Respiratory System

• Respiration is taking in oxygen to slowly 'burn' food and release the energy locked inside it.
• Inputs and outputs: O ₂ and glucose are used; CO ₂, water and energy are released.
• The main fuel broken down is glucose; fats and proteins can also be used when needed.
• CO ₂ is a harmful waste gas that the body must throw out continuously.
• Breathing is only the physical taking in and pushing out of air – the first step of respiration.
• Respiration is bigger than breathing: it adds the chemical release of energy inside cells.
• Breathing — Physical exchange of air (in and out)
• Respiration — Breathing + energy release in cells

Respiration is taking in oxygen to slowly 'burn' food and release the energy locked inside it.

Inputs and outputs: O ₂ and glucose are used; CO ₂, water and energy are released.

The main fuel broken down is glucose; fats and proteins can also be used when needed.

CO ₂ is a harmful waste gas that the body must throw out continuously.

Breathing is only the physical taking in and pushing out of air – the first step of respiration.

Respiration is bigger than breathing: it adds the chemical release of energy inside cells.

• The organ used depends on where the animal lives and how complex its body is.
• Simplest method is diffusion – gases spread from high to low concentration, no special organ needed.
• Sponges, coelenterates (Hydra), flatworms exchange gases by diffusion over the whole body surface.
• Earthworm breathes through its moist skin – called cutaneous respiration.
• Insects use a network of air tubes called tracheal tubes carrying air to inner tissues.
• Gills take dissolved O ₂ from water (fishes); lungs are used by land animals.
• The frog has lungs but also breathes through its moist skin (only via skin during hibernation).
• Sponge, Hydra, flatworm — Diffusion over body surface
• Earthworm — Moist skin (cutaneous)
• Insects — Tracheal tubes
• Fishes — Gills (branchial)
• Frog (amphibian) — Lungs + moist skin
• Reptiles, birds, mammals — Lungs (pulmonary)

Simplest method is diffusion – gases spread from high to low concentration, no special organ needed.

Sponges, coelenterates (Hydra), flatworms exchange gases by diffusion over the whole body surface.

Earthworm breathes through its moist skin – called cutaneous respiration.

Insects use a network of air tubes called tracheal tubes carrying air to inner tissues.

Gills take dissolved O ₂ from water (fishes); lungs are used by land animals.

The frog has lungs but also breathes through its moist skin (only via skin during hibernation).

• Air route: Nostrils → Nasal chamber → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.
• Nasal chamber filters dust, warms and moistens the incoming air.
• Pharynx (throat) is a common passage for both food and air.
• Larynx is the sound box (voice box); the epiglottis flap stops food entering the airway.
• Trachea (windpipe) divides at the 5th thoracic vertebra into right and left primary bronchi.
• Trachea and bronchi are kept open by incomplete Cshaped cartilage rings so airways never collapse.
• Each bronchiole ends in millions of thin-walled, bloodrich alveoli – the gas-exchange air sacs.

Nasal chamber filters dust, warms and moistens the incoming air.

Pharynx (throat) is a common passage for both food and air.

Larynx is the sound box (voice box); the epiglottis flap stops food entering the airway.

Trachea (windpipe) divides at the 5th thoracic vertebra into right and left primary bronchi.

Trachea and bronchi are kept open by incomplete Cshaped cartilage rings so airways never collapse.

Each bronchiole ends in millions of thin-walled, bloodrich alveoli – the gas-exchange air sacs.

• The branching bronchi, bronchioles and alveoli make up the two pink, elastic lungs.
• Each lung is wrapped in a double-layered membrane called the pleura.
• Pleural fluid between the layers reduces friction as the lungs move.
• Lungs sit in an air-tight thoracic chamber (chest cavity).
• Boundaries: vertebral column at back, sternum in front, ribs at sides, diaphragm below.
• The dome-shaped diaphragm is the main driver (muscle) of breathing.
• Nasal chamber — Filter, warm, moisten air
• Pharynx — Common food + air passage
• Larynx — Sound production (voice box)
• Epiglottis — Covers glottis during swallowing
• Trachea / bronchi — Carry air; held open by cartilage
• Alveoli — Site of gas exchange
• Diaphragm — Main breathing muscle

The branching bronchi, bronchioles and alveoli make up the two pink, elastic lungs.

Each lung is wrapped in a double-layered membrane called the pleura.

Pleural fluid between the layers reduces friction as the lungs move.

The dome-shaped diaphragm is the main driver (muscle) of breathing.

• The chest works like a bellows: make space bigger and air rushes in, smaller and air is pushed out.
• Two stages: inspiration (inhalation) draws air in, expiration (exhalation) pushes air out.
• We cannot squeeze lungs directly, so we change the chest volume and the lungs follow.
• Air always flows from high pressure to low pressure; lung pressure is the intra-pulmonary pressure.
• Muscles used: the diaphragm and the external and internal intercostal muscles between ribs.
• Inspiration: diaphragm flattens, ribs lift, chest volume rises, lung pressure falls below atmospheric.
• Expiration: muscles relax, ribs fall, chest volume shrinks, lung pressure rises above atmospheric.
• Diaphragm — Contracts, flattens — Relaxes, domes up
• Ribs / sternum — Move up and out — Move down and in
• Chest volume — Increases — Decreases
• Lung pressure — Below atmospheric — Above atmospheric
• Air movement — Air rushes in — Air pushed out

The chest works like a bellows: make space bigger and air rushes in, smaller and air is pushed out.

