GIT Physiology Flashcards
Parasympathetic innervation
- Long preganglionic (ACh)
- short postganglionic (ACh/ peptides)
Sympathetic innervation
- short preganglionic (ACh)
- Long postganglionic NE
Where is gastrin secreted
stomach
Where is secretin, cholecystokinin and gastric inhibitory peptide
duodenum/ jejunum
Function of saliva
buffer digests dilutes protects cleanses
acinar cells move in which direction?
blood to lumen
duct cells move in which direction?
Blood to lumen or lumen to blood
What type of secretion is parotid
thin, watery (PNS)
what type of secretion is sublingual
serous, thick (SNS)
submandibular
mixed
Mechanism of salivary secretion
isotonic –> hypotonic
(Na, Cl, K, HCO3 enter)
(K + HCO3 secreted in lumen, while Na Cl secreted into blood and H20 can’t get into blood)
Neural control?
parasympathetic main controller –> initiates and maintains salvation
Mechanism of pancreatic secretion
isotonic –> isotonic
Na + K is same
what does cholecystokinin (CCK)
I cells
stimulates the release of enzymes
What does secretin do?
S cells
natural antacid
stimualtes the release of bicarbonate
Small intestine where does absorption and secretion occur
absorption in villi (Na)
secretion in cyrpts (Cl)
A>S
What is succus entericus
- ions, water and mucus
- intestinal juice which is secreted in SI
gastric juice into lumen?
- mucus
- pepsinogen
- HCl
- intrinsic factor
secretions from paracrine into lamina propria
- gastrin (stimulates acid secretion)
- somatostatin (inhibits acid secretion)
- histamine
What cells secrete Gastrin
G cells in pyloric region
what cells secrete somatostatin
D cells in pyloric region
what cells secrete pepsinogen
chief cells
what cells secrete histamine
Enterochomaffin-like cells
what cells secrete HCl and intrinsic factor
parietal cells
Resting vs stimulated parietal cell
resting:
- basal levels of acid production, SA lumen is reduced
active:
- the lumen incr
- no. of pumps
Parietal cell via vagus nerve (direct)
- vagus nerve release ACh
- ACh stimulates M3 receptors
- M3 receptor stimulates parietal cells –> incr. intracellular conc of ca
- As [Ca] incr. it then binds with Calmodulin which stimulates K pump
histamine stimulation of parietal cells
- Histamine stimulates H2 receptors on parietal cells
- Stimulation of H2 receptors cause on increase in cAMP in parietal cells
- cAMP combines with Protein Kinase A and stimulates the H/K ATPase pump
ECL via vagus nerve (indirect)
- The vagus nerve releases ACh
- ACh stimulates M3 receptors
- ECL cells release Histamine
- Histamine stimulates H2 receptors on parietal cells
- Stimulation of H2 receptors cause on increase in cAMP in parietal cells
- cAMP combines with Protein Kinase A and stimulates the H/K ATPase pump
G cell (indirect)
- G cells secrete gastrin
- Gastrin is an endocrine secretion which stimulates ECL cells
- ECL cells release histamine
- Histamine stimulates H2 receptors on parietal cells
- Stimulation of H2 receptors causes an increase in cAMP in parietal cells (ATP binds –> cAMP –.> AMP via phosphodiestrase)
- cAMP combines with Protein Kinase A and stimulates the H/K ATPase pump
Feedback Regulation of HCl secretion
• G cells
o Gastrin (stimulates histamine release) o Incr. HCl production (mostly indirect)
Feedback Regulation of HCl secretion
- D cells
o Somatostatin
o Inhibits HCl production
Cephalic phase (30%)
thought/ smell of food
- vagally mediated
- stimulatory
- incr. motility
Gastric phase (50-60%)
part vago-vagal, part enteroendocrine
- stimulatory
- inc. motility
intestinal phase (10-20%)
inhibitory (turn off acid production)
enteroendorcrine
- decr. motility
vitamin B12 absorption steps
- cobalamin is bound to food
- pepsin and gastric acid release the cobalamin from food
- salivary and gastric glands to release haptocorrin which binds to cobalamin
- pariteal cells release IF
- the pancreas releases proteases and biocarbonates which degrades the haptocorrin and cobalamin is released
- IF-cobalamin complex forms
- IF cobalamin complex absorbed in terminal illeum
absorption of non-polar
intestinal epithelium via simple diffusion
absorption of polar substances occurs where and how
carrier mediated transport either active or passive
what are the dissachrides and what they made of
- Sucrose: fructose + glucose
- lactose: glucose and galactose
- maltose: glucose + glucose
Digestive process for carbohydrates
- luminal
2. membrane
intraluminal digestions - amalyase purpose?
