Hello class, this is Professor Mariah Evans. This is BSC 2085, Anatomy and Physiology 1, and this is the lecture on the integumentary system, which is the skin. So one of the things I want to tell you is that for your next exam, it's going to be on skin and bones.
Skin and bones. I say it like that because it sounds corny. So the integumentary system is the skin. It is much more than just the skin. Overview of the integumentary system will tell you that we'll be talking about skin and hair and nails as well.
And then we'll also have to include the skin that has sweat glands and sebaceous glands. And we also have sebaceous glands in our hair and the oil that's released from these sebaceous glands keep our skin moisturized and keep our hair moisturized. All right, so skin itself has two regions, an epidermis, which is the superficial region, and the dermis. And of course, superficial means closest to the body surface, right?
And then the dermis is the underlying, so it's underneath the epidermis, so it would be deeper to the epidermis. And hypodermis is actually below the skin. So hypo means below, dermis, of course, is referring to the skin. Hypodermis itself is not...
true layer of the skin, but it shares some of the same components that skin shares. So it's actually a layer below the skin. So skin only has two regions, the epidermis and the dermis, and then the hypodermis is beneath the skin.
Okay. Now here's a picture. And I like this picture because this shows the lining of the skin and these are keratinized stratified squamous epithelial cells.
And you learned about those in histology lab. So this is the epidermis. And the epidermis, which we're going to learn in a few minutes, is actually four or five layers.
And the reason why it's four or five layers is because when we're referring to thick skin, like the skin that's on the hills of your foot, that skin has five layers. And then thin skin only has four layers. So. Before we get to all of those layers, we're going to talk about the cells that we see in the epidermis. But again, epidermis has four or five layers depending on if it's thick skin or thin skin.
So these are pretty easy. The suffix site means cell. So carotid sites have keratin in them.
Melanocytes have melanin. Melanin is the pigment protein that gives us our color, our skin color. And as you go out in UV, and most of you know this, As you go out in UV, then melanin can concentrate.
So you get a tan when you go out in the sun. What? Who knew? We also have dendritic cells, which are also referred to as Langerhans cells.
For the exam, you will need to know both of them because I could say, what is the function of Langerhans cells? Or I could say, what is the function of the dendritic cells? So I could say one or the other.
So please make sure you know both names. But the function of these is that they have an immunological property. So what happens is these cells have the ability to phagocytize other cells.
So they are macrophages that patrol deep in the epidermis and they keep it clear from invading things. So they have an immune property to them. And then tactile or Merkel, you'll have to know again, both of these, because I could say one or the other on the exam.
And these are the sensory receptors. So sense of touch. If someone touched your skin very lightly, you'd be able to feel it.
If someone, you know. pressed on it very, you know, hard, you'd be able to feel it if someone flicked you, or if someone was, you know, taking your blood and stuck a needle in your arm, you would be able to feel it. So tactile or Merkel are the sensory receptors that allow us to perceive touch.
Now, this is what I was saying before about the layers that are in the epidermis. And I told you there's either four or five, and I was telling the truth about this. So there are five layers of skin in the thick.
skin, five layers of epidermis, excuse me, in thick skin, and then four layers of skin in the thin, four layers of epidermis in thin skin. So we're going to start from the bottom and go to the top. So started from the bottom, now we're here.
Started from the bottom, now my whole gang's here. Okay, sorry, I digress. But anyway, so basali is the basement.
So basali or basal layer is the bottom layer. The word stratum means that it's a layer. So stratum is in front of all of these. So the basement layer. and this spinosum, and then granulosum, and then lucidum, and then corneum.
Now, on the next couple of slides, they're going to explain to you that the basement layer is actively mitotic. So lots of mitosis takes place here. These are where the new and young cells are.
Spinosum is called spinosum because it's a spiny layer. It has these hyaline coronacyte cells, and they're kind of like prickly. So it's sometimes called the prickly layer or the spiny layer. And then granulosum has granules in it, like granules of sand, but granules. And then lucid, like if someone's lucid, that means that they're clear, they're seeing things clearly.
They're like, oh, you know, I'm really lucid. I see things clearly. So this stratum lucidum layer is a very thin, clear layer, and it's only found in thick skin. So that would be the fifth layer.
of the epidermis and thick skin. And then corneum is the most superficial layer. So the epidermis, again, has five layers if we're in thick skin, four layers in thin skin.
And then like I said, the next couple of slides are going to say exactly what I just said. So here we are with the basal or basement layer. These are actively mitotic cells.
