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Biology - The Endocrine System

Grade 10ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Endocrine glands are ductless glands that secrete chemical messengers called hormones directly into the blood stream to reach a target organ.

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The Pituitary Gland is the 'Master Gland' located at the base of the midbrain. It secretes hormones like Growth Hormone (GHGH), Thyroid Stimulating Hormone (TSHTSH), and Antidiuretic Hormone (ADHADH).

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The Thyroid Gland requires Iodine to produce Thyroxine. Hyposecretion in adults leads to Myxoedema, while in children it causes Cretinism. Hypersecretion leads to Exophthalmic Goitre.

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The Pancreas contains the Islets of Langerhans. β\beta-cells secrete Insulin (lowers blood glucose), α\alpha-cells secrete Glucagon (raises blood glucose), and δ\delta-cells secrete Somatostatin.

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The Adrenal Glands consist of the Cortex (secretes Cortisone/Aldosterone) and Medulla (secretes Adrenaline). Adrenaline is the 'Fight or Flight' hormone that prepares the body for emergencies.

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The Feedback Mechanism regulates hormone levels. For example, a rise in blood glucose levels triggers the secretion of insulin, which then lowers the glucose level, subsequently reducing insulin production.

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Diabetes Mellitus is caused by InsulinInsulin deficiency, leading to high blood sugar (HyperglycemiaHyperglycemia). Diabetes Insipidus is caused by ADHADH deficiency, leading to frequent urination.

📐Formulae

Glucose→InsulinGlycogen (Stored in Liver)Glucose \xrightarrow{Insulin} Glycogen \text{ (Stored in Liver)}

Glycogen→GlucagonGlucoseGlycogen \xrightarrow{Glucagon} Glucose

Basal Metabolic Rate (BMR)∝Thyroxine levels\text{Basal Metabolic Rate (BMR)} \propto \text{Thyroxine levels}

↓ADH  ⟹  Excessive dilute urine (Diabetes Insipidus)\downarrow ADH \implies \text{Excessive dilute urine (Diabetes Insipidus)}

💡Examples

Problem 1:

A patient presents with a swollen neck, increased heart rate, and protruding eyeballs. Identify the condition and the hormone responsible.

Solution:

The condition is Exophthalmic Goitre (a form of Hyperthyroidism), caused by the over-secretion of Thyroxine.

Explanation:

Hyperthyroidism increases the BMRBMR (Basal Metabolic Rate), causing the heart to beat faster and leading to the deposition of fat behind the eyes, which results in protruding eyeballs.

Problem 2:

Explain the biological response when a person is suddenly frightened by a wild animal.

Solution:

The Adrenal Medulla secretes Adrenaline (C9H13NO3C_9H_{13}NO_3) into the blood.

Explanation:

Adrenaline increases the heart rate, diverts blood flow from the digestive system to the muscles, and increases the conversion of Glycogen→GlucoseGlycogen \rightarrow Glucose to provide immediate energy for 'fight or flight'.

Problem 3:

Why is the Pituitary gland often called the 'Master Gland'?

Solution:

Because it produces 'Tropic Hormones' that regulate the activities of other endocrine glands.

Explanation:

For example, TSHTSH stimulates the Thyroid gland and ACTHACTH stimulates the Adrenal Cortex. Its function is coordinated by the Hypothalamus.