The Endocrine Glands

ICSE Class 10 Biology • Chapter 09

1. Characteristics of Hormones

Hormones: Chemical messengers secreted directly into the blood by endocrine glands (Ductless glands) that act on specific target organs.

Properties:

Secreted in very small amounts.
Poured directly into blood (No ducts).
Act on target organs away from source.
Protein or Steroid in nature.

2. Adrenal Glands

Location: Cap-like structures above each Kidney.

A. Adrenal Cortex (Outer)

Cortisone: Suppresses inflammation. Regulates glucose metabolism.
Mineralocorticoids: Regulates mineral balance (Na+, K+).
Disorder - Addison's Disease: Hyposecretion. Symptoms: Bronze skin, low BP.
Disorder - Cushing's Syndrome: Hypersecretion. Symptoms: Moon face, obesity.

B. Adrenal Medulla (Inner)

Adrenaline (Epinephrine): The "Emergency Hormone" (Fight or Flight).

Practice Q1: Emergency Hormone

THINKING Why is Adrenaline called the "Fight or Flight" hormone?

Ans: It prepares the body for emergency situations by increasing heart rate, blood pressure, and glucose supply to muscles.

3. Pancreas

A Heterocrine gland (both Exocrine and Endocrine). Endocrine part: Islets of Langerhans.

Practice Q2: Diabetes

BOARD QUESTION State the exact location of the Beta cells and their function.

Ans: Location: Islets of Langerhans in Pancreas. Function: Secrete Insulin to lower blood sugar.

Diabetes Mellitus: Caused by hyposecretion of Insulin. Features: High blood sugar (Hyperglycemia), Sugar in urine (Glycosuria), Thirst, Polyuria.

4. Thyroid Gland

Location: In the neck, below the larynx.

Thyroxine: Regulates Basal Metabolic Rate (BMR).

Disorders:

Simple Goitre: Swelling of neck due to Iodine deficiency.
Cretinism: Hyposecretion in children. Dwarfism + Mental retardation.
Myxoedema: Hyposecretion in adults. Swollen face, sluggishness.
Exophthalmic Goitre: Hypersecretion. Protruding eyes, high BMR, restlessness.

5. Pituitary Gland (Master Gland)

Location: Base of the brain. Attached to Hypothalamus.

A. Anterior Lobe

Growth Hormone (GH/STH): Promotes growth.
Hypo (child): Dwarfism.
Hyper (child): Gigantism.
Hyper (adult): Acromegaly (Large facial bones).
TSH (Thyroid Stimulating Hormone): Activates Thyroid.
ACTH: Activates Adrenal Cortex.
Gonadotropins (FSH/LH): Regulates reproductive organs.

B. Posterior Lobe

ADH (Vasopressin): Reabsorption of water from kidney tubules. Hyposecretion causes Diabetes Insipidus (Excess diluted urine, No sugar).
Oxytocin: Contraction of Uterus during childbirth. Milk ejection.

Exam Practice Questions

Practice Q3: Thyroid

CONCEPT CHECK Which mineral is essential for the synthesis of Thyroxine?

Ans: Iodine.

Q1: Why is the pancreas called a mixed gland?

Ans: It has exocrine part (Pancreatic duct secreting enzymes) and endocrine part (Islets of Langerhans secreting Insulin/Glucagon directly into blood).