to breakdown the polysacchrides down the middle, can’t cleaf the ends, can’t make glucose
Polysaccharides disaccharides, oligosaccharides (a few sugars in a chain)
membrane digestion
- Small intestional brush border enzymes (apical membrane of villus epithelial cells)
- Disaccharides, oligosaccharide monosaccharides (absorbable units)
SGLTI at brush border allow what to pass through
glucose/ galactose / Na
GLUT5 what passes through
fructose - all products empt into blood
Proteins to produce olipeptides and AA
Endopeptidases (aka proteases e.g. pepsin) –> can’t cleave off AA
exopeptidases –> can produce individual AA
protein process
- luminal
- membrane
- cellular
Luminal protein
gastric (pepsin) and pancreatic proteases (inactive form, as if active would be digested by pancreas)
when is pepsin active and not
pepsin is active at acidic pH
Pepsin is denatured in the duodenum when the pH rises
pancreatic exocrine secretion in protein luminal
- proteases (inactive)
- amalyses/ lipases (Active)
enzymatic component (acinar cells)
proteases (inactive)
- trypsinogen –> trypsin (once activated other proteases activated)
- Chymotrypsinogen chymotrypsin
- Procarboxypolpeptidase carboxypolypeptidase (can cleave an individual peptide)
- Proelastase elastase
cellular
AA absorption
Lipids digestion
entirely luminal
triglyceride
lipase –> FFA + Monoglycerides
Bile salts synthesis
- liver conjugates the bile acid with glycine to form bile salts
- conjugation makes the bile acids more water soluble at dudodenal pH
Thus bile salts are water soluble yet ampipathic
luminal lipid digestion
- emulisfication
- lipase action
- micelle formation
emulification
break up large fat drops to smaller ones
Lipase action
digests lipids into absorbable units (creates SA to allow lipase action)
micelle formation
transports products of digestion to luminal surface for absorption
hydrophillic shell outside and hydrophobic core inside
bile salts are
recycles
biliary secretion
- Yellow-green “soapy” solution
- Electrolytes – bicarbonate rich
- Important components include
o Bile salts (including bile acids) – 50%
o Phospholipids (lecithin and others) – 40%
o Bilirunin – 2% (to be eliminated)
o Cholestrol – 4% (to be eliminated) - ONLY Bile salts and lecithin aid digestion
Neural control of motility
PNS: motilin, increases motility
SNS: secretin, GIP, decrease motility, decr. acid secretion.
Oesophagus
- motility
- function
- control
Motility:
Swallowing
Peristalsis (progressive wave of SM contraction) – Primary and secondary
Function: move food –> stomach
Control:
- Initially voluntary then reflex
- Distention signals CNS to produce changes in muscle contraction
Gastric motility:
- motility
- function
- control
motility: relaxation (accomodates for food) and peristalis
Function: mixes and empties the stomach
control: cephalic, gastric, intestinal
gastric motility - storage Receptive relaxation
oesophageal gastric reflex initiated by pharynx with each swallow
Even before food has entered stomach, it prepares to receive by relaxing stomach
Adaptive relaxation (gastro-gastric reflex)
initiated by the stomach
Enterogastric reflex
o Food in intestine gastric relaxation
o food leaves stomach, control the rate of food entering into the intestine, if food enters too quickly it can affect fluid movement. Food enters intestines, decreases motility of the stomach
Small Intestine – Interdigestive phase
• Fasting- interdigestive patterns o MMC migrating myoelectric (motor) complex o From stomach to terminal ileum o Repeats every 90 minutes or so o Mediated by Motilin o Moving debris from stomach to LI
Gastroileal reflex
a feedforward reflex
-pushes valve open and relaxes sphincter
illeocecal valve: pushes valve closed and contracts sphincter
Feedback
slow organ above
o Enterogastric (neural) enterogastrone (hormonal)
Inhibits gastric emptying when duodenum distended
o Ileogastric/ ileojejunal/ ileal brake
Slows gastric or jejunal emptying when ileum distended
o Mostly achieved by increased sphincter tone; the stomach will not be emptying as quickly
Feedforward
stimulates organ below
o Gastroileal, gastrocolic reflexes
Stimulate ileal or colonic emptying when stomach is distended
o Most achieved by decreased sphincter tone
defaecation relfex
- rectal distention
- rectum contracts
- internal anal sphincter relaxes
- increased tone in the external anal sphincter