physl 210 GI ALL

what are the 3 layers of the mucosa?

what are the 3 layers of the mucosa?

epithelium

lamina propria

muscularis mucosa

what are the 4 layers of the GI tract?

mucosa

submucosa

muscularis externa

serosa

paracellular pathway

between cells (through tight junction)

transcellular pathway

across a cell

which layer of GI tract has a plexus of nerve cell bodies?

submucosa

is muscularis mucosa involved in contraction of GI tract?

no

3 parts of the muscularis externa?

-thick inner layer of circular muscle (narrow) -myenteric nerve plexus -thinner outer layer of longitudinal muscle (shorten)

where does blood flow to after it perfuses the intestine?

liver via the portal vein

what is the purpose of portal circulation?

allows liver to remove harmful substances & process nutrients (liver=filter)

why is the liver unusual?

receives blood from venous & arterial circulation

(blood to liver = low O2, high nutrient)

what are GI reflexes initiated by?

-distension of wall -osmolarity -pH -concentrations

can the GI system function independently of the CNS?

yes

what does the myenteric plexus influence?

smooth muscle

what does the submucosal plexus influence?

secretion

what does the ANS influence in the GIT?

-motility -secretion

what happens during rest/digest?

-stimulate flow of saliva (thick) -stomach: stimulate peristalsis and secretion -liver: stimulate release of bile

what happens during flight or flight?

-stimulate flow of saliva (thin) -stomach: inhibit peristalsis & secretion

4 GI hormones

-secretin -cholecystokinin (CCK) -gastrin -glucose dependent insulinotropic peptide (GIP)

what releases hormones?

lamina propria

what triggers CCK secretion?

fatty acids & amino acids in small intestine

what does circulating CCK stimulate?

-pancreas to increase digestive enzyme secretion -gall bladder contraction -release of bile acids for fat breakdown

what causes stimulation of CCK to stop?

when the fats & amino acids are absorbed

gastrin - major release site

stomach antrum (G cells)

gastrin - major stimuli for release

-peptides/amino acids in stomach -parasympathetic nerves

gastrin - major actions

-increase HCl -increase motility (stomach, ileum, large intestine)

secretin - major release site

small intestine (S cells)

secretin - major stimuli for release

acid in small intestine (pH < 4.5)

secretin - major actions

-decrease HCl -decrease stomach motility -increase HCO3-/H2O from pancreas & in bile

CCK - major release site

small intestine (I cells)

CCK - major stimuli for release

digested fat/protein in small intestine

CCK - major actions

-decrease HCl -decrease stomach motility -increase enzymes from pancreas -increase bile expulsion

GIP - major release site

small intestine (K cells)

GIP - major stimuli for release

glucose or fat in small intestine

GIP - major action

increase insulin

in peristalsis: which muscle contracts & which one relaxes?

-circular muscle contracts on oral side -longitudinal layer relaxes

where does segmentation occur? what happens?

-small intestine (mostly) -mixes contents with digestive enzymes -slows transit time to allow absorption of nutrients & water

where are the pacemaker cells? what do they do?

-smooth muscle cells -causes slow waves which cause the basic electrical rhythm

what are the slow waves propagated through?

gap junctions (between circular & longitudinal muscle layer)

hypothalamus: where is the feeding centre? what happens when this is activated? what happens when there is a lesion here?

-lateral region -activation increases hunger -lesion: weight loss

hypothalamus: where is the satiety centre? what happens when this is activated? what happens when there is a lesion here?

-ventromedial region -activation makes you feel full -lesion: obese

what are the 2 orexigenic factors? what do they do?

-neuropeptide Y (NPY) -ghrelin

makes you eat

what are the 4 anorexigenic factors? what doe they do?

-leptin -insulin -peptide YY -melanocortin

makes you not eat

what does neuropeptide Y do?

-neurotransmitter that stimulates hunger

when is ghlerin synthesized and released? what does it stimulate the release of?

-in stomach during fasting -stimulates release of NPY & other neuropeptides in hypothalamus feeding centre

where is leptin released from?

adipose

where is insulin released from?

pancreas

where is peptide YY released from?

intestines

where is melanocortin released from?

hypothalamus

how do you stimulate the thirst centre in the hypothalamus?

-increased plasma osmolarity (osmoreceptors) -decreased plasma osmolarity (baroreceptors) -dry mouth/throat -prevention of over-hydration

what happens when vasopressin is released?

water is conserved @ kidney

what activates the renin angiotensin system? what does it do?

