Gas Exchange (Core)

6.4.1 Distinguish between ventilation, gas exchange

and cell respiration

Breathing is NOT respiration!

Ventilation• Movement of

gases– 1st , in the lungs

where oxygen moves from the air into the bloodstream

– 2nd, in a capillary bed elsewhere in the body where the opposite gas exchange occurs, (O2 & CO2)

6.4.2 Explain the need for a ventilation system

Why do we need a ventilation system?

• We are large organisms. Oxygen cannot diffuse into all our cells directly from the air, nor can waste products be directly ejected from the body. The ventilation system ensures the blood can be the medium for this.

Why a ventilation system?

• We are land-borne.• Gases need moist

surfaces in order to diffuse

• Lungs are moist membranes

• Vent. System maintains a large concentration gradients

• The constant flow of blood past the alveoli brings blood with a high CO2 concentration and low O2 concentration

• Exhaling keeps the CO2 concentration in the alveoli low, so it diffuses out.

Ventilation System

• High concentration gradients must be maintained in the alveoli.

• Breathing in increases the concentration gradient of oxygen between the alveoli & blood (diffuse in)

• Breathing out removes (CO2) increasing the concentration gradient of CO2 between blood and alveolus – CO2

diffuses out

Gas Exchange

• If the alveoli were not ventilated, equilibrium would be reached and no gas could be exchanged.

Respiratory Basics

6.4.3 Describe the features of alveoli that adapt them to

gas exchange

Alveoli are well adapted to gas exchange

• Alveoli increase the surface area for gas exchange.

• Millions in number, each with their own network of capillaries

• Rich blood supply maintains a high concentration gradient of O2 and CO2

Surfaces are wetSurfaces are wet

Alveoli

• Membranes are very thin– Both of the alveoli

and the capillaries

• Diffusion path is short

Which process(es) of membrane transport are being used in gas exchange at the membranes of the alveoli?

How many membranes must an oxygen molecule pass through in order to enter an erythrocyte?

•

6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli.

6.4.5 Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

Gas Exchange

Gas exchange

Mechanisms of inspiration

1. The diaphragm contracts & at the same time the abdominal muscles and intercostal muscles help to raise the rib cage. All of these help increase the volume of the thoracic cavity.

2. Because of the increase in volume, the pressure inside the cavity decreases. Leads to less pressure “pushing on” the passive lung tissue

Mechanism of inspiration

3) The lung tissue increases its volume because there is less pressure exerted on it.

4) This leads to a decrease in pressure inside of the lungs, also known as a partial vacuum

5) Air comes in through your open mouth or nasal passages to counter the partial vacuum within the lungs

Mechanism of Expiration

• Previous steps reversed.