Human Body Systems
The Integrated Human Body
Major Organ Systems
The human body has 11 organ systems working in concert:
- Integumentary: skin, hair, nails — protection, thermoregulation, sensation
- Skeletal: 206 bones, cartilage, ligaments — support, protection, mineral storage, blood cell production
- Muscular: ~640 muscles — movement, posture, heat generation
- Nervous: brain, spinal cord, nerves — fast electrical signalling, coordination
- Endocrine: glands secreting hormones — slow chemical regulation
- Cardiovascular: heart, blood vessels, blood — transport of O₂, nutrients, wastes, hormones
- Lymphatic/Immune: lymph nodes, immune cells — defence, fluid balance
- Respiratory: lungs, airways — gas exchange (O₂ in, CO₂ out)
- Digestive: mouth to anus — mechanical/chemical digestion, absorption
- Urinary: kidneys, bladder — filtration, waste removal, water/electrolyte balance
- Reproductive: testes/ovaries — gamete production, hormones
Homeostasis by Negative Feedback
Body systems maintain homeostasis primarily through negative feedback:
- A receptor detects a deviation from the set point
- The control centre (often brain/hypothalamus) processes the signal
- An effector (muscle, gland) responds to correct the deviation
- Correction returns the variable toward set point, switching off the signal
Example: Body temperature rises → thermoreceptors detect → hypothalamus signals → sweat glands activate and blood vessels dilate → temperature falls → feedback signals off.
Which organ system is primarily responsible for maintaining blood pH and filtering metabolic waste?
The kidneys filter blood to remove urea and excess ions, and regulate blood pH by controlling bicarbonate reabsorption — core functions of the urinary system.
Correct answer: Urinary system
Negative feedback loops in homeostasis work by:
Negative feedback detects deviation from set point and triggers responses that oppose (correct) the change, restoring equilibrium.
Correct answer: Opposing a change to restore a set point
Explain how the cardiovascular and respiratory systems work together to supply oxygen to body tissues.
Together they form the cardiorespiratory system for gas exchange and delivery.
Correct answer: The respiratory system brings O₂ into the lungs and expels CO₂. In the alveoli, O₂ diffuses into blood and binds to haemoglobin in red blood cells. The cardiovascular system (heart + blood vessels) then pumps oxygenated blood through arteries to tissues. O₂ unloads at tissues, CO₂ is picked up, and deoxygenated blood returns via veins to the lungs. The two systems are functionally inseparable.