So this is where the youngest cells would go. And it says as cells die, they move towards the surface. But I feel like you know that because I feel like you've probably heard of microdermabrasia or you've done some type of skin, you know, scrub and you took off the, you know, the most superficial layer of your skin and you look rejuvenated. That's because those were the older dying cells.
Then we have the spinosum. Like I said, the prickly layer. These are the cranial sites that have the prickle or prickle cells.
So they're spiky. So that is the... spinosum or the prickly layer that's there.
Then we have the stratum granulosum and this has again the granules. They have cranohylin granules and they have these lamellar granules. So these are grains granules. So that's why it's called the granular layer or granosum granulosum.
And then lucidum, like I said, is the clear layer. It's only found in thick skin. So it's thin, translucent means it's clear, right? So a thin...
clear band. It's only two or three rows of cells that are there and it's superficial to the granulosum. So it goes granulosum, then lucidum, and then we're about to get to corneum. So corneum is the most superficial layer of the epidermis. It's a horny layer and this is 20 to 30 rows of flat enucleated keratinized dead cells.
So 20 to 30 rows, it's stratified, right? And that gives protection. So whenever there are several layers of cells, it's usually to give protection.
So that's all it says here is that this layer provides protection. What? No way.
It also prevents water loss because it's keratinized. And then keratinized is kind of like waterproofing. And then it protects against abrasion and penetration, again, because it's several layers, 20 to 30 rows of cells. And then it can act as a barrier against biological, chemical, and physical assaults. And then we're going to talk about some of those assaults as well.
So apoptosis is programmed cell death, and we do program our cells to die. Once they have lived out their lifespan or close to their lifespan, they no longer function the way that they should function. And as a result of that, we send them a signal to die.
So apoptosis is programmed cell death. Our dead cells slough off is either dandruff or dander. For those of you who may be allergic to pets, it's the pet dander that you're allergic to.
It acts as allergens, which causes your itchy eyes and your sneezing and whatever it is that you do when you are introduced to the allergen that's associated with pets. We shed about 50,000 cells, dead cells, of course. every minute, 50,000 dead cells every minute. This is why you should change the sheets on your bed every other day. All right.
Now this right here is a micrograph. So all this is, is a picture underneath a microscope. And this is stratum corneum, the stratum granulosum, the stratum spinosum and the stratum basale.
So I see one, two, three, four layers of cells. So if I see four layers, excuse me, of the epidermis, if I see four layers of the epidermis, I can conclude that this is thin skin. Why?
Because there are five layers of the epidermis in thick skin and they're only showing four here. So that means that this is thin skin. All right.
So now of that dermis, of that dermis, right? So we did the epidermis has four or five layers depending on whether or not it's thick or thin skin. Then we're going to the dermis and the dermis is actually separated into two layers itself. So a papillary layer and a reticular layer. And so what they do is they show you that this is the epidermis and up here is that keratin.
This is the stratified squamous epithelial cells that are here and that's all epidermis. And then this is the dermis. When you look at this, there should be a tissue type in here that looks familiar to you.
Like you should be able to identify it when you see it again. In this reticular layer of the dermis, this is actually dense irregular connective tissue. See?
Dense irregular connective tissue. All right. So now that papillary layer is the superficial layer of areolar connective tissue. What?
Areolar connective tissue? Never heard of that? before. Anyway, areolar connective tissue has collagen and elastic fibers that are there. And then this dermal papillae is a superficial region.
And it sends these finger-like projections up into the dermis. And what happens here is that there are tactile corpuscles. I love to say the word corpuscles. So tactile corpuscles or mesner corpuscles, and that allows us to perceive touch.
So there's free nerve endings there, and those have a lot of touch receptors called tactile corpuscles, or they could be called mesner corpuscles. Now, we do have these finger ridges as well, and believe it or not, they do serve a function. So we have unique fingerprints. I think most people know that. And these ridges that are on our finger, these little friction ridges, they actually help us hold on to things.
Now, if you've ever washed anything... out by hand and you use bleach, you know that your hands get slimy, right? They feel slimy.
And those friction ridges that we have actually aid or help us with gripping and they contribute to our sense of touch. And then they give us, of course, a unique fingerprint pattern. So this is a scanning electron microscope.
So we're scanning electron microscope down there. And these are the friction ridges. ridges of our fingertips.
So these again would be what would give us our fingerprint, right? So the friction ridges actually help us for gripping and then enhance, you know, the sense of touch that's there. And then of course, like I said, we have individual or unique fingerprints. Now in that reticular layer, as I showed you in the picture, in that reticular layer, we actually have the dense connective tissue.
So dense irregular connective tissue is there. And collagen fibers are there. So collagen is the most abundant protein in the body. Collagen is in your hair.
