Digestion 3: Secretion Flashcards
secretion
release of materials from cells that line the lumen of the GI
Where do secretion products end up?
- ISF: paracine action
- blood stream
- lumen of GI
where can goblet cells be found?
small & large intestines
which cells secrete mucus in the stomach?
Foveolar cells
largest endocrine system in the body is…
enteroendocrine cells (EEC) - cells that secrete hormones in the GI
there are ___ types of EECs, and ___ types of GI hormones
18-20;
18-20
EEC function is influenced by…
- GI contents
- ANS
describe EECs
single cells scattered throughout the length of the GI; secrete hormones
Goblet cells refer to…
mucus secreting cells that is shaped like a goblet (more like a comma “,”)
we take in about __ L of fluid a day, but there is __ L of fluid entering the GI tract in total due to…
2L;
7L;
secretions from the liver, pancreas, etc.
how much is secreted & absorbed in toe GI tract per day?
9 L total input
secretions into the GI include…
- saliva
- bile
- gastric secretions
- pancreatic secretions
- intestinal secretions
secretions into the GI = ___x the volume of ____
2x;
plasma
how are fluids removed from the GI?
- absorption: small (main effect) & large intestines
- excretion: feces (small effect)
How is SA in the GI increased?
1) folds (3x)
2) hills & valleys (10x)
3) microscopic protrusions (20x)
SA increase method that can be found in the stomach
folds & valleys (no hills!)
rugae
folds on the inside of your stomach to allow expansion
valleys in the stomach =
gastric pits
gastric pits = opening to…
gastric gland
entrance to gastric glands are within the ___
rugae
anatomy: upper curve of the stomach
fundus
anatomy: antrum
nearly closed cavity located immediately before the stomach outlet. It is lined by mucosa and it does not produce acid
hills & valleys =
hills = villi valleys = crypts
SA increase methods that can be found in the small intestines
- folds (plica or valvulae conniventes)
- hills (villi)
- valleys (crypts of Lieberkuhn)
- microscopic protrusions (microvilli)
differences between rugae and plica
plica is in small intestines, and is permanent
Crypts of Lieberkuhn extend to…
into the mucosa of the small & large intestines
SA increase in large intestines
1) folds (haustra)
2) valleys (crypts of Lieberkuhn) - no hills!
haustration
when food pushes the haustra outwards, creating bulges & increased SA
what causes haustra in the large intestines?
lack of resistance underlying the circular muscle in the large intestine during segmentation
what can haustration be classified as?
motility pattern
microvilli is supported by…
why?
microfilaments;
allow microvilli to waves around to increase flow in small intestines
celiac disease
- immune disease where patients allergic to gluten
- microvilli are shorter → less SA → less absorption of nutrients → malnutrition
where are goblet cells found in the small intestines?
between the epithelial cells making up the villi
salivary gland is made up of…
1) parotid gland
2) sublingual gland
3) submandibular gland
saliva contains….
- water
- electrolytes
- bicarb
- mucus
- IgA antibody
- lysozyme
- defensins
- enzymes (salivary amylase & lingual lipase)
function of saliva
- protection
- lubrication (try to prevent secondary peristalsis)
- taste
- digestion
defensins
antimicrobial proteins that break bac’t cell walls
salivation is controlled by…
CNS (salivary center in medulla)
conditioned response to salivation vs. unconditioned response
unconditioned: mechanoreceptors & chemoreceptors sense food in the mouth
conditioned response: see, smell, etc. becomes associated with taste of food
conditioned response to salivation
sight/smell of food → cerebral cortex → salivary center (medulla) → salivation
salivary center is at…
pons / medulla
effect on salivation: PNS vs. SNS
PNS: lots of watery saliva
SNS: small amount of thick saliva
PNS control on salivation (process)
salivary center → CN VII, IX → salivary glands → watery saliva
SNS control on salivation (proess)
thoracic spinal cord → pelvic nerves → superior cervical ganglion → post-ganglion fibres → salivary glands → thick saliva
what secretory cells are found in the stomach (order from lumen → gastric pit → gastric gland)?
- mucous cells
- parietal cells
- chief cells
- enterochromaffin-like cells
- D cells
- G cells
mucous cells secrete…
- mucus
- bicarb
parietal cells secrete…
- HCl
- intrinsic factor
chief cells secrete…
- pepsinogen
- gastric lipase
enterochromaffin-like cells secrete…
histamine
D cells secrete…
somatostatin
G cells secrete…
gastrin
physical layer of production in the stomach is ___, while chemical layer of production is ___
mucus;
bicarb
Zollinger-Ellison syndrome
hyperacidic stomach that breaks down protective barriers and damages cells of the stomach
pH of stomach lumen
2
symptoms of ZE syndrome
- GERD
- nausea
- pain
- malnutrition
- heartburn
GERD
reflux of acidic chyme up the esophagus → dull chest pain
function of HCl in stomach
- kill bacteria
- denature protein
- activate pepsinogen
function of intrinsic factor
binds to vit B12 → proper absorption in ileum
vit B12 is also known as…
cobalamin
How does parietal cells secrete HCl?
1) water dissociates to H+ and OH-
2) H+ is pumped into lumen by H/K-ATPase
3) OH- + CO2 → bicarb (catalyzed by CA)
4) bicarb leave on basolateral side using Cl/bicarb-exchanger
5) Cl- is pumped into lumen by Cl-transporter
6) Cl joins with H in lumen to form HCl
Alkaline tide
build up of bicarb in ISF of stomach (parietal cells), so blood leaving the stomach is very basic
how to activate pepsinogen?
