14: Digestion and Absorption

Question 1

What are the end results of digesting carbohydrates, fats, and proteins?

Answer 1

Carbs: poly or disaccharides converted to monosaccharides

Fats: triglycerides split into 3 FAs and a glycerol

Proteins: amino acids

Question 2

What is sucrose and what it it split into? What enzyme is used?

Answer 2

A disaccharide cane sugar

Split into glucose and fructose via sucrase in the intestine.

Question 3

What is lactose and what is it split into? What enzyme is used?

Answer 3

Disaccharide milk sugar.

Split into glucose and galactose via lactase in the intestine.

Question 4

What are starches and what are they broken into? What enzymes are used and where are they found?

Answer 4

Large polysaccharides frmo non-animal sources such as potatoes and grains.

Broken into maltose and 3-9 glucose polymers via Pytalin in saliva and pancreatic amylase.

Then made into glucose via maltase and dextrinase in the intestine.

Question 5

What is the function of pepsin? What percentage of protein digestion is this? What is needed?

Answer 5

Breaks down collagen, the connective tissue in meats.

10-20%

Pepsin is activated at low pH (2-3)

Question 6

What pancreatic secretions are involved in protein digestion?

Answer 6

Trypsin and chymotrypsin break proteins into smaller peptides.

Carboxypolypeptidase cleaves ends of polypeptides to amino acids.

Elastase digests the elastin fibers that hold meat together.

Question 7

Where are peptidases found and what is their function?

Answer 7

Found on brush border of duodenum and jejunum.

Break polypeptides and amino acids into amino acids.

Question 8

What are most fats ingested as? How are they digested?

Answer 8

Triglycerides.

Lingual lipase (10%)

Emulsification

Question 9

Where does emulsification begin and what is the purpose?

Answer 9

Begins with agitation in the stomach.

Bile salts and lecithin in bile reduce reduce tension and allow for fragmentation in the sm. intestine.

Increases surface area up to 1000 fold so pancreatic lipase can act.

Question 10

What happens once fat is emulsified?

Answer 10

Pancreatic lipase acts to break it into fatty acids and 2-monoglycerides.

Bile salts incorporate them into micelles for transport to the brush border for absorption.

Question 11

Why is the formation of micelles so important?

Answer 11

It keeps the parts of TG’s apart so they don’t come back together.

Allows them to be in an aqueous environment and aids in our bodies ability to absorb them.

Question 12

What is steatorrhea? What is it caused by?

Answer 12

A clinical condition in which stool floats due to fat in it.

This occurs when you don’t form micelles; Can be caused by chronic pancreatitis when pts can’t make lipase and thus can’t digest fats.

Question 13

What are the folds of the small intestine called? What nerves are involved in absorption here?

Answer 13

The valvulae conniventes, which are covered in vili for increased SA.

Meissner’s plexus.

Question 14

Describe water absorption with hypoosmotic chyme and hyperosmotic chyme?

Answer 14

Hypoosmotic chyme: water diffuses into cells (out of tube) by osmosis

Hyperosmotic chyme: water moves from plasma into chyme (tube)

Question 15

Describe the concentration of sodium in the intestinal lumen compared to the interstitial fluid?

Answer 15

Intestinal lumen: ~140

Interstitial fluid: ~50

Question 16

How are Na levels in the intestinal lumen and interstitial fluid maintained?

Answer 16

Na moves down its gradient (140 and 50) out of the cell and into the lumen.

Na is then pumped out via the Na/K ATPase and more needs to be continually moving into the cell to maintain the levels around 50.

Question 17

Describe chloride absorption?

Answer 17

It follows the movement of sodium in the duodenum and jejunum.

Question 18

Describe bicarbonate absorption?

Answer 18

Occurs in the duodenum and jejunum.

Bicarb from secretin on pancreatic and biliary epithelium combines with H to form carbonic acid.

H2CO3 dissociates into H2O and CO2. CO2 is expelled and water is absorped.

Question 19

Where are calcium and iron absorbed?

Answer 19

The duodenum

Question 20

Where are potassium, magnesium, and phosphate reabsorbed?

Answer 20

Throughout the small intestine.

Question 21

Where are bile salts and vitamin B12 absorbed?

Answer 21

Ileum

Question 22

What clinical measurement would you look at to determine which type of anemia a patient has? What are the three types based on this measurement?

Answer 22

Mean corpuscle volume (size of RBC)

Can be microcytic, normalcytic, or macrocytic.

Question 23

What is the most common cause of microcytic anemia?

Answer 23

Iron deficiency

Question 24

What is a common cause of macrocytic anemia?

Answer 24

Folate deficiency and vitamin B12 deficiency

Question 25

What are the two ways that carbohydrates are absorbed and what percentage does each make up?

Answer 25

80% absorbed as glucose

20% as galactose and fructose.

Question 26

How are glucose, galactose, and fructose absorbed?

Answer 26

Glucose and galactose are co-transported with sodium by active transport.

Fructose does not utilize the sodium transport mechanism.

Question 27

How are the majority of proteins absorbed?

Answer 27

By co-transport with sodium.

Question 28

What is the process by which fats are absorbed?

Answer 28

Micelles move to cell surface, monoglycerides and FAs diffuse out of the micelle into the interior of the cell where they’re converted to TGs and absorbed via lymphatics.

Ultimately get into the blood as chylomicrons.

Question 29

What happens to a small amount of short and medium chain fatty acids?

Answer 29

They are directly absorbed without conversion to triglycerides.

Question 30

How much fluid enters the colon? How much it typically excreted as stool?

Answer 30

~1500 mL enters colon and 100-200 mL is excreted as stool.

Question 31

What is absorbed in the large intestine? What does this result in?

Answer 31

Sodium and chloride are actively absorbed in the proximal large intestine; this is enhanced by aldosterone.

This causes a gradient that results in the absorption of water.

Question 32

What is secreted in the large intestine? What function does this have?

Answer 32

Bicarbonate is secreted in exchange for chloride.

Bicarb buffers neutralizes bacterial acidic waste products.