Internal Anatomy:

Parts of Internal Digestive System to Look for:

  • Epiglottis
  • Esophagus
  • Salivary Glands
  • Stomach
  • Liver
  • Pancreas
  • Small Intestine
  • Mesentery
  • Caecum
  • Large Intestine
  • Duodenum
  • Jejunum
  • Ileum
  • Rectum

Upper Part of Body

Within Mouth

Within Throat and Neck; Epiglottis would be more to the right

Middle Part of Body

Between Ribs and Legs
3 Parts to the Small Intestine
Under Liver


Lower Part of Body
End of Small Intestine leading to the Rectum and into the Anus


The difference between a male rat and a female rat, externally, is the fact that males have a penis and testes where as females just have a vagina.

Rats have four major sensory items: a tail, eyes, ears, and whiskers. The tail is the long body part, at the end of the rat, that doesn't have hair or fur. The tail has several different functions. It regulates body temperature while the lack of fur allows for heat to leave the body faster, maintaining homeostasis. The loss of heat is due to the large blood vessels in the tail close to the skin making it easier to loose heat to the environment. Keeping balance and walking on narrow pathways is made easier because of the tail. Rats have well-developed eyes and ears because these senses are vital to their survival. Rats' long whiskers allows them to sense the objects and ground around them in the dark.

A rat could either live in a field or a garden of some sort. This is because rats are omnivores, meaning they eat grass, vegetables, fruits and meats. The typical habitat for a rat would be somewhere full of grass, berries and a place to hide from predators. The strong grasp of their paws and phalanges would help them live in this environment easily. Also, long tails and whiskers would help sense a predator if it were near.

Digitigrade locomotion is the way a rat walks. Rats walk only on their phalanges, rather than how a human walks. Plantigrade is how a human walks, on the soles of their feet.

The food starts in the rats mouth where it is chewed up and saliva is released to help break it down, it then travels down the esophagus which is a muscular tube which connects the mouth to the stomach, so the food goes straight from the esophagus to the stomach. From the stomach it goes into the small intestine, to the liver, to the pancreas and then the materials travel to the large intestine. At the end of the large intestine is a tube, called the rectum, where materials are compressed to a muscular opening and is finally eliminated form the body through the anus.

Most physical digestion takes place in the stomach. There are three layers of muscle that contract to produce a churning motion. It mixes the foods and fluids using physical digestion.

The longest organ in the digestive system is the small intestine. It has to be long because most of the chemical digestion takes place there. Also, the pancreas and liver deliver their substances into the small intestine to help the chemical digestion. Therefore, it has to be long so that the digested material has time to mix with the enzymes and bile while the materials are still in the small intestine.

Digestion of food takes place when mucus inside the stomach covers food. At this point the food is still a solid. Stomach acids are also located in the stomach. The enzyme pepsin lines rats' stomachs because pepsin is only active in acidic environments. By the time the food gets to the caecum, the food has turned into materials for the body to use, absorb, or eliminate.

Although there are many similarities between humans' and rats' digestive systems, there are also some differences. Rats lack a gallbladder, so there is no place to store bile. Also, the caecum in a rat versus the caecum in a human differs in size. A rat's caecum is much larger than one in a human. Also, fermentation in the caecum of a rat allows for digestion of cellulose, whereas it does not take place in a human's.

In a human, the caecum is a small pouch. Named from the Latin word 'caecus' meaning blind. It is named this because it is referring to the pouch at the end of the caecum that leads nowhere. Unlike humans, rats can digest cellulose. The caecum, in a rat, is essentially a 'fermentation chamber' where bacteria, able to digest cellulose, is located. The food in the caecum "rots" and then byproducts can be absorbed by the rat.