1. IB BIOLOGY Year 1 Human Health and Physiology Topic 6.4 Gas Exchange

2. Overview of the Respiratory System

3. UNDERSTANDINGS
U1. Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in the alveoli and blood flowing in adjacent capillaries.
U2. Type 1 pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange.
U3. Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension.
U4.Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
U5. Muscle Contractions cause the pressure changes inside the thorax that force air in and out of lungs to ventilate them.
U6.Different muscles are requires for inspiration and expiration because muscles only do work when they contract.

4. A2. Causes and consequences of lung cancer.
APPLICATIONS
A1. External and internal intercostal muscles, and the diaphragm and abdominal muscles are examples of antagonistic muscle action.
A2. Causes and consequences of lung cancer.
A3. Causes and consequences of emphysema.
SKILLS
Monitoring of ventilation in humans at rest and after mild and vigorous exercise.
NATURE OF SCIENCE
Obtain evidence from theories: epidemiological studies have contributed to our understanding of the causes of lung cancer.

5. Why do we breath? I. The Human Respiratory System
A. The Functions of the Respiratory System
1. The respiratory system provides the body’s cells with the means of obtaining oxygen and eliminating carbon dioxide for our cells to produce ENERGY.

7. a. CELLULAR RESPIRATION occurs in the cytoplasm and mitochondria of cells to release the energy from food (oxidize organic compounds) into the form of ATP.

8. 2. Gas exchange - or the swapping of oxygen for carbon dioxide in the alveoli of the lungs.
a. Oxygen from the air taken into the alveoli of the lungs diffuses (H L) into the blood of the surrounding capillaries while high concentrations of carbon dioxide in the blood of the capillaries diffuse into the alveoli to be expelled by the lungs.
b. Diffusion and gas exchange also occurs in the tissues of the body with the blood.
alveoli
alveoli
tissue

10. 3. Ventilation- otherwise known as breathing, involves the physical movement of air into and out of the lungs.
a. Breathing helps to maintain the concentration gradients in the alveoli of the lungs.
INHALATION replaces the diffused O2 maintaining a HIGH oxygen concentration inside the alveoli and EXHALATION removes CO2 keeping carbon dioxide concentrations LOW.

11. This means oxygen can always diffuse down its concentration gradient (HL) from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient (HL) from the blood to the air.
* Add the HIGH’s and LOW’s
HIGH
LOW
LOW
HIGH

12. U4.Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.

13. B. Alveoli Air Sac Adaptations for Gas Exchange
1. Type 1 pneumocytes: flattened cells that make up a very thin single layer of epithelial cells for ease of diffusion ( less than .15 m across)
* majority of cells in the alveoli
2. Type 2 pneumocytes: are rounded cells in the alveoli that secretes an oily fluid called a surfactant.
The surfactant coats the inner surface of the alveoli in a film of moisture.
-Prevents alveoli from sticking.
- Allows for gases to dissolve for exchange.
Surfactant acts as a detergent to lower the surface tension.

14. 3. Very large surface area because of large number of air sacs
3. Very large surface area because of large number of air sacs. (140 square meters- about half of a tennis court)
4. Surrounded by dense capillary network.
5. Small distance for gas exchange with pulmonary capillaries, which are just large enough for a RBC to get through. ( distance as little as .5µm)

17. C. The Ventilation System

18. 1. Air enters the ventilation system through the nose or mouth and then passes down the trachea.
Nasal passage is lined with a ciliated mucus membrane.
The cilia and mucus filter, warm and moisten the air.
2. The TRACHEA (wind pipe) has cartilage rings to keep it open .

19. 3. Trachea divides into two smaller tubes into each of the LUNGS called BRONCHI (walls strengthened with cartilage) which further branch into smaller and narrower BRONCHIOLES.

20. Bronchioles have smooth muscle that can control the amount of air flow in the lungs.

21. 4. At the end of the narrowest bronchioles are clusters of tiny air sacs or ALVEOLI.

24. D. The Mechanism of Ventilation

25. 1. LUNGS are large spongy organs encased by the ribs and DIAPHRAGM.
a. DIAPHRAGM- muscle that forms the floor of the chest cavity and aids in the breathing process.
Relaxed- dome shaped and projects upward.
Contracted- flattened
2. Lungs have a double membrane. (Pleura)
a. One layer covers lung while outer layer is attached to the diaphragm and chest cavity allowing their movement to influence the pressure in the chest cavity.

27. 3. Muscles only do “work” when they contract and shorten creating a pulling force or tension causing movement in one direction.
Muscles lengthen when they relax. This is often caused by the contraction of another “opposite” muscle.
Muscles that work together in this “opposite” way are called ANTAGONISTIC MUSCLES.

28. 4. The internal and external intercostal muscles and the diaphragm and the abdominal muscles are antagonistic muscles used in ventilation.
When one is contracted and doing work the other is relaxed.

29. INSPIRATION (INHALATION)
External intercostal muscles contract, moving ribs up and out (Internal –relax)
Diaphragm contracts, Flattening and moving down.
Increased volume in thorax (chest cavity) lowers the pressure
Air flows in from environment (HIGH PRESSURE) into the lungs (LOW PRESSURE) to balance the pressure change
EXPIRATION (EXHALATION)
Internal intercostal muscles contract, moving ribcage down and in (External relax)
Abdominal muscles contract pushing the relaxed diaphragm up into a dome shape
Decrease in volume of thorax increases the air pressure
Air flows out from the lungs (HIGH PRESSURE) to the environment (LOW PRESSURE)