- Hormones are the chemical substances which coordinate the activities of living organisms and also their growth.
- These hormones coordinate the activities of living organisms and also their growth.
Characteristics of hormones
1. The hormones are secreted in small amounts by the endocrine glands.
2. The hormones are poured directly into the blood and carried throughout the body by the blood circulatory system.
3. The hormones have their effect at the sites different from the sites where they are made. So, they are also called chemical messengers.
4. The hormones act on specific tissues or organs (called target organs).
5. The hormones coordinate the activities of the body and also its growth.
THE ENDOCRINE SYSTEM
- A gland is a structure which secretes a specific substance (or substances) in the body.
There are two types of glands in the body:
(i) exocrine glands, and
(ii) endocrine glands.
- A gland which secretes its product into a duct (or tube) is called an exocrine gland.
- For example, the salivary gland secretes the saliva into a duct called salivary duct, therefore, salivary gland is an exocrine gland.
A gland which does not have a duct and secretes its product directly into the bloodstream is called an endocrine gland.
- The endocrine system is composed of several endocrine glands.
- A ductless gland is called endocrine gland.
- Endocrine gland secretes its product directly into the bloodstream.
- Hormones are produced in the endocrine glands.
- Hormone is mainly composed of protein.
- Hormones assist the nervous system in control and coordination.
- Nerves do not reach to every nook and corner of the body and hence hormones are needed to affect control and coordination in those parts.
- Moreover, unlike nervous control; hormonal control is somewhat slower.
Endocrine glands present in our body
- Different types of endocrine glands present in our body are the pituitary gland, the pineal gland, the hypothalamus, the thyroid, the parathyroid, the thymus, the adrenal gland, the pancreas, the testes and the ovary.
THE PITUITARY GLAND
- It is a pea-shaped gland located at the base of the brain.
- lt is considered to be a master gland as it secretes many hormones to regulate the organs as well as the other glands.
- Different hormones secreted by this gland include Growth hormone, TSH, FSH,LH, ACTH, MSH, Vasopressin and Oxytocin.
- It is a neuro-endocrine part of the brain.
- It links the nervous system and the endocrine system through the pituitary gland.
- Different hormones secreted by this gland include TRH, GnRH, GHRH, Somatostatin, Dopamine.
THE THYROID GLAND
- It is located in the neck, ventral to the larynx
- It is the one of the largest endocrine glands.
- The principal hormones produced by this gland are triiodothyronine and thyroxine.
- Thyroxine is a hormone that regulates the metabolism of carbohydrates, proteins and fats in the body.
- Hyposecretion of thyroxine leads to creatinine in children, and myxoedema in adults.
- Hypersecretion of thyroxine leads to exophthalmic goitre in adults.
- Goitre is caused due to deficiency of iodine in food.
- lodine is essential for the synthesis of thyroxine.
- These are two pairs of small, oval-shaped glands embedded on the dorsal surface of the thyroid gland present in the neck.
- They secrete parathormone.
- Parathormone helps in regulation of calcium and phosphate ions in the bones and blood.
- Hyposecretion leads to parathyroid tetany and hypersecretion causes osteoporosis.
THE ADRENAL GLANDS
- These are located above the kidneys and hence are called suprarenal glands.
- Two regions of the adrenal gland are adrenal cortex and adrenal medulla.
- Adrenal cortex secretes hormones like cortisol, aldosterone and androgens.
- Adrenal medulla secretes the hormones like adrenaline and noradrenaline.
- Adrenaline is also called the “hormone of fight or flight,” or the emergency hormone.
- It prepares the body to face an emergency condition of physical stress, like danger, anger and excitement.
- It is located just below the stomach within the curve of the duodenum.
- It is both exocrine and endocrine in function.
- It secretes hormones such as insulin, glucagon, somatostatin and pancreatic polypeptide.
- Insulin regulates the sugar level in our blood. Insulin secreted in small amounts .
- increases the sugar level in our blood which in turn causes a disease called diabetes mellitus.
Two types of gonads present in human beings are female gonads and male gonads.
- A pair of ovaries forms the gonads in females.
- Ovaries are the female sex organs that lie one on either side of the abdominal cavity.
- Ovaries produce two hormones, namely, oestrogen and progesterone and development in mammary glands.
- Oestrogen controls the changes that occur during puberty, like feminine voice, soft skin.
- Progesterone controls the uterine changes in the menstrual cycle, and helps in the maintenance of pregnancy.
- A pair of testes forms the gonads in males.
- A pair of testes is the male sex organ located in the scrotum, which is outside the abdomen.
- Testes produce the hormone testosterone.
- Testosterone controls the changes, which occur during puberty, like deeper voice, development of penis, facial and body hair.
THE PINEAL GLAND
- It is located near the centre of the brain, dorsal to the diencephalon
- It produces the hormone melatonin.
- Melatonin affects reproductive development, modulation of wake and sleep patterns and seasonal functions.
The thymus gland:
- It is located in front of the heart, in the upper part of the sternum.
- It produces the hormone thymosin.
- It helps in the maturation of T-lymphocytes.