Rest and digest physiology part 2 Flashcards
What is hydrolysis
splitting of a chemical bond by the insertion of a water molecule
what are glycosidic linkages in
carbohydrates
what are peptide bonds in
proteins
what molecule are ester bonds in
fats
what are 2 general classes of digestive enzymes
those that act within lumen of the gut
those that act at the membrane surface of the epithelium
Where do enzymes acting within the lumen originate from
major GI glands, including salivary glands, and especially the pancreas
What is the luminal phase of digestion
incomplete hydrolysis of nutrients and the formation of short chain polymers from the original macromolecule
What completes the hydrolytic process (membranous phase)
enzymes chemically bound to surface epithelium of small intestine
What is the membranous phase
enzymes break the short chain polymers from the luminal phase digestion into monomers that can be absorbed across the epithelium
What follows the membranous phase of digestion
absorption
3 phase of digestion
luminal phase
membranous phase
absorption
What elements are in carbohydrates
carbon, hydrogen adn oxygen
What are polysaccharides
long chain carbohydrates
what are oligosaccharides
medium sized molecules carbohydrates
what are disaccharides
2 molecule carbohydrates
what are monosaccharides
simple sugar molecule carbohydrate
3 main types of carbohydrates
fibers, sugars and starches
What is starch
energy storage carbohydrate of plants
What is glycogen
energy storage carbohydrate of animals
Name 3 most important simple sugars in animals diets
glucose, fructose and galactose
What form do carbohydrates need to be in to be absorbed
monosaccharide form
Name enzyme in luminal phase for carbohydrates
amylase
name some enzymes used in membranous phase to break down disaccharide into monosaccharide
Lactase, maltase, isomaltase, sucrase
Where is final step of carbohydrate digestion
apical surface of small intestinal epithelial cells
what makes up lactose
glucose and galactose
what makes up sucrose
glucose and fructose
How are glucose and galactose absorbed
secondary active transport through a co-transport or process ( sodium symporter)
How is fructose absorbed
transported across apical membrane via facilitated diffusion
Where are proteolytic enzymes secreted from and in what form
secreted from stomach glands and pancreas in form of inactive zymogens(precusors of enzymes)
Where does luminal phase happen for proteins
begins in stomach facilitated by gastric enzymes and HCL, completed in small intestine by action of pancreatic enzymes
What happens in stomach for protein digestion
acid denatures proteins and pepsinogen is activated to become pepsin jumpstarting chemical digestion proteins
What does pepsin do
cleaves covalent bonds in proteins to form shorter polypeptide chains
What happens in small intestine for protein digestion
polypeptide chains are broken down further into small peptide chains by pancreatic enzymes including trypsin, chymotripsin and carboxypeptidase
What form can proteins be absorbed as
tripeptides, dipeptides and simple amino acids
How are acidic and most neutral amino acids absorbed
transported via sodium symporters on apical surface of enterocytes like glucose and galactose
How are alkali amino acids absorbed
facilitated diffusion route like fructose
Most common dietary lipid/ fats
triglycerides which also include sterols and phospholipids
Why is it more complicated for digestion of lipids and why
hydrophobic nature so aggregate the aqueous environment of GI lumen makes more difficult for enzymes to access molecules
4 phases of lipid assimilation
emulsification, hydrolysis, micelle formation and absorption
Describe emulsification for lipids
churning action of stomach helps disperse lipids into smaller droplets and also addition of bile when they reach the small intestine
What does Bile contain to help to interact to lipids
salts with hydrophilic and hydrophobic regions allowing them to interact with both lipids and the GI environment
Describe hydrolysis for lipids
bile/ bile salts break large fat globules down into smaller droplets and interact with a co-enzyme to allow pancreatic anzymes to digest the lipid molecules
Describe micelle formation for lipids
products of hydrolytic lipid digestion combine with bile acids and phospholipids to form micelles
Describe absorption for lipids
micelles are considerably smaller and diffuse through the gut lumen into the apical membrane of the enterocytes
