Classification of hormones

Classification of hormones

Classification of hormones is based on chemical nature, Based on Physiological Functions. these are detailed described below-

Classification of hormone based on chemical nature-

Peptides and proteins Hormones

Peptides and proteins consist of chains of amino acids. Examples of small peptide hormones are TRH and vasopressin . Peptides composed of numerous amino acids are referred to as proteins . Examples of protein hormones include insulin and growth hormone. More complex protein hormones bear carbohydrate side chains and are called glycoprotein hormones(e.g) LH, FSH and TSH.

Steroid Hormones

Steroids are derived from cholesterol and contains basic cyclopentano perhydro phenantherene nucleus. (e.g) Estrogen, progesterone, cortisol. Being non-polar, they are able to pass through the phospho-lipid membrane of a cell and enter the cytoplasm.

Amines Hormones

Amines are derivatives of the amino acids tyrosine and tryptophan . (e.g) epinephrine, norepinephrine.

Iodinated Amino-acid Hormones

Iodinated amino acids – (e.g) Thyroxine

Fatty Acid Derivative Hormones

Fatty acids derivatives are Eicosanoids – they are a large group of molecules derived from Arachadonic acid. The principal groups of hormones of this class are prostaglandins, prostacyclins, leukotrienes and thromboxanes. These hormones are rapidly inactivated by being metabolized, and are typically active for only a few seconds.

Classification of hormones based on Physiological functions-

Hormones Regulating Energy Metabolism-

Insulin, Glucagon, Glucocorticoids, Epinephrine, ACTH, Thyroid hormone

Hormones Regulating Mineral Metabolism-

Aldosterone, Renin‑Angiotensin II & Natriuretic hormone, PTH, CT , Vitamin D3

Hormones Regulating Growth-

GH, Insulin, Estrogen, Androgen,  Somatostatin, Thyroxine and Cortisol

Hormones Regulating Reproduction-

GnRH, FSH, LH /ICSH, Estrogen, Inhibin Progestrone, Testosterone, Oxytocin, Prostaglandins and Relaxin, GnIH, Thyroxin, Cortisol, Prolactin and Gonadocrnin 

Hormones Regulating Milk Secretion-

Estrogen, Prolactin, TSH, ACTH, GH, Glucocorticoid, Placental Lactogen, Thyroxin, Insulin and Oxytocin 

Hormones Regulating Blood Pressure-

Renin‑Angiotensin, Epinephrine, Norepinephrine, Vasopressin, ACTH , Vasotocin, ADH and ANP

Hormones Regulating Water Balance-

Vasopressin (ADH), Renin‑Angiotensin, Glucocorticoids & Insulin

Local Hormones-

PGs, Histamine, Serotonin

Gut Hormones-

Gastrin, Secretin, CCK, Motilin, Bombesin Somatostatin, Gastric inhibitory peptide (GIP), Vasoactive intestinal Polypeptide & Substance P

Some Detailed explanation of Classification of hormones in animals-

Peptide hormone

Most hormones are peptide in nature and are composed of aminoacids. Like other proteins, they are synthesized on ribosomes where their specific aminoacids sequence is determined (translated) by a specific messenger RNA sequence. The nucleotide sequences of the mRNA are transcribed from specific nucleotide sequences in the DNA. The proteins are then released and transported into the rough endoplasmic reticulum. The initial protein formed is larger than the active hormone and is called preprohormone.

In the interior of RER, pre portion of the hormone is cleaved to form prohormone. This in turn transported in the transport vesicles to the golgi bodies where they may be altered (e.g) sulphated or combined with carbohydrate moieties and the hormone is in its final form within the Golgi apparatus.

Vesicles containing the hormone and possibly other products (proteolytic enzymes) are then pinched off the terminal cisternae of golgi bodies. These secretory vesicles are distributed within the cytoplasm. Protein hormones are stored within the gland until needed for release. Although some of the hormones are secreted continuously, most are excreted by a process of exocytosis of granules in response to specific signals. Exocytosis requires ATP and Ca²⁺

Steroid hormones

Steroid hormones are synthesized within the smooth endoplasmic reticulum. Steroid secreting cells contain large amounts of smooth endoplasmic reticulum within them. However, a complex multiple enzyme system is required for the synthesis of steroids. These enzymes are present within the mitochondria as well as the cytoplasm.

Majority of the steroids is formed from cholesterol, which is synthesized by the liver. Cho­lesterol is either utilized immediately for steroid synthesis or stored in granules in ester form within the cells.

The first step in the synthesis of all steroid hormones from cholesterol involves cleavage of side chain of cholesterol to form pregnenolone, which occurs within the mitochondria. Subsequent­ly modification of the steroid molecules may occur within the mito­chondrion (or) may involve the endoplasmic reticulum of the cell. The type of steroid hormone that is eventually synthesized depends upon the specific enzymes within the particular cell type.

There is no provision for storage of steroid hormones within the cells. On appropriate stimulation, enzymes in the steroid secreting cells can within minutes cause the necessary chemical conversions to the final hormone. They are secreted immediately after formation by simple diffusion across the cell membrane because of their lipophil­ic nature

Thyroid hormones

Thyroid hormone is a iodinated hormones which synthesized on a proteinaceous substrate (thyroglobulin) located extra cellularly, by iodination of tyrosine.

They are then taken up by endocytosis and transported through the follicular cells of the thyroid gland where they are enzymatically released from the carrier protein prior to secretion.