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Organ
System
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Description
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Digestive
system
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Breaks food into smaller molecules so they can be
absorbed by the body
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Gas
exchange system
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Transports air into the body so oxygen can be
absorbed into the circulatory system
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Circulatory
system
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Transports material in blood such as food and
oxygen to every cell and removes waste such as carbon dioxide
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Small intestine
- When chyme enters the duodenum it's mixed with alkaline bile which neutralises stomach acid and produces an alkaline environment suitable for enzymes from duodenum wall eg lactase and pancreas eg lipase.
- Lactase digests lactose in milk to give glucose. Lipase digests lipids to give fatty acid and glycerol.
- Lipids are insloluble so bile breaks larger droplets into smaller droplets to increase the surface area for lipase to act so they are digested quickly.
- Protease from the pancreas digests proteins into amino acids.
Structure of the small intestine
- The inside wall of the small intestine is folded into many finger-like villi that increase the surface area for contact with digested food and the wall to make absorption effective.
- Surface area is further increased by having folds, microvilli, in the membranes of the cell lining the wall. These increase the length of cell membrane in contact with digested food.
- The nutrients are passed into the capillary network and lacteal inside each villus. Soluble material (glucose and amino acids) are transported through the liver to cells that need them.
- amino acids are used to make proteins like enzymes and muscle. Glucose is used to produce energy by respiration.
- Insoluble products in the lacteal (fatty acids and glycerol) are dissolved in lymph and transported to the thoracic duct where they enter the bloodstream and go to cells.
- They can be used as an energy source in cells or stored.