What part of the micelle doesn’t diffuse into enterocytes
bile acids
What happens to lipids once inside enterocytes
Major lipids re-esterified to form triglycerides and phospholipids
repackaged with cholesterol and proteins to form chylomicrons
Chylomicrons too large for basolateral membrane
Expelled via exocytosis
too large and hydrophobic so cannot absorb by blood circulation
taken up by lymphatic system then drains back into venous bloodstream
What enzyme digests triglycerides
pancreatic lipase
what enzyme digests phospholipids
phospholipase
what enzyme digests lipid esters
cholesterol esterase
Where does most lipid digestion occur and where does small amounts of lipid digestion occur
most in small intestine
some in mouth via lingual lipases and stomach via gastric lipase
Do vitamins require digestion
no but vary chemical compositions so absorbed in different ways
How are fat soluble vitamins (A,D,E and K) absorbed
same absorption route as lipids and transport via micelles as they are entirely hydrophobic so would unlikely make it to the enterocyte alone
How are water soluble vitamins like C and B absorbed
diffusion or by passive and active transporters
How is water soluble vitamin C and B1 transported in by
c- sodium dependent transport
b1- sodium dependent transporter at low concentration
passive diffusion at high concs
How are other water soluble vitamins like B2 absorbed and B6
B2- facilitated transport
B6- simple diffusion
How does water absorption happen
osmosis and driven by concentration gradient
conc of solute in epithelial cells higher than chyme
remaining water absorbed in colon
What tells us that water is absorbed across tight junctions between enterocytes
hydrostatic and osmotic pressures in both small and large intestines
What do osmotic pressures arise from
nutrients such as glucose, ions like sodium, chloride, potassium, calcium, magnesium, phosphate
disruptions or genetic mutations to ion transporters can lead to diarrhea or constipation
How is mineral absorption controlled
It is not- minerals that enter intestine are absorbed whether needed or not
Iron and calcium are exceptions as absorbed in amount of bodys current requirements
How is calcium absorption controlled
blood levels of ionic calcium determine dietary calcium and regulated by hormones
normally passively absorbed by paracellular diffusion
lower luminal levels additional transcellular absorption process mediated by calcium channels in apical membrane
Calcium leaves basolateral membrane via sodium/calcium exchange and calcium ATPase regulated by vitamin D3
What can calcium absorption be affected by
number of factors
eg lactose enhance calcium absorption
dietary fiber can inhibit it
amount of soluble calcium available to be absorbed affected by pH
How is ionic iron absorbed and used
absorbed into mucosal cells via active transport
once inside mucosal cells it binds to protein ferritin creating iron-ferritin complexes that store iron until needed
store iron is lost when epithelial cells slough off
when needed increase uptake of iron from intestine and accelerated release of iron into blood stream
How are most ions absorbed
active transport in small intestine but absorption mechanisms can be conc dependent and vary in different parts of GI tract
How is sodium absorption
coupled to absorption of nutrients such as amino acids and glucose
How is chloride absorbed
cross epithelial barrier via both paracellular and transcellular routes
absored passiveley in proximal region of small intestine following + charged soidum
How is chloride absorbed in ileum and colon
actively via electroneutral route
What type of absorption do phosphate and magnesium also exhibit
both paracellular and transcellular
What happens due to the sodium and chloride absorption
results in sodium and chloride influx and hydrogen and bicarbonate efflux from the cell
What is the name of the chemical process responsible for breaking down macromolecules during digestion
hydrolysis
why does the stomach secrete zymogens
to avoid autodigestion
The mixing of bile with broken down smaller particles of food in the small intestine is part of which phase of lipid assimilation
emulsification
Why is the digestion of lipids arguably more complicated than that of carbohydrates and proteins
due to their hydrophobic nature
what is the main function of insulin
to drive glucose into cells to be used or stored
