HideShow resource information

Lung structure

Air enters the trachea

The trachea splits into 2 bronchi - one bronchus to each lung

Each bronchus branches into smaller tubes called bronchioles

The bronchioles end in small air sacs called the alveoli

Gases are exchanged in the alveoli

The diaphragm ruin cage and intercostal muscles all work together to force air out

1 of 12


Intercostal and diaphragm muscles CONTRACT
this causes the rib cage to move upwards and outwards , and the diaphragm to FLATTEN = INCREASINGLY the volume of the thorax
As the volume of the thorax increase, the lung pressure DECREASES
thus causes air to flow into the lungs
(Active process - requires energy)

Intercostal and diaphragm muscles RELAX
the ribcage moves downwards and inwards , the diaphragm becomes CURVED again
The thread volume DECREASES, causing the air pressure to INCREASE
Air is forced out of the lungs
(Passive process- doesn't require energy)

2 of 12

Alveoli structure

Single layer of thin flat cells - alveoli epithelium

Walls of capillaries are capillary endothelium

Walls of alveoli made from elastin (a protein)

3 of 12

Gas exchange in the alveoli

O2 diffuse out of the alveoli, across the alveoli epithelium and the capillary endothelium

O2 is bound to haemoglobin

CO2 diffuses into the alveoli , from the blood

CO2 is breathed out

4 of 12

Factors affecting diffusion&alveoli adaptations

A thin exchange surface - alveolar epithelium one cell thick

A large surface area - Large number of alveoli

A steep concentration gradient - a high concentration of O2 and CO2 between alveoli and capillaries = diffusion across . Steep concentration gradient maintained by blood flow and ventilation

5 of 12

Pulmonary ventilation

PV is a measure of lung function
PV is the volume of air taken into the lungs in one minute
Measured in dm3min-1

PV = tidal volume x ventilation rate

Tidal volume is = volume of air in each breathe
Ventilation is = number of breathes per minute

You can use spirometer traces to calculate PV

6 of 12

Explain the infection stage of TB

When infected with TB bacteria , immune system cells build a wall around the bacteria in the lungs - this forms small hard lumps called tubercles

Infected tissue in the tubercles dies and the gaseous exchange surface is damaged, so the tidal volume is decreased
TB causes fibrosis, which reduces the tidal volume further

If bacteria enter the bloodstream they can spread to other parts of the body

7 of 12

What are the symptoms of TB

Persistent cough, coughing blood and mucus , chest pains , fatigue

Many people with TB are asymptomatic as the infection is inactive - they means they are unable to pass it on
If they become weak from another disease/illness, it will become active- symptoms will be displayed and it can be passed on

8 of 12

How is TB transmitted

Droplet infection- infected person coughs or sneezes , tiny droplets of saliva and mucus containing the bacteria are released = infection transmission

TB is more common in areas where where hygiene levels are poor and where people live in crowded conditions

Vaccine available and can be treated with antibiotics

9 of 12


Formation of scar tissue on the lungs
Result of infection or exposure to asbestos or dust
Scar tissue is thicker and less elastic than Normal lung tissue
The alveoli are less able to expand so can't hold as much air - tidal volume is decreased
Harder to force air out of the lungs due to lost elasticity

Effect on gas exchange -
Reduces the rate of gas exchange
Diffusion slower across a thicker scarred membrane
Less O2 diffuses = aerobic Respiration is reduced

Symptoms - fatigue, dry cough, chest pain, increased breathing rate

10 of 12


Airways become inflamed and irritated - allergic reaction usually

In asthma attack, muscle lining the bronchioles contracts and lots of mucus is made - causes constriction of airways, making it difficult to breathe
Air flow severely reduced - less O2 in alveoli so less in blood = reduced rate of aerobic respiration

Symptoms - wheezing , tight chest, sudden onset of symptoms

Medicated with inhaler that relaxes bronchioles muscles

11 of 12


Caused by smoking or long term exposure to air pollution

Particles trapped in alveoli, which causes inflammation, which attracts phagocytes

Phagocytes produce an enzyme that breaks down the protein elastin

Loss of elastin means that alveoli can't recoil to expel air as well

Also, destruction of alveoli walls, which reduces surface area, which reduces gas exchange

Lack of O2 reaching cells

Symptoms - shortness of breathe , wheezing, increased breathing rate

12 of 12


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Human, animal and plant physiology resources »