pancrease Flashcards
descirbe the sorounding structures of the pancrease
look up on google
where is teh pancrease
a long, flat gland that lies horizontally behind your stomach. It has a role in digestion and in regulating the level of sugar in your blood.
draw a ct scan of the pancrease
draw
define endocrine
: Secretion into the blood stream to have effect on distant target organ (Autocrine/Paracrine) - Ductless Glands
defien autocrine
: Secretion into a duct to have direct local effect
Q. What are the main endocrine secretions of the pancreas & their actions?
Insulin: anabolic hormone
promotes glucose transport into cells & storage as glycogen
↓ blood glucose
promotes protein synthesis & lipogenesis
Glucagon: ↑s gluconeogenesis & glycogenolysis (↑s blood glucose)
Somatostatin: “Endocrine cyanide”
what makes up the endocrine of the pancrease
Islets of Langerhans
what is secreated by the islets of langerham
Secrete hormones into blood - Insulin & Glucagon (also Somatostatin and Pancreatic Polypeptide)
what are the function of each of the hormones
Regulation of blood glucose, metabolism & growth effects - (Endocrine course)
what is the exocrine function of the gland
Secretes pancreatic juice
Digestive function
where is pancreatic juice secreated
into duodenum via MPD/sphincter of Oddi/ampulla
what are acinini in the pancrease
Ducts
Acini are grape-like clusters of secretory units
what is teh function of the acinar cells
Acinar cells secrete pro-enzymes into ducts
what are islets in the pancrease
Formation of acini & islets from ducts in various stages of development
what do islets differntiate into
α- and β-cells secreting into blood
where are the islets higher in head or tail
tail
what is the compisition of teh islets
α-cells
β-cells
δ-cells
Acini
what is the function of the a cells
form about 15-20% of islet tissue and secrete glucagon
b cells
form about 60-70% of islet tissue and secrete insulin
delta
form about 5-10% of islet tissue and secrete somatostatin
what is another function of the islets
The islets are highly vascular, ensuring that all endocrine cells have close access to a site for secretion
how are acinar cells illustrated on a microscope sample
exocrine pancreatic cells
Large with apical secretion granules
big circle in them containg other smaller circles
how do ducts look like
Small & pale
how many components are the to the pancreatic juice
2
what are they
↓ (low) vol, viscous, enzyme-rich
↑ (high) vol, watery, HCO3- rich -
what secraetes the high vol, watery, HCO3- rich -
Duct & Centroacinar cells
what secreates the low vol, viscous, enzyme-rich
Acinar cells
so what produces teh bicarbonate secreation
duct & centroacinar cells
what does the p juice contain
↑ bicarbonate
~ 120 mM (mmol/L) - (plasma ~25 mM)
pH 7.5-8.0
what are the function of the pancreatic juice (x4)
Neutralises acid chyme from stomach
prevents damage to duodenal mucosa
Raises pH to optimum range for pancreatic enzymes to work
Washes low volume enzyme secretion out of pancreas into duodenum
what occurs when the deodenal ph goes from 5 to 3
linear ↑more in pancreatic HCO3- secretion
then platueas at ph of 3
what occurs when the deodenal ph is less than 3
→ not much more high in HCO3- secretion
Q. Why does HCO3- secretion stop when pH is still acid?
Bile also contains HCO3- and helps neutralise acid chyme (liver functions lecture).
Brunners glands secrete alkaline fluid (Small intestine lecture
what is the production of hco3- cataylsed by
when c02 enters the pancraetic duct cell combining with water to form h+ and hc03-
carbonic anhydrase
where does sodium move to and from
blood to lumen
how dies it move
down gradient via paracellular (“tight”) junctions
how and where does water move
follows h20 from blood to lumen
through paracellular junctions
how is the hco3- able to move out of the pancreatic duct cell to pancreatic duct cell
Cl-/HCO3- exchange at lumen (anion exchanger [AE])
How can the H+ movw out of teh PDC to the blood
Na+/H+ exchange at basolateral membrane into bloodstream (sodium-hydrogen exchanger (antiporter) type 1 [NHE-1])
what causes the exchanges to occur
High ElectroChemical gradient (blood) Na+ compared to IC (duct cell)
High Cl- in lumen compared to IC (duct cell)
(for that you must mantain the gradient)
what are the 2 exchanges
Cl-/HCO3- exchange at lumen (anion exchanger [AE])
Na+/H+ exchange at basolateral membrane into bloodstream (sodium-hydrogen exchanger (antiporter) type 1 [NHE-1])
How is the sodium gradient mantained
Na+ gradient into cell from blood maintained by Na+/K+ exchange pump
is it an active or a passive process
Uses ATP - Primary active transport
where do the k+ and cl- move back to
k+ ->returns to blood
Cl- ->returns to lumen
how is ch- returned to blood
via Cl-channel (cystic fibrosis transmembrane conductance regulator [CFTR]) doesn’t work properly with people with cf
and how is k+ returnes to blood
via K+-channel
what is the reaction to produxe pancreatic juice
H2O + CO2 H2CO3 H+ + HCO3-
Same reaction in gastric parietal cells (acid) and pancreatic duct cells (alkaline)
what is the relative ph of the gastric venous blood
H+ secreated into gastric juice
HCO3- secreated into blood
Thus
Gastric venous blood is alkaline
Ph of Pancreatic blood is
HCO3- secreted into pancreatic juice
H+ secreated into blood
Pancreatic venous blood is acidic
what do acinar cell enzyme secreations do and what enzymes
fat (lipases)
protein (proteases)
carbohydrates (amylase)
