Pathologies of the small intestine Flashcards
Describe the general structure of the intestine
- S.I: 6-Meters
- L.I: 1.5 Meters
- Mucosa
- Submucosa
- Muscularis
- Serosa/adventitia
Describe the general histology of the intestine
1) SI: Absorptive, Mucus, Paneth cells (secretes antimicrobial peptides and proteins), goblet cells, enterocytes and enteroendocrine cells
2) LI: Mucus, absorptive, enteroendocrine, contains crypts like the stomach and not Villi like the S.I
What are the different pathologies of the intestine?
1) Malabsorption
2) Obstructive
3) Congenital
4) Enterocolitis
5) Vascular
6) Diverticular
7) Tumors
8) Idiopathic Inflammatory Bowel Disease (IBD, Chronic condition, causes inflammation of the digestive tract, causing diarrhea, abdominal pain, weight loss and fatigue)
What are the different congenital disorders of the intestine?
1) Duplication
2) Malrotation
3) Omphalocele (associated with trisomy protrusion of the intestine with its cele)
4) Gastroschisis (protrusion of the intestine without a cele)
5) Atresia (Congenital condition where a body opening is completely absent or closed) /Stenosis (narrowing of a passage can be congenital or acquired)
What is duodenal atresia?
- The failure of the small bowel to canalize
- It is associated with down syndrome
- It presentations are:
1) Polyhydramnios (too much amniotic fluid surrounds the baby, as the baby is unable to swallow and absorb the amniotic fluid properly)
2) Double bubble distention (the stomach and the duodenum are distended)
3) Vomiting, and if it was distal to the bile duct a bilious fluid will be vomited
What is meant by meckel diverticulum?
- Occurs in the terminal ileum “vitelline duct”
- Most common congenital GI abnormality
- It is an out pocketing/bulge in the lower part of the small intestine
- It is due to the failure of the vitelline duct (yolk-sac to the midgut) to disappear during fetal development
- It is a true diverticulum which means that it contains all of the intestinal wall layers
- They are managed via endoscopic surgeries
What are the clinical presentations of meckel diverticulum?
1) Bleeding
2) Volvulus
3) Intussusception
4) Obstruction
5) Feeling of the feces behind the umbilicus on palpation
- It can get complicated developing a perforation, enter umbilical fistula, ulcerations, carcinoid and other tumors
What is intestinal obstruction?
- It is more common in the small intestine due to the narrower lumen
- It is considered a medical emergency
- It is caused by scarring and adhesions, neoplasms, volvulus and intussusceptions
What are the different causes of intestinal obstruction?
1) Adhesions (post-surgical)
2) Impaction
3) Hernia
4) Volvulus
5) Intussusception (fold on itself)
6) Tumors
7) Inflammation (like IBD)
8) Atresia
9) Stones, fecaliths, foreign bodies
What is meant by abdominal hernia?
It is the protrusion of a serosa-lined pouch of the peritoneum, due to a weakness or defect in the peritoneal cavity wall
- It is most common in the inguinal, umbilicus and femoral canals, plus surgical scars
- External herniation in inguinal hernias might entrap and impair the venous drainage leading to stasis and edema which can end with arterial and venous compromise or strangulation which can result in infarction
What is meant by volvulus?
- Twisting of the bowel along the mesentery (complete twisting of a loop of bowel around its mesenteric base of attachment producing an intestinal obstruction and infarction
What is meant by intussusception?
- It is the telescoping of the proximal segment of the bowel into distal segment (as if it folded inwards)
- It occurs when one part of the intestine gets pushed into the next segment (like a telescope), due to a wave of peristalsis
What is the cause of intussusception?
1) Children
- Swelling of the lymphoid tissue, especially in the terminal ileum (where the preyers patches are located)
2) Adults
- Tumors or adhesions, which leads to the squeezing of the BV’s which can cause infarction and tissue death
What are the clinical presentation of intussusception?
1) Current-jelly stools
2) Colicky pain
3) Palpable mass
What is the treatment of intussusception?
Enema (medical procedure in which a liquid or gas is introduced into the rectum and colon through the anus)
What is Hirschsprung disease?
- A congenital aganglionic megacolon, where the distal intestinal segment lacks both Meissner submucosal plexus and the Auerbach myenteric plexus
- It occurs due to part of the colon lacking nerve cells. Normally, nerve cells from the cecum (beginning of the colon) migrate to the rectum, but in this condition, this migration doesn’t happen. As a result, the affected part of the intestine can’t move stool properly, causing a blockage. The intestine dilates above the blockage due to buildup
- Patients are presented with an obstructive constipation
What are the vascular disorders of the bowel?
- The GIT is supplied by the celiac, superior mesenteric, and inferior mesenteric arteries
- As the superior and inferior arteries approach the intestinal wall they form a mesenteric arcade, which allows the small intestine and colon to handle the gradual loss of blood flow from one artery, However, if a major artery is suddenly blocked, it can cause infarction (tissue death) of large sections of the intestine.
- In case of gangrene it’ll be a surgical emergency and we might need to cut part of the intestine
What are the different ischemic bowel disease?
