Steps of the Inflammatory Response: Study with Video Lessons, Practice Problems & Examples

The inflammatory response consists of four key steps: tissue damage and infection, release of inflammatory mediators, vasodilation, and removal of invading microbes. Initially, tissue damage allows pathogens to breach innate immunity, prompting mast cells to release cytokines like histamine, which promote inflammation. Vasodilation increases blood vessel permeability, facilitating diapedesis, where immune cells migrate to the infection site. Finally, neutrophils and macrophages eliminate microbes through phagocytosis. While inflammation is protective, it can also cause accidental damage, highlighting its dual role in health and disease.

1) Tissue Damage & Infection

In this video, we're going to begin our lesson on the steps of the inflammatory response. And so really a series of just 4 events or 4 steps occur in the inflammatory response during tissue damage and infection of a microbe. In this video, we're only going to focus on the very first event, or the very first step of the inflammatory response, which is tissue damage and infection. But later in other videos, we'll talk about the other steps of the inflammatory response. In the first step of the inflammatory response, we have tissue damage and infection. Damage to the tissues allows microbes to bypass the first line of defense of innate immunity. So it can bypass our skin, mucus membranes, antimicrobials, and things of that nature. When they bypass the first line of defense, they can enter into the surrounding tissue cells. Immediately after the injury, blood vessels will briefly constrict via vasoconstriction. Vasoconstriction is the constriction or narrowing of the blood vessels. It does this in order to prevent blood loss. If we take a look at our image down below, we're showing you the very first event of the inflammatory response, which is tissue damage and infection by the microbe. Notice in this image, it is an image showing you our skin. You can see the epidermis layer is at the top here and the dermis layer is right here. Down below, notice that the blood vessel is at the bottom. When there is damage, like for example when a sharp object penetrates into your tissues, some of our immune system cells are already going to be present in the tissues. For example, mast cells can be present in the tissues. But, when there is penetration by a sharp object like this, it creates the opportunity for microbes to infect the tissues. This tissue damage can lead to infection by a microbe. Once again, the blood vessels are going to briefly constrict to prevent a large amount of blood loss. This here concludes our lesson on the first event of the inflammatory response, and we'll get to talk about the other events of the inflammatory response as we move forward. I'll see you all in our next video.

2) Release of Inflammatory Mediators & Other Cytokines

In this video, we're going to talk briefly about the second step in the inflammatory response, which is the release of inflammatory mediators and other cytokines. In response to a microbe invasion or tissue damage, local mast cells, which recall are very similar to basophils but reside in the tissues, will release cytokines and inflammatory mediators. These mast cells are already residing within the tissues, as you can see here in this image. They will begin to release cytokines and inflammatory mediators upon an infection. Inflammatory mediators refer to messenger molecules specifically involved in the inflammatory response. For example, histamine is an example of an inflammatory mediator, and the release of histamine will promote inflammation.

The release of inflammatory mediators will help to regulate changes in local blood vessels, potentially causing the local blood vessels to dilate, as we'll discuss in the next step. It will also signal immune system cells from the blood to the infected site, attracting immune system cells to the area of infection.

If we take a look at this image down below, we're focusing on the second step of the inflammatory response: inflammatory mediators and cytokines being released. These mast cells that are present in the tissues and reside there will begin to release cytokines and inflammatory mediators. These cytokines and inflammatory mediators will cause changes to the local blood vessels and also signal immune system cells to travel from the blood vessels to the area of infection to help eliminate the microbes.

This concludes our brief lesson on the second step of the inflammatory response, and we will be able to talk about the third and fourth steps of the inflammatory response as we continue to move forward. I'll see you in our next lesson video.

In the inflammatory response, which immune cells are the first to begin the immune response to an injury?

• A. The neutrophil cells are the first to respond to the injury and begin removing invading microbes.
• B. The mast cells release inflammatory mediators to recruit other immune cells to the injury site.
• C. The macrophages release histamine to dilate the blood vessels allowing immune cells to enter the injury site.

3) Vasodilation

In this video, we're going to talk briefly about the 3rd step of the inflammatory response, which is vasodilation. Vasodilation is the dilation or the enlargement of the blood vessels that increases the permeability of those blood vessels. The increased permeability allows for cells of the immune system to leave the bloodstream and enter the site of infection. This increased permeability is in response to inflammatory mediators. Inflammatory mediators that are released by mast cells lead to vasodilation, the enlargement of the blood vessels, and the increased permeability of those blood vessels.

The term diapedesis refers specifically to the migration of immune system cells through the intact walls of the blood vessels into the infected tissue. The term exudate refers specifically to the fluid mix of blood plasma, proteins, and immune cells that exit the bloodstream to the infected site. Recall from some of our previous lesson videos that neutrophils are the very first type of cells to be recruited to the site of infection. They are the first phagocytes that are recruited. Taking a look at our image down below, we have the 3rd step of the inflammatory response, which is vasodilation and diapedesis. What you'll notice here is that the cells in the infected area are battling many microbes. The mast cells, upon releasing those inflammatory mediators, lead to vasodilation. Here we have dilated blood vessels. These dilated blood vessels increase the permeability of the blood vessels, allowing for diapedesis. Diapedesis, again, is the migration of blood of immune cells from the blood into the site of infection. Macrophages and neutrophils can be recruited, and again, it's the neutrophils that are the first to be recruited to the site of infection.

