Difference Between Anterior and Posterior Pituitary Gland

Main Difference – Anterior vs Posterior Pituitary Gland

Anterior and posterior pituitary gland are the two lobes of the pituitary gland. Each lobe secretes hormones that regulate functions of the other endocrine glands such as adrenal gland, thyroid gland, ovaries, and testis. The pituitary gland is called as the ‘master’ gland of the endocrine system and it protrudes from the bottom of the hypothalamus at the base of the brain. The production and secretion of hormones of the pituitary gland are regulated by the hypothalamus. The anterior pituitary gland is called adenohypophysis whereas the posterior pituitary gland is called neurohypophysis. The main difference between anterior and posterior pituitary gland is that the action of the anterior pituitary gland is regulated through vessels connected to the hypothalamus whereas the action of the posterior pituitary gland is regulated through nerves connected to the hypothalamus.

Key Areas Covered

1. What is Anterior Pituitary Gland
      – Definition, Anatomy, Hormones, Regulation
2. What is Posterior Pituitary Gland
      – Definition, Anatomy, Hormones, Regulation
3. What are the Similarities Between Anterior and Posterior Pituitary Glands
      – Outline of Common Features
4. What is the Difference Between Anterior and Posterior Pituitary Glands
      – Comparison of Key Differences

Key Terms: Adenohypophysis, Adrenocorticotropic hormone (ACTH), Anterior Pituitary Gland, Follicle-stimulating hormone (FSH), Growth hormone (GH), Hypothalamus, Infundibular Stalk, Neurohypophysis, Oxytocin, Pars Distalis, Pars Intermedia, Pars Nervosa, Pars Tuberalis, Posterior Pituitary Gland, Thyroid-stimulating hormone (TSH), Vasopressin

What is Anterior Pituitary Gland

The anterior pituitary gland or the adenohypophysis is one of the two lobes of the pituitary gland, which regulates physiological functions such as growth, reproduction, lactation, and stress. The anterior pituitary gland is a fleshy structure, composed of multiple structures: pars distalis, pars tuberalis, and pars intermedia. The pars distalis is the distal part of the anterior pituitary, where most of the hormones are been produced. The pars tuberalis is the tubular part of the anterior pituitary. The pars tuberalis is a sheath extending from pars distalis and is wrapped around the pituitary stalk. The pars intermedia is found between pars distalis and the posterior pituitary. The anterior pituitary complex is shown in figure 1.

Difference Between Anterior and Posterior Pituitary Gland

Figure 1: Anterior Pituitary Complex

The anterior pituitary gland secretes several hormones, which act upon adrenal gland, thyroid gland, liver, and gonads.

Major Hormones Secreted from Anterior Pituitary Gland and Their Functions

Hormone	Function
Adrenocorticotropic hormone (ACTH)	Affects the adrenal gland, secreting glucocorticoid, mineralocorticoids, and sex corticoids
Beta-endorphin	Affects the opioid receptor, inhibiting the perception of the pain
Thyroid-stimulating hormone (TSH)	Affects the thyroid gland, secreting thyroid hormones
Follicle-stimulating hormone (FSH)	Affects the gonads, involving in the growth of the reproductive system
Luteinizing hormone (LH)	Affects the gonads, involving in the sex hormone production
Growth hormone (GH)	Affects the liver and adipose tissue, promoting the growth of the body.
Prolactin	Affects the ovaries and mammary glands, secreting estrogen, progesterone, and milk.

The hormone secretion from the anterior pituitary gland is regulated by the hypothalamus. The neurons projected from the hypothalamus release hormones to the hypothalamo-hypophysial portal vessels, which directly travel to the anterior pituitary gland, regulating the secretion of anterior pituitary hormones.

What is Posterior Pituitary Gland

The posterior pituitary gland or the neurohypophysis is the other lobe of the pituitary gland which serves as a part of the endocrine system. The posterior pituitary contains two parts; pars nervosa and infundibular stalk. The neuronal lobe of the posterior pituitary is called the pars nervosa. The pars nervosa stores hormones of the posterior pituitary gland. The infundibular stalk is also called the pituitary stalk and it bridges the hypothalamic and hypophyseal systems. The anatomy of the pituitary gland is shown in figure 2.

