Introduction to Organ Systems - Online Tutor, Practice Problems & Exam Prep

The human body comprises various organ systems, each with distinct functions. The integumentary system protects and regulates temperature, while the skeletal system provides structure and protection. The muscular system enables movement. Communication is facilitated by the nervous and endocrine systems, maintaining homeostasis through rapid electrical signals and slower hormonal responses. The circulatory system transports nutrients and waste, complemented by the lymphatic system for immunity. Gas, nutrient, and waste exchange occurs via the respiratory and digestive systems, with the urinary system managing waste removal. Lastly, the reproductive system ensures offspring production, highlighting biological diversity.

Introduction to Organ Systems

We're about to spend some time learning the organ systems of the body. Now just quickly remember, an organ system is a group of organs that coordinate to perform a common function. Now we're learning them now because the study of anatomy and physiology, this course, the course that you're taking, it's often broken up by these systems. If you look at the chapters in your textbooks, the units of their course, it's usually different organ systems or groups of organ systems. Here, as we go through them, we're going to group them by function, and the groups that we do here are pretty common, and it's quite often the order that you'll go through them in your course.

First off, we're going to have protection, structure, and support. That's going to be the integumentary system, your skin, the skeletal system, and the muscular system. Then we'll talk about communication and integration, your nervous system, and your endocrine systems. We'll talk about transport and immunity, the circulatory or cardiovascular system, and the lymphatic system. And as part of the lymphatic system, we'll talk about the immune system.

Next, we'll do nutrient gas and waste exchange. That's going to be your digestive system, your respiratory system, and your urinary system, sometimes called the excretory system. And lastly, we'll talk about reproduction. That's going to be the reproductive system, and each person has one of those systems, but obviously, there are two main variants, the male and female reproductive systems. Now it's important to remember that bodies are highly integrated.

No organ system does its job completely on its own, and organ systems also have many overlapping functions. So as we go through each system, we're going to list one or two or three of their main functions. Almost certainly, these systems do other things. We're just trying to hit the big ones right now. And as we list those functions, remember, almost certainly it doesn't do it on its own.

It can be really hard in the body to draw distinct lines that this does that and this does that, but we still try to group things because we're humans, and that's what we like to do. All right. Last thing to know: As we go through these different organ systems, we'll be talking about the different organs that belong to each one. You are not expected to know all the organs of the body at this point in the course. But you probably know a lot of organs already.

So the ones that you do know, you should start organizing in your head by body systems. With that, let's learn some body systems.

Protection and Support

We're going to start our tour of the organ systems by talking about systems that provide protection and support. First off, we have the integumentary system. The integumentary system is your skin, your hair, and your nails. Your skin, hair, and nails provide excellent protection. Your skin provides great protection against friction.

Right? We're always touching things, rubbing against things, our clothes are always rubbing on us. Skin is very tough, and you probably know if you ever have a place where skin is worn off, you really don't want to touch stuff because you don't have that protective barrier. Skin is also providing a waterproof barrier for your body, and it's keeping other random things from getting in. For example, you're covered in bacteria.

If you ever get a cut, you probably put some antibiotic ointment on it because that cut gives a way through your integumentary system for the bacteria to get inside your body. The integumentary system is also providing thermal regulation. In other words, it's regulating your body temperature. Now, most mammals, the integumentary system is doing this with body hair. We don't really use hair that way.

The way our integumentary system regulates temperature is through sweat glands and sweat. We cover our body with sweat, and then because we're largely hairless, it evaporates and cools the body. Now, interestingly, we're really the only animals that use sweat in exactly that way. So, next time you are covered and drenched in sweat and feeling disgusting, remember, it separates you from the animals. Alright.

Next up, we have the skeletal system. The skeletal system is your bones and your cartilage, and it is there largely to provide structure. The skeletal system is really the only hard stuff in your body. Without it, you'd be a lump of soft flesh, but your body has shape. It has structure because of the skeletal system.

It's also going to provide protection. Right? I can beat on my chest and I don't worry about it because I got a rib cage and a sternum that's protecting my internal organs. If I didn't have that rib cage, I would have just punched my heart repeatedly and that would have been a really poor choice. Next up, we have the muscular system, and the muscular system is going to provide movement.

Muscles are really the only thing in your body that can move on their own, at least on a tissue level. The way they move, well, they only move one way, they get shorter. And so when you flex a muscle, it gets shorter and pulls on things. For this reason, muscles and bones work really closely together. If you didn't have bones in your arm, if you flexed your bicep, your arm would just get shorter, but your bones can't get shorter.

