Exchange surfaces and breathing Flashcards
Why do multicellular organisms need exchange surfaces?
- Organisms need to obtain nutrients and excrete waste products in order to survive.
- Unicellular organisms can exchange substances through their outer surface (plasma membrane) as they have a very large surface area to volume ratio, allowing it to exchange these substances at a viable rate.
- Multicellular organisms have a small surface area to volume ratio, and have a higher nutrient requirement, so direct exchange with the outer surface does not acquire nutrients quickly enough to keep all cells alive.
- Exchange surfaces increase this exchange surface area, so nutrients enter the organisms at a rate which is enough to keep all cells alive.
What are the features of a typical exchange surface?
- Large surface area to allow for bigger diffusion area, usually achieved by folding of the walls (microvilli).
- Thin barriers to reduce diffusion distance of molecules.
- Constant supply of nutrients on one side to keep steep concentration gradient.
- Removal of nutrients on the other side to keep steep concentration gradient.
- Active transport for moving against concentration gradient.
What are some examples of exchange surfaces?
- Small intestine.
- Liver.
- Plant roots.
- Lungs.
- Hyphae in fungi.
How are the alveoli adapted to their function?
- Large surface area: The alveoli are shaped like raspberries to maximise their surface area for exchange. The lungs are also packed with dozens of these to further increase the surface area.
- Substance permeable barriers: The plasma membranes of the cells that make up the exchange surfaces are the only barrier to diffusion. They are fully permeable to oxygen and carbon dioxide.
- Thin barriers to diffusion: The alveoli and the capillaries that surround them are all made from a one cell-thick layer of squamous epithelial cells that are very thin. This reduces the distance the gas molecules have to travel across during exchange and thus maximises exchange rate.
- Diffusion gradient maintained: Lungs have a constant supply of blood high in carbon dioxide and low in oxygen. Inspiration and expiration supplies lungs with air high in oxygen and low in carbon dioxide.
How does a blood supply help maintain the diffusion gradient in the lungs?
- Blood supply brings blood rich in carbon dioxide to the lungs. This maintains a high carbon dioxide concentration on one side of the alveoli.
- Blood carries blood rich in oxygen away from the lungs. This maintains a low oxygen concentration on one side of the alveoli.
What processes are involved in inspiration?
- Diaphragm contracts and push digestive organs down.
- External intercostal muscles pull ribs up and out.
- Volume in chest cavity increases so pressure decreases below atmospheric pressure.
- Air rushes into the lungs to increase pressure.
What processes are involved in expiration?
- Diaphragm relaxes and is pushed up by abdomen.
- External intercostal muscles relax and ribs fall down and inwards (pulled in by internal intercostal muscles during heavy breathing).
- Volume in chest cavity decreases so pressure increases above atmospheric pressure.
- Air rushes out of the lungs to decrease pressure.
How does ventilation help maintain a steep diffusion gradient in the lungs?
- Inspiration brings air rich in oxygen into the alveoli. This maintains a high oxygen concentration on one side of the alveoli.
- Expiration removes air rich in carbon dioxide from the alveoli. This maintains a low carbon dioxide concentration on one side of the alveoli.
What feature must the airway have?
- Large with no obstructions to the flowing air.
- Strong to prevent collapse under low pressures.
- Flexible to allow for movement when breathing.
- Elastic to allow for stretching and recoil during ventilation.
What is the distribution of tissues in the airway?
- The trachea, bronchi and bronchioles are very similar in structure.
- The trachea is reinforced with c-shaped rings of cartilage at set intervals. The bronchi are reinforced with complete rings of cartilage. The bronchioles usually don’t have cartilage in its walls.
- Inside the cartilage is a layer called the loose tissue. This layer consists of glandular tissue, elastic fibres, smooth muscles and connective tissue.
- The inner most layer consists of a layer of ciliated epithelial cells as well as goblet cells.
What is the role of cartilage in the airway?
Cartilage is to provide support for the airway elements during inspiration so that they do not collapse under low pressure. The c-shaped cartilage of the trachea are to allow for flexibility so the trachea doesn’t constrict when the neck is moved and also to allow for some expansion when a bolus is travelling down the oesophagus.
What is the role of smooth muscle in the airway?
Smooth muscles are able to contract and narrow the lumen of the airway when required. This restricts airflow to the lungs and protects against harmful substances.
What is the role of elastic fibres in the airway?
Elastic fibre are responsible for returning the lumen to its original diameter after the smooth muscles have contracted.
What is the role of glandular tissue and goblet cells in the airway?
These are responsible for producing and excreting mucus to line the lumen of the airway. Mucus traps particulates and pathogens to prevent them from entering the lungs. This protects the lungs from damage.
What is the role of ciliated epithelial cells in the airway?
Ciliated epithelial cells are covered with hundreds of hair-like projections called cilia. These cilia pulse with a regular rhythm and wafts the mucus up the airway and into the throat where it can be swallowed into the stomach. Acid in the stomach destroys any bacteria trapped in the mucus.
