digestive system

• Digestive System


  • Ingest the food
  • Break down food into small molecules that can cross plasma membranes
  • Absorb these nutrient molecules
  • Eliminate non-digestible wastes
• Anatomy of the Digestive System: The Mouth


  • Receives food
  • Begins physical and chemical digestion

  
• Anatomy of the Digestive System: Human Teeth & Salivary Glands

  • Incisors = biting
  • Canine/cuspids = helps to tear food
  • Premolar teeth/bicuspids = grinding food
  • Molar = crushing & grinding food

  
• Anatomy of the Digestive System: Human Teeth & Salivary Glands

  • 3 pairs of salivary glands = send saliva via ducts to the mouth
  • Saliva = mucus + water + bicarbonate + salivary amylase (an enzyme)
  • The amylase begins the process of digesting carbohydrate, by moisten food & prepare it for swallowing

  
• Anatomy of the Digestive System: The Pharynx


  • Nasopharynx = not part of the digestive system
  • Oropharynx = passageway for both air and food
  • Laryngopharynx = passageway for food entering the esophagus

  
• Anatomy of the Digestive System: The Esophagus

  • Sole function of esophagus: Transport the food bolus from the mouth to the stomach
  • No chemical digestion of food involves

  
• Anatomy of the Digestive System: The Stomach

  • Cardiac region = near the heart, surrounds the lower esophageal sphincter where food enters the stomach
  • Fundic region = holds food temporarily
  • Body region = main part
  • Pyloric region = leading to duodenum

  
• Anatomy of the Digestive System: The Stomach


  • Stomach has columnar epithelial lining ~ has millions of gastric pits which lead into gastric glands
  • Gastric glands contains 4 types of secretory cells: Chief cells = secrete pepsinogen (which becomes pepsin), Parietal cells = produce HCl (activates pepsin for protein digestion), Enteroendocrine cells = produce hormone gastrin (regulates muscular contraction), Mucous cells = secrete mucus, protect the stomach wall

  
• Anatomy of the Digestive System: The Large Intestine

  • No digestive enzymes
  • Bacteria (normal flora of the large intestine) = It synthesize vitamin K and B
  • Absorption- restricted to vitamin K and vitamin B, some ions and remaining water
  • After 3 to 10 hours, 90% of H2O has been removed from chyme
  • Feces are semisolid by time reaches transverse colon
  • Feces = dead epithelial cells + undigested food such as cellulose + bacteria (live & dead)

  
• Accessory Organs of Digestion

  • Liver
  • Pancreas
  • Gallbladder
• Liver


  Major site of protein digestion
• Pancreas


  Digestive enzymes secreted

  
• Gallbladder


  • Travel to the liver
  • Liver distributes amino acids to cells/tissues
• Various digestive enzymes secreted and their role in the digestion of food in humans


  • Salivary amylase (ptyalin) - Converts starch into maltose
  • Pepsin - Converts proteins into peptones and proteoses
  • Trypsin - Converts peptones and small peptides into amino acids
  • Erepsin - Converts peptones and small peptides into amino acids
  • Sucrase - Converts sucrose into glucose and fructose
  • Maltase - Converts maltose into glucose
  • Lactase - Converts lactose into glucose and galactose
  • Lipase - Converts fats into fatty acids and glycerols
• Pepsinogen is converted to pepsin by HCl, which breaks down proteins in the stomach.
• Gastrin stimulates the secretion of hydrochloric acid (HCl) and pepsinogen into the stomach.
• The stomach is the organ that receives food from the esophagus, mixes it with gastric juices to form chyme, and stores it until it can be further processed by the small intestine.
• Absorption - process where nutrients are taken up by cells lining the small intestine and transported to other parts of the body via the bloodstream.