• (A) A-I, B-III, C-IV, D-II
• (B) A-III, B-I, C-IV, D-II
• (C) A-II, B-I, C-III, D-IV
• (D) A-IV, B-III, C-II, D-I

Step-by-Step Explanation

To solve this matching problem, we examine the endocrine functions of organs that are not primarily endocrine glands:

• A. Heart (III. Atrial natriuretic factor): The atrial wall of our heart secretes a very important peptide hormone called Atrial Natriuretic Factor (ANF). Its primary function is to decrease blood pressure by causing vasodilation.
• B. Kidney (I. Erythropoietin): The juxtaglomerular (JG) cells of the kidney produce a peptide hormone called Erythropoietin. This hormone travels to the bone marrow to stimulate erythropoiesis (formation of RBCs).
• C. Gastro-intestinal tract (IV. Secretin): The GI tract secretes several hormones. Secretin specifically acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions.
• D. Adrenal Cortex (II. Aldosterone): The adrenal cortex is divided into three layers. It secretes corticoids like Aldosterone (a mineralocorticoid), which helps in the maintenance of electrolytes, body fluid volume, and osmotic pressure.

Therefore, the correct match is A-III, B-I, C-IV, D-II, making (B) the correct choice.

Related Theory

While we usually focus on glands like the pituitary or thyroid, several other organs possess endocrine tissue and secrete vital hormones. This is a high-yield area for NEET Biology.

1. Hormones of the Heart

When blood pressure increases, the atrial walls of the heart stretch and release Atrial Natriuretic Factor (ANF). ANF is a potent vasodilator, meaning it relaxes the smooth muscles of blood vessels. By increasing the diameter of blood vessels, it effectively lowers blood pressure. It also acts as a check on the Renin-Angiotensin mechanism.

2. Hormones of the Kidney

The kidneys are not just excretory organs; they are endocrine powerhouses.

• Erythropoietin: Produced by JG cells in response to low oxygen levels (hypoxia), it stimulates the bone marrow to produce red blood cells.
• Renin: Part of the RAAS pathway, essential for regulating blood pressure and glomerular filtration rate (GFR).
• Calcitriol: The active form of Vitamin D, which helps in calcium absorption.

3. Hormones of the Gastro-Intestinal (GI) Tract

Four major peptide hormones are secreted by different parts of the alimentary canal:

• Gastrin: Acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen.
• Secretin: Acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions to neutralize stomach acid.
• Cholecystokinin (CCK): Acts on both the pancreas (secretion of enzymes) and the gallbladder (secretion of bile).
• Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.

4. Adrenal Cortex and Mineralocorticoids

The adrenal cortex produces three main types of steroid hormones (corticoids). Aldosterone is the primary mineralocorticoid. It acts mainly at the renal tubules and stimulates the reabsorption of $Na^+$ and water and the excretion of $K^+$ and phosphate ions. This is critical for maintaining electrolyte balance and blood pressure.

5. Clinical Correlations

• Anemia: Chronic kidney disease leads to a lack of erythropoietin, resulting in severe anemia.
• Conn's Syndrome: Overproduction of aldosterone leads to high blood pressure and low potassium levels.
• Digestive Disorders: Imbalances in secretin or CCK can lead to poor digestion and nutrient malabsorption.

6. Key Summary Table

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