Lecture 7: Digestion and Absorption of Vitamins and Minerals Flashcards
What forms do dietary lipids come in?
Triglycerides, cholesterol, phospholipids
How are lipids provided in the diet for domestic animals?
Oils of vegetable or marine origin, animal fats
What animal fat is tallow
Beef
What animal fat is lard
Pork
What fat is grease
From restaurants
What is the structure of triglycerides
Glycerol + 3 fatty acids
Lipids must be ______ in the SI for digestion and absorption
Solubilized
What part of the GIT initiates enzymatic digestion of lipids?
Stomach
What is the purpose of churning lipids in the stomach?
Breaks lipids into small droplets and increases SA
What hydrolyzes ~10% of ingested TAG?
Gastric lipase
What does TAG turn into when hydrolyzed by gastric lipase?
Glycerol and FFAs
Stomach __________ chyme into SI
slowly empties
Why does the stomach slowly empty chyme into the SI?
In order to allow time for pancreatic lipase to digest
What emulsifies lipids in the SI?
Bile salts
What is the purpose of bile salts emulsifying lipids?
Surround small lipid droplets to increase SA
__________ enzymes digest different lipids
Pancreatic
What are examples of pancreatic enzymes that digest different lipids?
Lipase, colipase, cholerstol ester hydrolase, phospholipase A2
______ binds to lipase and allows it to digest at lipid-water interface
Colipase
What hydrolyzes cholesterol ester
Cholesterol ester hydrolase
What happens to cholesterol ester when hydrolyzed by cholesterol ester hydrolase?
Free cholesterol + FA + releases glycerol from triglycerides
What is phospholipase A2 activated by?
Trypsin
What hydrolyzes phospholipids?
Phospholipase A2
What is the result when phospholipids hydrolyzed by phospholipase A2?
Iysolecithin + FA
Final hydrolyzed products must now be solubilized in _____ for absorption
Micelles
Bile salts solubilize products within SI lumen as _____ (except)
Micelles; except glycerol
Micelles diffuse to brush-border membrane of ______
Enterocyte
When micelles diffuse to brush-border membrane of enterocyte, products ______________ into cell
Release and diffuse
T/F: Bile salts do not diffuse in enterocyte
True
Products released and diffused into the enterocyte are then _______
Re-esterified to form original compounds
Re-esterified lipids are packaged with _______ to form _______
Apoproteins; chylomicrons
What is on the inside of chylomicrons
Cholesterol and triglycerides in core
What is on the outside of chylomicrons
Phospholipids and apoproteins
Why are apoproteins and important part of chylomicrons?
Needed for absorption
Chylomicrons package in secretory vesicles and exocytosed across basolateral membrane into ____________
Lymphatic capillaries (enter blood of thoracic duct)
Why can’t chylomicrons go into vascular capillaries?
Too big
Steatorrhea
Too much fat in poop
A problem at any step of digestion or absorption of lipids can result in
Steatorrhea
Pancreatic insufficiency (chronic pancreatitis) cause
Inadequate pancreatic enzymes; so TGs not digested
Acidity of duodenal contents can occur if
Chyme not neutralized in SI, pancreatic enzymes inactivated
Deficiency of bile salts causes…
No micelle formation since so bile salts
If an ileal resection occurs, what happens to bile salt recycling?
Does not occur
What happens with bacterial overgrowth?
Bacteria removes glycine and taurine from bile salts
What causes happens if decreased intestinal cells for absorption?
Less SA for absorption of lipid products
What causes failure to synthesize apoproteins?
Lack of Apo B causes abetalipoproteinemia (chylomicrons can’t form)
Vitamins are required as
Co-enzymes or co-factors for metabolic reactions
How are fat-soluble vitamins absorbed?
Within SI lumen, incorporated into micelles for absorption (incorporated into chylomicrons for transport)
How are most most water-soluble vitamins absorbed
Via Na+/dependent co-transporter in SI
What is the one water-soluble vitamin exception?
Vitamin B12 requires intrinsic factor for absorption
B12 is released from food by
Pepsin
B12 binds to ______ from salivary secretions
R Proteins
What in the SI degrade R proteins and release B12?
Proteases
B12 when released binds with
Intrinsic factor
Intrinsic factor is synthesized in
The stomach
______ complex resists proteases, travels to ileum for absorption
B12/IF
What do you need to absorb calcium in the SI
Vitamin D
Calcium is absorbed by passive or active transport mechanisms?
Both
On a low Ca diet, what transport mechanism is used for absorption
Active transport
What is required to transport Calcium to basolateral membrane
Calbindin
On high Ca diet, which transport method is used
Passive transport
What passive diffusion is used on high Ca diet
Paracellular
How is vitamin D activated?
Dietary Vitamin D3 (cholecalciferol) > 25-hydroxycholecalciferol in liver > 1,25 dohydroxycholecalciferol in kidney
Active vitamin D promotes synthesis of
Calbindin D-28 K
Lack of active Vitamin D or calcium results in
Rickets and osteomalacia
Rickets occurs in what age animals
Young
Osteomalacia occurs in what age animals
Adult
What are the two forms of iron
Free iron (Fe2+) or heme iron
What transporter is used for iron absorption?
DMT-1
Heme iron is digested into free iron by _______ enzymes inside enterocytes
Lysosomal
Free iron binds to _______ inside enterocytes for transport into blood via ferroportin
apoferritin
Once free iron binds to apoferritin it gets transported into blood via
ferroportin
What does free iron bind to in plasma
transferrin
Iron circulates bound to
transferrin
Iron is stored as
ferritin