Functions and Regulations of GI Flashcards
parts of the GI
tracts and glands
what does the GI system do
digestion, absorption of electrolytes and water, elimination of waste products
conduit in the GI system
esophagus
contains chyme
stomach
most of digestion is done where
small intestine
bile storage
gall bladder
what does the pancreas (exokrine) do
has digestive enzymes and HCO3- as H+ buffer
name the glands of the GI system
pancreas, liver, salivary glands, gall bladder
what does the liver do
bile (excretion, lipid digestion), metabolism, detoxification
difference between physical and chemical alteration of food
physical - mastication
chemical - involves breakdown of food with enzymes
difference between secretion and absorption
secretion - from ECF to lumen
absorption - lumen to ECF
what is motility
- movement and mixing
- contraction of smooth muscles
- requires ANS, hormones, and paracrines
4 layers of the GI tract
mucosa, submucosa, muscularis propria, serosa or adventitia
what are each layer of the GI tract made up of
mucosa - epithelium, lamina propria, muscularis mucosa
submucosa - meissner’s (submucosal) plexus
muscularis propria - circular muscle, (Auerbach’s myenteric plexus), longitudinal muscle
significance in the muscularis propria layers of the Auerbach’s plexus being in between the circular and longitudinal muscle
has to deal with motility
force of contraction in the smooth muscle of GI is the function of what?
calcium entry into the cell > 10^-7M
explain how a rise in intracellular calcium causes contraction of smooth muscle
- once an increase in intracellular calcium, calcium binds to calmodulin
- calmodulin activates myosin light chain kinase
- myosin light chain kinase phosphorylates myosin to myosin-Pi
- phosphorylated myosin interacts with actin and ATP and causes a contraction
how does the smooth muscle relax
- when the intracellular calcium drops, calcium and calmodulin disassociate
- the myosin light chain kinase becomes inactivated
- myosin light chain phosphatase dephosphorylates myosin-Pi causing relaxation
what does the contraction of the smooth muscle result in
peristalsis - propels food along tract
segmentation - mixes food
migration motor complex - cleans out gut in fasted state
what causes rumbling of the stomach
migration motor complex cleaning out the gut in the fasted state
what is GI effector 1
smooth muscle
what is GI effector 11
epithelia
nature of the cells in the epithelia
endocrine and secrete mucous
characteristics of epithelia
single layer that is 1cm thick, highly folded to increase surface area for absorption, invaginated for glands that secrete
mode of transcellular and paracellular passage
transcellular - passive or active
paracellular - passive
is the apical surface of a cell closer to lumen or to the blood
closer to the lumen
characteristics of tight epithelia and an example
- has high resistance
- do not want water going through
- highly regulated
- significant ionic gradients and transepithelial voltage
ex: distal colon
characteristics of leaky epithelia and an example
- low resistance
- water can pass through (high permeability)
- smaller ionic and voltage gradient
ex: small intestine
how are GI effector regulated
innervation, endocrine, paracrine
what controls absorption and secretion
meissner’s submucosal plexus
how to remember meissner’s plexus and myenteric plexus and what they do
- meissner in the submucosal –> mucous is wet –> secretion and absorption; glandular epithelium, intestine endocrine cells, submucosal blood vessels
- myenteric - M for motility and between those circular and longitudinal muscles
parasympathetic or sympathetic - which is most important in the GI and what does it do?
- parasympathetic (think rest and digest)
- increased motility and secretion
- distension, satiety, and nausea
what neurotransmitter does parasympathetic use in the GI
acetylcholine
role of sympathetics in the GI and its neurotransmitter used
- antagonizes parasympathetic
- contracts sphincter and vasoconstriction
- pain and nausea
- uses norepinephrine
what is the issue in Hirschsprung disease
- massive distension of proximal colon due to absent meissner submucosal and myenteric plexus
- aganglionic portion of large bowel
are all peptides hormones or are all hormones peptides
all hormones are peptides
two hormones released in the stomach
ghrelin and gastrin
hormones released in the duodenum
CCK, secretin, GIP, motilin
where is GLP-1 released
jejunum
another name for gastrin, its target, its action
- G cells
- target: enterochromaffin like cells (ECL) and parietal cells
- action: stimulates gastric acid and increases gastric mucosal growth
what increases and decreases secretion of gastrin
- increases: AA in stomach, distension, gastrin releasing peptide, Ach
- decreases - somatostatin and acid with pH less than 1.5
another name for CCK, its target, its action
-CCK is short for cholecystokinin aka I cell
-target: endocrine cells of SI and neurons of GIT
-action: motility: gall bladder, GIT, delivery of chyme from stomach
pancreatic secretions: enzymatic and increases satiety
what increases and decreases secretion of CCK
increases: FA and AA in SI, distension
decreases: somatostatin
another name for secretin, its target, its action
- S cell
- target: pancreas and stomach
- action: increase HCO3- secretion by pancreas, decreases gastric acid, neutralizes acid delivered to duodenum, allows intestinal enzymes to operate at optimum pH
what increases and decreases secretion of secretin
- increases: acid in SI
- decreases: somatostatin
actions of ghrelin and what increases is secretion
- X cell
- stimulates food intakes, GH release
- increased by hypoglycemia and low bodyweight
target and action of motilin and what increases its secretion
- M cell
- target: smooth muscle of antrum and duodenum
- action: stimulates migrating motor complex
- increased secretion when fasting - periodically every 1-2 hours
what are the incretins? examples of incretins and another name for each one named
- incretins are hormones released that stimulated decrease in blood glucose levels
- ex: GIP (K cell) and GLP-1 (L cell)
target, action, +secretion of GIP aka K cell
- target: beta cells of pancreas
- action: increase insulin secretion
- +secretion: glucose, FA, and AA in SI
target, action, +secretion of GLP-1 aka L cell
- target: Pancreas
- action: increase insulin secretion and glucagon release
- +secretion: carbohydrates in lumen
stimulates gastric acid release
histamine (ECL cell and mast cells)
stimulates gastric acid release
histamine (ECL cell and mast cells)
potent inhibitor
somatostatin
- pancreatic/ gastric secretion
- motility
- gall bladder contraction
- nutrient absorption
- vasoconstrictor
somatostatin (D cell)
- gut motility and secretion
- stimulus: distention of GI wall
serotonin (ECL cell)
what is happening in cephalic phase
- 40% of time in phase
- thought, smell, sight, taste and swallowing of food
what is happening in gastric phase
- 50% of time in phase
- what is happening in the stomach
what is happening in the intestinal phase
- 10% of time in phase
- what’s happening in the intestine
