Test 1

Question 1

Where does the digestion of carbs begin?

Answer 1

In the mouth, saliva is added to the food and the enzymes within it start breaking it down

Question 2

Where is saliva sourced from?

Answer 2

Parotid, sublingual (under the tongue), and submandibular glands

Question 3

What is saliva composed of?

Answer 3

• mostly water derived from extracellular fluids
• alpha amylase/salivary amylase
• mucoid proteins
• bicarbonates
• electrolytes
• lysosomes

Question 4

What is the purpose of lysosomes in the saliva?

Answer 4

Enzymes that break down protein and bacteria

Question 5

What is the purpose of mucoid proteins in saliva?

Answer 5

Gives saliva its viscous quality, helps lubricate the food, makes it easier to swallow

Question 6

What happens to carbs when you chew? What effect do we see when this is prolonged, with a cracker for example?

Answer 6

• chewing mixes saliva with food and increases contact area so that salivary amylase can start to breakdown glucose chains within starches
• PROLONGED CHEWING = taste sweeter because some starch will break down into disaccharide sugars like maltose which tastes sweeter than starch

Question 7

What first happens when the carbs are emptied from the stomach to duodenum?

Answer 7

Acid is neutralized by sodium bicarbonate from the pancreas, digestion proceeds fairly quickly

Question 8

The next step in the duodenum involves the addition of alpha amylase, what is this secreted by?

Answer 8

Secreted by the pancreas

Question 9

Describe the function of the additional alpha amylase in the duodenum

Answer 9

• continues to hydrolyze/break down the starches into small glucose polymers and maltose
• the hydrolysis of almost all starches to maltose is almost complete when the breakdown/chyme will enter into the illum

Question 10

What is the third step in the duodenum?

Answer 10

• the disaccharides and polysaccharides are further digested by specific enzymes that are located within the brush border of intestinal cells (as soon as the disaccharides come in contact with the brush border, they are digested by the enzymes (lactase, sucrase, maltase)

Question 11

What does lactase help break down?

Answer 11

Lactose > glucose and galactose

Question 12

What does sucrase help break down?

Answer 12

Sucrose>glucose and fructose

Question 13

What does maltase help break down?

Answer 13

Maltose>2 glucose molecules

Question 14

The major monosaccharides that result from the digestion of polysaccharides and disaccharides are _

Answer 14

glucose, fructose, galactose

Question 15

What are the major monosaccharides absorbed via?

Answer 15

Carrier mediated transport processes

Question 16

The transporters that actually help mediate/help with the uptake of monosaccharides in the epithelial cell are _

Answer 16

sodium monosaccharide co-transporters

Question 17

What are the most common transporters of monosaccharides?

Answer 17

Sglt1 (sodium dependent glucose transporter) and GLUT-5 (a sodium independent facilitated diffusion transporter with a specificity for fructose)

Question 18

For each molecule of glucose, _ are transported into _ via the co-transporter

Answer 18

2 sodium ions, epithelial cell

Question 19

What is the only other carb that uses sglt1 in the same way as glucose?

Answer 19

Galactose

Question 20

What transports sodium back into the gut lumen

Answer 20

Sodium potassium ATPase pump

Question 21

What happens to monosaccharides when they enter the enterocyte?

Answer 21

• a separate monosaccharide transporter on the contra-luminal side of the epithelial cell will accept all three of the monosaccharides (GLUT 2)
• the monosaccharides then enter the circulation to reach the hepatic portal vein which transports them to the liver

Question 22

What happens to transporters when we increase our amount of dietary carbohydrate intake?

Answer 22

The number and activity of these transporters isn’t static and may respond to nutrient uptake
- increased in sglt1 can be observed after increasing amount of dietary carbohydrate intake
** The REVERSE is also true

Question 23

What happens to transporters when we reduce dietary carbohydrate intake?

Answer 23

This will down regulate the transporters and reduce the absorptive capacity for each carb (there are 12 glucose transporters named glut 1-12 and all will use facilitated diffusion in order to transport the monosaccharides)

Question 24

The different glucose transporters have different functions and _

Answer 24

Are expressed at different levels of different tissues (ex. GLUT 4 in muscle)

Question 25

Protein digestion will breakdown ingested proteins into _

Answer 25

Simple amino acids, dipeptides and tripeptides

Question 26

The process called hydrolysis happens where? What is it dependent on?

Answer 26

- takes place in the stomach and small intestines (intestinal mucosa) - depends on very specific protein digesting enzymes known as proteases as well as the acidity of the stomach

Question 27

What PH level can we expect in the stomach?

