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Digestion Review 1

Chemical digestion is the result of hydrolysis.

The Enzymes and Hormones of Digestion

(hint: if the name of the molecule ends in ***ase then it is an enzyme, the first part of the enzyme name is usually what the molecule breaks down).

Enzyme

Location

Function

 

 

 

Amylase

salivary glands

breaks complex CHO into disaccharides

 

pancreas

 

 

 

 

Pepsin

stomach

breaks proteins into polypeptides

 

 

 

Sucrase

small intestine

breaks disaccharides into glucose, fructose and galactose

Maltase

 

 

Lactase

 

 

 

 

 

Peptidase

small intestine

breaks peptides into amino acids

 

pancreas

 

 

 

 

Lipase

small intestine

breaks fats into monoglycerides and fatty acids

 

pancreas

 

 

 

 

Enterokinase

small intestine

activates typsinogen (another digestive enzyme)

 

 

 

Hormones

Location

Function

 

 

 

Gastrin

stomach

stimulates the gastric glands, increasing the secretion of gastric juices

 

 

 

Secretin

small intestine

stimulates the pancreas to release bicarbonate (for neutralizing acid chyme)

 

 

 

cholecystokinin

small intestine

stimulates the gall bladder to contract and release bile

 

 

stimulates the pancreas to secrete digestive enzymes

 

Regulation of Gastric Secretions (pg 336)

Stage One: Cephalic Phase

  • Starts when the person first sees, smells, tastes, or thinks about food (it is a conditioned reflex).
  • There is an increase in the secretion of gastric juices, readying the stomach for food.

 

Stage Two: Gastric Phase

  • Starts when food reaches the stomach.
  • The stomach becomes distended stimulating an increase in gastrin secretion.

 

Stage Three: Intestinal Phase

  • Starts when the chyme passages through the pyloric sphincter into the duodenum.
  • The distention stimulates an increase in the secretion of intestinal hormones which in turn stimulates a decrease in gastric secretions, preventing anymore chyme from entering the small intestine.
  • After the chyme is neutralized and has moved further down, gastric secretions increase again.

 

Carbohydrate Digestion

                                                                        salivary and pancreatic amylase

Polysaccharides --------------------------------------------------------------> Disaccharides

                                                         sucrase, maltase and lactase (in the small intestine)

Disaccharides -----------------------------------------------------------------> Monosaccharides

 sucrose                                                                      glucose & fructose

 maltose                                                                      glucose & glucose

 lactose                                                                       glucose & galactose

 

Protein Digestion

                                  pepsin (in the stomach) and trypsin (in the pancreas)

Protein --------------------------------------------------------------------> Peptide

                                   peptidase (in the small intestine and the pancreas)

Peptide -----------------------------------------------------------------> Amino Acids

 

Lipid Digestion

                                                                       bile

Fat -------------------------------------------------------------------> Emulsified Fats

                                            lipase

Emulsified Fats -----------------------------------------------> Monoglycerides and Free Fatty Acids

 

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