Anterior Pituitary vs Posterior Pituitary: Difference and Comparison

The pituitary gland, which is also termed the ‘Master Gland’, is made up of the anterior pituitary and the posterior pituitary. This pea-shaped gland controls certain important organs and parts of the human body.

Two lobes perform different functions and receive signals from the hypothalamus about its steps and actions. The pituitary gland only acts after it has received a positive signal from the hypothalamus. 

Key Takeaways

1. The anterior pituitary gland produces and secretes several hormones, including growth hormone and prolactin, while the posterior pituitary gland stores and releases two hormones, oxytocin and vasopressin.
2. The anterior pituitary is controlled by releasing hormones from the hypothalamus, while the posterior pituitary is an extension of the hypothalamus.
3. Damage to the posterior pituitary can lead to a deficiency in oxytocin and vasopressin, while damage to the anterior pituitary can affect the production of multiple hormones.

Anterior Pituitary vs Posterior Pituitary

The posterior pituitary is the posterior part of pituitary gland existing below the hypothalamus. It is as small as a pea and releases two hormones oxytocin and antidiuretic hormone. Anterior pituitary is a small pea sized round projection at the front of pituitary gland underneath the hypothalamus releasing six different hormones controlling different body functions.

Comparison Table

Parameters of Comparison	Anterior Pituitary	Posterior Pituitary
Different names	The anterior pituitary is also known as Adenohypophysis.	The posterior pituitary is also known as Neurohypophysis.
Origin	The origin of the anterior pituitary is ectodermal.	The posterior pituitary can be claimed simply as an extension of the hypothalamus, formed during embryonic development.
Size	The anterior pituitary makes up almost 27% of the pituitary gland.	The posterior pituitary is smaller compared to the anterior pituitary and takes up only 25% of the pituitary gland.
Composure	The anterior pituitary comprises cells like eosinophilic, basophilic, and neutrophilic.	The posterior pituitary is made up of fewer cells and mostly contains cells like neutrons.
Hormones released	The anterior pituitary produces and releases many useful hormones like thyroid hormone, somatotropin, follicle-stimulating hormone, prolactin, luteinizing hormone, and adrenocorticotropic hormone into the system.	The posterior pituitary cannot produce hormones per se. But it stores hormones like oxytocin and vasopressin and later releases them into the system.

What is the Anterior Pituitary?

The anterior portion of the pituitary gland is known as the anterior pituitary. Though it is just 75% of a pea-shaped gland, it has some vital role in the body.

It comprises endocrine cells like eosinophilic, basophilic, and neutrophilic cells and has other endocrine glands as its targets. They do not release the hormones they produce directly into the bloodstream but send them to those target endocrine glands.

The tropic hormones released by the anterior regulate different functions. Let us take a look into the different hormones released and their different functions:

1. Follicle-stimulating hormone: In women, it takes control of the growth of ovaries, while in men, it aids in spermatogenesis. 
2. Somatotropin: Aids in human growth
3. Luteinizing hormone: Ovulation in women and testosterone release in men.
4. Adrenocorticotropic hormone: stimulates adrenal gland hormone production 
5. Thyroid hormone: stimulates different functions in the thyroid gland.
6. Prolactin: Aids in lactation

What is the Posterior Pituitary?

Neurohypophysis, or the posterior pituitary, happens to be the posterior lobe of the pituitary gland. Making up 25% of the pituitary gland, the posterior pituitary has no hand in synthesizing hormones.

It acts as an extension of the hypothalamus and stores the hormones released by the hypothalamus. It is composed of cells like that of neurons, and long axons link the posterior pituitary to the hypothalamus. 

Let us look at the two hormones stored in the posterior pituitary and their functions.

1. Vasopressin: Vasopressin is mainly an antidiuretic hormone. It plays a role in the kidney and urinary tract functions. In the kidneys, it performs a huge role in water absorption. It primarily acts as a urine-thickening agent and helps increase blood pressure when it goes low. 
2. Oxytocin: Oxytocin functions mainly in the uterus. It helps in the contraction of the smooth muscles. 

Main Differences Between the Anterior Pituitary and the Posterior Pituitary. 

1. As stated before, the pituitary gland comprises two lobes- the anterior pituitary is the anterior glandular lobe of the pituitary gland. In contrast, the posterior lobe is the posterior pituitary. 
2. The Anterior Pituitary and the Posterior Pituitary are completely different regarding looks. There are more cells in the Anterior Pituitary which tends to have a much darker colour than the Posterior Pituitary. But, the Posterior Pituitary is made up of a fewer number of cells and is less dark in comparison to the anterior pituitary. It has more nerve cells compared to the Anterior Pituitary.
3. Till now, we know that the hypothalamus controls the entire pituitary gland. Moreover, it is connected to the hypothalamus by a link known as the Infundibulum. The two lobes also control the hypothalamus, but they get their signals from different cells. The parvocellular neurons help send signals to the anterior pituitary, while magnocellular neurons send signals to the posterior one. 
4. The pituitary gland is responsible for a lot of functions in the body. While the anterior pituitary is solely responsible for producing many hormones and regulating different mechanisms, the posterior pituitary cannot produce hormones. It mainly stores the hormones secreted from the hypothalamus and releases them into the system when the body requires them. 
5. The hormones released by the anterior pituitary target endocrine glands and function like growth ovulation, stimulating the production of thyroid hormones and hormones of the adrenaline gland. On the other hand, the hormones released by the posterior pituitary help properly function the kidney and uterus muscle contraction. 

References 

1. https://science.sciencemag.org/content/213/4508/659.abstract