Physiology & anatomy Flashcards
Where does the blood supply of the liver come from
- Hepatic artery (from the celiac artery): 20% of blood flow, 50% of O2 supply
- Portal vein (from the cranial and caudal mesenteric veins + splenic and gastroduodenal (absent in cats) veins): 80% of blood flow, 50% of O2 supply
What are the different liver lobes
- Left lateral lobe
- Left medial lobe
- Quadrate lobe
- Right medial lobe
- Right lateral lobe
- Caudate lobe (caudate process and papillary process)
What is the normal diameter of the common bile duct
3-4mm
What is the normal portal pressure
8-13 cmH2O (6-10 mmHg)
What is the name of the enzyme conjugating bilirubin in the liver
UDP-glucuronyl-transferase
(UDP = uridine diphosphate)
Describe the metabolism of bilirubin and where it happens
- In the reticuloendothelial system (phagocytes): Hemoglobin -> biliverdin -> bilirubin
- In the liver: bilirubin ->conjugated bilirubin ->some excreted in urine and some excreted in bile
- In the GI: conjugated bilirubin -> urobilinogen (by bacteria) -> gets re-absorbed in the ileum and converted to urobilin / stercobilin in colon
Where are bile salts reabsorbed? With what solute?
Ileum
Cotransport with Na+ (ASBT = apical sodium-dependent bile salt transporter)
(Some get spilled in colon and can be deconjugated and reabsorbed in colon)
What is the composition of bile
- Secreted by hepatocytes: Bile salts (conjugated bile acids) + phospholipids + conjugated bilirubin + cholesterol + some urea
- Added by cholangiocytes: HCO3-, IgA
How are bile salts produced
- Primary bile acids (cholic acid and chenodeoxycolic acid) are produced by hepatocytes from cholesterol
- Some primary bile acids are converted to secondary bile acids (deoxycholic acid and lithocholic acid +/- ursodeoxycholic acid) by bacteria in the intestine
- Bile acids are conjugated with taurine and glycine to form bile salts
What causes emptying of the gallbladder
- CCK ->contraction of gallbladder + relaxation of sphincter of Oddi
- ACh ->contraction of gallbladder
- NO -> relaxation of sphincter of Oddi
- VIP (vasoactive intestinal peptide) ->relaxation of sphincter of Oddi
What major group of enzymes is responsible for detoxification of substances in the liver
Cytochrome P450 enzymes
What lines the sinusoids in the liver
- Endothelial cells forming very large pores (very permeable)
- Kupffer cells = resident macrophages
What is the name of the space between the endothelial lining of sinusoids and hepatic cells
Space of Disse (= perisinusoidal space)
Lose connective tissue between the sinusoidal endothelium and the basolateral membrane of hepatocytes
Describe the structure of a liver lobule (cells, vascularisation, ducts)
See picture
List metabolic functions of the liver
- Carbohydrate metabolism:
- Glycogenesis and storage of glycogen
- Gluconeogenesis from amino acids and triglycerides
- Conversion of galactose and fructose to glucose - Fat metabolism:
- Oxidation of fatty acids (beta-oxidation -> can join citric acid cycle)
- Synthesis of cholesterol, phospholipids, lipoproteins
- Synthesis of fat from carbohydrates and proteins - Protein metabolism:
- Deamination of amino-acids
- Formation of urea for removal of ammonia from the body
- Formation of plasma proteins (all except for globulins) - Storage of vitamins and iron (in the form of ferritin = combination of iron with apoferritin)
- Synthesis of coagulation proteins
- Metabolism of toxic substances
- Excretion of calcium via bile
What are the essential amino acids in cats and dogs
Cats: Arginine, methionine, histidine, phenylalanine, isoleucine, threonine, leucine, tryptophan, lysine, valine and taurine
Dogs: same except for taurine
What metabolic reaction leads to the formation of ammonia? Where?
Deamination of amino-acids
Mostly in the colon by bacteria, in the kidneys, in the muscles
What is the main transformation that happens to bile in the gallbladder
Concentration (removal of water) + removal of HCO3- and Cl- and some Na+
As a general rule, how are lipid-soluble and protein-bound substances eliminated from the body
Secreted in bile (vs water-soluble substances are secreted in urine)
What are the different bile ducts
- Right and left hepatic duct
- Common hepatic duct
- Cystic duct
- Common bile duct
What are the 2 ways of ammonia metabolism and where do they happen
- Conversion of ammonia into urea in the periportal hepatocytes (urea cycle)
- Transamination in the perivenous hepatocytes, brain, and skeletal muscle (ammonia + glutamate ->glutamine)
What is the role of the Kupffer cells?
Large phagocytic macrophages that remove bacteria from blood coming from GI as it passes through the sinuses
What is an anatomical difference in cats that may explain the frequent concurrence of hepatic and pancreatic disease?
The common bile duct and the pancreatic duct conjoin just before their entry into the duodenum at the major duodenal papilla
VS
In dogs, they are adjacent, but not joined
How much of liver mass must be lost to cause clinical hypoalbuminemia?
70-80%
All albumin is produced in the liver
