Digestive System 8

• Digestive system


  The system responsible for the digestion, the breakdown of organic compounds into their simple forms for use by the cells
• Digestion


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Egestion/Excretion
• Ingestion


  The journey of taking in food or any substance through the mouth
• Digestion


  The process that involves breaking down large food molecules into smaller molecules for easy absorption of the cells
• Absorption


  The process of passing the soluble food molecules in the wall of the small intestine through the villi
• Assimilation


  The movement of digested food nutrients into the blood vessels of the small intestine through diffusion and use of nutrients into the body cells through the microvilli

  
• Egestion/Excretion


  The release of undigested food collected in the rectum called feces and pushed out of the body through the anus by defecation
• Mouth


  • Entering of food
  • Tasting
  • Mechanical breakdown of food
  • Secretion of salivary glands (salivary amylase)
• Structures in the mouth that aid digestion


  • Teeth
  • Salivary glands
  • Tongue
• Salivary glands


  Produce and secrete saliva into the oral cavity
• Saliva


  Moistens the food and contains enzymes (ptyalin or salivary amylase) that begins digestion of starch into smaller polysaccharides
• Tongue


  Mixes and rolls food into tiny mashed up bits or called 'bolus.' It pushes the bolus toward the pharynx and into the esophagus when swallowing
• Swallowing


  1. Food is pushed into the pharynx by the tongue

  2. Tongue blocks the mouth

  3. Soft palate closes off the nose

  4. Larynx (adam's apple) rises so the epiglottis can close the opening of the trachea
• Esophagus


  • A straight muscular tube that connects the mouth with the stomach
  • Food takes 4 to 8 seconds to pass through
  • Its walls contain smooth muscles that contract in wavy motion called peristalsis
  • Cardiac Sphincter relaxes to allow food into the stomach

  
• Stomach


  • J-shaped muscular sac
  • Has inner folds called rugae that increases the surface area
  • Churns and grinds the bolus into smaller pieces
  • Mixes food with gastric juices (hydrochloric acid and enzymes)
  • HCL helps break down food and kills bacteria
  • Pepsin converts proteins into peptides
  • Mucus lubricates food and protects the gastric lining
  • Chyme is the converted bolus into a liquid after four hours of mechanical and chemical digestion
• Small Intestine


  • A 20 feet long coiled tube beneath the stomach
  • Has three parts: Duodenum, Jejunum, Ileum
  • Duodenum resumes chemical digestion and prepares for absorption
  • Jejunum absorbs small nutrient particles
  • Ileum absorbs conjugated bile salts
  • Mucosa secretes enzymes that act on the food
  • Pancreatic enzymes are emptied into the small intestine
  • Digested nutrients are absorbed through intestinal walls
  • Villi and microvilli increase the surface area for greater absorption
  • Peristalsis moves the undigested food to the large intestine

  
• Large Intestine


  • Also known as colon
  • Larger diameter but shorter (5 feet)
  • Absorbs water from undigested food making the waste harder
  • Divided into caecum, ascending colon, transverse colon, descending colon and sigmoid colon
  • Reabsorbs liquid, electrolytes and some vitamins
  • Waste stays for 10-12 hours and is pushed into the rectum
  • Appendix hangs on the right side
  • Completes absorption and compacts waste
• Liver


  • Largest gland and organ in the body
  • Located below the diaphragm
  • Connected to gallbladder and small intestine by ducts
  • Stores vitamins A, D, E and K, sugar and glycogen
  • Produces bile to aid in fat digestion
  • Produces glucose in the form of glycogen
  • Detoxifies alcohol, drugs and other harmful substances
  • Secretes bile to the gall bladder
• Gallbladder


  • Stores bile in between meals and releases it into the small intestines
  • Secretes bile to the duodenum through the bile duct
  • Bile contains bile salts, pigments, cholesterol and phospholipids
  • Bile is an emulsifier that dissolves fat
• Pancreas


  • Makes digestive enzymes
  • Makes hormones that regulate sugar levels
  • Secretes pancreatic juice into the duodenum
  • Produces amylase, peptidase and lipase to digest carbohydrates, proteins and fats respectively
• Organic compounds such as carbohydrates, proteins and fats are specifically broken down with the aid of different enzymes
• Carbohydrates


  Broken down into sugars by enzymes like amylase, maltase and lactase
• Proteins


  Broken down into amino acids by enzymes like trypsin and peptidase
• Fats


  Broken down into fatty acids by the enzyme lipase
• Chromosome

  • Chromatids
  • Centromere
  • Short arm (p arm)
  • Long arm (q arm)