1.4.3 Nutrient Assimilation

Question 1

Na+ dependent absorption of glucose is considered what?

Answer 1

Secondary active transport due to the energy of the sodium electrochemical gradient is established by the Na/K ATPase

Question 2

What are the requirements for optimal activity of pancreatic lipase?

Answer 2

Colipase

Neutral pH

Bile salts

Question 3

Where are the different breakdown products absorbed?

Answer 3

Question 4

How does flow rate alter the ionic composition of the pancreas secretions?

Answer 4

As flow increases the concentration of bicarbonate increases and the concentration of Cl- decreases

Question 5

Absorption of carbohydrates is dependent on what?

Answer 5

Na+ dependent through the specific transporter SGLT1

Question 6

What are the two types of passive transport?

Answer 6

Passive diffusion - permeable to the membrane

Facilitate diffusion - protein in membrane that forms channel

Question 7

Bile salts and vitamin B12 are have specific transport mechanisms where?

Answer 7

Ther terminal ileum

Question 8

What are some important characteristics of colipase?

Answer 8

Question 9

What is the membrane protein associated with facilitated diffusion of Glucose, galactose and fructose in the gut?

Answer 9

GLUT 5

Question 10

What is a main protein digestors in the intestinal lumen?

Answer 10

Pancretic proteases

Question 11

What is this an image of?

Answer 11

Microvillus Membrane

Question 12

Protein digestion begins in the stomach with what enzyme?

Answer 12

Pepsin

Question 13

What is the importance of bile salts in lipid digestion?

Answer 13

Bile salts emulsify lipids into micelles and assist binding of colipase to the lipase at the droplet interface

Question 14

What is the major lipolytic enzyme?

Answer 14

Pancreatic lipase

Question 15

Small peptides are absorbed by what membrane channel?

Answer 15

PEPT1 - an H+ dependent transporter

Question 16

What is this an image of?

Answer 16

Question 17

How do the villus and crypts differ?

Answer 17

Question 18

What is this an image of?

Answer 18

Enterocyte - formation of the chylomicrons

Question 19

What is the difference between these two images of the gall bladder?

Answer 19

Left - resting

Right - active

Electron micrographs of gallbladder. Note the microvilli (MV) on the apical surface of the cells. These epithelial cells transport sodium chloride from the lumen to the subjacent connective tissue. Water follows passively, causing the bile to become concentrated. Notice large numbers of mictochondria (dark ovals) consistent with active electrolyte/fluid transport. When the epithelium is actively transporting electrolytes/fluid, the intercellular spaces become distended (Active).

Question 20

Knockout of what two genes can cause problems in sodium recycling?

Answer 20

Cldn2 and Cldn15

Question 21

Where does amylase cleave starches at?

Answer 21

alpha-1,4-bonds

Question 22

Enterokinase activates what?

Answer 22

Converts trypsinogen to trypsin

Trypsin will activate all others!

Question 23

What are these images?

Answer 23

Left bile canalicus

Sinusoid

Question 24

What is the process of Na recycling in the gut?

Answer 24

Na+ is able to be recycled paracellularly and transverse tight junction proteins.

Claudin proteins control paracellular Na+ permeability

Question 25

What is this an image of?

Answer 25

Tight junctional complexes

Question 26

Fill in this chart

Answer 26

Question 27

Describe the unstirred layer in the intestine lipid digestion and absorption

Answer 27

Question 28

What is the difference between an endopeptidase and exopeptidase?

Answer 28

Endopeptidase - cleave internally yielding products that are 2-6 AA long

Exopeptidase - cleaves at the terminal segment yielding free AA

Question 29

During times between meals how does trypsin affect CCK release?

Answer 29

Where there is no protein to break down, Trypsin will continually break down CCK-RP and Monitor peptide and keep them from binding to the CCK cell (I cell)

Question 30

Monosaccharides exit through what in the basolateral membrane of the intestine?

Answer 30

The GLUT2 transporter

Question 31

Single AA absorption is dependent on what?

Answer 31

Na-AA transport

Question 32

Where are chylomicrons synthesized?

Answer 32

Smooth endoplasmic reticulum

Question 33

In the proximal duct what is the main mechanism of bicarbonate secretion?

Answer 33

There is little of it and it works with the CFTR channel that is secreting Cl- into the lumen and exchanges HCO3- for luminal Cl- through the antiporter.

Question 34

Bicarbonate is always secreted with?

Answer 34

Mucous

Question 35

How does bicarbonate secretion change in the distal channel of the pancreas?

Answer 35

The CFTR channel acts as a direct secretor of HCO3-

Question 36

What is the importance of oligosaccharidases present in the brush border?

Answer 36

These convert oligosaccharides and disaccharides to monosaccharides for absorption

Only monosaccharides can be absorbed

Question 37

CCK-RP release by enterocytes will have what effect?

Answer 37

It is activated by FAs and AAs which will bind to receptor on CCK cell and CCK will be released into the bloodstream

Question 38

Explain the process of lipid digestion and absorption?

Answer 38

The process of dietary lipid digestion and absorption. a | Dietary lipid digestion begins in the stomach, where lipids are subjected to partial digestion by gastric lipase and form large fat globules with hydrophobic triacylglycerol (TAG) cores surrounded by polar molecules, including phospholipids (PLs), cholesterol (CL), fatty acids (FAs) and ionized proteins. The digestive processes are completed in the intestinal lumen, where large emulsions of fat globules are mixed with bile salts (BS) and pancreatic juice containing lipid digestive enzymes to form an aqueous suspension of small fatty droplets to maximize exposure to the pancreatic lipases for lipid hydrolysis. Monoacylglycerol (MAG), diacylglycerol (DAG) and free FAs that are released by lipid hydrolysis join BS, CL, lysophosphatidic acid (LPA) and fat-soluble vitamins to form mixed micelles that provide a continuous source of digested dietary products for absorption at the brush-border membranes of the enterocytes. b | FAs and MAG enter the enterocytes by passive diffusion and are facilitated by transporters, such as intestinal FA-binding protein (IFABP), CD36 and FA-transport protein-4 (FATP4). They are then re-esterified sequentially inside the endoplasmic reticulum by MAG acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT) to form TAG. Phospholipids from the diet as well as bile — mainly LPA — are acylated by 1-acyl-glycerol-3-phosphate acyltransferase (AGPAT) to form phosphatidic acid (PA), which is also converted into TAG. Dietary CL is acylated by acyl-CoA:cholesterol acyltransferase (ACAT) to cholesterol esters (CE). Facilitated by microsomal triglyceride transfer protein (MTP), TAG joins CE and apolipoprotein B (ApoB) to form chylomicrons (CM) that enter circulation through the lymph.

Question 39

What are the three types of active transport?

Answer 39

Symport - two substances brought in together

Antiporter- “exchange” of molecules

Primary active transport - ATP creates energy to drive the molecule against its gradient

AGAINST THE GRADIENT

Question 40

Describe the protein cleavage of some of the peptidases?

Answer 40

Question 41

How does digestion of long chain triglycerides differ from short and medium chain triglycerides?

Answer 41

Question 42

What is the main carbohydrate digestive enzyme?

Answer 42

Pancreatic-alpha-amylase