Digestive System Structure and Function PDF

10.2 The Human Digestive System  4 Stages of Digestion 1. ingestion – taking in nutrients 2. digestion – breakdown of molecules 3. absorption – taking up of digested molecules into digestive tract. 4. elimination – removal of waste food from the body. ...

10.2 The Human Digestive System  4 Stages of Digestion 1. ingestion – taking in nutrients 2. digestion – breakdown of molecules 3. absorption – taking up of digested molecules into digestive tract. 4. elimination – removal of waste food from the body.  Mouth 1. Chemical digestion: salivary glands that secrete saliva, contains the enzyme amylase which is released to breakdown starch into simple sugars. 2. Mechanical: Teeth break down food, tongue helps turn the food into a soft bolus.  Esophagus A hollow muscular tube that transports the bolus to stomach by peristalsis = wave-like muscular contractions; mucus keeps passage moist. - Epiglottis near windpipe prevents bolus from entering lungs. Epiglottis  Stomach - Food stored here temporarily → further chemical & mechanical digestion. - J-shaped, muscular → churns food into chyme (thick liquid) -food triggers secretion of gastric juice, a mixture of a) HCl (aq) (acid) – breaks down food (parietal cells) b) mucus – protects stomach lining from acid c) enzymes - pepsin breaks down proteins, is inactive until acid is released (chief cells) d) salt and water  Small Intestine. Lined with villi = tiny finger-like projections that ↑ surface area to improve nutrient absorption into the blood. - Each villus is covered in microvilli  Small intestine … Three parts (in order) 1. duodenum: ~0.5m, most digestion occurs here due to secretions from pancreas & gall bladder 2. jejunum: 2.5m, has a large # of folds and continues digestion & absorption 3. ileum: 3m, has fewest villi, undigested material pushed through  Three Accessory Organs 1. Pancreas 2. Liver 3. Gall bladder 1. Pancreas: leaf-shaped, fluid contains enzymes to break down food, releases bicarbonate to neutralize acidic chyme and raise pH, also makes insulin --> controls blood sugar levels 2. Liver: largest internal organ in body Produces bile to break down lipids and is stored in the gall bladder Stores glycogen, Fe and vitamins Disposes of body wastes (alcohol, drugs, etc.) Bile: is green-ish, yellow, made of bile pigments & bile salts 3. Gall Bladder: stores bile & releases bile into duodenum for fat digestion.  Nutrient Absorption in the Small Intestine Monosaccharides → go to liver to be converted into glucose → energy. Any excess is converted into glycogen in the liver and stored for “back up” Amino acids → go to the liver to be turned into waste or new proteins. Glycerol + fatty acids→ reassembled to form triglycerides and then can be absorbed for energy.  Large Intestine (Colon) - Shorter but wider than small intestine - Main function: water is re-absorbed (into blood) home to anaerobic bacteria: continue food breakdown and produce vitamins & minerals (folic acid, vit. B and K) Dried content → feces → pushed through by muscle contractions to the rectum → anus Why is feces typically brown in colour? Why does feces have an odour? VESTIGIAL appendix → Diarrhea & Constipation Diarrhea - not enough water being absorbed by the large intestine Constipation - too much water being absorbed by the large intestine