5a.) Chyme, Liver & Pancreas Flashcards
Describe the properties of chyme as it leaves stomach, include:
- pH
- Hypo- or hypertonic
- How much it is digested
- low pH (acidic) ~pH2
- Hyppertonic
- Partially digested
How does the duodenum deal with the hypertonicity of chyme?
Duodenum is relatively permeable to water so adds water from ECF to the hypertonic chyme
What glands are present in the duodenum, and what do they secrete, to help protect duodenum against acidity of chyme?
Brunner’s glands secrete alkaline mucus which protects mucosa from acidic chyme. Brunners glands DO NOT help neutralise the acid chyme, only protect mucosa
State 2 reasons why chyme is hypetonic when it leaves the stomach
- Digestion of food in stomach makes solutes- increase hypertonicity
- Stomach wall largely impermeable to water (cannot dilute the chyme)
Why must chyme release be tightly controlled?
So as not to overwhelm the duodenum/release too much chyme into the duodenum to the point where duodenum cannot correct the hypertonicity and acidity of chyme. Pyloric sphincter controls release
How does the duodenum deal with the low pH (acidity) and partially digested food in chyme?
What two hormones does the duodenum secrete in response to chyme and what do these hormones do?
Secretin:
-
Pancreas:
- stimulate release of aqueous bicarbonate (HCO3-)
-
Liver
- Aqeuous bicarbonate secretion
CCK:
- Pancreas: stimulate release of enzymes
- Gallbladder: causes contraction of gallbladder and relaxation of sphincter of oddi to allow bile secretion
Chyme causes the duodenum to secrete secretin and CCK; what specific properties/components of chyme stimulates each of the hormones to be secreted?
- Secretin: low pH stimulates
- CCK: hypertonicity and the small peptides and fats in chyme
Pancreatic secretions are stimulated by what two things (broadly speaking)?
HINT: hormones & _____
- Hormones (CCK, secretin)
- Autonomics
State the effects of the following on pancreatic secretions (exocrine function):
- Sympathetics
- Parasympathetics (vagus nerve)
- Sympathetics: inhibit
- Parasympathetics (vagus): stimulates
What proportion of the pancreas is exocrine function?
90%
Describe the structure of the pancreas in terms of it’s functional areas
Acini and ducts make up the functional areas of pancreas
Describe the stimulation of acini in the pancreas, include:
- Role of acini
- What stimulates them
- What they release
- Acini produce enzymes
- CCK and parasympathetics from vagus stimulate release of enzymes
- Release amylases & lipases (which are ready to go) and proteases (which are inactive and stored as zymogens)
Proteases, released by acinar cells of pancreas, are stored in zymogen granules (they are inactive) unlike amylase and lipase secretions from acinar cells. State 4 proteases that are released (state activated name)
- Trypsin
- Chymotrypsin
- Elastase
- Carboxypeptidase
What is a zymogen?
Pro-enzyme/inactive form of an enzyme
What is a zymogen granule?
Membrane bound secretions that contain an inactive precursor of an enzyme
Why must proteases be stored as zymogens in zymogen granules?
To avoid auto-digestion of the pancreas. They are only activated once they make contact wtih duodenum
Describe the stimulation of ducts in the pancreas, include:
- Role of ducts
- What stimulates them
- Why they are required
- Duct cells secrete alkaline aqeuous component of pancreatic secretions (aqueous part is isotonic, alkali part is bicarbonate)
- Stimulated by secretin
- Secretions neutralise acidic chyme
Describe the pathway secretions from pancreas must take to reach the duodenum
- Terminal duct
- Pancreatic duct
- Ampulla of Vater
State 3 of the many roles of the liver
- Energy metabolism
- Detoxification
- Protein synthesis
What does the liver secrete?
Where are it’s secretions stored?
Bile
Secretions stored in gall bladder
Approximately how much bile is secreted per day?
250ml - 1000ml
What are the 3 components of bile?
- Bile acids
- Bile pigments
- Alkaline solution
What is the role of bile?
To emulsify fats (break large fat globules into smaller ones) in duodenum so that they can be readily digested by lipases secreted by pancreas
What is the largest single organ in the body?
