Gas exchange in Humans

Gas exchange system

is responsible for getting oxygen into the blood and removing carbon dioxide as a person breathes.

Gas exchange surfaces

in order for gas exchange to take place efficiently, there are certain gas exchange surface features humans have:
1. Large surface area: gives more space for diffusion to take place thereby speeding up the rate of gas exchange.
2. Thin surface: reduces the distance across which gases must diffuse for faster diffusion rate
3. Good blood supply: ensures that concentration gradients are always maintained; deox blood is constantly arriving and ox blood is constantly being carried away
4. Good ventilation with air: ensures that the concentration gradient of oxygen and carbon dioxide are maintained. 

Breathing System

1. Larynx: the area containing the vocal chords.
2. Trachea/windpipe: connects the throat to the lungs
3. Bronchi: tubes that branch out into 2 from the trachea carrying air from trachea to lungs
4. Lungs: main organs in the respiratory system containing the surfaces where gas exchange takes place.
5. Bronchioles: smaller tubes branched off from the bronchi leading to the alveoli
6. Alveoli: tiny air sacs surrounded by capillaries, gas exchange takes place here
7. Capillaries: surrounding the alveoli are blood vessels thru which blood passes
8. Diaphragm: a flat sheet of muscle under the lungs which helps change the volume of the chest during breathing
9. Ribs: the bones that protect the lungs and other organs
10. Intercostal muscles: found between ribs, control the movement of ribs during breathing. Internal on the inside of ribcage/external on the outside of ribcage. Both these muscles are important for ribcage movement during inhalation and exhalation.

Function of cartilage in trachea

trachea is lined with rings of cartilage that strengthen and support the trachea; keep trachea open during breathing and prevent it from collapsing.

Ventilation

the act of moving air into and out of the lungs to allow gas exchange to occur

Inspiration/Inhalation

the act of breathing in
1. External intercostal muscles contract & internal relaxes since they are antagonistic pairs of muscles (one muscle contracts, other relaxes). Pulls rib cage upwards and outwards.
2. Diaphragm (dome shaped when in normal relaxed position) contracts and moves downwards, flattening.
3. Both of these lead to thorax (chest area) volume to increase
4. When thorax volume increases, air pressure in lungs decreases because force exerted by gas molecule movement against lung walls is low since more space
5. Pressure inside lungs is lower than surrounding air, so air moves into the lungs from outside

Expiration/Exhalation

act of breathing out.
1. Internal intercostal muscles contract & external relaxes since they are antagonistic pairs of muscles (one muscle contracts, other relaxes). Pulls rib cage downwards and inwards.
2. Diaphragm relaxes and moves back upwards into original dome shape
3. Both of these lead to thorax (chest area) volume to decrease 
4. When thorax volume decreases, air pressure in lungs increases because force exerted by gas molecule movement against lung walls is high since less space
5. Pressure inside lungs is higher than surrounding air, so air moves out of the lungs to outside

Composition of air investigation

the differences in composition of inhaled air and exhaled air can be investigated with limewater as a test for carbon dioxide because limewater turns from clear to cloudy/milky in the presence of carbon dioxide
1. When we breathe in, fresh air will flow in from outside and go thru boiling tube A
2. When we breathe out, air will flow thru boiling tube B
3. The limewater in boiling tube A will remain clear, while the limewater in boiling tube B will turn cloudy/milky. Proves that exhaled air has more carbon dioxide than inhaled air.

Differences in composition of air

1. more oxygen in inspired (around 21%) than expired (16%) because inhaled oxygen diffuses thru alveoli walls and enters bloodstream, since conc. of oxygen in blood is lower
2. Less co2 in inspired (around 0.04%) than expired (4%) because concentration of co2 in blood surrounding alveoli is higher than inhaled co2 so it diffuses out
3. Water vapour: less in inspired than expired because the body’s warmth causes water from alveoli surface to evaporate into the expired air

Gas exchange in alveoli

Oxygen diffuses from alveoli into blood, co2 diffuses from blood into alveoli

Effect of physical activity on breathing investigation

1. Count the number of breaths taken during one minute of rest
2. Measure how much chest expands during each breath using measuring tape, find average chest expansion over 5 breaths.
3. Exercise for a fixed amt of time eg. 3 mins
4. Immediately after exercise, count no. of breaths taken in 1 minute
5. Measure average chest expansion over 5 breaths
6. Because of exercise, no of breaths in 1 minute increases and chest expansion also increases, therefore exercise increases rate and depth of breathing

Investigation explanation

exercise increases rate and depth of breathing because exercise causes the body cells to respire faster and release more energy.
More co2 is produced so there is increased co2 in blood.
Brain detects this so signals body to increase rate and depth of breathing to allow gas exchange to happen more rapidly; so co2 is removed faster from body and increased intake of oxygen to supply to respiring cells quickly.

Breathing system protection

a thin layer of mucus secret by goblet cells and ciliated epithelial cells lines the breathing system. The cells have tiny hairs on them called cilia. The mucus produced by goblet cells trap pathogens and particles. The cilia beat and push mucus away from lungs into throat where it can be swallowed and destroyed.