What are hormones?

Hormones are essentially chemicals that carry signals or messages from the organs to the body cells. Hormones are secreted by endocrine (ductless) glands which pour out their secretions directly into the bloodstream through which they reach the cells.

How do hormones act?

The body cells have certain receptors to which the specific hormone, meant for that body cell, binds itself.  This binding of the hormone is what causes alteration in the functioning of the cell.

The receptor may be located either on the surface of the cell (on the plasma membrane) or inside the cell (intracellular).

General effects of hormones

• Stimulation/Retardation of growth.
• Regulation of the Basal metabolic rate.
• Controlling the sugars/mineral content of the blood.
• Development of mood swings, tension, stress or excitement.
• Regulation of the whole reproductive cycle including the development of secondary sexual characters.
• Regulates the blood pressure and heart-beat.

Types of hormones

The two types of hormones in the body

¶ Steroids: These hormones are derived from lipids. They are responsible for the sexual maturation and all such processes concerned with reproduction and fertility. They are essentially produced form cholesterol (before birth) or gonads and adrenal glands (after birth).  The receptors for these type of hormones are usually located inside the cell. 

Example: Testosterone

¶ Peptides: These consist of a chain of amino acids. They are responsible for all the other activities in the body like regulation of sugar, fat metabolism, growth of the body, sleep, providing immunity etc. The receptors for these type of hormones are usually found on the plasma membrane of the cell.

Example: Insulin

Tropic hormones such as Thyroid Stimulating Hormone (TSH) are a group of hormones which control the production of hormones by other glands.

List of Hormones in the Human body

The glands, their location, the hormones secreted by them along with their hormonal effects are enumerated below:

THYROID GLAND

Location: Covering the trachea on either sides

Hormones: Thyroxine and triiodothironine

Effect: Influences the body metabolism.

PARATHYROID GLAND

Location: On the posterior surface of the thyroid gland

Hormones: Parathormone

Effect: Regulates calcium level in the blood.

ADRENAL GLANDS

Location: Top of each kidney

Hormones:

• Aldosterone, Cortisone, Androgens and Estrogens (by the adrenal cortex)
• Adrenalin and Noradrenalin (by the adrenal medulla)

Effects:

-Regulate minerals like sodium and potassium in the bloodstream

-Maintain the sugars and fats in the blood

-Preserves the secondary sexual characteristics in males and females

-Increases the cardiac rate and the release of glucose into the blood in times of excitement

PANCREAS

Location: Posterior to the stomach.

Hormones: Insulin, Glucagon

Effect:  Controls the metabolism of sugars in the cells as needed by the conversion of the blood glucose to glycogen and vice versa.

GONADS (ovaries in female and testes in male)

Location: Abdominal region

Hormones: Estradiol and Progesterone (by ovaries in females) testosterone (by testes in males)

Effects: Development of secondary sexual characteristics

PITUITARY GLAND

Location: Base of the brain

Hormones & Effects:

♦ Somatotropin: Growth of bone tissue

♦ Thyroid Stimulating hormone(TSH): Stimulates the growth of thyroid gland and its secretion

♦ Adrenocorticotropic hormone(ACTH): Stimulates the growth of adrenal gland and its secretion

♦ Follicle-stimulating hormone(FSH) Aids in production of sperms(in males) and eggs( in females).

♦ Luteinising hormone(LH) : Aids in production of testosterone(in males) and progesterone (in females)

♦ Prolactin: Stimulates milk production after birth.

♦ Melanocyte-stimulating hormone: Controls the production of melanin

♦ Oxytocin: Initiates uterine contractions during childbirth.

♦ Vasopressin: Stimulates reabsorption of water by the kidney.

The gastrointestinal tract and the kidneys, though not treated as glands, produce hormones-erythropoietin, gastrin, secretin and cholcystokinin. Erythropoietin helps in production of RBCs while the other hormones aid in the digestion process.

Hormones secreted during pregnancy

Some hormones are secreted exclusively at the time of pregnancy in females. Most of these hormones are produced by the placenta. They are:

-- Progesterone and estradiol, in extra amounts for the maintenance of the uterine lining during pregnancy.

-- Relaxin for expansion of the pelvic muscles and the development of mammary glands.

-- Somatomammotropin for increasing the nutrition level in the maternal blood

-- Human Chorionic Gonadotropin (hCG) for nourishing the foetus.