Biology · Chapter 03

🫀 Human Body Systems

Overview of all 11 organ systems.

💡 11 Systems Working Together

Your body has 11 organ systems — each with a specific job, all working as one team. No single system can survive alone.

The systems:

• Skeletal — bones, support, protects organs
• Muscular — movement, posture
• Nervous — brain, nerves, controls everything
• Circulatory — heart, blood, transport
• Respiratory — lungs, gas exchange
• Digestive — stomach, intestines, food breakdown
• Excretory — kidneys, waste removal
• Endocrine — hormones, slow control
• Reproductive — making offspring
• Immune — defense against disease
• Integumentary — skin, hair, nails

🤝 Systems work together (interdependence)

When you run a 100m sprint:
• Nervous system sends signals → muscular system contracts
• Respiratory system brings more oxygen
• Circulatory system pumps faster
• Skeletal system provides the framework
• Endocrine system releases adrenaline

All 5+ systems coordinate in less than a second — that's why life is amazing.

🧠 Master controller — the brain

The brain has only 2% of body weight but uses 20% of body's energy. It controls everything via two communication systems:

1. Nervous — fast (milliseconds) — electrical signals through nerves
2. Endocrine — slow (minutes to hours) — chemical hormones through blood

💡 NEET high-yield facts

• Longest bone: Femur (thigh)
• Smallest bone: Stapes (ear)
• Largest organ: Skin (~2m² surface area)
• Strongest muscle (by force): Masseter (jaw)
• Hardest substance: Tooth enamel
• Adult human has 206 bones; baby has ~270 (some fuse later)
• 5 litres of blood in an average adult — pumped by heart ~100,000 times/day

🎬

Explore the Body Systems

Animation

Tap any organ. See which system it belongs to and what it does.

🔬

Match the System to its Job

Interactive

Pick a system to see its main organs and function.

Main organsHeart, blood vessels, blood

Main functionTransport O₂, nutrients, hormones

Blood has 3 types of cells: RBC (carry O₂), WBC (immune defence), platelets (clotting).

Practice (NCERT): Which system removes urea from the body, and which organ is mainly responsible?

The excretory system removes urea. The main organ is the kidney. Urea is produced in the liver as a waste product of protein breakdown, carried by blood to kidneys, filtered into urine, stored in the urinary bladder, and finally excreted through the urethra.

Practice (NEET): Which gland is called the "master gland" and why?

The pituitary gland is called the master gland because it controls many other endocrine glands by releasing hormones that regulate them. For example, it releases TSH (which controls thyroid), ACTH (controls adrenal cortex), FSH/LH (controls reproductive glands), and growth hormone. It's a tiny pea-sized gland at the base of the brain.