The Small Bowel

Learning Objective 1.Describe the normal anatomy of the smal

bowel2. Discuss the physiology of intestinal

absorption, secretion, and motility.

Small Bowel

• The small intestine is a tubular structure that begins distal to the pyloric sphincter of the stomach and extends to the cecum of the large intestine.

• Several functions of the small bowel:– Digestive– Absorptive – Secretory – Barrier and immunologic

Small Bowel

• Small intestine is c-shaped• Called the duodenum

– Begins at the pyloric sphincter and ends at the ligament of Treitz.

– The common bile duct empties into the duodenum at the ampulla of vater

– Jejunum is made up of two fifths of the proximal small intestine.

– The distal three fifths of the small bowel is known as ileum and extends from the jejunum to the ileocecal valve.

The Small Bowel

– An outer serous layer composed of mesothelial cells that overlie loose connective tissue

– A muscular layer contains outer longitudinal and inner circumferential muscles, separated by intrinsic ganglion cells and nerve fiber called the myenteric or Auerbach’s nerve plexus.

The Small Bowel

• A submucous layer of dense connective tissue containing numerous arteries as well as venous and lymphatic plexuses; also contains Meissne’s plexus, a collection of autonomic nerves that communicate with Auerbach’s plexus.

• A inner mucous layer containing simple epithelial ells that overlie the lamina propria and rest on the the smooth muscle layer know as the muscularis mucosae.

The Small Bowel

• Villus-intestinal villi are the numerous threadlike projections that cover the surface of the mucosa of the small bowel and serve as the sites of absorption of fluids and nurtients.

• Crypts of lieberkukn- a simple tubular gland in the mucous membrane of the intestine, opening between the bases of the villi and containing argentaffin cells.

The Small Bowel

• Paneth’s cells are located at the base of the crypts, the are round or oval nucleus close to the base of the cell, occurring in the fundus of the crypts of Lieberkuhn. These cells contain large secretory guanules that mya contain peptidase.

• Brunner’s gland is a tubulo-alveolar gland in the submucosa of the duodenum, which opens into a crypt of liberkuhn

The Small Bowel

• Primary function is to absorb nutrients from the chyme.

• Small intestine absorbs 8 leaders of fluid and passes only 500 to 1000 ml to the large intestine.

• Absorption of nutrients takes place at different locations in the small intestine. – Duodenum is iron and calcium – Jejunum is fats, proteins, and carbohydrates. – Ileum is vitamin B-12 and bile acids.

The Small Bowel

• Secretion, cells located in the small bowel secrete digestive juices, mucus and variety of hormones.

• Receives secretions from the liver and pancreas.

• Goblet cells are located on and between the villi on the mucosa secrete a protective mucus.

Small Bowel

• Motility– Three types of movement contribute to the

mixing of the chyme• Concentric- segmenting contraction, takes place in

the jejunum, give the small intestine the look of a chain of sausage links. Helps mix secretions of the small intestine with the chyme particles

• Short, propulsive contractions or peristaltic waves slowly push the chyme to the colon.

• The continuous shortening and lengthening of the villi constantly stirs the intestinal contents.

The Small Bowel

• Duodenal Ulcers– Peptic ulcers

• Most common in men• In persons with type O blood• Can develop in the lower esophagus, stomach,

pylorus, duodenum, or jejmunum• 80% of all peptic ulcers are in the duodenal ulcers• Occurs when the protective mucosa cannot resist

corrosion by above normal hydrochloric acid levels

The Small Bowel

• Parasitic diseases

• Giardiasis-infection with flagellate protozoan Giardia lamblia, characterized by protracted, intermittent diarrhea with symptoms suggesting malabsorption, abdominal pain, distention and gas.

