The Bio Brief

 What are Hormones?

• Hormones are chemical messengers.
• They are released by endocrine glands.
• They travel through blood to reach target organs.
• They help in control and coordination of body activities.

Unlike nerves (electrical signals), hormones:

• Act slowly
• Affect many organs at the same time
• Have long-lasting effects

 Why are Hormones Needed?

Some situations need whole-body preparation, not just one organ.

Example: A squirrel in danger

• It must fight or run
• Needs:
  • More energy
  • Faster breathing
  • More blood to muscles

This is done using a hormone called adrenaline.

Adrenaline – “Emergency Hormone”

• Secreted by: Adrenal glands
• Released directly into blood

Effects of Adrenaline:

Danger / Fear

      ↓

Adrenal glands release adrenaline

      ↓

Blood carries adrenaline

      ↓

Target organs respond

Changes in the body:

•  Heart beats faster → more oxygen to muscles
•  Breathing rate increases
•  Blood supply to digestion decreases
•  Blood supply to skeletal muscles increases

 Result: Body is ready to fight or run

 Endocrine System

• A group of hormone-secreting glands
• Controls:
  • Growth
  • Metabolism
  • Puberty
  • Blood sugar
  • Stress responses

 Role of Hormones in Growth

Animals don’t grow in random directions like plants.
Growth is controlled and specific.

Example:

• We grow hands where hands should be
• Not fingers on the face

Hormones ensure proper body design.

Important Hormones and Their Functions

1. Thyroxin

• Gland: Thyroid gland
• Needs: Iodine
• Function:
  • Regulates metabolism of:
    • Carbohydrates
    • Proteins
    • Fats
  • Supports growth and energy balance

 Iodised salt provides iodine
 Iodine deficiency → Goitre (swollen neck)

Low iodine

    ↓

Less thyroxin

    ↓

Poor metabolism

    ↓

Goitre

2. Growth Hormone

• Gland: Pituitary gland
• Function:
  • Controls height and body growth

 Deficiency in childhood → Dwarfism
 Excess → Gigantism

3. Sex Hormones (Puberty Changes)

Hormone	Released in	Effects
Testosterone	Males	Deep voice, beard, muscles
Oestrogen	Females	Breast development, wider hips

 Responsible for puberty changes (10–12 years)

4. Insulin

• Gland: Pancreas
• Function:
  • Controls blood sugar level

 Less insulin → Diabetes
 Patients may need insulin injections

High blood sugar

      ↓

Pancreas releases insulin

      ↓

Sugar enters cells

      ↓

Blood sugar decreases

Feedback Mechanism (Very Important!)

Hormone release is self-regulated.

Example: Insulin

Blood sugar rises

      ↓

Pancreas secretes insulin

      ↓

Blood sugar falls

      ↓

Insulin secretion reduces

This keeps hormone levels balanced

 Key Differences: Nervous vs Hormonal Control

Nervous Control	Hormonal Control
Electrical signals	Chemical signals
Very fast	Slow
Short-lasting	Long-lasting
Acts on few organs	Acts on many organs

 SUMMARY

• Hormones = chemical messengers
• Travel through blood
• Control growth, metabolism, stress, puberty
• Adrenaline prepares body for emergencies
• Thyroxin needs iodine
• Growth hormone controls height
• Insulin controls blood sugar
• Feedback mechanism maintains balance