Liver
State the chief functional cell of the liver and what % of liver mass they make up
- Hepatocytes
- 80% liver mass
Describe some adapatations of hepatoctyes (chief funtional cell of liver) to enable them to perform their role
Hepatocytes are highly metabolically active producing proteins and lipids for export so have:
- Lots of rough/smooth ER
- Stacks of golgi membranes
- Lots of glycogen
What % of blood from gut drains into the liver and via which vein?
ALL blood from gut drains into liver via portal vein
Describe the macro anatomy of the liver (hint, describe the lobes)
- Left and right divided by falciform ligament
What is the strucutral unit of a liver?
A liver lobule (a hexagonal structure with a central vein in centre and portal triads at the apices)
What is the functional unit of a liver?
Acinus (functional diamond shape)
State the general direction of blood flow in a liver lobule
Blood from portal vein and hepatic artery passes through sinusoids to central vein
Describe the structures that bile flows through
Bile flows out through:
- Canaliculi
- Bile duct
- Into duodenum
Acina are areas of liver lobule where function is orientated; true or false
True
Describe the zones in a liver acinus
Which zone of liver acinus is a toxic injury most likely to damage?
Zone 1 (toxins meet this part first)
Which zone of a liver acinus is an ischaemic injury most likely to damage?
Zone 3 (furthest from blood supply)
What cells produce bile?
Is bile production continous?
- Hepatocytes and ducts cells
- Continously produced (but only needed intermittently)
What does the gallbladder do to bile (apart from store it)?
Concentrates bile by removing water and ions
If bile is concentrated too much what can this lead to?
Gallstones
Describe the path of bile from liver to duodenum
- Canaliculi
- Bile duct
- Ampulla of Vater
- Duodenum
Bile is made up of bile acids, bile pigments and alkaline juices; state which cells produce each of the above
- Bile acids & bile pigments: hepatocytes
- Alkaline juices: cells lining bile ducts (stimulated by secretin)
Describe:
- How bile salts are formed
- Structure of bile salts
- Function
- Formed when bile acids are conjugated to amino acids (glycine, taurine) in liver
- Amphipathic structure:
- Hydrophilic end
- Hydrophobic end
… allows them to work at oil/water interface
- Function is to emulsify lipids
Why does emulsification aid digestion?
Increases SA for lipases
How do the hydrophobic breakdown products of lipids travel towards enterocytes?
Once lipases have broken lipids down into cholesterol, monoglycerides, free fatty acids etc… the bile salts create micelles with the breakdown products. Hydrophobic products are at centre of micelles meaning they can move through an aqueous environment
Once hydrophobic lipids have been transported through aqueous environment to the luminal membrane of enterocyte, how do they get into the enterocyte?
What happens to bile salts?
Diffusion down conc gradient
Then get entero-hepatic circulation of bile salts:
- Bile salts remain in lumen when lipids diffuse
- Reabsorbed by terminal ileum
- Returned to liver via portal blood
Are bile salts recycled?
YES- think about entero-hepatic circulation of bile salts
What happens to lipids once they have diffused into enterocytes?
- Lipids are re-estified back to triglycerides, phospholipids & cholesterol
- Packed with apoproteins into chylomicrons
- Chylomicrons exocytosed from basolateral membrane into lymphatic capillaries and then travel to thoracic ducts (too large to enter capillaries)
Briefly summarise digestion of lipids from being large globule to being in subclavian vein
What is steatorrhoea?
What does it look like?
Undigested fats in faeces
- Pale
- Floating
- Foul smelling
What can cause steatorrhoea?
Pathologies which cause bile acids/salts or pancreatic lipases to not be secreted in adequete amounts
Chyme is generally isotonic when it leaves the duodenum; true or false?
True
State an alternative name for the ampulla of Vater
Hepatopancreatic duct
(confluence of pancreatic and common bile duct)
Another role of bile, alongside emulsifying fats, is to excrete waste products such as bilirubin; true or false?
True
What percentage of bile is made of bile salts?
61%
- Right and left hepatic ducts
- join to form common hepatic duct
- Cystic duct connects common hepatic to the gallbladder
- cystic joins common hepatic we know call it common bile duct
- Common bile duct joins with major pancreatic duct to form ampulla of Vater
- Sphincter of Oddi determines whether contents can enter duodenum
