Hormones: Definition, Function, and Examples

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Hormones Definition

Hormones are endocrine system chemical messengers generated by glands. The bloodstream or other tissue fluids carry items secreted by endocrine tissues to their target cells. Hormones attach to receptors on the cell membrane of their target cells to activate them.

Steroids, amino acid derivatives, and peptide hormones are the three types of human hormones. Steroid hormones are cortisone and oestrogen, amino acid derivatives are epinephrine and thyroxine, and polypeptides are insulin and growth hormone.

Hypothalamus and Pituitary Gland

The pituitary gland and the brain control a large number of hormones. The pituitary is located right below the hypothalamus, which is a tiny area near the base of the brain. 

The hypothalamus secretes releasing hormones that tell the anterior pituitary gland which hormones to secrete. Thyroxine, a thyroid hormone, is one of the hormones controlled by the hypothalamus-pituitary axis. 

The hypothalamus generates thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH). The TSH encourages the thyroid gland to produce thyroid hormones. The thyroid hormones, in turn, inhibit the synthesis of pituitary and hypothalamic hormones.

The hypothalamus and thyroid each generate their own hormones, such as growth hormone from the anterior pituitary and antidiuretic hormone from the hypothalamus. Although the anterior and posterior pituitaries are located together, they are distinct structures.

The hypothalamic hormones are stored in the posterior pituitary, which is a component of the hypothalamus. The anterior pituitary is generated from the roof of the mouth, but throughout early development it migrates to the brain.

1. The hypothalamic releasing hormone identifies its target region in the anterior pituitary. It attaches to the receptor, which sends a chemical message to the cell, telling it to produce pituitary hormone.

2. The target tissue will be instructed to release its product by the released pituitary hormone. The adrenal cortex, thyroid, testes, and ovaries are among the endocrine glands controlled by the hypothalamus and anterior pituitary in this fashion.

Hormones Uses

Hormones are used for a variety of purposes in humans, including:

Insulin and glucagon are peptide hormones generated by pancreatic islet cells that regulate blood sugar levels. Insulin reduces blood sugar by increasing sugar absorption into different cells, whereas glucagon raises blood sugar by stimulating glucose release from liver glycogen storage.

Thyroid hormones are amino acid derivatives that assist regulate metabolism and are generated by the thyroid gland.

The ovaries and testes generate the steroid hormones oestrogen, progesterone, and testosterone. They control sex traits in both men and women, as well as egg and sperm production and pregnancy.

The adrenal cortex produces cortisone, a corticosteroid hormone that serves to control stress reactions. The adrenal medulla produces epinephrine (adrenalin), an amino acid derivative that mediates the “fight or flight” response to hazardous conditions.

The anterior pituitary produces growth hormone, which is a peptide hormone. It boosts metabolism while also stimulating cell growth and reproduction. The anterior pituitary produces prolactin, a peptide hormone that increases milk supply during breastfeeding.

The antidiuretic hormone (ADH) is a peptide hormone generated by the brain that controls how much water is reabsorbed by the kidneys.

Hormones Citations
  • The endocrine system: an overview. Alcohol Health Res World . 1998;22(3):153-64.
  • Hormones and Muscle Atrophy. Adv Exp Med Biol . 2018;1088:207-233.
  • The role of hormones in muscle hypertrophy. Phys Sportsmed . 2018 Feb;46(1):129-134.
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