Difference Between Anterior Pituitary and Posterior Pituitary

The pituitary gland is a small endocrine organ. It is located in a saddle-shaped depression in the body of the sphenoid bone of the human skull called sella turcica (Turkish saddle). The pituitary gland is connected to the hypothalamus.

The pituitary is isolated from the bone wall of the skull with a thick, dense layer of connective tissue.

It has an oval shape. Its dimensions are: length: 12-15 mm, width: 8-10 mm, height: 5-6 mm.

In terms of weight, it shows large individual differences. In men, pituitary weighs an average of 1.6 g. In women, during pregnancy, it increases and after birth does not return to its original size. Therefore, in women with several children, it can weigh more than 1 g.

The gland is divided into two parts −

• Anterior pituitary

• Posterior pituitary

The two pituitary units have a different cellular structure and supply the body with different hormones.

What is Anterior Pituitary?

The anterior glandular lobe of the pituitary gland is called adenohypophysis. It is about 75% of the gland. The anterior pituitary has an ectodermal origin.

The anterior pituitary is built up of several types of endocrine cells with different affinity for colorants −

• Eosinophilic cells − Colored by acidic coloring agents;

• Basophilic cells − Colored by basic coloring agents;

• Neutrophilic (chromophobic) cells − Have no affinity for coloring agents.

Eosinophilic and basophilic cells synthesize and secrete hormones. The neutrophilic cells are “backup cells” that, if necessary, undergo a maturation process and differentiate into eosinophilic or basophilic cells.

The anterior lobe of the pituitary synthesizes and secretes the so-called tropic hormones. These are hormones that have other endocrine glands as their target and do not directly regulate processes in the body.

Anterior pituitary produces the following hormones −

• Somatotropin – human growth hormone;

• Prolactin – regulates the development of the breasts and the lactation;

• Follicle stimulating hormone – regulates ovarian follicle growth in women and spermatogenesis in men;

• Luteinizing hormone – causes ovulation and yellow body formation in women, and the release of testosterone in men;

• Thyroid hormone – stimulates the function of the thyroid gland;

• Adrenocorticotropic hormone stimulates the production of hormones in the adrenal gland.

What is Posterior Pituitary?

The posterior glandular lobe of the pituitary gland is called neurohypophysis. It is about 25% percent of the gland.

It is formed in embryonic development as an appendage of the hypothalamus.

The posterior pituitary is built up of identical cells similar to the neurons. The cells are connected to the hypothalamic neurons through long axons. While the anterior pituitary cells synthesize certain hormones that are secreted into the blood, in the posterior pituitary hormones are not synthesized. The posterior pituitary stores and releases two hormones. They are synthesized in the hypothalamus.

These hormones are −

• Vasopressin Antidiuretic hormone, stimulates the absorption of water in the curved kidney tubules, resulting in primary urine thickening, and constricting blood vessels, resulting in increased blood pressure;

• Oxytocin Acts on the smooth muscles of the uterus, stimulates their contraction.

Differences: Anterior and Posterior Pituitary

ACTH is responsible for stimulating the adrenal gland to secrete cortisol, which is involved in the body's stress response. TSH stimulates the thyroid gland to produce thyroid hormone, which is essential for regulating metabolism. FSH and LH play a role in the reproductive system. FSH stimulates the development of follicles in the ovaries or testes, while LH triggers ovulation or testosterone production. GH is responsible for promoting growth and development, while prolactin is involved in lactation and breast development in females.

On the other hand, the posterior pituitary is also known as the neurohypophysis. It is composed of nervous tissue and does not synthesize hormones itself. Instead, it stores and releases two hormones produced by the hypothalamus, oxytocin, and vasopressin (also known as antidiuretic hormone, ADH). These hormones are synthesized by the hypothalamus and transported through nerve fibers to the posterior pituitary, where they are stored until they are released into the bloodstream.

Oxytocin plays a critical role in childbirth and lactation. During labor, oxytocin stimulates uterine contractions, which helps the fetus move through the birth canal. After birth, oxytocin stimulates milk ejection from the mammary glands. Vasopressin is involved in regulating water balance in the body. It acts on the kidneys to reduce the amount of water excreted in the urine, which helps maintain normal blood volume and blood pressure.

The following table highlights the major differences between Anterior and Posterior Pituitary −

Characteristics	Anterior Pituitary	Posterior Pituitary
Definition	Anterior pituitary is the anterior glandular lobe of the pituitary called adenohypophysis.	Posterior pituitary is the posterior glandular lobe of the pituitary called neurohypophysis.
Origin	Anterior Pituitary: The anterior pituitary has an ectodermal origin.	Posterior Pituitary: The posterior pituitary is formed in embryonic development as an appendage of the hypothalamus.
Size	Anterior Pituitary: The anterior pituitary is about 75% of the gland.	Posterior Pituitary: The posterior pituitary is about 25% of the gland.
Cells	The anterior pituitary is built up of eosinophilic, basophilic and neutrophilic (chromophobic) endocrine cells.	The posterior pituitary is built up of identical cells similar to the neurons.
Hormones	The anterior pituitary synthesizes and secretes somatotropin, prolactin, follicle stimulating hormone, luteinizing hormone, thyroid hormone, adrenocorticotropic hormone.	The posterior pituitary stores and releases vasopressin and oxytocin.

Conclusion

In summary, the anterior and posterior pituitary glands have different functions and characteristics. The anterior pituitary is composed of glandular tissue and secretes six hormones that are involved in regulating various physiological functions, including stress response, metabolism, growth, and reproduction. It is regulated by the hypothalamus, which secretes releasing hormones that stimulate or inhibit hormone secretion.

On the other hand, the posterior pituitary is composed of nervous tissue and stores and releases two hormones produced by the hypothalamus, oxytocin, and vasopressin. Oxytocin is involved in childbirth and lactation, while vasopressin regulates water balance in the body.