small intestine Flashcards
what is the basic anatomy of small intestine ?
duodenum
jejunum
Ileum
6 meters
large intestine is 1.5 meters
mucosa
submucosa
muscularis
serosa/adventitia
what is the main function of small intestine ?
absorption
we have villi to increase the surface area to absorb
what is the basic histology of small intestine ?
Absorptive
mucus
paneth ( secrete antimicrobial peptides and proteins )
goblet cells
enterocytes
enteroendocrine cells
Villi
describe the basic histology of Large intestine ?
Mucus
absorptive
enteroendocrine
Crypts like stomach
no villi
what are the 2 major pathologies of small intestine ?
Malabsorption
intestinal obstruction happen in small intestine more than large intestine because its narrower lumen
what are some intestinal pathology ?
Congenital
Enterocolitis
Malabsorption
Malabsorption
IBD ( inflammatory bowel disease )
Vascular
Diverticular
Obstruction
tumors
what are congenital disorders of intestine ?
Duplication
Malrotation
Gastroschisis
Omphalocele ( trisomy )
Atresia/ stenosis spectrum –> in any part of GIT
what is omphalocele ?
Cele = sac
intestine, liver, other organs
are outside the abdomen inside a SAC
the sac is made by peritoneum , amnion
what is gastroschisis ?
Intestines are outside of the abdomen through a hole in the abdomen
what is atresia ?
Congenital condition where a body passage or opening is absent or closed
what is stenosis ?
narrowing of a body passage or blood vessels , which can be congenital or acquired
which part of the pregnancy is more sensitive ?
First trimester ( first 3 months )
very sensitive because it is when the babys organ brain, heart start forming
any harm from infection, drug, alcohol, poor nutrition can cause birth defect or miscarriage
describe duodenal atresia ?
failure of small bowel to canalize
what is duodenal atresia associated with?
Down syndrome
what are the clinical presentation of duodenal atresia?
Polyhydramnios - not being to swallow amniotic fluid = leads to increased amniotic fluid
Stomach distension + distended blind loop of duodenum = DOUBLE BOUBLE SIGN ( cuz stuff cant pass )
Bilious ( greenish ) vomiting - Backs up and includes bile as atresia after proximal duodenum
what is MECKEL diverticulum ?
terminal ileum , vitelline duct
outpouching or bulge in the lower part of small intestines ( ileum )
Most prevalent congenital abnormality of GIT in 2% of normal population
it is a true diverticulum ( contain all layers of intestinal wall )
describe the meckel diverticulum disease?
normally the vitelline duct ( yolk sac to the midgut )
it will atrophy and become fibrous cord connecting umbilicus and bowel
in the disease the proximal vitelline duct will be persistent leading to the bulging of terminal ileum
what are the rule of two in meckel diverticulum
2 inches
2:1 male to female
2 ft away from ileocecal junction
what is the clinical presentation of meckel diverticulum ?
Bleeding
Heterotopic gastric mucosa - acid producing
Volvulus
Intussusception
obstruction
usually first 2 years of life
feel feces behind umbilicus on palpitation
most are asymptomatic
ASSOCIATED WITH OTHER CONGENITAL ANOMALIES
what are the complications of meckel diverticulum ?
perforation
entero umbilical fistula
ulceration
Hemorrhage
Intussusception
obstructions
carcinoids and other tumors
what causes intestinal obstruction?
More common in small intestines because narrow lumen
Scarring
adhesions –> MOST IMPORTANT
neoplasm
volvulus
intussusceptions
Inflammation
Stones
Strictures
Atresias
Hernias
Fecal impaction
ITS A SURGICAL EMERGENCIES
what is abdominal hernia?
Weakness or defect peritoneal cavity wall
protrusions or serosa lined pouch of peritoneum —> hernia sac
what are the common abdominal hernias ?
inguinal
femoral canals
umbilicus
surgical scars
describe the external herniation in inguinal hernia?
inguinal hernias ( narrow orifices )
small intestine may be entrapped and impair venous drainage leading to STASIS AND EDEMA
leading to permanent entrapment or incarceration ending with arterial and venous compromise or strangulation can result infarction
what is volvulus ?
twisting of bowel along mesentery
complete twisting of a loop bowel about its mesenteric base of attachment produces intestinal obstruction and infarction
what is intussusception ?
Telescoping of proximal segment of bowel into the distal segment
one segment of the intestine , constricted by a wave of peristalsis suddenly becomes TELESCOPED into immediately distal segment of bowel
Once trapped the invaginated segment is propelled by peristalsis farther into distal segments
pulling its mesentery along behind it
what causes intussusception ?