Main Difference - Anterior vs Posterior Pituitary Gland

Figure 2: Anatomy of the Pituitary Gland

Major Hormones Secreted from the Posterior Pituitary Gland and Their Functions

Hormone	Function
Oxytocin	Involved in the creation of positive feedback loop
Vasopressin (Antidiuretic hormone, ADH)	Affects the collecting ducts in the kidney, facilitating the reabsorption of water from the filtrate.

The posterior pituitary is a collection of axonal projections, which begins from the hypothalamus. These axonal projections extend from the supraoptic and paraventricular nuclei of the hypothalamus. The posterior pituitary hormones are released from the axonal projections into the circulation of the pituitary gland. Then, those hormones are stored in the posterior pituitary in neurosecretory vesicles called Herring bodies and released into the systematic blood circulation.

Similarities Between Anterior and Posterior Pituitary Gland

The anterior and posterior pituitary glands are the two components of the pituitary gland.
Both anterior and posterior pituitary glands are endocrine glands, releasing hormones to regulate the functions of most of the organs and glands in the body.
The production and release of hormones by the anterior and posterior pituitary glands are regulated by the hormones released by the hypothalamus.

Definition

Anterior Pituitary Gland: The anterior pituitary gland is a part of the pituitary at the base of the brain and produces hormones for the regulation of physiological functions such as growth, reproduction, lactation, and stress.

Posterior Pituitary Gland: The posterior pituitary gland is an endocrine gland, which is the back portion of the pituitary, releasing oxytocin and vasopressin.

Known as

Anterior Pituitary Gland: The anterior pituitary gland is known as adenohypophysis.

Posterior Pituitary Gland: The posterior pituitary gland is known as neurohypophysis.

Anatomy

Anterior Pituitary Gland: Anterior pituitary gland is a fleshy, glandular structure.

Posterior Pituitary Gland: Posterior pituitary is a collection of axonal projections.

Structure

Anterior Pituitary Gland: The anterior pituitary gland is composed of three structures; pars distalis, pars tuberalis, and pars intermedia.

Posterior Pituitary Gland: The posterior pituitary gland is composed of two structures: pars nervosa and infundibular stalk.

Hormones

Anterior Pituitary Gland: The anterior pituitary gland releases ACTH, beta-endorphin, TSH, FSH, LH, GH, and prolactin.

Posterior Pituitary Gland: The posterior pituitary gland releases oxytocin and vasopressin.

Role

Anterior Pituitary Gland: The anterior pituitary gland is mainly involved in regulating physiological functions such as growth, reproduction, lactation, and stress.

Posterior Pituitary Gland: The posterior pituitary gland is mainly involved in creating positive feedback loops in the body.

Regulation

Anterior Pituitary Gland: The anterior pituitary gland is regulated via hypothalamo-hypophysial portal vessels from the hypothalamus.

Posterior Pituitary Gland: The posterior pituitary gland is regulated via axonal projections from the hypothalamus.

Conclusion

Anterior and posterior pituitary glands are the two components of the pituitary gland. Both glands release hormones to regulate functions of most of the organs and glands in the body such as the adrenal gland, thyroid gland, liver, and gonads. The anterior pituitary gland is a fleshy, glandular structure whereas the posterior pituitary gland is composed of axonal projections starting from the hypothalamus. Therefore, the release of hormones by the anterior pituitary gland is regulated by the hypothalamic hormones released to the blood vessels, which extend to the anterior pituitary gland from the hypothalamus. The release of hormones by the posterior pituitary gland is regulated by the axonal projections extending from the hypothalamus. Therefore, the main difference between anterior and posterior pituitary gland is the hormones released by the each gland and the regulation of hormone release in each gland.

Reference:

1. “An Overview of the Pituitary Gland.” EndocrineWeb. N.p., n.d. Web. Available here. 13 July 2017.
2. “The Anterior Pituitary.” Boundless. N.p., 23 Oct. 2016. Web. Available here. 12 July 2017.
3. “The Posterior Pituitary.” Boundless. N.p., 23 Oct. 2016. Web. Available here. 12 July 2017.

Image Courtesy:

1.”1808 The Anterior Pituitary Complex” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2.”Gray1181″ By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 1181 (Public Domain) via Commons Wikimedia