In this chapter of AS/ A-Level Biology, we will learn about different organs within the Digestive System and their functions.

• 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

• 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

• 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

• Absorbs water, salt and minerals
• Has a folded wall for larger surface area for increase absorption
• Bacteria can decompose some undigested nutrients

• Faeces are stored here and then pass through sphincter muscles at the anus during defecation

This is the end of this topic~

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