Collagen is in your skin. Collagen is in your muscle. Collagen is in your bones. Collagen is on your skin.
I'm telling you, collagen everywhere. So collagen fibers help provide strength and resiliency in this reticular layer of the dermis. Now, we also see in this dermis the blood vessels, and then we can also see nerve fibers that are in there and pockets of adipose tissue as well. Now, also in that reticular layer, we see these cleavage lines.
And the cleavage lines are kind of cool because surgeons use these. So they make incisions that are parallel to those cleavage lines. And that allows the incision to heal better.
And it basically blends in. Like a lot of times if they do it properly, of course. Um, you won't even see, you know, where your scar is because they made it parallel to the, um, the cleavage lines. And as a result of that, they heal better.
So that's kind of cool. Now, I'm not going to pretend to judge anyone who believes in, um, fortune tellers, the people who read the palms of your hands. What I will tell you is this, is that if you yourself look at the palm of your hand and you bend your fingers towards you, you will see that the lines that are in your hand are flexure lines. They are flexure lines because there's joints in your hand, and when you move your hand, those flexure lines become creased. If you look at your fingers, you'll learn, because we're about to start the skeletal system in the lab, you'll learn that each of your fingers, not your thumb, which is digit number one, but each of your fingers has...
three phalanx and at each phalanx there is a joint and so you can bend your finger in three places because there's one, two, three, right? So a joint in each of them. Your thumb only has two phalanx. It has a distal and a proximal phalanx whereas your fingers has a distal.
which is the furthest distance from the body, proximal, which is the closest distance to the body, and then middle, so it's in between. So your fingers have three phalanx and your thumbs have two. Now, those flexure lines are because they're at joints. So every time you bend your fingers or bend your hand or look at your hands and bend, it's bending along those lines.
So those are the flexure lines. And then these are stretch marks. So this is evidence that your skin stretches. They leave striae, like striations, right?
So they leave striae, and they're commonly referred to as stretch marks. So extreme stretching of the skin is what causes these scars to occur. So other things that can happen as far as skin being damaged is that if you suffer a second-degree burn, you get a blister. And that's...
the fluid in between the dermis and the epidermis. You can also get a blister from friction. So if you wear shoes that are too small, they could be rubbing up against your heel and you get that blister on the back of your heel and it's so painful.
And that's because there's trauma to the skin. And then the fluid feels again, separating, like I said, the dermis and the epidermis. So we talked about melanocytes and I told you that... melanocytes had the melanin and melanin is a pigmented protein that's responsible for our skin color.
Well, melanin is also responsible for your eye color and your hair color and freckles and moles. So, you know, not liking someone or treating someone differently because of their skin color would be the same as treating someone differently because they had freckles or because they had brown hair or because they had a beauty mark like Cindy Crawford, you know. So melanin is what gives the pigmentation, right? So it's made by the melanocytes, as we said earlier. And then I said that, you know, if we go out in the sun, the UV would cause an accumulation or concentration of melanin.
So you get darker, right? You get a suntan from being out in the sun. So melanin does have a variety of shades that are associated with it. So reddish yellow to like a brownish black color.
And then all humans have the same number of the cranocytes. but different colored differences are due to the amount of melanin that are there. And then, like I said, freckles and moles are accumulations of melanin, okay? And, oh, let me just go back to this really quick.
The difference between a freckle and a mole is that freckles do not have any texture to them whatsoever, and moles do have texture. So if you see this accumulation of melanin on your skin and you rub over it and you can feel it, it's a mole. If not, then it's a freckle.
Now, other skin colors besides that range of, you know, going up to what they call this brownish black color, right? So reddish yellow to brownish black color is keratin. And like carrots, this is a yellow orange color.
So a yellow to orange pigment. It's obvious in the... Palms of your hands and the soles of your feet. And keratin can be converted into vitamin A, which is good for your eyesight. And we'll talk about that at the end of this six weeks when we talk about the special senses, because we will talk about vision and we'll talk about how beta keratin is our source of vitamin A and how that's good for your eyes.
Then hemoglobin is in your blood. So people who are fair skin, like... Caucasians, right? Here, and I love this, that they call them transparent. But basically what happens is, is that if you're very fair skinned and you get excited or flustered, then you turn red, right?
People look at you and like, oh my God, your face is so red. So when you get excited, your face turns red. If you're embarrassed, your face turns red. If you get hot, your face turns red, you know, and that's the hemoglobin that we can see underneath this transparent layer of skin. So hemoglobin has a pinkish hue.
