Pituitary Gland: Structure, Hormones, and Function
Pituitary Gland (पीयूषग्रन्थि)
The pituitary, or hypophysis cerebri, is a small, pea-sized gland that plays a major role in regulating vital body functions.
It is also called the “master gland” because it controls the activity of other hormone-secreting glands. The gland lies in the hypophyseal, or pituitary fossa, which is roofed by the diaphragma sellae.
The weight of the pituitary gland is about 500mg.
Relations
Superiorly, the pituitary gland is related to:
- Diaphragma sellae (a fold of dura mater)
- The optic chiasma
Inferiorly, the pituitary gland is related to:
- The hypophyseal fossa
- The sphenoidal air sinuses
Laterally, on the right and left side, the hypophysis cerebri is related to the corresponding cavernous sinus.
Anatomical Structure
The pituitary gland is a ‘2-in-1’ structure consisting of the anterior pituitary and posterior pituitary. These parts have different embryonic origins and functions.
Anterior Pituitary (Adenohypophysis)
It is further divided into three parts:
- Pars anterior: It is the largest part of the gland and responsible for hormone secretion.
- Pars intermedia: It is a thin epithelial layer that separates the anterior pituitary from the posterior pituitary.
- Pars tuberalis: It is an upwards extension of the pars anterior that surrounds the anterolateral aspect of the infundibulum. Because of the tubular shape of this extension, it is called the pars tuberalis.
Posterior Pituitary (Neurohypophysis)
It consists of nervous tissue and comprises three parts:
- Pars posterior: It is smaller than the pars anterior, contains numerous nerve fibers, and is directly continuous with the central core of the infundibulum.
- Infundibular stem: It contains neural connections of the posterior pituitary.
- Median eminence: It is continuous with the infundibulum.
Hormones Released by Different Parts of the Pituitary Gland
Anterior Pituitary
The anterior pituitary produces the following hormones and releases them into the bloodstream:
- Adrenocorticotropic hormone (ACTH)
- Growth hormone (GH)
- Luteinizing hormone (LH)
- Follicle-stimulating hormone (FSH)
- Prolactin, which stimulates milk production.
- Thyroid-stimulating hormone (TSH)
Posterior Pituitary
Two hormones are produced by the hypothalamus and then stored in the posterior pituitary before being secreted into the bloodstream. These are:
- Antidiuretic hormone (vasopressin): This hormone controls the reabsorption of water and controls water balance.
- Oxytocin: It controls the contraction of smooth muscle of the uterus (during labor) and of the mammary glands.
Intermediate Pituitary
It lies between the anterior and posterior pituitary and secretes melanocyte-stimulating hormone (MSH), which acts on the skin to stimulate the production of melanin.
Blood Supply
The hypophysis cerebri is supplied by the superior and inferior hypophyseal arteries (branches of the internal carotid artery).
Veins: Short veins emerge on the surface of the gland and drain into the dural venous sinus.
Clinical Anatomy
- Pituitary adenoma: A tumor of the pituitary gland.
- Gigantism and acromegaly: Conditions caused by the secretion of excess growth hormone in childhood and adulthood, respectively.
- Hypothyroidism: Caused by a deficiency of thyroid-stimulating hormone.
- Diabetes insipidus: A deficiency of antidiuretic hormone causes diabetes insipidus. In this disease, a large amount of urine is passed (polyuria), resulting in dehydration, leading to excessive thirst (polydipsia) and dryness of the skin.
- Cushing’s syndrome: A tumor in the anterior pituitary causes excessive secretion of adrenocorticotropic hormone (ACTH), resulting in abnormal deposition of fat over the face, neck, and trunk. The limbs remain thin and weak.