ICSE 10 Biology Endocrine System Basic

1.0 The Endocrine System

The endocrine system consists of ductless glands that secrete chemical messengers called Hormones directly into the bloodstream. Unlike the nervous system, endocrine coordination is slower but has long-lasting effects.

Key Definition

Hormones: These are chemical secretions produced in minute quantities by endocrine glands, transported by blood, and act on specific Target Organs.

The Thyroid Gland

The Thyroid is a bilobed, butterfly-shaped gland located in the neck, just below the larynx, in front of the trachea.

Hormone Secreted: Thyroxine
Function: Regulates the Basal Metabolic Rate (BMR) of the body.

Disorders of Thyroid Gland

Condition	Cause	Key Symptoms
Simple Goitre	Iodine deficiency	Swelling of the thyroid gland in the neck.
Cretinism	Hyposecretion (Children)	Stunted growth, mental retardation.
Myxoedema	Hyposecretion (Adults)	Swelling of face/hands, sluggishness.
Exophthalmic Goitre	Hypersecretion	Protruding eyeballs, high BMR, restlessness.

⚠️ Exam Tip:

Exocrine glands have ducts (e.g., salivary, sweat glands). Endocrine glands are ductless. Some glands like the Pancreas are "Heterocrine" (both exocrine and endocrine).

💡 Did You Know?

Iodized salt is recommended because Iodine is the raw material needed by the thyroid gland to synthesize Thyroxine!

2.0 The Adrenal Glands

Often called the Supra-renal glands, they play a critical role in responding to stress and regulating salt balance in the body.

1. Adrenal Medulla (Inner Part)

Secretes Adrenaline (Epinephrine), also known as the Emergency Hormone or the "3F" Hormone (Fight, Flight, or Fright).

Functions of Adrenaline:

• Increases heartbeat and blood pressure.
• Stimulates the breakdown of liver glycogen into glucose for instant energy.
• Increases the rate of respiration.
• Dilates the pupils and increases blood supply to muscles.

2. Adrenal Cortex (Outer Part)

Secretes a group of hormones collectively known as Corticoids. The most important ones for the ICSE syllabus are:

• 🛡️ Mineralocorticoids (e.g., Aldosterone): Regulates mineral metabolism (sodium and potassium).
• 🛡️ Glucocorticoids: Regulates carbohydrate, protein, and fat metabolism.

Disorders of Adrenal Cortex

Condition	Cause	Symptoms
Addison's Disease	Hyposecretion	Loss of weight, muscle weakness, skin pigmentation.
Cushing's Syndrome	Hypersecretion	Obesity, "moon face", high blood sugar.

⚠️ Exam Comparison:

Remember that Adrenaline works with the Sympathetic Nervous System. Both prepare the body for the same goal: rapid action during an emergency.

💡 Did You Know?

Adrenaline is often called the Emergency Hormone because it prepares the body to either stand and fight or turn and run away!

3.0 The Pancreas

The pancreas is located behind the stomach. Its endocrine function is carried out by the Islets of Langerhans, which contain three types of cells secreting different hormones.

Cell Type	Hormone	Primary Function
Alpha (α) Cells	Glucagon	Raises blood sugar by converting Glycogen → Glucose.
Beta (β) Cells	Insulin	Lowers blood sugar by converting Glucose → Glycogen.
Delta (δ) Cells	Somatostatin	Inhibits the secretion of both Insulin and Glucagon.

Diabetes Mellitus

Insufficient secretion of Insulin leads to a high level of glucose in the blood, which is eventually excreted in the urine. This condition is called Diabetes Mellitus.

Symptoms of Diabetes Mellitus:

• Hyperglycemia: High blood sugar level.
• Glycosuria: Excretion of glucose in urine.
• Polyuria: Excessive urination.
• Polydipsia: Excessive thirst.

Feedback Mechanism

The timing and amount of hormone released are controlled by Feedback Mechanisms. For example, as blood glucose levels rise, the Beta cells detect the change and release insulin. As the sugar level falls, insulin secretion is reduced. This is Negative Feedback.

⚠️ High-Frequency Distinction:

Do not confuse Diabetes Mellitus (Insulin deficiency) with Diabetes Insipidus (ADH deficiency). In Mellitus, urine contains sugar; in Insipidus, urine is tasteless and dilute.

💡 Did You Know?

Insulin was the first hormone to be synthesized in a laboratory and the first used for treating a human disease!

4.0 The Pituitary Gland

The Pituitary consists of two lobes: the Anterior Lobe and the Posterior Lobe. While the Anterior lobe produces its own hormones, the Posterior lobe only stores and releases hormones produced by the Hypothalamus.

Hormones of the Anterior Lobe

• 📏 Growth Hormone (GH): Essential for the growth of bones and muscles.
  • Hyposecretion (Childhood): Dwarfism.
  • Hypersecretion (Childhood): Gigantism.
  • Hypersecretion (Adults): Acromegaly (thickening of facial bones and hands).
• 🦋 TSH (Thyroid Stimulating Hormone): Stimulates the thyroid gland to produce thyroxine.
• 🔋 ACTH (Adrenocorticotropic Hormone): Stimulates the adrenal cortex.
• 🐣 Gonadotropic Hormones: Regulate the activities of the testes and ovaries.

Hormones of the Posterior Lobe

Hormone	Primary Function
ADH (Vasopressin)	Regulates water reabsorption in kidney tubules. Deficiency causes Diabetes Insipidus.
Oxytocin	Stimulates uterine contractions during childbirth and milk ejection from mammary glands.

5.0 Nervous vs. Endocrine Control

Feature	Nervous System	Endocrine System
Transmission	Electrical impulses via nerves	Chemical messengers via blood
Speed	Rapid (Instant)	Slower
Duration	Short-lived	Long-lasting

⚠️ Exam Alert:

In "Name the Following," if asked for the hormone that controls the basal metabolic rate, it's Thyroxine. If asked for the hormone that controls the secretion of thyroxine, it's TSH.

💡 Did You Know?

The Hypothalamus is the link between the nervous and endocrine systems. It tells the pituitary gland exactly when to release its hormones!