1. 6.4 – Gas Exchange

2. Essential Idea: The lungs are actively ventilated to ensure that gas exchange can occur passively.
6.4
Gas Exchange
Understandings:
Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries
Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange
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
Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles
Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them
Different muscles are required for inspiration and expiration because muscles only do work when they contract
Applications:
Causes and consequences of lung cancers
Causes and consequences of emphysema
External and internal intercostal muscles, and diaphragm and abdominal muscles are examples of antagonistic muscle action
Skill:
Monitor ventilation in humans at rest and after mild and vigorous exercise

3. Respiratory System
A. Purpose is to take in oxygen for cellular respiration and get rid of CO2 made by it
1. Ventilation – act of breathing in and out using lungs
a. Can’t get O2 by diffusion across surface (skin)
b. Maintains concentration gradient for diffusion in lungs

4. 2. Gas exchange – diffusion of O2 and CO2
a. occurs between alveoli and capillaries in lungs and then between capillaries and other tissues all over the body

5. 3. Cellular Respiration – making ATP using glucose and O2, producing H2O and CO2

7. II. Anatomy of Ventilation

8. A. Process
Air moves in through mouth or nasal passages
Goes down trachea
Separates into R & L bronchi
Bronchi branch into bronchioles
End in clusters of alveoli

9. Alveoli – air sacs, ~300 million/lung
1. Each one surrounded by capillary bed
2. Blood coming from heart high in CO2, low in O2 – relies entirely on diffusion based on concentration gradient
Adaptation
Advantage
Spherical shape
Large surface area
Single cell thickness
Less for gases to diffuse through
Moist inner lining
Efficient diffusion
Capillary bed adjacent
Short distance for diffusion

10. 3. Composed of pneumocytes a
3.Composed of pneumocytes a. Type I – thin, large surface area, cannot be replaced b. Type II – produce and secrete a solution that acts as a surfactant (reduces surface tension) and prevents alveoli from sticking to each other, can be replaced if damaged

11. Mechanisms of Breathing
A. There is no muscle in the lungs (can’t inflate/deflate on their own)
B. Based on the inverse relationship between pressure and volume

12. Inhale - Diaphragm contracts (moves down) and external intercostals and abdominal muscles contract (expands rib cage) causing an increase in the volume of the thoracic cavity. Increase in volume leads to a decrease in pressure making pressure in lungs lower than air pressure outside body (partial vacuum) which sucks air into the lungs.

13. D. Exhale – Diaphragm relaxes (moves up) and internal intercostals contract (shrinking rib cage) causing a decrease in volume of the thoracic cavity, increasing pressure, and pushing air out.

14. A. Emphysema (COPD)– alveoli destroyed 1. Causes – smoking, pollution
Lung disorders
A. Emphysema (COPD)– alveoli destroyed
1. Causes – smoking, pollution
2. Alveoli become large, thicker walled, irregularly shaped with gaping holes which reduces surface area for gas exchange and increases distance
Healthy
Diseased

15. Lung Cancer
1. Prone to metastasize to brain, bones, liver, adrenal glands (high mortality rate – only 15% survive 5 years)
2. Takes over space of healthy tissue
3. Often caused by smoking (about 87% of cases), 3% from second hand smoke, 5% from other air pollutants