Lecture 5: pancreatic secretions and the spleen Flashcards
What are the functions of the pancreas?
- it has 2 distinct functions in the body
- acts as an** endocrine gland** - secretes hormones insulin & glucagon into the bloodstream
- also has exocrine functions, it acts as an accessory digestive organ that secretes enzyme rich fluid into the duodenum through a series of ducts
Describe the** structure of ducts in the pancreas
- the pancreas is made up of lobules consisting of acinar cells that secrete enzymes and fluid into a system of microscopic ducts
- these ducts then drain their enzymes into the interlobular ducts which in turn are emptied into the main pancreatic ducts
What is another name for the main duct in the pancreas?
Duct of Wirsung
What is the accessory pancreatic duct called? what is it’s function?
- duct of santorini
- this duct drains directly into the duodenum
What cells are involved in the **endocrine function **if the pancreas?
- islet of langerhans
- they secrete insulin and glucagon
What type of cells are involved in the exocrine function of the pancreas?
acinar cells and ductal cells
* acinar cells produce enzymes
* ductal cells produce the aqueous component
what are the 2 components in pancreatic juice?
- aqueous (watery) component
- enzymatic component
What is the exocrine pancreas stimulated and inhibited by?
- stimulated by the vagus nerve
- inhibited by the sympathetic system
What is the aqueous component of pancreatic juice composed of?
- produced by centroacinar ductal cells
- fluid is slightly hypertonic, rich in bicarbonate ions (Na+ and K+ ions conc similar to plasma lvl)
What is the function of the bicarbonate in the aqueous component of pancreatic juice?
- to neutralise the gastric acid that flows into the duodenum
what hormone stimulates the secretion of bicarbonate from duct cells?
the hormone secretin
How is the aqueous component produced by ductal cells?
- Bicarbonate is** formed in the cell by the enzyme carbonic anhydrase - needs co2 and w**ater
- bicarbonate also comes from the basolateral HCO3/Na+ symporter
- bicarbonate is secreted into the pancreatic duct in exchange for chloride in the apical membrane (2 diff channels)
What are the** 2 types of chloride channels** located on the apical membrane of the duct cell?
- CFTR Cl- channel which is regulated by cAMP NB this one is important for normal HCO3- secretion
- calcium dependent chloride channel
What is the ionic composition of the bicarbonate dependent on?
it is dependent on the flow rate of the pancreatic juice
* ie if the flow rate is low, the bicarbonate concentration of secretion is low
how is the pancreatic secretion of the aqueous component controlled?
- TO DO WITH LVL OF ACID IN SI
* if there is an increase in acid in the stomach, the S cells in the SI will release more secretin
* an increase in [secretin] in the plasma will cause an increase in bicarbonate secretion from the pancreas into the SI
* this will then neutralise the acid in the SI
Give a summary of the key points involving the aqueous component of pancreatic juice
What is the enzymatic component of pancreatic juice produced by? what is the component composed of?
produced by : acinar cells
* digestive enzymes
* including - amylase, DNAase, RNAase, 3 lipases and 3 proteolytic enzymes
what hormone stimulates the secretion of enzymes by the acinar cells?
CCK released from the I cells of the duodenum and jejenum
What are the 3 lipases in the enzymatic component?
- triaglycerol hydrolase
- cholesterol ester hydrolase
- phospholipase
What are proteolytic enzymes? What are examples of them in the enzymatic component?
- enzymes that play an important role in protein digestion
- examples : trypsinogen which is activated by enterokinase on the duodenum brush border to trypsin
What 2 proteolytic enzymes does trypsin activate?
- chymotrypsinogen
- procarboxypeptidase
How is the pancreas’ enzymatic secretion controlled?
by the level of intestinal fatty acids and amino acids
* if there is an increase of ^^, then the small intestine will increase CCK secretion
* CCK acts on the acinar cells and increases the enzymatic secretion and therefore increases the flow of enzymes into the pancreas
What is pancreatitis?
- a disease characterised by the inflammation of the pancreas
what is pancreatitis caused by?
- gall stones (stone in gallbladder made of precipitate of bile components - ie solids leave solution)
- excessive alcohol
- infection
what is a good method used to diagnose pancreatitis?
- measurement of the serum lipases
What is the spleen?
an organ of the lymphatic system
what is the function of the spleen?
- it’s main function is to filter blood - ie can remove old rbc’s
- contains red pulp which functions to remove red blood cells and recycle iron
- contains white pulp which contains lymphocytes that produce antibodies
