Nutritional Biochemistry - Twining Flashcards
Which enzymes are secreted by the pancreas?
Which are secreted as zymogens and which are secreted as active enzymes?
Proteases, a-mylases, lipases, phospholipases, cholesterol esterases, RNAses, DNAses
The proteases are the only ones secreted as zymogens, which makes sense since you don’t want them digesting the pancreas.
What are the three phases of enzyme secretion?
What are chemical and neural controls to release the enzymes?
- Cephalic- controlled by the vagus/muscarinics and acetylcholine
- Gastric- controlled by the vagus/muscarinics and acetylcholine as well as gastrin from the G cells
- Intestinal- CCK from I cells and secretin from S cells
What prompts the pancreas to release HCO3?
How is HCO3 concentrated into the duct lumen?
Acetylcholine from the vagus/muscarinics OR Secretin
- HCO3 is produced in the duct cells using Carbonic Anhydrase
- HCO3 is released into the lumen via the Cl/HCO3 exchanger
- A chloride gradient is maintained by the Cystic Fibrosis Transmembrane Regulator
What steps are involved in fat digestion?
- Lingual lipase digests a small amount
- Gastric lipase breaks down large fat droplets into smaller droplets
- In the duodenum, pancreatic lipase, co-lipase, and bile salts break down small droplets into micelles
- Micelles are absorbed across the microvilli
How are fats transported from the lumen of the duodenum/jejunum to the body?
Smaller fats (Glycerol, SCFA, and MCFA) diffuse through the enterocyte straight into the blood stream
All other fats are absorbed into the enterocyte as a micelle and reformed into cholesterol and fatty acids in the enterocyte. They are then packaged as chylomicron/VLDL, excreted into the lymph, and sent to the liver.
What is an endopepetidase?
Which endopeptidases are found in the stomach?
Which are found in the small intestines?
A pepetidase that cleaves in the center of a pepetide, not from the end
Pepsin
Trypsin, Chymotrypsin, Elastase
What is an exopepetidase?
Which exopeptidases are found in the stomach?
Which exopepetidases are found in the small intestine?
Pepetidase that cleaves from either the N- terminal or the -C terminal of the peptide
Trick question; there are none
Carboxypeptidases
How are the following enzymes activated?
Pepsinogen
Trypsinogen
Chymotrypsinogen
Proelastase
Procarboxypeptidase
- Pepsinogen- HCl or pepsin
- Trypsinogen- Enteropeptidase
- Chymotrypsinogen- Trypsin
- Proelastase- Trypsin
- Procarboxypeptidase- Trypsin
How are proteins absorbed from the intestine and distributed throughout the body?
- Peptides are broken down to tri-, di-, or mono-peptides in the lumen of the small intestine
- Tri-, di-, and mono- peptides are transported into the enterocytes by transporters
- Tri- and di- pepetides are broken down by tripeptidases and dipeptidases in the enterocyte
- Single amino acids are transported across the enterocytes, into the blood stream
How are carbohydrates transported across the enterocyte into the blood stream?
- SGLT1 cotransports 2Na to move galactose or glucose into the enterocyte
- GLUT5 transports fructose into the enterocyte
- GLUT2 transports sugars across the basal membrane into the bloodstream
What is Vitamin B1/Thiamine used for in the body?
What does a deficiency result in?
Bonus: What is the USMLE sterotype for thiamine deficiency?
NADPH synthesis, neural membrane maintenance
- Dry beriberi (polyneuropathy)
- Wet beriberi (dilated cardiomyopathy)
- Wernicke-Korsakoff syndrome (ataxia, psychosis)
Alcoholics
What is Vitamin B5/Pantothenic acid used for in the body?
What does a deficiency result in?
General metabolism (Coenzyme A) and fatty acid synthesis
(Attacks epithelial cells)
Dermatitis
Enteritis
Alopecia
Adrenal Insufficiency
What is Vitamin B2/Riboflavin used for in the body?
What does a deficiency result in?
Electron carrier (citric acid cycle, dehydrogenases)
Cheilosis
Dermatitis
Corneal neovascularization
What is Vitamin B3/Niacin used for in the body?
What does a deficiency result in?
Where can niacin be obtained other than the diet?
Basis of NAD and NADP
Glossitis
Pellagra
Synthesized from tryptophan (7 steps, extremely inefficient)
What is Vitamin B7/Biotin used for in the body?
What does a deficiency result in?
Carboxylase co-factor (holds CO2 in place)
Dermatitis
Alopecia
Enteritis
