Written By Priyanka Srivastava
Last Modified 25-01-2023

Hormones in Humans: Classification, Characteristics & Functions

Hormones in Humans are of different types and categorised differently. Control and coordination are very important for the normal functioning of the body. For this, two types of systems have been developed in our body, i.e., the nervous system and the endocrine system.

Our nervous control is very fast, but its action is short-lived, and nerve fibres of this system cannot innervate all over the body cells. But regulation of cellular function is needed continuously, so a separate special system called the endocrine system developed, which secretes chemical messengers called hormones. Hormones in Humans are needed in very small quantities to carry out physiological processes. In this article, we will learn more about Hormones.

What is Hormone?

“Hormone” literally means to stimulate (Gr. Hormoein = to excite). But now we know that a hormone can stimulate or inhibit any action of any organ. Hormones are chemical substances secreted by the endocrine glands, carried by the blood to another part of the body that regulate the biological processes in the organisms.

Hormone- Discovery

Secretin is the first hormone discovered by two English physiologists, William M. Bayliss and Ernest H. Starling, in \(1903\). The term “hormone” was coined by Starling in \(1905\).

Transport of Hormones

Hormones are released by endocrine cells into the extracellular fluid, which then diffuses into the bloodstream. This blood carries the hormones to the site of action. Target organs have receptors of their specific hormone, either on the cell membrane or inside the cell, to which specific hormone binds after recognition and are capable of acting in that cell. These receptors are absent in the non-target cell.

Classification of Hormones

Hormones can be classified into \(3\) groups on the basis of their chemical nature-
1. Amino acid derivatives– Some hormones are derived from amino acids like epinephrine, and norepinephrine hormones are derived from tyrosine amino acids.
2. Peptides (short and long peptides)– Some hormones are made of short and long peptides. Like oxytocin and vasopressin are short peptides, while glucagon is long peptides. Proteins (polypeptides)– Gonadotropic, insulin and somatotropic hormones are made of polypeptide chains of proteins. Relaxin from the ovary and placenta and hCG from the placenta are peptide hormones.
3. Steroids– Some hormones are synthesized from cholesterol and are called steroids. Hormones from the adrenal cortex, testes, ovaries (estrogen and progesterone) and placenta (progestogens and estrogens) are steroids.

Characteristics of Hormones

1. Hormones are the chemicals secreted by living cells.
2. They are carried by the blood to the target organs.
3. They are secreted in low quantities.
4. Effective in low concentration.
5. Act away from the site of production.
6. Can regulate specific physiological processes.
7. Some hormones are secreted in inactive forms like that of insulin, secreted as proinsulin.
8. Slow in action.

Difference between Hormones and Enzymes

Hormones	Enzymes
a. Have low molecular weight.	a. Have very high molecular weight.
b. Maybe amino acid derivatives, peptides, proteins, or steroids in nature.	b. These are complex proteins except ribozyme which is nucleic acid in nature.
c. Secreted at one site and transported via the blood to the target organs.	c. Secreted at one site and passed via a duct to the site of action.
d. They are often used up in their regulatory activities.	d. They remain unaffected in the reaction they catalyze.
e. Their mode of action is slow.	e. Their mode of action is fast.
f. It accelerates or inhibits any physiological processes.	f. Speed up any biochemical reaction.

Hormones in Humans

Endocrine glands secrete different hormones. In the following table, different hormones with their source and function are tabulated below:

