Lecture 51: Dig. & Absorb. of Lipids, Vitamins, and Minerals Flashcards
What are the three forms of dietary lipids?
Triglycerides (glycerol + 3 fatty acids)
Cholesterol
Phospholipids
How does the stomach aid in digestion of lipids?
Stomach churns and mixes lipids which initiates enzymatic digestion, churning also breaks lipids into small droplets to increase surface area for enzymes
Gastric lipase also hydrolyses about 10% of ingested lipids into glycerol and FFAs
The stomach slowly empties digesta into the small intestine which allows time for pancreatic lipase to digest
What are the two main steps of digestion of lipids in the small intestine?
1) Bile salts emulsify lipids: surround small lipid droplets to increase surface area
2) Pancreatic enzymes digest different lipids: lipase, colipase, cholesterol ester hydrolase, phospholipase A2
Phospholipase A2 is activated by what enzyme?
Activated by trypsin- it hydrolyzes phospholipids into lysolecithin and fatty acids
List the steps of lipid absorption from the SI lumen.
1) Bile salts solubilize products within the SI lumen as micelles
2) Micelles diffuse to brush-border membrane of the enterocyte, products are released from bile salts and diffuse into the cell
3) Products are re-esterified inside the enterocyte to form original compounds
4) Re-esterified lipids are packaged with apoproteins to form chylomicrons
5) Chylomicrons are packaged into secretory vessels and exocytosed across basolateral membrane into lymphatic capillaries
What enzyme is essential for proper function of pancreatic lipase?
A) phospholipase A2
B) Cholesterol ester hydrolase
C) Gastric lipase
D) Colipase
Colipase
How are fat-soluble vitamins absorbed?
Within the SI lumen, incorporated into micelles for absorption
Incorporated into chylomicrons for transport
How are Water-Soluble vitamins absorbed?
Most absorbed via the Na+/dependent co-transport in the SI
*Exception: vitamin B12 (cobalamin) which requires intrinsic factor for absorption
What vitamin is needed to absorb calcium?
Active vitamin D
What results from a lack of active Vitamin D or calcium?
rickets or osteomalasia
In what form must lipid products be in order for absorption to occur?
A) Emulsion droplet
B) Micelles
C) Chylomicrons
D) Vesicles
Micelles
How is iron absorbed?
Free iron binds to apoferritin inside enterocytes for transport into blood via ferroportin —> binds to transferrin in plasma
Iron circulates bound to ________ and is stored as _________.
Transferrin
Ferritin
