Gas Exchange

In Humans• We need Oxygen, we don't need Carbon Dioxide (Waste product)

"The entry of oxygen into the body and removal of carbon dioxide"

How do humans achieve this?

The respiratory system

The respiratory system• Q. Can you describe the respiratory system in human?

Air enters through the nose or mouth (separated by the palate – Why?)Breathing in through the nose is better – Why?

Inside the nasal cavity:goblet cells – moisten dry airCilia – hair-like projections – trap bacteria/dust

From the nose air passes through the  tracheaTop of the trachea is the epiglottis – stops food going down the trachea (windpipe)

Larynx – protects the trachea

Vocal cords tighten to produce sound as air passes over it

Q. Can you guess why the trachea needs rings of Cartilage?

The trachea stretches down from the neck to the thorax, where it then divides into two The two trachea branches (bronchi), go, one into each lung.(1 = broncus, 2 = bronchi)The bronchi then form smaller branches in the lungs (bronchioles)

The lungs are protected by the thoracic ribs.The pleural membranes form the pleural cavity (containing pleural fluid) which is essential to allow the lungs to move easily in the thoracic cavity.

At the end of the bronchioles are the alveoli (1 = alveolus)These air sacs are the site of gas exchange.

They are thin to allow gases to diffuse across quicklyThey are surrounded by blood vessels (capillaries) to transport gases to and fromThey have a large surface area, so a lot of gas can diffuse at the same time

These air sacs (tiny spaces of air) give lungs a light and spongy feeling

Side note• Cilia are also along the Trachea, and Bronchi - Constantly "sweeping"

upwards so trapped dust/bacteria can be swallowed

• Preventing, for example, pathogens entering into the lungs

Another side note• Inside the alveoli, WBC are found, in order to destroy bacteria that

manages to get in

Gas exchangePulmonary arteries bring deoxygenated blood

Pulmonary veins take away oxygenated blood

• Air enters into the alveolus, causing it to inflate.• Walls are thin between alveoli and capillary (1 cell thick)

Enormous surface area

Breathing• 2 muscles involved. Intercostal muscles and diaphragm

• Internal and External Intercostal muscles between ribs• Diaphragm is large sheet of muscle stretching under the lungs

Breathing in (Inspiration)• Breathing in makes the volume of the thorax larger, air is sucked in

• The diaphragm contracts – pulling it downwards• The external intercostal muscles contract – pulling the rib cage upwards and

outwards

• Increased volume = reduced pressure (below atmospheric pressure)

Breathing out (Expiration)• Breathing out reduces the volume of the thorax, squeezing air out

• The diaphragm relaxes – springing upwards• The external intercostal muscles relax – dropping the rib cage

downwards and inwards (normal position)

• Decreased volume = air squeezed out