1. 6.4 Gas exchange

2. 6.4
Essential idea: The lungs are actively ventilated to ensure that gas exchange can occur passively.

3. Cellular respiration is the controlled release of energy in the form of ATP from organic compounds in cells. It is a continuous process in all cells.
Aerobic:
C6H12O6 + 6O2  6CO2 + 6H2O + ATP

4. To support aerobic cellular respiration, cells take in oxygen from their environment and give out carbon dioxide, by a process called gas exchange.
Gas exchange ultimately relies on diffusion.

5. Most animals have evolved specialized respiratory systems
All animal respiratory systems share two features that facilitate diffusion:
Respiratory system must remain moist (gases must be dissolved in water to diffuse into or out of cells)
Respiratory system must have large surface area in contact with environment to allow adequate gas exchange
Most animals have evolved specialized respiratory systems

6. 6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
In general, gas exchange in most respiratory systems occurs in the following stages:
Air or water, containing oxygen, is moved past a respiratory system by bulk flow (fluids or gases move in bulk through relatively large spaces, from areas of higher pressure to areas of lower pressure) – commonly facilitated by muscular breathing movements

7. 6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries. O2
Oxygen and carbon dioxide are exchanged through the respiratory surface by diffusion; oxygen is carried into capillaries of circulatory system and carbon dioxide is removed
CO2
Capillary

8. 6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
Gases are transported between respiratory system and tissues by bulk flow of blood as it is pumped throughout body by heart

9. 6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
Gases are exchanged between tissues and circulatory system by diffusion (oxygen diffuses out into tissue and carbon dioxide diffuses into capillaries based on concentration gradients)

10. This results in the need for a ventilation system:
6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
Because the lungs are protected in the thorax (chest), air must be brought in.
This results in the need for a ventilation system:
A ventilation system is a pumping mechanism that moves air into and out of the lungs efficiently, thereby maintaining the concentration gradient for diffusion.

11. 6.4.U1 Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries.
Human Respiratory System (and other vertebrates) is divided into two parts:
The conducting portion – series of passageways that carry air to gas-exchange portion
The gas exchange portion – gas is exchanged with the blood in tiny sacs in lungs

12. Passageway of air in respiratory system:
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Passageway of air in respiratory system:
Nostrils – air enters body
Nasal cavities – air is warmed, filtered and moistened
Lined with ciliated epithelium that trap particles in mucus and move it to the throat to be swallowed
Cilia

13. 6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles. #3
Pharynx #1
Nose
Pharynx – back of nasal cavities that is continuous with the throat; passageway for both food and air #2
Mouth

14. Larynx – Pharynx leads to Larynx “voice box”
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Epiglottis – flap of tissue that automatically covers opening to larynx during swallowing; prevents food from entering lungs
Larynx – Pharynx leads to Larynx “voice box”
Contains vocal cords
Cartilage is embedded in walls to prevent collapse #5
Larynx #4
Epiglottis
The respiratory system is responsible for the exchange of oxygen and carbon dioxide.
Epiglottis

15. Bronchi – two branches off the trachea that lead to a lung
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Trachea – also called windpipe; tube that carries air down to lungs – reinforced with cartilage to prevent collapse
Bronchi – two branches off the trachea that lead to a lung
Lungs #6 #7
Trachea
Bronchus
The respiratory system is responsible for the exchange of oxygen and carbon dioxide.

16. Bronchioles – smaller tubes of the bronchi that lead to the alveoli
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Bronchioles – smaller tubes of the bronchi that lead to the alveoli #9
Alveoli #8
Bronchiole
Bronchioles
The respiratory system is responsible for the exchange of oxygen and carbon dioxide. After reaching the lungs, the trachea branches into smaller and smaller tubes called bronchioles, which end in alveoli, or air sacs.

17. Lungs – large, paired spongy organs
Right lung is divided into 3 lobes
Left lung is divided into 2 lobes
Each is covered by a pleural membrane – forms a sac and lines the thoracic cavity
Secretes a fluid that provides lubrication between lungs and chest wall

18. Alveoli – each bronchiole ends in a cluster of tiny air sacs
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Alveoli – each bronchiole ends in a cluster of tiny air sacs
Numerous small clusters for increased surface area
Walls of alveoli are extremely thin (one cell thick)
The respiratory system is responsible for the exchange of oxygen and carbon dioxide.

19. Two types of cells make up the alveoli wall:
6.4.U2 Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange. AND 6.4.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.
Two types of cells make up the alveoli wall:
Type I pneumocytes – extremely thin; adapted to carry out gas exchange
Type II pneumocytes – secrete a solution containing surfactant that allow gases to dissolve and diffuse, prevents walls of alveoli from sticking together & decreases surface tension making it easier to inflate
Most cells in the epithelium lining the alveoli are Type I pneumocytes
Type II pneumocytes make up about 5% of the alveolar surface area

20. Type I pneumocytes in alveolus wall
6.4.U1 Students should be able to draw a diagram to show the structure of an alveolus and an adjacent capillary
Type I pneumocytes in alveolus wall
Phagocyte
The respiratory system is responsible for the exchange of oxygen and carbon dioxide.
Network of blood capillaries
Type II pneumocytes in alveolus wall

