Bowel Function, Elimination, and Pathophysiology Notes
Anatomy and Function of the Small and Large Intestines
The Role of the Small Intestine
Main Goal: The primary objective of the small intestine is the digestion of nutrition and food taken into the system.
Digestion Process: Food is broken down into a near-liquid form. This requires the addition of a significant amount of water so that the fecal matter becomes fairly liquefied.
Absorption: The liquid state of the matter aids in the absorption of nutrients, fluids, and electrolytes from the gastrointestinal (GI) tract into the bloodstream.
Electrolyte Movement: The small intestine allows for bidirectional movement; while it absorbs substances into circulation, it also allows some electrolytes to move back out of circulation into the GI tract.
Active Phase: This section of the bowel is where the most active phases of digestion and absorption occur.
The Transition to the Large Intestine
Anatomic Location: Fecal matter moves from the small intestine into the large intestine at the cecum, located in the lower right quadrant of the abdomen, near the area of the appendix.
Path of the Large Bowel:
The large bowel moves upward on the right side of the abdominal cavity.
It crosses the top of the abdominal cavity toward the left upper quadrant.
It moves downward again on the left side.
It eventually ends at the sigmoid area and the rectum.
Elimination Role: Unlike the small intestine, the large intestine is primarily involved in eliminating stool or fecal matter from the body.
Functions of the Large Intestine
Reabsorption: The main function of the large intestine is to reabsorb water and electrolytes from the liquefied fecal material back into systemic circulation.
Solidification: As the material moves through the large bowel and water is removed, the waste becomes increasingly solid.
Storage: Fecal material accumulates in the rectum until the rectal sphincter relaxes to allow for a bowel movement.
Pathological Changes: Alterations in bowel patterns typically manifest as changes in the quality, moisture level, and consistency of the stool.
Neurological Control of Defecation
Involuntary Control (Autonomic Nervous System)
The movement of food and fecal substances through the small and large intestines is controlled by the Autonomic Nervous System (ANS).
Nervous System Branches: Both the parasympathetic and sympathetic nervous systems impact GI functioning.
Peristalsis: These involuntary activities drive the rhythmic contractions that move waste through the system and facilitate water removal.
Voluntary Control and the Defecation Reflex
The act of defecation (having a bowel movement) is under voluntary control once the fecal matter reaches the rectum.
Rectal Distension: As the rectum fills with stool, it becomes distended. This distension sends an impulse via afferent nerves up to the brain.
Brain Interpretation: The brain recognizes that the rectum is full and processes whether the current time and location are appropriate for defecation.
The Stimulating Response (Appropriate Timetables): If the brain determines it is an appropriate time, it sends a stimulating impulse back down. This cause the rectal muscles to contract and the external sphincter to relax, allowing for a bowel movement.
The Inhibitory Response (Inappropriate Timetables): If the brain determines it is not an appropriate time, it sends an inhibitory impulse down the nerves. This directs the anal sphincter to stay constricted to retain the stool.
Clinical Assessment of Bowel Patterns and Stool Characteristics
General Characteristics
Moisture and Composition: Stool contains water and should have some moisture. It is composed of compact solids by the time it reaches the rectum.
Normal Color: Stool is normally a shade of brown due to a pigment called stercobilin.
Stercobilin: This is a product of bilirubin breakdown in the liver. Bilirubin is processed by the liver, put into the bile, and contributes the brown pigment to the stool.
Clinical Indicators via Stool Color
Clay-Colored Stool: This occurs when bilirubin is not being broken down properly (e.g., in liver disease or hepatitis), meaning no pigment is contributed to the bile or stool.
Dark Stool (Dietary): High intake of iron can create very dark stool.
Dark Stool (Pathological): Very dark stool can be a concern as it may indicate the presence of blood.
Assessment Metrics for Nurses
Frequency and Volume: How often an individual goes to the bathroom and the amount of stool produced.
Texture and Consistency: Whether the stool is soft, moist, semisolid, or very solid and dry. These characteristics provide data on GI tract health, liver function, and the body's overall fluid balance.
Shape and Odor: Additional characteristics used in the analysis of elimination patterns.
Alterations in Bowel Functionality
Altered Motility
This involves interference with peristalsis.
Ileus: A condition where a section of the bowel does not respond to neurological signals, resulting in a lack of contraction and an interruption of rhythmic peristaltic activity.
Altered Perfusion
Decreased Blood Flow: Insufficient blood supply to an area of the bowel affects its function.
Hemorrhage: Introducing blood into the bowel through active bleeding impacts the GI system.
Altered Patency (Obstructions)
Physiological Structures: Such as a tumor blocking the passage.
Physical/Mechanical Structures: Such as constipation where stool has extremely low moisture content.
Foreign Bodies: Objects or undigested materials that interfere with the opening of the bowel.
Case Study: Asparagus Obstruction
Scenario: A patient presented with abdominal pain and evidence of a bowel obstruction. Imaging did not indicate a tumor. Non-invasive approaches to move the stool failed.
Surgical Findings: Upon performing surgery, the surgeon found the obstruction was caused by undercooked asparagus. The woody stems of the asparagus had not been digested or broken down, creating a physical blockage.
Outcome: The surgeon performed what he jokingly called an "asparagus-tomy" to open the bowel and remove the stems. This highlights how undigested food can act as a foreign body interfering with bowel patency.
Signs, Symptoms, and Diagnostics of GI Problems
Clinical Manifestations
Changes in Stool: Alterations in volume, patterns, and characteristics.
Melena: Black, tarry-looking stool. This indicates the presence of blood that has been broken down by digestive enzymes as it traveled through the system.
Occult Bleeding: "Occult" means hidden. This refers to microscopic blood in the stool that is not visible to the naked eye and requires specific testing to identify.
Pain and Distension: Abdominal distension occurs due to inflammation or injury. The abdomen becomes larger and firmer, described as being "drum-like."
Systemic Effects: These include anorexia (loss of appetite), nausea, and fever, which are general responses to major irritation or infection.
Diagnostic Procedures
History and Physical Standpoint: Reviewing the patient's elimination patterns.
Radiographic Testing: X-rays and CAT scans.
Barium Studies: Swallowing dye (barium) to track peristaltic movement or locate obstructions.
Direct Visualization (Scoping):
Sigmoidoscopy: A tube with a camera used to view only the first section of the large intestine starting from the rectum.
Colonoscopy: A scope that migrates all the way back to the cecum to observe the entire intestinal lining for injury, inflammation, or obstructions.
Treatment Principles
Addressing the Underlying Cause: Definitive treatment requires identifying the root cause of the issue.
Resting the Bowel: Often used for irritated or inflamed sections of the bowel.
Removing Obstructions: This may be achieved through surgical intervention (open surgery) or via a scope, depending on the severity and location of the blockage.
Goal: The primary goal is to eliminate the cause to resolve the associated pain and discomfort.