Digestive System

• Functions of the Digestive System

  • Ingestion
  • Digestion
  • Propulsion
  • Absorption
  • Elimination
• Mechanical Digestion

  • which involves the mastication and mixing of food
• Chemical Digestion

  • which is accomplished by digestive enzymes secreted along the digestive tract.
• Digestive Tract consists of

  • Oral Cavity
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
  • Anus
• Oral Cavity

  • is bounded by the lips and cheeks and contains the teeth and tongue.
• Lips and Cheeks

  • involved in mastication and speech
• Tongue

  • involved in speech, taste, mastication, and swallowing
• Two parts of the Roof of the Oral Cavity:

  • Hard Palates
  • Soft Palates
• Teeth

  • Mastication is accomplished, which cut, tear, and crush the food into smaller fragments.
• Types of Tooth

  • Incisors - cutting or nipping off pieces of food
  • Canines - tearing and piercing
  • Premolars - Grinding and crushing
  • Molars - Best grinders
• Parts of a Tooth

  • Crown
  • Neck
  • Root
• Three Major Parts of Salivary Glands

  • Parotid
  • Submandibular
  • Sublingual Glands
• Saliva

  • helps protect the mouth from oral bacteria, starts starch digestion, and provides lubrication.
• Pharynx

  • which connects the mouth with the esophagus
• Three Parts of Pharynx

  • Nasopharynx - does not usually transmit food
  • Oropharynx
  • Laryngopharynx
• Esophagus

  • connects the pharynx to the stomach.
• Peristalsis

  • is the alternate waves of contraction and relaxation of muscles in the organ walls.
• Three Parts of Deglutition

  • Voluntary
  • Pharyngeal
  • Esophageal
• Voluntary Phase

  • a bolus, or mass of food, is formed in the mouth and pushed by the tongue against the hard palate, until it is forced toward the posterior part of the mouth and into the oropharynx.
• Pharyngeal Phase

  • swallowing is a reflex that is initiated when a bolus of food stimulates receptors in the oropharynx. As food passes through the pharynx, the vestibular and vocal folds close, and the epiglottis is tipped posteriorly, so that the opening into the larynx is covered.
• Esophageal Phase

  • swallowing is responsible for moving food from the pharynx to the stomach. Muscular contractions of the esophagus occur in peristaltic waves.
• Stomach

  • enlarged segment which functions as a storage and mixing chamber
  • connects to the esophagus at the gastroesophageal opening and to the duodenum at the pyloric opening.
• Three Muscle Layers of Stomach

  • Longitudinal
  • Circular
  • Oblique
• Surface mucous cells and Mucous neck cells

  • produce mucus, which coats and protects the stomach lining.
• Parietal cells

  • produce hydrochloric acid and intrinsic factor; Hydrochloric acid produces the low pH of the stomach’s contents which kills microorganisms and activates pepsinogen to pepsin. Intrinsic factor is a glycoprotein that binds with vitamin B12, making the vitamin more readily absorbed in the ileum.
• Chief Cells

  • produce pepsinogen, a precursor of the proteindigesting enzyme pepsin.
• Endocrine Cells

  • produce regulatory chemicals such a histamine, gastrin, and somatostatin.
• Histamine

  • stimulates acid secretion by parietal cells.
• Gastrin

  • stimulates additional HCl and pepsinogen.
• Somatostatin

  • inhibits gastrin and insulin secretion.
• Small Intestine

  • where the greatest amount of digestion and absorption occurs.
• Three parts of Small Intestine

  • Duodenum
  • Jejunum
  • Ileum
• Circular Folds

  • folds force chyme to spiral through the lumen, slowing its movement and allowing time for full nutrient absorption.
• Villi

  • columnar cells which absorbs nutrient and bring it to both the capillary blood and the lacteal
• Microvilli

  • bear enzymes referred to as brush border enzymes, which complete the digestion of carbohydrates and proteins in the small intestine
• Goblet Cells

  • produces mucus
• Enteroendocrine Cells

  • secretes secretin and cholecystokinin
• Segmental Contractions

  • are mixing contractions that occur in the small intestine.
  • These contractions do not propel food from one end of the digestive tract to the other but, rather, move it back and forth within the digestive tract to mix it with digestive secretions and help break it into smaller pieces.
• Liver

  • the largest internal organ of the body.
  • Contains four lobes of portal triads
• Gallbladder

  • saclike structure for bile storage.
  • It is on the inferior surface of the liver.