4 C: Anatomy, Physiology and Path of the Large Intestine (Colon) Flashcards
The diameter of the colon is _________ than that of the small intestine
GREATER
What is teniae coli?
The fibers of its external muscular layer are collected into longitudinal bands
What are Haustra?
Because these bands are shorter than the rest of the colon, the colon wall forms OUTPOUCHINGS between the teniae.
Are there vilii on the mucosa?
In the large intestine?
NO
What do the general parts of the colon include?
The cecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, & rectum.
What are crypts of Lieberkuhn?
Glands composed of simple columnar type of epithelium
What are the 4 cells that constitute this epithelium?
1) Mucus-producing goblet cells
2) Absorption cells that fxn in absorbing nutrients, electrolytes, and fluid
3) Regenerative cells that proliferate and replace the other cells of the epithelium
4) Enteroendocrine cells that release paracrine hormones
What is the outer longitudinal layer is called what?
The Muscularis Externa
Note: it is gathered into the teniae coli
What is frequently noted in BOTH the small and large intestine?
Lymphatic nodules and lymphoid infiltration
What are the function of the large intestine?
1) propulsion & storage of unabsorbed material
2 ) place of residence for flora (bacteria)
3) absorption of small amounts of water and electrolytes
4) defecation
The large intestine is home to what?
A complex family of bacteria (500 diff species of bacteria reside in the colon)
What role do the bacterial species play?
In the maintenance of health and prevention disease
Where are large masses of bacteria passed in?
Stool
When do the intestinal bacterial flora become established?
At birth, the colon is sterile, but the intestinal bacteria flora becomes established EARLY in life
What are some of the established roles of intestinal flora?
Fermentation of undigestible dietary fiver to generate fatty acids, which are major nutritional source for the colon and have trophic effects to promote normal mucosal growth and development.
What is responsible for the slightly acidic nature of stools?
What is the pH?
The organic acids
pH= 5.0- 7.0
What leads to gas formation?
Fermentation of indigestible sugars
What prevents the colonization of the GI tract?
Creation of an environment that is inhospitable to pathogenic microorganisms
What is the mechanism is believed to be apart of the colonization of bacteria?
Not completely understood, but the fact that if there is a million good then it is hard for bad bacteria to take over.
***Another factor is pH
Why is pH a factor?
Many of the normal flora have a low pH optimum, where many pathogens favor a neutral or more alkaline environment
Intestinal flora is also involved in what 3 things?
1) Creation of an environment that is inhospitable to pathogenic microorganisms
2) Metabolism of various compounds including bile salts, certain drugs
3) Creation of vitamin K, vitamin B12 & folic acid
What is vitamin K essential to?
The liver for the efficient synthesis of certain blood clotting factors (e.g., prothrombin, VII, IX, & X)
What is vitamin B 12 and folic acid essential for?
Important for final maturation of erythrocytes
What are some cause of Diarrhea?
Infectious, drug-induced, food-related, post-surgical, inflammatory, transit-realted, and psychologic
What are the 4 distinct mechanisms that produce diarrhea?
1) increased osmotic load
2) increased secretion
3) inflammation
4) decreased absorption time
When does Osmotic diarrhea occur?
1) When unabsorbable, water-soluble solutes remain in the bowel, where they retain water.
2) Sugar intolerance - including lactose intolerance caused by lactase deficiency
3) w/ use of poorly absorbed salts( Mg sulfate, Na phosphates) as laxatives or antacids
Ingestion of large amounts of the hexitols (e.g, sorbital, mannitol) are used as sugar substitutes cause what? Why?
Osmotic diarrhea as a result of their SLOW absorption and stimulation of rapid small-bowel motility (“dietetic food” or “chewing gum” diarrhea)
What can eating too much of some foods, like certain fruits can cause?
Osmotic diarrhea
What is secretory diarrhea? What does it include ?
Occurs when the small & large bowel secrete more
electrolytes and water than they absorb.
-Secretagogues include bacterial toxins (e.g–in cholera), enterophogenic viruses, bile acids & unabsorbed dietary fat
What is exudative diarrhea? What does it include ?
Occurs with several mucosal diseases (e.g.–reginal enteritis, ulcerative colitis, lymphoma, cancer) that cause mucosal inflammation, ulceration, or tumefaction.
What results from exudative diarrhea?
Outpouring of plasma, serum proteins, and mucus increases fecal bulk and fluid content.
***Involvement of the rectal mucosa may cause urgency and increased stool frequency because the inflamed rectum is more sensitive to distention.
When does decreased absorption time occur?
When chyme is not in contact with an adequate absorptive surface of the GI tract for a long enough time so that too much water remains in the feces.
What factors decrease the contact time?
Small or large-bowel resection, gastric resection, vagotomy, surgical bypass of intestinal segments, and drugs that speed transit by stimulating intestinal smooth muscle (as a side effect)
What is constipation?
