finals-digestive

• Functions of the digestive system

  • Digestion – breakdown of ingested food
  • Absorption – passage of nutrients into the blood
  • Metabolism – production of cellular energy (ATP)
• Components of the digestive system

  • Alimentary canal/Gastrointestinal (GI) tract — mouth, pharynx, esophagus, stomach, small intestine, and large intestine
  • Accessory digestive organs — teeth, tongue, gallbladder, salivary glands, liver, and pancreas
• Gastrointestinal (GI) Tract


  • A continuous, hollow coiled tube that digests food, breaks it down, and absorbs the fragments through its lining into the blood
• Digestive process


  • Ingestion
  • Mechanical digestion
  • Propulsion
  • Chemical digestion
  • Absorption
  • Defecation
• Ingestion


  Taking food into the digestive tract
• Mechanical digestion


  Chewing, mixing, and churning food
• Mechanical digestion


  • Biting: using of teeth to cut the food
  • Mastication: chewing or grinding of food
• Propulsion


  Deglutition and peristalsis
• Propulsion


  • Deglutition: swallowing
  • Peristalsis: waves of contraction and relaxation of muscles in the organ
• Chemical digestion


  Catabolic breakdown of food (conversion/breakdown of food into simpler components that includes catabolism)
• Chemical digestion


  • Initial digestion: stomach
  • Final digestion: small intestine
• Absorption


  Movement of nutrients from the GI tract to the blood or lymph via the villi and microvilli
• Defecation


  Elimination of indigestible and unabsorbed solid wastes
• Mouth (Oral Cavity) Anatomy

  • Lips (labia)
  • Cheeks
  • Hard palate
  • Soft palate
  • Uvula
  • Vestibule
  • Tongue
  • Frenulum
  • Tonsils
• Tonsils


  • Palatine tonsils — associated with preventing infections in the respiratory and digestive tract
  • Lingual tonsils — to prevent infections; contains the B and T lymphocytes
• Processes of the Mouth

  • Mastication (chewing) of food (mechanical digestion)
  • Mixing masticated food with saliva (chemical digestion)
• Enzymes in saliva


  • Salivary amylase: enzyme digests starch
  • Mucin: slippery protein (mucus); protects soft lining of digestive system; lubricates food for easier swallowing
  • Buffers: neutralizes acid to prevent tooth decay
  • Anti-bacterial chemicals: kill bacteria that enter mouth with food
• Different tastes: salty, sweet, bitter, sour, umami, spicy
• There are about 10,000 taste buds and they are replaced every 2 weeks
• Older people: the more they age, taste buds become weaker; 5,000 taste buds
• Initiation of swallowing


  By the tongue
• Pharynx (throat)


  Connected to trachea and esophagus, serves as passageway for air and food
• Pharynx


  • Food is propelled to the esophagus by two muscle layers: longitudinal inner layer and circular outer layer
  • Food movement is by alternating contractions of the muscle layers (peristalsis)
• Epiglottis


  Covers the trachea so the food will go down to our esophagus
• Esophagus


  Runs from pharynx to stomach through the diaphragm, conducts food by peristalsis
• Stomach


  • Located on the left side of the abdominal cavity, holds about 1 gallon of food, food enters at the cardio-esophageal sphincter and exits at the pyloric sphincter
• Stomach Functions


  • Acts as a storage tank for food
  • Site of food breakdown
  • Produces 2-3L/day of gastric juice (HCl, enzymes, and mucus)
  • Chemical breakdown of protein begins
• Pepsin


  Enzyme that breaks down proteins; secreted as pepsinogen (inactivated enzyme); activated by HCl
• Hydrochloric acid


  Functions to kill the bacteria and sanitize the food
• Achlorhydria


  Condition in which the stomach could not be able to produce HCl
• Chyme


  Partly digested food
• Hormones and peptides that help in digestion

  • Motilin: A polypeptide that has a role in fat metabolism
  • Gastrin: A hormone that stimulates the production of gastric acid in the stomach
  • Secretin: A peptide hormone secreted by the duodenum that serves to regulate its acidity
• Stomach Diseases and Disorders

  • Heartburn
  • Hiatal hernia
  • Vomiting
• It takes 4 HOURS for the stomach to empty after WELL-BALANCED MEAL and 6 HOURS for FATTY MEAL
• Small Intestine


  • The body's major digestive organ, site of nutrient absorption into the blood, muscular tube extending from the pyloric sphincter to the ileocecal valve, suspended from the posterior abdominal wall by the mesentery
• Subdivisions of the Small Intestine

  • Duodenum
  • Jejunum
  • Ileum
• Chemical Digestion in the Small Intestine


  Source of enzymes that are mixed with chyme, acid food from stomach mixes with digestive juices from accessory glands
• Enzymes in the Small Intestine

  • Peptidases: digests proteins/breaks peptide bonds (trypsin, chymotrypsin, carboxypeptidase)
  • Pancreatic amylase: digests starch
  • Lipase: needed to digest fat
  • Nucleases: digests nucleic acids
• Bile


  Breaks up fats (helps lipase to digest fats), enters the small intestine from the gallbladder
• Villi of the Small Intestine

  • Fingerlike structures formed by the mucosa, give the small intestine more surface area