how are the enzymes
Zymogens = pro-enzymes
where are they stored and sythesised
→ synthesised & stored in zymogen granules
Q. What might be the problem for an organ making a cocktail of digestive enzymes?
You could start digesting yourself so you need saftey mechanisms
Proteases are released as inactive pro-enzymes
protects acini & ducts from auto-digestion
Pancreas also contains a trypsin inhibitor to prevent trypsin activation
Enzymes only activated in duodenum
Blockage of MPD may overload protection -> auto-digestion (= acute pancreatitis)
what is the Duodenal mucosa secretes an enzyme and where is it produced
Enterokinase (enteropeptidase)
brush border
what does it do
converts trypsinogen -> trypsin.
what is the function of trypsin
Trypsin then converts all other proteolytic & some lipolytic enzymes into active form
are the pancreatic secraetions modifiable
Pancreatic secretions adapt to diet:
e.g. ↑ protein, ↓ carbs → ↑s proportion of proteases & ↓ proportion of amylases
what can a lack of pancreatic enzyme cause
Pancreatic enzymes (+ bile) essential for normal digestion of a meal: Lack of these can → malnutrition even if dietary input is OK. (unlike salivary, gastric enzymes)
Q. Anti-obesity drug Orlistat inhibits pancreatic lipases – what side effects might you expect?
more increased faecal fat
occurs when pancreatic lipase secretion ↓ed
e.g. cystic fibrosis, chronic pancreatitis, Orlistat (↓s intestinal fat absorption)
what are the 3 stages to the pancreatic juice secreation
Cephalic phase
Gastric phase
Intestinal phase
what is the cephalic phase
Reflex response to sight/smell/taste of food
Enzyme-rich component only.
Low volume - “mobilises” enzymes
secreation of enzymw rich component from acini only
what is the gastric phase
Stimulation of pancreatic secretion originating from food arriving in the stomach
Same mechanisms involved as for cephalic phase
what is the intestinal phase
Hormonally mediated when gastric chyme enters duodenum.
BOTH components of pancreatic juice stimulated
enzymes & HCO3- juice flows into duodenum
how is Pancreatic juice enzyme secretion controlled in acini by:
- Vagus nerve –
Cholinergic
Vagal stimulation of enzyme secretion (& communicates information from gut to brain) - Cholecystokinin (CCK) (Ca2+/PLC)
Pancreatic juice bicarbonate secretion controlled in duct & centroacinar cells by:
Secretin (cAMP)
how do the abdominal accesory organ grow
as foregut outgrowtha
does everyone have a accessory pancreatic duct
no
where are the transverse colon and stomach to the pancrease
anterior
what are the parts of the pancrease
head neck body tail
where does the pancrease fit
head of pancrease fits in deodum
what do the pancreatic acinus sorround
duct
what are between the pancreatic acinar cells
cellular canaciculi
how is enzyme secreation controllled in acini
vagus via ach stimulates pancrease to produce pancreatic enzymes
how is CCK controlled (where realased as well)
stimulation
secreated from duodenal I cells
stimulated by fatty acid and amino acids in the lumen of the duodenum
how is CCK inhibited
via trypsin
is the acinar fluid more or less concentrated in ions that the plasma
acinar is isotonic so same
what stimulates release of acinar fluid and protiens it contains
CCK
what does secretin do
stimulates secretion of H2O & HCO3- from cells lining extralobular ducts.
why
in response for absorption in CL-
what is richer is in hco3- out of acinar fluid or secretin stimulated secreation
Secretin-stimulated secretion is richer in HCO3−cf acinar secretion because of Cl−/HCO3−exchange
how is hco3- secreation controlled
secretin
negative feedback loop in response to low luminal ph in duodenum
what happens
low ph in duodenem
stimulates s cells
secretin released
pancreatic and ductal hco3- secreation
how much does hco3- get secreated when cck acts alone
no effect alone
same with vagus nerve
secretin has a minumun affect alone
what produces the biggest affect
both cck and secretin
how does secretin effect enzyme secreation
no effect
outlines what happens when you have a meal
Food mixed, digested in stomach, pH 2
Chyme squirted into duodenum
H+ ions in duodenum -> ^ secretin -> ^pancreatic juice
+ bile & Brunner’s gland secretions
both causing ^s pH to neutral/alkaline.
Peptides & fat in duodenum cause sharp ^ in CCK & vagal nerve stimulation
-> stimulates pancreatic enzyme release
Peaks by 30 mins, continues until stomach empty.
CCK potentiates effects of secretin on aqueous component
Necessary as most of duodenum not at low pH
