6.4 Gas Exchange

★Distinguish between ventilation, gas exchange and cell respiration.

★Explain the need for a ventilation system.

★Describe the features of alveoli that adapt them to gas exchange

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

★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.

• Our lungs must act together with our transport system (heart/blood vessels) to make sure our body is well supplied with O2 and is able to get rid of CO2

• Cell Respiration: the process that requires O2 (and gives off CO2) - this is aerobic

• Remember: pathway where chemical bonds in a glucose molecule are broken and that energy is stored as ATP.

• Respiration = chemical reaction to obtain ATP

• Ventilation: continuously repeat filling our lings with air and breathing the air out.

6.4 Gas Exchange

• Gas Exchange: the movement/diffusion of gases, happens in 2 places.

• 1. In the lungs where O2 moves from the air of the lungs into the bloodstream (CO2 moves in opposite direction)

• 2. In a capillary bed elsewhere in the body where the opposite gas exchange happens - O2 diffuses out of bloodstream and into a body cell (CO2 diffuses out of body cell and into capillary bed to take back to lungs)

6.4 Gas Exchange

• The Human Ventilation System

• Our bodies are so thick that oxygen cannot diffuse directly into our body - O2 would have to make it through millions of cells to reach our blood stream.

• We need lungs for diffusion, but thin skinned organisms like worms do not need a ventilation system (O2 diffuses directly through their skin).

• Our ventilation (respiratory) system and circulatory system function together to pick up O2 molecules in the inner lungs and transport that O2 to body cells deep in our tissues.

6.4 Gas Exchange

• Remember: for diffusion to occur, there must always be a concentration gradient with a higher level of the diffusing substance in one area than in another.

• Air inside alveoli contain a higher concentration of O2 than the blood, so O2 diffuses into the blood.

• Blood contains a higher level of CO2 than inhaled air, so CO2 diffuses into alveoli for us to later exhale and rid of the waste.

• A ventilation system is needed to maintain high concentration gradients in the alveoli!

6.4 Gas Exchange

Alveoli Efficiency

6.4 Gas Exchange

Adaptation Advantage

Spherical shape of alveoliProvides a large surface area

for respiratory gases to diffuse through

Single layer of flattened cellsPrevents respiratory gases

from having to diffuse through more cell layers

Moist inner lining of alveolus Allows for efficient diffusion

Dense network of capillaries

Rich blood supply maintaing concentration gradient and

carries absorbed gases away rapidly

• Anatomy of the Ventilation System

6.4 Gas Exchange

• Pharynx: both air and food share this pathway

• Epiglottis: flap of skin that separates the trachea and esophagus (air and food)

• Larynx: voice-box, first place for just air

• Trachea: single ridged air tube

• Bronchi: trachea forks into 2 main branches

• Bronchioles: bronchi continue to branch out into smaller tubes

• Alveoli: last stop for air, tiny air sacs for gas exchange

6.4 Gas Exchange

• Mechanism of Ventilation:

• Lungs are not muscles and cannot move by themselves.

• Breathing happens by 2 sets of muscles:

• Intercostal muscles: muscles between ribs

• Diaphragm: sheet of muscle separating the thorax from the abdomen

• Air is inhaled into the lungs through the trachea, bronchi and bronchioles (exhaled opposite route)

• Muscles are used to lower and raise the pressure inside the lungs to cause the movements of air

6.4 Gas Exchange

6.4 Gas Exchange

Inhalation Exhalation

External intercostal muscles contract, moving the ribcage up and out

Internal intercostal muscles contract, moving the ribcage down and in

Diaphragm contracts, becoming flatter and moving down

The abdominal muscles contract, pushing the diaphragm up into a dome shape,

diaphragm relaxes

Thoracic cavity has increased its volume, so pressure inside the cavity decreases - leads to less pressure 'pushing on' the

lung tissue

These muscle movements decrease the volume of the thorax

A decrease in pressure inside the lungs, also known as a partial vacuum

The pressure inside the thorax rises above

Air comes in through your open mouth or nose to counter the partial vacuum within

the lungs (and fills alveoli with air)

Air flows out from the lungs to outside the body until the pressure inside the lungs

falls to decrease partial vacuum

• 1. Which of the following is correct about the blood found in these structures?

• Answer: C

6.2 Transport System/Circulatory

AortaLeft

VentriclePulmonary

Artery

A oxygenated deoxygenated deoxygenated

B deoxygenated oxygenated oxygenated

C oxygenated oxygenated deoxygenated

D oxygenated oxygenated oxygenated

• 2. Which vessel directly supplies the heart muscle with blood?

