GI tract Flashcards
how is intake regulated
neural and endocrine pathway
2 major parts of the GI system
GI tract and accessory glands
what does the GI system supply the body w
water, electrolytes and nutrients
what are the 8 essential amino acids in humans
tryptophan, methionine, valine, threonine, phenylalanine, leucine, isoleucine, lysine
how long is the gut
15ft
what are the 4 layers of the GI tract (inside to out)
mucosa, submucosa, muscularis externa, serosa
What makes up the mucosa
mucous membrane, lamina propria, muscularis mucosae
what makes up the mucous membrane
enterocytes- epithelial cell layer, absorptive cells, exocrine cells, goblet cells, endocrine cells
what do goblet cells do
secrete mucous
what is the lamina propria
layer of connective tissue with blood vessels, nerves and lymphatic system
what is the muscularis mucosae
thin layer of smooth muscle
what is the submucosa made of
connective tissues so that vol of stomach can stretch, enteric nervous system
what is the enteric nervous system made of
submucosal plexus and myenteric plexus
what is a plexus
where nerves meet
what is the muscularis externa
2 separate layers of smooth muscle which contract to narrow lumen or lengthen. inner later generates spontaneous depolarisations
what is the inner layer of the serosa made of
fibrous connective tissue, structural support
what is the outer layer of the serosa made of
epithelial tissue - the mesothelium, mesenteries - sheets of connective tissues
what does the mesothelium do
protects GI tract from friction by lubricating organs so they can slide past eachother
what are the muscles in the esophagus like
upper 1/3 is skeletal, lower 2/3 are smooth
what happens in the swallowing reflec
tongue pushes the bolus to the back of the mouth, upper esophageal sphincter relaxes, epiglottis closes, food moves down
what does the stomach do
secretes gastric juice, releases food to intestine slowly
what are the 3 regions of the stomach and their characteristics
fundus, body- storage and mixing, antrum- release of food to intestine
what are rugae
folds in stomach that flatten on expansion
why is the stomach acidic
pepsinogen can only be activated in acidic environments, denature proteins, kill bacteria
gastric pits - what are the secretory products
pepsinogen, H+, intrinsic factor, gastrin
gastric pits - what secretes pepsinogen
chief cells
gastric pits - what secretes H+
parietal cells
gastric pits - what secretes intrinsic factor
parietal cells
gastric pits - why is intrinsic factor important
so that B12 can be absorbed
gastric pits - what secretes gastrin
G cells
what are the 3 divisions of the small intestine
duodenum, jejunum, ileum
what is secreted into the duodenum
pancreatic juice and bile
what are crypts of lieberkuhn
epithelial cells that secrete bicarbonate-rich fluid in small intestine
what happens in the hepatic portal system
delivers fresh blood to liver, nutrients travel from liver to heart
what are the 3 divisions of the large intestine
cecum, colon and rectum
function of colon
concentrate wastes to faeces, absorption of water
what are the 4 sections of the colon
ascending, transverse, descending, sigmoid
what type of muscle is the internal anal sphincter
smooth
what type of muscle is the external anal sphincter
skeletal
GI gland types
surface glands, mucosal/submucosal glands, deep tubular glands, specialised glands
characteristics of salivary glands
rich in bicarbonate, contain mucous, salivary amylase, lysozyme
saliva - what does a serous secretion contain
salivary amylase
saliva - what does a mucous secretion contain
mucins
3 types of glands in the stomach
cardiac, oxyntic/gastric, pyloric
gastric juice: what do the cardiac glands secrete
mucous
gastric juice: what do the oxyntic glands secrete
HCl, pepsinogen, mucous
gastric juice: what do the pyloric glands secrete
pepsinogen, mucous
what causes peptic ulcers
too much acid and too much pepsin. Too much mucous or irritation/ infection vof the mucosa
how do helicobacter pylori make ulcers
activate the immune response which destroys the tissue of the stomach
what is in the pancreatic juice
bicarbonate, amylase and lipase, proteases, nucleases
how does the pancreas not digest itself
