Learning about the Rat

Rattus Domesticus

by Vidheha Ranjan, Eena Shrestha and Utkristha Mulmi

29 October 2017

An Overview

by Vidheha Ranjan

Many cats come here. Mommy cats and baby cats. 1, 2, 3, 4 cats come here. In the beginning they would not come close. But now I can hold them. While boxing I carried one of them, it was black and white. There is another one that is brown with stripes. I love cats. I like baby cats so much and I like mommy cats too.

This morning, a cat brought a rat to the art gallery. The rat was dead. I did not see the cat. So we were going to dissect the rat. Because a rat can be yucky, we did the dissection outside. All of us were there, Eena, Utu, Shila, Bishesh, Amulya, Anita didis and dadas were there.

We sat around the rat. The rat was brown like brown tea! It had a tail which was long, there were small stripes on it. First we thought it was a daddy rat. It was a mommy and it had nipples. We counted 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 nipples. Fishes are Pisces, birds are Aves, rat is a mammal. We are also mammals. Elephants are mammals. Mammals feed babies milk. There were sharp nails on the rat’s feet. The nails were very small. They were very sharp. Our nails are shaped like the rainbow. A rat’s nail was long and pointy. It had four feet. The ones in front were smaller and the ones at the back were slightly bigger.

Then we looked at the head. I liked the ears. They were small and stood up a little bit. It had round eyes. Ours are more triangular on the edges and rectangular in the middle. The nose was long and a little like ours on the rounded tip. It had whiskers. There were many hairs on the left and right. I liked the whiskers that were long. 

It had teeth that we were told keep growing longer and longer. If it does not gnaw [discussion on bite, chew and gnaw at this point] on things, they keep growing longer and longer and kill the mouse. The rat can bite my clothes and make holes in them. The color of the teeth was yellow. My teeth are white because I brush them a lot. Rats don’t brush. Rats are living beings like us. I liked that rat. 

Dissection: Baba used forceps to hold the rat. Forceps can hold things very well. It can also pinch fingers therefore, kids should not use them, goat babies are also called kids. I can use forceps once I am grown up like Utu dada.

Next Baba used a scalpel to cut the tummy. Scalpel is a knife. They are smaller and children should not touch them. Only Anita didi should use it Baba says. Eena, Shila didis and Utu dada cannot use them either.

Baba cut the rat open up to the neck. Under the feathers and fluff [here we discuss aves and pisces and reptiles and mammals and what their outer coverings are called J]. Under the fur were the lungs. Baba pointed them out and everyone who was big including Eena and Anita didi and Utu dada wore gloves so they could hold pointing things and look closer and show us also.

I saw the heart. I saw the wiggly wiggly things [intestines]. Last time when we cut the goat, Baba put his mouth on the lungs and blew them up until they became very big. Baba did not do that to the rat lungs because they are small and because a rat is dirty.

I also saw liver and kidneys. I like dissections but they smell yucky. I have seen dissection of bunny, fish, chicken, earthworm, duck, and I have seen the insides of the goat that we cut during Dasain. In our school I have also looked at the dung beetle, parrot, praying mantis, house fly, honey bee, wasp, as well as cockroach.

Research: the head and thorax

by Eena Shrestha

I was assigned to work on the head, thoracic cavity and the abdominal cavity of the rat. The three areas of my focus were the head are the teeth, vibrissae and the ears. Rats are mammals and rodents.

They have really long teeth that don't stop growing, if they don't stop them from growing they die. In order to live they continuously gnaw and can be very destructive around the home.

The rat's whiskers are highly sensitive to touch. When a whisker touches an object it bends and sends a message to the rat's brain. As the rat moves, it feels objects and textures near its face, and constructs an image of the world around itself. This image may be far more detailed than what the rat can see through his eyes.

The long flexible fold of the ear is called the "pinna". It is composed of cartilage covered by skin. In the living animal, the pinna can be rotated to catch the slightest sound from almost any direction. This is useful for an animal whose activity is mainly confined to the darkness.

Now we come to the thorax. It is separated from the abdominal cavity by the diaphragm. In a rat’s lung, there is one lobe on the left, and four on the right. There is a lobe called the accessory lobe, which sits closer to the left side of the lungs, but is actually part of the right lung. Therefore, the Cranial, Middle, Caudal and Accessory lobe make up the right lung; however the left lung does not have multiple lobes.

Blood flows throughout the rat's body. The blood that flows through the body is some sort of a mass road. Oxygen is picked up in the lungs by the red blood cells and distributed to the other cells in the body such as muscles, organs, and the heart itself. The blood also brings energy, vitamins, and minerals to the cells in the organs and muscles of the body. Finally once dropping off the 'cargo' the red blood cells take the waste from the cells and get rid of it.

When the rat goes to inhale, its barrier separating the thoracic cavity from the abdominal cavity pulls down, this creates a vacuum effect. When the rat inhales, the air travels to the esophagus, then it goes down the windpipe. Once in the windpipe the air travels through the pleura then inside of the lungs and finally into the alveoli. Once in the alveoli gas exchange can occur. This is when the red blood cell in the nerves and the alveoli trade gasses. The red blood cells get rid of the carbon dioxide and pick up the oxygen while the alveoli let the oxygen go and take in the carbon dioxide.