And people who are very fair skin look pink or red when they get embarrassed or, you know, flustered, et cetera. Now, the sun is damaging to skin. So excessive sun exposure damages the skin. And that's because the UV can damage DNA. And damaged DNA can lead to abnormal cellular periferations.
and abnormal cellular proliferations could become tumors, and tumors could become malignant. So let's see if I put this all together right. I just told you that the sun can cause cancer.
But you know that. You know that because we live in Florida, and you know that malignant melanoma runs really high in places where people are exposed to a great deal of sun. So we're Florida, we're the sunshine state, right?
And so we have to protect ourselves from the damage that the UV can do to our DNA, and we do that with sunblock, okay? So damaging to the DNA could lead to skin cancer. UV light also destroys folic acid.
and folic acid is necessary for proper DNA synthesis. Women who are pregnant have to make sure that they get the right amount of folic acid. If not, it would lead to birth defects, so neural tube defects in their child. We also have a photosensitivity, which could mean that people have reactions when they get too much sun.
So some drugs like antibiotics and antihistamines. and perfumes could cause this photosensitivity. So you could be on an antibiotic and you could get too much sun exposure and you could end up with some type of rash because of the antibiotic that made you photosensitive.
Okay, now other colors of skin that are problematic. You should not be blue. I just want to put that out there on the table. You should not be blue. It is not normal for you to be blue unless you are Smurf.
or an avatar, or you are a member of the blue man group. That's it. If you are blue and you are not one of those characters, then something is wrong.
It is usually an indication that there's low or no oxygen. So cyanosis is when the skin becomes blue and it's usually, again, due to the fact that there's no oxygen there. Your athema is redness and that should make sense because in histology.
we learned that their red blood cells were called urethrocytes. And we know the suffix cyte means cell, so red cells. So urethema would be redness.
Pallor is exactly what it sounds like. You're pale, right? Your skin becomes pale.
It happens sometimes if you're really anemic, it can happen if your blood pressure is really low. It can happen if you're scared. If someone says, oh my God, what's wrong?
You look like you've seen a ghost because people get really pale. And it can also happen when you're angry. And then there's jaundice.
and jaundice gives you this yellow cast to your skin, and it's usually an indication of liver disorder. So a lot of times if there's excess bilirubin that has built up, then we put you under UV light, and UV breaks down that bilirubin, and it helps take away the jaundice color of the skin. Then there's bronzing, and this, of course, this is abnormal.
This is not like I went to go, you know, I didn't put on a bronzer. I didn't go and put on... some type of, you know, tanning oil to get me this color or spray tan.
These are abnormal colors that are an indication of disease. So bronzing is usually inadequate steroid hormones. And we see that in Addison's disease.
And then a bruise is when you've damaged the vessels and the blood is leaked out of them and it's clotted underneath your skin. And if you've ever had a really good bruise, I know you saw the black. and the blue and some purple and red and even yellow colors in bruises. I mean, if you had a really, really good one. And then we're going to move on to hair because remember, integumentary system is not just the skin, but it's also your hair and your nails.
So when we look at the hair, we have hair all over our body. We are mammals. And that is one of the characteristics of mammals is that they have hair all over their entire body.
But there are places where there's no hair. We do not hair. have hair on the palms of our hands, the soles of our feet. We do not have hairs on our lip, now above the lip and below the lip. So beards and mustaches, yes.
We do not have hairs on our nipples. Men can have hair around their nipples, like in the areola. Women usually don't, but I guess they could.
And then portions of the external genitalia, there is no hair on the shaft of the penis or the head of the penis. Now there is pubic hair, right? So pubic means genital. But there is that hair.
It just isn't on the actual shaft of external genitalia. Now, hair serves a function. It warns us that insects are crawling on us.
I think that's funny that they put that there, but obviously it's a function of hair. Hair on your head protects you against physical trauma. If you have a lot of hair on your head and it's really thick, all that means is that, you know, you could hit your head against something and it wouldn't hurt as much because there was a lot of hair there to protect you.
Hair also protects you from heat loss. So I was born and raised in Michigan and it snows in May in Michigan. And so I was always told as a little girl that I had to wear my hat when we went out to play in the snow. And that's to hold the heat in.
So protect from heat loss. Your hair does that. And then, of course, if you put a cap on top of it, that aids it even more. And then if you've ever seen anyone who's bald head and they live here in Florida, you've seen them sunburned. So you've seen their head, you know, completely burnt.
And that's because they don't have the hair. to protect them from the sunlight. All right, so hairs are also called pili. And if you have erector pili muscles, which we all do, those are what give you goosebumps.
