A&P Exam 8

• Nutrients


  Smaller components that the body can make use of
• Digestive System


  Acts as a disassembly line to break down nutrients into forms that can be used by the body
• Gastroenterology


  The study of the digestive tract and the diagnosis and treatment of its disorders
• Digestive Function


  The organ system that processes food, extracts nutrients, and eliminates residue
• Five stages of digestion

  1. Ingestion: selective intake of food

  2. Digestion: mechanical and chemical breakdown of food into a form usable by the body

  3. Absorption: uptake of nutrients molecules into the epithelial cells of the digestive tract and then into the blood and lymph

  4. Compaction: absorbing water and consolidating the indigestible residue into feces

  5. Defecation: elimination of feces
• Mechanical digestion


  The physical breakdown of food into smaller particles
• Mechanical digestion


  • Cutting and grinding action of the teeth
  • Churning action of stomach and small intestines
• Chemical digestion


  A series of hydrolysis reactions that breaks dietary macromolecules into their monomers
• Digestive enzymes


  • Salivary amylase
  • Lingual lipase
  • Pepsin
  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase
  • Pancreatic amylase
  • Pancreatic lipase
  • Ribonuclease
  • Deoxyribonuclease
• Some nutrients are present in a useable form in ingested food and can be directly absorbed
• Directly absorbable nutrients


  • Vitamins
  • Amino acids
  • Minerals
  • Cholesterol
  • Water
• Digestive tract


  Open to environment at both ends, 30ft long muscular tube extending from mouth to anus
• Parts of the digestive tract

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Accessory organs


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


  Lining of the digestive tract lumen, consisting of inner epithelium, lamina propria, and muscularis mucosa
• Submucosa


  Thicker layer of loose connective tissue
• Muscularis externa


  Consists of usually two layers of muscle near the other surface
• Serosa


  Composed of a thin layer of areolar tissue topped by simple squamous mesothelium
• Regulation of the digestive tract

  Both nervous and endocrine
• Regulation of the digestive tract

  1. When food is seen, smelled, tasted: Vagus Nerve stimulates gastric secretion

  2. When food reaches stomach: Myenteric and Vagovagel reflex stimulate gastric secretion, Histamine and Gastrin stimulate gastric secretion

  3. When Chyme arrives at small intestine: Intestinal gastrin stimulates stomach, Enterogastric reflex, secretin and cholecystokinin (CKK) inhibit gastric secretion and motility
• Mouth


  Also known as the oral or buccal cavity
• Functions of the mouth

  • Ingestion (food intake)
  • Mechanical (Chewing) and chemical digestion (salivary enzymes: salivary amylase and lingual lipase)
• Pharynx


  Muscular funnel connecting oral cavity to esophagus and nasal cavity to larynx
• Esophagus


  Straight muscular tube 25-30 cm long, extends from pharynx to cardial orifice of stomach passing through esophageal hiatus in diaphragm
• Lower esophageal sphincter


  Food pauses here because of constriction, prevents stomach contents from regurgitating into the esophagus
• Swallowing


  1. Oral Phase: under voluntary control

  2. Pharyngeal phase: involuntary

  3. Esophageal phase- peristalsis: involuntary wave of muscular contraction that pushes the bolus ahead of it
• Stomach


  A muscular sac in upper left abdominal cavity immediately inferior to the diaphragm, mechanically breaks up food, liquefies it, and begins chemical digestion of protein and fat
• Chyme


  Soupy or pasty mixture of semi-digested food in the stomach
• Most digestion occurs after the chyme passes on to the small intestine
• Gastric rugae


  Longitudinal wrinkles in the mucosa and submucosa when the stomach is empty
• Layers of the muscularis externa of the stomach


  • Outer longitudinal
  • Middle Circular
  • Inner Oblique Layers
• Gastric pits


  Depressions in the gastric mucosa, lined with simple columnar epithelium and open to tubular gastric glands
• Gastric juice


  1. 3 L per day produced by gastric glands, mainly a mixture of water, hydrochloric acid, and pepsin
• Pepsin


  Digests dietary proteins into shorter peptides
• Hydrochloric acid


  Activates pepsin and lingual lipase
• Gastric motility is controlled by enteric pacemaker cells in the longitudinal layer of the muscularis externa, creating a ring of constriction every 20 seconds to churn the food, mix it with gastric juice, and promote its physical breakdown and chemical digestion
• Vomiting


  Forceful ejection of the stomach and intestinal content from the mouth
• Liver


  Reddish brown gland located immediately inferior to the diaphragm, the body's largest gland weighing about 1.4 kg (3lbs)
• Gallbladder


  Adheres to a depression on the inferior surface of the liver, right between the right and quadrate lobes, serves to store and concentrate bile
• Bile


  Yellow green fluid containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids, aids in fat digestion and absorption