Hormones are mainly chemical messengers that are secreted directly into the bloodstream, which helps in carrying them to organs and tissues of the body to exert their functions. There are different types of hormones that serve different aspects of bodily functions and processes. A few of them include:
-
Development and growth
-
Metabolism of food items
-
Sexual function and reproductive growth
-
Cognitive function and mood
-
Maintenance of body temperature and thirst
Hormones are secreted from the endocrine glands that are present in the body. These glands are ductless, so hormones are secreted directly into the bloodstream rather than viaducts. Some of the important endocrine glands in the body are the Pituitary gland, pineal gland, thymus, thyroid, adrenal glands, pancreas, testes and ovaries. These organs secrete hormones in microscopic amounts and it takes only very small amounts to bring about some major changes in the body. Even a very slight excess of hormone secretion might lead to disease states, just like the slightest deficiency in a hormone.
Hypothalamus and the Pituitary Gland
Various hormones are regulated via the pituitary gland and the hypothalamus. The hypothalamus is represented by a small region situated at the base of the brain and the pituitary hangs just below it. The hypothalamus secretes releasing hormones that help to instruct the anterior pituitary gland to secrete certain hormones. One of the hormones regulated via this hypothalamus-pituitary axis is thyroxine, one of the thyroid hormones.
The hypothalamus secretes a thyrotropin-releasing hormone (TRH), that activates the secretion of the thyroid-stimulating hormone (TSH) from the anterior pituitary. The TSH further stimulates the release of thyroid hormones from the thyroid gland. The thyroid hormones in turn try to suppress both pituitary and hypothalamus hormone production.
Both the hypothalamus and the thyroid also help in the production of hormones of their own, e.g. growth hormone released from the anterior pituitary and the antidiuretic hormone from the hypothalamus.
It must be noted that the anterior and posterior pituitary are found together, but usually originate as separate structures. The posterior pituitary is a part of the hypothalamus and it stores some hypothalamic hormones. The anterior pituitary is generally derived from the roof of the mouth but migrates to the brain during early development.
Hormone Use
Some of the uses of hormones that are put to human use are discussed below:
-
Insulin and glucagon are mainly peptide hormones that are produced via the islet cells in the pancreas and help regulate blood sugar concentration. Insulin usually lowers the blood sugar by stimulating the uptake of sugar by various cells, whereas glucagon raises the blood sugar levels by stimulating the further release of glucose from glycogen stored in the liver.
-
Thyroid hormones are amino acid derivatives that are produced via the thyroid gland and help to regulate metabolism.
-
Estrogen, progesterone and testosterone are referred to as steroid hormones that are produced by the ovaries and testes. They help regulate male and female sex characteristics, egg and sperm production, and also pregnancy.
-
Cortisone is a corticosteroid hormone that is produced by the adrenal cortex and functions to mediate stress responses.
-
Epinephrine (adrenalin) is an amino acid derivative produced by the adrenal medulla and mediates the “fight or flight” response during any dangerous situations.
-
Growth hormone is mainly a peptide hormone that is produced via the anterior pituitary. It helps in cell growth and reproduction and also in increasing metabolism.
-
Prolactin is a peptide hormone produced by the anterior pituitary and stimulates milk production during breast-feeding
-
ADH, it is known as an antidiuretic hormone, is a peptide hormone that is produced by the hypothalamus and helps in the regulation of the amount of water that is reabsorbed by the kidneys.
Hormonal stimuli
It represents the release of a hormone in response to any other hormone. Several endocrine glands release hormones when stimulated by the hormones released by other endocrine glands. For example, the hypothalamus produces hormones that activate the anterior portion of the pituitary gland. The anterior pituitary in turn releases hormones that further regulate hormone production by other endocrine glands. The anterior pituitary releases the thyroid-stimulating hormone, which then activates the thyroid glands to produce the hormones T3 and T4. As and when the blood concentrations of T3 and T4 increase, they inhibit both the pituitary and the hypothalamus in a negative feedback loop.
Neural Stimuli
In some cases, the nervous system directly activates the endocrine glands to release hormones, this is referred to as neural stimuli. In a short-term stress response, the hormones epinephrine and norepinephrine are very crucial for providing the bursts of energy needed for the body to respond. In this, neuronal signalling from the sympathetic nervous system directly activates the adrenal medulla to release the hormones epinephrine and norepinephrine in response to stress.
Conclusion
Hormone levels are mainly controlled via negative feedback, in which increasing levels of a hormone inhibit its further release. The three mechanisms of hormonal release are humoral stimuli, hormonal stimuli, and neural stimuli.
Humoral stimuli mean the control of hormonal release in response to any changes in the extracellular fluid levels or ion levels. Hormonal stimuli mean the release of hormones in response to hormones that are released by other endocrine glands. Neural stimuli represent the release of hormones in response to any neural stimulation.