ENDOCRINE GLANDS:

''In the body of vertebrates, there is a system of glands which are ductless and their secretion is directly poured into blood known as ENDOCRINE GLANDS. Their secretion is called as HORMONES.'' 

 HORMONES: 

A hormone is defined as;

''A special chemical substance which is poured by certain group of cell or organs, and are secreted directly into the blood and by its circulation they are carried to the place where they are required. ''
Hormones are also called as CHEMICAL MESSENGERS. 

FUNCTION: 

They are secreted in small amounts and help to co-ordinate processes such a metabolism, growth etc. Their influence in the body is often profound and long lasting.

IMPORTANT ENDOCRINE GLANDS:

1-PITUITARY GLANDS:

  • Pituitary glands are situated at the lower region of hypothalamus (in brain) and attached by a small structure.
  • Its size is like a pea-seed.
  • It is a very important gland, and directly influence other endocrine glands, it is therefore, said to be MASTER GLAND.

FUNCTIONS: 

Pituitary gland has two parts, which perform different function.

ANTERIOR LOBE:

  • They secrete number of hormones one of them is called GROWTH HORMONE.
  • This hormone controls the growth of bones and other tissues, thus it affect the size of the body.
  • Some other hormones secreted by this lobe helps to regulate other endocrine glands, such as thyroid, ovaries etc.

POSTERIOR LOBE:

This lobe produces two hormones, one of these hormones controls the excretion of urine by kidney and the other hormone causes contraction of smooth muscles in the urinary bladder.

2-THYROID GLANDS:

  • Thyroid glands are present in the lower region of neck, in front of trachea.
  • It is butterfly shaped, and consists of two lobes; one is located on each side of trachea.
  • It’s important hormone is THYROXIN.

FUNCTIONS:

  • Thyroxin affects many chemical reactions in the cells, and controls the rate of metabolic activities in cells that releases energy from nutrients.
  • This hormone is essential for normal growth and mental development especially in children.
  • In early age, failure of thyroid to produce its hormones can results in stunned growth and severe mental retardation, known as CRETINISM.

3- PARATHYROID GLANDS: (PTG)

  • These glands are small sized and two paired glands, located adjacent to the two lobes of the thyroid glands.
  • It secrets a hormone called PARATHORMONE.

FUNCTION:

  • It controls the amount of sugar in the blood and helps to increase re absorption of Calcium in kidney.
  • The PTH regulated the storage of minerals of mineral elements in bones and teeth.
  • It also controls the excretion of these substances from the body.
  • The over secretion of this hormone is also harmful as it produces stones in the kidney and causes rickets.

4- PANCREAS:

  • Pancreas is located in the abnormal cavity near the stomach. It is a gland which secrets hormones as well as enzymes.
  • In pancreas hormones are secreted by some cells called ISLETS OF LANGERHANS.
  • In islets of Langer Hans two types of cells are present, which are called Alfa cells and Beta cells and perform two functions.

FUNCTIONS:

  • ALPHA cells secrets GLYCOGEN hormone. It is produced when amount of glucose in blood is decreased. This hormone converts GLYCOGEN into GLUCOSE, to produce energy.
  • BETA cells produce INSULIN hormone. It is responsible to keep the amount balanced form in blood.
  • By the help of this hormone extra amount of glucose is converted into GLYCOGEN.
  • It stimulates liver and muscles tissues to receive and store glycogen.

5- ADRENAL GLAND:

  • Adrenal glands are two in number, each of which is present on the anterior end of a kidney.
  • Each adrenal gland consists of two parts, ADRENAL CORTEX (outer part) and ADRENAL MEDULLA (inner part).

FUNCTIONS:

  • ADRENAL CORTEX secrets number of hormones, which are collectively called CORTICOSTIROIDS.
  • They regulate amino acids and concentration of certain minerals elements in the blood and tissues of the body.
  • ADRENAL MEDULLA produces a hormone called ADRENALIN or EMERGENCY HORMONE.
  • They prepare the body to face a situation of emergency, e.g. at the situation of FIGHT or FLIGHT.

6- GONADS:

Gonads i.e. TESTES and OVERIES are important reproductive organs, but they also act as endocrine glands and productive hormone.

FUNCTIONS:

  • TESTES: Testes are male reproductive organs, and they secrete hormones, called ANDROGEN.
  • Testosterone is one of the important hormones of androgen, which is responsible for the development of secondary sexual characteristics, such as deepening of voice, appearance of moustaches and beard etc.
  • OVARIES: Ovaries are female reproductive organs, but they also act as endocrine gland, and secrete two hormones.
  • They hormones control the development of secondary sexual characters in female.
  • OESTROGENS are one of the two hormones, helps to develop and maintain the characters of female sex.
  • PROGESTERONE is another hormone, which helps in the implantation of ova, maintains pregnancy and also in the development of mammary glands.