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In this chapter of AS/ A-Level Biology, we will learn about different organs within the Digestive System and their functions.
Oesophagus
- The tube that takes food from the mouth to the stomach using waves of muscle contractions called peristalsis; the muscle layer is thick to help with this
- Mucus is secreted from tissues in the walls, to lubricate the food’s passage downwards
Stomach
- A small sac with many folds which allow it to expand
- The entrance and exit are controlled by the sphincter muscles
- The gastric juice produced here help digest food
- It consists of hydrochloric acid, pepsin, and mucus
- Pepsin hydrolyses proteins into smaller polypeptide chains and only works in acidic conditions
- The mucus protects the stomach from acid damage and pepsin
- Peristalsis of the stomach churns the food in a fluid called chyme
The Small Intestine
- In AS/ A-Level Biology, it has two main parts: duodenum and ileum
- Chyme is moved along it by peristalsis
- In the duodenum, bile (an alkali) and pancreatic juice neutralises the chyme and breaks it down
- Small, soluble molecules are absorbed in the ileum through the villi in the gut wall by diffusion, facilitated diffusion and active transport; the villi increase surface area so that soluble molecules are absorbed quickly
The Large Intestine
- Absorbs water, salt and minerals
- Has a folded wall for larger surface area for increase absorption
- Bacteria can decompose some undigested nutrients
Rectum
- Faeces are stored here and then pass through sphincter muscles at the anus during defecation
This is the end of this topic~