The erector pili muscles give you goosebumps and it makes your hair stand up on end. So erector, like standing erect, and then pili, like hair. So erector pili muscles are responsible for your goosebumps. Now, I'm not going to ask you. any questions on the exam about the structure of hair.
But there is keratin, as I mentioned before. So keratin is found on our skin, keratin is found in our hair, and keratin is found in our nails. The difference between the keratin is that it has this loose lattice formation when it's in our hair and our skin. And then when it's in our nails, it's really hard and it's just brought together really, really close. So it's brought together really close and then it's hard and durable.
And if you didn't know this, rhinoceroses'horns are also made of keratin. So keratin, nice and hard. Okay, so let's see. So the rest of that is about the structure of the hair.
I just wanted to mention the keratin part. And so the medulla is the middle and cortex is the outer side. That's going to hold true for everything that we talk about.
Um, when we get to the nervous system, we're going to talk about the, um, the medulla and we're going to talk about the cortex. And when we talk about lymph nodes, we're going to talk about the medulla, which is the middle part and the cortex, right? So this is going to hold true for everything that we talk about coming up next. And then cuticles, as you guys know, um, that's this, you know, little layer on the outside there overlapping.
Now, hair has melanocytes in it as well because The melanocytes are what give us our hair color, right? So the melanin that's there. So again, we have a combination like yellow and rust colored and brown and black to give us the hair colors.
And then when you get gray hairs like I do, so I have about, I don't know, eight or nine of them now, they result from the reduced production of melanin. So if melanin is given the pigmentation and the older you get, and I know people get gray hairs much earlier in life. But the older you get, the less functioning the melanin production is. And as a result of that, the hair has these bubbles in it, and then there's no melanin there.
So you see them as gray or silver. And again, there won't be any pictures. You don't have to draw out the pictures.
But this is a hair follicle. Now, I do want to say this about the hair follicle, is that if you want to get DNA from someone's hair, you have to pull it out from the roots. You have to pull it out from the roots.
There are some things that we can learn from hair. We can like determine whether or not the person has dyed their hair and then how recently they dyed their hair by what it looks like in the cortex versus the medulla. We can also tell or give an approximation on whether or not we think, and it is, we are approximating because we are assuming that coarser hair is negroid hair and that it is not. The softer hair is Caucasian hair. So we can make approximations, assumptions about that.
But we can also determine feline hair from other animal hair like canines. So feline is cat hair and canine would be dog hair and then human hairs and things like that. So there are some really cool things we can determine from hair, but we cannot get any DNA unless the hair has been pulled out by the bulb.
Okay. Now, as far as the vellus hair is, this is what adult females have all over their faces, for example, and on their bodies. And then children have this as well.
The terminal hairs are the ones that you find on your eyebrow, your scalp, your axillary region. So, of course, your underarm region, your pubic hair, those are terminal hairs. And then males, the beards and the mustaches, those are considered to be terminal hairs. They're much coarser hairs. And then we have the fact that we lose about 90 scalp hairs daily.
But if you are stressed out or you're getting older, then you lose many, many more. All right. So in this picture down here, this is hertzoism.
And hertzoism is when there's excess hair growth on the face. So if you look, these are the family members that inherited the gene for that. And alopecia. is when you have a loss of hair. Heritism is excessive hair growth, and alopecia is hair loss.
Okay, so here's alopecia, and it does happen as you get older. So as I was saying, so I'm 49, and so I'm losing more hairs. And then there's true or frank baldness, and that is sex influence. And then there's male pattern baldness, and that's based on the dihydrotestosterone. So yes, men do go bald, women go bald as well, and hair thinning is normal after the age of 40. So your hair does get thinner, and that's normal to aging.
And then all this does is show a picture of the nail, and the only reason why I bring this up is because I know you guys know you can cut your fingernails without feeling it. There's no nerve endings. This is the free edge.
However, this body part of the nail, if you look under here, we see vessels. So the red ones are arteries, the blue ones are veins, and there's also nerves. So if you bend back your nail too far or you pull off your nail, which is a torture technique, if you guys have watched any of those shows, it's very, very painful because of the nerve endings that are there.
Now we're moving on to the sweat glands. So remember, we have sweat glands. We sweat to keep us cool.
right? So that is one of our negative feedback mechanisms. You go outside, it's like yesterday, 106 degrees heat index.
You go outside, you begin to sweat and increase blood flow to the surface of your skin. Evaporative cooling cools you down, brings your body temperature down. Well, we have sweat glands, so pseudoriferous, so like odor glands that are there.
There's two main types. We have these eccrine glands, which are sometimes called mericrine glands. And then we have apricot glands.
