The Digestive System

• what is the function of the Digestive System?

  The mechanical and chemical breakdown of food into small, absorbable units
• What are the two components of the digestive system?

  the GIT and accessory glands/organs
• What is the gastrointestinal tract?

  Long muscular tube running from the mouth to the anus
• The GIT consists of multiple organs joined in series
• What are the components of the GIT?

  Oral cavity, oesophagus, stomach, small intestine, large intestine, rectum
• Accessory glands and organs are located outside the GIT
• What are the accessory organs?

  Salivary glands, gall bladder, liver, pancreas
• THe mucosa is the inner lining of the GIT wall
• The mucosa has a role in absorption and secretion
• The submucosa is the middle layer of the GIT wall
• The submucosa consists of connective tissue with blood and lymph vessels, and nerves
• The muscularis externa is the outer wall of the GIT
• The muscularis externa consists of circular and longitudinal muscles
• In the stomach, the muscularis externa also has oblique muscle
• The serosa is the covering connective tissue of the GIT wall
• The serosa provides structure and support
• The serosa anchors the GIT organs together and within the body
• Mouth, upper third of the oesophagus, and external portion of the anus have different GIT wall compositions because they are involved in voluntary control
• In the small intestine, the mucosa has villi to aid in absorption
• In the small intestine, the submucosa has submucosal plexus to control secretions
• In the small intestine, the muscularis externa has myenteric plexus to control muscle contractions
• Secretion:

  Movement of molecules from cells into the lumen or ECF
• What are the four layers of the GIT wall?

  mucosa, submucosa, muscularis externa, serosa
• Digestion:

  Chemical and mechanical breakdown of food into absorbable units
• Absorption:

  Movement of material from GI lumen to cells or blood
• Motility


  Muscle contraction to ensure food travels in the correct direction
• Mastication = chewing
• Mastication is the mechanical digestion by lips, tongue and teeth to generate a bolus that can be swallowed
• Salivation softens and moistens food, allows for taste, helps with digestion, and defence
• Saliva contains water, ions, mucus, enzymes, and proteins (e.g. immunoglobulins)
• Enzymes in saliva include amylase, lipase, and lysozymes
• amylase breaks down carbohydrates
• lipase breaks down fats
• lysozymes breaks down bacteria cell wall
• The sublingual gland is mucus-rich
• Where is the sublingual gland?

  Under the tongue
• The parotid gland is watery
• Where is the parotid gland?

  Under the hinge of the jaw
• The submandibular gland is mixed
• Where is the submandibular gland?

  Under the jaw bone