Give the 3 basic features of Chyme and related these features to the actions of the duodenum
Aciditicy corrected in duodenum via secretion of HCO3- from pancreas, liver and duodenal mucosa
Corrected via osmotic movement of water over duodenal wall
Digestion completed with enzymes from pancreas and small intestal mucosa ans well as bile salts from the liver
What are the two major functions of the pancreas?
Outline the exocrine pancreas functions
What structural features are responsible for the exocrine functions of the pancreas?
Exocrine tissue is glandular:
Glands secrete enzymes
Ducts secrete Alkaline juice
Describe how the pancreas produces enzymes
Enzymes synthesised by ribosomes of Acinar gland epithelium
- mostly as inactive precursors
Then packaged into condensing vacuoles by golgi
Then form zymogen granules
- Secretory granules that appear dense
Zymogens granules secreted via exocytosis
Enzymes activated in the intestine by enzymatic cleavage
What is a haematological sign of pancreatic damage?
Pancretic enzymes appearing in blood (Amylase commonly looked for)
outline the control of Acinar secretion in the exocrine pancreas
Stimulated by cholecystokinin (CCK) during the Intestinal phase of GI control
- CCK released from duodenal APUD cells
CCK release stimulated by:
Some receptors also stimulated by gastrin due to receptor homology
Vagus nerve also stimulates via Ach during the cephalic phase of control (Advance secretion in preparation of food)
OUtline the process of ductal secretion in the exocrine pancreas
Ductal cells secrete HCO3-:
Basolateral Na+/K+ ATPase creates Na+ gradient across apical membrane
Basolateral Na+/H+ exchanger exports H+ to react with HCO3- in the ECF
CO2 and H2O taken into the cell and react
H+ produced is recycled
HCO3- is exported to duct lumen
How is ductal secretion in the exocrine pancreas controlled?
Stimulated by Secretin:
Secreted from jejunal cells
In response to low pH within jejunum
Action facilitated by CCK
What are the functions of the liver?
Plasma protein synthesis
Secretion of Bile (0.25-1.0L.day-1)
- Contains bile acids and alkaline juice for digestion as well as excreting bile pigments
Label this image
What does this image show?
Branch of hepatic portal vein
Branch of hepatic artery
Blood flow into the liver
Central canal (blood flow out of liver)
Image shows the components of a liver lobule (Functional unit)
What are the two components of Bile and where are they snythesised?
Bile acid dependent:
Secreted into canaliculi (which drain into branches of the bile duct) by hepatocytes
Contains Bile acids and pigments
Bile acid independent:
Secreted by duct cells
Alakaline juice like that of the pancreas
What are bile acids?
Give examples and describe function
Related to cholesterol:
E.g. Cholic acid, Chenodeoxycholic acid
Conjugated to amino acids
Travel in the bile as micelles containing bile acids, cholesterol and phopsholipids
Needed for digestion and absorption of fat
Outline the breakdown of globules of fat in the GI tract
Fats tend to form large globules as stomach acid breaks down natural emulsions
- Low surface area for enzymes
Bile acids emulsify the fat into smaller globules with increased surface area
Lipases have greater area to act and cleave fatty acids and glycerol
Colipase links bile acids and lipases to spread them over the surface of globules
What form do fatty acids take once lipase has separated them from glycerol?
Give a brief description of form and function
Polar groups of bile acids surround hydrophobic fats
4-6nm in diameter (20 lipid molecules)
Requires a certain conc of bile acids
Also sequesters cholesterol, ADEK vitamins and phospholipids
Carries the fatty acids throught he aqueous limunal contents to the unstirred layer next to epithelia
Fatty acids etc. are released and enter cells via diffusion
What happens to fatty acids once they enter the epithelial in the gut?
Resynthesised as lipids internally
Exported to lymphatics as chylomicrons
- Lipid coated with polar protein and phospholipids
Describe the enterohepatic circulation of Bile acids
Bile acids formed in liver and released into the bile duct
Released into lumen of the gut after fatty acids have been absorbed
Absorpted actively by terminal ileum
Return to hepatic portal blood to hepatic sinusoids
Hepatocytes actively take up and resecrete bile acids
Most bile acid recovered, some unconjugated by gut bacteria and lost
Hepatocytes synthesise more
How is the gall bladder involved in enterohepatic circulation of bile acids?
BAs returned to liver between meals
Secreted by canalicular cells well before needed next
Gallbladder used for storage
Gallbladder concentrates the BAs via uptake of water and salt across its epithelium
What is the problem with storing high concentration Bicle acid in the gallbladder?
High concentration increases risk of precipitation (stone formation)
Outline control of the enterohepatic circulation
CCK stimulates gall bladder muscle, ejecting bile acids along with enzymes from pancreas
What is the concequence of bile acids and pancreatic enzymes not being released in adequate amounts?
- Pale, floating, foul smelling
What are bile pigments?
Give an example and how it's formed and excreted
-Breakdown of haemoglobin produces an unconjugated form
- Conjugated in liver
- Secreted into bile
- Excreted in faeces
- Accumulates in blood with liver dysfunction leading to jaundice
Describe where the liver lies in the body using anterior surface markings/areas
Occupies mainly the right upper quadrant
Lies deep to ribs 7-11 on the right side and crosses the midline towards the left nipple
Liver occupies most of the right hypochondrium, the upper epigastrum and extends into the left hypochondrium
Label the image
Top to bottom:
Neutral respiratory position
Occupied 4-8cm at the midline
Occupies 6-12cm at right midclavicular line
Describe the surfaces of the liver and their relation
Convex diaphragmatic surface
Flatter visceral (postero-inferior) surface
Separated anteriorly by the inferior border that follows the right costal margin, inferior to diaphragm
Label this diagram
From top left clockwise:
Left triangular ligament
Round ligament (ligamentum teres)
Label this diagram
From top left clockwise:
Left triangular ligament
Right triangular ligament
What are the subphrenic reccesses?
What structure separates them?
Superior extentions of the peritoneal cavity (greater sac) between the liver (superior and anterior aspects and the diaphragm
Split into left and right recesses by the falciform ligament wich extends between the liver and the anterior abd. wall
What structure is found within the falciform ligament?
Round ligament, the embryonic remnant of the umbilical vein
What are the subhepatic spaces?
Portions of the Supracolic compartment of the peritoneal cavity directly infeior to the liver