Hormone	Source	Function
Releasing hormones	Hypothalamus	Stimulate pituitary activity
Follicle-Stimulating Hormone (FSH)	Anterior Pituitary (Pars distalis)	Male: It stimulates sperm formation. Female: It stimulates the growth of follicles in the ovaries
LH (Luteinizing Hormone)	Anterior Pituitary (Pars distalis)	Male: Stimulates testes to produce testosterone. It is also called ICSH in males. Female: Causes ovulation, development of corpus luteum.
TSH (Thyroid Stimulating Hormone)	Anterior Pituitary (Pars distalis)	Responsible for thyroid growth and production of thyroid hormones.
Adrenocorticotropic hormone (ACTH)	Anterior Pituitary (Pars distalis)	Helps in secretion of glucocorticoid and mineralocorticoid hormones
Somatotrophic or Growth Hormone	Anterior Pituitary (Pars distalis)	Growth of body by acting on the epiphyseal plates, division of chondrocytes of cartilage, production of IGF-1
Prolactin	Anterior Pituitary (Pars distalis)	Stimulates formation of milk in mammary alveoli and hence called lactating hormone.
MSH (Melanocyte Stimulating Hormone)	Intermediate lobe of Pituitary (Pars intermedia)	Stimulates melanin secretion from melanocyte
Oxytocin	Formed in the hypothalamus but stored and secreted from the posterior pituitary	Induces contraction of smooth muscles of the uterus. Also called “birth hormone”.
Vasopressin (ADH)	Formed in the hypothalamus but stored and secreted from the posterior pituitary	Regulates urine production
Melatonin	Pineal (Epiphysis)	Associated with the sleep-wake cycle, makes skin colour lighter, and regulates working of gonads.
Thyroxine (T₄) and Triiodothyronine (T₃)	Thyroid gland	Regulates metabolism, growth and development.
Calcitonin (TCT or thyrocalcitonin)	Thyroid gland	Hypocalcemic effect and mineralisation of bones.
Parathormone (PTH)	Parathyroid Gland	Hypercalcemic effect and demineralisation of bones.
Thymosin	Thymus	Stimulates development of T- lymphocytes.
Aldosterone (Mineralocorticoids)	Adrenal cortex (Zona glomerulosa region)	Regulates mineral metabolism and controls sodium and potassium ratio, maintains water and electrolyte balance and blood volume in the body
Glucocorticoids	Adrenal cortex (Zona fasciculata region)	Regulate metabolism of carbohydrates, proteins and fats, and increase the blood sugar level. Cortisol has an antiinflammatory effect also.
Sexocorticoids	Adrenal cortex (Zona reticularis region)	Development of gonads
Epinephrine and Norepinephrine	Adrenal medulla	Fight or Flight response
Renin	Kidney	Converts inactive plasma protein, angiotensinogen to angiotensin
Atrial Natriuretic Factor (Atrial Natriuretic Peptide)	Wall of cardiac atria	Decrease blood pressure, vasodilation and inhibition of renin.
Insulin	Pancreas (Beta cells of Islets of Langerhans)	Stimulate glycogenesis, and enables the tissues to take up and use glucose as a source of energy i.e. reduces blood sugar level (Hypoglycemic effect)
Glucagon	Pancreas (Alpha cells of Islets of Langerhans)	Hyperglycemic effect
Pancreatic somatostatin	Pancreas (Delta cells of Islets of Langerhans)	Inhibits insulin and glucagon secretion
Hypothalamic somatostatin	Hypothalamus	Inhibits secretion Growth hormone (GH)
Testosterone	Testes	Promotes development of sperm and secondary sexual characters in males
Estrogen	Ovaries (Theca interna of Graffian follicle)	Promote the growth of uterine lining and secondary sexual characters in female
Progesterone	Ovaries (Corpus luteum)	Maintains pregnancy by thickening of the endometrial lining and inhibiting GnRH

Fig: Hormones of Pituitary gland

Fig: Thyroid hormones- T₃ and T₄

Hormones in Humans- Associated Disorders

Hormone	Hyposecretion	Hypersecretion
Growth Hormone	Dwarfism	Acromegaly or Gigantism
Thyroid Hormone	Cretinism (children) Myxedema (adults)	Graves’ disease (Hyperthyroidism)
Antidiuretic Hormone (ADH)	Diabetes insipidus	Syndrome of inappropriate ADH
Parathormone	Hypoparathyroidism (Tetany)	Hyperparathyroidism (Hypercalcemia)
Glucocorticoids	Addison’s disease	Cushing’s syndrome
Insulin	Diabetes mellitus	Hypoglycemia
Sexocorticoids	–	Adrenal virilism

Summary

From the above discussion, we came to know about different hormones, their source, function and related disorders. Hormones are the chemical messengers that regulate the biological processes in organisms. Hormones are secreted by the endocrine glands. It is transported to distant organs with the help of blood to regulate physiology and behaviour. The hormone is needed in a very small amount for different physiological processes.
Hormones help in the metabolism of carbohydrates, fats and protein for proper growth and development of the body. Hormones depending on their chemical nature can be steroids, peptides or proteins and amino-derived in nature.

FAQs

Q.1. What are the examples of hormones?
Ans: Examples of Hormones are as follows:
i. Growth hormone
ii. Thyroxine
iii. Melatonin
iv. FSH
v. Melatonin
vi. Parathormone
vii. Antidiuretic hormone
viii. Aldosterone
ix. Epinephrine and Norepinephrine
x. Thymosin
xi. Testosterone
xii. Estrogen
xiii. Progesterone

Q.2. What is a hormone in biology?
Ans: Hormones are chemical substances secreted by the endocrine glands, carried by the blood to another part of the body that regulate the biological processes in the organisms.

Q.3. What is the growth hormone in Humans?
Ans: Growth hormone is the hormone secreted by the anterior pituitary which is responsible for the growth and development of the body.

Q.4. What are the functions of hormones?
Ans: Some of the functions of hormones are:
i. Hormones stimulate or inhibit the growth of the body.
ii. Regulates sleep cycle.
iii. Regulates metabolism of the body.
iv. Activates the immune system.
v. Prepares the body for new phases of life, like puberty.
vi. Develops reproductive system.

Q.5. What are the female hormones?
Ans: Female hormones are estrogen and progesterone, which are secreted from ovaries.

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