Download BY 124 SI Test III Session II Food Type Enzyme Source Products

BY 124 SI
Test III Session II
Food Type
Carbohydrates
Proteins
Fats
Enzyme
1. Salivary Amylase
2. Pancreatic Amylase
3. Maltase
1. Pepsin
2. Trypsin
3. Peptidases
1. Lipase
Source
1. Salivary Glands
2. Pancreas
3. Small Intestine
1. Stomach mucosa
2. Pancreas
3. Intestinal Mucosa
1. Pancreas
Products
1. Maltose
2. Maltose
3. Glucose
1. Peptides
2. Peptides
3. Amino Acids
1. FA and
monoglycerides
Digestion in the Stomach
Gastric juice is a mixture of HCl and pepsinogen
What is the purpose of HCl in digestion? Where is HCl secreted?
HCl is secreted from parietal cells. The acidic nature of HCl denatures proteins to expose their peptide
bonds.
How does hydrochloric acid function to aid the other digestive enzyme in the stomach?
HCl converts pepsinogen to pepsin. Pepsin is the active form so now it can function. Once pepsin has been
generated it can work on itself (pepsinogen) to create even more pepsin. This chain reaction allows a large
amount of pepsin to be activated in a short amount of time.
Where is pepsin secreted? What is its role in digestion?
Chief cells secrete pepsin. Pepsin is a protease that works by attacking peptide bonds. Pepsin breaks down
the proteins into smaller polypeptides. Protein digestion starts in stomach and ends in the small intestine!
Explain how the HCl/pepsin system is turned on? Do you constantly have HCl and pepsin residing in your
stomach?
Gastrin is a hormone produced by the lower portion of the stomach. Gastrin travels through the blood
stream, to the upper portion of the stomach, and causes the release of HCl and pepsin from parietal and
chief cells. If the concentration of HCl is too high it will inhibit gastrin (negative feedback)
No you don’t always have HCL and pepsin in your stomach. HCl is so acidic that if left in your stomach all
the time, it would deteriorate the lining of your stomach. This is controlled by a negative/positive feedback
mechanism using gastrin.
Digestion in the Small Intestine
The first portion of the small intestine is called the: duodenum
When chyme enters the small intestine, what method of negative feedback occurs?
When chyme enters the duodenum, it stimulates the release of secretin and CCK which inhibits peristalsis,
slowing the rate at which chyme enters.
What stimulates the release of secretin? What does secretin cause to be released through positive
feedback?
HCl in the chyme (so the acidic nature) stimulates the release of secretin. Secretin stimulates the pancreas
to release sodium bicarbonate. This functions to neutralize the chyme.
You need to neutralize the chyme because the enzymes in the duodenum do not function at an acidic pH!
BY 124 SI
Test III Session II
What stimulates the gall bladder to release bile? How does bile function in digestion?
When chyme enters the duodenum, it stimulates the release of CCK. CCK stimulates the release of the
pancreatic zymogens AND bile. Bile contains bile salts that help to emulsify fats in the chyme (there are no
enzymes in bile)
Small intestine: Pancreatic zymogens
What causes the release of zymogens from the pancreas?
The presence of food in the duodenum stimulates the release of CCK. CCK causes the release of zymogens
from the pancreas
Small intestine: Pancreatic zymogens
-­‐ Trypsinogen is converted to trypsin by a membrane bound enteropeptidase
-­‐ Trypsin can
o Convert trypsinogen à trypsin
o Convert chymotrypsinogen à chymotrypsin
o Convert Procarboxypeptidase à carboxypeptidase
Endopeptidase vs. Exopeptidase
- Endopeptidases cut polypeptide chains internally
Examples: pepsin, trypsin, chymotrypsin
- Exopeptidases cut polypeptide chains externally
Examples: aminopeptidase and carboxypeptidase
CCK
Causes the release of: bile from gall bladder, zymogens and bicarbonate from the pancreas, and inhibits
peristalsis
Secretin
Causes the release of sodium bicarbonate from the pancreas, inhibits peristalsis
Absorption in Small Intestine
Occurs in the: ileum and jejunum
The surface area of the small intestine is increased by the presence of __
__microvilli________________. Collectively, these are called the ______brush_______ ____
___border_________
Which types of nutrients are pumped directly to the blood stream by active transport?
Fructose, amino acids, small peptides, vitamins, and most glucose molecules
How are fats absorbed? Where are the fats sent to after they enter the epithelial cell?
Triglycerides are broken down into fatty acids and monoglycerides in the lumen of the intestine. These
molecules are absorbed by the epithelial cells and are re-formed into fats. This fat is then coated with
protein, cholesterol and phospholipids to create a chylomicron. The chylomicron exits the cell and enters
the lacteal. The lacteal dumps into the lymphatic system which then dumps into the blood system
BY 124 SI
Test III Session II
What is the function of the hepatic portal vein?
The hepatic portal vein functions to control the release of nutrients from the liver. Think about it.. what
would happen if your body absorbed all of the sugar you ate during one meal? You’d go into a coma! The
blood vessels that carry the absorbed nutrients from the small intestine converge at the hepatic portal vein.
Here the nutrients can be released in a controlled manner depending upon the body’s needs.
Absorption in Large Intestine
The colon functions to: absorb water and get rid of salt
The last sphincter the feces pass through is the: anal sphincter and it is voluntary!
A student conducts an experiment to observe the efficiency of protein digestion by altering digestive
enzymes. The student runs a control experiment with all digestive enzymes present and then runs an
experiment using an altered enzyme. In his variable test he notices that the time of digestion slows
substantially. What could be a possible reason for his results?
a. diluted gastrin
b. elimination of endopeptidase
c. elimination of Exopeptidase
d. elimination of lipase
e. diluted HCl