Pancreas and Liver Flashcards
1
Q
List the key properties of chyme leaving the stomach
A
- Low pH
- Hypertonic
- Partially digested
2
Q
Explain why chyme enters the SI as hypertonic and how that changes
A
- Stomach wall largely impermeable to water
- Water cannot move into stomach to dilute chyme
- Duodenum relatively permeable to water
- Hypertonic chyme draws movement of water from ECF/circulation into duodenum
- Chyme release must be controlled to not overwhelm duodenum with water
- Chyme is isotonic when is leaves the duodenum
3
Q
What is secreted from the exocrine pancreas and where are these made
A
- Digestive enzymes and aqueous bicarbonate solution
- Digestive enzymes produced in the acini
- Bicarbonate solution released from duct cells
4
Q
Describe the enzymes produced from the pancreas
A
- CCK and vagus stimulate acini to produce enzymes
- Amylases and lipases
- Proteases (in inactive form)
- Proteases when activated include
- Trypsin
- Chymotrypsin
- Elastase
- Carboxypeptidase
- Pancreatic proteases released in inactive forms to prevent self-digestion of pancreatic tissue
- Can lead to pancreatitis
- Protease enzymes are concentrated and stored in zymogen granules
- Zymogen granules contain zymogen (inactive precursor to an enzyme)
5
Q
Describe the control of pancreatic and biliary secretions
A
- Secretin acts on pancreas to stimulate release an aqueous bicarbonate component of the pancreatic secretion
- Released from duodenum in response to low pH of chyme
- CCK acts on pancreas to stimulate release of enzyme component of pancreatic secretion
- Also acts on gall bladder to contract it
- Also relaxes sphincter of oddi
- Released from duodenum in response to hypertonicity/small peptides/fats within chyme in duodenum
- Autonomic nervous system also controls pancreatic secretions
- Sympathetic inhibits secretion, parasympathetic stimulates secretion
6
Q
Outline the flow of blood and bile in the liver lobules
A
- Blood enters a lobule via hepatic artery and portal vein
- Blood flows in towards central vein via sinusoids
- Bile flows out along canaliculi to the bile duct and into the duodenum
7
Q
Describe the acinus and the creation of zones
A
- Functional area of the lobule is called the acinus
- Blood drains from the periphery of lobule to center
- Substances brought to liver from gut as well as oxygen therefore start at periphery and work towards middle
- Creates a series of zones corresponding to distance from arterial blood supply
- Zone 1 is well oxygenated and first exposed to substances from the gut
8
Q
Describe how toxic substances and ischaemia affect the zones of the acinus
A
- Toxic hepatocyte damage most likely will damage zone 1 as they are the first cells to be exposed to the toxin
- Ischaemic hepatocyte damage most likely will damage zone 3 as it has the lowest oxygen perfusion
9
Q
Where is bile created
A
- Bile is created by hepatocytes and duct cells in liver
- Continuously produced but only needed intermittently
10
Q
Describe the components and action of bile
A
- Bile consists of:
- Bile acids and bile pigments
- Alkaline solution
- Bile emulsifies fats in duodenum so that they can be readily digested by lipases secreted by pancreas
11
Q
Differentiate between bile-acid dependent and independent
A
- Bile-acid dependent - bile acids and pigments
- Secreted into canaliculi by hepatocytes
- Bile-acid independent - alkaline juices
- Secreted by bile duct cells
- Stimulated by secretin
- Secreted by bile duct cells
12
Q
Explain what bile salts are and why they are formed
A
- Bile salts are conjugated bile acids
- 2 main bile acids - cholic acid, chenodeoxycolic acid
- Bile salts are bile acids conjugated with amino acids (glycine, taurine)
- Conjugation needed as bile acids do not work well in the low pH of the early duodenum
- Bile salts better at emulsifying fats in the duodenum
- Bile acids are not always soluble at duodenal pH
- Bile salts have an amphipathic structure
- Hydrophilic head and hydrophobic tail
13
Q
Describe the function of the gall bladder
A
- Bile stored in the gall bladder
- Concentrates bile - removes water/ions
- Can lead to formation of gall stones
- CCK released from duodenum stimulates gall bladder contraction
- Bile secreted via common bile duct, then ampulla of vater into duodenum
14
Q
Describe the mechanism of digestion of fats
A
- Lipids tend to form large globules when they reach duodenum
- Small surface area for lipases to act
- Bile salts emulsify fat into smaller units
- Disperse droplets increasing surface area for lipases to act
- Hydrophobic tail attach to lipids
- Disperse droplets increasing surface area for lipases to act
15
Q
Decsribe the mechanism of transport of fats
A
- Bile salts then create micelles with products if lipid breakdown
- Hydrophobic tail surrounds fat to make it water soluble as hydrophilic heads exposed
- Micelles transport hydrophobic molecules towards luminal membrane of enterocytes
- Breakdown materials of lipids being transported include cholesterol, monoglycerides and free fatty acids
- Lipids diffuse into intestinal epithelial cell
- Lipids are re-estified - built back to triglycerides, phospholipids and cholesterol
- Packed with apoproteins within enterocytes - chylomicrons
- Chylomicrons exocytosed from basolateral membrane of enterocyte (gut)
- Too large to enter capillaries
- Enter lymphatic capillaries -> thoracic duct
- Too large to enter capillaries