In kids : lymphoid hyperplasia , especially terminal ileum cuz of peyers patches dragged into cecum
Adults : Tumors
what happens due to intussusception ?
Infarction due to blood vessels being squashed as sucked into distal bowl
current jelly stools
colicky pain
palpable mass
what is the treatment of intussusceptions ?
Enema
Surgery
what is hirschsprung disease ?
congenital aganglionic megacolon
Congenital defect in colonic innervation
disruption of migration of neural crest cells from the cecum to the rectum
Resulting in distal intestinal segment lacking both meissners submucosal plexus and auerbach myenteric plexus ( aganglinosis )
absence of coordinated peristaltic contractions
resulting in functional obstruction results dilation proximal to affected segment ( DILATION ) –> the thing wont be able to contract and secrete stool resulting in dilation and obstruciton
1 of 5000 live births , more common in males but more severe in females
what is the clinical presentation of hirschsprung disease?
failure to pass meconium ( first stool pass by newborn )
obstructive constipation
what is the blood supply of Bowel?
Celiac ( foregut )
Superior mesenteric ( Midgut )
Inferior mesenteric ( hindgut )
as they approach the intestinal wall the superior and inferior mesenteric arteries
fan out to form mesenteric arcades
what is the point of these mesenteric arcades / connections ?
the interconnections between arcades and collateral supplies and make it possible for Small intestines and colon
To tolerate slowly progressive loss of blood supply from one artery
BUT acute compromise of any major vessels can lead to infarction of several meters of intestine
what are the types of ischemic bowel disease ?
mucosal infarction
mural infarction
transmural infarction
what is mucosal infarction ?
infarction no deeper than muscularis mucosa
it is in the mucosa only
what is mural infarction ?
mucosa and submucosa
what are the causes of mucosal and mural infarction ?
hypoperfusion —> cardiac failure, shock , dehydration
what is transmural infarction ?
all 3 layers are affected
what are the causes of transmural infarction ?
acute vascular obstruction like severe atherosclerosis
aortic aneurysm
oral contraceptive
embolization
aortic atheromas
which parts of intestinal segments are susceptible to ischemia?
the intestinal segments at the end of their respective arterial supplies
its called the watershed zone
they have less blood flow and relay smaller blood vessels for nutrients
these areas are more susceptible for ischemia
example splenic flexure
why are small bowel infarction very susceptible ?
Cuz high ATP requirement
what are arterial infarct causes ?
Emboli
thrombi
Dissection
what are venous infarct causes ?
strangulation
volvulus
adhesion
stasis
thrombus
what causes transmural infarction ?
Embolism/thrombosis of SUPERIOR MESENTERIC ARTERY
due to atrial fibrosis
vasculitis ( polyarteritis nodosa- abdo pain , melena )
Thrombosis of mesenteric veins :
Polycythemia vera
Lupus anticoagulant - increases inappropriate thrombosis
describe mucosal infarction ?
marked by hypotension
lumenal worst as furthest from supply
Present :
abdominal pain
bloody diarrhea
Decreased bowel sounds
what is angiodysplasia ?
Malformed submucosal and mucosal blood vessels ( twisted , dilated )
pathogenesis is unknown
what is the most common location of angiodysplasia ?
Cecum or right colon
occur in elderly , less than 1% in adult population
20% of major episodes of lower intestinal bleeding
may be chronic and intermittent or acute massive
what is hemorrhoids ?
dilated anal and perianal collateral vessels that connect the portal and caval venous system
Relieve elevated venous pressure within the hemorrhoid plexus
5% of the general population
what are the causes of hemorrhoids ?
increased abdominal pressure
pregnancy
chronic constipation
what are malabsorption syndromes?
defective absorption of fats, fat and water soluble vitamins , proteins , carbohydrates, electrolytes, minerals and water
could involve any of the 4 phases of nutrients absorption
what are the 4 phases of malabsorption syndromes?
Intraluminal digestion
Terminal digestion
Transepithelial transport
Lymphatic transport
what is intraluminal digestion ?
proteins , carbohydrates and fats are broken down into :
absorbable forms by pancreatic enzymes , bacteria , st acids
what is terminal digestion ?
hydrolysis of carbonhydrates and peptides by disaccharidass and peptidase
respectively in the brush border of Small intestine mucosa
what is transepithelial transport ?
nutrients fluids and electrolytes are transported across and processed within the small intestinal epithelium
what is lymphatic transport?
of absorbed lipids
what are the sign and symptoms of malabsorption ?
diarrhea ( nutrients malabsorption and excessive intestinal secretion , flatus abdominal pain )
Weight loss
inadequate absorption of vitamins and minerals leading to :
anemia
mucositis due to pyridoxine , folate , vitamin b12 deficiency
bleeding due to vitamin K deficiency
osteopenia due to calcium or vitamin D deficiency
Neuropathy due to vitamin A or B12 deficiency
what are the other names of celiac disease ?