This concludes our brief lesson on the 3rd step of the inflammatory response, vasodilation, and we will be able to get some practice applying these concepts and talk about the 4th and final step of the inflammatory response as we move forward in our course. I'll see you all in our next video.

Which of the following is needed for vasodilation and diapedesis to occur at an infection site?

• A. Mast cells releasing histamines and cytokines to dilate the blood vessels & recruit immune cells.
• B. Adhesion proteins on the endothelial cells of the blood vessels allowing the immune cells to leave the blood stream.
• C. Exudate full of blood, plasma, proteins and immune cells exiting the blood stream to the infection site.
• D. All are needed for vasodilation and diapedesis to occur at the site of an infection.

4) Removal of Invading Microbes

This video, we're going to talk about the 4th and final step of the inflammatory response, which is the removal of the invading microbes. The phagocytic cells that migrated from the blood into the infected area are going to destroy or eliminate those invading microbes. Now the neutrophils are going to remove microbes through degranulation or through phagocytosis, and macrophages are going to perform phagocytosis and engulf the cells, the dead cells in the area to help destroy and eliminate all of the microbes that have invaded. Taking a look at this image down below, the 4th and final step of the inflammatory response is phagocytosis of the invading microbes, and removal of those invading microbes. Notice in this image we have neutrophils and we also have macrophages. Together, they will work to eliminate these microbes and remove those microbes. This here concludes our lesson on this 4th and final step of the inflammatory response. Moving forward, we'll be able to get practice on these concepts and also continue to talk more about the innate immune responses. So I'll see you all in our next video.

Which immune cells are responsible for removing dead or damaged host material at an injury site?

• A. Macrophages.
• B. Mast cells.
• C. Neutrophils.
• D. Platelets.

Match the scenario to the step of the inflammatory response it belongs in.

1. Tissue Damage & Infection.
2. Release of Inflammatory Mediators & Cytokines.
3. Vasodilation and Diapedesis.
4. Removal of Invading Microbes and Damaged Tissue.

_____ Local mast cells release histamines and cytokines when encountering an invading microbe.
_____ Neutrophils destroy the invading microbes found in the injury site.
_____ Peter accidentally cuts his finger with a kitchen knife.
_____ Fluid full of plasma, proteins and immune cells exits the blood stream at injury site.
_____ Macrophages remove the epidermis and dermis cells damaged by the injury.
_____ The blood vessels in the region of the injury dilate releasing immune cells and proteins.
_____ Pathogenic bacteria enter the host's body.

Okay, everyone. Here we have our next practice problem, and it's kind of a matching problem. So we're going to match the scenario with the step of the inflammatory response it belongs to. We have the 4 steps right here. And then we have all of our different scenarios. We're going to put a 1, a 2, a 3, or a 4, depending on where it belongs in the inflammatory response. So let's start with the first one. Local mast cells release histamines and cytokines when encountering an invading microbe. When does this happen? This is going to happen right after injury or infection, which means it's going to be the signaling stage or the release of the inflammatory mediators. So I'm going to put a 2 right here. Okay. So what about the second one? Neutrophils destroy the invading microbes at an injury site. That's going to be when all of the immune cells are there trying to do their function of removing all of the infectious material. So I think that's going to be number 4, removal of invading microbes and damaged tissue. And then we have the third one. Pete, poor Pete, accidentally cuts his finger with a kitchen knife. That's going to be how the infection occurs, how the bacteria from the kitchen knife get into Pete's body. So that's going to be tissue damage and infection, number 1. So this is what started the whole process, his injury. The fourth one, fluid full of plasma proteins and immune cells exits the bloodstream at the injury site. So this is going to be how the body is getting the immune cells and all of those immune proteins to the site that it's needed at the injury site, so at his cut finger. And this is going to happen when the blood vessels are dilated in a process of vasodilation, and this is called diapedesis when all of these things exit the bloodstream. So this is number 3, step 3. So then we have the fifth scenario. Macrophages remove the epidermis and dermis cells damaged by the injury. So we know that the epidermis and dermis are going to be skin layers. And if macrophages are removing the dead or damaged cells from that cut that Pete made, that's going to be step number 4. The second to last scenario, blood vessels in the region of injury dilate, releasing immune cells and proteins. This is going to be the process of vasodilation, which is going to be step 3. And then we have the very last scenario, pathogenic bacteria enter the host's body. This is going to happen whenever Pete cut his finger. So that's actually going to be step number 1. So we've added all of the steps that these different scenarios belong to in the inflammatory response. Okay, everyone. Let’s move on to our next video.

