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Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Chemical Coordination covers endocrine glands and hormones — focus on matching each gland with its hormone and disorder.
Key Concepts (Quick Recap)
Endocrine vs Exocrine Glands
| Feature | Endocrine Glands | Exocrine Glands |
|---|
| Ducts | Ductless (no ducts) | Have ducts |
| Secretion | Hormones directly into blood | Enzymes/sweat/etc. through ducts |
| Target | Specific organs/tissues (distant) | Local surface |
| Examples | Pituitary, thyroid, adrenal | Sweat glands, salivary glands, liver |
Endocrine Glands and Their Hormones
| Gland | Hormone | Function | Disorder |
|---|
| Hypothalamus | Releasing/inhibiting hormones | Controls pituitary | — |
| Pituitary (Anterior) | GH (Growth Hormone) | Growth of body | Hyper: Gigantism, Acromegaly; Hypo: Dwarfism |
| Pituitary (Anterior) | TSH (Thyroid-stimulating) | Stimulates thyroid | — |
| Pituitary (Anterior) | ACTH (Adrenocorticotropic) | Stimulates adrenal cortex | — |
| Pituitary (Anterior) | FSH and LH | Gamete production, sex hormones | — |
| Pituitary (Anterior) | Prolactin | Milk production | — |
| Pituitary (Posterior) | ADH (Vasopressin) | Water reabsorption in kidney | Hypo: Diabetes insipidus |
| Pituitary (Posterior) | Oxytocin | Uterine contraction, milk ejection | — |
| Thyroid | Thyroxine (T₄), Triiodothyronine (T₃) | Metabolism, growth, development | Hyper: Graves' disease; Hypo: Goitre, Cretinism |
| Thyroid | Calcitonin | Lowers blood calcium | — |
| Parathyroid | PTH (Parathyroid hormone) | Raises blood calcium | Hypo: Tetany; Hyper: Bone demineralisation |
| Adrenal Medulla | Adrenaline (Epinephrine) | Fight or flight response | — |
| Adrenal Cortex | Cortisol | Stress response, metabolism | Hyper: Cushing's; Hypo: Addison's |
| Adrenal Cortex | Aldosterone | Na⁺ reabsorption, K⁺ secretion | — |
| Pancreas (β-cells) | Insulin | Lowers blood sugar | Hypo: Diabetes mellitus |
| Pancreas (α-cells) | Glucagon | Raises blood sugar | — |
| Pineal | Melatonin | Sleep-wake cycle | — |
| Testis | Testosterone | Male sex characteristics | — |
| Ovary | Oestrogen, Progesterone | Female sex characteristics, pregnancy | — |
| Thymus | Thymosin | T-lymphocyte development | — |
Hormone Properties
| Property | Details |
|---|
| Definition | Chemical messengers secreted by endocrine glands directly into blood |
| Target | Act on specific target organs/tissues that have receptors for that hormone |
| Quantity | Produced in very small amounts (micrograms) |
| Speed | Slower than nervous system, but longer lasting |
| Types | Peptide/protein (insulin, GH), Steroid (testosterone, cortisol), Amino acid derivatives (adrenaline, thyroxine) |
Hormonal Disorders
| Disorder | Hormone | Effect |
|---|
| Diabetes mellitus | Insulin deficiency (or resistance) | High blood sugar, excessive thirst, frequent urination |
| Diabetes insipidus | ADH deficiency | Large volumes of dilute urine, excessive thirst |
| Goitre | Iodine deficiency → low thyroxine | Enlarged thyroid gland |
| Cretinism | Thyroxine deficiency in childhood | Mental retardation, stunted growth |
| Graves' disease | Excess thyroxine | Weight loss, rapid heartbeat, bulging eyes |
| Myxoedema | Thyroxine deficiency in adults | Weight gain, fatigue, cold intolerance |
| Gigantism | Excess GH in childhood | Excessive height |
| Acromegaly | Excess GH in adults | Enlarged hands, feet, face |
| Dwarfism | Deficient GH in childhood | Short stature |
| Cushing's syndrome | Excess cortisol | Moon face, obesity, thin skin |
| Addison's disease | Deficient cortisol and aldosterone | Fatigue, low BP, skin darkening |
| Tetany | Deficient PTH | Muscle spasms, cramps (low calcium) |
I. Choose the Best Answer (MCQs)
Q1. The master gland of the body is (a) Thyroid (b) Adrenal (c) Pituitary (d) Pancreas
Answer(c) Pituitary — The pituitary gland is called the master gland because it controls the activity of most other endocrine glands. It secretes TSH (thyroid), ACTH (adrenal), FSH and LH (gonads), and other hormones. However, the pituitary is itself controlled by the hypothalamus.