Defined as the infrequent passage of stools
***Difficulty w/ this definition arises from the many individuals variations of function that is normal
When does problems increase with constipation?
With age
***There is a sharp rise in health care visits for constipation after 65 years of age
Constipation can occur as a ?
primary problem or as a problem associated with another disease condition
What are some common causes of constipation?
1) failure to repsond to the urge to defecate
2) inadequate fiber in the diet
3) inadequate fluid intake
4) weakness of the abdominal muscles
5) inactivity and bed rest
6) pregnancy
7) hemorrhoids
What are some disorders associated with chronic constipation?
Neurologic disease such as:
1) spinal cord injury
2) Parkinson’s disease
3) Multiple Sclerosis
4) Endocrine disorders: hypothyroidism or diabetic neuropathy
5) obstructive lesion i the GI tract
What drugs are associated with chronic constipation?
Opiates, anti-cholinergic agents, valium channel blockers, diuretics, iron supplements and aluminum antacids tend to cause constipation
What is Irritable Bowel Syndrome (IBS)?
Used to describe a functional GI disorder characterized by a variable combination of chronic and recurrent intestinal symptoms not explained by structural or biochemical abnormalities.
What does evidence suggest about IBS?
10-20% of people in Western counties have the disorder, most do not seek medical attention
What is IBS characterized by?
Persistence or recurrent symptoms of abdominal pain, altered bowel function, and varying complaints of flatulence, belatedness, nausea, and anorexia, constipation or diarrhea, and anxiety or depression.
What is the hallmark of IBS?
Abdominal pain (intermittent, cramping, and in lower abdomen) that is relieved by defecation and associated with a change in consistency or frequency of stools.
***Does not occur at night or interfere with sleep
What is the condition believed to result from?
The dysregulation of intestinal motor and sensory functions modulated by the CNS
Persons with IBS tend to experience what?
Increased motility and abnormal intestinal contractions in response to psychological and physiologic stress
What kind of neural response plays a role in IBS?
- Parasympathetic nervous system plays a role in the regulation of colonic and gastrointestinal motility
- Central nervous system actuation of nerves located in the muscular layers of the intestine trigger the symptoms of IBS
- Medulla (Vagus n.)
The role that psychological factors play is?
- The disease is uncertain
- Changes in intestinal activity are normal responses to stress, these responses appear to be exaggerated in persons with IBS
What gender is affected more?
*Women
**Menarche (1st menstrual cycle)
-Women notice an exacerbation of symptoms during the pre-mentrual period, suggesting a hormonal component
What kind of markers does IBS lack?
Anatomic or physiologic
What is diagnosis usually based on?
Signs and symptoms of abdominal pain or discomfort, bloating, constipation, diarrhea, or an alternation between both.
What is Inflammatory Bowel Disease?
Used to designate two related inflammatory intestinal disorders
What are the 2 intestinal disorders:
1) Crohn disease
2) Ulcerative colitis
What do the 2 intestinal disorders have in common?
BOTH lack conferring evidence of a proven causative agent and can be accompanied by systemic manifestations.
Crohn’s disease has what appearance on the colon?
- Cobble stone-like appearance
- No ulcers, but swells and is inflammed
What are the clinical manifestations of both Crohn’s and Ulcerative colitis?
The result of activation of inflammatory cells with elaboration of inflammatory mediators that cause non-specific tissue damage
What are both diseases characterized by?
The remission and exacerbations of diarrhea, fecal urgency and weight loss
What are acute complications that may develop?
Intestinal obstruction may develop during periods of fulminant disease
Macroscopically what is the bowel region affected in Crohn’s and Ulcerative Colitis?
Crohn’s= Iluem +/- colon
Ulcerative Colitis= Colon only
Macroscopically what is the rectal involvement in Crohn’s and Ulcerative Colitis?
Crohn’s= Sometimes
Ulcerative Colitis= ALWAYS
Macroscopically what is the distribution in Crohn’s and Ulcerative Colitis?
Crohn’s= Skip lesions
Ulcerative Colitis= Diffuse
Macroscopically what is the Stricture in Crohn’s and Ulcerative Colitis?
Crohn’s= Yes
Ulcerative Colitis= Rare
Macroscopically what is the Bowel wall appearance in Crohn’s and Ulcerative Colitis?
Crohn’s= Thick
Ulcerative Colitis= Thick
Macroscopically what is the Inflammation in Crohn’s and Ulcerative Colitis?
Crohn’s= Transmural
Ulcerative Colitis= Limited to mucosa & submucosa
Macroscopically what is the Psedopolyps in Crohn’s and Ulcerative Colitis?
Crohn’s= Moderate
Ulcerative Colitis= Marked
Macroscopically what is the Ulcers in Crohn’s and Ulcerative Colitis?
Crohn’s= Deep, knife-like
Ulcerative Colitis= Superficial, board-based
Macroscopically what is the Lymphoid reaction in Crohn’s and Ulcerative Colitis?
