PHYSIOLOGY DEFECATION

Defecation• Defecation is the process of passing out

stool (feces) through the anus. This eliminates waste material from the rectum and colon. The process of defecation should be painless, regular and to a certain degree, it is under voluntary control.

Defecation reflexes• An involuntary response of the lower bowels to

various stimuli thereby promoting or even inhibiting a bowel movement.

• These reflexes are under the control of the autonomic system and play an integral role in the defecation process along with the somatic system that is responsible for voluntary control of defecation.

• The two main defecation reflexes are known as the intrinsic myenteric defecation reflex and parasympathetic defecation reflex.

Other Defecation Reflexes

• Apart from the two main defecation reflexes mentioned above, other reflexes can also influence the defecation process.– Gastrocolic reflex – distention of the stomach while eating or

immediately after a meal triggers mass movements in the colon.– Gastroileal reflex – distention of the stomach while eating or

immediately after eating triggers the relaxation of the ileocecal sphincter and speeds up peristalsis in the ileum (end portion of the small intestine). This causes the contents of the ileum to rapidly empty into the colon.

– Enterogastric reflex – distention and/or acidic chyme in the duodenum slows stomach emptying and reduces peristalsis.

– Duodenocolic reflex – distention of the duodenum a short while after eating triggers mass movements in the colon.

PROCESS OF DEFECATION

Phase of Defecation

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=spinalcord&part=A2598

CONSTIPATION

Definitions

• Definition :– Constipation is a symptom– issues of stool consistency (hard, painful stools)– issues of defecating behavior• Infrequency (<3x per week)• Difficulty in defecation• Straining during defecation (>25% bowel movement)• Subjective sensation of hard stool• Incomplete bowel evacuation

– For surgical purposes :• Change in the bowel habit• Defecatory behavior that results in acute or chronic

symptoms• Diseases that would be resolved with relief of the

constipation

– Health care providers : • Frequency of bowel movements (ie, less than 3 bowel

movements per week) to define constipation

• According to Rome III (at least 2 symptoms over the past 3 months) :– Less than 3 bowel movements per week– Straining– Lumpy/hard stools– Sensation of anorectal obstruction– Sensation of incomplete defecation– Manual maneuvering required to defecate

Causes

Common causes of constipation are:• not enough fiber in the diet• lack of physical activity (especially in the elderly)• medications• milk• irritable bowel syndrome• changes in life or routine such as pregnancy, aging, and travel• abuse of laxatives• ignoring the urge to have a bowel movement• dehydration• specific diseases or conditions, such as stroke (most common)• problems with the colon and rectum• problems with intestinal function (chronic idiopathic constipation)

Causes

• 2 main groups :– Primary Constipation– Secondary Constipation

Primary Constipation• Primary (idiopathic, functional) constipation can

generally be classified into 3 categories:– Normal-transit constipation (NTC)

• Patients perceive difficulty in evacuating their bowels

– Slow-transit constipation (STC) • Infrequent bowel movements, decreased urgency, or straining to

defecate. (mild abdominal distention or palpable stool in the sigmoid colon)

– Pelvic floor dysfunction (ie, pelvic floor dyssynergia) • dysfunction of the pelvic floor or anal sphincter. Patients often

report prolonged or excessive straining, feeling of incomplete evacuation, or the use of perineal or vaginal pressure during defecation to allow the passage of stool or report digital evacuation of stool.

Secondary Constipation

• Diet and exercise • Structural • Endocrinopathic and metabolic• Drugs• Neurologic• Connective-tissue disorders• Toxicologic • Psychologic

Types of Constipation and Causes Examples

Recent onset :

- colonic obstruction Neoplasm, stricture, ischemic, diverticular, inflammatory

- Anal sphincter spasm Anal fissure, painful hemorrhoids

- Medications

Chronic

- IBS Constipation-predominant, alternating

- Medications Ca²⁺ blockers, antidepressants

- colonic pseudo-obstruction Slow transit constipation, megacolon (rare Hirschsprung’s, chagas)

- Disorders of rectal evacuation Pelvic floor dysfunction,anismus,descending perineum syndrom,rectal mucosal prolapse, rectocele

- Endocrinopathies Hypothyroidism, hypercalcemia, pregnancy

- Psychiatric disorders Depression, eating disorders, drugs

- neurologic disease Parkinsonism, multiple sclerosis, spinal cord injury

- generalized muscle disease Progressive systemic sclerosis

Patophysiology

• Constipation occurs if defecation is delayed for too long

• The longer colonic contents being retained, the more amount of H2O is absorbed hard & dry in consistency

DIAGNOSTICMedical History- The doctor may ask a patient to describe his or her constipation, including

duration of symptoms, frequency of bowel movements, consistency of stools, presence of blood in the stool, and toilet habits—how often and where one has bowel movements. A record of eating habits, medication, and level of physical activity will also help the doctor determine the cause of constipation.

