The endocrine glands in human body are: pituitary gland, pineal gland, thyroid gland, parathyroid gland, thymus gland, islets of Langerhans, adrenal gland, ovary and testis.
1. Pituitary Gland:
It is a small gland which weighs 500 mg. It hangs from a part of the forebrain, diencephalon. There is an area in the diencephalon, called the hypothalamus. Pituitary gland hangs from this area of the brain by means of a stalk called infundibulum. Three different areas can be recognized in the pituitary gland, if its section is examined under the microscope.
The anterior part is called adenohypophysis. “Six different hormones are secreted from this part. They are:
Growth hormone (CG):
It promotes the growth of the body during early life when the animal is growing. It influences the growth of long bones and muscles. Excess secretion of this hormone during this period will lead to gigantism, which means an abnormal condition of overgrowth. On the other hands, less secretion of growth hormone will stunt or retard the growth leading to dwarfism, which is an abnormal condition of undergrowth. In adults, growth hormone production is stopped. If for any reason growth hormone production starts for the second time, it will not promote growth any more. But it will increase the thickness of lower jaw, hands and feet giving a gorilla-like appearance. This appearance is known as acromegaly. Growth hormone production is increased by exercise, fasting and sleep.
Thyroid stimulating hormone (TSH):
Controls the growth and function of outer part of the adrenal gland, called adrenal cortex. Pituitary gland secretions control the activities of other endocrine glands. For this reason, pituitary gland is called master gland of the body.
Prolactin or Luteotrophic hormone (LTH):
It controls the secretion of milk in the mammary gland. In the male, prolactin hormone brings about a change in behavior with the result that the male beings to pay attention to the care of the eggs or the young. This is called parental care.
Follicular stimulating hormone (FSH):
It is a gonadotrophic hormone in that it influences the gonad. Gonad in male is the testis and in the female is the ovary. In males, it goes to the testis and influences the somniferous tubules, finally leading to increase production of sperms. In the female, FSH goes to the ovary and causes the ovum to mature [see reproductive system in human (woman)].
Luteinizing hormone (LH)
It is also a gonadotrophic hormone. In the male, it goes to the testis and inside the testis it influences the leydig cells to secrete testosterone hormone. The secretion of testosterone influences the development of secondary sexual characters. Secondary sexual characters are those which allow us to distinguish a male from a female in appearance. Beard in man may be taken as an example.
The middle part of pituitary gland is called pars intermedia. From this part, only one hormone is released. This is called melanocyte stimulating hormone (MSH). This hormone is effective in lower vertebrates (for example, frog) wherein it goes to the sink to influence a kind of cell, called chromatophore. It is pigment bearing call, which beings to expand due to the influence of MSH. As a result, there is a dispersion of pigment granules in the chromatophores and consequent darkening of the skin can be observed.
The posterior part of pituitary gland is termed neurohypophysis. From this part two hormones are released:
This hormone brings about contraction in the wall of the uterus at the time of birth of animal. When oxytocin sets the contraction of the uterine wall, this causes a kind of pain to the mother, termed labour pain.
This hormone is also called antidiuretic hormone (ADH). It influences the areas of nephron so that water may be reabsorbed and brought back to the blood. In this way, the volume of urine is reduced.
Pituitary gland is under the control of hypothalamus. The latter produces a number of release factor (RF). For each hormone of the pituitary gland, there is a release factor, which controls the release of the hormone into the blood.