Damaging Effects of the Inflammatory Response

This video, we're going to talk a little bit about the damaging effects of the inflammatory response. And although inflammation is designed to eliminate microbes and protect us from microbes, sometimes inflammation can result in significant damage to the host. This is really accidental damage because the inflammatory response is supposed to be eliminating microbes. The inflammatory response can be somewhat similar to a sprinkler system in a building, where the sprinkler system is designed to project water and eliminate and prevent fires. However, sometimes, the sprinkler system can also cause accidental damage to electrical equipment. That's why the inflammatory response can be an analogy to a sprinkler system because it's designed to eliminate microbes, but sometimes it can cause accidental damage to the host.

Depending on the location of where inflammation occurs within the host, inflammation can actually be life-threatening. For example, if inflammation occurs in the brain, it can be very life-threatening. The suffix -itis is found in many disease names and it specifically means inflammation. You can find that suffix in terms like meningitis or encephalitis. That suffix -itis means inflammation. Below, we're showing you just an image of rheumatoid arthritis, which is basically inflammation that occurs in the joints. Meningitis and encephalitis are basically just inflammation of the meninges or the membranes of the brain, or inflammation of the brain itself, which again can be life-threatening. It's important to keep in mind about the inflammatory response that occasionally it can have some damaging effects.

This concludes our brief lesson on the damaging effects of the inflammatory response. Once again, we'll be able to get some practice applying these concepts as we move forward. I'll see you all in our next video.

Which of the following statements about the inflammatory response is false?

• A. It includes vasodilation of the blood vessels and the release of immune cells from the blood stream.
• B. Neutrophils are the first cells to exit the blood stream during the inflammatory response.
• C. Apoptosis of infected cells triggers the inflammatory response.
• D. Chronic triggering of the inflammatory response can damage the host.
• E. Major signs of inflammation include:redness, swelling, heat, pain, and loss of function.

Rheumatoid arthritis is an autoimmune disease, meaning that the body's immune system attacks the body's joint tissues. Why are many autoimmune diseases associated with chronic inflammation?

• A. The tissues the immune system is 'fighting' are always present, so the inflammatory response does not shut off.
• B. The invading microbes are not easily killed and keep reforming causing chronic inflammation.
• C. The invading virus goes dormant in the body and later reemerges causing prolonged periods of inflammation.

Which of the following is FALSE in regards to inflammation?

• A. It is a component of the second line of defense.
• B. It is caused by antibody­antigen complexes.
• C. It is a component of the first line of defense.
• D. It can be caused by endotoxins.

Here’s what students ask on this topic:

What are the four key steps of the inflammatory response?

The four key steps of the inflammatory response are: 1) Tissue damage and infection: This initial step involves the breach of innate immunity due to tissue damage, allowing pathogens to enter. 2) Release of inflammatory mediators: Mast cells release cytokines and inflammatory mediators like histamine, which promote inflammation. 3) Vasodilation: Blood vessels dilate and become more permeable, facilitating the migration of immune cells to the infection site. 4) Removal of invading microbes: Neutrophils and macrophages eliminate the pathogens through processes like phagocytosis. These steps collectively help in containing and eliminating infections, although they can sometimes cause accidental damage to host tissues.

How do mast cells contribute to the inflammatory response?

Mast cells play a crucial role in the inflammatory response by releasing cytokines and inflammatory mediators such as histamine. These substances are released in response to tissue damage or microbial invasion. Histamine, for example, promotes inflammation by causing local blood vessels to dilate and become more permeable. This increased permeability allows immune cells to migrate from the bloodstream to the site of infection, facilitating the elimination of pathogens. Thus, mast cells help regulate the inflammatory response and attract other immune cells to the affected area.

What is vasodilation and how does it aid in the inflammatory response?

Vasodilation is the process of blood vessels enlarging and becoming more permeable. This occurs in response to inflammatory mediators released by mast cells. The increased permeability allows immune cells, such as neutrophils and macrophages, to leave the bloodstream and migrate to the site of infection. This migration, known as diapedesis, enables these immune cells to reach and eliminate invading pathogens more effectively. Vasodilation is thus a critical step in the inflammatory response, facilitating the rapid deployment of immune defenses to the affected area.

What are the potential damaging effects of the inflammatory response?

While the inflammatory response is designed to eliminate pathogens and protect the host, it can sometimes cause accidental damage to host tissues. This is similar to how a sprinkler system can damage electrical equipment while extinguishing a fire. Inflammation can be particularly harmful if it occurs in sensitive areas like the brain, where it can be life-threatening. Conditions such as meningitis (inflammation of the meninges) and encephalitis (inflammation of the brain) illustrate the potential dangers. Chronic inflammation can also lead to diseases like rheumatoid arthritis, where persistent inflammation damages the joints.

What role do neutrophils and macrophages play in the inflammatory response?

Neutrophils and macrophages are key phagocytic cells involved in the final step of the inflammatory response, which is the removal of invading microbes. Neutrophils are the first to arrive at the infection site and can eliminate pathogens through degranulation or phagocytosis. Macrophages follow and continue the process of phagocytosis, engulfing and digesting pathogens as well as dead cells. Together, these cells help to clear the infection and restore tissue health. Their coordinated action is essential for the effective resolution of inflammation and the prevention of further tissue damage.