- The clinical definition of constipation is having any two of the following symptoms for at least 12 weeks—not always consecutive—in the previous 12 months:

• straining during bowel movements• lumpy or hard stool• sensation of incomplete evacuation• sensation of anorectal blockage/obstruction• fewer than three bowel movements per week

Physical Examination- A physical exam may include a rectal exam with a gloved, lubricated finger to

evaluate the tone of the muscle that closes off the anus—also called anal sphincter—and to detect tenderness, obstruction, or blood. In some cases, blood and thyroid tests may be necessary to look for thyroid disease and serum calcium or to rule out inflammatory, metabolic, and other disorders.

- Extensive testing usually is reserved for people with severe symptoms, for those with sudden changes in the number and consistency of bowel movements or blood in the stool, and older adults. Additional tests that may be used to evaluate constipation include:

• a colorectal transit study• anorectal function tests• a defecography- Because of an increased risk of colorectal cancer in older adults, the doctor

may use tests to rule out a diagnosis of cancer, including a• barium enema x ray• sigmoidoscopy or colonoscopy

TREATMENTDiet• A diet with enough fiber (20 to 35 grams each day) helps the body form

soft, bulky stool. • High-fiber foods include beans, whole grains and bran cereals, fresh fruits,

and vegetables such as asparagus, brussels sprouts, cabbage, and carrots.• For people prone to constipation, limiting foods that have little or no fiber,

such as ice cream, cheese, meat, and processed foods, is also important.

Lifestyle Changes• Other changes that may help treat and prevent constipation include

drinking enough water and other liquids, such as fruit and vegetable juices and clear soups, so as not to become dehydrated, engaging in daily exercise, and reserving enough time to have a bowel movement.

Laxatives

• Bulk-forming laxatives • Stimulants • Osmotics • Stool softeners • Lubricants • Saline laxatives • Chloride channel activators

GI BLEEDING

Lower tractA. Necrotizing Enterocolitis.

It is important to exclude this diagnosisin infants. Condition is most commonly seen in preterm infants with rectal bleeding, feeding intolerance, and systemic instability, but 10% of cases occur in full-term infants. Antenatal exposure to maternal cocaine and formula feeding are risk factors.

B. Obstructive Lesions. C. Milk-Protein Allergy.

Affects approximately 2% of infants younger than 2 years of age. Clinical spectrum ranges from immediate-type reactions, including urticaria and angioedema, to intermediate and late-onset reactions, such as atopic dermatitis, gastroesophageal reflux, enterocolitis, and proctitis.

D. Anorectal Fissure. E. Infectious Enterocolitis.

Lower tract

F. Vasculitis. Henoch-Schönlein purpura (HSP) and hemolytic uremic syndrome (HUS) are common vasculitides in children.

G. Inflammatory Bowel Disease. Ulcerative colitis or Crohn disease must be considered in older children or adolescents who present with rectal bleeding. Search for extraintestinal manifestations, as noted earlier.

H. Structural Anomaly, Intestinal Duplication, or Meckel Diverticulum. I. Vascular LesionsJ. Polyps. K. Coagulopathy. L. Tumors..M. Ingestions.

Treatment1. Treatment is directed at underlying problem.

– Allergic colitis is managed with hydrolyed formula. – Necrotizing enterocolitis is managed with supportive care.

Appropriate antibiotics, most notably metronidazole, are used in treatment of C difficile colitis.

– Immunosuppressive agents are used in management of inflammatory bowel disease; they have also been successful in patiens with rapidly proliferating hemangiomas.

2. Endoscopic Therapy. Most common indication for this therapy is polypectomy

3. Surgery.

Histologic Findings

• The bleeding vessel lies in the deepest layer of the ulcer. • Fibrinoid necrosis is observed at the site of perforation of

the vessel. • Pseudoaneurysmal dilation of the vessel may be present at

the site of perforation. Biopsy samples should be taken from the edge of a gastric ulcer to rule out carcinoma.

• The characteristic lesion of H pylori is chronic active gastritis with the organisms observed after routine staining.

• The lesion of gastric antral vascular ectasia is capillary dilation with fibrin clots and fibromuscular hyperplasia.

ANAL FISSURE

ANAL FISSUREDefinition A linear ulcer of the lower half of the anal canal, usually located in the

posterior commissure in the midline Etiology Associated with constipation, diarrhea, infectious etiologies, perianal trauma,

and Crohn's disease.Epidemiology Occur at all ages but are more common in the third through the fifth decades

Pathogenesis Trauma to the anal canal occurs following defecation irritation increased resting pressure of the internal sphincter blood supply to the sphincter and anal mucosa enters laterally relative ischemia in the region of the fissure poor healing of the anal injury

Diagnosis - On examination, most fissures are located in either the posterior or anterior position- A lateral fissure is worrisome as it may have a less benign nature, and systemic disorders should be ruled out. A chronic fissure is indicated by the presence of a hypertrophied anal papilla at the proximal end of the fissure and a sentinel pile or skin tag at the distal end- Often the circular fibers of the hypertrophied internal sphincter are visible within the base of the fissure.- Anal manometryelevation in anal resting pressure and a sawtooth deformity with paradoxical contractions of the sphincter muscles are pathognomonic

Treatment - non – pharmacologic:stool softeners for those with constipation, increased dietary fiber, topical anesthetics, glucocorticoids, and sitz baths are prescribed and will heal 60–90% of fissures- pharmacologic: nifedipine or nitroglycerine, botulinum toxin type A- surgical: anal dilation and lateral internal sphincterotomy

Clinical Manifestation

• Painful defecationpain is sharp or burning and may persist for hours after defecation; may lead to constipation.

