TRANSCRIPT

Girl1: Hi Doctor D.

Man1: Hi kids.

Girl2: We need to learn more about cells and how they operate. Can you help us?

Man1: Sure. A cell is a basic building block of the body. Your body has about ten trillion cells.

Girl2: Ten trillion? That's a one followed by thirteen zeros. That's a lot.

Man1: Here are some examples of cell you might find in your body. This nerve cell is long and has a lot of branches. It's very different from this white blood cell. What do they both have in common?

Girl1: Well it looks like they all have that thing in the middle.

Man1: That thing in the middle is called the nucleus. They also have a membrane which holds the cells together. And this semi-fluid region inside of each cell is called the cytoplasm.

Girl1: That's cool.

Girl2: Over there it looks like you have a lot of cells together. What's that called?

Man1: Cells of the same structure and function that are grouped together are called tissue. Like this muscle tissue or like this tissue which is the outer layer of the skin.

Girl1: This skin model looks like shingles on a roof.

Man1: Very good. It's designed to keep moisture in and microbes out. Now when you combine various tissues together, you get an organ.

Girl2: You mean like a heart or the lungs?

Man1: Exactly. Now here's a model of the largest organ in the body.

Girl1: It looks like skin.

Man1: It is. Now when you combine two or more organs of a common task, they are called an organ system.

Girl1: Doctor, our textbook mentioned something about body systems.

Man1: Let's look at this human torso for example. This is the digestive system. It starts with the teeth, the tongue and salivary glands. Then the esophagus. Then the stomach and the intestines. They all work together to digest food.

Girl2: The body is very complex.

Man1: Yes it is. It's amazing how the systems work together for the good of the body. The body works really hard to keep itself in homeostasis.

Girl1: Wait a minute Doctor D. That's a big word.

Man1: Okay. Homeostasis means keeping the body's internal environment like its temperature fairly constant. It has what are called feedback controls that act to reverse any changes. It's like thermostat. Let me show you how a thermostat works.

Man1: When I heat up this bimetal strip, it bends upward. When it touches this rod it makes an electrical connection which turns on this fan and cools things down. And when the metal becomes cooler, it straightens out and breaks the electrical connection and turns off the fan.

Girl2: That's pretty cool. But what does that have to do with the body?

Man1: Well when the body heats up, the feedback controls cause the body to perspire and the blood vessels near the skin to dilate, or get larger in diameter. When the perspiration evaporates, it cools the body and the increased blood flow through the larger vessels also releases more heat.

Girl1: So when these things cool the body down, the perspiration stops and the blood vessels return to normal?

Man1: That's right.

Girl2: So are different body systems affected differently?

Man1: Yes. Some systems like the digestive system and the respiratory system are more susceptible to infection. DO you know why?

Girl2: I guess we all have to eat and breathe. Viruses and bacteria can get into the food we eat and the air that we breathe.

Man1: That's right.

Girl1: Thanks Doctor D, but we still need to learn more about how cells are infected.

Man1: I thought you might. When you take you Petri dishes to Mister Frank at PCC this afternoon, you can also ask him about infection.

Girl2: Great. Thanks doctor D.

Man1: You're welcome. Let me know what you find out.