1) Mucosal infarction (not deeper than muscularis mucosa)
2) Mural infarction (affects the mucosa and submucosa)
- In both 1 and 2 it is caused by hypoperfusion like cardiac failure, shock, and dehydration
3) Transmural infarction (the three layers are affected)
- It is caused by an acute vascular obstruction (severe atherosclerosis, aortic aneurysm, oral contraceptive, embolism or aortic atheroma)
Describe the small bowel infarction
- Highly susceptible due to high ATP requirement (lots of glands are present for absorption and digestion)
- Arterial infarction (due to emboli, thrombi or dissection)
- Venous infarction (due to strangulation, volvulus, adhesions, or stasis thrombi)
- They could be:
1) Transmural infarction (embolism/thrombosis of the superior mesenteric artery) due to AF, vasculitis or thrombosis of the mesenteric vein (like due to polycythaemia vera)
2) Mucosal infarction (marked hypotension, the lumen gets the worst as it is the furthest from the blood supply)
What is the clinical presentation of a small bowel infarction?
1) Abdominal pain
2) Bloody diarrhea
3) Decreased bowel sounds
Describe the microscopic photo of an ischemic bowel disease
1) Due to ischemia some glands will be detached (white area) + some inflammatory cells are present
2) with time we will see that villi will disappear due to ischemia and between the glandular areas there are less cells and more pinkish material which represents fibrosis
What is meant by angiodysplasia?
- Twisted and dilated (Malformed) submucosal and mucosal blood vessels
- The pathogenesis is unknown
- It occurs most often in the cecum or right colon
- It might be chronic and intermittent or acute and massive
What is heamorrhoids?
- Occurs in 5% of the general public
- It is when the anal and perianal collateral vessels which connects the portal and caval systems gets dilated in order to relieve the elevated venous pressure within the hemorrhoid plexus
- It is often caused by increased abdominal pressure (like pregnancy or chronic constipation)
What are the malabsorption syndrome?
- Defective absorption of fats, fat- & water-soluble vitamins, proteins, carbohydrates, electrolytes, minerals and water
- It can be involved of the four phases of nutrient
1) Intraluminal digestion: proteins, carbohydrates and fats are broken down into absorbable forms by the pancreatic enzymes, bacteria and acid
2) Terminal digestion: Hydrolysis of carbohydrates and peptides by disaccharides and peptidases, respectively in the brush border of the S.I mucosa
3) Transepithelial transport: Nutrients, fluid, and electrolytes are transported across and processed within the S.I epithelium
4) Lymphatic transport: absorbed lipids
- In malabsorption there is a problem in one or all of these stages
What are the signs and symptoms of malabsorption syndromes?
1) Diarrhea
2) Weight loss
3) Inadequate absorption of vitamins and minerals (anemia, mucositis or vitamin B12 deficiency)
4) Bleeding due to vitamin K deficiency
5) Osteopenia due to calcium or vitamin D deficiency
6) Neuropathy due to vitamin A or B12 deficiency
What is the celiac disease?
- AKA gluten-sensitive enteropathy
- Most common in white people and European
- It is an immune-mediated enteropathy triggered by the ingestion of gluten-containing cereals such as wheat, rye, or barley in genetically predisposed persons
- It immobilizes T-cells, progressive mucosal “atrophy, villous flattening”, and it is relieved by gluten withdrawl
What is the pathogenesis of celiac disease?
Gluten is broken down by enzymes into amino acids and peptides, including gliadin. The gliadin peptide is resistant to complete digestion and is modified by an enzyme called transglutaminase. This modified gliadin interacts with specific proteins (HLA-DQ2 or HLA-DQ8) on immune cells, triggering a response from T cells. The T cells release cytokines, which cause tissue damage and the typical changes seen in the intestinal lining. Additionally, B cells contribute to the immune response.
Having the HLA-DQ2 or HLA-DQ8 genetic markers increases the risk of developing Celiac disease, as they play a role in the immune response to gluten. However, having these markers alone is not enough to cause the disease; other factors like gluten exposure and an immune reaction are also needed
Inflammation and death of mucosal cells will lead to flattening of the lining epithelium and villi
What are the clinical presentation of the celiac disease?
1) Kids
- Abdominal distention
- Diarrhea
- Failure
2) Adults
- Chronic diarrhea
- Bloating
- Dermatitis herpetiformis (skin condition causes itching, blistering rashes)
How to diagnose celiac disease?
A biopsy of the second part of the duodenum or the proximal part of the jejunum is taken (as they have the highest concentration of dietary gluten)
Describe the microscopic photo of the celiac diseased jejunum
1) Villous blunting
2) Chronic inflammatory infiltrate of the lamina propria
What it tropical sprue?
- It is a chronic diarrheal disease, possibly of an infectious origin
- It involves the S.I and characterized by the malabsorption of nutrients
What is the difference between tropical sprue and celiac disease?
1) Tropical sprue occurs in tropical places
2) Unlike celiac tropical sprue rises after an infectious diarrhea
3) Unlike Celiac tropical sprue responds to antibiotics
4) Unlike celiac which occurs in the duodenum and jejunum, tropical sprue occurs in the jejunum and ileum
- The duodenum absorbs iron, the jejunum is responsible for the absorption of folic acid, while the ileum is responsible for vitamin b12 absorption
What is pseudomembranous colitis?
- Pseudomembranous translates as a false membrane, while colitis means the inflammation of the colon
- It is triggered by an antibiotic therapy, which disrupts the normal microbiota and allows C.difficile to grow
- C.difficle will then release toxins which disrupts the normal epithelial function
Describe the gross and microscopic photo of pseudomembranous colitis
1) Gross:
- Hyperemic mucosal surface, which is covered by a yellow-green exudate (a pseudomembrane)
2) Microscopically:
- We see areas the forms a volcano/eruptive histology (and this exudated material is mainly neutrophils and other inflammatory cells)
