Body Systems - Year 8 Science: Respiratory system

Lungs and Respiratory System

The lungs and respiratory system allow us to breathe. They bring oxygen into our bodies (called inspiration, or inhalation) and send carbon dioxide out (called expiration, or exhalation).
This exchange of oxygen and carbon dioxide is called respiration.

Top 5 Functions of the Respiratory System: A Look Inside Key Respiratory Activities

Through breathing, inhalation and exhalation, the respiratory system facilitates the exchange of gases between the air and the blood and between the blood and the body’s cells. The respiratory system also helps us to smell and create sound.

Function of the respiratory system

The function of the respiratory system is to :

• Breath in air from the environment.
• Transfer oxygen into the blood.
• Remove carbon-dioxide from the blood.
• Return air back to the environment.
• Create speech ( as air is moved out over the larynx )

Inhalation and exhalation

Inspiration:

The DIAPHRAGM muscle contracts & flattens, whilst the INTERCOSTAL muscles raise the thorax and sternum out.

The chest cavity is now bigger which lowers the pressure in the lungs to less than that of the environment.

Air is drawn into the lungs ( as gases will always move from higher pressure to lower pressure areas ).

Expiration:

The DIAPHRAGM muscle relaxes and forms a dome shape, whilst the INTERCOSTAL muscles relax to lower thorax and sternum in.

The chest cavity is now smaller which raises the pressure in the lungs to more than that of the environment.

Air is drawn out of the lungs ( as gases will always move from higher pressure to lower pressure areas ).

Gas Exchange:

Capillaries -> Muscle tissue

• When oxygenated blood arrives at the muscle it has a high concentration of oxygen.
• The working muscle has a low concentration of oxygen.
• Therefore oxygen will diffuse from the capillaries into the muscle cells.

Muscle tissue -> Capillaries

• The working muscles will produce a waste product called carbon-dioxide ( CO2 )
• The working muscle builds up a high concentration of CO2.
• The capillaries arriving at the muscle will have a low concentration of CO2.
• Therefore CO2  will diffuse from the muscle into the capillaries.
• ( only about 20 % of CO2 is carried by the haemoglobin – the rest is dissolved in the plasma or in the form of a bicarbonate ion )

Capillaries -> Alveoli

• The blood arriving back at the lungs has a high concentration of CO2.
• The alveoli have a low concentration of CO2.
• Therefore CO2 will diffuse from the capillaries into the alveoli so it can be breathed out.

Measurements / lung volumes

VITAL CAPACITY– the max amount of air that can be breathed out after a max inspiration.

TIDAL VOLUME – the amount of air breathed in and out with each breath.

INSPIRATORY RESERVE VOLUME – the max amount of air that can be breathed in on top of a normal inspiration.

EXPIRATORY RESERVE VOLUME – the max amount of air that can be breathed out after a normal expiration.

RESIDUAL VOLUME – the amount left in the lungs after a max forced expiration.

TOTAL LUNG CAPACITY – residual volume plus vital capacity.

Pathways

The pathway of air from the environment to the lungs is as follows:

1. NOSE & MOUTH – air is breathed in through the nose & mouth.

2. PHARYNX – air passes through the throat.

3. LARYNX – air passes over the larynx ( or voicebox ).

4. Air travels down the TRACHEA (or windpipe)

5. Air branches into the LEFT BRONCHUS & RIGHT BRONCHUS.

6. The bronchi divide into smaller BRONCHIOLES.

7. At the and of the bronchioles are the ALVEOLI ( tiny air sacs ) where the transfer of gases takes place.

Responses to exercise

The acute responses of the respiratory system to exercise are :

• Increased respiratory rate from 15 at rest to 40-50 during exercise.
• Increased tidal volume from 0.5 litres at rest to 2.5 litres during exercise.
• Increased ventilation ( RR X TV ) from 6 or 7 litres at rest to about 125 litres during exercise.
• Increased lung diffusion ( alveoli to blood )
• Increased O2 uptake ( amount of O2 used by body per minute ) – VO2 max is the maximum amount of oxygen that can be consumed and is a measure of a person’s aerobic capacity.