Difference Between Anterior Pituitary and Posterior Pituitary (With Table)

The pituitary gland which is also termed as the ‘Master Gland’ is made up of the anterior pituitary and the posterior pituitary. This pea-shaped gland has full control over certain important organs and parts of the human body. It’s two lobes perform different functions and receives signals from the hypothalamus about its steps and actions. The pituitary gland only acts after it has received a positive signal from the hypothalamus. 

Anterior Pituitary vs Posterior Pituitary

The difference between the anterior and the posterior pituitary is that the anterior pituitary produces a lot of hormones that ultimately help in different bodily functions, but the posterior pituitary does not release hormones on its own. 

Comparison Table Between Anterior Pituitary and Posterior Pituitary

Parameters of ComparisonAnterior PituitaryPosterior Pituitary
Different namesThe anterior pituitary is also known as Adenohypophysis.The posterior pituitary is also known as Neurohypophysis.
OriginThe origin of the anterior pituitary is ectodermal.The posterior pituitary can be claimed simply as an extension of the hypothalamus which was formed during the embryonic development stage
SizeThe 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. 
ComposureThe anterior pituitary is made up of cells like eosinophilic, basophilic, and neutrophilic.The posterior pituitary is made up of fewer cells and mostly contains cells like that of neutrons.
Hormones releasedThe anterior pituitary produces and releases a lot of useful hormones like thyroid hormone, somatotropin, follicle-stimulating hormone, prolactin, luteinizing hormone, adrenocorticotropic hormone into the system.The posterior pituitary cannot produce hormones per se. But it stores hormones like oxytocin and vasopressin, and later releases it 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 roles to play in the body. It is mostly made up of endocrine cells like eosinophilic, basophilic, and neutrophilic cells, and have other endocrine glands as their targets. 

They do not release the hormones they produce directly into the bloodstream, but send it 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 for 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 take a 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 different functions of the kidney and the urinary tract. In the kidneys, it performs a huge role in the absorption of water. It primarily acts as a urine thickening agent, and at the same time helps in increasing the blood pressure when it goes low. 
  2. Oxytocin: Oxytocin has 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 is made up of two lobes- the anterior pituitary happens to be the anterior glandular lobe of the pituitary gland, while the posterior lobe is the posterior pituitary. 
  2. The Anterior Pituitary and the Posterior Pituitary are completely different when it comes to looks. There are more cells in the Anterior Pituitary for which it tends to have a much darker color 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 entire pituitary gland is controlled by the hypothalamus. Moreover, it is connected to the hypothalamus by a link known as the Infundibulum. The two lobes are also in control of the hypothalamus, but they get their signals from different cells. The parvocellular neurons help in sending 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 the production of a lot of hormones and regulating different mechanisms, the posterior pituitary is not capable of hormone production. It mainly stores the different types of hormones secreted from the hypothalamus, and later released them into the system when the body requires them. 
  5. The hormones released by the anterior pituitary target endocrine glands and have functions like growth, ovulation, stimulate the production of thyroid hormones as well as hormones of the adrenaline gland. On the other hand, the hormones released by the posterior pituitary help in the proper functioning of the kidney and uterus muscle contraction. 

Conclusion

The anterior and the posterior pituitary are just the two different lobes of the pituitary glands. They might be part of the same gland but have havoc differences in their characteristics and functions. While the anterior pituitary is made up of cells and has a darker appearance, the posterior pituitary has fewer cells and more nerve ends. The anterior pituitary is also involved in producing and releasing the hormones while the posterior pituitary stores the hormones released by the hypothalamus. 

References 

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

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