• A. The aorta

• B. The pulmonary artery

• C. The pulmonary vein

• D. The coronary artery

• Answer: D

6.2 Transport System/Circulatory

• 3. Which of the following is transported by the blood?

• A. Heat

• B. Starch

• C. Glycogen

• D. Gametes

• Answer: A

6.2 Transport System/Circulatory

• 4. What is a role of the pacemaker or sinoatrial node (SAN)?

• A. To initiate contraction of the ventricle

• B. To pass the excitation through the Purkinje fibers

• C. To originate excitation in myogenic muscle

• D. To cause the relaxation of the atria

• Answer: C

6.2 Transport System/Circulatory

• 5. Which chamber of the heart has the thickest walls?

• A. Left atrium

• B. Left ventricle

• C. Right atrium

• D. Right ventricle

• Answer: B

6.2 Transport System/Circulatory

• 6. Which of the following describes arteries?

• A. They carry blood from the lungs

• B. They carry blood towards the heart

• C. They usually contain valves

• D. They have thick muscular walls

• Answer: D

6.2 Transport System/Circulatory

• 7. Which vessel carried deoxygenated blood?

• A. The coronary artery

• B. The pulmonary artery

• C. The aorta

• D. The pulmonary vein

• Answer: B

6.2 Transport System/Circulatory

• 8. Which of the following is part of the process of cellular respiration?

• A. Glycolysis

• B. Changes in the volume of the thoracic cavity

• C. Exchange of gases across the surface of the alveoli

• D. Exchange of gases across the surface of capillaries

• Answer: A

6.4 Gas Exchange

• 9. What is the function of the structure labelled X?

• A. Inspiration

• B. Gas Exchange

• C. Respiration

• D. Ventilation

• Answer: B

6.4 Gas Exchange

• 10. What causes air to be breathed out by the lungs?

• A. The internal intercostal muscles contract and the ribs rise

• B. The diaphragm contracts and internal intercostal muscles contract

• C. The ribs rise and the external intercostal muscles relax

• D. The diaphragm relaxes and the ribs fall

• Answer: D

6.4 Gas Exchange

• 11. What normally prevents the membranes of the alveoli from sticking together during expiration?

• A. Internal intercostal muscles and abdomen wall muscles

• B. Internal intercostal muscles and diaphragm

• C. External intercostal muscles and diaphragm

• D. External intercostal muscles and abdomen wall muscles

• Answer: C

6.4 Gas Exchange

• 12. What muscles contract to cause air to pass into the lungs through the trachea?

• A. The pressure within the thoracic cavity

• B. The dense net of fluids in the inner surface of the alveoli

• C. The secretion of fluids in the inner surface of the alveoli

• D. The thickness of the single-cell layer of alveoli membranes

• Answer: D

6.4 Gas Exchange

• 13. Capillaries surround the alveoli in the lungs. Which pair of statements correctly describes the concentrations of oxygen and carbon dioxide in the lungs?

• Answer: B

6.4 Gas Exchange

Oxygen Carbon Dioxide

A Lower in the capillaries Higher in the alveoli

B Higher in the alveoli Higher in the capillaries

C Lower in the alveoli Higher in the capillaries

D HIgher in the capillaries Higher in the alveoli

• 14. What feature of alveoli adapts them to efficient gas exchange

• A. A dense network of capillaries surrounds them

• B. They have muscles which pump air in and out regularly

• C. A constant blood supply flows through them

• D. Their membranes are more permeable to gases than water

• Answer: A

6.4 Gas Exchange

• 15. Which feature maintains a high concentration gradient of gases in the ventilation system?

• A. Blood flowing in the capillaries

• B. A moist lining of the alveoli

• C. Thin-walled alveoli

• D. Thin-walled capillaries

• Answer: A

6.4 Gas Exchange

• 16. What change occurs to the pressure and volume of the lungs when the external intercostal muscles contract?

• A. Both pressure and volume increase

• B. Pressure decreases and volume increases

• C. Both pressure and volume decrease

• D. Pressure increases and volume decreases

• Answer: B

6.4 Gas Exchange

• 17. What muscle action is associated with an increase in the volume of the thoracic cavity during inspiration?

• A. The external intercostal muscles relax

• B. The internal intercostal muscles contract

• C. The diaphragm contracts

• D. The abdominal muscles contract

• Answer: C

6.4 Gas Exchange