Breathing and Exchange of Gases: chapter on a page

A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).

About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.

This note's current text has no applied fact-check on record.

Mind map

Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.

The mind map as a list

Key ideas
- Respiratory organs
- Breathing involves pressure changes
- Lung volumes
- Partial pressure gradients
- Haemoglobin
- Carbon dioxide transport
- Regulation of breathing
Formulas and facts
- Tidal volume (TV)
- Inspiratory reserve volume (IRV)
- Expiratory reserve volume (ERV)
- Residual volume (RV)
- Vital capacity (VC) = TV + IRV + ERV
- Total lung capacity (TLC) = VC + RV
- Oxygen-haemoglobin equation
Worked examples
- Calculating vital capacity
- Direction of gas diffusion
- Effect of exercise on the…
Watch out for
- Confusing breathing (a mechanical…
- Believing that lungs actively expand…
- Thinking that oxygen is transported…
- Adding residual volume when…
- Assuming expiration is always an…

What this chapter is about

This chapter explains how the human body obtains oxygen from the atmosphere and releases carbon dioxide, a metabolic waste product. Breathing, also called pulmonary ventilation, is the mechanical process of moving air into and out of the lungs. Gas exchange refers to the diffusion of oxygen and carbon dioxide across respiratory surfaces. Both processes are essential because cellular respiration in mitochondria requires a continuous supply of oxygen to release energy from nutrients.

Key ideas

Respiratory organs in humans include the nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and alveoli; the alveoli are the sites of gas exchange.
Breathing involves pressure changes: contraction of the diaphragm and external intercostal muscles increases thoracic volume, lowers intra-pulmonary pressure below atmospheric pressure, and draws air in; relaxation reverses these changes for exhalation.
Lung volumes (tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume) and lung capacities (vital capacity, total lung capacity, functional residual capacity, inspiratory capacity) quantify pulmonary function.
Partial pressure gradients drive diffusion: oxygen moves from alveolar air (pO₂ ≈ 104 mm Hg) to deoxygenated blood (pO₂ ≈ 40 mm Hg); carbon dioxide moves in the opposite direction.
Haemoglobin (Hb) binds oxygen cooperatively; the oxygen-haemoglobin dissociation curve is sigmoidal and shifts right under low pH, high pCO₂ or high temperature, releasing oxygen to active tissues.
Carbon dioxide transport occurs in three forms: dissolved in plasma (about 7 %), as bicarbonate ions (about 70 %), and bound to haemoglobin as carbamino-haemoglobin (about 23 %).
Regulation of breathing is primarily by the respiratory centre in the medulla oblongata, influenced by chemoreceptors sensitive to blood pCO₂, pH and, to a lesser extent, pO₂.

Formulas and facts to remember

Tidal volume (TV): volume of air inspired or expired during normal breathing; about 500 mL in a healthy adult.
Inspiratory reserve volume (IRV): additional air that can be forcibly inhaled after a normal inspiration; about 2500–3000 mL.
Expiratory reserve volume (ERV): additional air that can be forcibly exhaled after a normal expiration; about 1000–1100 mL.
Residual volume (RV): air remaining in lungs after maximum exhalation; about 1100–1200 mL.
Vital capacity (VC) = TV + IRV + ERV: maximum air a person can breathe out after deepest inhalation; roughly 3500–4500 mL.
Total lung capacity (TLC) = VC + RV: total volume of air lungs can hold; about 5000–6000 mL.
Oxygen-haemoglobin equation: Hb + O₂ ⇌ HbO₂ (oxyhaemoglobin); equilibrium favours HbO₂ at high pO₂ (lungs) and favours release of O₂ at low pO₂ (tissues).
Bicarbonate formation in RBC: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻; catalysed by carbonic anhydrase inside red blood cells.

Common mistakes

Confusing breathing (a mechanical, physical process) with cellular respiration (a biochemical process in mitochondria) → remember that breathing supplies the oxygen that cellular respiration uses.
Believing that lungs actively expand on their own → the lungs expand passively because the diaphragm and intercostal muscles enlarge the thoracic cavity, lowering pressure inside.
Thinking that oxygen is transported mainly as dissolved gas in plasma → about 97 % of oxygen is carried bound to haemoglobin, not dissolved.
Adding residual volume when calculating vital capacity → vital capacity does not include residual volume; it is TV + IRV + ERV only.
Assuming expiration is always an active process → quiet expiration is largely passive, caused by elastic recoil of lungs; forceful expiration requires internal intercostal and abdominal muscles.

Quick revision

Alveoli are the thin-walled sacs where gas exchange occurs; their large surface area and moist lining aid diffusion.
Inhalation occurs when intra-pulmonary pressure drops below atmospheric pressure due to expansion of the thoracic cavity.
Vital capacity = tidal volume + inspiratory reserve volume + expiratory reserve volume.
Haemoglobin carries about 97 % of blood oxygen; its sigmoidal curve allows efficient loading in lungs and unloading in tissues.
About 70 % of carbon dioxide is transported as bicarbonate ions formed inside red blood cells.
The medulla oblongata's respiratory centre adjusts breathing rate mainly in response to blood pCO₂ and pH.