Topic 6.4 - Gas exchange

Question 1

Ventilation

Answer 1

Exchange of gas (O₂ and CO₂) in alveoli. Maintains blood O₂ and CO₂ concentrations.

Occurs due to concentration gradients.

Question 2

Type I pneumocytes

Answer 2

Extremely thin alveolar cells that are adapted for gas exchange. They are flattened with a thickness of around 0.15 um

Question 3

Type II pneumocytes

Answer 3

More alveoli cells, secrete a solution surfactant. This causes moistening of the walls and prevent them from adhering to each other.

This moist surface allows O₂ to dissolve and diffuse into blood and CO₂ to evaporate into the air for exhalation

Question 4

Airways for ventilation

Answer 4

Start with nasal cavity which filters the air using mucus and cilia;
Head into pharynx which contains the junction for food and air (epiglottis blocks food from entering the respiratory system);
Larynx next (voice box);
Then trachea which is a cylinder tube supported by rings of cartilage which supports the trachea;
Primary bronchi, branches into secondary bronchi;
Secondary bronchi, SA even smaller;
Teriary bronchi, SA even smaller;
Bronchioles, SA even smaller;
Terminal bronchioles lead to alveolar sacs;
Alevolar sacs, contain alveoli for gas exchange

Question 5

Path of air in airways

Answer 5

Nasal cavity -> Pharynx -> Larynx -> Trachea -> Primary bronchi -> Secondary bronchi -> Tertiary bronchi -> bronchioles -> Terminal bronchioles -> Alveolar sacs

Question 6

Inspiration and expiration

Answer 6

Inspiration - occurs when intercostal muscles push ribs outwards and diaphragm down. Increased area causes a decrease in pressure. Thorax pressure drops to below atmospheric pressure. High pressure -> low pressure so air is drawn into the lungs.

Question 7

Rib and diaphragm - antagonist movement

Answer 7

Diaphragm:

Diaphragm - contracts, moving it downwards. Relaxes, pushed upwards into a dome shape
Abdominal muscles - relaxes, moving downwards as it’s moved by diaphragm. Contracts, pushing diaphragm up

Ribcage:

External intercostal muscles - contract, pushing ribs out. Relaxes, pulling ribs in.
Internal intercostal muscles - relax as ribs are pushed out. Contract, pulling ribs inwards and downwards.

Question 8

Lung cancer

Answer 8

Causes: Smoking, air pollution

Symptoms: difficulty with breathing, weight loss, fatigue, loss of appetite, constant coughing, coughing up blood, chest pain

Treatment: removal of the tumour in the lung before it becomes too severe, normally by radiotherapy or chemotherapy

Question 9

Emphysema

Answer 9

Context: Thin-wall alveoli are replaced with larger, thicker walls. Because of this, the surface area for gas exchange is much smaller.

Causes: Genetic factors, smoking - chemical irritants cause a build-up of phagocytes in the alveoli. These phagocytes release elastase (a protein-digesting enzyme). Elastase, as part of the immune response, starts to break down the alveoli wall.

Symptoms: Low blood O₂ level - leads to shortness of breath after vigorous or mild activity, lack of energy, ventilation is laboured and more rapid

Question 10

Importance of type II pneumocytes

Answer 10

Prevents lungs from collapsing, premature babies are often born without sufficient type II pneumocytes so have to either be given oxygen or pulmonary surfactant obtained from animals.

Question 11

Experiments to measure ventilation rate

Answer 11

Checking how often someone breathes.

Using a spirometer.

Question 12

Lungs

Answer 12

Right lung - bigger, 3 lobes

Left lung - smaller, 2 lobes and a cardiac notch (to give heart more space)

Question 13

Expiration

Answer 13

Expiration - occurs when intercostal muscles push ribs inwards and diaphragm up. Decreased area causes an increase in pressure. Thorax pressure drops to below atmospheric pressure. High pressure -> low pressure so air is drawn into the lungs.

Question 14

Chronic diseases

Answer 14

Diseases that last multiple months and becomes worse over time. Ie lung cancer, emphysema.