the enzymes it secretes are zymogens (inactivated enzymes)
where are zymogens stored
in zymogen granules in acinar cells
key liver functions
secrete bile, processes nutrients
what is the ampulla of vater
where the liver and pancreatic duct join
what enzymes are found in the brush boarder
dextrinase, glucoamylase, sucrase, lactase, maltase
what does dextrinase do
break down limit dextrins into glucose
how are zymogens activated
they are cleaved, once one is cleaved a cascade begins
how is pepsinogen (zymogen) FULLY activated
HCl partially activates it and then it acts on other molecules of pepsinogen to activate them
what are the brush border proteases
aminopeptidase and enterokinase
what are the pancreatic proteases
trypsin, chymotrypsin, carboxypeptidase
which vitamins are fat soluble
A,D,E,K
How is vit B12 absorbed
by being bound to intrinsic factor
when is K+ secreted
when lumenal concentrations are low
how is Ca2+ absorbed
binds to calcium-binding protein on brush border
how does Vitamin D effect Ca2+ absorbtion
increases it as it increases the conc of calcium-binding protein
what is the feeding centre called
lateral hypothalamus
what is the satiety centre (fullness) called
ventromedial hypothalamus
what are the chemical satiety signals
glucostatic and lipostatic (release of leptin)
what is the nervous satiety signal
reflexes initiated by distension
what is the hormonal satiety signal
feedback by cholecystokinin
how are endocrine pathways effected by neural pathways in relation to the GI tract
breakdown products trigger receptors which in turn trigger enteric nervous system leading to a change in secretory activity in the endocrine cells. The receptors can also trigger CNS and then ANS which then does the same as the short pathway
GI hormones: Gastrin
in stomach and stimulated by proteins and protein products as well as stretch
GI hormones: Cholecystokinin (CCK)
in duodenum and jejunum and stimulated by fat or protein digestion
GI hormones: secretin
in duodenum or jejunum and stimulated by acid in duodenum
GI hormones: glucose-dependent insulinotropic peptide (GIP)
in duodenum and jejunum and stimulated by glucose, fats or acids in duodenum
what does CCK do
inhibits gastric secretion and motility
what does secretin do
potentiates actions of CCK, inhibits gastric secretion
phases of GI control: cephalic phase
thoughts, taste and smell of food. Requires CNS input
phases of GI control: gastric phase
stimuli in stomach, long and short reflex, GI hormones
Phases of GI control: intestinal phase
stimuli originate in small intestine, long and short reflex, GI hormones
how is saliva secretion stimulated?
taste and texture of food stimulates mechanoreceptors and taste receptors in the mouth, salivary center in medulla is stimulated which triggers ANS which leads to saliva secretion
what type of saliva is produced by PNS
watery
what type of saliva is produced by SNS
more mucus, thick saliva
what causes gastric secretion
PNS, gastrin, histamine
what inhibits gastric secretion
food leaving stomach, drop of pH, increased osmolarity and distention of small intestine
what does secretin do
stimulates bile secretion in the liver
how does the electrical activity in the GI smooth muscle work
spontaneous slow waves of depolarisation, PNS leads to excitation and SNS leads to inhibition
what are the interstitial cells of cajal
cells that trigger the slow waves of depolarisation in GI tissue
how does peristalsis occur
circular and longitudinal muscles contract and relax at different times
what is being stimulated when vomiting
stretch receptors and chemoreceptors
vomiting reflex summary
afferent nervous impulses from GI lining through sympathetic and vagal nerves to brain, mediated through vomiting center in medulla
what happens when you trigger the vomiting centre
reverse peristalsis in duodenum and relaxation of pyloric sphincter, respiration is suppressed
what is the migrating motility complex
intense contractions in small intestine that cleans it between meals
what is the colonocolonic reflex
distention of colon in one area causes relaxation in other areas
what is the gastrocolic reflex
food in stomach increases colonic motility
