Topic 5.5 Gas Exchange

Ventilation: for gas Ventilation: for gas exchangeexchange

•The flow of air in and out of the alveoli is called ventilation and has two stages: inspiration (or inhalation) and expiration (or exhalation).

•Lungs are not muscular and cannot ventilate themselves, but instead the whole thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm

Gas ExchangeGas ExchangeThis is the diffusion of gases (oxygen and carbon

dioxide) There are two sites for gas exchange(A)Alveoli: Oxygen diffuses into the blood from

the alveoli and carbon dioxide diffuses from the blood into the alveoli

(B)Tissues: Oxygen diffuses from blood into the cells and carbon dioxide diffuses from cells to the blood

Cell Respiration:

The synthesis of ATP•Aerobic respiration uses

oxygen in the mitochondria and produces carbon dioxide

•Anaerobic respiration does not use oxygen but still produces carbon dioxide

Function of the ventilation system•A ventilation system is needed to maintain

concentration gradients in the alveoli•The steep concentration gradient across the

respiratory surface is maintained in two ways: by blood flow on one side and by air flow on the other side. The ventilation system replaces diffuses oxygen (keeping the concentration high) and removes carbon dioxide (keeping the concentration low).

•This means oxygen can always diffuse down its concentration gradient from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient from the blood to the air.

Figure 42.23ab The mammalian respiratory system

Human Ventilation Human Ventilation SystemSystem

• When you breathe, air goes down the larynx and into the trachea (windpipe).

• The trachea branches into 2 bronchi, one leading into each lung.

• The bronchus branches repeatedly into thin tubes called bronchioles.

• The bronchioles are covered by a thin layer of mucus and cilia.

Human Ventilation Human Ventilation SystemSystem

• The bronchioles dead-end as a cluster of tiny air sacs called alveoli.

• O2 diffuses into the alveoli and CO2 diffuses out.

Structure of the ventilation system

• a) Trachea• b) Cartilage ring

support• c) Bronchi (plural)

Bronchus (single)• d) Lung• e) Heart• f) Sternum• g) Rib cage • h) Bronchioles • j) Alveoli • k) Diaphragm

Alveoli Adaptations (increase the rate of gas exchange) exchange)•Large surface area due to

the combined spherical shape (600 million alveoli = 80 m2

•Flattened epithelial cells of alveoli and close association with capillaries

•Short diffusion distance from alveoli to blood (0.5-1.0 um)

•Dense capillary network•Moist surface for the

solution of gases

Figure 42.24 Negative pressure breathing

Ventilation of the Ventilation of the lungslungs:

• External intercostal muscles contract, moving ribs up and out

• Diaphragm contracts, fattening and moving down

• Increased volume in thorax lowering pressure

• Air flows into the lungs to balance the pressure change

Inhale

Ventilation of the Ventilation of the lungslungs:

• Internal intercostal muscles contract, moving ribcage down and in

• Abdominal muscles contract pushing the diaphragm up into a dome shape

• Decrease in volume of thorax increasing air pressure

• Air flows out from the lungs

Exhale: