Describe how the various parts of the human digestive system are adapted to their functions

Adaptations of the mouth for digestion

• Contains space to receive food by ingestion,
• contains teeth to break food into small particles by mastication
• contains saliva to soften and lubricate food for swallowing
• Saliva contains ptyalin for digestion of starch

Adaptation of esophagus

It is hollow muscular tube to allow passage of food

Adaptations of the stomach to digestion

• Has muscular walls for pounding food and mix it with digestive juices
• Produces Hydrochloric acid that kills germs and provide pH for the action of pepsin
• Produces an enzyme pepsin which breaks down proteins into short polypeptide chains. Pepsin is secreted as an inactive precursor pepsinogen to prevent the gastric gland being destroyed by its own enzyme (auto-digestion).
• Produces an enzyme renin coagulates casein, the soluble protein of milk, forming insoluble card which is then attacked by pepsin.
• Dilated to provide temporary store of food

Adaptation of the duodenum

• Receives bile from the liver for emulsification of fats
• Received the following enzymes from the pancrease
• Pancreatic amylase: breaks down starch to disaccharide maltose.
• Pancreatic lipase: breaks down tri-glycerides in the emulsified fat into mono-glyceride and fatty acids.
• Protease and nucleases for digestion of proteins and nucleic acids into nucleotides
• Bicarbonate neutralise acidic chime from the stomach

Adaptations of ileum to digestion

Produces various enzymes for final digestion

• Maltase: hydrolyses maltose to glucose, thus completing digestion of starch.
• Sucrase hydrolyses sucrose (Sugar cane) to glucose & fructose.
• Lactase hydrolyses lactose (Milk sugar) to glucose & galactose.
• Nucleotidases split nucleosides into constituent submits.
• Peptidases breakdown dipeptides and tripeptides into amino acids

Adaptations of ileum for absorption

• Long to allow food enough time for absorption
• Villi and microvilli increase surface area for absorption
• Well supplied by blood to carry away absorbed food so as to maintain diffusion gradient
• The villi have thin membrane to reduce diffusion gradient
• Villi have high concentration of mitochondria to provide energy for active transport.
• circular fold increase surface area for absorption

Adaptations of colon for absorption of water

Long with slow peristaltic  movements