Here we are providing the short notes on Biology which will be help to crack science part in may examinations like SSC, Railway and other competitive exams



The endocrine system is a collection of glands that secrete chemical messages we call hormones. These signals are passed through the blood to arrive at a target organ, which has cells possessing the appropriate receptor.

Exocrine glands (not part of the endocrine system) secrete products that are passed outside the body. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands.

Hormones are grouped into three classes based on their structure:

  1. steroids 2. Peptides 3. amines


The Nervous and Endocrine Systems

The pituitary gland (often called the master gland) is located in a small bony cavity at the base

of the brain. A stalk links the pituitary to the hypothalamus, which controls release of pituitary hormones. The pituitary gland has two lobes: the anterior and posterior lobes.

Too little or two much GH(Growth hormone) can cause dwarfism or gigantism, respectively.

Prolactin is secreted near the end of pregnancy and prepares the breasts for milk production.



ADH(Antidiuretic hormone) controls water balance in the body and blood pressure. Oxytocin is a small peptide hormone that stimulates uterine contractions during childbirth.

Thyroid secretion is usually higher in winter than in summer.

Endocrines: The Postal System of Communication and Co-Ordination

  • Hormones are chemical substances manufactured by organs called endocrine glands or ductless glands. Ductless glands are also sometimes called ‘exocrine glands’.




Adrenal gland

The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline.

They are found above the kidneys.



The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions.

Function:  link the nervous system to the endocrine system via the pituitary gland.


Pituitary gland

It is an endocrine gland about the size of a pea and weighing 0.5 grams in humans.

Hormones secreted from the pituitary gland help control:

  • growth,
  • blood pressure,
  • certain functions of the sex organs,
  • metabolism,
  • pregnancy,
  • childbirth,
  • nursing,
  • water/salt concentration,
  • temperature regulation
  • pain relief.



The thyroid gland, or simply the thyroid is one of the largest endocrine glands in the body.

It is found in the interior neck, below the Adam’s apple.

  • It secretes two hormones: triodothyro (T3) and tetraiodothysonine (T4), are called tyrosine. Both these hormones contain iodine.
  • Hypothyroidism (hypo, ‘under’)–diminished thyroid activity. Hypothyroi-dism in childhood gives rise to a conditions called cretinism.


It controls

  • rate of use of energy sources, protein synthesis,  controls the body’s sensitivity to other hormones.

Goiter– is called enlargement of the thyroid gland. It manifests itself as a swelling in the neck.

A goiter may be associated with increased, normal or descreased activity of the thyroid gland.

Government of India launched the Universal salt iodisation programme in 1986.



The pancreas is a glandular organ in the digestive system and endocrine system of vertebrates.

In humans, it is located in the abdominal cavity behind the stomach.


It produce several important hormones

  • including insulin,
  • glucagon,
  • somatostatin, and
  • pancreatic polypeptide which circulate in the blood.


The pancreas is also a digestive organ, secreting pancreatic juice containing digestive enzymes that assist digestion and absorption of nutrients in the small intestine. These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.


Reduction on the quantity of effective insulin gives rise to diabetes mellitus (diabetes, siphon, mellitus of honey) commonly called simply diabetes.


Saliva: Tylene, Maltase

Gastric Juice: Pepsin, Renin

Pancreatic Juice: Trypsin, Amylase, Lipase

Intestinal Juice: Erepsin, Maltase, Lactase, Sucrase, Lipase


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