First-Line Defenses: Chemical Barriers: Study with Video Lessons, Practice Problems & Examples

The first line of innate immunity includes various chemical barriers that protect against microbial growth. Key components are sebum, which lowers skin pH; sweat, containing lysozyme that degrades bacterial cell walls; earwax, which controls pH and physically blocks microbes; saliva, rich in enzymes like lysozyme; and gastric juice, which kills bacteria through its acidic environment. Additionally, antimicrobial peptides (AMPs) such as defensins disrupt microbial membranes, enhancing defense mechanisms. Understanding these barriers is crucial for grasping how the body maintains homeostasis and prevents infections.

Chemical Barriers

This video, we're going to continue to talk about the first line defenses of innate immunity by focusing specifically on the chemical barriers. And so once again certain types of chemical factors play important roles in the first line defense mechanisms of innate immunity. And so here we have just a little bit of a warning that if our lesson hasn't already, it may get a little bit gross in this part of the lesson because we're going to talk about things like sweat and ear wax and saliva and stuff like that. And so here, notice we're showing you our map of the lesson on innate immunity, and already we've talked about the physical barriers of the first line of defense. So now we're moving on to the chemical barriers in the first line of defense. And so notice that sebum, sweat, earwax, saliva, gastric juices, and AMPs are all part of the chemical barriers of the first line of defense of innate immunity. And so moving forward in our course, we're going to talk more about each of these different types of chemical defenses that you see here in this lesson. And so, I'll see you all in our next video.

Sebum

This video, we're going to talk more about the chemical defenses of the first line of defense of innate immunity by focusing specifically on sebum, and how sebum helps to prevent microbial growth as a protective layer on our skin. And so sebaceous glands are specific glands on our skin that produce an oily substance called sebum. And so sebum, this oily substance, serves as a chemical barrier that can prevent hair from becoming stiff and brittle, but it also can contain fatty acids that can help lower the pH of the skin. And the lowering of the pH of the skin can thereby help to prevent the growth of certain types of microbes, thereby protecting us from certain types of microbes. And so if we take a look at our image down below, notice we're showing you our little map over here with the first line of defenses, specifically the chemical barriers, and we're focusing in on sebum right now at the moment. And so we're showing you here the sebaceous glands that are present in the skin here and, we can label this as the sebaceous, sebaceous gland. And the sebaceous gland is able to secrete oil so that the oil, that sebum, which contains oil, is going to be on the surface of our skin, and again, that can help to protect us from certain types of microbes. Here's another image that's showing you how a micrograph of the sebaceous glands can look like. And so this here concludes our brief, brief introduction to sebum as a chemical defense mechanism, and we'll be able to talk about other chemical defense mechanisms as we move forward in our course. And so I'll see you in our next video.

The ____________ glands create sebum which makes the skin more __________ which decreases microbial growth.

• A. Lacrimal glands; basic.
• B. Salivary glands; hydrophobic.
• C. Sweat glands; alkaline.
• D. Sebaceous glands; acidic.

Sweat Glands

This video, we're going to continue to talk about chemical defenses by briefly focusing on sweat. And sweat glands prevent microbial growth by perspiration. And so perspiration is the process of sweating, or in other words, the process of releasing sweat from the sweat glands on the skin. And this release of sweat helps to lower the body temperature, and it can also help to remove microbes from the surface of our skin. Also, sweat contains many different types of chemicals, including an enzyme that we refer to as lysozyme. And so lysozyme is an enzyme that degrades bacterial cell walls, and therefore it can help to protect us from pathogenic microorganisms that are trying to invade our bodies. Now lysozyme, this enzyme, lysozyme, is also found in tears, saliva, urine, mucus, and tissue fluids. And so this chemical, lysozyme, can really be beneficial to help protect several different areas and regions of our body.

And so if we take a look at our image down below at our map, notice we're focusing on the first line of defense, specifically the chemical barriers, and this time we're focusing specifically on sweat. And so here in this image, we're showing you an image of the sweat glands. And so notice that the sweat glands in this image are over here and over here. And once again, they're able to release sweat onto the surface of our skin, which can help protect us in many different ways from invading microbes.

And so this here concludes our brief lesson on sweat as a chemical defense mechanism and lysozyme as a chemical defense mechanism. And so we'll be able to learn more about other chemical defenses as we move forward in our course. And so I'll see you all in our next video.

