Jacinto

Question 1

WHat are. The different types of transporters in the microvilli?

Answer 1

In the basement membrane, almost all of the transporters are passive and rely on gradients. On the Apical side we have passive transporters too but mostly secondary active transporters where we do a swap or we bring in two things, one down their conc gradient. On the lateral side we have primary active transporters to create a gradient for other things to come in.

Question 2

What is the role Of salivary amylase

Answer 2

To break down starches that have either a 1,6 or 1,4 linkage into monomers in the saliva. Once it gets to the stomach, the low pH stops its action.

Question 3

Pancreatic amylase

Answer 3

Whatever wasn’t broken down by salivary amylase is broken down by pancreatic amylase in the lumen.

Question 4

What are some of the enzymes in the membranes of intestinal cells that break down starches

Answer 4

Maltase, lactase, sucrase, dextrinase, trehalase

Question 5

What are the final products of the breakdown of these starches?

Answer 5

Glucose, galactose, fructose

Question 6

What are some of the glucose transporters responsible for glucose absorption?

Answer 6

GLUT-5 - brings in fructose into epithelial cell.
SGLT-1 - Brings in both Na and either glucose or galactose into epithelial cell. Secondary active transporter.
GLUT-2 - On the basolateral side and brings in fructose, glucose, or galactose into circulation.
- There is also constantly sodium being kicked out on the lateral side to create a gradient.

Question 7

What is the difference between where glucose is absorbed and where lactose is absorbed?

Answer 7

Glucose is absorbed rather early/easily in the duodenum and jejunum. Lactose on the other hand is digester later/slower and is mostly done in the jejunum and ileum due to the lesser concentration of digestive enzymes for lactose.

Question 8

Why can H2 breath test tell you if a person is lactose intolerant?

Answer 8

Because if the lactose isn’t broken down in the small intestine then it goes to the colon where the gut bacteria break it down and release H2.

Question 9

What are the Benefits of the gut bacteria breaking down carbs into small chain fatty acids when the SI can’t do it?

Answer 9

1) Salvages calories
2) Saves water from being pooped out in diarrhea because it lessens osmotically active particles that would suck out water
3) Fight intestinal inflammation.

Question 10

What are the major enzymes involved in the breakdown of proteins and how are they activated/

Answer 10

• Pepsinogen is released from chief cells in the stomach where they are activated by the H+ in the stomach to become pepsin.
• trypsinogen is a pancreatic enzyme that is released into the duodenum. It is activated by enterokinase/enteropeptidase in the brush border to become trypsin. It then activates the rest of the pancreatic Enzymes such as chymotripsongen –> chymotripson or proelastase –> elastase

Question 11

How do the proteins get absorbed?

Answer 11

As we know, they get broken down by the pancreatic enzymes. Eventually they get broken down by cytoplasmic peptideses into AAs or di/tri-peptides. They are then taken up by a carrier and spit out into circulation.

Question 12

How are di/tri-peptides absorbed??

Answer 12

There is a NHE3 transporter which brings in sodium and out H+. This creates a gradient for H+ to want to come back into the cell. Therefore, it is cotransported with the di/tri-peptides into the cell where hydrolases get to them and break them down.

Question 13

Where is protein mostly digested/absorbed?

Answer 13

Through the small intestine but mostly in the jejunum and ileum. It is not as efficiently absorbed as carbs.

Question 14

How are nucleoproteins digested/absorbed?

Answer 14

1) Pancreatic DNAase and RNAase break them down somewhat.
2) Then polynucleotides are broken down by brush border phosphodiesterases and nucleotidases.
3) eventually they are absorbed by nucleoside transporters.
4) Whatever isn’t absorbed is broken down into purines and pyramid investment. And either reabsorbed or excreted out into the urine.

Question 15

vitamin B12 (cobalamin) digestion

Answer 15

It is usually found in dairy and meat products. In the saliva, we have R protein, which binds to B12 to protect it from stomach acid. Once in the small intestine, R gets digested by pancreatic enzymes and B12 is released. B12 then binds to Intrinsic Factor from the stomach. In the small intestine you have transporters for the B12-IF complex.