• Bleeding : scanty & bright red in color.• Chronic discharge.• Urinary tract symptoms : frequency, dysuria,

urinary retention.

Treatment

Acute Fissure• Avoiding constipation bulk laxatives.• Dietary fibers.Chronic Fissure• Surgical treatment : pectenoctomySecondary Fissure• Treatment is directed to the underlying

problem.

Examinations1.Flexible sigmoidoscopy.

2.Colonoscopy

3.Anal manometry.

NonSurgical Treatment1. Fiber supplements. 2. Sitz baths. Soaking in warm water for 10 to 20 minutes several times a day, especially after

bowel movements, will help relax the sphincter and promote healing. 3. Medicated creams (Anusol-HC, zinc oxide, others) to help relieve discomfort from a mild fissure.4. Nitrogylcerin. Applying nitroglycerin ointment to the anus widens blood vessels and increases

blood flow to the fissure, promoting healing5. Botox. Injecting a small dose of onabotulinumtoxinA (Botox) into the anal sphincter

paralyzes the muscle for several months, causing the spasm to relax. Possible side effects include pain at the injection site or temporary, mild leakage of gas or stool (anal incontinence).

6. Calcium channel blockers. The blood pressure medications nifedipine (Adalat) and diltiazem (Cardizem), taken

orally or ground into a gel and applied to the fissure, also may help.

Risk Factors• Infancy. Many infants experience an anal fissure during their first year of life,

although experts aren't sure of the reason.

• Aging. Older adults may develop an anal fissure partly because of slowed

circulation, resulting in decreased blood flow to the rectal area.

• Constipation. Straining during bowel movements and passing hard stools

increase the risk of tearing.

• Childbirth. Anal fissures are more common in women after they give birth.

• Crohn's disease. This inflammatory bowel disease causes chronic inflammation

of the intestinal tract, which may make the lining of the anal canal more

vulnerable to tearing.

Complications

1. become chronic, meaning it lasts for more than six weeks.

2. increased risk of another anal fissure.

3. extend into the ring of muscle that holds your anus closed

(internal anal sphincter).

• To prevent anal fissures in infants, be sure to change diapers frequently.

• To prevent fissures at any age:* Keep the anal area dry* Wipe with soft materials or a moistened cloth or cotton pad* Promptly treat any constipation or diarrhea* Avoid irritating the rectum

Prevention

HAEMORRHOIDS

Definition

• The term hemorrhoids refers to a condition in which the veins around the anus or lower rectum are swollen and inflamed.

• Haemorrhoid is widening in the venous plexus which did not constitute state haemorrhoidalis pathological

• Type:– Internal haemorrhoid: plexus V. haemorrhoidalis superior

above the mucocutaneous line and covered by mucosa; There are three primary Position: right-front, right-rear, left-lateral

– Haemorrhoid extern: enlargement and protrusion of haemorrhoid plexus inferior distal to the mucocutaneous line within the tissue under the epithelium of the anus

Epidemiology

• Symptomatic hemorrhoids affect >1 million individuals in western civilization per year.

• The prevalence of hemorrhoidal disease is not selective for age or sex.

• However, age is known to have a deleterious effect on the anal canal.

• The prevalence of hemorrhoidal disease is less in underdeveloped countries.

• The typical low-fiber, high-fat western diet is associated with constipation and straining and the development of symptomatic hemorrhoids.

Frequency

• 10 million• Peak ages: 45-65 years• ½ of adults experience hemorrhoids by age 50• Common among pregnant women– Temporary

Symptoms

• Rectal Bleeding• Bright red blood in stool• Pain during bowel movements• Anal Itching• Rectal Prolapse• Thrombus

Causes

• Pressure–Constipation –Diarrhea– Sitting or standing for long periods of time–Obesity–Heavy Lifting–Pregnancy

Risk Factor

• Hemorrhoids may result from straining to move stool.

• Other contributing factors include pregnancy, aging, chronic constipation or diarrhea, and anal intercourse.

• Hemorrhoids are either inside the anus—internal—or under the skin around the anus—external.

Exams and Tests

A doctor can often diagnose hemorrhoids simply by examining the rectal area. If necessary, tests that may help diagnose the problem include:

• Stool guaiac (shows the presence of blood)• Sigmoidoscopy • Anoscopy

Complications

• The blood in the enlarged veins may form clots and the tissue surrounding the hemorrhoids can die (Necrosis)

• This causes painful lumps in the anal area.• Severe bleeding can occur causing iron

deficiency anemia.

treatment

Prevention

• Eat high fiber diet• Drink Plenty of Liquids• Fiber Supplements• Exercise• Avoid long periods of standing or sitting• Don’t Strain• Go as soon as you feel the urge

Prognosis

• Most treatments are effective, but to prevent the hemorrhoids from coming back, you will need to maintain a high-fiber diet and drink plenty of fluids.