Functions of the Gastrointestinal System

  • To prepare food for absorption into the body and utilization by the cells
  • To excrete any food material of no use to the body

 

Gastrointestinal System composed of:

  • Gastrointestinal tract
  • Accessory organs and structures

 

Gastrointestinal Tract

  • Approx 4.5 meters in length
  • Almost doubled when no muscle tone
  • A fibromuscular tube

 

Gastrointestinal tract is made up of:

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large Intestine

 

Accessory organs & structures are:

  • Salivary glands
  • Teeth
  • Tongue
  • Liver
  • Gall bladder
  • Pancreas

 

Digestive Processes – 5 stages:

1.    Ingestion

2.    Movement of food

§  Peristalsis

3.    Digestion

§  Mechanical

§  Chemical

4.    Absorption

5.    Defecation

 

Mucosal layers (3)

  • protection
  • secretion
  • absorption

 

Mouth

  • Provides an entrance to the gastrointestinal system
  • Initiates digestion by the mechanical breakdown of food material
  • Normal swallowing mechanisms move the food bolus to the esophagus
  • Mediated by Cranial nerves IX, X, and XII

 

Functions of the Mouth

  • Chewing, grinding and mixing of food
  • Formation of a bolus
  • Initiation of digestive processes
  • Swallowing
  • Taste
  • These functions assisted by teeth, tongue, salivary glands and sensory nerve endings

 

Pharynx

  • Food passes through the oropharynx and laryngopharynx to reach the esophagus
  • Once a bolus of food reaches the pharynx swallowing is no longer voluntary

 

Swallowing

  • swallowing initiates peristalsis

 

Peristalsis

  • An involuntary activity of the longitudinal and circular layers of smooth muscle within the wall of the tract
  • Rhythmic, pulsatile contractions of these muscle layers move the contents of the tract forward

 

Esophagus

  • Hollow tube connecting mouth to stomach
  • Runs through mediastinum
  • Attaches to the stomach just below the diaphragm
  • Mucus membrane lining secreting protective mucoid substance

 

Functions of the esophagus

  • Transport of food
  • Movement of food by peristalsis
  • Mechanical dispersion of food as the first part of digestion

 

Cardiac Sphincter

  • A one-way valve preventing reflux of stomach contents into the esophagus
  • Relaxes as peristaltic wave approaches so that food can enter the stomach
  • Also known as the lower esophageal sphincter

 

Stomach

  • A dilation of the intestinal tract between the esophagus and the beginning of small intestine
  • Separated form the small intestine by the pyloric sphincter
  • Has three regions:
    1. fundus
    2. body
    3. pylorus

 

Stomach

  • Food bolus enters the stomach moving slowly towards the pylorus (2 – 6 hours)
  • Fluid mass in stomach called chyme
  • Chyme pumped through pyloric sphincter into the small intestine
  • Rate of movement of stomach contents depends on:
    1. food type and consistency
    2. rate of pancreatic and biliary secretions
  • Functions of the Stomach
    1. Temporary storage
    2. Mixing
    3. Exocrine secretions
      • hydrochloric acid
      • intrinsic factor
      • pepsinogen
      • mucus
    4. Outflow regulation of processed food particles to the small intestine
    5. Extraction of iron from food
    6. Limited absorption

 

Control of Gastric Activity

  • Gastric secretion is regulated by nervous and hormonal activity
  • Gastric emptying is stimulated in response to stretch, stomach gastrin, and certain food types
  • Gastric emptying is inhibited by reflex and hormonal activity

 