And the apricot glands, this is easy since they start with an A. The apricot glands are in the axillary region, so your armpit, and the anal genital area, so your, you know, genital area. And this is where the funky sweat comes from. Like, no lie, this is the funky sweat.
It is a thick, viscous, yellow sweat that bacteria love. And since bacteria love it. They multiply in it very, very quickly, rapidly, and that's what causes you to be funky.
Now, the eccrine, these are the most abundant. So these are the ones like when you see someone sweating on their forehead or you see their arms like sweat coming, you know, from the pores of their arms. Those are the eccrine glands.
So the most abundant ones, apocrine glands, like I said, axillary and anal genital funky. This is the funky stuff right there. And then it's going to tell you the same thing I just said, I promise.
So, eccrine, the most numerous ones, your forehead, the palms of your hands, the soles of your feet, these are the ones that help you with thermal regulation. So, you sweat, of course, to cool down. And then they're just showing you how the sweat glands, because we're going to talk about sebaceous glands too, which these are they right here, but the sweat glands are in the skin, which is why we're talking about them in the integumentary system. And then these are the apricot glands.
And I've already told you about these. So axillary, anal genital. So apal, right?
Axal and anal, all As. Like I said, it's yellow. It's thick. It's viscous.
Bacteria love it. And this is what leads to funk. So body odor.
Let's see. They begin functioning at puberty. And we believe that their function may act as a sexual scent. So yes, a sexual scent.
And now we have some modified sweat glands. So mammary glands, which secrete milk, right, are actually modified sweat glands. And your sermonian glands or simonious glands are the ones that allow you to secrete earwax.
So again, both of those are modified sweat glands. And then they secrete earwax and milk, you know, versus sweat. Now, the sebaceous glands, like I said earlier on, The sebaceous gland secrete oil, the oil is to help lubricate our skin so it softens our skin, but it also softens our hair.
If you are, you know, Latino or if you are African American, we typically don't wash our hair daily because we want those natural oils to build up and protect our hair from being brittle and dry and breaking off. We actually add oils to our hair. for that very reason. So sebaceous glands are widely distributed throughout our skin, of course, and then of course it's in our hair as well.
And there is the sebum, right, that the sebaceous glands secrete. This could actually lead to acne, which I think most people know as well. But anyway, so it's oily, it can be bactericidal, which means it can kill some bacteria.
And again, its function, it works to soften our hair and our skin. All right, and then they just show you, so this is a sebaceous gland here, this is a sebaceous gland here, those were the sweat glands, and they just show you what they look like on a micrograph, so a photomicrograph, so underneath a microscope. So this is what I was saying about having acne or pimples, right, zits. So whiteheads are blocked sebaceous glands, so if you've ever squeezed a whitehead, you saw the little, you know, white stuff come out.
If it becomes oxidized, then it's a blackhead. And if you, again, if you've ever watched any episode of Dr. Pimple Popper, or if you've popped your own pimples at any time in your life, then understand that the sebaceous glands are what leads to your whiteheads and your blackheads. So acne is when it becomes inflamed, inflamed, and we get these pustules that are there. If you've seen anyone with really bad acne, you see that it's red and inflamed around the area. where you see the pustules, so the actual pimple.
And then my granddaughter has cradle cap, and so it's called saborea dermatitis, and it's this overactive sebaceous glands, and they get these like flakes on the top of their head. They're like this yellow to brownish color. Now, this picture that I'm about to show you is not nearly, my granddaughter's is not nearly this bad, but this is.
And also my granddaughter has a lot of hair, so it might be a little bit more difficult to see. But this baby right here has saborea dermatitis. And so that's cradle cap. And I sometimes say it too fast and I'd be like cradle crap, but cradle cap, I said it right this time. All right.
So now what are our functions of skin? We know that skin is the largest and the most vulnerable organ. It's the largest because it covers our entire body. It's vulnerable because it's on the outside.
It offers us protection. We've already talked about the fact that the epidermis is several layers, right? And then if you looked at the stratified squamous epithelium, that's part of the stratum cornea, which is the most superficial layer of the epidermis. So again, the more layers there are, the more protection it offers. Another thing that skin helps us do is regulate our body temperature.
So I mentioned yesterday that the heat index was 106 degrees because it was. And so when you go outside... Um, that heat causes increased blood flow to the surface of your skin that causes perspiration, which leads to evaporative cooling. So when, um, when your sweat evaporates from the surface of your skin, it actually brings down your body temperature. And then cutaneous sensations just means that you can feel things on your skin.
