Digestive 1

• Function


  The purpose or role of something
• Digestive system function

  To help convert large food molecules into simpler molecules (monomers) that can be absorbed by the cells of the body
• Digestive process


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Excretion
• Ingestion


  The process of taking in food, drink, or another substance into the body by swallowing it
• Digestion


  The breaking down of food into smaller pieces that the body can absorb and use
• Mechanical digestion


  • Physical preparation of food for digestion (chew, mash, tear, grind, mix)
• Chemical digestion


  • The breaking down of food into smaller molecules that can be absorbed
• Mechanical digestion process


  1. Chewing

  2. Grinding

  3. Saliva secretion
• Chewing


  Breaks food into small fragments

  
• Mastication


  The official name for chewing
• Saliva


  Aids the mechanical and chemical process of digestion
• Swallowing process


  1. Bolus formation

  2. Pharynx passage

  3. Epiglottis closure

  4. Esophagus movement
• Peristalsis


  Alternate waves of muscular contraction and relaxation in the primary digestive organs to squeeze food from one part of the system to the next
• Absorption


  The process of taking up nutrients
• Villi


  • Line the walls of the small intestine and absorb nutrients into capillaries of the circulatory system and lacteals of the lymphatic system

  
• Assimilation


  The process of using the nutrients by the body
• Large intestine process


  1. Absorption of remaining nutrients and water

  2. Compaction of waste into feces
• Excretion/Defecation


  The removal/elimination of the waste products from the body
• Defecation process


  1. Contraction of rectal muscles

  2. Relaxation of internal anal sphincter
• Defecation reflex


  Mostly involuntary, under the command of the autonomic nervous system, but the somatic nervous system also plays a role to control the timing of elimination
• Organs of the digestive system

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
• Mouth


  • Teeth mechanically break down food
  • Tongue mixes food with saliva

  
• Pharynx


  The hollow tube inside the neck that starts behind the nose and ends at the top of the trachea (windpipe) and esophagus
• Epiglottis


  A flap-like structure at the back of the throat that closes over the trachea, preventing food from entering it
• Stages of swallowing


  1. Oral preparatory stage

  2. Oral transit/propulsive stage

  3. Pharyngeal stage

  4. Esophageal stage
• Oral preparatory stage


  1. Food is kept in the front part of the mouth

  2. Food is moistened with saliva

  3. Food is chewed into a softer consistency
• Oral transit/propulsive stage


  1. Back of the tongue drops to allow the bolus to move into the back of the mouth

  2. Tongue raises up against the hard palate
• Pharyngeal stage


  1. Bolus is propelled into the esophagus

  2. Larynx elevates

  3. Epiglottis flips down protecting the airway
• Esophageal stage


  Involuntary movement of the bolus through the esophagus and into the stomach
• Esophagus


  • Approximately 20 cm long
  • Secretes mucus
  • Moves food from the throat to the stomach using muscle movement called peristalsis
  • If acid from the stomach gets in here that's heartburn

  
• Stomach


  • J-shaped muscular bag that stores the food you eat
  • Breaks down food into tiny pieces
  • Mixes food with Digestive Juices that contain enzymes to break down Proteins and Lipids
  • Acid (HCl) in the stomach Kills Bacteria
  • Food found in the stomach is called Chyme
• Small Intestine


  • Roughly 7 meters long
  • Lining of intestine walls has finger-like projections called villi, to increase surface area
  • The villi are covered in microvilli which further increases surface area for absorption
  • Nutrients from the food pass into the bloodstream through the small intestine walls
  • Secretes digestive enzymes
  • Absorbs 80% ingested water, Vitamins, Minerals, Carbohydrates, Proteins, Lipids

  
• Duodenum


  • First part of the small intestine that the stomach feeds into
  • Short, descending chute (about 10 inches long) that curves around the pancreas in a "C" shape before connecting to the rest of the coiled intestines
  • Receives digestive juices from other organs including liver, gallbladder and pancreas

  
• Jejunum


  • Middle section of the small intestine
  • Characterized by many blood vessels, which give it a deep red color
  • Food moves into the jejunum after chemical digestion in the duodenum
  • Muscle work of digestion picks up, with nerves in the intestinal walls triggering its muscles to churn food back and forth (segmentation) and move it gradually forward (peristalsis)

  
• Ileum


  • Last and longest section of the small intestine
  • Walls of the small intestine begin to thin and narrow, and blood supply is reduced
  • Food spends the most time in the ileum, where the most water and nutrients are absorbed
  • Segmentation slows down and peristalsis takes over, moving food waste gradually toward the large intestine
  • Ileocecal valve separates the ileum from the large intestine

  
• Large Intestine


  • About 1.5 meters long
  • Accepts what small intestines don't absorb
  • Absorbs more water
  • Bacterial digestion
  • Concentrates wastes
  • Ferments carbohydrates

  
• Rectum


  • Last several inches of the large intestine closest to the anus
  • Collects and holds poop until it's time to release it
  • Rectum relaxes and stretches to accommodate the waste as it gradually comes in from the colon
• Main groups of organs in the digestive system

  • Digestive Organs
  • Accessory Digestive Organs

  
• Accessory Digestive Organs


  • Teeth
  • Tongue
  • Gall bladder
  • Salivary glands
  • Liver
  • Pancreas

  
• Teeth


  • Break down foods by crushing or cutting them before you swallow
  • Most humans have 32 teeth
  • Enamel (the protective outer layer of your teeth) is the hardest substance in the human body