Hypophysis or the pituitary gland of human is small pea-shaped gland weighing about 0.5 gm which makes up 80 percent of the gland’s overall weight. It is located under the brain, just behind the bridge of the nose between the hypothalamus and the pineal gland. It is enclosed within a small bony cavity, the sella turcica, of the sphenoid bone. A small stalk known as pituitary stalk attaches the pituitary with the hypothalamus. It is also known as the master gland because it regulates the secretion of many other endocrine glands. It collects messages from the brain (hypothalamus) which influences all the other hormone-producing glands to produce their own hormones. Hence, it is often referred to as the ‘master gland’.
Hypophysis or the pituitary gland consists of the following two parts:
- Anterior Lobe or Adenohypophysis and
- Posterior Lobe or Neurohypophysis
Anterior Lobe or Adenohypophysis: It is the glandular part which develops from the bud of the embryonic mouth epithelium. It has three parts such as (i) Anteriorly the parsdistalis (ii) Medially the pars intermedia and (iii) superiorly the pars tuberalis.
The pars distalis and pars tuberralis are collectively known as the anterior lobe. They constitute about 80% of the gland. Pars intermedia lies between the pars distalis and the pars tuberalis which is absent in certain mammals such as whale, Asian Elephant, and Armadillo, and it is rudimentary in the human but in other species, it is more developed. It is originated from a depression in the dorsal wall of the pharynx of the alimentary canal. The pars tubaralis has no endocrine functions. Pars distalis is the only functionally active part of the anterior pituitary gland.
Histologically, pars distalis consists of non-secretory agranulated chromophobe cells (50%) and secretory granulated chromophil cells (50%). Chromophil cells are of two types such as eosinophils or α-cells (15%) and basophils or β–cells (35%). The α-cells secrete somatotrophic hormone (STH) and prolactin whereas the β–cells secrete Thyroid stimulating hormone (TSH), Adrenocorticotrophic hormone (ACTH), Luteinizing hormone (LH)and Follicle stimulating hormone (FSH). The pars intermedia is composed of polygonal cells which secrets Melanophore stimulating hormone (MSH).
Location of Hypophysis or pituitary and its different parts
The anterior pituitary consists of different types of cells which synthesize and produce hormones. Among them at least 5 types of cells can be differentiated. The following table shows the anterior pituitary hormones and their functions.
| Name of the cell and their Percentage (%) | Produced Hormones | Functions |
|---|---|---|
| Somatotropes (30-40%) |
Human Growth Hormone (hGH) Or Somatotropic Hormone (STH) |
|
| Thyrotropes (3–5%) | Thyroid Stimulating Hormone (TSH) |
|
| Corticotropes (20%) | Adreno Corticotrophic Hormone (ACTH) |
|
| Gonadotropes (3–5%) | Gonadotropic Hormone: Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) |
|
| Lactotropes (3–5%) | Prolactin |
|
| Melanocyte | Melanocyte Stimulating Hormone (MSH)/melanotropins or intermedins |
|
Posterior Lobe or Neurohypophysis: It is the neural part which develops from the base of the brain and remains connected with each other. It consists of (i) pars nervosa – the chief part (ii) Median eminence-the upper expanded part of neural stalk and (iii) Infundibular stem. Anatomically, the pars nervosa and pars intermedia are together known as posterior lobe of the pituitary gland.
Histologically, three parts of the neurohypophysis are composed of similar tissues. They consists of (i) numerous unmyelinated nerve fibers (ii) pituicyte- the branched cells (iii) nerve cells of different types, (iv) mast cells (v) blood vessels and (vi) hyaline bodies.
Hormones of Posterior Pituitary
The posterior pituitary gland releases two specific hormones which are collectively known as neuro-hormones. The name of posterior pituitary hormones, sources, nature and their functions are stated below:
Hormone 1: Vesopressin or ADH (antidiuretic hormones) or arginine vasopressin ( AVP)
Sources: It releases from the supraoptic nucleus in the hypothalamus.
Nature: Protein in nature and contains nine essential amino acids.
Functions:
- It increases re-absorption of water from the renal tubules and decreases the volume of excretory urine (antidiuresis) with small dose.
- It causes diabetes insipidus due to lack of vasopressin.
- It stimulates and contracts all the voluntary muscles in the body.
- It also stimulates plain muscles of urinary bladder, ureter, intestine, uterus, etc.
- It raises the blood pressure by causing arteriolar and capillary constriction.
You might also read: ADH V Aldosterone: Definition, Functions and Differences
Hormone 2: Oxytocin
Sources: It releases from the paraventricular nucleus in the hypothalamus.
Nature: Protein in nature and contains nine amino acids.
Functions
- It enhances during the late period or pregnancy.
- It contracts pregnant uterus and also helps in parturition.
- It also contracts lactating mammary gland of breast.
- It helps in ejection of accumulated milk in the gland`s alveoli with small dose.
- It helps in transport of sperm in the genital tract.
Pituitary Hormones and their Target Organs
| Hormone | Target Organ or Tissue |
|---|---|
| Adrenocorticotropic hormone( ACTH) | Adrenal glands |
| Melanocyte stimulating hormone (MSH) | Skin |
| Follicle-stimulating hormone FSH) | Ovaries or testes |
| Growth hormone (GH) | Muscles and bones |
| Luteinizing hormone (LH) | Ovaries or testes |
| Oxytocin | Uterus and mammary glands |
| Prolactin | Mammary glands |
| Thyroid-stimulating hormone (TSH) | Thyroid gland |
| Vasopressin (antidiuretic hormone or ADH) | Kidneys |
Hypophysis or Pituitary Disorder
In many cases, cerebrospinal fluid can fill the space around the pituitary gland and makes the space compact resulting in empty sella syndrome. In this case, hypophysis or the pituitary gland produces too much or too little hormones. Too little or too much hormone can cause wide variety of symptoms.
|
Overproduction Disorders | Hormones |
|---|---|
| Acromegaly or gigantism | Growth hormone |
| Galactorrhea | Prolactin |
| Erectile dysfunction | Prolactin |
| Underproduction Disorders | . |
| Central diabates insipidus | Vasopressin |
| Hypopituitarism | Multiple hormones |
Concluding Remarks
Hypophysis or the pituitary gland is an extremely important endocrine gland, which maintains the overall functions of the endocrine system and ultimately it maintains your overall health. It works with the hypothalamus and makes sure the body`s internal processes work correctly.