Digestive System (GI tract or Alimentary Canal)

It’s designed to transport food and water, modify it, and make it suitable for absorption and excretion.

Digestion – Breakdown of nutrients into particles suitable for absorption.

Absorption – movement of these broken down nutrients into the bloodstream.

Path	GI Functions	Digestive enzymes	What’s digested	What’s absorbed	Movement type
Lips	Eating
Teeth	Cut and grind food
Oral cavity	Tongue and palate mix food and aid in swallowing	salivary amylase	Starch	-----	deglutition
Pharynx	swallowing	-----	-----	-----	deglutition
Esophagus	Move food from mouth to stomach	-----	-----	-----	peristalsis
Stomach	Storage, mixing, digestion	Pepsin	Protein	alcohol	peristalsis
Small Intestine (duodenum, jejunum, ileum)	Digestion, nutrient absorption, water reabsorption	Brush border enzymes: maltase, sucrase, dextrinase, glucoamylase, lactase, peptidase, nucleosidase, etc.	Carbohydrates Protein Fat Nucleic Acids	monosaccharides Amino Acids Fatty acids Nucleotides	Peristalsis and segmentation
The Pancreas secretes the following enzymes into the duodenum of the small intestine: Pancreatic amylase, Maltase, sucrase, lactase, trypsin, chymotripsin, lipase, peptidase, ribonuclease, deoxyribonuclease
Large Intestine (cecum - colon)	Water reabsorption and waste elimination	-----	-----	-----	Mass peristalsis
Rectum
Anus

Lower esophageal sphincter – prevents reflux (GERD = gastroesophageal reflex disease)

Thick layer of mucus protects stomach from HCl and Pepsin. Ulcers – caused by helicobacter pylori bacteria or Non-steroidal anti-inflammatory drugs (NSAIDs).

Liver – secretes bile. Bile is stored in the gallbladder then sent to duodenum. Bile is green and contains bile salts that emulsifies fat. Stores carbohydrates in the form of glycogen. Gallstones cause fatty stool because they prevent emulsification of fat.

Pancreas – secretes pancreatic juice that contains sodium bicarbonate to neutralize acidic chyme. It secretes pancreatic juices into the duodenum.

If water is not reabsorbed properly in the colon it can lead to diarrhea which causes dehydration.

Feces is 75% water and 25% solid matter. One-third of the solid matter is intestinal bacteria.

Digestive Enzyme actions:

Salivary amylase breaks starch down to Maltose (a disaccharide).

Maltase breaks maltose down to glucose.

Lactase breaks lactose down to glucose and lactose.

Sucrase breaks sucrose down to glucose and fructose.

Pepsin and trypsin break proteins down into peptides (oligopeptides or polypeptides.)

Peptidases breaks peptides down to amino acids.

Ribonuclease breaks RNA down to nucleotides.