NEG 8-10, Digestion and hormones

Question 1

Protease

Answer 1

A protease is any enzyme that performs proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in a polypeptide chain.

Question 2

Stomach protease: what is it, where is it secreted, how is it activated, and where does it cleave?

Answer 2

Pepsinogen, secreted by chief cells, activated to pepsin by HCL, and endopeptidase.

Question 3

What are the proteases and their zymogens in the small intestine?

Answer 3

Trypsinogen -> trypsin
Chymotrypsinogen -> chymotrypsin
Proelastase -> elastase
Procarbxypeptidase -> carboxypeptidase

Question 4

Where do peptidases of the small intestine come from and what activates their zymogen?

Answer 4

Small intestine, activated by zymogen.

Question 5

Of the small intestine peptidases, which are enteropeptodases and which is a carboxypeptidase (terminal cleavage)?

Answer 5

Trypsin; endopeptidases
Chymotrypsin; endopeptidases
Elastase; endopeptidases
Carboxypeptidase; enteropeptodases

Question 6

Trypsin; what type of amino acids does it cleave?

Answer 6

Basic amino acids

Question 7

Elastase; what type of amino acids does it cleave?

Answer 7

Hydrophobic amino acids

Question 8

Chymotrypsin; what type of amino acids does it cleave?

Answer 8

Small amino acids

Question 9

Carboxypeptidase; what type of amino acids does it cleave?

Answer 9

Hydrophobic and basic terminal amino acids.

Question 10

Where are carbohydrates digested?

Answer 10

Stomach and small intestine

Question 11

Alpha-amylase; where is it produced, what does it do, and what deactivates it?

Answer 11

Produced in salivary glands, hydrolyzes glycosidic bonds, and deactivated by low pH in stomach.

Question 12

Brush border enzymes

Answer 12

Enzymes that are anchored on the microvilli of the brush border. Includes:
Sucrase
Maltase
Lactase
Trehalase
Aminopeptidase
Carboxypeptidase

Question 13

Products of carbohydrate digestion

Answer 13

Glucose
Fructose
Galactose

Question 14

Brush border

Answer 14

A brush border is the microvilli-covered surface of simple cuboidal epithelium cells found in the small/large intestine and kidney..

Question 15

Enterocyte

Answer 15

Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells found in the small intestine. Microvilli on the surface increase surface area for the digestion and transport of molecules from the intestinal lumen. The cells also have a secretory role.

Question 16

Where does most absorption occur?

Answer 16

Most absorption occurs in the proximal small intestine. Almost all digestion occurs by the time the chyme reaches the jejunum.

Question 17

Peptide vs amino acid absorption into enterocyte

Answer 17

Peptides: Accounts for the the majority of protein absorption and occurs more rapidly. Symported into cell with H+, the gradient of which is maintained by Na/H antiporter. Peptides are then metabolized fully into free amino acids within the enterocyte.

Amin Acids: Occurs slower and is energy dependent. Amino acid symported inside enterocyte with Na. The Na gradient is maintained by Na/K ATPase.

Question 18

Basolateral membrane

Answer 18

The side of a cell that is facing ETC or other cells, rather than the tubular side (lumen).

Question 19

Lumen

Answer 19

Lumen, meaning “an opening”; is the inside space of a tubular structure, such as an artery or intestine.

Question 20

Transport of amino acids across the basolateral membrane

Answer 20

Released into ETC by facilitated diffusion and co-transport, where it is transported by the hepatic vein to the portal artery. Glutamate and aspartame, however, are used for energy in by the enterocyte.

Question 21

Absorption of monosaccharides into enterocyte

Answer 21

Facilitated diffusion:
SLGT1
GLUT5

Alternatively it can be done by passive diffusion but this process is slow.

Question 22

SGLT1

Answer 22

Na/Glucose linked transporter.

Transports glucose from lumen to enterocyte. One glucose enter with 2 Na moving with concentration gradient. Na gradient maintained by Na/K ATPase.

Question 23

GLUT5

Answer 23

Fructose Transporter from lumen to enterocyte.

Question 24

Emulsification

Answer 24

An important aspect of lipid digestion. Emulsification is the clustering of immiscible lipid in polar water. Mastication breaks down fats into small drops, allowing access by enzymes.

Question 25

Digestive lipase of the stomach

Answer 25

Linguinal, gastric.

Question 26

Bile

Answer 26

Bile is produced by the liver, stored in the gall bladder, and secreted into the duodenum to improve the digestion of lipids in the small intestine, including fat soluble vitamins. Bile salt anions are hydrophilic on one side and hydrophobic on the other side; consequently, they aggregate around lipid droplets to form micelles, with the hydrophobic sides towards the fat and hydrophilic sides facing outwards.

Question 27

Chylomicron

Answer 27

Chylomicrons are lipoprotein particles that consist of triglycerides, phospholipids, cholesterol. They transport dietary lipids from the intestinal enterocyte to other locations in the body through lymph.

Question 28

Lipid digestion summary

Answer 28

Fats are emulsified by mastication. They are then broken into smaller droplets by lingual and gastric lipase. Small droplets then travel to the duodenum where they encounter pancreatic lipase and bile. Bile breaks up the lipid clusters by forming micelles that expose the lipids for lipase hydrolysis. Triacylglycerides are broken into 2 fatty acids and a monoacylglycerol, which are small enough to diffuse into a cell.

Question 29

Lipid digestion transportation summary

Answer 29

Lipid monomers are small enough to diffuse into enterocyte in small intestine. Once within, the are transported to the ER, where they are packaged into chylomicrons and head to the Golgi apparatus where they get placed into endocytotic vesicles, travel to basolateral border, and are secreted into extracellular fluid and travel through lymphatic system.

Question 30

Lipid digestion transportation summary

Answer 30

Lipid monomers are small enough to diffuse into enterocyte in small intestine. Once within, the are transported to the ER, where they are packaged into chylomicrons and head to the Golgi apparatus where they get placed into endocytotic vesicles, travel to basolateral border, and are secreted into extracellular fluid and travel through lymphatic system.

Question 31

Absorption of Haem-iron

Answer 31

Haem-iron is absorbed entirely into the enterocyte. Fe2+ is released by haem oxidase.

Question 32

Absorption of non-haem iron

Answer 32

Fe3+ is more abundant in the acidic stomach. In the duodenum it is reduced to Fe2+ by duodenal cytochrome and is then transported into enterocyte by divalent metal transporter (only transports 2+ ions).

Question 33

Types of jaundice and lab finding, in regards to un/conjugated serum bilirubin, ALT/AST, and ALP.

Answer 33

Pre: Only an increase in serum unconjugated bilirubin.

Intra: Increased serum unconjugated and conjugated bilirubin. Increased ALT/AST.

Post: Increase in serum conjugated bilirubin (causing dark urine). No conjugated bilirubin makes it to the SI though, so pale stool.

Question 34

steatorrhoea

Answer 34

The presence of excess fat in the feces due to reduced fat absorption in the intestines. May be caused by pancrease issues, bile obstuction (posthepatic jaundice), or malabsorption issues (celiac).

significant weight loss, hypolipidemia, deficiencies of fat soluble vitamins (DEKA) that are absorbed with lipids
Failure to thrive