The Digestive System
The function of the digestive system is digestion and absorption. Digestion is the breakdown of food into small
molecules which are then absorbed into the body as nutrients.
Digestive System Organs
Mouth- Used for chewing and it breaks down starches.
Salivary Glands
Serous cells produce amylase – splits starch and glycogen into disaccharides
Mucous cells produce mucus – lubrication during swallowing.
1. Parotid Glands
2. Submandibular Glands
3. Sublingual Glands
Esophagus- It is used for swallowing the food particles.
Stomach- The upper muscle in the stomach relaxes to let the food in and the lower muscle in the stomach mixes the
food with digestive juices, the stomach breaks down proteins.
Small Intestine- Uses juices to break down starches, proteins and, carbohydrates.
Large Intestine- reabsorbs water and passes along material that was not digested; contains intestinal flora (bacteria
to break down cellulose, also produce intestinal gas)
Cecum – beginning of the large intestine, pouchlike, closed end called the appendix (ileocecal valve)
Pancreas- Also uses juices to break down starches, fats, and protein.
Liver- maintains blood glucose, breakdown of lipids and fats, protein metabolism, stores iron and vitamins, destroys
damaged red blood cells, removes toxic substances, secretes bile.
Bile aids in digestion, bile salts break down fats.
Hepatic portal vein – delivers blood to the liver
>>The Endoderm forms the lining of the digestive tract.
>>Special Cells are in the mouth, stomach, and the other layer the small intestine and liver that secret digestive
enzymes.
>>Bacteria in the GI tract, also called “microbiome”.
How It Works
Digestion works by moving food through the GI tract. Digestion begins in the
mouth with chewing and ends in the small intestine. As food passes through
the GI tract, it mixes with digestive juices, causing large molecules of food
to break down into smaller molecules. The body then absorbs these smaller
molecules through the walls of the small intestine into the bloodstream,
which delivers them to the rest of the body. Waste products of digestion pass
through the large intestine and out of the body as a solid matter called
stool.The digestive system is made up of the gastrointestinal (GI) tract—also
called the digestive tract—and the liver, pancreas, and gallbladder. The GI tract is a series of hollow organs
joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the
mouth, esophagus, stomach, small intestine, large intestine—which includes the rectum—and anus. Food enters
the mouth and passes to the anus through the hollow organs of the GI tract. The liver, pancreas, and gallbladder
are the solid organs of the digestive system. The digestive system helps the body digest food.
Interaction
The digestive system works very closely with the circulatory system to get the absorbed nutrients distributed
through your body. The circulatory system also carries chemical signals from your endocrine system that
control the speed of digestion. The digestive system also works in parallel with your excretory system (kidneys
and urination). While the digestive system collects and removes undigested solids, the excretory system filters
compounds from the bloodstream and collects them in urine.
Comparing and Contrasting the Human Digestive to Animal Digestive System
Fish Digestive System
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Stomach, Liver, Pancreas, Intestine, Pyloric caecae, esophagus, anus
Pyloric caecae: slender tubes that secrete digestive enzymes
Intestines: Carnivore- short intestine Herbivore- long intestine
Bird Digestive System
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Esophagus, Stomach, Gizzard, Intestine, Crop, Anus
Gizzard: serves as a filter, holds back insoluble items, like bones
Crop: a loose sac in the throat that stores food
Amphibians Digestive System
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Esophagus, Stomach, Gallbladder, Liver, Cloaca, Small & Large Intestine, Pancreas, Anus
Cloaca: also known as the vent; is an exit cavity like the rectum in humans.
Reptiles Digestive System
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Esophagus, Pharinx, Small & Large Intestine, Liver,
Digestion is a lot slower than mammals.
Pharinx: a muscular tube that permits food getting into the animal's lungs.