Earwax

This video we're going to briefly talk about earwax as a chemical defense. And so earwax can help prevent microbial growth by controlling the pH. And so earwax can actually serve as both a physical and a chemical barrier in the first line defenses of innate immunity. And so it can physically prevent microbe entry into the ear, and, earwax can also control, once again, the pH of the environment. And so earwax which is a complex mixture that contains sebum which is rich in fatty acids, that can actually help to lower the pH. And the lowering of the pH can help to inhibit microbial growth. Also, earwax also contains many skin cells, and these skin cells from the ear canal contain keratin. And keratin, once again, is going to help create a dry environment that can also help to protect our bodies as well. And so if we take a look at our image down below over here on the left-hand side, notice we're showing you our first line defense map, focusing in on the chemical barriers and focusing in on ear wax here in this image. And so over here on the right, once again, we're focusing on ear wax as a chemical defense, as well as a physical barrier as well. And so notice here that we're showing you an image of the ear and the ear canal here. And you can see that there's earwax within the ear canal. And, of course, this earwax is going to contain chemicals, antimicrobial chemicals that help protect us from microbes, and, it can also help to lower the pH to inhibit microbial growth, and it can also physically block microbes from entering as well. So notice this image over here is portraying that, and you can see these microbes that are trying to enter through our ear canal are getting stuck in the ear wax. And so that serves as a physical barrier as well. And so this here concludes our brief lesson on ear wax as a chemical defense, as well as a physical barrier. And we'll get to talk more about other chemical defenses as we move forward in our course. And so I'll see you on our next video.

Lysozyme is effective at destroying bacteria pathogens because it does what?

• A. Waterproofs skin.
• B. Disrupts the bacterial cell membrane.
• C. Hydrolyzes peptidoglycan cell walls.
• D. Propels the cilia of the gastrointestinal tract.

Saliva

This video, we're going to briefly talk about saliva as a chemical defense that can prevent microbial growth. And so, saliva is a complex mixture that contains enzymes that can actually inhibit microbial growth. For example, the enzyme lysozyme. And so, recall from our previous lesson videos that the enzyme lysozyme, is an enzyme that is going to degrade the peptidoglycan layer of bacterial cell walls, thereby preventing microbes, those bacteria, from growing. And so, if we take a look at our image down below over here on the left-hand side, once again we're showing you our map of the first line defenses, focusing in on the chemical defenses here, and focusing in on saliva. And so, saliva, once again, which can be found in our mouths, is going to contain some enzymes, and those enzymes can inhibit microbial growth. And so, notice, zooming into this little cartoon that we have here, notice that these microbes here are not able to grow in the conditions with the saliva. And so, our saliva contains enzymes that limit microbial growth and prevent many microbes from being able to fully settle and cause harm. And so, this here concludes our brief lesson on saliva as a chemical defense mechanism, and we'll be able to talk about other chemical defenses as we move forward in our course. And so, I'll see you all in our next video.

Gastric Juice

In this video, we're going to briefly talk about gastric juice as a chemical defense that can help prevent microbial growth by lowering the pH. Gastric juice is really just going to be a complex mixture of many different substances that includes hydrochloric acid or HCl, as well as several different types of enzymes, for example, lysozyme and mucus, all in the stomach. This highly acidic solution is going to lower the pH of the stomach, which is therefore going to kill most of the bacteria that are ingested. It will also inactivate most toxins as well. It does serve as a first line defense, a chemical means of protecting us.

If we take a look at this image down below on the left-hand side, notice we're showing you our map of the first line of defense, specifically the chemical barriers, and we're focusing in on the gastric juices here. Gastric juice, again, is going to be a complex mixture found in our stomachs, as you can see here. We can label this gastric juice. You'll notice that the pH is going to be very, very acidic. Notice here it says the pH is about 2.5. Notice through this little cartoon here that these microbes are not most microbes are not capable of surviving in these acidic conditions. And so it is so acidic here, and notice this one saying is, it burns. It's just showing you here that many microbes are not capable of surviving those acidic environments within the gastric juice within our stomach.

This here concludes our brief lesson on gastric juice as a chemical defense mechanism, and we'll be able to apply some of these concepts that we've learned as we move forward in our course, and then we'll get to talk a little bit more about some other chemical defenses. So, I'll see you all in our next video.

Which of the following statements about the defensive roles of saliva and gastric juices are true?

• A. Saliva’s main function is to move microbes through and out of the gastrointestinal system.
• B. Saliva possesses enzymes that inhibit microbial growth and digest microbes.
• C. Gastric juice’s main function is to destroy microbes and toxins eaten by the host.
• D. Gastric juice is incredibly acidic which breaks down most pathogens.
• E. All of the above are true statements.

