Endocrine System: Hormones and Glands – NDA Biology Notes

Introduction

What is the Endocrine System?

The body has two types of glands:

Exocrine glands — release their secretions through ducts (tubes) to a specific location. Example: salivary glands release saliva into the mouth.

Endocrine glands — release their secretions directly into the blood. They have no ducts. The secretions travel through the blood to distant target organs.

The secretions of endocrine glands are called hormones.

A hormone is a chemical messenger. It is produced in one organ and travels through the blood to another organ, where it produces a specific effect.

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Properties of Hormones

This was tested as a multi-statement question in CDS. Two statements were correct:

Correct:

• Hormones are steroids, proteins, peptides, or amino acid derivatives. They come in different chemical forms. [NDA tested via CDS]
• Hormones do NOT influence the organ that secreted them. They act on distant target organs. [NDA tested via CDS]

Incorrect (common exam traps):

• Hormones are NOT taken from outside the body as supplements — they are produced by the body’s own glands.
• Hormones are NOT co-enzymes. Co-enzyme function belongs to vitamins and minerals, not hormones.

Key Glands and Their Hormones

1. Pituitary Gland

The pituitary gland is at the base of the brain. It is a single gland — it is unpaired. [NDA tested via CDS]

It is called the master gland because it controls the secretions of other endocrine glands.

Hormones produced by the pituitary:

• Growth Hormone (GH) / Somatotrophin — stimulates growth of bones and body. [NDA tested via CDS]
• TSH (Thyroid Stimulating Hormone) — tells the thyroid gland to produce thyroxine. [NDA tested via CDS]
• LH (Luteinizing Hormone) — triggers ovulation in females. [NDA 2007-I]
• FSH (Follicle Stimulating Hormone) — stimulates egg and sperm development. [NDA 2025-I]

The pituitary is the only major endocrine gland that is NOT paired. Adrenal glands, testes, and ovaries are all paired (one on each side). [NDA tested via CDS]

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2. Thyroid Gland

The thyroid gland is at the front of the neck. It is the only gland in the body that stores iodine. [NDA tested via CDS]

Hormone produced: Thyroxine

What thyroxine does: It controls the body’s metabolic rate — how fast the body uses energy. [NDA 2019-III]

What thyroxine needs: Iodine. The thyroid uses iodine to make thyroxine. Without enough iodine, it cannot produce enough thyroxine. [NDA 2015-I] [NDA 2025-I]

This is why iodized salt is important — it supplies iodine to the body.

Deficiency effects:

• Goitre — when there is not enough iodine, the thyroid enlarges as it tries to capture more iodine from the blood. This swelling of the thyroid gland in the neck is called goitre. [NDA 2008-I] [NDA tested via CDS]
• Cretinism — severe thyroxine deficiency in early childhood causes stunted physical and mental development. This is caused by under-secretion of thyroxine — not adrenal hormone, not cortisone, not glucagon. [NDA 2006-III]

Common exam traps about iodine — CDS question:

Only ONE statement about iodine was correct:

• Correct: Iodine deficiency leads to goitre. ✓
• Wrong: Iodine helps make adrenaline. ✗ (Adrenaline is made by the adrenal gland, not thyroid.)
• Wrong: Iodine is secreted by the pancreas. ✗ (Iodine is used by the thyroid, not the pancreas.)
  [NDA tested via CDS]

3. Pancreas

The pancreas is unique. It has TWO functions:

Exocrine function: Releases digestive enzymes (lipase, amylase, trypsin) into the small intestine.

Endocrine function: Releases hormones (insulin and glucagon) into the blood.

This makes the pancreas the only organ that secretes both hormones and digestive enzymes. [NDA 2007-II]

Both insulin and glucagon are produced by special cells in the pancreas called the Islets of Langerhans. [NDA 2009-II]

Insulin:

• Released when blood glucose is HIGH.
• It signals body cells to absorb glucose from the blood.
• Blood glucose level falls back to normal.
• Insulin deficiency causes Diabetes mellitus (high blood sugar disease).
• Insulin is a peptide hormone — made of amino acid chains. [NDA tested via CDS]
• It was discovered by F.G. Banting. [NDA tested via CDS]

Glucagon:

• Released when blood glucose is LOW.
• It signals the liver to release stored glucose back into the blood.
• Blood glucose rises back to normal.
• Glucagon works opposite to insulin.

	Insulin	Glucagon
Released when	Blood glucose HIGH	Blood glucose LOW
Effect	Lowers blood glucose	Raises blood glucose
Action	Cells absorb glucose	Liver releases glucose
Problem when absent	Diabetes	Low blood sugar

[NDA 2006-I] [NDA 2006-III] [NDA 2009-II] [NDA tested via CDS]

The organ controlling blood sugar = Pancreas. The region = Islets of Langerhans. The hormone = Insulin. All three phrasings give the same answer.

4. Adrenal Glands

There are two adrenal glands — one above each kidney. They are paired glands.

The adrenal gland has two parts:

• Adrenal medulla (inner part) — produces adrenaline.
• Adrenal cortex (outer part) — produces cortisol and aldosterone.

Adrenaline:

• The “fight-or-flight” hormone.
• Released during stress, danger, or excitement.
• Increases heart rate and prepares the body for rapid action. [NDA 2022-II]
• Adrenaline is produced by the adrenal gland — not the thyroid, not the pancreas.

Cortisol:

• Produced by the adrenal cortex.
• Involved in stress response and reducing inflammation. [NDA tested via CDS]

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5. Ovaries

The ovaries are the female reproductive glands. They are paired.

Hormones produced:

• Oestrogen — controls female sexual development and the menstrual cycle.
• Progesterone — maintains pregnancy.

The menstrual cycle in females is controlled jointly by the ovary and the pituitary gland. [NDA 2025-I]

Ovulation (release of an egg) is triggered by a surge of LH (Luteinizing Hormone) from the pituitary. [NDA 2007-I]

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6. Kidneys

The kidneys are primarily excretory organs, but they also have an endocrine function.

The kidneys produce the active form of Vitamin D. Vitamin D is needed for calcium absorption in the body. [NDA tested via CDS]

Gland–Hormone–Function Reference Table

This is the direct matching question format used in CDS 2014.

Gland	Key Hormone	Main Function
Pituitary	GH (Somatotrophin)	Body growth
Pituitary	TSH	Stimulates thyroid
Pituitary	LH	Triggers ovulation
Pituitary	FSH	Egg/sperm development
Thyroid	Thyroxine	Metabolic rate
Parathyroid	Parathormone	Calcium regulation
Pancreas	Insulin	Lowers blood glucose
Pancreas	Glucagon	Raises blood glucose
Adrenal medulla	Adrenaline	Heart rate; fight-or-flight
Adrenal cortex	Cortisol	Stress response
Ovaries	Oestrogen	Female development
Ovaries	Progesterone	Maintains pregnancy
Testes	Testosterone	Male development
Kidneys	Vitamin D (active)	Calcium absorption

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Important Scientists — Tested in CDS

Scientist	Work
F.G. Banting	Discovered insulin
J. Lister	Used carbolic acid as antiseptic in surgery
Louis Pasteur	Established germ theory of disease
E. Jenner (Edward Jenner)	Developed smallpox vaccine (introduced vaccination)

[NDA tested via CDS]

The most common confusion is between Pasteur (germ theory) and Jenner (vaccination). Banting → insulin is the endocrine system connection.

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