Crohn’s= Marked
Ulcerative Colitis= Moderate
Macroscopically what is the Fibrosis in Crohn’s and Ulcerative Colitis?
Crohn’s= Marked
Ulcerative Colitis= Mild to none
Macroscopically what is the Serositis in Crohn’s and Ulcerative Colitis?
Crohn’s= Marked
Ulcerative Colitis= NO
Macroscopically what is the Granulomas in Crohn’s and Ulcerative Colitis?
Crohn’s= Yes (35%)
Ulcerative Colitis= NO
Macroscopically what is the Fistulas/sinuses in Crohn’s and Ulcerative Colitis?
Crohn’s= Yes
Ulcerative Colitis=Yes
Macroscopically what is the Clinical Perianal fistula in Crohn’s and Ulcerative Colitis?
Crohn’s= Yes (in colonic disease)
Ulcerative Colitis= No
Macroscopically what is the Fat/vitamin malabsorption in Crohn’s and Ulcerative Colitis?
Crohn’s= Yes
Ulcerative Colitis= NO
Macroscopically what is the Malignant potential in Crohn’s and Ulcerative Colitis?
Crohn’s= With colonic involvement
Ulcerative Colitis= Yes
Macroscopically what is the Recurrence after surgery in Crohn’s and Ulcerative Colitis?
Crohn’s= Common
Ulcerative Colitis= NO
Macroscopically what is the Toxic megacolon in Crohn’s and Ulcerative Colitis?
Crohn’s= NO
Ulcerative Colitis= Yes
What is Diverticulosis?
Condition which the mucosal layer of the colon herniates throughout the muscular is layer
What is Diverticulosis characterized by?
The presence of diverticula in the colon (usually sigmoid) generally asymptomatic
What does Diverticulosis result from?
High intraluminal pressure on areas of weakness in the bowel wall
What is Diverticulitis?
When diverticula become inflamed = Diverticulitis
What is the most common compliant with Diverticulitis?
Pain in the lower left quadrant accompanied by nausea, vomiting, tenderness in the lower left quadrant, a slight fever, and an elevated white blood cell count
What are complications with Diverticulitis?
Perforation with peritonitis, hemorrhage and bowel obstruction
What is Acute Appendicitis?
Inflammation of the vermiform appendix due to an obstruction with stool or a twisting of the organ or its blood supply
With Acute Appendicitis what symptoms present?
On the lower right quadrant, fever, rebound tenderness
When can Peritonitis occur?
If swollen appendix bursts before surgery
What is Tx for Peritonitis?
With antibiotics
What is the major mechanical causes of intestinal obstruction?
1) Herniation of a segment in the umbilical or inguinal regions
2) Adhesion between loops of intestine
3) volvulus
4) Intussusception
What is the Defecation Reflex?
Distention of the rectum with feces initiates relax contractions of its musculature and the desire to defecate
What kind of neural reflex is this?
A spinal cord mediated parasympathetic reflex that causes the walls of the sigmoid colon and the rectum to contract and the internal anal sphincter (smooth muscle) to relax
As feces are forced into the anal canal what signals are generated?
Electrical signals reach the brain allowing us to decide whether the external and sphincter (skeletal muscle) should relax and remain open or be constricted to stop the passage of feces temporarily
During defecation what happens to the muscles of the rectum? How do we aid this process?
- They contract to expel the feces
- We aid this process by voluntarily by closing the glottis and contracting our diaphragm and abdominal muscles (Valsalva maneuver)
What can bleeding from the GI tract be evidenced by?
By the blood that appears in the vomitus or the feces
What can bleeding from the GI tract result from?
Disease or trauma to the GI structures (e.g.-peptic ulcers) blood vessel abnormalities (e.g.-esophageal varicose, hemorrhoids) or disorders in blood clotting
What can bleeding in the stomach cause?
It is usually irritating and causes vomiting
Hematemesis is what? Appearance?
- Refers to blood in the vomitus
- Appears as bright red or have a “coffee-ground” appearance because of the action of the digestive enzymes
What color does blood in the stool range from
?
From bright red to tarry black
What is bright red stool indicate?
When it coats the stool, it is the result of?
- That the bleeding is from the lower bowel
- Result of bleeding hemorrhoids
What is melena?
- Greek for “black”
- Refers to the passage of black and tarry stools
- These stools have a characteristic odor that is not easily forgotten
What do Tarry stools indicate?
The source of the bleeding is above the level of the ileocecela valve (however, this is always not the case!)
Occult (hidden) blood can be detected how?
What is it caused by?
- Only by chemical means
- Caused by gastritis, peptic ulcer, or lesions of the intestine
What is the most common cancers in the Western world?
Adenocarcinoma of the Colon & Rectum
What is the Peak incidence?
6th-7th decades
What does it present as ?
Normal mucosa–>polyp–>cancer–>metastatic tumor
What are the predisposing factors?
1) Polyps
2) Long standing UC
3) Genetic factors
4) low fiber, high animal fat diet