Antimicrobial Peptides

In this video, we're going to continue to talk about chemical barriers that serve as first line defenses of innate immunity by focusing specifically on antimicrobial peptides. And so antimicrobial peptides are commonly abbreviated as AMPs. As their name implies, antimicrobial peptides, or AMPs, are going to be short chains of amino acids with antimicrobial activity. Now, these AMPs can be found in many organism types and they are generally made in response to an invading microbe. There are many different types of AMPs that include defensins, bacteriocins, cathelicidin, dermecidin, and histatins. But here in this video, we're only going to focus briefly on defensins. And so defensins are a type of AMP, and they are positively charged AMPs that actually damage microbial membranes by inserting into the microbial membranes and causing those microbial membranes to lyse, and so it causes lysis. Now these defensins can be produced by our own epithelial cells, epithelial skin cells, to help protect our skin and to help protect our mucus membranes in order to prevent an infection. And so if we take a look at our image down below over here on the left-hand side, notice that we're showing you the map of our lesson on the first line defenses here, specifically focusing in on the chemical barriers and talking about the AMPs here in this video. And so these antimicrobial peptides, which again can be abbreviated as AMPs, are going to be these short little peptide chains, short little amino acid chains with antimicrobial activity. And so, we can label these as the antimicrobial peptides. And notice that these antimicrobial peptides can be released by our epithelial cells, and they can affect these microbes here and affect the membranes of those microbes and cause cell lysis. And so, this here concludes our brief lesson on antimicrobial peptides as a chemical barrier, protecting us as a first line defense in innate immunity. And so we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

Defensin antimicrobial peptides kill microbes by:

• A. Blocking protein synthesis.
• B. Blocking DNA synthesis.
• C. Lowering cellular pH levels.
• D. Disrupting or destroying the cell membrane.

All of the following are chemical defenses against microbial infection except which of these answers?

• A. Bodily environments with acidic pH to inhibit microbial growth or kill microbes.
• B. Synchronized movement of mucus and microbes within the mucus out of the body.
• C. Bodily fluids containing digestive enzymes to degrade invading microbes.
• D. Positively charged amino acid chains that destroy cell membranes of invading microbes.

What property of antimicrobial peptide allows them to disrupt bacterial cell surfaces?

• A. Net positive charge.
• B. Presence of disulfide bonds.
• C. Short peptide length.
• D. Large amount of hydrophobic residues.

Here’s what students ask on this topic:

What are the chemical barriers in the first line of defense of innate immunity?

The chemical barriers in the first line of defense of innate immunity include sebum, sweat, earwax, saliva, gastric juices, and antimicrobial peptides (AMPs). Sebum, produced by sebaceous glands, lowers skin pH to inhibit microbial growth. Sweat contains lysozyme, an enzyme that degrades bacterial cell walls. Earwax controls pH and physically blocks microbes. Saliva is rich in enzymes like lysozyme that inhibit microbial growth. Gastric juice, with its highly acidic environment, kills ingested bacteria. AMPs, such as defensins, disrupt microbial membranes, causing cell lysis. These barriers collectively help maintain homeostasis and prevent infections.

How does sebum function as a chemical barrier in innate immunity?

Sebum, an oily substance produced by sebaceous glands, functions as a chemical barrier in innate immunity by preventing microbial growth. It contains fatty acids that lower the skin's pH, creating an acidic environment that inhibits the growth of certain microbes. Additionally, sebum helps to keep hair from becoming stiff and brittle, which can also contribute to maintaining the integrity of the skin as a physical barrier. By lowering the skin's pH and providing a protective oily layer, sebum plays a crucial role in the first line of defense against microbial invasion.

What role does lysozyme play in the first line of defense?

Lysozyme is an enzyme that plays a significant role in the first line of defense by degrading the peptidoglycan layer of bacterial cell walls, leading to the destruction of bacteria. It is found in various body fluids, including sweat, tears, saliva, urine, mucus, and tissue fluids. By breaking down bacterial cell walls, lysozyme helps to prevent the growth and spread of pathogenic microorganisms, thereby protecting different regions of the body from infections. Its presence in multiple body fluids makes it a versatile and effective component of the innate immune system.

How does gastric juice act as a chemical defense mechanism?

Gastric juice acts as a chemical defense mechanism by creating a highly acidic environment in the stomach, which is lethal to most ingested bacteria and inactivates many toxins. This acidic environment is primarily due to the presence of hydrochloric acid (HCl), which lowers the pH to around 2.5. Additionally, gastric juice contains enzymes like lysozyme and mucus, which further contribute to its antimicrobial properties. By killing bacteria and inactivating toxins, gastric juice serves as an effective first line of defense against pathogens that enter the body through the digestive system.

What are antimicrobial peptides (AMPs) and how do they function in innate immunity?

Antimicrobial peptides (AMPs) are short chains of amino acids with antimicrobial activity, playing a crucial role in innate immunity. They are produced in response to invading microbes and can be found in various organisms. AMPs, such as defensins, are positively charged and disrupt microbial membranes by inserting into them, causing cell lysis. These peptides are produced by epithelial cells and help protect the skin and mucous membranes from infections. By damaging microbial membranes, AMPs enhance the body's ability to prevent and control infections, making them an essential component of the first line of defense.