• If you lose your ileum the then you will have issues absorbing B12.
• If you have too little R in saliva you’ll have issues
• if you have too little IF in the stomach you’ll have issues.

Question 16

Why is it that when a patient gets gastric bypass they often need Vitamin B12 supplements via IV?

Answer 16

Because they essentially bypass the majority of the stomach so you are severely lacking IF.

Question 17

Lipid digestion and solubilizaion

Answer 17

First the lipids are emulsified. This happens both in the stomach and duodenum. In the stomach, there is churning and mixing of the lipids just like you would mix up a salad dressing in order to make all of the fats and. Stuff mix. In the duodenum we have bile salts. This occurs from the signal of CCK to cause delivery of the bile. Secretin is involved as well to help bile and pancreatic HCO3- secretion. As it gets closer to the intestinal Mucosa it gets more acidic and the lipids are released to the transporters.

Question 18

Where does most of the lipid Absorption take place?

Answer 18

Mostly in the jejunum and ileum but not all of it gets digested there. Some gets digested in the colon and can also give fatty stool.

Question 19

Talk about the Villi structure

Answer 19

There is a intestinal crypt where the cells are born. They slowly migrate toward the top of the villi as cells die on top. Eventually. They make it to the top. The intestinal cells are highly proliferative. We also have capillaries and lymphatics running through in order to bring. The nutrients into circulation

Question 20

WHat happens when you have too little or too much bile acid salts?

Answer 20

Too much - you will have very efficient absorption of fats.

Too little - absorption of fat is extremely poor.

Question 21

WHat are some things that might cause abnormalities in lipid digestion and absorption?

Answer 21

• bile deficiency
• pancreatic insufficiency
• Ulcerative colitis/Chron’s disease (lessens surface area)
• Zollinger-Ellison syndrome - tumor where you are producing too much gastrin, which causes acidity in the stomach. It ends up inactivating a lot of the pancreatic enzymes.
• celiac disease.

Question 22

Duodenal iron absorption

Answer 22

Fe+3 is converted to Fe2+ And is brought into the duodenal epithelial cell. Once in the cell it is converted back into Fe3+ by ferroxidase and bound in ferritin. If it is not to be stored then it is excreted from the cell by ceruloplasmin and picked up by carrier protein to circulate through the blood.

Question 23

Calcium absorption

Answer 23

When you want to hang on to calcium, you want to increase the amount of calcium transporters on the basolateral side and you also want to increase the amount of calcium binding protein. Once calcium is in the cell, it binds to calcium binding protein and then they are sent out of the cell by Ca ATPases. When calcium is getting low in the body our main signal is PTH.

Question 24

What is the main organ for reabsorbing water?

Answer 24

Mostly the small intestine but some also occurs in the colon. We also excrete a bit.

Question 25

Where do fluids come from that are reabsorbed?

Answer 25

Diet, saliva, gastric juice, pancreatic juice, SI secretions.

Question 26

What occurs to the epithelial cells as you go along the SI and colon?

Answer 26

The tight junctions change. In the beginning, by the duodenum the tight junctions and leaky. As you go further down they get tighter. This makes sense why most of the reabsorption occurs in the SI and less in the colon.

Question 27

What is the driving force behind water reabsorption?

Answer 27

OSmotically active particles being Reabsorbed such as glucose and sodium in the duodenum (SGLT-1).

Question 28

How does the water get in from the epithelial cells the circulation?

Answer 28

Paracellular junctions but mostly aquaporins.

Question 29

Why is it that when we have diarrhea we can get hypokalemia?

Answer 29

Because potassium is not as efficiently absorbed as Na so it stays in the lumen so you are more likely to poop it out

Question 30

Why is water reabsorption so low in the colon?

Answer 30

No SGLT transports and the tight junctions are too tight. There is a Na/H exchanger tho so some water can come back in.