Endocrine Glands: Anterior pituitary and Posterior pituitary - NEET PG Physiology

Endocrine glands and their hormones play a critical role in regulating many physiological processes in the human body, such as growth, metabolism, reproduction, and homeostasis. Therefore, understanding the anatomy, physiology, and pathology of endocrine glands is crucial for medical professionals, including those who will be taking the NEET PG exam. 

Endocrine-related questions are frequently tested in the exam, making it important for candidates to have a good grasp of this topic.

In this blog, you will get a quick overview of this important physiology topic for NEET PG exam preparation.

Major Glands

1. Pituitary gland
   • Pituitary gland has two lobes
     • Anterior pituitary 
     • Posterior pituitary 

Anterior pituitary

It has got glandular elements so it is called adenohypophysis.Cells in the anterior pituitary are

• Chromophobe cells - These constitute 50% of the anterior pituitary cells. They do not attract any color / stain 
• Chromophyl cells- They constitute the rest 50% of the anterior pituitary cells. They attract some stains. These cells are further divided into two types

Acidophil cells	Basophil cells
These cells constitute 70% of the chromophyl cells These cells attract the acidic stain  They synthesize two hormones: GH & Prolactin   These are further divided into two parts: Somatotrophs These cells help in GH synthesis  They comprise of almost 50% of the acidophil cells  Lactotrophs  These cells are mainly for prolactin synthesis They comprise almost 15-20% of acidophil	These cells attract basic stains  They constitute around 20-30% of the chromophyl cells  They synthesize the following hormones: ACTH TSH FSH LH

Posterior Pituitary

It has neural elements because of which it is called neurohypophysis. Hormones of posterior pituitary are: 

• ADH
• Oxytocin 

These hormones are synthesized in the hypothalamic neurons. The nuclei where they are synthesized are supra optic nucleus (for ADH) & paraventricular nucleus (for Oxytocin).

Now let us discuss all the hormones of Anterior Pituitary and Posterior Pituitary individually.

Anterior Pituitary hormones

All anterior pituitary hormones are controlled by hypothalamic factors or hormones, EXCEPT, “prolactin”. For e.g. GH is controlled by GH inhibiting hormone called Somatostatin  

Important Information

• TRH acts as prolactin releasing hormone 

Following are the major anterior pituitary hormones

1. GH (Growth Hormone)

GH is an anti-Insulin, diabetogenic hormone GH performs two types of function:

• Metabolic functions 
• Non-metabolic functions

Metabolic functions 

Metabolic functions of GH can be studied w.r.t. carbohydrates, proteins & fats that are discussed below: 

1. Growth Hormones & Carbohydrates
   • GH is a hyperglycemic hormone. It causes hyperglycemia by preventing the peripheral utilization of glucose. In that way GH is acting upon exogenous glucose. As GH is diabetogenic, it results in Pituitary diabetes because of excessive GH secretion.
2. Growth Hormone & Protein synthesis
   • GH does not allow the protein breakdown as it promotes growth, rather it causes protein synthesis.
3. Growth hormone action on fats 
   • GH causes breakdown of triglycerides. Therefore, it increases FFA (Free Fatty Acids) levels in the plasma. 

Non-Metabolic functions of growth hormones 

• GH causes somatic growth.
• Somatic growth means, the growth initiated by the action of mediators called Somatomedin or IGFs.

Disorders of growth hormones 

Disorders of GH can be caused by either excess or deficiency of GH. Both of them are discussed below:-

• Excessive GH
  • Excess of GH before puberty can lead to Gigantism. 
  • Excess of GH after puberty will lead to Acromegaly.
• Deficiency of GH
  • Deficiency of GH before puberty leads to Dwarfism.
• Dwarfism is of three types :-
  • Pituitary dwarf: These individuals have an absolute lack of GH before puberty.
  • Levi- Lorain dwarfism: In this, the GH is normal but there is a deficiency of Somatomedin C (IGF I).
  • Normal or increased GH dwarfism (Laron’s dwarfism): It is due to normal or increased GH but resistance to GH action (GH receptor insensitivity).

Regulation of GH secretion

• The stimulators of GH are :-
  • GH- RH 
  • Hypoglycemia 
  • Exercise 
  • Arginine 
  • Sleep
• The inhibitors of GH are: 
  • GH – IH 
  • FFAs
  • Hyperglycemia 

Posterior Pituitary hormones 

1. ADH

• ADH results into two actions

Vasoconstriction	Water reabsorption from Renal tubules
It is mediated by a V1 receptor.	It is mediated by V2 receptors It happens when ADH binds with the V2 receptor in the collecting duct, there are insertions of channels called Aqua-porins II (AQP II) that results in reabsorption of water in the collecting duct.

Important Information 

• Neurophysin
  • These are the proteins which bind ADH & Oxytocin and carry them down to the posterior pituitary gland.
• Herring bodies 
  • These are the bulb like bodies released from the axonal endings in the posterior pituitary.

2. Oxytocin

• It is involved in the positive feedback mechanism and neuroendocrine reflex. Oxytocin performs the following important functions:
  • Milk ejection by contraction of the Myo-Epithelial cells of the breast.
  • Parturition i.e. the delivery of a baby.
  • Luteolysis i.e. degeneration of the corpus luteum.

Important Information 

Neuro-endocrine reflex 

• It is the reflex for which afferent limb is neuron and efferent limb is hormonal. 
  • For e.g. milk ejection.

To learn about the endocrine glands in detail watch the video lectures available on the PrepLadder app.