The endocrine or the hormonal system
along with nervous system, run the body in a controlled and
coordinated manner. The main function of the endocrine system is the
production of secondary sexual characters, reproduction, and growth.
There are two types of
glands, Endocrine and Exocrine, that release substances called
secretions into or onto the body.
- Exocrine release their secretions along ducts into spaces within the body- such as salivary glands release saliva in mouth or sweat glands release sweat.
- Endocrine glands do not have
ducts and release their secretions, called hormones, directly
into the blood stream.
Functioning of Hormones:
- Hormones travel into the blood stream to deliver a chemical message to a specific target area where it has effect. Some target all the tissues whereas others have effect only on a particular tissue.
- The system works slowly and has a long lasting effect as compared to the nervous system, which uses electrical impulses that travel at high speed and has an immediate and short lasting effect.
- Pea sized, pituitary gland is located just below the brain and releases more than 8 hormones, many of which control other endocrine glands. However pituitary is controlled by hypothalamus.
- Growth hormone-
- Stimulates growth during childhood and adolescence.
- Thyroid stimulating hormone-
- Stimulates the release of thyroid hormone by thyroid gland.
- Adrenocorticosteroid hormone-
- Stimulates release of glucocorticoid hormones by adrenals.
- Follicle-stimulating hormone-
- Stimulates release of estrogen in ovaries, stimulates sperm production in testes and stimulates egg maturation in ovaries.
- Luteinizing hormone-
- Stimulates ovulation and progestrone production in ovaries and testosterone production in testes.
- Prolactin hormone-
- Stimulates milk production in mammary glands.
- Oxytocin-
- Stimulates uterus to contract in childbirth and mammary gland to release milk.
- Antidiuretic hormone (ADH) -
- Acts on kidneys to reduce volume of urine released.
- The butterfly shaped thyroid gland is present in front of the neck, on the trachea and just below the larynx. It releases three hormones; triiodothyroxine, thyroxine (together known as thyroid hormone), and calcitonin.
- Thyroid hormone is called the body's accelerator as it speeds up the metabolic rate. It also promotes growth during childhood and adolescence, and maintains the normal function of the heart and nervous system.
- Calcitonin, the third hormone, helps control the calcium levels of blood.
- Parathyroid glands are four in number, embedded in the posterior aspect of the thyroid gland. They release parathyroid hormone, which raises the calcium levels in the blood by breaking down the bones, by increasing the uptake of calcium from digested food, and by increasing the resorption of calcium into the blood via the kidneys.
- They are present on top of the kidneys, one on each side.
- They produce cortico-steroids, epinephrine(adrenaline) and, norepinephrine(noradrenaline).
- The latter two are helpful in "fight or flight" situations when there is crisis i.e. to stay or run in a crisis situation.
- Lies horizontally below the stomach, it has a head, neck and a tail.
- It is both an exocrine and an endocrine gland.
- 90% of it produces digestive juices and the remaining i.e. Islets of Langerhans, produces Glucagon and Insulin.
- These hormones ensure that a stable level of glucose in the blood by having an opposing effect.
- Two ovaries lie on either side of the uterus and are the primary female sex organs.
- They store the eggs (releases one mature ovum each month between puberty and menopause) and releases two sex hormones, estrogen and progesterone- that maintain the reproductive system and prepare the body for pregnancy when needed.
- Two, oval shaped, lie in the scrotum that hangs in between the legs.
- They are the primary sex organs for men and have two functions- manufacturing of sperms throughout the life from the age of fourteen, and release male sex hormone called Androgen