GI Module 4 Flashcards
What connective tissue does the liver consist of?
- Falciform ligament
- Glisson’s capsule
What is Glisson’s capsule?
- Connective tissue that surrounds the liver
- Invaginates at hilum of liver
What is the functional unit of the liver?
Liver lobule
What is a liver lobule?
- Functional unit
- Hexagonal arrangement of hepatocytes and microvasculature
- Central vein
- Portal triad at each outer corner of hexagon
- Microvasculature consists of sinusoids and bile canaliculi
What is a portal triad?
- Outer corner of hexagon in liver lobule
- Consists of hepatic artery, portal vein, bile duct
What is the biliary pathway?
Bile canaliculi - terminal bile ducts - R/L hepatic ducts - common hepatic duct
- Then cystic duct - gallbladder
- And common bile duct - pancreatic duct - duodenum
Hepatic circulation generally consists of:
- Afferent pathways to liver (portal and arterial)
- Sinusoids
- Efferent pathway from liver
- Lymphatic circulation
Where does the hepatic portal vein receive blood from?
GI tract, spleen, pancreas
What is the hepatic portal anastomosis?
- Collateral venous circulation w/numerous veins of abdominopelvic region
- Consists of: gastroesophageal vein, rectal, paraumbilical, portorenal
Describe portal hypertension
- Portal circulation is congested and reverses blood flow toward portal anastomoses
- Occurs when cirrhosis develops
Where does the hepatic artery originate from and what does it do?
- Originates from celiac trunk
- Delivers oxygenated blood to liver
- Approx 25% of blood flow to liver
What is the hepatic artery’s relationship with portal HTN?
Blood flow to liver from hepatic artery is NOT impaired
What is the function of sinusoids?
- Act as capillary bed for hepatocytes
- Receives blood from 2 of 3 portal triad vessels
- Merges nutrient rich and O2 rich blood
- Exposes hepatocytes to blood flow
- Drains into central vein
General structure of sinusoid/hepatocyte interface
- Kupffer cells
- Fenestrated endothelium
- Space of Disse
- Microvilli of hepatocyte
Describe Kupffer cells including location and function
- Monocyte/macrophage origin
- Located along surface of endothelium
- Serves as early defense against liver injury (phagocytic removal, RBC degradation)
Describe fenestrated endothelium
- Large holes in endothelial lining of sinusoid vessel
- Allows nutrients/lipids to travel through and flow to microvilli of hepatocyte
- Pinocytosis function to actively transport molecules as well
What are stellate cells? Function and location?
- Located in Disse Space of sinusoids
- Stores Vit A
- Produces/secretes hepatic GF for liver regeneration
What happens to stellate cells in some sort of pathology?
- Transform into fibroblastic function (produce collagen) and myoblastic function (contractile)
- Role in fibrosis
What are pit cells? Location and function?
- Aka granular lymphocytes (NK cells)
- Located surface of endothelium in sinusoids
- Front line immune defense
- Some role in liver regeneration too
Which organ produces the largest amount of lymph fluid in the body?
Liver (approx 20% of total)
What are the two regional zones of hepatocytes in liver lobule?
- Periportal hepatocytes
- Centrilobular hepatocytes
- Sometimes a 3rd zone mid-way between is identified
Describe periportal hepatocytes
- Part of liver lobule circulation
- First to receive blood
- First to regenerate
- Last to experience necrosis
Describe centrilobular hepatocytes
- Part of liver lobule circulation
- Last to receive blood
- Susceptible to ischemia/necrosis
- Region of drug metabolism
What is the region of drug metabolism in the liver?
Centrilobular hepatocytes
How does the liver function in drug metabolism?
- Serves as intermediate step
- Converts drugs from hydrophobic to hydrophilic to allow excretion
What is gluconeogenesis?
Production of glucose from non-carb source (fatty acids, AAs, lactate)
What is the rate limiting step of gluconeogenesis?
- Amt of available substrate
- NOT liver enzymes
How does the liver function in fat metabolism?
Removes FFA and lipoproteins from plasma
Lipoproteins in order from largest to smallest in size:
- Chylomicrons
- VLDL
- LDL
- HDL
Lipoproteins by function
- Chylomicrons - transport TGs
- VLDL - transport TGs to periphery
- LDL - transport cholesterol to peripheral tissue
- HDL - remove cholesterol from periphery to liver
Bile fluid contains:
- Bile acids
- Phospholipids
- Cholesterol
- Other things via micelle complex
Function of bile
- Assist in intestinal fat digestion
- Excretion of hydrophobic substances
Bile pathway during fasting
- 75% flows into gallbladder to be concentrated
- 25% continues on and flows into duodenum
Bile pathway during feeding
- Gallbladder contracts via CCK and vagal stimuli
- Bile reaches duodenum and enters enterohepatic circulation
What is bilirubin?
Byproduct of RBC breakdown
-Heme is broken down into biliverdin which is broken down into bilirubin
How is RBC broken down?
- Hemoglobin is exposed
- Globin broken down to AAs
- Heme broken into iron and biliverdin
Is bilirubin fat or water soluble?
Fat soluble so it travels to liver to be conjugated for excretion
What is urobilinogen?
- Bilirubin in the intestine that is converted by bacteria
- Remains in colon to be excreted in stool (80%)
- 20% is reabsorbed into bloodstream
What is jaundice?
- Hyperbilirubinemia
- Yellowing of skin and membranes
- Sign of disease that affects bilirubin metabolism
What is pre-hepatic jaundice?
- Location of pathology is “before” bilirubin is conjugated by the hepatocytes
- RBC breakdown, genetic diseases, kidney
What is post-hepatic jaundice?
- Pathology located “after” bilirubin is conjugated and secreted
- Impaired transport to GI tract
- Gallstones or pancreatic obstruction
- Pale stools, dark urine
What are the different types of gallstones?
- Cholesterol (MC, yellowish/green)
- Pigment (black or brown)