Q2. Insulin is secreted by (a) Alpha cells of pancreas (b) Beta cells of pancreas (c) Delta cells of pancreas (d) Adrenal cortex
Answer(b) Beta cells of pancreas — Insulin is secreted by the beta (β) cells of the Islets of Langerhans in the pancreas. It lowers blood sugar by promoting glucose uptake by cells and glycogen synthesis in the liver.
Q3. Goitre is caused by deficiency of (a) Calcium (b) Iodine (c) Iron (d) Sodium
Answer(b) Iodine — Goitre (enlarged thyroid gland) is caused by iodine deficiency. Iodine is essential for the synthesis of thyroxine. Without enough iodine, thyroxine production decreases, and the pituitary produces more TSH, causing the thyroid to enlarge.
Q4. The fight or flight hormone is (a) Insulin (b) Thyroxine (c) Adrenaline (d) Cortisol
Answer(c) Adrenaline — Adrenaline (epinephrine) is secreted by the adrenal medulla in response to stress, fear, or danger. It prepares the body for fight or flight by increasing heart rate, blood pressure, breathing rate, and blood sugar levels.
Q5. Dwarfism is caused by (a) Excess growth hormone (b) Deficient growth hormone in childhood (c) Excess thyroxine (d) Deficient insulin
Answer(b) Deficient growth hormone in childhood — Dwarfism is caused by under-secretion of growth hormone (GH) from the anterior pituitary during childhood. It results in short stature but normal body proportions. Excess GH in childhood causes gigantism.
II. Fill in the Blanks
1. The pituitary gland is called the master gland. 2. The pituitary gland is controlled by the hypothalamus. 3. Growth hormone is secreted by the anterior pituitary. 4. Thyroxine requires iodine for its synthesis. 5. The hormone that lowers blood calcium is calcitonin (secreted by the thyroid). 6. The hormone that raises blood calcium is parathyroid hormone (PTH) (secreted by the parathyroid). 7. Insulin is secreted by the beta (β) cells of the Islets of Langerhans. 8. Glucagon is secreted by the alpha (α) cells of the Islets of Langerhans. 9. Diabetes mellitus is caused by deficiency of insulin. 10. Diabetes insipidus is caused by deficiency of ADH (antidiuretic hormone / vasopressin). 11. The adrenal medulla secretes adrenaline (epinephrine). 12. The hormone that regulates the sleep-wake cycle is melatonin (secreted by the pineal gland).
III. True or False (with corrections for false statements)
Q1. The pancreas is only an endocrine gland.
AnswerFalse — Correction: The pancreas is BOTH an endocrine and an exocrine gland. Its endocrine function is secreting insulin and glucagon (Islets of Langerhans) into the blood. Its exocrine function is secreting digestive enzymes (trypsin, amylase, lipase) through ducts into the duodenum.
Q2. Adrenaline is called the emergency hormone.
AnswerTrue — Adrenaline is called the emergency hormone or fight or flight hormone because it is rapidly secreted in response to stress, fear, anger, or danger. It prepares the body for emergency action by increasing heart rate, blood pressure, breathing rate, and blood sugar.
Q3. Cretinism is caused by excess thyroxine in childhood.
AnswerFalse — Correction: Cretinism is caused by deficient thyroxine in childhood. It results in mental retardation, stunted growth, and delayed development. Excess thyroxine in childhood causes hyperthyroidism (Graves' disease).
Q4. The hypothalamus controls the pituitary gland.
AnswerTrue — The hypothalamus controls the pituitary gland through releasing hormones and inhibiting hormones. It connects the nervous system and the endocrine system, making it the link between the brain and the endocrine glands.
Q5. Glucagon lowers blood sugar.
AnswerFalse — Correction: Glucagon raises blood sugar by stimulating glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (new glucose synthesis) in the liver. Insulin lowers blood sugar by promoting glucose uptake by cells.
IV. Match the Following
| Column A | Column B | Answer |
|---|
| 1. Pituitary | (a) Lowers blood sugar | (f) Master gland, controls other glands |
| 2. Thyroid | (b) Raises blood sugar | (g) Metabolism, requires iodine |
| 3. Adrenal medulla | (c) Sleep-wake cycle | (h) Fight or flight (adrenaline) |
| 4. Pancreas (β-cells) | (d) Fight or flight | (a) Lowers blood sugar (insulin) |
| 5. Pancreas (α-cells) | (e) Calcium regulation | (b) Raises blood sugar (glucagon) |
| 6. Pineal | (f) Master gland | (c) Sleep-wake cycle (melatonin) |
V. Answer Briefly (2-mark questions)
Q1. Distinguish between endocrine and exocrine glands.
