What is the Difference Between Neurohypophysis and Adenohypophysis

The main difference between neurohypophysis and adenohypophysis is that neurohypophysis is the posterior lobe of the pituitary, whereas adenohypophysis is the anterior lobe of the pituitary.

Neurohypophysis and adenohypophysis are two lobes of the pituitary gland. The pituitary gland (hypophysis) is a small pea-sized gland at the base of the brain, below the hypothalamus. It is a part of the body’s endocrine system, secreting hormones.

Key Areas Covered

1. What is Neurohypophysis
     – Definition, Structure, Function
2. What is Adenohypophysis
     – Definition, Structure, Function
3. Similarities Between Neurohypophysis and Adenohypophysis
     – Outline of Common Features
4. Difference Between Neurohypophysis and Adenohypophysis
     – Comparison of Key Differences

Key Terms

Adenohypophysis, Neurohypophysis

What is Neurohypophysis

The neurohypophysis is the lobe of the posterior pituitary located at the base of the brain. During embryogenesis, it forms from the infundibulum, the neuroectodermal layer. The three regions of the neurohypophysis include median eminence, infundibulum, and pars nervosa. The primary function of neurohypophysis is to secrete oxytocin and vasopressin. Magnocellular neurosecretory cells in the hypothalamus produce these hormones. The paraventricular and supraoptic nuclei of the hypothalamus project axons to the neurohypophysis. Neurohypophyseal capillaries store hormones and release them into systemic circulation.

Figure 1: Posterior Pituitary

Furthermore, dysfunctions of the posterior pituitary can affect the homeostasis of the hormones. It can cause diabetes insipidus (DI) and SIADH (syndrome of inappropriate antidiuretic hormone). Neurohypophysis also contains pituicytes that function like glial cells to support and modulate hormone release.

What is Adenohypophysis

The adenohypophysis is the anterior lobe of the pituitary gland. It has three parts: pars distalis, pars tuberalis, and pars intermedia. The majority of the hormone production occurs in the pars distalis. The distal part of the adenohypophysis is the pars distalis, making the majority of the adenohypophysis. Pars tuberalis is a tubular sheath extending from pars distalis. It winds around the pituitary stalk. Pars intermedia occurs between the posterior pituitary and pars distalis. It contains large pale cells. The primary hormone secreted by pars intermedia is MSH (melanocyte-stimulating hormone).

Figure 2: Anterior Pituitary

Moreover, the majority of hormones of the pituitary gland are secreted by adenohypophysis. Prohormones secreted by the hypothalamus direct the secretion of hormones by the pituitary gland. The other hormones secreted by the adenohypophysis include ACTH (adrenocorticotropic hormone), PRL (prolactin), LH/FSH (luteinizing hormone/follicle stimulating hormone), GH (growth hormone), and TSH (thyroid stimulating hormone).

Similarities Between Neurohypophysis and Adenohypophysis

• Neurohypophysis and adenohypophysis are two lobes in the pituitary gland.
• Their function is to secrete hormones.

Difference Between Neurohypophysis and Adenohypophysis

Definition

Neurohypophysis refers to the posterior lobe of the hypophysis (pituitary gland), which stores and releases oxytocin and vasopressin produced in the hypothalamus. Meanwhile, adenohypophysis refers to the anterior part of the pituitary gland derived from the embryonic pharynx and is primarily glandular in nature.

Significance

Neurohypophysis is the posterior lobe of the pituitary, while adenohypophysis is the anterior lobe of the pituitary.

Proportion

Moreover, neurohypophysis forms 25% of the pituitary gland, while adenohypophysis forms 75% of the pituitary gland.

Connection to the Hypothalamus

Neurohypophysis contains axonal knobs and blood vessels connecting to the hypothalamus, while adenohypophysis contains a portal system with blood sinusoids connecting the hypothalamus.

Parts

Neurohypophysis contains three parts: median eminence, infundibulum, and pars nervosa, whereas adenohypophysis contains three parts: pars tuberalis, pars distalis, and pars intermedia.  

Function

In addition, neurohypophysis stores the two hormones produced by the hypothalamus, while adenohypophysis secrets seven hormones according to the signals from the hypothalamus.  

Conclusion

In brief, neurohypophysis and adenohypophysis are two lobes of the pituitary gland. The neurohypophysis is the pituitary gland’s posterior lobe, forming 25% of the pituitary gland. It connects to the hypothalamus through axonal knobs and blood vessels. The three parts of the neurohypophysis are median eminence, infundibulum, and pars nervosa. The primary function of the neurohypophysis is to secrete hormones of the hypothalamus. In comparison, adenohypophysis is the anterior lobe of the pituitary gland, which makes up 75% of the pituitary gland. It connects to the hypothalamus through a portal system with blood sinusoids. The three parts of the adenohypophysis are pars tuberalis, pars distalis, and pars intermedia. The primary function of the adenohypophysis is to secrete seven hormones. Therefore, the main difference between neurohypophysis and adenohypophysis is their structure and function.

References:

1. Santos Fontanez SE, De Jesus O. Neurohypophysis. [Updated 2023 Feb 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.
2. Ilahi S, Ilahi TB. Anatomy, Adenohypophysis (Pars Anterior, Anterior Pituitary) [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-.

Image Courtesy:

1. “1807 The Posterior Pituitary Complex” By OpenStax College – Own work (CC-BY 3.0) via Commons Wikimedia
2. “1808 The Anterior Pituitary Complex” By OpenStax College – Own Work (CC-BY 3.0) via Commons Wikimedia