lecture 27 Flashcards
What is absorption?
the net passage of substances from the GI lumen across the lining of the intestine into the interstitial fluid or lymph
Where is the primary site of absorption?
Small intestine
Sites of absorption?
Mouth, oesophagus, stomach
Small and large intestine
What is absorbed at mouth, oesophagus and stomach?
lipid soluble substances
What is absorbs at small intestine?
90% of water and sodium, all nutrients
what is absorbed at large intestine?
9% of water and sodium
factors effecting absorption?
Motility
surface area
transport across epithelium
removal of interstitial fluid
what does correct rate of propulsion allow?
digestion and absorption
what exposes products of digestion to absorptive surfaces?
motility and segmentation
rate of absorption is proportional to?
surface area
what anatomic adaptions maximise surface area?
length of intestine
circular folds
villi
microvilli
what acts as a barrier between outside world and bloodstream?
intestinal epithelium
why is there so many microbiomes in GI tract?
the lumen of the intestine is continuous with the outside world
What are the two pathways of transport of molecules across epithelium?
paracellular gaps
cellular
what is the non-selective barrier that binds cells together?
tight junction
what is required for cells to do paracellular travel?
a concentration gradient
how many membranes do the solutes have to pass to reach blood or lymph?
two membranes, apical and basal
what reduces nutrients into their smallest possible units?
chemical digestion
benefits of transport proteins?
Absorb what is required
allows active transport
why is there a large blood flow to intestine?
for removal of substance from interstitial fluid
villi are arranged around?
blood vessels and lacteals?
how do you lose water?
Sweat, urine, faeces, breath
what is the total water delivered to small intestine?
~9-10L per day
What is the mechanism of water absorption?
osmosis
what is osmosis?
passive movement of water from lumen into the blood
How is sodium absorbed?
Passive movement via paracellular pathway
active transport via cells
mechanisms of sodium absorption?
Na+ channels
Na+ transport coupled to monosaccharides
Na+ transport coupled to amino acids
Going from lumen into epithelial cells Na+?
moves down the concentration gradient through channels and Na+/H+ transporters
To move from epithelial cells to interstitial fluid, Na+ requires?
active transport to move up the gradient
2 mechanisms for carbohydrate absorption?
Passive or active
Passive absorption of carbohydrates is?
monosaccharides diffusing down concentration gradient via paracellular pathway
Active absorption of carbohydrates requires co-transport with?
Na+ via cellular pathway
how are di and tri - peptides transported?
via H+ dependent cotransport
how are amino acids transported?
via Na+ dependent cotransport
Do products of fat digestion require a transporter?
No, they are lipid soluble and diffuse freely
How are products of fat digestion delivered to brush border?
micelles
What happens to products of fat digestion when it enters the cell?
resynthesised into triglycerides, packaged into chylomicrons which exit via exocytosis and enter lacteals
in the ileum how are bile salts absorbed?
active transport processes
apical Na+ dependent bile acid cotransporter
How is bile salts absorbed in the colon?
passive absorption
when does bile salt absorption occur?
after fat absorption is complete
What are fat soluble vitamins?
A, D, E, K
when are fat soluble vitamins absorbed?
Absorbed with fats
What is a water soluble vitamin and how are they absorbed?
Na+ dependent absorption
vitamin c
How is vitamin B12 absorbed?
Absorbed in the ileum bound to intrinsic factor
