What is one of the most important functions of helper T cells? a. helper T cells distinguishes...

Blood flows continually through your heart and blood vessels. As the needs of the body change, blood flow needs to increase or decrease. Learn how vasodilation, vasoconstriction and other factors change the amount of resistance within your blood vessels to change blood flow through your body.

Molecular clocks help us tell time on an evolutionary scale instead of by minutes or hours. This video lesson will teach you about molecular clocks, how they are useful, and what problems still remain.

Fat is the subject of daily discussion in this country. We understand it can carry tremendous health risks and could destroy our bodies, but surprisingly, it is essential for our daily function. In this lesson, we'll explore the answers behind the body tissue adipose - the connective tissue that contains fat - and see how it protects, warms, and fuels our daily lives.

Your immune system uses antigens to identify which cells belong to you and which should be destroyed. In this lesson, learn about nonself-antigens, self-antigens, and allergens, and how your immune system responds to them.

Eosinophils are a specific type of white blood cell that protects your body against certain kinds of germs, mainly bacteria and parasites. They're also what causes you to have allergic reactions. Read about how eosinophils function in your body to try to protect you.

In this lesson, you're going to learn the fundamental facts about the three phases of wound healing. These phases include inflammation, proliferation, and maturation. When you are through, take the quiz to see what you have learned.

Oil and water don't mix! In this lesson learn about emulsions and how they work. Through examples, learn about their abundance in foods and what kinds of foods use an emulsion.

How do simple animals know what they need to accomplish? How do insects such as ants understand that they have to find food and bring it back to the nest? The answer: fixed action patterns.

What is a gene? How are genes expressed? What does the term gene expression mean? Can we analyze gene expression? These questions will be addressed in this lesson.

Even though there are germs all around us all the time, we rarely get sick. That's because our immune system is constantly on guard, protecting us from infections. In this lesson, learn about neutrophils, the first responders of the immune system.

Did you know that a sarcomere is the fundamental functional unit of striated muscle? This lesson describes the thick and thin filaments of a sarcomere and how they interact with each other to cause sarcomere shortening and muscular contraction.

Our immune systems are pretty good, but sometimes pathogens can sneak in and infect living cells. Luckily, we've got a back up system. Let's explore cell-mediated response and see how this protects our bodies from infections that may otherwise go untreated.

In this lesson, we'll learn how enzymes function to lower the activation energy of a chemical reaction. Enzymes bind to their substrates to perform all kinds of important and essential cellular processes, as well as processes that help you enjoy a slice of pizza!

Hemoglobin carries almost all the oxygen to our metabolizing tissues. This lesson discusses physiological factors that stimulate hemoglobin to unload oxygen in our tissues. For example, temperature, carbon dioxide, pH and metabolism all influence the affinity of hemoglobin for oxygen.

A macrophage is a type of white blood cell that cleans the body of unwanted microscopic particles, such as bacteria and dead cells. Learn more about this important cell and take a quiz at the end.

In this lesson, you'll learn some historical facts about viruses and the material they are composed of. Find out more as we review the capsid, nucleic acids, the viral envelope, viruses, virions, bacteriophages and virology.