Answer 27

So acidic that the pH in the stomach and the gastric contents typically sit around 2.0

Question 28

What is pepsin and where does it come from?

Answer 28

- an important group of proteases - will be secreted originally as a precursor (pepsinogen) from the cells of the stomach wall - will be initially inactive but as soon as pepsinogen contacts the hydrochloric acid within the stomach it's immediately converted into the active pepsin that will break down the protein

Question 29

What is pepsin's role in digestion?

Answer 29

- will degrade some of the collagenous connective tissue fibers around meat and after dismantling these fibers, other proteases can digest the remaining animal protein

Question 30

What percent of ingested proteins will stomach enzymes and acids break down?

Answer 30

10-20% (will attack some of the longer and more complex protein strands)

Question 31

What effect does the pH in the stomach cause on proteins?

Answer 31

The low peach in the stomach will cause denaturing of the proteins - the 3D structure of the protein and coils and is broken down into smaller polypeptide/peptide units

Question 32

What happens to pepsin when the chyme passes into the small intestine?

Answer 32

Becomes inactivated due to the relatively high pH in the duodenum

Question 33

What is trypsin, where does it come from, and what does it do?

Answer 33

Protease - released from the pancreas - will become active to digest some of the remaining proteins and polypeptides

Question 34

Pancreatic juice is rich in what?

Answer 34

Very rich in the precursors for all sorts of proteases, which will help digest polypeptides into tripeptides, dipeptides, and single amino acids - ultimately can be transported across some of the enterocytes

Question 35

At the absorption stage of proteins, we've broken everything down into _?

Answer 35

Amino acids, dipeptides or tripeptides

Question 36

Amino acids, dipeptides and tripeptides can be absorbed through _. Describe the absorption process

Answer 36

Active transport - usually coupled to transport of sodium within the small intestine, ultimately will be delivered to the liver via the hepatic portal vein - any dipeptides or tripeptides that have been transported across the endothelial membrane will be broken down inside of the cell into their amino acid constituents by specific dipeptidases and tripeptidases

Question 37

The majority of amino acids will be transported across the epithelium against _. Therefore we need _

Answer 37

Concentration gradient, need carrier mediated transport

Question 38

Aside from transport proteins, we also have

Answer 38

Brush border enzymes

Question 39

How long are short chain fatty acids? What about large chain fatty acids?

Answer 39

10-12 carbons, more than 10-12 carbons

Question 40

Describe how short chain fatty acids are absorbed

Answer 40

- short chain fatty acids can just diffuse through the brush border since our cell membranes are made of phospholipids - from there they can diffuse through the basolateral surface and ultimately be taken up by the capillaries along with the amino acids/monosaccharides

Question 41

Larger fatty droplets or structures need to be broken down via a process called _. What does this rely on?

Answer 41

Emulsification - realize on bile salts to transform the large lipid droplets into much smaller ones

Question 42

Describe the function of bile salts

Answer 42

- bile salts mix with lipids and act as a detergent in order to disrupt those lipid droplets and therefore decrease the droplet size - this in turn will increase the surface area of the lipid exposed to various lipases/digestive enzymes/transporters and they can continue to move along

Question 43

When bile salts surround large chain fatty acids we get _

Answer 43

Micelles

Question 44

What is the function of micelles

Answer 44

Facilitate the movement of larger fatty acid chains directly to the brush border - drops contents off and the fatty acid chain can be brought into the cell via simple diffusion - this allows them to pass through and reform as triglycerides

Question 45

Reform triglycerides are packaged into _

Answer 45

Chylomicrons (large molecules surrounded by a protein coat)

Question 46

What happens to chylomicrons after they are formed?

Answer 46

- chylomicrons can't be taken up in the capillary and instead are exocytosed to the lacteals present in the lamina propria - eventually the fat will be carried to a larger vessel (thoracic duct) together, monosaccharides, amino acids, and small short chain fatty acids can be taken up into the blood - however anything that must initially be contained within a chylomicron will be taken up initially by the lacteal and eventually return to the blood in larger veins

Question 47

Describe the thoracic duct

Answer 47

The thoracic duct is a part of the lymphatic system and connects to the cardiovascular system at a junction where the left internal jugular vein will come in contact with the left subclavian vein

Question 48

Where do the absorbed nutrients go?

Answer 48

- they're gathered up in the villa and transported to the liver via blood flow, ultimately leading to the hepatic portal vein - liver will filter them before sending off the fuel to the rest of the body - the lacteals will send the chylomicrons to the larger lymphatic vessels, ultimately to the thoracic duct - this connects to venous system at left subclavian vein (fat rejoins circulation) = Pumped into heart + around body = absorbed nutrients