-baroreceptors in kidney afferent arteries -production of angiotensin II (increase thirst)

what is saliva composed of?

-water -electrolytes -digestive enzymes -glycoproteins -other

saliva is rich in which electrolytes and poor in which electrolytes?

-rich in K+, HCO3- -poor in Na+, Cl-

what do the acinar cells do?

secrete initial saliva (initially isotonic)

what do the ductal cells do?

modify the initial saliva to a hypotonic & alkaline state

is the salivary gland regulated by hormones?

no, para & sympa stimulate (mostly para)

2 other functions of para stimulation

-increased protein secretion from acinar cells -stimulates myoepithelial cells

what is parasympathetic stimulated by? (salivary gland)

-smell & taste -pressure receptors in mouth -nausea

what is parasympathetic inhibited by? (salivary gland)

-fatigue -sleep -fear -dehydration -some drugs (with dry mouth side effect)

what do sympathetic & parasympathetic both stimulate? (in salivary gland)

myoepithelial cells

what does sympathetic do? (salivary gland)

-modestly increase salivary flow -increase protein secretion from acinar cells -stimulate myoepithelial cells

where is starch digestion initiated?

mouth (amylase)

how is amylase inhibited?

acidic pH in stomach

where are most carbohydrates digested?

small intestine (starch = amylose + amylopectin)

is lingual lipase active in the stomach?

yes, it's acid stable

what are 3 consequences of impaired salivary secretion?

-dry mouth -decreased oral pH (tooth decay) -difficult to lubricate & swallowing (poor nutrition)

how is swallowing initiated?

pressure receptors in walls of pharynx (food/liquid entering pharynx) -receptors send signals to swallowing centre in brainstem

which muscles receive signals from the swallowing centre in the brainstem?

-pharynx -esophagus -respiratory muscles

what muscle surrounds the upper third of the esophagus? what muscles surrounds the lower part?

skeletal - upper smooth - lower

is there any absorption in the esophagus?

no

what/where is the upper esophageal sphincter?

-ring of skeletal muscle -just below pharynx

what/where is the lower esophageal sphincter?

-ring of smooth muscle -at stomach

when are sphincters open?

-swallowing -vomiting -burping

when does the glottis open again?

when the upper esophageal sphincter closes

what is the main driving force of swallowing?

peristalsis (NOT gravity)

what does a small amount of acid in the esophagus do?

-stimulate peristalsis -increase salivary secretion -neutralization & clearance

what causes heart burn?

-inefficient lower esophageal sphincter -after a big meal -during pregnancy

what does pepsinogen do?

-gets converted to pepsin -pepsin digests protein

what does HCl secreted in the stomach do?

-dissolve food -partially digest macromolecules -sterilize food

what controls the rate at which food enters the small intestine?

stomach

what does the stomach secrete which is necessary for absorption of vitamin B12 in the ileum?

intrinsic factor

why is vitamin B12 important? what if we don't have enough B12?

-required for RBC formation -pernicious anemia (RBC deficiency)

which has a thicker layer of smooth muscle: fundus & body (top & middle of stomach) or the antrum (bottom of stomach)?

antrum

what do the fundus & body and the antrum both secrete? what do they each secrete that is different?

both: -mucous -pepsinogen fundus & body: -HCl antrum: -gastrin

major secretions in the stomach?

-mucous -HCl -pepsinogen

minor secretions in the stomach?

-intrinsic factor -gastrin -histamine -somatostatin

what does gastrin do?

-stimulate HCl production -stimulate GI motility

what does histamine do?

stimulate HCl production

what does somatostatin do?

inhibit HCl production

what do chief cells secrete?

pepsinogen

what do enteroendocrine cells secrete? what's another name for these cells? where are they found

-G cells -secrete gastrin -found in the antrum

what does gastrin do?

-stimulate HCl production -stimulate GI motility

what are enterochromaffin-like cells also called? what do they secrete?

-ECL cells -histamine

what do D cells secrete?

somatostatin (inhibit HCl secretion)

where are parietal cells found? what do they secrete?

-fundus/body -HCl & intrinsic factor

what kind of cell has a better defined canaliculus?

actively secreting cell

purpose of canaliculi?

-increase surface area -maxmize secretion into stomach lumen

what does histamine amplify the effect of?

gastrin ACh

when is pepsin active?

at low pH (inactivated when it enters the small intestine)

when chief cells release pepsinogen, what do they also release?

HCl