Integumentary System

0:00Skin. Another thing on a long list of things that amoebas don’t have – but

0:08greatly admire – because skin, which is your largest organ, is remarkable.

0:12Being the largest organ, it’s very fitting that it’s part of a system with a very long word:

0:17integumentary system. Skin - and structures associated

0:20with it – make up the integumentary system.

0:22Why do we admire skin so much? Well, skin is critical for homeostasis because it

0:28helps maintain internal body temperature and fluid balance. As a physical barrier,

0:33it protects your internal structures and organs from being damaged. It protects from invasion of

0:37pathogens like bacteria or fungi for example. Skin is where Vitamin D is produced. Skin also

0:43has sensory functions – for example, if a ladybug lands on your arm, you are usually aware of it.

0:48The integumentary system, which includes skin, has some depth to it:

0:52this system has layers. Layers of different tissues and cell types.

0:56And you’ll find major layers can be divided into smaller layers as well. We’re going to

1:01take a little exploration of this – and a reminder- this is a general exploration.

1:04We’re going to start with the epidermis –first, I want to mention cells that can

1:09be found in different locations in the epidermis called keratinocytes. These are cells that make

1:14keratin. Keratin is actually a protein – a protein that helps cells be water resistant

1:19and tough. Keratinocytes are produced at the bottom layer of the epidermis – which

1:23we’ll get to on our tour – and they get pushed upward to the top, superficial layer of the

1:28epidermis where they are considered cornified. Cornified cells are hardened , flattened,

1:33and tough – they’re also dead – they’ve lost their organelles and are just full of keratin.

1:37Now before we start exploring the layers of the epidermis, I think it’s really helpful

1:41to have a mnemonic to remember the different layers of the epidermis from the outer layer

1:46to the inner layer. Here’s an epidermis mnemonic: Can lemurs get some bamboo? I

1:52may or may not have made that mnemonic up and there are probably better ones out there but

1:55many lemurs do like bamboo… something to be said for factual mnemonics. The first letter in each word

2:01stands for each epidermal layer- which will be called a stratum - which we’ll get to now.

2:06Outer top layer: we’ve got the stratum corneum. This layer consists of cornified cells – dead

2:12cells. They are continuously shed off with replacement cells coming from layers below.

2:16Now the next layer down, the stratum lucidum, is not in all skin areas.

2:22It’s generally just for thick skin areas like the bottom of your feet

2:25or on your palms. This layer also consists of cornified cells. They contain a type of

2:31protein that gives them a transparent kind of appearance, hence the name of this layer.

2:36Next, stratum granulosum. In this particular layer, keratinocytes that have been pushed from

2:41the lower layer and they will develop a flatter structure in this layer. They contain granules

2:45– like the name of the layer suggests- that have a variety of functions. The keratinocytes

2:50here will eventually lose their organelles and become the cornified cells of the layers above.

2:55Next, stratum spinosum. There are many layers of keratinocytes here,

2:59but there’s also a type of cell that will consume worn out cells or bacteria and by

3:03doing so – it acts like a macrophage. By the way, the name of this layer is related to how

3:09the layer looks under the microscope when it’s stained – the layer looks spiny when stained.

3:13Now, the deepest layer of the epidermis: the stratum basale. The stratum basale consists of

3:19one layer of cells called basal cells. These cells are the ones constantly doing mitosis and actually

3:25give rise to the keratinocytes in the layers above. Interesting fact: do you have especially

3:30thick skin on your feet? Or maybe on a finger? This could be a callus. Calluses generally form

3:36when the stratum basale layer is trying to respond to frequent abrasion by making more cells, which

3:42mature and result in a thicker stratum corneum. The stratum basale also has other types of cells

3:48like melanocytes – this is the cell that makes a protein called melanin. Melanin is a pigment that

3:53can result in an array of different skin colors, and melanin protects skin from being damaged by

3:58ultraviolet (UV) rays. The melanin actually gets transported to the keratinocytes in organelles

4:03called melanosomes. Merkel cells are another cell type and while their exact function is a bit

4:09uncertain – check out the further reading links on that – they are thought to have involvement

4:13with the nervous system as they work with nerves in helping us have the sense of touch. The stratum

4:18basale layer of the epidermis will be bonded to the dermis, which we’ll move into right now!

4:23The dermis. Unlike the epidermis, you will find blood vessels in the dermis. The dermis is a type

4:28of connective tissue, which is a non-epidermal type of tissue that connects things together

4:32in the body. You’ll also find sweat glands, hair follicles, and nerves in the dermis.

