DIGESTIVE SYSTEM

• Gastroenterology

  The study of the gastrointestinal system
• Functions of the digestive system

  • Ingestion
  • Secretion
  • Digestion (chemical and mechanical)
  • Mixing and propulsion
  • Absorption
  • Defecation

  
• Alimentary canal (GI tract)


  Extends from the mouth to the anus through the ventral body cavity (approximately 9 m, or 30 ft.)
• Accessory organs of the digestive system

  • Teeth
  • Tongue
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas

  
• Catabolism


  Larger molecules are broken into smaller molecules (mouth, stomach, duodenum)
• Anabolism


  Smaller molecules are used as building blocks for larger molecules (liver)
• Mechanical digestion processes


  • Mastication
  • Swallowing
  • Mixing
  • Increase contact of food with digestive chemicals
  • Peristalsis

  
• Peristalsis


  Movement of muscles within the GI tract that facilitates movement of food
• Chemical digestion


  1. Using water to break chemical bonds (hydrolysis)

  2. Fats are broken down into fatty acids and glycerol

  3. Carbohydrates are broken down from polysaccharides into monosaccharides

  4. Proteins are broken down into polypeptides and amino acids
• Layers of the GI tract wall

  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa/adventitia
• Lumen


  The inside of the GI tract tube
• Peritoneum


  The body's largest serous membrane, wraps around most abdominopelvic organs
• Major peritoneal folds


  • Greater omentum
  • Falciform ligament
  • Lesser omentum
  • Mesentery
  • Mesocolon

  
• Greater omentum


  Drapes over the transverse colon and the anterior coils of the small intestine like a "fatty apron"

  
• Falciform ligament


  Attaches the liver to the anterior abdominal wall and diaphragm

  
• Lesser omentum

  Suspends the stomach and duodenum from the inferior edge of the liver, contains blood vessels and bile duct

  
• Mesentery and mesocolon


  Attach the bowel to the posterior abdominal wall, holding the intestines loosely in place

  
• Retroperitoneal organs


  • Kidneys and ureters
  • Most of the pancreas
  • Adrenal glands
  • Aorta and inferior vena cava

  
• Phases of digestive activities

  • Cephalic phase
  • Gastric phase
  • Intestinal phase

  
• Cephalic phase


  Smell, sight, thought, or initial taste of food activates neural centers to prepare for digestion

  
• Gastric phase

  Neural and hormonal mechanisms promote secretion of gastric juice and increase gastric motility
• Intestinal phase

  Neural and hormonal responses promote continued digestion of foods that have reached the small intestine

  
• Oral/buccal cavity


  Formed by the cheeks, hard and soft palates, and the tongue

  
• Digestion - breaking down large molecules of carbohydrates, proteins, fats, vitamins, minerals, etc., into smaller units that can be absorbed through the walls of the intestines.
• Secretion - release of substances from cells or organs to the outside of the body or another part of the body.
• Ingestion - taking food into the body by mouth.
• Motility - movement of contents within the GI tract.
• Absorption - process where nutrients are taken up by the bloodstream and transported throughout the body.
• Defecation - elimination of feces (waste products) from the body.
• Absorption - movement of digested nutrients from the lumen of the GI tract across the epithelial lining and into the bloodstream or lymphatic vessels.
• Motor functions include peristaltic movements (waves of contraction) that move food along the alimentary canal and mix it with digestive juices.
• Defecation - elimination of undigested material (feces) from the body via the anus.
• The oral cavity is also known as the buccal cavity.
• It contains teeth, which are used for biting and grinding food, and salivary glands, which secrete saliva containing enzymes such as amylase that begin the process of starch breakdown.
• Elimination - removal of waste products from the body.
• Absorption - process whereby nutrients are taken up by the bloodstream and carried throughout the body.
• The nervous system controls motor function, including swallowing, vomiting, and defecation.
• The pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anal canal make up the gastrointestinal tract.
• The sensory receptors located on the tongue can distinguish between different tastes, while olfactory receptors in the nose allow us to sense odors.
• Alimentary canal includes oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.