3.2.4 gas exchange (humans)

List the structure of the human gas exchange system

• trachea

• Bronchi

• Bronchioles

• Alveoli and capillary network

What are the features of the alveolar epithelium that made it adapted for gas exchange

• flattened cells/ 1 cell thick so short diffusion distance

• Folded so large surface area

• Permeable so allows diffusion of O2/ CO2

• Moist so gases can dissolve for diffusion

• Good blood supply from large network of capillaries so maintain concentration gradient

How does gas exchange occur in the lungs (Oxygen)

• oxygen diffuses from alveolar air space into blood down its concentration gradient

• Goes across the alveolar epithelium, then across capillary endothelium

Describe how gas exchange occurs in the lungs (carbon dioxide)

• carbon dioxide diffuses from blood into alveolar air space down its concentration gradient

• Across capillary endothelium, then across alveolar epithelium

Explain the importance of ventilation

• bring in air containing higher concentration of oxygen

• Also removes air with lower concentration of oxygen

• This maintains concentration gradients

What is inspiration

Breathing in

Describe the process of inspiration

1. Diaphragm muscles contract and flatten

2. External intercostal muscles contract and internal intercostal muscles relax (antagonistic)

3. Ribcage is pulled up and out

4. This increases volume and decreases pressure (below atmospheric) in thoracic cavity

5. So air moves into lungs down pressure gradient

What is expiration

Breathing out

Describe the process of expiration

1. Diaphragm relaxes and moves upwards

2. External intercostal muscles relax and internal intercostal muscles may contract

3. Ribcage moves down and in

4. This decreases volume and increases pressure (above atmospheric) in thoracic cavity

5. So air moves out of lungs, down pressure gradient

Why is expiration normally passive at rest

• because internal intercostal muscles do not normally need to contract

• As expiration is aided by elastic recoil in alveoli

How does thickened alveolar tissue (fibrosis) reduce the rate of gas exchange

Increases diffusion distance

How does alveolar wall breakdown reduce the rate of gas exchange

Reduces surface area

How does reduced lung elasticity reduce the rate of gas exchange

Lungs expand and recoil less which reduces the concentration gradient of O2/ CO2

How does reduced lung elasticity affect ventilation

• lungs expand and recoil less which

• This reduces the volume of air in each breath (tidal volume)

• Therefore reducing the maximum volume of air breathed out in one breath (forced vital capacity)

How does narrow airways/ reduced airflow affect ventilation (e.g asthma)

reduces the maximum volume of air breathed out in 1 second (forced expiratory volume)

How does reduced rate of gas exchange affect ventilation

Leads to increased ventilation rate to compensate for the reduced oxygen in the blood

Why does people with lung disease experience fatigue

Cells recieve less oxygen so rate of aerobic respiration is reduced, so less ATP is made

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Explain the difference between correlation and causation

Correlation = change in one variable reflected by a change in another

Causation = change in one variable causes a change in another