Brush border enzymes are the digestive enzymes sitting on the microvilli-covered epithelial cells lining the small intestine. They are the terminal sites of carbohydrate digestion and also assist in absorption.
A pancreatic duct is the part of the pancreas that connects to the small intestine and carries pancreatic secretions to the duodenum.
The pancreas secretes bicarbonate through the duct to neutralize the acidic chyme entering from the stomach.
The brush border enzymes activate pancreatic trypsin. Specifically, enterokinase (enteropeptidase) activates trypsin.
Once activated, trypsin activates chymotrypsin and other pancreatic enzymes.
Trypsin and chymotrypsin are proteases that digest proteins and break them down into amino acids.
The gallbladder stores bile synthesized in the liver and releases it into the duodenum to emulsify fats. This allows for the fat-digesting enzymes to access the fat molecules by keeping fats in solution.
Lipase released from the pancreas breaks lipids down into free fatty acids.
Goblet cells in the duodenum secrete mucus that buffers the acidic chyme coming in and protects the walls of the duodenum.
Amylase released from the pancreas continues the breakdown of carbohydrates into simple sugars that began in the mouth.
Nucleases released from the pancreas break down DNA and RNA molecules which are absorbed in the ileum as sugar, base, and phosphate.
All of the digestive functions of the small intestine occur in the duodenum, which is the first part of the small intestine. An easy way to remember this is that duodenum and digestion both start with "D". The other two parts are the ileum and jejunum.
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