Lesson 11: Human Body Systems
The human body is made up of 11 organ systems that work together to maintain homeostasis — a stable internal environment. Each system has specialized organs that carry out specific functions, but no system works in isolation.
Key Concepts
Cardiovascular System
Heart pumps blood through ~60,000 miles of blood vessels. Arteries carry oxygenated blood away from the heart. Veins return deoxygenated blood. Capillaries are where gas/nutrient exchange occurs.
Respiratory System
Lungs exchange O₂ and CO₂ with the blood. Diaphragm contracts to inhale (negative pressure), relaxes to exhale. Gas exchange occurs across the thin alveoli walls.
Digestive System
Breaks food into nutrients: mouth (mechanical & chemical), stomach (acid + enzymes), small intestine (absorption of nutrients), large intestine (water absorption, waste formation).
Nervous System
Brain (central processing), spinal cord (highway), peripheral nerves (sensors & effectors). Neurons communicate via electrical impulses and neurotransmitters across synapses.
Immune System
First line: skin & mucus (physical barriers). Second line: inflammation & fever (non-specific). Third line: lymphocytes — B cells make antibodies; T cells destroy infected cells. Vaccines train this system.
🔬 Virtual Lab: Body Systems Flashcard Quiz
A body system is described — identify it! Click the correct system name.
✅ Check Your Understanding
1. Where does gas exchange (O₂/CO₂) occur in the lungs?
2. Which cells produce antibodies in the immune system?
3. What does the small intestine primarily do?