Gastrointestinal System Module 1

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Gastrointestinal SystemModule 1

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GI System--Structure

• Mouth
• Esophagus
• Stomach
• Small Intestine
• Large intestine
• Rectum
• Anus

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GI System--Structure

• GI tract is about 30 feet long from mouth to anus
• Layers from inner to outer
• Mucosa
• Submucosa
• Muscle- 2 layers
• Circular (inner)
• Longitudinal (Outer)
• Serosa except esophagus (fibrous)

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GI System--Structure

• Innervation
• Sympathetic-inhibitory
• Parasympathetic-excitatory
• Example
• Peristalsis is increased with parasympathetic
  stimulation

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GI System--Structure

• GI tract receives 25-30 of cardiac output
• Venous blood empties into portal vein which
  peruses liver
• Upper portion of GI tract receives blood from
  splanchic artery
• Small intestine receives blood from hepatic and
  mesentery arteries
• Large intestine receives blood supply from
  superior and inferior mesenteric arteries

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GI System--Structure

• Two types of movement
• Mixing (Segmentation)
• Propulsion (Peristalsis)
• Hormones and enzymes for digestion
• Mucous provides protection, lubrication, water,
  electrolytes

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GI System--Structure

• Abdominal organs are covered by peritoneum
• Two layers of peritoneum
• Parietal-lines abdominal cavity wall
• Visceral-covers abdominal organs
• Peritoneal cavity- space between parietal and
  visceral
• Two folds of peritoneum
• Mesentery-attaches small intestine to posterior
  abdominal wall
• Lesser omentum-hangs from stomach like apron,
  contains fat and lymph nodes

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GI SystemIntrinsic/Enteric layer

• GI tract has its own nervous system
• Enteric or intrinsic
• Two intrinsic layers
• Lies between mucosa and the circular muscle layer
• Other layer lies between circular and
  longitudinal layer
• Innervation contributes to coordination of GI
  motor and secretory activities
• Enteric nervous system is also known as the gut
  brain
• Ability to control movement and secretion of GI
  tract

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GI System-Function

• Supply nutrients to body cells
• Ingestion (taking in) and propulsion (movement)
• Digestion-breakdown
• Absorptiontransfer of food products into
  circulation
• Elimination-Excreting waste products

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GI System-Function/Ingestion

• Swallowing (deglutition)-mechanical component of
  ingestion
• Mouth
• Lips
• Oral cavity
• Three pairs of salivary glands
• Parotid
• Submaxillary
• Sublingual
• Glands produce saliva (water, protein, mucin,
  salts, amylase(pytalin))

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GI System-Function/Ingestion

• Pharynx
• Esophagus
• Upper third striated muscle
• Distal two thirds-smooth muscle
• With swallowing, peristaltic wave moves bolus
  into esophagus
• Lower esophageal sphincter (LES) remains
  contracted except when swallowing, vomiting, or
  belching
• LES-important barrier that prevents acid reflux
  from stomach

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GI System-Digestion/Absorption

• Digestion is mechanical and chemical
• Mouth
• Lubricates and softens mass
• Stomach
• Stores food
• Mixes food with gastric secretions
• Empties contents into small intestine

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GI System-Digestion/Absorption-Stomach

• Parts of stomach
• Fundus
• Chief cells (secrete pesinogen)
• Parietal cells (secrete HCL, water, and intrinsic
  factor)
• Acid Ph protects against ingested organisms
• Intrinsic factor promotes cyclocobalamin (B 12)
  absorption in the small intestine
• Body
• Antrum

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GI System-Digestion/Absorption-Stomach

• Pylorus
• Small portion of antrum
• Lies proximal to pyloric sphincter
• Pyloric sphincter guards entrance to and from
  entrance to stomach
• Rugae-folds in stomach, contains glands

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GI System-Digestion/Absorption-Small Intestine

• Two functions
• Digestion
• Absorption-uptake of nutrients from gut to
  bloodstream
• Approximately 23 feet long
• Extends from pylorus to ileo cecal valve
  (prevents reflux from small intestine to large
  intestine)
• Large surface area for absorption

