Question
Name the five major organ systems of the human body. Describe the main function and key organs of each system: skeletal, muscular, digestive, respiratory, and circulatory.
Solution — Step by Step
The skeletal system provides support, protection, and movement. It includes 206 bones in an adult human, along with cartilage and joints. The skull protects the brain, the ribcage protects the heart and lungs, and the vertebral column protects the spinal cord.
Muscles are attached to bones by tendons. When muscles contract, they pull on bones to produce movement at joints. The three types: skeletal muscles (voluntary — walking, writing), smooth muscles (involuntary — intestine, blood vessels), and cardiac muscle (involuntary — heart).
The digestive system breaks down food into nutrients the body can absorb. The tract: mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus. Key accessory organs: liver (produces bile), pancreas (digestive enzymes + insulin), salivary glands.
We breathe in oxygen and breathe out carbon dioxide. The pathway: nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli (tiny air sacs where gas exchange happens). The diaphragm and intercostal muscles drive breathing.
The heart pumps blood through blood vessels to deliver oxygen and nutrients to cells and remove waste. Arteries carry blood away from the heart. Veins carry blood back. Capillaries are the exchange sites. The human heart has 4 chambers: 2 atria and 2 ventricles.
flowchart TD
A[Human Body Systems] --> B[Skeletal: Support + Protection]
A --> C[Muscular: Movement]
A --> D[Digestive: Break down food]
A --> E[Respiratory: O₂ in, CO₂ out]
A --> F[Circulatory: Transport]
B --> B1[206 bones, joints]
C --> C1[Skeletal, smooth, cardiac muscles]
D --> D1[Mouth to anus + liver, pancreas]
E --> E1[Lungs, alveoli, diaphragm]
F --> F1[Heart, arteries, veins, capillaries]Why This Works
Each system has a specific role, but they all work together. The digestive system provides nutrients, the respiratory system provides oxygen, the circulatory system delivers both to every cell, the skeletal system provides the framework, and muscles enable movement. No system works in isolation.
Common Mistake
Students say “the heart pumps oxygenated blood.” Only the left side of the heart pumps oxygenated blood (to the body). The right side pumps deoxygenated blood to the lungs. The heart is essentially two pumps in one.
For Class 7 exams, remember the flow of blood: Right atrium → Right ventricle → Lungs (pick up O₂) → Left atrium → Left ventricle → Body → Back to right atrium. This is the double circulation pattern.