21. CO2 Alveoli are surrounded by capillaries
6.4.U4 Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
Alveoli are surrounded by capillaries
Gases diffuse freely through the wall of the alveolus and capillary (oxygen diffuses into blood and CO2 diffuses into alveoli)
CO2
The respiratory system is responsible for the exchange of oxygen and carbon dioxide.
Capillary

23. 6.4.U5 Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them.
Breathing (ventilation) is the mechanical process of moving air from the environment into the lungs and expelling air from the lungs
The thorax is an airtight chamber and pressure changes in the lungs occurs when the volume of the thorax changes
Pressure changes allow for air to be forced into or out of the lungs

24. Inspiration (inhalation):
6.4.U6 Different muscles are required for inspiration and expiration because muscles only do work when they contract.
Inspiration (inhalation):
Diaphragm (dome-shaped muscle forming floor of thoracic cavity) contracts and moves downward
Abdominal muscles relax
External intercostal rib muscles contract lifting ribs up and out (internal intercostal muscles relax)
This increases volume of thoracic cavity which lowers air pressure inside (below atmospheric pressure)
Air from outside rushes into lungs to equalize air pressure

25. Expiration (exhalation)
6.4.U6 Different muscles are required for inspiration and expiration because muscles only do work when they contract.
Expiration (exhalation)
Diaphragm relaxes and returns to dome-shape (moves up)
Internal intercostal muscles contract causing ribs to drop back down (external intercostal muscles relax)
This decreases the volume of the thoracic cavity which increases air pressure inside
Air from inside lungs rushes out to equalize air pressure
When you breathe forcefully, your abdominal muscles also contract. This squeezes your abdominal organs which puts pressure on the diaphragm.

26. Inspiration Expiration
6.4.A3 External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action.
Inspiration
Expiration
Diaphragm contracts (moves down) Abdominal muscles relax
Diaphragm relaxes
(moves up) Abdominal muscles contract
External intercostal muscles contract
Internal intercostal muscles relax
External intercostal muscles relax
Internal intercostal muscles contract

27. Control of Breathing Rate
Breathing rate is controlled by the respiratory center in brain – located in medulla just above spinal cord
muscles are stimulated to contract by impulses from respiratory center
nerve cells in respiratory center generate cyclic bursts of impulses that cause the alternating contraction and relaxation of respiratory muscles

28. Respiratory center receives input from several sources and adjusts breathing rate and volume to meet body’s changing needs
CO2 concentration in blood is the most important chemical stimulus for regulating rate of respiration
Chemoreceptors in medulla, and in walls of the aorta and carotid arteries are sensitive to changes in arterial CO2 concentration

29. 6.4.A2 Causes and consequences of emphysema.
Emphysema is a chronic lung disease. The large number of small alveoli are replaced by a small number of much larger much less elastic air spaces.

30. 6.4.A2 Causes and consequences of emphysema.
Total surface area for gas exchange is considerably reduced & the distance over which diffusion of gases occurs is increased, so gas exchange is much less effective. Lungs become less elastic, so ventilation is more difficult.
Symptoms are breathlessness and forced breathing. It is a type of chronic obstructive pulmonary disease (COPD). It is a progressive disease for which there is no cure.

31. Alpha-1-antitrypsin deficiency emphysema (rare)
6.4.A2 Causes and consequences of emphysema.
Causes:
Cigarette smoking
Air pollution
Marijuana smoking
Manufacturing fumes
Alpha-1-antitrypsin deficiency emphysema (rare)
Leading causes
Eric Lawson, known as the Marlboro man, died of respiratory failure as a result of COPD. He began smoking at age 14.

32. How do the alveoli become damaged?
6.4.A2 Causes and consequences of emphysema.
How do the alveoli become damaged?
Cilia become damaged and cease to function and mucus builds up, causing infection.
Toxins in cigarette smoke and polluted air cause inflammation and damage to white blood cells in the lungs.
Protease (trypsin) is released from damaged cells & phagocytes which digest elastic fibers in the lungs and eventually causes complete breakdown of alveolus walls.

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34. 6.4.A1 Causes and consequences of lung cancer.
Lung cancer is the most common cancer in the world, both in terms of the number of cases and deaths.

35. Second hand smoke (passive smoking) Air pollution
6.4.A1 Causes and consequences of lung cancer.
Causes:
Cigarette smoking – tobacco smoke contains many carcinogens; causes nearly 90% of all cases
Second hand smoke (passive smoking)
Air pollution
Radon gas – in some areas it leaks out of rocks, especially granite
Asbestos and silica
Healthy lung Lung with tar
deposits

36. Difficulties breathing Persistent coughing Coughing up blood
6.4.A1 Causes and consequences of lung cancer.
Consequences:
Difficulties breathing
Persistent coughing
Coughing up blood
General fatigue
Chest pain
Loss of appetite
Weight loss
Only 15% of patients with lung cancer survive for more than 5 years. If caught early enough, all or part of the affected lung may be removed. Chemotherapy and radiation may also be needed.

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