Digestion

• Hydra


  An organism related to the jellyfish, quite small, and lives in freshwater
• Hydra's structure


  • Basic, undifferentiated, sack-like gut with a single opening surrounded by tentacles, serving as both a mouth and an anus
• Digestion in Hydra


  1. Involves both extracellular and intracellular processes

  2. Mechanical digestion occurs through the contracting of its gut cavity

  3. Chemical digestion starts with extracellular hydrolytic enzymes

  4. Partially digested food fragments are absorbed by the cells lining the gut through phagocytosis

  5. Intracellular digestion then completes the breakdown of food within food vacuoles

  6. Undigested material is egested
• Gastrovascular cavity


  The cavity that handles both digestion and nutrient transport in Hydra
• Digestion in humans


  1. Mechanical digestion in the mouth involves chewing

  2. Chemical digestion in the mouth involves salivary amylase breaking down starch into maltose

  3. Food moves down the esophagus via peristalsis, involving circular and longitudinal muscles

  4. In the stomach, both mechanical and chemical digestion occur - pepsinogen, activated by hydrochloric acid into pepsin, breaks down proteins

  5. The stomach mixes and churns food into chyme, which passes to the small intestine
• Small intestine


  • Consists of the duodenum and the ileum
  • Duodenum is where bile and pancreatic juice aid digestion - bile helps break down fats, pancreatic juice contains enzymes like trypsin, lipase, and amylase essential for digestion
  • Small intestine is lined with villi, which increase surface area for absorption
• Large intestine's role


  1. Reabsorption of water

  2. Cecum is where undigested food and remaining water and minerals enter the large intestine

  3. Colon absorbs the rest of the water and mineral salts, forming semi-solid feces composed of undigested food, dead cells, and bacteria

  4. Rectum temporarily stores feces before egestion