(2g) Gas exchange in humans

Ribs description

Bone ‘cage’ surrounding lungs

Ribs function

Protect internal organs

Intercostal muscle description

Muscles found between the ribs

Intercostal muscle function

Control movement of ribs during inhalation and exhalation

Diaphragm description

Muscular sheet at bottom of thorax

Diaphragm function

Changes pressure in thorax to control inhalation and exhalation

Trachea description

‘Windpipe’ running from mouth/nose to lungs

Trachea function

Connect mouth and nose to the lungs allowing gases to pass between them

Bronchi description

2 large tubes branching off the trachea

Bronchi function

Each bronchus leads into one lung

Bronchioles description

Bronchi divide into smaller tubes

Bronchioles function

Connect to the alveoli

Alveoli description

Tiny air sacs

Alveoli function

Where gas exchange takes place

Pleural membrane description

Found on outside of lungs and inside of chest cavity

Pleural membrane function

Reduce friction when breathing

Where are cilia found?

On ciliated epithelial cells which line the passages to the lungs

What do cilia do?

Beat and push mucus up towards the nose and throat where it can be removed

How is mucus produced?

Made by goblet cells

What does mucus do?

Traps particles, pathogens and dust to prevent them damaging the lungs

What do the internal intercostal muscles do?

Contract to pull ribcage down and in when forced exhaling

What do the external intercostal muscles do?

Contract to pull ribcage up and out when inhaling

What happens to the diaphragm when you inhale?

Diaphragm contracts and flattens

Describe inhalation

Diaphragm contracts and flattens. External intercostal muscles contract pulling ribcage up and out. Thorax volume increases drawing in air.

Why does the thorax volume increasing draw air in?

There is a decrease of air pressure inside the lungs relative to outside the body

Describe exhalation

Diaphragm relaxes into a dome shape. External intercostal muscles relax so ribs drop down and in. Thorax volume decreases forcing air out.

Why does the decrease in thorax volume force air out?

There is an increase of air pressure inside lungs relative to outside the body.

What happens in forced exhalation?

Internal intercostal muscles contract to pull ribs down and in to force air out quicker

Why might forced exhalation be needed?

Need to increase the rate of gas exchange i.e. during exercise - greater need to get rid of CO2 produced

Name the features of the alveoli which adapt it for gas exchange.

Round alveolar sacs; thin single layer of cells; capillaries; moist surface

How are the rounded alveolar sacs adapted for gas exchange?

Provide large SA:V ratio

How is diffusion distance minimised in the lungs?

Alveoli and capillaries have thin single layers of cells

How is a large concentration gradient maintained between air in alveoli and the blood

Large network of tiny capillaries provide good blood supply

How does ventilation (breathing) adapt the alveoli for gas exchange?

Maintains high levels of O2 and low levels of CO2 in the alveolar air space

How is the layer of moisture on the surface of the alveoli adapted for gas exchange?

Helps diffusion as gases can dissolve in the moisture

Name 3 diseases associated with smoking.

Chronic bronchitis, emphysema, cancer

Name 3 harmful compounds associated with smoking.

Tar, carbon monoxide, nicotine

How might someone develop chronic bronchitis?

Tar stimulates goblet cells and mucus glands to enlarge and produce more mucus. This damages cilia, blocks small bronchioles, and leads to infections.

How might someone develop emphysema?

Emphysema develops as a result of frequent infection. Alveoli become less elastic and break down or fuse. This results in less surface area > less gas exchange/diffusion > breathlessness

How might smoking lead to cancer?

Tar is a carcinogen

What are the harmful effects of tar?

Carcinogenic; stimulates mucus glands and goblet cells to enlarge and produce more mucus.

What are the harmful effects of carbon monoxide?

Binds irreversibly to haemoglobin in red blood cells, reducing the oxygen carrying capacity of the blood so less oxygen reaches cells.

How does carbon monoxide increase risk of CHD and stroke?

The blood is carrying less oxygen, placing a strain on the circulatory system to pump blood faster around the body, raising blood pressure

How is smoking a risk factor for CHD?

Chemicals in smoke cause an increase in plaque build up and an increase in blood pressure

What are the harmful effects of nicotine?

Narrows blood vessels and increases heart rate leading to higher blood pressure. Makes blood clots more likely to form in arteries leading to heart attack or stroke

What is the practical to investigate the effect of exercise on breathing?

Calculate breathing rate at rest. Exercise for set time. Calculate breathing rate immediately after then every minute after exercise for 5 minutes.

Why does breathing frequency increase when exercising?

Muscle cells aerobically respire to provide energy for movement. More O2 needs to be delivered and more CO2 needs to be removed.

Why does breathing rate remain elevated for a while after exercise?

To repay the oxygen debt as the oxygen is needed to break down the lactic acid. Lactic acid from anaerobic respiration must be removed as low pH can denature enzymes.