Human gas exchange flashcards

Topic 9: Human gas exchange

Features of gas exchange surfaces

Large surface area (more diffusion at once); thin surface (short diffusion distance); good blood supply and good air supply (both keep the concentration gradient steep).

Route of air into the lungs

Larynx → trachea → bronchi → bronchioles → alveoli (with associated capillaries).

Composition of atmospheric air

Nitrogen about 78%, oxygen 21%, argon and other noble gases about 0.9%, carbon dioxide 0.04%, water vapour variable.

Inspired vs expired air, with reasons

Oxygen ~21% → ~16% (diffuses into blood, used in respiration). Carbon dioxide ~0.04% → ~4% (made in respiration). Water vapour: expired air saturated (evaporates from alveoli). Expired air is also warmer.

Breathing in: muscles, ribs, diaphragm, volume, pressure

External intercostals contract; ribs move up and out; diaphragm contracts and flattens; thorax volume increases, pressure falls below atmospheric, so air flows in.

External vs internal intercostals

External raise the ribs (in); internal lower them in forced breathing out.

Breathing vs respiration

A physical process moving air vs chemical reactions in cells.

Why do breathing rate and depth increase during exercise?

Muscles respire faster, so more carbon dioxide is made. The rise in blood carbon dioxide concentration is detected by the brain, which increases the rate and depth of breathing.

How goblet cells, mucus and cilia protect the gas exchange system

Goblet cells secrete mucus, which traps pathogens and particles. Cilia beat and move the mucus up to the throat to be swallowed.

Limewater vs hydrogencarbonate indicator

Limewater shows carbon dioxide only by turning milky; the indicator changes colour (red/orange to yellow) as carbon dioxide rises.