Quick answer: Growth hormone is secreted by the pituitary gland. Too little growth hormone in childhood causes dwarfism, and too much causes gigantism. The thyroid gland needs iodine to make the hormone thyroxin, so a diet lacking iodine causes goitre (a swollen neck). This is why doctors advise using iodised salt.
The nervous system uses fast electrical impulses for quick actions, such as blinking or pulling your hand away from a hot object. Slow, long-term processes like growth, metabolism and sexual maturation are controlled differently: by hormones, chemical messengers that travel through the blood to reach their target organs.
A small, pea-sized gland at the base of the brain controls how much we grow. If it releases too little growth hormone during childhood, a person develops dwarfism; if it releases too much, the result is gigantism. In the neck, another gland uses iodine from our food to make a hormone that controls metabolism. Without enough iodine, this gland swells, causing goitre.
In CBSE Class 10 Science, Chapter 6 (Control and Coordination), the pituitary gland and growth hormone, dwarfism and gigantism, the thyroid gland and thyroxin, and why iodised salt is advised are frequently asked board exam topics.
What You Will Learn
- What endocrine glands are and how they differ from exocrine glands
- Why the pituitary gland is called the master gland
- The functions of growth hormone (GH)
- Dwarfism (too little GH) vs gigantism (too much GH)
- Where the thyroid gland is and what thyroxin does
- Why iodine is needed to make thyroxin
- What goitre is and why iodised salt prevents it
1. What Are Endocrine Glands?
Exocrine glands, such as salivary glands and tear glands, release their secretions through tubes called ducts. Endocrine glands work differently:
- Endocrine glands are ductless. They have no ducts.
- They release their secretions, called hormones, directly into the blood.
- Blood carries hormones all over the body, but each hormone acts only on specific target organs or tissues.
| Feature | Pituitary gland | Thyroid gland |
|---|---|---|
| Location | Base of the brain, attached below the hypothalamus | Neck, in front of the windpipe (trachea) |
| Key hormone (Class 10) | Growth hormone (GH) | Thyroxin |
| Main role | Controls growth and regulates other endocrine glands | Regulates carbohydrate, protein and fat metabolism |
| Linked disorder | Dwarfism, gigantism | Goitre (iodine deficiency) |
2. The Pituitary Gland and Growth Hormone
The pituitary gland is a pea-sized endocrine gland at the base of the brain, attached to the hypothalamus. It is called the master gland because many of its hormones control the activity of other endocrine glands, such as the thyroid, adrenal glands and the gonads (testes and ovaries).
Functions of Growth Hormone
- Regulates the growth and development of the body, especially bones and muscles, during childhood and adolescence.
- Promotes the growth of long bones, such as the bones of the arms and legs.
- Stimulates protein synthesis, which helps tissues grow.
3. Dwarfism vs Gigantism
The amount of growth hormone in the blood must be balanced. Too little or too much during childhood causes a growth disorder.
| Disorder | Cause | Effect on the body |
|---|---|---|
| Dwarfism | Deficiency (too little) of growth hormone in childhood | Very short height; body proportions are usually normal |
| Gigantism | Excess (too much) of growth hormone in childhood | Unusually tall height due to excessive growth of long bones |
Key point: Dwarfism is caused by a deficiency of growth hormone from the pituitary gland during childhood, while gigantism is caused by an excess of growth hormone during childhood.
4. The Thyroid Gland and Thyroxin
The thyroid gland is a butterfly-shaped gland in the neck, located in front of the windpipe (trachea), just below the voice box (larynx). It secretes the hormone thyroxin.
Functions of Thyroxin
- Regulates metabolism: Thyroxin regulates carbohydrate, protein and fat metabolism in the body, which controls how fast cells use nutrients to release energy.
- Supports growth and development: It is needed for normal physical growth and brain development in children.
- Helps maintain body temperature: By controlling the rate of metabolism, it affects how much heat the body produces.
5. Why Is Iodised Salt Advised? (The Goitre Connection)
Common board question: Why is the use of iodised salt advisable? Which disease is caused by a deficiency of iodine in the diet?
Answer
1. Iodine is needed to make thyroxin. The thyroid gland uses iodine to make the hormone thyroxin. Without enough iodine in the diet, the thyroid gland cannot produce enough thyroxin.
2. Iodine deficiency causes goitre. When the diet lacks iodine (more common in hilly and mountainous areas, where soil and water are low in iodine), the thyroid gland cannot make enough thyroxin. The gland enlarges, causing a visible swelling in the front of the neck called goitre.
3. Iodised salt is a simple solution. Common salt is iodised by adding small amounts of potassium iodate () or potassium iodide (). Since almost everyone uses salt every day, iodised salt is an easy way to provide the iodine the body needs, helping to prevent goitre and support normal growth and brain development in children.
Model answer: Iodine is essential for the thyroid gland to make thyroxin, which regulates carbohydrate, protein and fat metabolism. A deficiency of iodine in the diet causes goitre, a swelling of the neck. Iodised salt provides the iodine we need, so its use is advised.
6. Summary Table
| Endocrine gland | Location | Hormone | Disorder |
|---|---|---|---|
| Pituitary gland | Base of the brain | Growth hormone | Dwarfism (deficiency), gigantism (excess) |
| Thyroid gland | Neck | Thyroxin | Goitre (due to iodine deficiency) |
| Pancreas | Below the stomach | Insulin | Diabetes (high blood sugar) |
7. Exam Tips and Common Mistakes
Exam Tip: If asked "Which mineral is needed to make thyroxin?", write iodine. If asked for the disease caused by its deficiency, write goitre and mention its main symptom, a swollen neck.
Common Mistake: Do not say goitre is caused by too little growth hormone. Goitre is linked to the thyroid gland and iodine deficiency, while dwarfism is linked to the pituitary gland and growth hormone deficiency.
Common Mistake: Do not confuse the timing. Dwarfism and gigantism are caused by too little or too much growth hormone during childhood, when the body is still growing.
Frequently Asked Questions
Which gland secretes growth hormone?
Growth hormone is secreted by the pituitary gland, located at the base of the brain.
What causes dwarfism?
Dwarfism is caused by a deficiency of growth hormone from the pituitary gland during childhood.
What causes gigantism?
Gigantism is caused by an excess of growth hormone from the pituitary gland during childhood.
Why is the pituitary gland called the master gland?
Because many of its hormones control the activity of other endocrine glands, such as the thyroid, adrenal glands and gonads.
Why is iodised salt advised in our diet?
Iodine is needed by the thyroid gland to make thyroxin. A lack of iodine causes goitre, so iodised salt is advised to make sure we get enough iodine.
What is goitre?
Goitre is a swelling of the neck caused by enlargement of the thyroid gland, usually due to a deficiency of iodine in the diet.