Block 7 (GI) - L16 to L19 Flashcards
What systems are required for digestion and absorption?
- Mechanical (chewing, trituration, peristalsis)
- Enzymatic/chemical (amylase, HCl, pepsin, lactase)
- Hormonal (CCK, peptide YY)
- Structural (villi, intestinal length, IC valve)
- Transport proteins and barrier functions (GLUT, desmosomes)
- Microbiome (vitamin K, fermentation)
- Lymphatic (chyle transport)
- Vascular (nutrient transport, tissue oxygenation)
- Metabolic (mitochondria, glycogen storage/glycolysis)
- Neurologic (control center)
- Electric (gastric pacemaker waves)
Absence of brush border enzymes causes what common malabsorption disorder?
Lactose intolerance
What can cause temporary lactose intolerance?
Infection
What is useful in short gut syndrome and fat malabsorptive disorders and why?
Medium chain triglycerides (directly absorbed across the mucosa into the portal vein - no bile salts, lipase, colipase, or ileum required)
What are the limitations of MCT oil?
- Doesn’t contain essential fatty acids (can cause EFA deficiency)
- Excess is metabolized to ketones (can cause metabolic acidosis)
What is primarily absorbed in the duodenum?
Calcium, iron
What is primarily absorbed in the jejunum?
Monosaccharides, water soluble vitamins, electrolytes, trace minerals, fat, fat soluble vitamins, protein, water, alcohol, magneisum
What is primarily absorbed in the ileum?
Vitamin B12 and bile salts
What is primarily absorbed in the colon?
Water, electrolytes, SCFAs
List the components of bile. How much is secreted daily?
- Bile acids (cholic, chenodeoxycholic, deoxycholic, lithocholic)
- Phospholipids (lecithin)
- Cholesterol
- Pigments (bilirubin)
- Inorganic ions
250mL-1L
List the components of pancreatic secretions. How much is secreted daily?
- Aqueous component: bicarbonate - neutralizes acid and activates enzymes
- Enzymatic component: amylase, lipase, protease
Where is iron, B1, and folate absorbed?
Duodenum
What are clinical signs of malabsorption?
- Diarrhea
- Steatorrhea
- Bloating
- Weight loss
- Dehydration
- Growth retardation/failure to thrive
- Edema
- Anemia/bleeding tendencies
- Muscle cramping
- Bone deterioration
Watery diarrhea indicates ___ malabsorption.
Carbohydrate
Anemia/bleeding tendencies indicates possible malabsorption of what 4 things?
B12, iron, folate, vitamin K
Muscle cramping indicates possible malabsorption of what 4 things?
Ca2+, Mg2+, phosphorus, vitamin D
Bone deterioration indicates possible malabsorption of what 2 things?
Vitamin D, calcium
List 7 classic malabsorptive disorders.
- Celiac disease
- CF
- Chronic pancreatitis
- Lactose intolerance
- bacterial overgrowth
- Whipple’s disease
- Tropical sprue
What is celiac disease?
Multifactorial autoimmune disorder in genetically susceptible individuals
What triggers celiac disease?
The protein gluten, found in wheat, and proteins in rye and barley
Describe the pathogenesis of celiac disease.
Infiltration of the SI by lymphocytes attacking TTG causes an inflammatory reaction leading to flattening of the SI mucosa
What is the genetic mutation associated with celiac disease?
HLA DQ2/8
Malabsorption of what things is common in celiac disease?
Iron, folate, calcium, vitamin D (B12 is rare)
How is celiac disease screened and confirmed?
Screen with serum TTG Ab test
Confirmed with small bowel biopsy
What can hypoalbuminemia and/or anemia indicate RE malabsorption?
Folate or B12 deficiency (macroscopic anemia)
Iron deficiency (microscopic anemia)
What is the most important test for suspected malabsorption?
Sudan stain of fecal fat
What does a lactose hydrogen breath test indicate?
If hydrogen is elevated >20ppm in response to lactose ingestion (?)
Fecal elastase is low in ___.
Pancreatic insufficiency
Stool pH is low in ___.
Carbohydrate malabsorption
What is D-xylose test used for?
Differentiates malabsorption secondary to mucosal damage from malabsorption due to pancreatic sufficiency/other
What is seen on microscopic examination in Whipple’s disease?
Foamy macrophages, positive PAS stain
What are three broad categories of hepatic circulatory disorders?
- Hepatic vein outflow obstruction
- Impaired intrahepatic blood flow
- Impaired blood inflow
What are causes of hepatic vein outflow obstruction?