So instead, they work like a lever and they bend. So muscles and bones work really closely together, so closely together, that sometimes they're taught as one system. Sometimes they're taught as the musculoskeletal system. That's going to be especially true if you're taking a physiology only class. Alright.

With that, we have 3 systems down, and I'll see you in the next video.

Communication and Integration

Up next, we have two systems that provide communication and integration: the nervous system and the endocrine system. These two systems are most responsible for maintaining homeostasis in the body, which is the maintenance of a stable internal environment. We're not going to spend a lot of time talking about homeostasis right now, but we will discuss it in depth going forward. When we do, you'll want to keep in mind how these systems function. Both the nervous system and the endocrine system provide communication, but they do it very differently.

We'll start with the nervous system. The nervous system is comprised of the brain, the spinal cord, and all the nerves of the body, and sometimes it will include the special senses of the body as well. The nervous system communicates and integrates through rapid communication using electrical signals. When I think of the nervous system, I think of direct point-to-point communication happening very quickly. If I touch something, a message goes up to my brain, and I feel it almost instantly.

If I want to move a muscle, a signal goes from my brain directly to the specific muscle, and my arm moves in a very specific way. That's rapid communication using electrical signals. In contrast, the endocrine system is compiled of various glands. You don't need to know all the different glands right now, but just understand that the endocrine system consists of endocrine glands.

These endocrine glands are adept at providing whole-body coordination and communication using chemical messengers called hormones. The endocrine system functions by producing hormones and releasing them into the blood. These chemicals then travel throughout our body since our blood reaches every part. The messages from the endocrine system spread everywhere. However, not every cell responds to the message; different cells respond differently, and it can take a while for the blood to reach all areas and for the responses to occur.

The endocrine system, unlike the nervous system, usually takes at least a few minutes for a response to happen, and more often, it is in the timeline of hours or even days. To provide an analogy, think about sending out messages to friends or people on my college campus. If I need to send a very specific message to just a few people, I would send a text message. It arrives on their phone immediately; they see it right away. That direct point-to-point communication using electrical signals represents the nervous system.

On the other hand, if I put up flyers all over campus announcing something, everybody will see it. Not everyone will care, different people will respond differently, and it will take a little longer for everyone to see it. That is much more like the endocrine system.

With that, we have two more systems down, and I'll see you in the next video.

Transport and Immunity

Here we have systems that provide transport and immunity. First up, we have the circulatory system, also known as the cardiovascular system. Alright. The circulatory or cardiovascular system is made up of your heart, arteries, capillaries, veins, and your blood. Basically, you have a pump, your heart, that pumps blood through blood vessels.

Now it does that to transport materials to the body. Now what materials? I'm going to put in parentheses here, O₂, because that's what your blood is most specialized for carrying. That's what red blood cells are for. But your blood is going to carry all sorts of materials.

It's going to carry waste. It's going to carry nutrients. It's going to carry hormones. It's going to carry water, and so on and so forth. Anything in your body that needs to get from one place in the body to another is probably going to use the circulatory system to get there.

Now, we have a sort of what's sometimes called a secondary circulatory system, and that's our lymphatic system. Our lymphatic system is made mostly of lymphatic vessels, and those are largely designed to transport water. Your circulatory system lets out a lot of water into the extracellular space of your body, and it starts to collect there. And to keep you from blowing up like a water balloon, you have these lymphatic vessels which sort of funnel that water back up and then put it back into the circulatory system. Now, we put here the immune system as part of the lymphatic system.

The immune system is kind of funny because it doesn't have a lot of or it doesn't really have large organs of its own. It's comprised of all these sort of independent cells that are traveling throughout the body. So we put it with the lymphatic system because one way that the immune system travels through the body is through these lymphatic vessels. And there's specialized structures of the lymph system of the lymphatic system that the immune system uses. Those are going to be lymph nodes, tonsils, thymus, and spleen.

Basically, these things are places where the immune system can sort of stage fights against infection or be specialized places where they can fight infection. You're probably familiar with when you get sick, you might get swollen lymph nodes. That's because the immune system is collecting in the lymphatic system to fight an infection. Okay. With that, we've done transport and immunity, and I'll see you in the next video.

Gas, Nutrient and Waste Exchange

Now we're going to talk about systems that perform gas, nutrient, and waste exchange. What these systems have in common is they exchange material between the outside of the body and the blood. Before we go on, I just want to think about what we mean when we say "inside" and "outside" the body. You probably think that when you inhale something or eat something, it goes into your body. I want to think about things a little bit differently.

To be inside your body, something has to cross into the tissue of your body, has to be in a tissue or the blood or the cells of your body. So, for example, if you eat a penny, that penny is going to go into your digestive tract and it'll go down and through your body and it'll come out the other side, but it has no chance of ever getting into the tissues of your body. It has no chance of being in the blood or the cells. For our purposes, that penny was never really in your body. It was just kind of traveling through the middle of you.

