Respiratory System

ROLE: To bring oxygen into the body and to get rid of the carbon

dioxide from the body.

The respiratory system

The respiratory system

When you breathe in:

intercostal muscles between the ribs contract, pulling the chest walls up and out

the diaphragm muscle below the lungs contracts and flattens, increasing the size of the chest

the lungs increase in size, so the pressure inside them falls. This causes air to rush in through the nose or mouth.

Mechanisms of breathing – inspiration

Diaphragm contracts and moves down

Intercostal muscles pull ribs

up and out

Mechanisms of breathing – expiration

When you breathe out:

Intercostal muscles between the ribs relax so that the chest walls move in and down.

The diaphragm muscle below the lungs relaxes and bulges up, reducing the size of the chest.

The lungs decrease in size, so the pressure inside increases and air is pushed up the trachea and out through the nose or mouth.

Diaphragm relaxes and bulges up

Ribs move in and down

Mechanisms of breathing – inspiration

Mechanisms of breathing – expiration

The respiratory system

Respiratory system – 3 main processes

• Pulmonary respiration– The breathing of air into and out of the lungs

• External respiration– Exchange of O2 and CO2 between the lungs

and the blood

• Internal respiration– Exchange of O2 and CO2 between the blood

and muscle tissues

Gaseous Exchange

• Gaseous exchange refers to the exchange of gases, namely O2 and CO2 and relies on a process called diffusion

How does Diffusion happen?• PP – partial pressure of a gas is the pressure it exerts

within a mixture of gases.• EXAMPLE:- Air – Nitrogen (79%); Oxygen (21%); Carbon Dioxide

(0.03%)- Together they exert a pressure of 760mmHg but

individually they exert pressures of:- O2 – 160mmHg- How do you work it out? – - Partial Pressure = Atmospheric pressure x fractional

concentration- 760mmHg x 0.21 = 159.6mmHg* Gases always move from an area of high pressure to

an area of low pressure

Diffusion

• Diffusion is the movement of gases from an area of high pressure to an area of low pressure.

• The difference between the high and low pressure is called the diffusion gradient – the bigger the gradient, the greater the diffusion and gaseous exchange that takes place.

Gas exchange at the alveoli

External Respiration (Alveoli) – What makes it so efficient?

1. Alveoli walls very thin – diffusion distance is very short. 2. Huge amount of alveoli with massive surface area for

diffusion3. Vast supply of capillaries – huge surface area for

diffusion4. Diameter of capillaries is slightly narrower than area of

red blood cellsA) Causes red blood cells to distort to increase surface

area for gas exchangeB) Forces red blood cells to go through capillaries in

single file to maximise exposure to oxygen

Internal Respiration (muscles) – why is it so efficient?

• Big diffusion gradient (65mmHg)

• Myoglobin in muscles has a higher affinity for oxygen than haemoglobin sp attracts oxygen from blood

• Extensive capillary network – huge surafce area

• Capillary wall only one cell thick – very short distance for diffusion