The pituitary gland is a round, pea-sized structure measuring about 1.3 cm in diameter. it lies in the brain, attached to the hypothalamus by a stalk-like structure called the infundibulum.
The pituitary gland is divided structurally and functionally into the anterior lobe and the posterior lobe. Between these lobes lie the intermediate lobe.
- Anterior lobe: It constitutes about 75% of the total weight of the gland. A system of blood vessels connects it with the hypothalamus.
- Hormones secreted by the anterior lobe control the activities of the thyroid (thyroid stimulating hormone-TSH), Adrenal glands (ACTH adreno cortic trophic hormone) and the gonads (follicle stimulating hormone-FSH and the luteinising hormone-LH). TSH, ACTH, FSH and LH are called trophic hormones as they stimulate other endocrine glands to secrete their hormones.
- It secretes hormones which stimulates general body growth, and especially influence bone growth. These hormones are known as human growth hormones (Hgh somatotropin).
- It plays an important role in the birth process by secreting prolactin that stimulates production of breast milk.
- Intermediate lobe: It is a small relatively avascular region which secretes hormones that stimulate the pigment forming cells(melanocyte) in the skin.
- Posterior lobe: It contains axon termination of neurons whose cell bodies are located in the hypothalamus. It stores and released two important hormones produced by the hypothalamus:
- Vasopressin (Antidiuretic hormone- ADH): An antidiuretic is any chemical substance that prevents excessive urine production. As such, vasopressin regulates the amount of water excreted in the urine. ADH can also raise blood pressure by bringing about constriction of arterioles.
- Oxytocin: It stimulates the contraction of the uterus during child birth and affects milk ejection (Milk letdown response.)