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

Chemical barriers are crucial components of the innate immune system's first line of defense. Key elements include sebum, which lowers skin pH to inhibit microbial growth; 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 uses hydrochloric acid to kill ingested bacteria. Additionally, antimicrobial peptides (AMPs) such as defensins disrupt microbial membranes, enhancing protection against pathogens.

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.

Chemical Defenses: Sebum Prevents Microbial Growth as a Protective Layer

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. Sebaceous glands are specific glands on our skin that produce an oily substance called sebum. 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. 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.

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. We're showing you here the sebaceous glands that are present in the skin, and we can label this as the sebaceous gland. The sebaceous gland is able to secrete oil so that the sebum, which contains oil, is going to be on the surface of our skin. 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. This here concludes our 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. 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.

Chemical Defenses: Sweat Glands Prevent Microbial Growth by Perspiration

This video, we're going to continue to talk about chemical defenses by briefly focusing on sweat. Sweat glands prevent microbial growth through perspiration. Perspiration is the process of sweating, or in other words, the process of releasing sweat from the sweat glands on the skin. This release of sweat helps to lower the body temperature, and it can also help to remove microbes from the surface of our skin. Additionally, sweat contains many different types of chemicals, including an enzyme that we refer to as lysozyme. 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. Lysozyme, this enzyme, is also found in tears, saliva, urine, mucus, and tissue fluids. This chemical, lysozyme, can really be beneficial in helping to protect several different areas and regions of our body.

If we take a look at our image 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. Here in this image, we're showing you an image of the sweat glands. Notice that the sweat glands in this image are depicted here and here. 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.

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

Chemical Defenses: Earwax Prevents Microbial Growth by Controlling pH

This video we're going to briefly talk about earwax as a chemical defense. Earwax can help prevent microbial growth by controlling the pH, serving as both a physical and a chemical barrier in the first line defenses of innate immunity. It can physically prevent microbe entry into the ear, and earwax can also control, once again, the pH of the environment. Earwax, which is a complex mixture that contains sebum, rich in fatty acids, can actually help to lower the pH, inhibiting microbial growth. Also, earwax contains many skin cells from the ear canal, which contain keratin. Keratin helps create a dry environment that also protects our bodies.

If we take a look at our image down below on the left-hand side, notice we're showing you our first line defense map, focusing in on the chemical barriers and earwax. Over on the right, we're focusing on earwax as a chemical defense and a physical barrier as well. Notice here we're showing you an image of the ear and the ear canal, and you can see that there is earwax within the ear canal. This earwax contains chemicals, antimicrobial chemicals that protect us from microbes, help to lower the pH to inhibit microbial growth, and physically block microbes from entering as well. So notice this image is portraying that, and you can see these microbes trying to enter through our ear canal are getting stuck in the earwax, serving as a physical barrier as well.

This here concludes our brief lesson on earwax as a chemical defense and a physical barrier. We'll get to talk more about other chemical defenses as we move forward in our course. I'll see you in 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.

Chemical Defenses: Saliva Can Prevent Microbial Growth

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 on the chemical defenses here, and focusing 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 limits microbial growth and prevents many microbes from being able to fully settle and causes 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.

Chemical Defenses: Gastric Juice Prevents Microbial Growth by Lowing pH

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. And so, 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. And so, 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. And it will also inactivate most toxins as well. And so, it does serve as a first line of defense, a chemical means of protecting us.

And so, 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. And so, gastric juice, again, is going to be a complex mixture found in our stomachs, as you can see here. And so, we can label this gastric juice. And what you'll notice is that the pH is going to be very, very acidic. And so, notice here it says the pH is about 2.5. And so, 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. And so, it's just showing you here that many microbes are not capable of surviving those acidic environments within, the gastric juice within our stomach.

And so, 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. And 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. And there are many different types of AMPs that include defensins, bacteriocins, cathelicidin, dermcidin, and histidins. 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 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?

Chemical barriers are crucial components of the innate immune system's first line of defense. Key elements include sebum, which lowers skin pH to inhibit microbial growth; 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 uses hydrochloric acid to kill ingested bacteria. Additionally, antimicrobial peptides (AMPs) such as defensins disrupt microbial membranes, enhancing protection against pathogens. These chemical barriers work together to create an inhospitable environment for pathogens, preventing their growth and entry into the body.

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

Sebum, produced by sebaceous glands in the skin, acts as a chemical barrier in innate immunity by creating an oily layer on the skin's surface. This oily substance contains fatty acids that lower the skin's pH, making it more acidic. The acidic environment inhibits the growth of many types of microbes, thereby protecting the body from potential infections. Additionally, sebum helps to keep the skin and hair from becoming dry and brittle, which can also serve as a physical barrier to microbial entry.

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

Lysozyme is an enzyme that plays a crucial role in the first line of defense by degrading the peptidoglycan layer of bacterial cell walls. This action effectively kills bacteria, preventing them from causing infections. Lysozyme is found in various body fluids, including sweat, tears, saliva, urine, mucus, and tissue fluids. By being present in these fluids, lysozyme helps to protect multiple areas of the body from bacterial invasion, making it a vital component of the innate immune system's chemical barriers.

How does gastric juice contribute to the body's defense against pathogens?

Gastric juice, found in the stomach, is a highly acidic mixture containing hydrochloric acid (HCl), enzymes like lysozyme, and mucus. The low pH of gastric juice, around 2.5, creates an environment that is hostile to most ingested bacteria and pathogens. This acidity not only kills most bacteria but also inactivates many toxins, providing a chemical barrier that prevents infections from foodborne pathogens. The enzymes in gastric juice further aid in breaking down microbial cell walls, enhancing the stomach's protective role.

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

Antimicrobial peptides (AMPs) are short chains of amino acids with antimicrobial properties, playing a significant role in innate immunity. AMPs, such as defensins, are produced by epithelial cells in response to microbial invasion. These peptides are positively charged and can insert themselves into microbial membranes, causing membrane disruption and cell lysis. By damaging microbial membranes, AMPs effectively kill pathogens and prevent infections. They are found in various tissues and fluids, providing a broad-spectrum defense against a wide range of microbes.