4:37The dermis has fibers of two types of proteins: collagen– providing support - and elastin – which

4:43gives it elasticity. These proteins are made by specialized cells in this layer called

4:48fibroblasts. The dermis has two general layers: a papillary layer – which has connective tissue

4:54that is more loose – and a deeper reticular layer – where connective tissue is more tightly packed.

5:00Now before we move to one more layer – this is a good time to mention scars. Many cuts that are

5:05isolated to the epidermis won’t scar but if a cut makes it to the dermis, it can often scar. Scars

5:12tend to look different from the rest of the skin, because they aren’t put together exactly like the

5:16original skin was. What I mean by that is that when the fibroblasts are generating collagen

5:21to fix the damage, they tend to not arrange it in the pattern that had originally been

5:26there before and accessory structures that we’ll get to later (like sweat glands or

5:30hair) won’t be re-created there. Scar tissue also tends to have less elasticity – meaning

5:36really large scars from large wounds can even affect range of movement. And occasionally,

5:42the collagen production keeps on going even after everything is healed, and you result in

5:47a raised scar that can be referred to as a keloid. That’s from this excessive producing of collagen.

5:52Ok – moving on to the last layer we’ll discuss. The hypodermis.

5:55It’s under the dermis

5:57and it connects the skin above to bone and muscle tissue. The hypodermis contains adipose tissue,

6:02which is stored body fat, and this has important functions such as insulation.

6:06Now after looking at the layers, there are accessory structures that are part of the

6:10integumentary system that we haven’t mentioned. Sweat glands, for example. We talked about sweat

6:15in our homeostasis video and how important for being used to cool the body. We should

6:19point out that sweat glands aren’t the only ways that your skin helps with temperature

6:23regulation. Blood vessels in your dermis will dilate (meaning widen) so that heat can escape

6:29through the skin. And if you’re really cold? Those same blood vessels will now

6:33constrict and be kept away from the surface of the skin so that heat can be conserved.

6:37Sebaceous glands are another accessory structure. They produce oil and help keep the skin – and hair

6:43–waterproof. They also help lubricate all those dead keratinocytes we’ve been talking about.

6:48Hair. Remember which layer we said has hair follicles? That’s right,

6:52the dermis. There are cells that are found in this hair bulb that are doing mitosis rapidly,

6:57and when they do, the cells get pushed outward as the hair root

7:00grows. The hair shaft you see itself is made of keratin and non-living.

7:04Nails. The base of your nail is part of the epidermis. While the nail body – that portion that

7:10protects the ends of fingers and toes- is made of dead keratinocytes, the nail root has cells

7:16that are doing mitosis frequently and as those cells get pushed outward, they help the nail grow.

7:20So we always like to mention the “why” – why learn about the integumentary system? Well first of all,

7:26we do want to mention that skin cancer – which according to the American Academy of Dermatology

7:30is the most common cancer in the United States – can occur when some of the integumentary cells

7:35we’ve been talking about start to not function correctly and divide out of control. For example,

7:40basal cells can also give rise to the most common type of skin cancer in humans,

7:45the basal cell carcinoma. Melanocytes can give rise to a type of skin cancer called

7:50melanoma. Merkel cells can give rise to an aggressive rare type of cancer called Merkel

7:56cell carcinoma. It is by understanding and studying the integumentary system

8:00that we can better understand how to treat these types of skin cancers.

8:04In continuing to emphasize how important the functions of the integumentary system are – let’s

8:10consider a condition where the functions can be compromised such as a burn. The degree of a burn

8:15tends to be placed in a type of category depending on which levels are affected. I do want to point

8:20out though that we’ve noticed classification of burn degrees are not consistent across all

8:24sources; check out our further reading to learn more. If going on a system that recognizes four

8:29different classification categories of a burn: a first degree burn generally is isolated to

8:33the epidermis, a second degree burn affects the epidermis and part of the dermis, a third degree

8:38burn affects the epidermis and all of the dermis, and a fourth degree burn goes beyond these layers

8:43to even affect bones and muscles. In third and fourth degree burns, the nerves are often damaged,

8:49so it can actually be less painful despite being more severe of a burn. Significant burns can be

8:55dangerous because those functions we talked about with the skin like maintaining fluids

9:00and protecting all the internal structures – that function is compromised with a significant burn.

9:06In addition, the skin is now very vulnerable to getting infected so that needs to be addressed.

9:11There are medical personnel trained to work specifically with burns, and they have to

9:16have extensive knowledge of the integumentary system in order to make a treatment plan and

9:20restore the integumentary system so that it can do all those amazing functions we’ve mentioned.

9:26Well, that’s it for The Amoeba Sisters, and we remind you to stay curious.