. It produce the hormones adrenaline (epinephrine) mainly.This hormone is part of the fight-or-flight response initiated by the sympathetic nervous system. It plays central role in short-term response to stress, increases heart rate and supply of blood with oxygen and glucose to the brain and muscles, while suppressing other non-emergency bodily processes, such as digestion.

Adrenal cortex
Is is the site of steroid hormone synthesis. In contrast to the medulla that is controlled directly by the nervous system, the cortex is regulated by hormones secreted by the pituitary gland. In adrenal cortex are produced:
Cortisol, often called the "stress hormone" as it is involved in the response to stress, and is involved in restoring homeostasis after a stressful event. Cortisol increases blood pressure, blood sugar levels and has an immunosuppressive action.
Aldosterone regulates balance of salt and water in the body. It stimulate sodium reabsorption in the kidneys. This increases blood volume and, therefore, increases blood pressure

The ovaries of females and the testes of males are the gamete producing organs, or gonads. Ovaries in females are homologous to testes in males. In addition to producing gametes, an exocrine action, the gonads are endocrine glands that produce steroid sex hormones. Sex hormones secretion is controled by the gonadotropines produced in pituitary gland.
The sex hormones produced in testes are called androgens. The main androgen produced by the testes is testosterone. Testosterone is responsible for development of the male sex organs and secondary sex characteristics of males such as facial hair and deepening of the voice .
In females the ovaries produce two hormones: estrogen and progesterone. Estrogen causes the release of an egg from the ovaries and progesterone prepares the uterus for a possible implantation by a fertilized egg. Both hormans take part in control the menstrual cycle.
The placenta is an endocrine gland of pregnancy because it secretes estrogens and progesterone which are important for maintaining a pregnancy.

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