Antidiuretic Hormone (ADH)

What is the ADH Hormone?

The full form of ADH is Antidiuretic Hormone. As its name implies, an antidiuretic is a substance that decreases urine production. ADH causes the kidneys to return more water to the blood, thus decreasing urine volume. In the absence of ADH, urine output increases from the normal 1 to 2 litres to about 20 litres a day. ADH also decreases the water lost through sweating and causes constriction of arterioles, which increases blood pressure. This hormone’s other name, vasopressin, reflects this effect on blood pressure.

Synthesis and Storage of ADH Hormone in Hypothalamus and Pituitary

Although the posterior pituitary gland lobe, or neurohypophysis, does not synthesise hormones, it does store and secrete two peptide hormones, namely oxytocin and vasopressin. Antidiuretic Hormone is one of the two neurohormones synthesised by the neurosecretory cells present in the hypothalamus and carried to the neurohypophysis along the nerve fibres, where it is stored along with oxytocin.

Specialised neurons of the hypothalamus with the ability to secrete, known as “neurosecretory cells,” synthesise these hormones, which are then transported axonally via neurohypophysial capillaries to the posterior lobe. Thus, the antidiuretic hormone (ADH or vasopressin hormone) is secreted into the bloodstream by the posterior lobe of the pituitary gland, present at the base of the brain.

Factors Affecting ADH Hormone Release and Regulation

The release of Antidiuretic Hormone into the bloodstream is regulated by various factors. These include:

Functions of ADH Hormone in Water Balance and Blood Pressure

Some of the major functions of Antidiuretic Hormone is discussed below:

• The antidiuretic hormone causes vasoconstriction and clot formation.

• The antidiuretic hormone plays a significant role in regulating the biological clock.

• ADH maintains the body's homeostasis, blood volume & the smooth and proper flow of urine from the kidneys.

• Apart from this, ADH also maintains an appropriate volume of water in the spaces surrounding the cells inside the body.

• The antidiuretic hormone also aids in smooth cellular functions.

Mechanism of Action of Antidiuretic Hormone (Vasopressin)

The Antidiuretic Hormone mechanism of action can be explained as follows-

Antidiuretic Hormone exerts an antidiuretic action by enhancing the reabsorption of water from the kidneys back into circulation. Antidiuretic or vasopressin affects V1 and V2 receptors to produce its effects.

Effects of ADH Hormone on Kidneys, Blood Vessels, and Homeostasis

ADH causes constriction of blood vessels and raises blood volume or blood pressure, which is why it is called vasopressin.

Disorders Related to ADH Hormone

Excess secretion of Antidiuretic Hormone can also lead to some major side effects in the body. Some of them are mentioned below:

• A low level of ADH in the blood results in diabetes insipidus, where the reabsorption of water is reduced.

• This results in excessive water loss through dilute urine.

• Antidiuretic hormone often lowers blood pressure and increases urine volume.

• Hyposecretion of ADH also causes damage to the hypothalamus and pituitary gland.

• A high ADH level causes the blood to dilute and the plasma to be low in sodium.

• Hypersecretion of ADH can result in acute conditions with symptoms such as nausea, headache, dehydration, vomiting, etc.

A hyper- or hypo-secretion of ADH often results in several disorders. These are as follows-

• Insomnia

• Head injuries

• Infertility - Causes and Types of Solutions

• Delayed puberty

• Frequent urination

• Autoimmune disorders

• Change in appetite etc.

ADH Hormone NEET MCQs

Q1. The Pars distalis region of the pituitary does not produce these hormones

a. Melanocyte-stimulating hormone

b. Vasopressin

c. Prolactin

d. Growth hormone

1. I and IV

2. II and IV

3. II and III

4. I and II

Correct answer: 4) I and II

Explanation:

Hormones released from Posterior Lobe:

1. Oxytocin:

• This hormone stimulates the contraction of smooth muscles of the uterus in pregnant women and causes easy childbirth.

• It also contracts the smooth muscles of mammary glands in lactating mothers and facilitates the flow of milk at the time of suckling.

• Oxytocin also stimulates the relaxation of the gallbladder, urinary bladder, and intestine.

2. Vasopressin or Antidiuretic Hormone (ADH):

• The primary function of vasopressin is to increase the reabsorption of water in the distal convoluted tubules and collecting tubules of the kidney.

• So its deficiency in the body increases the volume of urine causing diabetes insipidus.

• This type of diabetes is different from diabetes mellitus in that the urine is free from sugar.

• Another important function of ADH is to bring about the contraction of smooth muscles of the intestine, gallbladder, urinary bladder, and blood vessels.

• Hence, large quantities of the hormone cause the arterial blood pressure to rise due to the contraction of peripheral arterioles.

• Intake of alcohol reduces ADH secretion.

Hence, the correct answer is option 4) I and II.

Q2. Which of the following statements accurately describes the hormones produced and secreted by different parts of the pituitary gland?

A. The pars distalis is responsible for the production and release of growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH).

B. The pars intermedia solely secretes a single hormone known as melatonin.

C. The posterior lobe of the pituitary gland is alternatively referred to as the neurohypophysis or pars nervosa.

D. The posterior pituitary gland stores and releases two hormones: oxytocin and vasopressin.

1. A, B, C

2. B, C, D

3. A, C, D

4. B and C

Correct answer: 3) A, C, D

Explanation:

In the pituitary gland:

(A) The anterior part, called the pars distalis, is responsible for producing and releasing growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH).

(C) The posterior lobe of the pituitary gland is indeed referred to as the neurohypophysis or pars nervosa.

(D) The posterior pituitary gland stores and releases two hormones: oxytocin and vasopressin (also known as antidiuretic hormone or ADH).

Hence, the correct answer is option 3) A, C, and D.

Q3. The hormone not secreted by adenohypophysis is

1. Adrenocorticotropic Hormone (ACTH)

2. Thyroid Stimulating Hormone (TSH)

3. Antidiuretic Hormone

4. Follicle Stimulating Hormone (FSH)

Correct answer: 3) Antidiuretic Hormone

Explanation:

The Pituitary Gland and Its Anterior Lobe -

Hormones of Adenohypophysis

• Growth Hormone (GH)

• Adrenocorticotropic Hormone (ACTH)

• Thyroid Stimulating Hormone (TSH)

• Follicle Stimulating Hormone (FSH)

• Luteinizing Hormone (LH)

• Prolactin

Hence, the correct option is option 3) The hormone not secreted by adenohypophysis is the Antidiuretic Hormone.

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