Two stages: inspiration (inhalation) draws air in, expiration (exhalation) pushes air out.

We cannot squeeze lungs directly, so we change the chest volume and the lungs follow.

Air always flows from high pressure to low pressure; lung pressure is the intra-pulmonary pressure.

Muscles used: the diaphragm and the external and internal intercostal muscles between ribs.

Inspiration: diaphragm flattens, ribs lift, chest volume rises, lung pressure falls below atmospheric.

Expiration: muscles relax, ribs fall, chest volume shrinks, lung pressure rises above atmospheric.

• A healthy human breathes about 12–16 times per minute at rest.
• Relaxed breathing is enough at rest; during heavy exercise we use abdominal muscles for forced breathing.
• A spirometer measures the volume of air a person moves.
• Spirometry is used for the clinical assessment of lung (pulmonary) function.

A healthy human breathes about 12–16 times per minute at rest.

Relaxed breathing is enough at rest; during heavy exercise we use abdominal muscles for forced breathing.

A spirometer measures the volume of air a person moves.

• Breathing only brings air to the alveoli; the real swap happens at the alveoli and at the tissues.
• Both exchanges occur by simple diffusion, never by active pumping.
• Partial pressure (pO ₂, pCO ₂) is the share of pressure of one gas in a mixture.
• Rule: each gas moves from higher partial pressure to lower partial pressure.
• At alveoli: high pO ₂ sends O ₂ into blood; high pCO ₂ in blood sends CO ₂ into alveoli to be breathed out.
• At tissues: O ₂ leaves blood for cells; CO ₂ from cells enters the blood.
• Alveoli — Air → blood — Blood → air (out)
• Tissues — Blood → cells — Cells → blood

Breathing only brings air to the alveoli; the real swap happens at the alveoli and at the tissues.

Both exchanges occur by simple diffusion, never by active pumping.

Partial pressure (pO ₂, pCO ₂) is the share of pressure of one gas in a mixture.

• About 97% of oxygen is carried by haemoglobin in red blood cells as oxyhaemoglobin.
• The remaining ~3% of oxygen is carried dissolved in blood plasma.
• Most CO ₂ (about 70%) is carried as bicarbonate ions in the plasma.
• About 20–23% of CO ₂ binds haemoglobin as carbamino-haemoglobin; ~7% stays dissolved.
• The pigment haemoglobin gives blood its red colour and binds oxygen reversibly.
• Carbon monoxide (CO) binds haemoglobin far more strongly than O ₂, so it is a dangerous poison.
• O₂ — Oxyhaemoglobin — 97%
• O₂ — Dissolved in plasma — 3%
• CO₂ — Bicarbonate ions — 70%
• CO₂ — Carbamino-haemoglobin — 20–23%
• CO₂ — Dissolved in plasma — 7%

About 97% of oxygen is carried by haemoglobin in red blood cells as oxyhaemoglobin.

The remaining ~3% of oxygen is carried dissolved in blood plasma.

Most CO ₂ (about 70%) is carried as bicarbonate ions in the plasma.

About 20–23% of CO ₂ binds haemoglobin as carbamino-haemoglobin; ~7% stays dissolved.

The pigment haemoglobin gives blood its red colour and binds oxygen reversibly.

Carbon monoxide (CO) binds haemoglobin far more strongly than O ₂, so it is a dangerous poison.

• Dolphins and whales are mammals that breathe air through blowholes on top of the head.
• Fish die out of water because gills work only with dissolved O ₂ in water, not with air.
• Aerobic respiration uses O ₂ and gives more energy; anaerobic works without O ₂.
• In our muscles during heavy exercise, lack of O ₂ forms lactic acid, causing cramps.
• Yeast respires anaerobically producing alcohol and CO ₂ (fermentation).
• Aerobic — Yes — CO₂ + water + much energy
• Anaerobic (muscle) — No — Lactic acid + little energy
• Anaerobic (yeast) — No — Alcohol + CO₂ + little energy

Dolphins and whales are mammals that breathe air through blowholes on top of the head.

Fish die out of water because gills work only with dissolved O ₂ in water, not with air.

Aerobic respiration uses O ₂ and gives more energy; anaerobic works without O ₂.

In our muscles during heavy exercise, lack of O ₂ forms lactic acid, causing cramps.

Yeast respires anaerobically producing alcohol and CO ₂ (fermentation).

• CPR stands for Cardio-Pulmonary Resuscitation – emergency aid to restart breathing and heartbeat.
• Asthma: bronchioles narrow causing difficulty in breathing and wheezing.
• Emphysema: alveolar walls are damaged, reducing gasexchange surface (often from smoking).
• Pneumonia: infection that fills alveoli with fluid, blocking gas exchange.
• Occupational lung diseases like silicosis and asbestosis come from inhaling dust/fibres at work.
• Tobacco smoking is the leading preventable cause of lung damage and lung cancer.

CPR stands for Cardio-Pulmonary Resuscitation – emergency aid to restart breathing and heartbeat.

Asthma: bronchioles narrow causing difficulty in breathing and wheezing.

Emphysema: alveolar walls are damaged, reducing gasexchange surface (often from smoking).

Pneumonia: infection that fills alveoli with fluid, blocking gas exchange.

Occupational lung diseases like silicosis and asbestosis come from inhaling dust/fibres at work.

Tobacco smoking is the leading preventable cause of lung damage and lung cancer.