5. Pancreas And Liver Flashcards
What are the properties of chyme?
Hypertonic - increases as digestion takes place
Acidic
Only partially digested
What helps to make chyme less hypertonic and digest it further?
Water from ECF
Secretions from pancreas (enzymes, bicarbonate ions), from liver (bicarbonate ions, bile)
Why is chyme hypertonic?
Food produces lots of solutes that are dissolved in gastric juice
Stomach wall is largely impermeable to water so water cannot dilute solute in chyme
What does the acinus secrete in the pancreas?
Enzymes - amylase/lipase (active), proteases (inactive) - trypsin, chymotrypsin, elastase, carboxypeptidase
What do the centroacinar cells secrete?
Aqueous component of pancreas secretions
What happens in the pancreatic ducts?
Modifies aqueous secretions
What are the pancreatic secretions innervated by?
Parasympathetic - vagus, hormones
Sympathetic inhibits
What is the acinus of the pancreas stimulated by?
Vagus and chylocystokinin (CCK)
How are the enzymes produced in the acinus?
Formed on RER Moved to Golgi Condensing vacuoles Concentrated in zymogen granules Released with appropriate stimulus
What are zymogen granules?
Membrane bound
Contain zygomen - inactive precursor of an enzyme
What signifies pancreatic damage?
Pancreatic enzymes (amylase, lipase) appear in blood
What happens if pancreatic secretions are at higher flow rate?
Increased secretion of HCO3
What is the liver for?
Energy metabolism
Detoxification
Plasma protein production
Secretion of bile
Why do hepatocytes contain lots of RER/SER and Golgi?
Very active at producing proteins/lipids for export
Why do heaptocytes contain lots of glycogen?
Needed when glucose needs to be accessed quickly
What is in a portal triad?
Bile duct
Branch of hepatic artery
Branch of portal vein
What is the hepatic acinus?
Functional unit of liver
3 zones - 1 is closest to portal triad, 3 is closest to central vein
Which zone of the acinus is most likely to be damaged by ischeamia?
3
Which zone of the acinus is most likely to be damaged by toxins?
1
Where does the venous blood from the gut drain through?
The liver, in portal vein
What flows into the liver?
Venous portal blood
Arterial blood
All flowing towards central vein, which then drains into hepatic veins (vena cava)
What flows out of the liver?
Bile, along canaliculi
Bile ducts to duodenum
What are the 2 components of bile?
Bile acid dependent
Bile acid independent
What is bile acid dependent component secreted by?
Secreted by hepatocytes into canaliculi
What is bile acid independent component secreted by?
Secreted by duct cells
What is release of bile acid independent component stimulated by?
Secretion
What does bile acid dependent component contain?
Bile acids and pigments
What is bile acid independent component made of?
Similar alkaline solution to pancreatic duct cells
How can bile salts help remove cholesterol?
Fibre can bind cholesterol to other bile salts and allow it to be excreted in faeces
What are the 2 primary bile acids?
Cholic acid
Chenodeoxycholic acid
What are bile salts?
Bile acids that are conjugated with the amino acids (glycine, taurine)
Why do we have bile salts, not just bile acids?
Bile acids are not always soluble at duodenal pHs - bile salts generally are
Bile salts have an amphipathic structure (hydrophilic end and hydrophobic end) - act at oil/water interface, crucial for emulsification of dietary lipids
Why do bile acids need to emulsify fat into smaller units?
Lipids tend to form large globules by the time they reach the duodenum
This gives a low SA for enzymes to act
Bile acids can help disperse droplets and increase SA for lipases to act
Bile acids then form micelles with products of lipid breakdown
What are micelles?
Vehicle to carry hydrophobic molecules through an aqueous medium
What are the products of lipid digestion?
Cholesterol
Monoglyceride
Free fatty acids
What happens when micelles come in contact with brush border of enterocyte cells?
- Lipids diffuse down conc gradient into intestinal epithelial cell
- Inside the cell, lipids are re-esterified back to triglycerides, phospholipids and cholesterol
- Then packaged with apoproteins to form chylomicrons
How are chylomicrons transported out of enterocytes?
Exocytosis from basolateral membrane
Then enter lymph capillaries (lacteals) as too big to enter blood capillaries
Travel through lymphatic system, then re-enter vascular circulation at the thoracic duct into left subclavian/internal jugular vein
Where are bile salts reabsorbed and where do they go?
In terminal ileum, return to liver in portal blood, liver extracts bile salts and reuses them
What does the gallbladder do?
Stores bile
Concentrates bile - removes water and ions
What stimulates gallbladder contraction?
CCK - relaxes sphincter of oddi
What happens if bile acids or pancreatic lipases are not secreted in adequate amounts?
Fat appears in faeces (steatorrhoea)