- Hepatic vein thrombosis (Budd-Chiari syndrome)
2. Veno-occlusive disease
What are causes of impaired intrahepatic blood flow?
- Cirrhosis
- Sinusoid occlusion
- Systemic circulatory compromise
What are causes of impaired blood inflow?
- Hepatic artery compromise
- Portal vein obstruction
- Intra- or extra-hepatic thrombosis
How does hepatic vein outflow obstruction manifest?
Ascites, hepatomegaly, abdominal pain, elevated transaminases, jaundice
How does impaired intrahepatic blood flow manifest?
Ascites (cirrhosis), esophageal varices (cirrhosis), hepatomegaly, elevated transaminases
How does impaired blood inflow manifest?
Esophageal varices, splenomegaly, intestinal congestion
What is Budd-Chiari Syndrome and what are its symptoms?
Hepatic vein obstruction/thrombosis
Hepatomegaly, ascites, abdominal pain, hepatic dysfunction
What are some etiologies of Budd-Chiari Syndrome?
- Primary myeloproliferative disorders
- Inherited disorders of coagulation
- Antiphospholipid syndrome
- Paroxysmal nocturnal hemoglobinuria
- Intra-abdominal cancers
- Oral contraceptives
- Pregnancy
What is seen histologically in Budd-Chiari syndrome?
Centrilobular congestion
What is sinusoidal obstruction syndrome?
Hepatic venous outflow impairment is due to occlusion of the terminal hepatic venules and hepatic sinusoids
Who is at risk for sinusoidal obstruction syndrome?
Bone marrow transplant patients (highest risk in first 3 weeks), chemotherapy patients, drugs (such as azathioprine)
What is the pathogenesis of sinusoidal obstructive syndrome?
Toxic injury to the sinusoidal endothelium with resulting fibrotic occlusion of small hepatic veins
What are the symptoms of sinusoidal obstructive syndrome?
- Acute RUQ tenderness
- Hepatomegaly
- Ascites
- Weight gain
- Jaundice
What is seen on histology in sinusoidal obstruction syndrome?
Fibrous obliteration of the central vein
What is acute fatty liver of pregnancy?
Sudden catastrophic illness occurring exclusively in the 3rd trimester characterized by microvesicular fatty infiltration that can lead to acute liver failure and encephalopathy
What is seen histologically in acute fatty liver disease of pregnancy?
Microvesicular steatosis (fat in the hepatocyte does not push the nucleus to the side)
What is the most common non-malignant tumor of the liver?
Focal nodular hyperplasia (FNH)
What causes FNH?
Localized overgrowth of hepatocytes
What are the two major features of FNH?
- Solitary
2. Central stellate scar
What age group is affected by FNH?
20-40 year olds
What is the malignant potential of FNH and what is the treatment?
No malignant potential
No treatment necessary
What is nodular regenerative hyperplasia?
Transformation of the hepatic parenchyma into small regenerative nodules in the absence of fibrosis
What can nodular regenerative hyperplasia cause?
Non-cirrhotic portal hypertension
What are conditions associated with nodular regenerative hyperplasia?
- Solid organ and bone marrow transplant
2. HIV
What is a hepatic adenoma?
Benign tumor of the liver
Hepatic adenomas are common in ___ and are associated with what two things?
Young women; pregnancy and oral contraceptive use
What is seen on histology in a hepatic adenoma?
Sheets and cords of normal hepatocytes with ABSENT portal tracts and prominent solitary arterial vessels
Does hepatic adenoma have a risk of transforming into hepatocellular caricinoma?
Yes, though it is rare
What is a hemangioma?
Most common benign tumor of the liver
What is seen histologically in hemangioma?
Benign vascular channels and fibrous tissue
What is the most common primary malignant liver tumor of childhood?
Hepatoblastoma
Hepatoblastoma affects ___ > ___.
M>F
What is seen on physical exam and labs in hepatoblastoma?
RUQ mass
Elevated alpha fetoprotein
95% of ___ cases occur in patients with cirrhosis. What is the exception to this rule?
Hepatocellular carcinoma; can occur independent of cirrhosis in hepatitis B
What are causes of hepatocellular carcinoma?
- Cirrhosis of any cause (NASH, alcohol, hepatitis C, hemochromatosis)
- Chronic hepatiti B
- NASH
- Food contaminants (Aflatoxin - Africa)
- Hereditary Tyrosinemia