Digestive System

 The digestive system is an important part of our bodies also. It gives us the energy, and nutrients we requrie to survive. It also gets rid of unwanted waste in our bodies, as well as others, too.
 Each of the digestive systems is similar in these ways:

• they all have mouths
• they all have "guts"
• they all have an anus

-All of these things probably evolved in similar ways. As creatures first began to evolve, they needed a way for food to get in and get out, using their mouths, and anuses. They also needed a way to digest their food, which is why they physically needed guts.

The rat, and human digestive systems are similar.

picture from enchantedlearning.com

-There are two types of digestion: mechanical, and chemical.
-Chemical digestion is when pepsin splits the complex molecules into smaller chains of amino acids.
-Mechanical digestion is when things are broken into chunks of food, rather than a whole.
-The human digestive system, and some mammals too, produce saliva. This saliva is more than just water. It softens and lubricates food, and it helps our food stay together.
-I'm sure we first started out as eating things that are whole, such as nuts, which is why human jaws were bigger back then. As we began to eat less strained things, mechanical digestion came into play, so that we don't choke.

-Our stomach uses chemicals called gastric juices to try and make food tinier. This takes about 3 or 4 hours.
-Unlike the frog, our liver is not bulit to withhold our weight in jumping. It is though, built to hold glycogen, and break down toxic substances.
-The nutrients in the complex digestive system are absorbed in the small intestine. Humans have a lot of surface area, which is helpful when it comes to absorbing more nutrients.
-The pancreas is in charge of breaking down carbohydrates, and the gallbladder is in charge of breaking down fats.
-The large intestine is used to absorb water, which is possible thanks to osmosis.
-And like almost all other things, the waste we produde is removed through the anus.

A frog's digestive system.

Liver & stomach(left), Stomach lining(right)

-The frog's liver takes up a big portion of its entire body. Making it the largest organ in its digestive system.
-The reason its so big is because it needs to make bile. Bile assists the digestion in the small intestine. It rids waste. The liver also stores vitamins, and processes toxins for its kidneys. This is similar in the humans.
-The gallbladder stores the bile produced by the liver.
-The elastic esophagus, and stomach help the frog eat a large amount of food. This is an advantage because the more you eat, the more energy you'll recieve.
-The frog's pancreas is built to have insulin. This insulin is used for homeostasis, which proves as an advantage.
-When food enters the frog, it goes to the stomach, into the small intestine. From there, the food moves to the large intestine, then the cloaca (frog bladder), and lastly out the anus.
-One disadvantage to having a small and large intestine is that if you loose one, you die, and homeostasis is needed to keep it running.
-Nutrients are absorbed in the capillary walls. Note the difference. Humans absorb their nutrients from the small intestine. This means the frog digestive system came first, because its simple, and doesn't need to absorb their food the way we do.

The crayfish's digestive system.
-The food the crayfish eats enters to the esophogus, then to the stomach. It enters the intestine, and digestive gland, and like the human, leaves through the anus.
-In the crayfish, nutrients are absorbed in the intestine, and digestive glands, just as a humans.
-The crayfish has two stomachs. This has it's advantages and it's disadvantages. For one, it can eat more, and it can eat things that take long to digest, like grass.
-The digestive glands are packed with enzymes, with allow it to digest faster, and can recieve it's energy faster.

The earthworm's digestive system.

-Earthworms eat soil, and the nutrients they recieve are absorbed from the typhlosole, or an infolding of the intsestinal wall.
-The food in the earthworm moves from mouth, to muscular pharynx, to esophagus, to crop, then to gizzard, and finally out the anus. Just like the human, frog, and crayfish.
-The purpose of a worm's crop is to temporarily store soil, which is all a worm can eat.
-The purpose of the gizzard is to grind the soil, and realease
and break up organic matter. The worm does this by using pebbles, or mechanical digestion.
-Also, a worm doesn't need homeostasis or enzymes to perform any actions, unlike us.
-The nutrients from the soil are absorbed by the blood.
-The purpose of the typhlosole is to increase the surface area for digestion and absorption.
-And, alike the others, the undigested waste exits through the anus.