Study sheet: Human Gaseous Exchange

📋 Course Outline

1. Gaseous Exchange System
2. Breathing Mechanics
3. Breathing Model and Measurements
4. Gas Exchange at Alveoli
5. Gas Exchange in Tissues
6. Respiratory Homeostasis
7. Altitude and Oxygen Transport

📖 1. Gaseous Exchange System

🔑 Key Concepts & Definitions

• Cellular respiration : a chemical process within cells that releases energy needed by plants and animals for survival
• Gaseous exchange : a physical process involving the exchange of gases between the air and the blood in the lungs

📝 Essential Points

• The human gas exchange system consists of:
  • air passages
  • lungs
  • the muscles involved in ventilation

💡 Memory Hook

ALM: air passages, lungs, muscles

📖 2. Breathing Mechanics

★ Must-know

• 🔄 During inhalation: the diaphragm contracts, flattens, and moves downward, the external intercostal muscles contract, the ribcage lifts upward and moves outward, chest volume increases and lung pressure decreases, air flows into the lungs because atmospheric pressure is greater

• 🔄 During exhalation: the diaphragm relaxes and moves upward, the external intercostal muscles relax, the ribcage moves downward and inward, lung pressure increases relative to outside air pressure, air is forced out until pressures equalise

Further detail

• Oxygen is used by cells in cellular respiration, carbon dioxide is produced by cellular respiration and must be removed, and nitrogen is not used in the human breathing system.

💡 Memory Hook

Inhalation lowers lung pressure; exhalation raises it

📖 3. Breathing Model and Measurements

🔑 Key Concepts & Definitions

• Tidal volume : the amount of air inhaled or exhaled during a normal breath
• Vital capacity : the maximum amount of air a person can exhale after taking the deepest possible breath
• Lung capacity : the total amount of air the lungs can hold
• Residual volume : the amount of air remaining in the lungs after maximal forced exhalation

📝 Essential Points

• A spirometer measures the volume of air entering and leaving the lungs during inhalation and exhalation.

💡 Memory Hook

A bell jar, balloon lungs, and rubber-sheet diaphragm model the thorax

📖 4. Gas Exchange at Alveoli

📝 Essential Points

• At the alveoli, oxygen diffuses from inhaled air into the blood and carbon dioxide diffuses from the blood into the alveoli because of concentration gradients.

📌 Blood arriving at the alveolar capillaries from the heart is deoxygenated and has a low oxygen concentration, whereas blood leaving the alveoli is oxygenated and has a high oxygen concentration.

💡 Memory Hook

Concentration gradients → oxygen enters blood and carbon dioxide enters alveoli

📖 5. Gas Exchange in Tissues

📝 Essential Points

• Most oxygen is transported by red blood cells when it combines with haemoglobin to form oxyhaemoglobin.

• Most carbon dioxide is transported in the blood plasma in the form of bicarbonate ions.

• In tissue capillaries, oxygen diffuses from oxygenated blood into cells, while carbon dioxide produced by cellular respiration diffuses from cells into the blood and is transported to the lungs for exhalation.

💡 Memory Hook

Oxygen moves from blood to cells, whereas carbon dioxide moves from cells to blood

📖 6. Respiratory Homeostasis

🔑 Key Concepts & Definitions

• Negative feedback : a mechanism that stabilises a system and returns it to its normal state

★ Must-know

• 🔄 During exercise: cellular respiration increases, blood carbon dioxide levels rise, the respiratory centre in the medulla oblongata detects the increase, the respiratory muscles increase the rate and depth of breathing

• Homeostasis is the ability of the body to return carbon dioxide levels to normal.

Further detail

• During homeostatic control, heart rate increases to increase blood flow and transport gases rapidly, while increased breathing brings in more oxygen and removes more carbon dioxide.

💡 Memory Hook

Exercise raises carbon dioxide → the medulla increases breathing rate and depth

📖 7. Altitude and Oxygen Transport

🔑 Key Concepts & Definitions

• Altitude : the height of a place above sea level, measured in metres

📝 Essential Points

📌 At high altitudes, less oxygen is absorbed by red blood cells, so the body compensates by trying to produce more red blood cells to carry oxygen.

💡 Memory Hook

Higher altitude → less oxygen absorbed by red blood cells → increased red blood-cell production

📊 Synthesis Tables

Lung Volume Terms

Term	Meaning
Tidal volume	Air inhaled or exhaled during a normal breath
Vital capacity	Maximum air exhaled after the deepest possible breath
Residual volume	Air remaining after maximal forced exhalation
Lung capacity	Total amount of air the lungs can hold