So how do things get in and out of those tissues? Well, the first way is the respiratory system. The respiratory system consists of tubes that lead to the very important lungs. The lungs are the site of gas exchange, and gases, chiefly oxygen (O₂) and carbon dioxide (CO₂), are involved. Oxygen is the major requirement for cellular respiration and carbon dioxide is the major waste product.

Importantly, anything that's in different concentration in the air, in the blood, and soluble in both will be exchanged in the lungs. So, for example, that's why a breathalyzer test works. If a person has alcohol in their blood, while alcohol is soluble in both the blood and the air, it's going to be at a higher concentration in the blood. So when they exhale, it's going to dissolve into the air, come out, and be registered by a breathalyzer test. With that in mind, we'll move on to the digestive system.

The digestive system consists of the mouth, the esophagus, the stomach, the small intestines, and the large intestines. That’s the tube that just goes through you from one end to the other, and then you have some accessory organs, like your liver, pancreas, gallbladder, and salivary glands. The function of the digestive system is to obtain water and nutrients from food. The first half of that tube is all about breaking that food up, crushing it, ripping it, getting it wet.

We add acids and enzymes to it to break it down to its component molecules, and the second half is all about absorbing it into the blood. Now you'll note I didn't say removing waste as a major function of the digestive system. The waste of the digestive system that comes out in your feces is really more like the penny. You eat a lot of food that your body just doesn't use, so it travels through your body, but it never has a chance to get into your tissues or your blood.

When we think of getting rid of waste, we want to think of waste generated in the tissues. Very little waste is actually put into the digestive system. The majority of it is just stuff that passes through. So how does your body get rid of waste? Well, the first way was the respiratory system, but another way is the urinary system.

The urinary system consists of your kidneys, the ureters, which are tubes that connect the kidneys to the bladder, and your urethra, which is the tube that connects the bladder to the outside world. The urinary system removes waste and excess water from the blood. The waste is largely urea, a nitrogenous waste that gives urine its characteristic smell and color, but plenty of other waste will be removed as well. Now in terms of water, your kidneys are responsible for keeping a constant water level in your body. If you drink a big glass of water, that water is going to be absorbed in the digestive system.

It'll enter the blood. Now you have too much water in your blood. The kidneys of the urinary system will take that water out, put it in the urine, and you can pass it out of your body. Alright. With that, 3 more systems down. I'll see you in the next video.

Reproduction

Finally, we're going to talk about reproduction, and by that, I mean to produce offspring. Now every person has only one reproductive system, but it comes in two main flavors, the male reproductive system and the female reproductive system. Let's start with the female reproductive system. The female reproductive system consists of the mammary glands, the ovaries, the uterine tubes, the uterus, and the vagina. And the female reproductive system has a number of jobs to do in order to support reproduction.

First off, it needs to produce eggs, eggs being the gametes or the sex cells that females produce. Next, it needs to receive the sperm so the egg can be fertilized. That fertilized egg will implant in the uterus where the female can support fetal development. Of course, once the baby is developed, there will be birth. And even after birth, the female can support the baby with milk from the mammary glands.

Now in contrast, the male reproductive system consists largely of the testes, the ductus deferens, those are the tubes that connect the testes to the urethra, the prostate gland, and the penis. The male reproductive system really has one job, and that is to produce and deliver sperm to the female, and that's the reproductive system. Now at this point, I think it's important to pick your favorite organ system and to be able to defend why it is your favorite. Now that's unlikely to be a test question, though I used to ask it on my tests, but it's fun to talk about. I bring this up here because my favorite organ system is the reproductive system.

That's because of all the different organ systems, it's the only one where there are fundamental differences between people. And think about your life. How much of your life in some way was based on the reproductive system that you were born with? Now in contrast, you don't need a reproductive system. Of course, people need reproductive systems for there to be people on earth, but you personally can live without one.

Plenty of people have their reproductive systems largely removed, whether it's due to cancer or other reasons, and they go on to live normal lives. That contrast, a system that you don't need and yet dominates so many aspects of our life, I find that forever fascinating. Now maybe your favorite system is the digestive system because you really love cookies. That's defensible as well. With that, we have finished our tour of the organ systems, and I just want to say, good job everybody.

The digestive and respiratory systems are both responsible for taking in useful molecules into the body. When taken in by these systems, where do the molecules go first?

• A. The muscular system.
• B. The cardiovascular system.
• C. The endocrine system.
• D. The urinary system.

Which system is the least responsible for keeping you alive on a day-to-day basis?