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GI System-Digestion/Absorption-Small Intestine

• Villi
• Functional units of small intestine
• Contains goblet cells
• Secrete mucous
• Epithelial cells
• Produce digestive enzymes
• Mirovilli-assist villi to increase surface area
• Crypts of Liberkuhn-contain base columnar cells
• Brunners glands-secrete mucous in duodenum

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GI System-Physiology of Digestion

• Salivary gland-breakdown of starch
• Stomach-releases of pepsinogen from chief cells
• Acid in stomach converts of pepsinogen in to
  pepsin-initial breakdown of proteins
• Stomach has minimal impact on breakdown of
  starches and fat
• Food stays in stomach 3-4 hours

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GI System-Physiology of Digestion-Small Intestine

• Carbohydrates broken down into monosaccharides
• Fats to glycerol
• Proteins to amino acids
• Chyme (food mixed with gastric secretions)

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GI System-Physiology of Digestion-Small Intestine

• Enzymes secreted from pancreas
• Bile from liver
• Intestinal secretions
• Hormones secretin stimulates pancreas to produce
  bicarb (neutralizes acid in chyme)
• Duodenum secretes mucous to protect small
  intestine from acid
• Hormone cholecystokinin stimulates gall bladder
  contraction and relaxation of the sphincter of
  Oddi-bile released-digest fat

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GI System-Physiology of Elimination-Large
Intestine

• 5-6 feet long
• Four parts
• Cecum and Appendix
• Colon
• Rectum
• Anus
• Most important function-absorption of water and
  electrolytes

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GI System-Physiology of Elimination-Large
Intestine

• Forms feces until defecation
• Feces
• Water
• Bacteria
• Unabsorbed minerals
• Undigested food
• Bile pigment
• Epithelial cells

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GI System-Physiology of Elimination-Large
Intestine

• Bacteria-
• Responsible for breakdown of proteins not
  digested by small intestine
• Synthesize Vitamin K and some B vitamins
• Production of flatus
• Slow movement-haustral churning
• Defecation
• Voluntary and involuntary muscles
• Valsalva maneuver

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Physiology of Elimination-Liver

• Largest internal organ in body
• Right and left lobes
• Lobules-functional unit
• Rows of hepatic cells (hepatocytes)
• Kupfer cells-phagocytic activity-removes
  toxins/bacteria from blood
• Portal circulatory system brings blood to liver
  from stomach, intestine
• Involved in metabolism, detoxification,
  destruction of RBC

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Physiology of Elimination-Biliary Tract

• Consists of
• Gallbladder-concentrate, store bile
• Duct system
• Bile-produced by hepatic cells
• Moves down common bile duct, enters duodenum at
  ampulla of Vater
• In intestine, bilirubin converts to
  stercobilirubin (color of stool) and urobilirubin
  (color of urine)
• Sphincter of Oddi keeps ampulla closed

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Physiology of Elimination-Biliary Tract

• Bilirubin metabolism
• Breakdown of Hemoglobin
• Bound to albumin for transport to liver
  (uncongugated)
• In liver, conjugated with glucuronic acid
• Conjugated bilirubin is soluable

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Physiology of Elimination-Pancreas

• Exocrine and endocrine functions
• Exocrine-digestion-pancreatic enzymes
• Endocrine
• Islets of Langerhans
• Beta cells-insulin
• Alpha cells-glucagon
• Delta-somatostatin
• F cells-pancreatic polypeptides

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GI System and Aging

• Periodontal disease-loss of teeth
• Taste buds, smell, salivary secretions decrease
• Delayed gastric emptying
• Motility of GI tract diminishes
• Decrease in HCL secretion
• Reduction in secretion of acid and intrinsic
  factor
• Liver size decreases

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GI System-Factors that Influence Function

• Stress/anxiety
• Dietary intake
• Ingestion of ETOH/caffeine
• Cigarette smoking
• Fatigue
• Organic diseases
• Others?