- Acid in stomach
- Pepsin (activates itself)
function of gastrin
- stimulates secretion of acid, histamine, pepsinogen, mucus
- increase stomach motility & mass movements (gastrocolic reflex)
what stimulates release of gastrin?
peptides in the lumen of the stomach
G cells are mostly found in ___ region of the stomac
pyloric
2 ways in which gastrin can stimulate the release of HCl (and describe)
1) directly: gastrin → bloodstream → parietal cells → secrete HCl
2) indirectly: gastrin → bloodstream → enterochromaffin-like cells (ECL) → histamine → parietal cells → secrete HCl
gastrin is responsible for ___ reflex
gastrocolic
cause of ZE syndrome
hypersecretion of gastrin
- gastrin secreting tumour in pancreas
which cells in the pancreas secrete things? where are they secreted into?
- acinar cells
- duct cells
secreted into pancreatic duct
what do acinar cells secrete?
- pancreatic amylase, lipase, nuclease, inactive protease
proteases secreted by acinar cells
- trypsinogen
- chymotrypsinogen
- procarboxypeptidase
- proelastase
duct cells secrete…
- bicarb
- water
pancreatic secretions into the small intestines is controlled by…
sphincter of Oddi
How are pancreatic enzymes activated in the small intestines?
by enterokinase / enteropeptidase
enterokinase
enzymes embedded in brush border that is required for the activation of proteases secreted by the pancreas
how is bicarb secreted in the GI tract? (slide 20)
1) water + CO2 dissociate → bicarb + H (catalyzed by CA)
2) bicarb goes into lumen via bicarb/Cl-exchanger
3) H leaves the cell via NHE
4) NKCC transporter pumps stuff into lumen
5) Cl leaves cell via CFTR to lumen
6) Na leaves the cell to ISF via Na/K-ATPase
Why is the blood leaving the pancreas / small intestines acidic?
bicarb is secreted in lumen while H is secreted into ISF
- this balances alkaline tide from stomach
CFTR
cystic fibrosis transmembrane regulator
how is water secreted in the GI tract?
- Na attracted to lumen because it’s very negative from bicarb and Cl-
- water is attracted to solutes in lumen
- both transported to lumen via paracellular pathway
only way for Cl to exit in the lumen is…
CFTR
Why do people with cystic fibrosis have to ingest ____? Why?
pancreatic enzymes;
- defective CFTR channels
- no watery bicarb (only thick mucus from duct cells)
- mucus blocks pancreatic duct
- no enzymes can reach small intestines
- no digestion
bile is made up of…
- bile salts
- lecithin
- cholesterol
- bilirubin
- bicarb
where does bile come from?
- synthesized by liver
- diet
- secretions from duct cells
- remainders from body (e.g. bilirubin, cholesterol)
bile salt recycling =
enterohepatic circulation
bile salt recycling happens ___ x per day
5 - 15
define: enterohepatic circulation
cycling between the liver and small intestines
- connected by hepatic portal vein
primary bile acids are synthesized by…
liver
secondary bile acids are syntheiszed by…
bacterial conversion in intestines
bile acid → bile salt
conjugation with glycine or taurine (amino acids)
difference between bile acid vs. bile salt
bile acid is lipophilic, so it wants to leave the lumen;
bile salt is conjugated, so can be soluble in the lumen
process of bile salt recycling
1) liver makes primary bile acids
2) gets conjugated and enters small intestines
3) return to hepatic portal vein by…
- passive transport
- active transport
- bacteria mediated absorption (→ bile acids or continue → secondary bile acids)
4) goes back to liver
bacteria mediated absorption
convert bile salt → bile acids so it can easily cross epithelial membrane
convert the bile salt → bile acid → secondary bile acid → reabsorbed or lost in feces
fate of secondary bile acids
reabsorbed or lost in feces
secondary bile acids (specific names and fate)
[MAYBE NOT ACCURATE]
- deoxycholic acid (reabsorbed)
- lithocholic acid (lost)
what hormone is released by the stomach?
gastrin
what hormones are released from small intestines?
- secretin
- CCK
- GIP
- Motilin
- GLP-1
glucose-dependent insulintropic protein is secreted from…
K cells (mostly jejunum, some duodenum)
why is GIP secreted?
in response to mixed meal (glucose, fat, protein)
effect of GIP
- increase insulin
- decrease acid
motilin is secreted by…
M cells
when is motilin secreted?
during fasting
function of motilin
regulates migrating motor complex (MMC)
secretin is secreted by…
S cells in duodenum
function of secretin
decrease acid in small intestines
- more pancreatic bicarb
- less gastric acid secretion
- less gastric emptying
CCK is secreted by…
I cells in duodenum and jejunum
CCK is secreted in response to…
fatty acids & AA in small intestines
CCK causes…
- contraction of gall bladder (more bile)
- increased release of pancreatic enzymes (increase small intestines)
- decreased gastric acid secretion & gastric emptying (slow stomach)
GLP-1 (glucagon-like peptide-1) is secreted by…
L cells of the ileum
GLP-1 is secreted in response to…
fatty acids & cabs in the small intestines
effects of GLP-1
- decreased gastric acid secretion & emptying (slows stomach)
- increased insulin & B-cell growth; decreased glucagon
GLP-1 causes feeling of…
satiation