• A. The reproductive system.
• B. The cardiovascular system.
• C. The digestive system.
• D. The endocrine system.

Distinguish between the endocrine system and the nervous system.

• A. The nervous system sends messages using chemical signals, while the endocrine system uses electric signals. 
• B. The endocrine system's communication mechanisms tend to work more slowly than the nervous system.
  
• C. The endocrine system uses direct point-to-point communication; the nervous system sends whole-body messages.
  
• D. Both the systems use hormones, but hormones from the endocrine system enter the blood.

Which two systems allow materials to move from one region of the body to another?

• A. Endocrine and cardiovascular.
• B. Respiratory and digestive.
• C. Digestive and integumentary.
• D. Circulatory and lymphatic.

Which organ systems directly allow waste materials to be passed out of the body?

• A. Respiratory and endocrine.
• B. Circulatory and digestive.
• C. Urinary and respiratory.
• D. Circulatory and lymphatic.

Of all your systems, the integumentary, respiratory, and digestive most regularly experience infection from microorganisms. Which answer best describes why that may be the case?

• A. All three systems are in regular contact with substances from outside the body that may contain bacteria.
• B. All three systems are closely linked to the immune system, meaning they protect against microorganisms.
• C. All three systems have limited blood supply, meaning the body has difficulty fighting infection in those places. 
• D. All three systems function to transfer materials from outside of the body to inside the body, giving microorganisms and entry point.

Here’s what students ask on this topic:

What are the main functions of the integumentary system?

The integumentary system, comprising the skin, hair, and nails, serves several critical functions. Firstly, it provides a protective barrier against physical damage, pathogens, and harmful substances. The skin is tough and waterproof, preventing friction injuries and bacterial infections. Secondly, it regulates body temperature through sweat glands, which cool the body via evaporation. Additionally, the integumentary system aids in sensory perception, allowing us to feel touch, pain, and temperature changes. Lastly, it plays a role in vitamin D synthesis when exposed to sunlight, which is essential for bone health.

How do the nervous and endocrine systems maintain homeostasis?

The nervous and endocrine systems are crucial for maintaining homeostasis, the stable internal environment of the body. The nervous system uses rapid electrical signals for immediate responses. For example, touching a hot surface sends a quick signal to the brain, prompting an instant reaction. In contrast, the endocrine system uses hormones released into the bloodstream for slower, long-term regulation. Hormones like insulin and adrenaline help regulate blood sugar levels and stress responses, respectively. Together, these systems ensure that the body's internal conditions remain stable despite external changes.

What organs are involved in the circulatory system, and what are their functions?

The circulatory system, also known as the cardiovascular system, includes the heart, arteries, capillaries, veins, and blood. The heart acts as a pump, circulating blood through the arteries to various body parts. Arteries carry oxygen-rich blood away from the heart, while veins return oxygen-poor blood back to the heart. Capillaries are tiny blood vessels where the exchange of oxygen, nutrients, and waste products occurs between blood and tissues. Blood itself transports essential materials like oxygen, nutrients, hormones, and waste products, ensuring that all body cells receive what they need to function properly.

What is the role of the lymphatic system in immunity?

The lymphatic system plays a vital role in immunity by transporting lymph, a fluid containing infection-fighting white blood cells, throughout the body. It includes lymphatic vessels, lymph nodes, tonsils, thymus, and spleen. Lymph nodes filter harmful substances and house immune cells that can respond to pathogens. The thymus is where T-cells mature, and the spleen filters blood, removing old or damaged red blood cells and pathogens. By circulating lymph and housing immune cells, the lymphatic system helps protect the body against infections and diseases.

How does the respiratory system facilitate gas exchange?

The respiratory system facilitates gas exchange primarily through the lungs. When you inhale, air travels through the respiratory tract to the alveoli, tiny air sacs in the lungs. Here, oxygen from the inhaled air diffuses into the blood, while carbon dioxide, a waste product of cellular respiration, diffuses from the blood into the alveoli to be exhaled. This exchange is driven by concentration gradients, with oxygen moving from high concentration in the air to low concentration in the blood, and carbon dioxide moving in the opposite direction.

What are the main components of the digestive system, and what are their functions?

The digestive system includes the mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas, and gallbladder. The mouth initiates digestion by mechanically breaking down food and mixing it with saliva. The esophagus transports food to the stomach, where acids and enzymes further break it down. The small intestine absorbs nutrients into the bloodstream, while the large intestine absorbs water and forms feces. The liver produces bile to aid in fat digestion, the pancreas secretes digestive enzymes, and the gallbladder stores bile. Together, these organs ensure the efficient breakdown and absorption of nutrients.