PPP - digestive system Flashcards
Where does the digestion of carbohydrates start?
in the mouth by amylase in saliva
What are lymphatics important for in the GI tract?
intestinal absorption of fat
What are the major salivary glands?
sublingual, submandibular and parotid
What are the layers of the GI tract?
Mucosa
Submucosa
Muscularis externa
Adventitia/serosa
What are the stages of gastric acid secretion?
basal/fasting phase stimulated phases: - cephalic - gastric - intestinal
What are the secretions of the gastric pit cells?
neck cells - mucus
parietal cells - HCl
chief cells - pepsinogen
endocrine cells - gastrin
What happens when parietal cells are activated?
tubulovescicles fuse at the membrane to form the H+/K+ pump
What 3 factors regulated parietal cell secretion of HCl?
Ach, histamine, gastrin
What are the main components of pancreatic juice?
proteases, amylase, lipase and bicarbonate
What does CCK stimulate in the biliary system?
gallbladder contraction and relaxation of sphincter of Oddi
What does secretin do in the biliary system?
stimulates liver duct secretion
What is the relationship of bile with blood flow and pressure?
- bile flow has a linear relationship with blood flow to liver
- independent of pressure
What is the composition of bile?
bile acids, bilirubin, ions, cholesterol, phospholipids, fatty acids
How are bile acids concentrated?
- NaCl and HCO3- are taken up via Na-H and Cl-HCO3- exchanges
- Na+ moves to interstitial space via Na/K+ pump
- Cl- leaves via channels
- H20 follows ion movement, concentrated bile acids
How does bilirubin travel in blood?
bound to albumin
What is conjugated bilirubin?
when it is conjugated with glucaronic acid
How does obstructive jaundice occur?
blockage of bile ducts means conjugated bilirubin can’t be excreted
What happens to bilirubin when it is taken up by the liver?
conjugated with glucaronic acid and secreted into bile canaliculi
What is bilirubin broken down to for excretion?
urobilinogen
What is the total pool of bile acids?
around 3g
What happens to bile acids in the intestine?
95% are reabsorbed and brought back to the liver
How can liver clearance be measured?
BSP
How are medium and short chain fatty acids absorbed?
can pass through fenestrations directly into blood in stomach
When does the duodenum release CCK and GIP?
when fatty acids, low pH etc are sensed in the duodenum
How are lipids transported from the small intestine?
packaged into chylomicrons and exported into lacteals
What factors control bile secretion?
Vagus - increases
VIP and serotonin - decreases
Secretin - increases watery secretion (not bile salts)
What are the causes of gallstones?
- excess water in bile
- excess bile acid absorption
- excess cholesterol in bile
- epithelium inflammation
What is the purpose of saliva?
to lubricate food for swallowing and initiate starch digestion
What is the maximum rate of saliva flow?
1ml/min.g
What is the order of salivary ducts?
- acinar cells surrounding central lumen
- intercalated duct
- large ducts
- main excretory duct
What stimulates saliva secretion?
taste, smell, touch of food, chewing etc
What is the 2 stage process of saliva secretion?
- primary isotonic fluid produced by acinar cells
2. duct cells reabsorb Na+/Cl- and secrete K+/HCO3- to make hypotonic saliva
What stimuatles secretion in salivary acinar cells?
SNS -> noradrenaline on a/b receptors
PNS -> VIP and AcH (muscarinic)
What is the result of saliva acinar cell stimulation?
- intracellular rise in Ca2+
- activates basolateral K+ channel and Cl- luminal channel
- H20 and Na+ move into lumen paracellularly
What can cause hyposalivation?
gland atrophy caused by aging, drugs and disease
What type of epithelium is in the stomach?
simple columnar
- contains gastric pits and mucus cells
What is the turnover of cells in the stomach?
2-6 days
What are the features of cardia mucosa?
- highly coiled and branched
- mainly secretes mucus
- no peptic or parietal cells
What are the features of pyloric mucosa?
secrete alkaline mucus and electrolytes
- characterised by deep gastric pits
What are the features of the fundus and body mucosa?
- numerus gastric pits
- key HCl secretion
- G cells
What are the 3 regions of gastric pits?
- isthmus - parietal and neck cells
- neck - parietal and neck cells
- base - chief and endocrine cells
What can stimulate granule release in the stomach?
aspirin, food, stress, ethanol
What are the steps of acid secretion in the stomach?
- G-cells secrete gastrin
- gastrin acts on CCK receptor on ECL cells
- Release of histamine
- histamine acts on H2 receptors on parietal cells
- parietal cells release HCl
How is Hcl secretion in the stomach terminated?
- Hcl acts on D cells
- D cells release somatostatin which inhibts gastrin release from g cells
What is omeprazol?
A PPI
- prevents HCl release from parietal cells
- inhibits 80% of secretions
What is an alternative method of preventing HCl secretion?
H2 agonists
e.g. famotidine
What is omeprazol used to treat?
Peptic ulcers and reflux
What can other factors can stimulate parietal cells along with histamine?
- Gastrin on CCK2 receptors
- Ach on M3 receptors
How is the stomach protected from low pH
Bicarbonate rich mucus layer
What happens in the cephalic phase?
activated by smell, chewing etc
- vagus stimulation is sent to stomach in anticipation of digestion
What happens in the gastric phase?
- food enters the stomach
- stomach distention triggers acid secretion and gastrin release
What is the intestinal phase of digestion?
food enters the inestine and is sensed by duodenal cells -> release of pancreatic enzymes
What is zollinger-ellison syndroem?
gastrin-secreting tumours
- increase Hcl secretion
- cause peptic ulcers and other symptoms
What are the components of pancreatic juice?
high conc of bicarbonate, trypsinogen, chymotrypsinogne, other proteases, amylase, lipase
What is the type of fluid is secreted along with pancreatic juice?
NaCl-rich isotonic fluid
How is isotonic fluid made in the pancreas?
- Na/K/Cl cotransporter brings Cl into cells from interstitial space
- Cl- enters lumen via Cl channels
- Na+ and water move paracellularly
Where is CCK released from?
I-cells in the small intestine
What stimulates peristalsis in the stomach?
distention
What is the neuronal control of gut motility?
PNS via vagus - Ach +, VIP & ADP -
SNS: inhibitory via noradrenaline
What are the hormonal controls of gut motility?
Gastrin, CCK and motilin
What are the effects of gastrin and CCK on stomach motility?
increase antrum contraction and relax proximal stomach
-> reduces gastric emptying
What is the stomach plasticity?
it’s ability to maintain constant pressure until it contains 1L of food
What type of chyme moves fastest to the duodenum?
carb-rich > protein-rich
What are the plexuses of the enteric nervous system?
myenteric/auberbach’s & submucosal/meissner’s
What do the ENS neurones respond to?
mechanical and chemical stimuli and temperature
What type of neurons are in the ENS?
sensory, motor and interneurons
What are the effects of secretin?
increases bicarbonate secretion
inhibits stomach activity
what are the effects of CCK?
stimulates gallbladder
inhibits stomach activity
What are the effects of GIP?
inhibits gastric contractions
What are the effects of motilin?
increases motility