Metabolic functions. For example, we synthesize vitamin D because UV penetrates our skin. skin and the synthesis of vitamin D. 5% of our blood is in our skin.
So that's why it says blood reserve there and well, blood reservoir there. And then when we do sweat, we do get rid of like nitrogenous waste. So excretion of waste, all of those are functions of skin. So here's that protection that we were talking about with the skin protects us against microorganisms and abrasions and temperatures and harmful chemicals. We have chemical barriers, physical barriers and biological barriers.
Biological barriers are going to be cells, right? Because cells are living. A physical barrier is the fact that there are many things that can't penetrate intact skin.
And then there's chemicals like... pH, because our skin has this, you know, acid mantle that's on it. And a lot of things do not like acid.
So as a result of that, it's protective. Okay. So the chemical barriers, again, we have the sweat, we have some sebum, we have that acid mantle, as I said before, it retards bacterial multiplication, most bacteria don't like pH, so it retards their growth. And then the melanin actually protects us from UV. So what that means is this, is that darker skin people have more melanin, right?
So concentration of melanin, which gives them more protection against UV. And that's good. It doesn't mean that darker skin people can't get malignant melanoma. It just means that their risk of getting malignant melanoma is a lot lower than people who are very fair skin. So very fair skin people or really light Caucasians.
increase their chances of getting skin cancer because they have decreased melanin and it doesn't offer the protection. Now, subsequently, because African-Americans or dark-skinned African-Americans or dark-skinned Latinos or African-Latinos, what happens is because their skin has an accumulation of the melanin, UV doesn't penetrate the skin. And they are usually the demographic of people who are deficient in vitamin D.
So just an interesting, you know, type of concept there. Now, the physical barrier, as I said before, is that most things can't get through our intact skin, right? So skin isn't really, you know, something that can be easily penetrated. Now, there are some things that can penetrate the skin. So plant oils like poison ivy, those can penetrate the skin.
organic solvents like acetone or paint thinner can heavy metals like lead or mercury like you can actually um when i was younger because i'm 49 i don't mind saying this but when i was younger we actually had glass thermometers that had mercury in them and that's how temperatures were read is that there was mercury so if you drop that glass thermometer on the floor and it broke You saw this silver metallic. It was so cool to me because I did play at Mercury when I was little because I didn't know. But you saw this little beaded up drop of Mercury that was on the ground.
And you played with it. I played with it because when you touched it, it kind of moved with you. But then when you let it go, it went back.
It was just really cool. But anyway, don't do that because it could lead to heavy metal poisoning. Anyway, and then nitroglycerin can penetrate the skin.
And then there's other drug agents that enhance or carry other drugs across the skin. So again, the skin itself is a barrier against most things, but some things can penetrate the skin. If you think about it, we put Neosporin on scratches or little wounds, right?
And the Neosporin is an antibiotic and it has the ability to penetrate the skin. Okay. Now, as far as biological barriers, I already told you that these would be cells, right?
So biological or living things. So we do have cells that are phagocytic. So remember the dendritic cells are the longer Han cells.
I told you that they are phagocytic. So they have the ability to engulf or phagocytize foreign antigens. And so that helps with our immune response. And then macrophages also help. with the immune response, and those are in the dermis.
And then DNA can absorb harmful UV radiation and convert it into harmless heat. And DNA, of course, is found in the nucleus of all cells, right, that are eukaryotic cells. And so all of these are biological barriers, so cellular base. I've already talked about how it regulates our body temperature. So under normal resting body temperature conditions, we only...
produce about 500 milliliters of sweat a day and it's kind of unnoticeable. We call that insensible perspiration. But as we go out there and try to, I don't know, weed your yard or do some type of landscaping when the heat index is 106, you're going to be sweating gallons, like literally gallons.
So up to three gallons of noticeable sweat. That's gross, three gallons of sweat. Anyway, that's called the sensible perspiration, and that is what is designed to keep us cool.
Okay. Now, if you go outside and it's really cold and you're not protected from the elements, one of the things that normally happens is that your blood is shunted to the core of your body. So it doesn't go to like your fingertips or your toes.
So people who are like, um, got lost in, in avalanches or. or something happened to them while they were skiing, and they... you know, had to be out there in the elements, you know, for a long period of time, their fingertips and their toes could be frostbitten and they could actually lose those because the body naturally takes the blood, right? Because it's regulating body temperature. It takes the blood and holds it to the core because that's where your organs are.
So the body is like, hey, we can do without a couple of fingers, but I'm going to need this heart and the kidneys and the lungs. I'm going to need them to continue to function. The cutaneous, of course, means skin. So we do have sensation, right? There's sensory receptors that are on our skin.
