DIGESTIVE

• Function of the digestive system

  Break down the foods you eat<|>Release their nutrients<|>Absorb those nutrients into the body
• Digestive process

  1. Break down food

  2. Release nutrients

  3. Absorb nutrients
• In our saliva, we already have enzymes like salivary amylase that already degrades some form of sugar that we need to absorb in our intestines
• Salivary amylase


  Acts on starch, a form of carbohydrate, and converts it into simple sugar
• As early as in the mouth, we are already digesting food
• The alimentary canal is a one-way tube about 25 feet in length
• Alimentary canal


  Main function is to nourish the body by digesting food and absorbing released nutrients
• The alimentary canal begins at the mouth and ends at the anus
• The alimentary canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the body

  
• Only through the process of absorption do the nutrients in food enter into and nourish the body’s “inner space”
• Canal


  A medium where food passes through
• Accessory structures

  Sprout from the lining cells of the developing gut and augment its function
• Accessory organs are usually activated during parasympathetic
• Histology of the alimentary canal

  Composed of the same four tissue layers: mucosa, submucosa, muscularis, and serosa
• Mucosa


  Consists of epithelium, lamina propria, and muscularis mucosa
• Epithelium


  In the mouth, pharynx, esophagus, and anal canal, primarily a non-keratinized, stratified squamous epithelium; in the stomach and intestines, a simple columnar epithelium

  
• Goblet cells


  Secrete mucus and fluid into the lumen, lessening friction during swallowing
• Enteroendocrine cells


  Secrete hormones into the interstitial spaces between cells
• The epithelium is in direct contact with the lumen
• The epithelium is rapidly renewed to help preserve the alimentary canal despite wear and tear
• The epithelium is mitotically active, which is why it is prone to abnormal mutation (cancer)
• Lamina propria


  Consists of loose connective tissue containing blood and lymphatic vessels
• Lamina propria serves an immune function by housing clusters of lymphocytes, making up the mucosa-associated lymphoid tissue (MALT)
• Peyer’s patches are usually seen in the distal ileum
• Muscualris mucosa


  A thin layer of smooth muscle in a constant state of tension, increasing surface area for digestion and absorption
• Serosa


  Consists of a layer of visceral peritoneum overlying a layer of loose connective tissue
• Serosa serves to hold the alimentary canal in place near the ventral surface of the vertebral column
• The adventitia is a dense sheath of collagen fibers in the mouth, pharynx, and esophagus instead of serosa
• Nerve supply

  Enteric nervous system provides intrinsic innervations of the alimentary canal
• Enteric neurons


  Grouped into two plexuses: myenteric plexus and submucosal plexus
• Myenteric plexus


  Responsible for motility, especially the rhythm and force of contractions of the muscularis
• Submucosal plexus


  Responsible for regulating digestive secretions and reacting to the presence of food

  
• Autonomic nervous system


  Provides extrinsic innervations of the alimentary canal
• Sympathetic activation


  Restricts the activity of enteric neurons
• Parasympathetic activation


  Increases GI secretion and motility by stimulating neurons of the enteric nervous system
• The first function of blood supply is to transport protein and carbohydrate nutrients absorbed by mucosal cells after food is digested
• The second function of blood supply is to supply the organs of the alimentary canal with nutrients and oxygen needed for cellular processes
• The anterior part of the alimentary tract is supplied by the aortic arch and thoracic aorta
• The posterior part of the alimentary tract is supplied by the abdominal aorta
• Celiac trunk


  A main branch of the aorta that supplies other organs