• Treatment, meds Flagyl

The Small Bowel

• Coccidiosis- caused by intracytoplasmic protozoans – Isospora belli– Isospora bominis – Isospora natelenis

S/S- acute diarrhea, Steatorrhea (fatty stools)

Treatment- fluid and electrolyte replacement

The Small Bowel

• Cryptosporidiosis– Caused by coccidial sporoaoa cryptosporidium– Colon and small bowel most common sites for

infection. – Transmission is fecal-oral, – May be transmitted between animal and humans but

rarely transmitted from human to human. – Before 1981, only eight cases had been reports in

humans. Immunocompromised pts susceptible – Diagnosis- serial stool examinations, intestine bx,– Three-step procedure that involves using a sugar

flotation tech, iodine staining and a modifed acid fast stain.

The Small Bowel

• Crohn’s Disease– Inflammatory bowel disease (IBD) – Regional enteritis– Granulomatous clolitis– Transmural colitis

• Is a transmural predominantly submucosal inflammation that may affect any part of the GI tract from the mouth to the anus.

• Commonly occurs in the terminal ileum.

The Small Bowel

• Crohns Disease – Spreads slowly and progressively with periods of

remission often alternating with exacerbation. Segmental inflammation and rectal sparing are features that distinguish Crohns from ulcerative colitis.

– Deep longitudinal “rake ulcer” appear in the bowel. – Deep ulcers appear between islands of edematous

inflamed mucosa, ”cobblestone appearance.

The Small Bowel

• Crohns Disease– Diarrhea, Abdomianl pain Steatorrhea,

• Anorexia, Wt lossNutritional deficiences• Diagnosis

– Clinical history and physical examination – Endoscopic exams, BE, – Histologic exams

• No cure for Crohns dx,– Medical and surgical therapies are palliative – Drug therapy

The Small Bowel

• Meckel’s diverticulm – Is a congenital anomaly of the gi tract, results

from incomplete separation of the fetal gut– More commonly seen in male population– Intestinal obstruction may result either from a

vovulus or intussusciption – S/S-obstruction, abd pain, vomiting and/or

passage of bright red “current jelly” stools

The Small Bowel

• Meckel’s Diverticulum– Cannot be diagnosed by endoscopic or x-ray – a meckel’s scan allows diagnosis

– Vitamin B-12 Deficiency • Gastrectomy

Pernicious anemia

Pancreatic insufficiency

Zollinger_ellison syndrom

The Small Bowel

• Celiac Disease– Gluten sensitive enteropthy – Celiac sprue

• Is characterized by poor food absorption and intolerance of gluten,which is a protein found in wheat, oats, rye, barley and their produscts

Pathologically the proximal intestinal mucosa loses it villous structure, surface epithelial cells exhibit degenerative changes, and their absorptive function is severely impaired.

S/S diarrhea, vomiting, steatorrhea, abd distentin, gas, stomach cramps and weakness. Anorexia increased appeited w/o wt gain, muslce wasting delayed developmentand anemia

The Small Bowel

• Celiac Disease– Treatment

• Lifelong elimination of gluten from the pt’s diet

• Whipples Disease– Is a rare disorder characterized by chronic diarrhea

and progressive wasting. – Affects caucasian men ages 20 -67– S/S arthralgia, vague abd pain,

diarrhea,steatorrhea,impaired intestinal absorption, progressive wt loss, fever, hyperpigmentation, peripheral, mesenteric, periaortic and celiac lymphadenopathy and occasional splenomeglay.

The Small Bowel

• Whipples Disease– Treatment

• Hospitalization and 14 day course of therapy with penicillin G procaine and streptomycin

• Daily tetracycline for 10-12 months

• Short Bowel Syndrome– Is a malabsorptive disorder that occurs as a result of

decreased functional mucosal surface area, usually due to a massive resection of the small bowel

The Small Bowel

• Small bowel turmors– Peutz-Jeghers syndrome

• Is characterized by mucocutaneous pigmentation on the face, hands, and feet, and in the perianal and genital areas.

• GI hamartomas may appear anywhere from the cardiac sphincter to the anus, but are regularly present in the small bowel.