Absorption

Question 1

Where are the end products of digestion absorbed in mammals?

Answer 1

Jejunum and ileum

Question 2

What is absorbed by the ileum?

Answer 2

Vitamin B12, bile salts, and whatever products of digestion that were not by the jejunum

Question 3

How is the surface area of the small intestine increased for absorption?

Answer 3

They have villi which posses microvilli

Question 4

What are the end products of carbohydrate digestion?

Answer 4

glucose, galactose and fructose

Question 5

How does monosaccharide absorption occur?

Answer 5

Monosaccharide absorption occurs due to the gradient between their concentrations within the lumen and inside the enterocyte. This occurs via facilitated diffusion.
However, there is normally a high concentration of monosaccharides within the cell and thus active transport and co-transport is used

Question 6

How is glucose and galactose absorbed into the enterocyte cytoplasm?

Answer 6

They enter the cell through sodium-dependent transport using SGLT-1.

Question 7

How does fructose enter the enterocyte?

Answer 7

It uses GLUT5, another transporter

Question 8

How are the monosaccharides transported into the blood stream?

Answer 8

They use the transporter GLUT2 to be transported across the basolateral membrane, then diffuse down the concentration gradient into the capillary blood

Question 9

What do proteins needs to be digested into before absorption takes place?

Answer 9

Amino acids, dipeptides and tripeptides

Question 10

How are amino acids absorbed?

Answer 10

The same as glucose
They use sodium-dependent transporter, which undergoes a conformational changes that transports sodium and amino acids into the cell. This only takes place after the sodium has binded

Question 11

How are dipeptides and tripeptides transported into the enterocyte?

Answer 11

By co-transport with H+ ions using PepT1

Question 12

What happens to the dipeptides and tripeptides once inside the enterocyte?

Answer 12

They are digested into amino acids by cytoplasmic peptidases and exported from the cell into the blood

Question 13

What happens to the sodium that was transported with amino acids?

Answer 13

It is extruded from the basolateral membrane of the cell by Na-K ATPase

Question 14

How does the amino acid leave the basolateral membrane?

Answer 14

It travels down its concentration gradient into the portal blood using a facilitated transporter

Question 15

What are the products of lipid digestion?

Answer 15

Fatty acids and monoglycerides

Question 16

How are short chain fatty acids aborbed?

Answer 16

These are water soluble and enter the cell via simple diffusion. They then have the same path as monosaccharides and amino acids into the blood

Question 17

What are the components of a micelle?

Answer 17

Large lipids, bile salts and lectin

Question 18

How do large lipids enter the cell once inside the micellle?

Answer 18

The micelles easily squeeze between the microvilli and get near the luminal surface
At this point the lipids exit the micelle and enter the enterocyte through simple diffusion. However, some enter through a fatty acid transporter protein

Question 19

What happens to the free fatty acids and monoacylglycerides once inside the enterocyte?

Answer 19

The enter the ER, where they are reincorporated into triglycerides
Continuing in the golgi, the triglycerides are mixed with phospholipids and cholesterol, and a surrounding protein coat
This forms a chylomicron
After processing in the golgi, the chylomicrons are extruded into exocytotic vesicles to the basolateral membrane and then undergo exocytosis

Question 20

What happens to the chylomicrons once extruded from the enterocyte?

Answer 20

They are too large to bass into the capillary and thus enters the lacteal

Question 21

What happens to the chylomicron once it enters the blood stream?

Answer 21

Lipoprotein acts on the triglycerides forming free fatty acids and glycerol, which then pass into cells for energy or are stored in adipocytes.

Question 22

What happens to the remaining chylomicrons?

Answer 22

They are used by the liver to form lipoproteins