Once oxygen is carried by the red blood cells they are pumped through the left side of the heart. The red blood cells carrying oxygen enter through the Pulmonary Vein into the Left Atrium. From here it goes into the Left Ventricle where it is pumped into the aorta and from there to the body. After this the cells give the red blood cells carbon dioxide and other waste to get rid of. When the carbon dioxide gets to the lungs it is traded for oxygen and is then exhaled the same way it came in. In a rat’s body, the circulatory system and the respiratory system work together very well. Their job overall is to get oxygen and nutrition to the muscles and organs and get rid of the waste.

The circulatory system has three major roles in the body: excretion, respiration, and nutrition. Excretion refers to the transport of waste products to the kidneys, respiration refers to the carrying of carbon dioxide from the tissues to the respiratory organs which takes place after the carrying of oxygen from the respiratory surfaces to the tissues, and nutrition refers to the transport of nutrients from the alimentary canal to the tissues.

The heart of a rat consists of two separate pumps which are located together in the same organ. The left side takes oxygenated blood from the lungs and delivers it to the body. The right half of the heart takes the deoxygenated blood from the body and pumps it out to the lungs.

Research: the abdominal cavity

by Utkrishta Mulmi

The rat’s abdominal cavity is below the diaphragm which separates the chest from the abdominal cavity. The abdominal cavity contains the stomach, kidney, spleen, pancreas, liver, gall bladder, small intestines and large intestines among other parts.

The stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives food from the oesophagus. As food reaches the end of the oesophagus, it enters the stomach through a muscular valve called the lower oesophageal sphincter. The stomach secretes acid and enzymes that digest food. Ridges of muscle tissue called rugae line of the stomach. The stomach muscles contract periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

The spleen is an organ in the upper far left part of the abdomen, to the left of the stomach. The spleen varies in size and shape between people, but it’s commonly fist-shaped and purplish. Because the spleen is protected by the rib cage, you can’t easily feel it unless it’s abnormally enlarged. The spleen plays multiple supporting roles in the body. It acts as a filter for blood as part of the immune system. Old red blood cells are recycled in the spleen, and platelets and white blood cells are stored there. The spleen also helps fight bacteria that cause pneumonia and meningitis.

The kidneys are two bean-shaped organs that extract waste from blood, balance body fluids, form urine, and aid other important functions of the body. They reside against the back muscles in the upper abdominal cavity. They sit opposite from each other on either side of the spine. The right kidney sits a little bit lower than the left to accommodate the liver. When it comes to components of the urinary system, the kidneys are multi-functional powerhouses of activity.

The small intestine begins with the duodenum. The duodenum begins at the duodenal bulb and goes around the head of the pancreas and ends as up of the colon and the rectum. The colon is a tubular structure that is around 1.5 m in humans, about one quarter of the length of the small bowel. Its largest diameter is at the cecum. The peritoneal cavity is a thin membrane cavity that covers the organs within the abdomen with some exceptions. The remainder of the small intestine is suspended within the peritoneal cavity by a thin, broad-based mesentery. This allows free movement of the small intestine within the abdominal cavity. After the duodenum comes the next 40% of the mobile small intestine called the jejunum. The remaining 60% is the ileum.The jejunum occupies the left upper portion of the abdomen while the ileum is positioned in the right side and upper part of the pelvis. Absorption takes place via primary cell type of the epithelial layer. It secretes an alkaline mucus that neutralizes the gastric acid. The small intestine is the part of the intestines where 90% of the digestion and absorption of food occurs, the other 10% taking place in the stomach and large intestine. The main function of the small intestine is absorption of nutrients and minerals from food. Digestion involves two distinct parts. The first is mechanical digestion by chewing, grinding, churning and mixing that takes place in the mouth and the stomach. The second part of digestion is the chemical digestion that uses enzymes, bile, acids. The large intestine comprises of the second part of the alimentary canal. The large intestine consists of the cecum and colon. It begins  in the region just at or below the right waist where it continues from the small intestine and continues up the abdomen. Thereafter it traverses across the width of the abdominal cavity, and turns down, continuing to its endpoint at the anus. The large intestine comprises of the second part of the alimentary canal. The large intestine consists of the cecum and colon.

The pancreas is a glandular organ in the upper abdomen, but it actually serves as two glands in one: a digestive exocrine gland and a hormone-producing endocrine gland. As an exocrine gland, the pancreas excretes enzymes to break down the proteins, lipids, carbohydrates, and nucleic acids in food. Functioning as an endocrine gland, the pancreas gives out the hormones insulin and glucagon to control blood sugar levels throughout the day. Both of these functions are important to the body’s survival. For example, lack of proper release of chemicals results in conditions like diabetes. 

The liver is a chemical factory because it performs over 500 chemical functions in your body. The liver takes some materials in your body and turns them into something else. For example: your liver turns proteins and sugar into things that your body needs. The liver also produces a greenish fluid called bile. Tubes, called bile ducts connect the liver and the gallbladder to the small intestine. The bile that is made by the liver helps to digest fats in the small intestine. The liver produces blood clotting factors that are needed to help you heal after an injury. It also stores vitamins, hormones, cholesterol, and minerals. Your liver releases these chemicals and nutrients when your body needs them, and they flow into blood.