Extero is exactly what it sounds like. If it's an extero receptor, it's on the outside of the body. And so, yes, someone can touch you on the outside of your body and you can feel it.
And we've already talked about those free nerve endings because we talked about those when we talked about the friction ridges. And I told you there's a concentration of those. And so your fingertips are very sensitive. If you've ever given blood, and thank goodness they don't do this anymore, but they used to do a little finger stick to check your hemoglobin to see if your hemoglobin was high enough for you to give blood. And the finger stick, in my opinion, was the worst part of donating blood.
And that's because, again, the concentration of those free nerve endings makes them very sensitive to pain. Okay? Now, metabolic, and again, I said this, is that the synthesis of vitamin D.
So UV has to penetrate our skin in order for us to synthesize vitamin D. And vitamin D is needed for calcium absorption in the intestine. So vitamin D is extremely important, extremely important.
And we're going to talk about its importance again in reference to calcium when we get to the bone chapter. And the bone chapter is going to be next week. But when we get to the bone chapter, because our bones store calcium.
And if you're not getting enough calcium in your diet, then we'll send a signal and rob the bones of calcium to put it in your blood. But if you're on a calcium supplement and you're not taking vitamin D, then it's not going to help you absorb the calcium. So it doesn't do you any good. Let's see. So metabolic functions, vitamin D.
The skin also makes this collagenase and this aids in the natural turnover of collagen. It helps prevent our wrinkles. And then I told you again, 5% of our blood is in our skin. So it's called a blood reservoir.
5% of our blood is in our skin. And then the excretion of nitrogenous waste, like I said, so like when we sweat, we lose some salt and some water. And so we excrete nitrogenous waste, ammonia, urea, and uric acid. These are actually the result of amino acid. breakdown or protein breakdown.
So all amino acids have nitrogen and nitrogen is a component of all proteins because it's a component of amino acids. So urea and uric acid. And then skin cancer is not on the test. I leave skin cancer in the lecture because we live in Florida and there's a lot of common sense stuff in here that is helpful, but skin cancer is not on the test. Burns are, though, I will tell you that when you go back and read about skin cancer, the worst of these is the malignant melanoma, which is here.
Basal cell carcinoma is usually treated just by doing a surgical excision of the area that is known to be cancerous on your skin. Squamous cell carcinoma usually doesn't metastasize, but it can. And so once we do an excision of... the surgical excision of the area that is known to be cancerous. We usually follow up with some type of radiation.
And then malignant melanoma is the deadliest. Again, skin cancer is not on the exam, but I want to mention it to you just so you have an idea and then go back, of course, and read over it. And so you have to protect yourself, right?
So we have lotion. So we have sunblock. I know you've heard of it and I know you've read.
that it has, you know, UV protection, 50, 70, 90, 120, and then UVA, UVB rays, et cetera, et cetera. So protection against the UV. And then these are the cancers, and this is, again, malignant melanoma is the most deadly, most deadly.
It's highly metastasizable, so it does metastasize, and it's resistant to chemotherapy, which aids in its, you know, deadly, deadliness. And then burns are on the exam. This is what you need to know about burns is that if you have a first degree burn. The epidermis is damaged and you get some reddening and some swelling and of course pain because it's a burn. The second degree burn, I talked about it already when we talked about damage or trauma to the skin.
And the second degree burn gives you a blister and that's because it affected the epidermis and the dermis as well. And the blister has fluid that separates those two layers. Then we have the third degree burn and the third degree burn goes through the entire... thickness of the skin.
The color turns like this gray white or this cherry red or this blackened color. And edema is seen and third degree burns are actually less painful than second degree burns. And that's because you usually destroy the nerves. And the burns are so bad that we usually have to do skin grafting as far as treatment of the scars. So in this picture here is a little kid.
First degree burns on his or her fingers. And then the second degree burn on this baby's palm probably touched a hot pan or a hot stove. And then, of course, got first and second degree burns. And then this one is a third degree burn.
All right. So this is the treatment of burns. I don't know if you guys have heard of debridement, but we have to remove that.
burned tissue. Scarring is horrific and unfortunately infection runs high in people with burn wounds. And so sometimes the antibiotics won't penetrate through the eschar, which is the scar of a burn. So we have to do debridement and intravenous antibiotics, excuse me, temporary covering.
I don't know if you guys have seen this lately, but there's some really cool things going on with treating burns now. by putting fish skin on the burns. It's a real thing.
You should look it up. And then, of course, the skin grafts, taking skin from some other area and grafting it to where the burn is. Okay. And that is the end of the integumentary system lecture.