Celiac sprue
gluten sensitive enteropathy
white people , european ( 0.5 -1%)
what is celiac disease ?
immune mediated enteropathy triggered by ingestion of gluten containing cereals :
wheat , rye , barely
in genetically predisposed persons
what happens in celiac disease ?
Immobilization of T cells
Progressive mucosal atrophy –> villous flattening
Relieved by gluten withdrawal
describe the pathogenesis of celiac disease ?
Gluten is digested by luminal and brush border enzymes into amino acids and peptides
One of the peptides is gliadin ( resistant to degradation proteases )
Gliadin is deamidated by tissue TRANSGLUTAMINASES (tTS)
and the modified gliadin interacts with HLA- DQ2 or HLA-DQ8 on antigen presenting cells and be presented to CD4 + T cells
T cells produce cytokines that are likely to contribute to the tissue damage and characteristics mucosal histopathology in addition to characteristics B cells
having HLA-DQ2 and HLA-DQ8 genetics markers increase the risk of developing celiac disease
what is the clinical presentation of celiac disease ?
Kids :
Abdominal distention
Diarrhea
Failure to thrive
Adults :
Chronic diarrhea
Bloating
what is celiac disease associated with ?
Dermatitis herpetiformis
what is dermatitis herpetiformis ?
Skin condition linked to celiac disease
itchy , blistering rashes
appear on elbows, knees , buttocks
occur because the immune system to gluten , similar to how it affects intestines in celiac disease
what are serology tests done in celiac disease ?
Anti gliadian
anti transglutamase
how is diagnosis done ?
Biopsy from second portion of the duodenum or proximal jejunum ( exposed to the highest concentration of dietary gluten )
compare normal intestine to celiac disease intestine ?
Mucosa of celiac disease has :
blunting and flattening of villi
dense plasma cells infiltrating the lamina propria
Chronic infiltration
what is tropical sprue ?
chronic diarrheal disease
from possibly infections origin
involves small intestines and it is characterized by malabsorption of nutrients
what is the difference between celiac disease and tropical sprue?
Occurs in tropical places
Arises after infectious diarrhea
Responds to antibiotics
Damage more to jejunum and ileum ( DUODENUM IS LESS INVOLVED )
Jejunum absorbs folic acid so this may be deficient
Ileum absorbs vitamin B12
describe lactase ( disaccharidase ) deficiency ?
Lactase deficiency gives raise to osmotic diarrhea
so cant break down lactose , disaccharide
osmotically active lactose remains in the lumen
osmotically active so draw in water
causes watery diarrhea
Present when persons drink milk :
abdominal distension
Diarrhea
what are the 2 types of lactase deficiency ?
Congenital lactase deficiency : rare , autosomal recessive disorder caused by mutation in gene encoding lactase
Acquired lactase deficiency :
downregulation of lactase gene expression
Common among native americans and african americans , chinese
what are viral infections causing enterocolitis ?
Rotavirus ( 69% )
Calciviruses
Norwalk like
Sapporo likes
enteric adenovirsuses
Astroviruses
what are the bacterial infections causing enterocolitis ?
E. coli
salmonella
Shigella
Campylobacter
Yersinia
Vibrio
Clostridium difficile
Clostridium perfringens
TB
bacterial overgrowth
what are the parasitics causes of enterocolitis ?
Ascaris
Strongyloides
Necator
Enterobius
Trichuris
Diphyllobothrium
Tenia , hymenolepsis
Amebiasis
Giardia
what causes pseudomembranous colitis ?
Antibiotic therapy that disrupts normal microbiota
allow C. difficile to grow
these organism release toxins that disrupt epithelial function
what are the grossly features pseudomembranous colitis ?
Hyperemic mucosal surface
covered by yellow green exudate
what are the microscopic features of pseudomembranous colitis ?
Inflammatory response
Volcano like eruption of neutrophils
Mucopurulent Pseudomembranous
Describe S.I tumors ?
Rare 3-6^ of GIT neoplasm
Benign :
Adenomas : Single or multiple , most often in duodenum and ileum , they increase the risk of malignancy
Malignant :
Carcinoids
Adenocarcinomas
