Gas Exchange in Humans Flashcards
Examples of diffusion
O2 and CO2 in the alveoli
Glucose and amino acids in the ileum
Examples of active transport
Glucose and amino acids at the microvilli
As organism size increases…
SA:Vol decreases, because volume increases faster than SA
Diffusion specialisations
Specialised gas exchange system:
• Flattened body - very thin - short distance
• mass transport system
• high conc. gradient created by movement of environmental medium and internal medium
• selectively permeable
• high SA:Vol
Why are specialised exchange surfaces internal
- v thin; easily damaged
* lead to water loss- dehydration
Alveoli specialisations
• cell walls of one squamous endothelial cell thick
• folds which increase their SA
• small volume, increasing their SA:Vol
• a capillary bed that creates a large concentration gradient of O2 (because ventilation is constant), as the oxygen is constantly swept away from the alveoli – but this is slow, allowing time for diffusion to occur
• squamous epithelial cells are selectively permeable, creating a wet layer of superfactant that has a lower surface tension than water, further decreasing diffusion distance (allows alveoli to expand quickly – prevents collapsing and sticking together)
There are loads and loads of them!
RBCs flattened against capillary wall
Elastic tissue between cells recoils on muscle relaxation; passive exhalation
C-shaped rings in cartilage in bronchi
Prevents trachea collapse during inhalation so that air can flow into the alveoli
Allows expansion of the œsophagus during swallowing
Smooth muscle in bronchi and bronchiole walls
Allows diameter of smaller tubes to be altered to control flow of air to the alveoli
Adaptations of the lungs
- Very high SA, increased by the many hundreds of alveoli, which have folds in them to create a high SA:Vol increasing rate of diffusion
- Surrounded by a large capillary bed which has slow moving blood- allows oxygen to diffuse out of the capillaries and into the alveoli
- many capillaries create high SA
- Squamous epithelium is thin and flattened, decreasing the diffusion distance
- Superfactant liquid decreases diffusion distance by having a surface tension lower than water
- The trachea, bronchi and bronchioles constantly move the air, ventilating the lungs and provide constant oxygen supply - high conc. gradient
Forced expiration
- external intercostal muscles relax and recoil, as does the diaphragm
- internal intercostal muscles are contracted further than they would be at rest, requiring ATP
- greater decrease in the thoracic cavity volume, and therefore a greater increase in thoracic cavity pressure which becomes greater than intrapulmonary pressure to a larger degree, resulting in intrapulmonary pressure becoming greater than atmospheric pressure to a larger degree, so air moves out of the lungs from a high pressure to a low pressure faster
Increasing heart rate
- Chemoreceptors in the carotid artery detect lower pH cause by increased concentration of acidic CO2, sending more nervous impulses along the nervous system to the medulla oblongata
- The medulla oblongata then send more nervous impulses along the sympathetic nervous system (releasing noradrenaline at synapses) to the sinoatrial node, causing an increase in heart rate
Rise in blood pressure
Decrease in heart rate:
Baroreceptors send impulses to medulla oblongata via parasympathetic nerves to SAN, releasing ACh which decreases impulses to atrioventricular node
Gross structure of human gas exchange
Air moves down trachea into bronchi and then through bronchioles into the lungs where it reaches the alveoli.
Inspiration
- External intercostal muscles contract, causing ribcage to move up and outwards
- Diaphragm contracts (flattens)
- Causes increase in volume of thoracic cavity, and therefore a decrease in pressure of the thoracic cavity
- When intrapulmonary pressure exceeds thoracic cavity pressure, lungs expand, causing na increase in volume and adectease in intrapulmonary pressure
- When intrapulmonary pressure is lower than atmospheric pressure, air moves into the lungs from high pressure to low pressure
Expiration
• External muscles relax and recoil, as does the diaphragm
• Internal muscles contract causing the ribcage to move down and inwards
• This causes a decrease in the volume of the thoracic cavity and therefore an increase in pressure of the thoracic cavity, causing it to become greater than intrapulmonary pressure
This causes the volume of the lungs to decrease, increasing intrapulmonary pressure so that it is greater than atmospheric pressure and air moves out of the lungs from high pressure to low pressure