Small Intestine

  • 2.5cms wide and 6m long
  • Fills most of the abdomen
  • Begins at the pyloric sphincter and ends with its connection to the large intestine at the ileocecal valve
  • 3 parts:
    1. Duodenum
      • First 25cms of small intestine
      • Receives chyme from the stomach through the pyloric sphincter
      • Fluids from the pancreas and gall bladder via the common bile duct
      • Manufactures intestinal juice
      • Susceptible to inflammatory processes  
  • Function:
    • Neutralizes the acidic chyme from the stomach
    • Mixes chyme with pancreatic, biliary and intestinal secretions
  1. Jejunum
    • Jejunum – the largest section of small intestine
    • 8 feet
    • Absorption of Magnesium, Calcium, Iron
  2. Ileum
    • last 40cms of small intestine
    • Chyme moves slowly towards the ileocecal valve (3 – 10 hours)

 

  • Functions of Small Intestine
    1. Forward propulsion of contents
    2. Major site of digestion
    3. 90% absorption
    4. Protection against infection
    5. Hormone secretion
    6. Intestinal juice secretion

 

Large intestine

  • 2.5cms wide 1.5m long
  • Stretches from ileocaecal valve to rectum
  • Often described in 7 parts
    • cecum
    • ascending colon
    • transverse colon
    • descending colon
    • sigmoid colon
    • rectum
    • anal canal
  • Exit tract controlled by anal sphincters
  • Functions of the Large Intestine
    • Reabsorption water and electrolytes
    • Microbial activity
    • Mass movement
    • Defecation – reflex action, abdo/diaphragmatic contraction
    • Feces
      • Water
      • Inorganic salts
      • Eplithelial cells
      • Bacteria – E- Coli is the main bacteria present
      • Undigested food

 small-bowel1

Normal enteroclysis- nasojejunal tube inserted to DJ flexure. Contrast outlines the duodenum and the first bit of jejunum. Note the irregular gas bubble in the stomach.

 

 

 

 

 

acute-gi-bleed2

 

Upper GI Bleed VS Lower GI Bleed

 

ü 

 

 

Melena is described as black tarry in color from an upper GI source, “tarry” feces that are associated with gastrointestinal hemorrhage. The black color is caused by oxidation of the iron in hemoglobin during its passage through the ileum and colon.

ü  Hematochezia – passing a large loose, bright red or maroon colored stool, considered frank bleeding usually from the rectum, considered a lower GI Bleed.

ü  Coffee ground stool is classic of an upper GI bleed as it is old blood that had been decomposed by the stomach acid.

ü  Ischemic bowel disease-  - a blood clot  or other blockage has cut off blood flow to the colon as a result of reduced blood flow Ischemia seen in the elderly, a twisting of the intestine that is not relived, those with hx of atrial fib throw clots.

ü  Mallory –Weiss tear- Repeated or profuse vomiting may cause erosions to the esophagus or small tears in the esophageal mucosa

ü  Diverticula -are found throughout the colon, and sustained dark red lower GI bleeding from the large intestine is characteristic of  a bleeding diverticula

ü  Exanguination ( bleeding out) the fatal process of total hypovolemia ( Blood loss) commonly known as bleeding to death can be from the following caused:

1.      Mallory-Weiss tear

2.      Esophageal varices ( may be torn- ie: Mallory Weiss seen in protracted vomiting, and  by an alcoholic vomiting with end-stage liver disease,

3.      or distended varices due to backed up hepatic/portal circulation with loss of clotting factors in end stage Liver disease – cirrhosis

4.      Slitting the throat in suicide (cutting any of the arteries carotid, radial, brachia, ulnar, and femoral.

Treatment of an Upper GI Bleed

1.       Fluid resuscitation by restoring blood volume with Normal Saline.

2.      Maintain open airway – us of oxygen, and mechanical ventilation if needed.

3.      Coffee ground, melena indicative  of upper GI. Bleeding

4.      If unable to stabilize, usually if flushing NGT does not clear, patient will go stat to GI lab for endoscopy.

 

 

Treatment of Lower GI Bleed

1.       Establish underlying cause, and location of bleed,

2.      Hematochezia

3.      If unstable based on labs and patient VS – IV Fluids and will go to GI Lab for colonoscopy STAT