12.3 Flashcards
How is the ileum adapted to the function of absorbing the products of digestion? (4)
(1) the wall of the ileum = folded (large S.A.)
(2) has villi (large S.A.)
(3) They have thin walls lined with epithelial cells (maintains conc. gradient)
(4) has a rich network of blood capillaries (maintains conc. gradient)
What properties does the villi have that aids in absorption? (5)
(1) they have a large S.A.
(2) they’re very thin walled
(3) they contain muscle so they can move (helps in maintaining conc. gradients)
(4) they’re well supplied with blood vessels
(5) the epithelial cells lining the villi possess microvilli
Villi contains muscles so they can move. How does that aid in absorption? (3)
(1) it helps maintain diffusion gradients
(2) because their movement mixes the content of the ileum
(3) which ensures that new material rich in the products of digestion replaces it
How does facilitated diffusion help in the process of absorption? (5)
(1) as carbs & proteins are being digested continuously, the conc. of carbs & proteins is higher in the ileum than the blood
(2) so glucose moves from the ileum into the blood via facilitated diffusion
(3) The glucose being absorbed is constantly being used up by the cells during respiration, because the blood keeps circulating the body
(4) This maintains the conc. gradient between the ileum and the blood
(5) This helps increase the rate of absorption
Not all of the glucose & amino acids is absorbed due to diffusion. How else can glucose & amino acids be absorbed into the cells and the blood? (1)
co-transport / active transport
Describe how sodium ions, potassium ions and glucose are transported between the ileum and the bloodstream. (6)
(1) sodium ions move into the blood via active transport
(2) while potassium ions move into the epithelial cell (sodium-potassium pump)
(3) the low conc. of sodium ions in the cell causes sodium ions to move INTO the cell via co-transport
(4) as the sodium ions move into the cell, it carries a glucose with it
(5) the glucose molecules move into the cell against their conc. gradient
(6) then the glucose molecule moves INTO the bloodstream via facilitated diffusion
What powers glucose and amino acids to move into the cells? (1)
the conc. gradient of sodium ions
During co-transport, is glucose moving down or against the conc. gradient? (1)
against
During co-transport, are sodium ions moving down or against the conc. gradient? (1)
down
Is co-transport a form of active transport? (1)
Yes, it’s an indirect form.
What is the diameter of micelles? (1)
4-7 nm
Describe the process of triglyceride absorption. (7)
(1) triglycerides are emulsified into micelles using bile salts
(2) the micelles break down into fatty acids & monoglycerides
(3) because they’re non-polar molecules, they can easily diffuse into the epithelial cells
(4) the fatty acids & monoglycerides move into the endoplasmic reticulum, where they recombine to form triglycerides
(5) then they move into the golgi apparatus, where they associate with cholesterol & lipoproteins
(6) so they form chylomicrons
(7) these chylomicrons move out of the cell and into the lacteals (type of blood vessels) via exocytosis
When the chylomicrons move through the blood vessels, what happens to the chylomicrons inside them? (3)
(1) the triglycerides in the chylomicrons are hydrolysed by an enzyme
(2) in the endothelial cells of blood capillaries
(3) and then they diffuse into cells.
List 3 organelles that you would expect to be numerous and/or well developed in an epithelial cell of the ileum, giving a reason for your choice in each case. (3)
(1) ER = to re-synthesize triglycerides from monoglycerides and fatty acids
(2) Golgi apparatus = to form chylomicrons from triglycerides, lipoproteins & cholesterol
(3) Mitochondria = to provide ATP for co-transport of glucose / amino acids