Answer
| Feature | Endocrine Glands | Exocrine Glands | |---|---|---| | Ducts | Ductless (no ducts) | Have ducts | | Secretion | Hormones into blood | Enzymes/sweat through ducts | | Target | Distant organs (via blood) | Local surface | | Speed | Slow, long-lasting | Fast, short-lasting | | Examples | Pituitary, thyroid, adrenal | Sweat glands, salivary, liver |
Q2. What is diabetes mellitus? What are its symptoms?
Answer
Diabetes mellitus is a metabolic disorder caused by insufficient insulin production (Type 1) or insulin resistance (Type 2), resulting in high blood sugar (hyperglycaemia). Symptoms: 1. Excessive thirst (polydipsia) 2. Frequent urination (polyuria) 3. Excessive hunger (polyphagia) 4. Weight loss despite eating more 5. Fatigue and weakness 6. Glucose in urine (glycosuria)
Q3. What is the role of the hypothalamus in endocrine control?
Answer
The hypothalamus is the link between the nervous system and the endocrine system. It: 1. Produces releasing hormones that stimulate the anterior pituitary to release its hormones 2. Produces inhibiting hormones that suppress anterior pituitary hormone release 3. Produces ADH and oxytocin, which are stored in and released from the posterior pituitary 4. Controls body temperature, hunger, thirst, and sleep-wake cycle
Q4. What are the effects of adrenaline (fight or flight response)?
Answer
Adrenaline prepares the body for emergency action: 1. Increases heart rate and blood pressure 2. Dilates pupils 3. Increases breathing rate (bronchodilation) 4. Increases blood sugar (glycogenolysis in liver) 5. Diverts blood from skin and digestive system to muscles 6. Causes sweating
VI. Answer in Detail (5-mark questions)
Q1. Describe the endocrine glands and their hormones with functions and disorders.
Answer
1. Hypothalamus: - Produces releasing and inhibiting hormones that control the pituitary - Produces ADH and oxytocin (stored in posterior pituitary) - Links the nervous system and endocrine system 2. Pituitary Gland (Master Gland): Anterior Pituitary: - GH (Growth Hormone): Growth of body — Hyper: Gigantism (child), Acromegaly (adult); Hypo: Dwarfism - TSH (Thyroid-Stimulating Hormone): Stimulates thyroid gland - ACTH (Adrenocorticotropic Hormone): Stimulates adrenal cortex - FSH (Follicle-Stimulating Hormone): Gamete production (sperm/egg) - LH (Luteinising Hormone): Ovulation, testosterone production - Prolactin: Milk production in mammary glands Posterior Pituitary: - ADH (Vasopressin): Water reabsorption in kidneys — Hypo: Diabetes insipidus - Oxytocin: Uterine contractions during childbirth, milk ejection 3. Thyroid Gland: - Thyroxine (T₄) and Triiodothyronine (T₃): Regulate basal metabolic rate (BMR), growth, development - Requires iodine for synthesis - Hyper: Graves' disease (weight loss, rapid heartbeat, bulging eyes) - Hypo in children: Cretinism (mental retardation, stunted growth) - Hypo in adults: Myxoedema (weight gain, fatigue, cold intolerance) - Iodine deficiency: Goitre (enlarged thyroid) - Calcitonin: Lowers blood calcium by promoting calcium deposition in bones 4. Parathyroid Glands: - PTH (Parathyroid Hormone): Raises blood calcium by stimulating bone resorption and calcium reabsorption in kidneys - Hypo: Tetany (muscle spasms due to low calcium) 5. Adrenal Gland: Adrenal Medulla: - Adrenaline (Epinephrine): Fight or flight hormone — increases heart rate, blood pressure, blood sugar, breathing rate - Noradrenaline (Norepinephrine): Similar effects, maintains blood pressure Adrenal Cortex: - Cortisol (Glucocorticoid): Stress response, carbohydrate metabolism, anti-inflammatory - Hyper: Cushing's syndrome (moon face, obesity) - Hypo: Addison's disease (fatigue, low BP, skin darkening) - Aldosterone (Mineralocorticoid): Na⁺ reabsorption, K⁺ secretion in kidneys 6. Pancreas: - Insulin (β-cells): Lowers blood sugar — promotes glucose uptake, glycogenesis - Hypo: Diabetes mellitus (high blood sugar, glycosuria, polyuria) - Glucagon (α-cells): Raises blood sugar — promotes glycogenolysis, gluconeogenesis 7. Pineal Gland: - Melatonin: Regulates sleep-wake cycle (circadian rhythm) 8. Thymus: - Thymosin: Promotes T-lymphocyte development (immune function)
Q2. Compare the nervous system and endocrine system.
