Pituitary Gland – Class 11 | Chapter – 22 | Biology Short Notes Series PDF

Pituitary Gland: The hypophysis, or pituitary gland, is a pea-sized endocrine gland located at the base of our brain. Because it generates some of the body’s most vital hormones, it’s known as the “Master Gland.” It is located in the Pituitary Fossa, a bony structure directly below the hypothalamus and near to the optic nerve. The lobes of the pituitary gland are separated into three sections:

  • Anterior pituitary
  • Intermediate pituitary (Absent in adult human beings)
  • Posterior pituitary

Pituitary Gland Anatomy

The pituitary gland is a ductless endocrine gland that secretes hormones into the bloodstream directly. The pituitary gland’s position on the underside of the brain is referred to as hypophysis (from the Greek meaning “lying under”). Because its hormones regulate other important endocrine glands, such as the adrenal, thyroid, and reproductive glands (e.g., ovaries and testes), and in some cases have direct regulatory effects in major tissues, such as those of the musculoskeletal system, the pituitary gland is known as the “master gland.”

Hormones of Pituitary Gland

The anterior and posterior halves of a healthy adult human’s pituitary gland are separated. During pregnancy, the Intermediate Pituitary regresses, and in adult humans, it is absent. Hormones have the following major functions:

Anterior Pituitary Hormones

The anterior pituitary hormones are proteins made up of one or two long polypeptide chains. TSH, LH, and FSH are classified as glycoproteins because they contain glycosides, which are complex carbohydrates. Each of the three hormones is made up of two glycopeptide chains, one of which, the alpha chain, is the same in all three. 

The other chain, the beta chain, has a different structure for each hormone, which explains why TSH, LH, and FSH have varied activities. The anterior pituitary hormones, like all protein hormones, are produced as giant inactive molecules termed prohormones in the cytoplasm of the cells. These prohormones are kept in granules, where they are split into active hormones and released into the bloodstream.

Anterior Pituitary Hormone

Peptides produced from the hypothalamic’s median eminence neurons into the hypophyseal-portal veins, which travel a short distance to the pituitary microvasculature, control the generation and secretion of each of the major anterior pituitary hormones. 

Thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone, gonadotropin-releasing hormone, and growth-hormone-releasing hormone are some of the peptides involved. Dopamine and somatostatin, which are powerful inhibitors of prolactin and GH, are also produced in the hypothalamus.

Pituitary-hormone signalling is complicated by feedback loops involving pituitary hormones and their target glands. Thyroid hormone, for example, suppresses TRH secretion while simultaneously inhibiting TRH’s action on thyrotrophs. Negative feedback loops like these aid in maintaining a healthy equilibrium between pituitary hormone release and hormone secretion by pituitary target glands. Physiological disturbances, such as stress’s impact on the pituitary-adrenal axis and neuroendocrine cycles, can upset this equilibrium. The anterior pituitary is in charge of producing and secreting various important hormones in the body. The following hormones are among them:

Human Growth Hormone (HGH): This hormone is in charge of the body’s cell growth and repair.

Thyroid Stimulating Hormone (TSH): Inspires the thyroid gland to produce its own hormone, thyroxine. Thyrotropin is another name for TSH.

Adrenocorticotropic Hormone (ACTH): Induces the release of Cortisol, also known as the “stress hormone,” by the adrenal gland. Corticotropin is another name for ACTH.

Luteinising Hormone (LH) and Follicle-Stimulating Hormone (FSH): Luteinising Hormone (LH) and Follicle-Stimulating Hormone (FSH) are two hormones that control male and female sexual and reproductive characteristics.

Prolactin (PRL) is a hormone that causes the breasts to produce milk. Though it is present at all times, it secretes more during PREGNANCY

Posterior Pituitary Hormones

Vasopressin (antidiuretic hormone) and oxytocin are two important neurohypophyseal hormones that are produced and integrated into neurosecretory granules in the nuclei’s cell bodies. Those hormones are made up of a precursor protein that also contains one of the hormones and a protein called neurophysin. 

The precursor protein is broken after synthesis and inclusion into neurosecretory granules, resulting in distinct hormone and neurophysin molecules that are loosely connected to one another. The granules are transported via the axons and stored in the pituitary gland’s posterior lobe.

The granules fuse with the cell wall of the nerve endings when the nerve cells are stimulated by internal or external events (e.g., breast suckling in the case of oxytocin-secreting neurons), the hormone and neurophysin dissociate from one another, and both the hormone and the neurophysin are released into the bloodstream. The hormones are released into the bloodstream in response to nerve impulses passed from the hypothalamus to the posterior pituitary lobe.

Oxytocin increases uterine contractions, which are necessary for labour and delivery, as well as milk ejection during breastfeeding. Vasopressin lowers blood pressure and enhances water reabsorption from the kidneys, preserving bodily fluid and preventing dehydration. Increased serum osmolality, which is a sign of dehydration, stimulates vasopressin release.

Disorders of Pituitary Gland

Pituitary disorders affect the functioning of the pituitary gland, increasing or decreasing the level of certain hormone secretion. This generally happens because of a non-cancerous tumour called the pituitary adenoma.

A Pituitary macroadenoma (tumour larger than 10 mm) can also cause the impairment of blood supply into the gland. It can either cause overflow or stop the flow of blood completely into the gland. This is called pituitary apoplexy.

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By Team Learning Mantras