the gastrointestinal system Flashcards
difference between chyme and bolus
a mass of chewed food mixed with saliva that is ready to be swallowed
while
chyme is the semi-fluid mixture of partially digested food and digestive juices that is formed in the stomach. After swallowing, the bolus travels down the esophagus and enters the stomach, where it undergoes further digestion and mixing with gastric juices to form chyme.
the six essential activities of the GI system
ingestion, propulsion, mechanical digestion, chemical digestion, absorption, defecation
the primary digestive organs
mouth– pharynx,– oesophagus,– stomach,– small intestine– large intestine
all others are accesory digestive organs
the three divisions of the small intestine
duodenum
jejunum
ileum
is water a class of nutrients
yes
main function of the GI tract
to process food
basic compositon of saliva in the mouth
water
salivary amylase
mucins
Ions, buffers, metabolites, antibodies, etc
mucins are high molecular weight proteins that secrete mucous to lubricate the mouth and food
the four layers of the walls of the GI tract
mucosa,– submucosa,– muscularis externa,– serosa
walls of the GI always have these same 4 layers
what releases pepsinogen when stimulated
zymogen granules
what converts inactive pepsinogen to pepsin(the active form)
HCl
note that pepsin is a protease.
which cells contain the zymogen granules which release pepsinogen
chief cells
H/K ATPase function
Pumps H+ and K+ into stomach, Cl- follows passively, creating acidic environment for digestion and nutrient absorption.
the main substances that the parietal cell secretes
HCL
Intrinsic factor
note that the intrinsic factor is required for Vitamin B12 absorption in the intestines
the three main endocrine cells
G, D and Enterochromaffin-like cells
G cells secrete gastrin , D cells secrete somatostatin, Enterochromaffin-like cells secrete histamine
function of gastrin
acts directly on parietal cells to stimulate the secretion of gastric acid (HCl) by parietal cells in the stomach.
histamine function
indirectly stimulates parietal cells to release HCl into the stomach lumen
it does this indirectly by stimulating the proton pump( (H+/K+ ATPase) through histamine(H2) receptors on parietal cells.
are carbohydrates and proteins absorbed in the small intestines?
no, they are too large
note that fats are not digested nor absorbed in the SI, but carbs and proteins can be partially digested in the SI
Sphincter of Oddi function
opens to allow entry of bile into the duodenum
when closed, entry is blocked
acinar cells
exocrine gland cells that secrete numerous susbstances, and are found on numerous organs
in the pancreas they secrete pancreatic juice into the pancreatic duct
contain watery alkaline fluid and Hydrogen carbonate, and digestive enzymes
trypsinogen activated to trypsin by?
enteropeptidases like enterokinase
intestinal juice has a neutral pH, true or false
true
non digestible carbohydratre is aka
fibre
where does protein digestion begin in the GI tract
the stomach
the main enzymes that carry out protein digestion
endopetidase(like pepsin, trypsin…etc): break down bigger protein molecules, from their midpoint
exopetidases: further breaks down peptide fragments produced by endopeptidases into individual amino acids or smaller peptides that can be absorbed by the intestinal epithelium.
most abundant dietary fats
triglycerides
