1. GI Part 5 Flashcards
what are the most abundant organic molecules in nature
carbohydrates
list the functions of carbohydrates (4)
- energy source
- storage form of energy
- cell membrane component (communication)
- structural component (cell wall of bacteria)
what are all carbohydrates made of
monosaccharides
what is an example of a 5 carbon monosaccharide and a 6 carbon monosacchraide
5 carbons: pentoses – ribose
6 carbons: hexoses – glucose
what are disaccharides
monosaccharides linked by glycosidic bonds
what is an oligosaccharide
what is a polysaccharide
3-10 monosaccharides
> 10 monosaccharides (up to 100)
what are examples of disaccharides
sucrose
lactose
maltose
what is lactose
glucose + galactose connected by B linkage
milk sugar
where does carbohydrate digestion start in pigs and humans
begins in mouth – alpha-amylase in salivary glands
what are the major dietary carbohydrates (4)
- starch
- glycogen
- saccharose
- lactose
how is further digestion of carbohydrates achieved
how is digestion finished
further digestion achieved by pancreatic enzymes
digestion is finished by enzyme secreted in the intestinal mucosa
where does absorption of carbohydrates take place
duodenum and upper jejunum
what is the absorption of carbohydrates mediated by
mediated by a Na-dependent transport mechanism (SGLT1) present at apical membrane
mediated by facilitated transport mechanisms at the apical membrane (GLUT5) and the basolateral membrane (GLUT2)
where are proteins denatured
in the stomach
what are proteins partially hydrolyzed by
what percentage of ingested proteins are hydrolyzed by this
pepsin
12-15%
where does final digestion and absorption of proteins take place
small intestine
what does pepsin turn proteins into
what does it turn peptides into
pepsin hydrolyzes proteins into oligopeptides
pepsin hydrolyzes peptides into amino acids
what type of transport system do most amino acids use
what type of transport system do di and tripeptides use
most amino acids use secondary transport systems
di and tripeptides use tertiary transport systems
how do amino acids get into the portal vein
facilitated diffusion
what is amphipathic character
what parts of lipids are in each category of amphipathic character
both hydrophobic and hydrophilic
CH3(CH2)n – hydrophobic hydrocarbon chain
COO- – hydrophilic carboxyl group (ionized at pH 7)
what are lipids used to synthesize (6)
- prostaglandins
- steroid hormones
- phospholipids
- platelet activating factor (PAF)
- sphingomyelin – component of myelin in nerve fibers
- bile acids produced from cholesterol
where does emulsification occur and what does it do and why is it important
emulsification occurs in the duodenum
aims to reduce the surface area of the hydrophobic lipid droplets
crucial for lipase function which binds at the interface droplet/aqueous solution
what emulsifies fat droplets
bile acids
what do bile acids consist of
sterol ring
side chain of amino acids (taurine or glycine)
what character of lipids allows emulsification
amphipathic character
what are the main dietary lipids (3)
- cholesterol esters
- phospholipids
- triglycerides
where does lipid digestion start
stomach – gastric lipase
steps of lipid digestion (6)
- bile acids emulsify large fat droplets
- emulsified fat droplets are still too large to enter the spaces of the microvilli
- pancreas lipases hydrolyze triglycerides into monoglycerides and free fatty acids
- these are surrounded by bile acids to form micelles
- micelles can get into cell by diffusion, bile salts remain in the lumen
- inside the cell monoglycerides and free fatty acids combine to create triglycerides
what forms mixed micells
monoglycerides
free fatty acids
cholesterol
liposoluble vitamins
what are the liposoluble vitamins
A
D
E
K
how are mixed micelles absorbed
mixed micelles approach the brush border membrane of enterocytes where they will be absorbed
do short chain fatty acids form mixed micelles
no
they are small enough to be directly absorbed
what happens to long chain fatty acids once they are absorbed
long chain fatty acids go into the endoplasmic reticulum for re-esterification (re-synthesis) of more complex lipids – MAG + FFA = TAG
what do triglycerides then become after re-esterification
chylomicrons
how are chylomicrons release and where to
chylomicrons are released by exocytosis into the lymphatic vessel
how do chylomicrons get to the blood
once in the lymphatic vessel they travel through the thoracic duct to the left subclavian vein and into the blood
do chylomicrons go through the liver
no they bypass the liver because they go into the lymphatic system instead of the portal vein
