Gas exchange in humans

Ventilation

• mechanical process

• breathing (inhalation and exhalation)

• fresh air brought into alveoli

• stale air breathed out

Thorax

• the ribs and upper backbone

• organs found in the chest

Ribcage

protects the lungs and heart, situated in the thoracic cavity.

Intercostal muscles

found in-between each rib

• intercostal muscles contract, and ribs are lifted up and outwards.

Diaphragm

sheet of muscle that separates thoracic cavity from abdominal cavity

• relaxed position = dome shape

• when intercostal muscles contract, diaphragm is pulled flatter and size of thoracic cavity increases.

Pleural membranes

pleural membranes form double layers and closely surround each lung.

• fluid between the layers allows the smooth movement of the lungs as they inflate/deflate.

• They slide smoothly against wall of thoracic cavity.

Trachea (windpipe)

carries air from the nose to the bronchus

• trachea strengthened by rings of cartilage.

• rings of cartilage keep airway open, but allow flexibility when food passes down oesophagus.

Cilia

tiny hairs on the trachea, bronchi, and bronchioles.

• carries mucus (containing dust and bacteria) away from the lungs towards the mouth.

• keeps air in the lungs clean

Bronchi (Right/Left bronchus)

passageway for air to get into the lungs (branch off from the trachea)

Bronchioles

smaller ‘branches’ from the bronchus. connected to the alveoli.

Alveoli

air sacs

• site of gas exchange during breathing

• alveoli surrounded by capillaries. carbon dioxide and oxygen can diffuse in/out of alveoli.

• CO2 exhaled.

• O2 binds to haemoglobin and transported around the body.

Explain the role of the intercostal muscles and the diaphragm in inhalation

1. intercostal muscles contract. Raises ribcage up and outwards. Volume of thoracic cavity increases.

2. diaphragm muscles contract. flattens diaphragm. volume of thoracic cavity increases.

Explain the role of the intercostal muscles and the diaphragm in exhalation

1. intercostal muscles relax. ribcage drops down and inwards. volume in thoracic cavity decreases.

2. diaphragm muscles relax. diaphragm resumes dome shape. volume decreases.

   air is forced out

adaptations of the alveoli

• very large surface area

• alveoli walls very thin

• short diffusion distance between alveoli and capillaries

• ventilation of lungs during breathing maintains concentration gradient

• blood moving through capillaries maintains concentration gradient. (freshly absorbed oxygen transported away in red blood cells, and supplies unwanted carbon dioxide to the surface of the alveoli.)

damage smoking causes to the circulatory system

1. damages walls of alveoli - surface area decreases.

2. tar in cigarettes damages cilia. chest infections.

3. tar irritates bronchi/bronchioles. mucus can’t be cleared effectively by damaged cilia. chest infections.

effects of smoking - coronary heart disease and cancer

1. carbon monoxide in cigarette smoke reduces amount of oxygen blood can carry. increased blood pressure. damages artery walls. blood clots and heart attacks.

2. tobacco smoke contains carcinogens. carcinogens cause cancer.

explain a practical to investigate the effect of exercise on breathing.

1. measure breaths per minute before exercising.

2. run continuously for 3 minutes.

3. record total number of breaths taken each minute following exercise. do this for 5 minutes.

why does breathing rate increase with exercise?

• muscles respire more.

• therefore, muscles need more oxygen and so more carbon dioxide is removed.

• therefore, breathing rate increases.

explain an experiment to investigate the release of carbon dioxide in breathing

1. set up two boiling tubes. each contains equal amounts of limewater.

2. put mouth around mouthpiece and breath in/out several times.

3. limewater remains clear in tube A because very little carbon dioxide is inhaled.

4. limewater is cloudy in tube B because carbon dioxide is breathed out, as a waste product of respiration.