Answer
| Feature | Nervous System | Endocrine System | |---|---|---| | Mode of signalling | Electrical impulses (neurons) | Chemical messengers (hormones) | | Speed | Very fast (milliseconds) | Slow (seconds to hours) | | Duration | Short-lasting | Long-lasting | | Pathway | Specific nerves to specific organs | Bloodstream to target organs | | Target | Specific cells/muscles/glands | Target organs with specific receptors | | Recovery | Immediate after signal stops | Gradual (hormone must be metabolised) | | Examples | Reflex action, muscle movement | Growth, metabolism, reproduction | Both systems work together: - The hypothalamus links the nervous and endocrine systems - Nervous signals can trigger hormone release (e.g., adrenaline in response to fear) - Hormones can affect neural activity (e.g., thyroxine affects brain development) - Both systems maintain homeostasis through feedback mechanisms
Q3. Explain feedback mechanisms in hormonal regulation.
Answer
Feedback mechanisms regulate hormone levels to maintain homeostasis. There are two types: 1. Negative Feedback (Most Common): Negative feedback reverses a change to restore the normal level. When the level of a substance rises above normal, the body reduces its production; when it falls below normal, the body increases its production. Example 1: Thyroxine Regulation - Hypothalamus releases TRH (Thyrotropin-Releasing Hormone) - TRH stimulates anterior pituitary to release TSH - TSH stimulates thyroid to release thyroxine (T₄) - When thyroxine levels rise above normal, they inhibit TRH and TSH production - This reduces further thyroxine release → levels return to normal - When thyroxine levels fall, inhibition is removed → more TSH and thyroxine are produced Example 2: Blood Sugar Regulation - High blood sugar → Pancreas releases insulin → Blood sugar decreases - Low blood sugar → Pancreas releases glucagon → Blood sugar increases - This keeps blood sugar within the normal range (70-110 mg/dL) 2. Positive Feedback (Rare): Positive feedback amplifies a change, pushing the system further from the normal level. Example: Childbirth (Oxytocin) - Uterine contractions stimulate oxytocin release - Oxytocin causes stronger contractions - Stronger contractions stimulate more oxytocin release - This positive feedback loop continues until the baby is born - Then the loop stops (the stimulus is removed) Example: Lactation (Milk Let-Down Reflex) - Baby suckling stimulates oxytocin release from posterior pituitary - Oxytocin causes milk ejection - Continued suckling → more oxytocin → more milk
Common Mistakes to Avoid
- Confusing insulin and glucagon: Insulin LOWERS blood sugar (promotes glucose uptake). Glucagon RAISES blood sugar (promotes glycogen breakdown). They have opposite effects.
- Calling the pituitary the highest gland: The pituitary is the MASTER gland, but it is controlled by the HYPOTHALAMUS. The hypothalamus is the true link between the nervous and endocrine systems.
- Mixing up diabetes mellitus and diabetes insipidus: Diabetes mellitus = insulin deficiency (high blood sugar). Diabetes insipidus = ADH deficiency (large volumes of dilute urine). They are completely different disorders.
- Confusing cretinism and myxoedema: Cretinism = thyroxine deficiency in CHILDHOOD (mental retardation, stunted growth). Myxoedema = thyroxine deficiency in ADULTS (weight gain, fatigue).
- Forgetting that the pancreas is both endocrine and exocrine: Endocrine = insulin and glucagon (into blood). Exocrine = digestive enzymes (through ducts to duodenum).
- Mixing up calcitonin and PTH: Calcitonin (thyroid) LOWERS blood calcium. PTH (parathyroid) RAISES blood calcium. They have opposite effects.
Exam Checklist
- [ ] Can you distinguish between endocrine and exocrine glands with examples?
- [ ] Can you list the major endocrine glands, their hormones, and functions?
- [ ] Can you match each hormone with its gland, function, and disorder?
- [ ] Can you explain the role of the hypothalamus in endocrine control?
- [ ] Can you explain why the pituitary is called the master gland?
- [ ] Can you describe the fight or flight response (adrenaline effects)?
- [ ] Can you explain blood sugar regulation (insulin and glucagon)?
- [ ] Can you explain thyroxine regulation by negative feedback?
- [ ] Can you distinguish between negative and positive feedback with examples?
- [ ] Can you name and describe hormonal disorders (diabetes, goitre, cretinism, gigantism, dwarfism, Cushing's, Addison's)?
