Okay, welcome back to the second part now, the second half of the lecture and we have discussed previously the fibers constituting the dermis. We have discussed the different cell types that we see in a dermal biopsy. In this part of lecture, we will discuss different structures that we see in dermis. I will not go into much detail, like for example, I will not discuss the histology of hair follicle.
It's very much, it's very very complex to be discussed in one video. If we are learning about the histology of hair. in atresicency level or histology of nerve or histology of apocrine and anacrine glands but we'll quickly go through how to identify them in a biopsy slide okay so let's start let's start with the first and the most important easily identifiable structure the vessels the vessels constitute three three things you have capillaries you have veins or venules and you have arteries or arterioles.
Okay. The capillaries are round to oval, thin-walled, and they are mostly seen in papillary dermis. That means in the upper part of dermis, the upper dermis.
The veins are irregularly shaped to flattened lumen. So, if capillaries are circled, round, the veins are flattened like this or like this. Okay. Flattened lumen.
They have irregularly shaped or stellate lumen. What do we mean by stellate lumen? That means star shaped.
So they can be flattened to this extent so that the lumen might look like a star. Just imagine through a pathologist's eye. The veins are lined by a single endothelial cell layer and they are found in mid to deep dermis. So the layer constituting the venules or the veins will be a single layer.
Single layer. Okay. In contrast, the arteries are round, thickly walled structures. So what you see is a lumen and a thick wall around it. And inside the wall, you will have muscular layer.
So you have a thick wall which has muscles inside. So thick wall with muscle layer in the walls and a round lumen. So that is how you differentiate between the three vessels. Capillaries are round to oval, thin wall.
So in fact in the capillaries also you have a single layer endothelial cell. Small round single lined by endothelial cells. Large flattened single lined by endothelial cells are veins. Thicker round lumen with muscle in the walls are derrules.
Clear? Let's move forward. So in this slide you can easily see dilated capillaries. Okay, so these are all round capillaries and you can appreciate the individual endothelial cells. Okay, so these are all capillaries and we can see that these are the basal cell layer.
So it is there in the capillary dermis. Now this shows venules. So you can see that they are flattened. Let me change the pen color.
Yeah, so they are flattened. They are not round like capillaries. So these are flattened with a flattened lumen.
In fact here you can see somewhat of a capillary. If I'm not wrong these are also capillaries. While here you can see another venule and you can see the wall that they are singly lined.
That means only one cell layer thick. Isn't it? So these are larger flattened venules. If we see arteries here, so it is thick wall. The wall starts from somewhat here.
Okay, so arterioles are thicker. They have thicker walls. They have round lumen and they have muscle fibers in between.
So these are all muscle fibers are there. Okay, why? Because we know that arteries have muscles in the wall. So these are muscularly wall lined arteries. Okay, so that's how you differentiate between different vessels that you see in the dermis.
Coming to the second structure, the nerves. The nerves are wavy light pink fibers. so they are baby okay baby pink fibers they are sent they have centrally elongated nucleus with pointed ends so if you look at the nucleus it is centrally located so look at the diagram the nucleus is at the center it is elongated with the pointed ends the ends are pointy the ends are tapering so look at this the ends are tapering They are found in mid to deep dermis and also at the level of subcutis.
Okay, so these are the nerves. Nerves are essential to identify because when you're analyzing disorders like Hansen's or leprosy, you will see perineural infiltrate. That means infiltrate around the nerves. But if you see, if you're looking at a biopsy from a Hansen patient and you see a group of infiltrates in the dermis, analyze the infiltrate and you might find a nerve in between, a nerve twig in between and that is known as perineural inflammation.
Look at this slide. Can you appreciate here? Let me change the pen color. If you can appreciate here, look at this area. Just focus on this area.
You can see these wavy cells, elongated wavy cells. And you can appreciate that the nucleus is also flattened. Nucleus is flattened and the ends are pointed. So this is actually a nerve fiber in between. Look at this, look at this wavy nature.
You can easily appreciate. Let me just get rid of these markings. And you can easily appreciate the wavy nature. And here, this whole area is actually inflammation.
So what you are looking at is perineural inflammation. That is inflammation surrounding the nerves. So perineural inflammation.
So that is how you identify nerves. They are located at mid to deep dermis. They are spindly eosinophilic with a basophilic elongated flattened nuclei with pointed ends which is located at the center of the cell body.
Let's move forward. Now hair follicles, I will not be going into very much detail about hair follicles. We'll just go through how to identify hair follicles in a dermal slide.
Now hair follicles are divided into two segments. Let's just make a diagram of a hair follicle very roughly. This is the part where the epigrain gland enters this is the part where the sebaceous gland opens up and this is the part where erector pylori muscle is attached and this is the bulb very rough diagram of a hair follicle okay now upper segment okay upper segment is at the level is from the erectile let me change the color yeah upper segment is from the attachment of the erector pylori to the ostea yeah so this is the ostea ostea is the hole from which the hair shaft comes out of the body okay austria so from the attachment of erector pylori to the ostea is the upper segment From the electropylori to the root of the shaft is the lower segment.
The upper segment is stationary. That means it stays as it is. While the lower segment is transient as is seen during the growth phase. So when the hair enters the catheterine phase, the lower segment is lost. Now the further partition of hair follicles is as follows.
You have infundibulum. Infundibulum means funnel. So if you look at the Ostia and then from here if you look at the hair it looks like a funnel or an inverted funnel and that is known as Infundibulum.
Infundibulum is the part of the hair follicle that starts from the Ostia and is towards the sebaceous duct opening. So let me change the color again. From the Ostia to the sebaceous gland is the Infundibulum. infundibulum. From the opening of the sebaceous gland to the attachment of the erector pylori is isthmus.
Isthmus means neck. So from the opening of sebaceous gland to the erector pylori muscle attachment is the isthmus. Now the differentiating factor is that the lining of the infundibulum is same as epidermis and it has a granular layer. So granular layer is present in the infundibulum while the isthmus does not have a granular layer.
So that is a differentiating feature between these two. So where the granular layer stops, you have the starting of the isthmus. The lower segment has the stem which is the base of the isthmus to Adamson's fringe.
Adamson's fringe is basically the tip of dermal papilla here. We'll discuss these terms again when we are discussing histology, don't worry. So from the attachment of E. pylori to this Adamson's ridge you have the stem so this is the stem and while below that you have the bulb in which you have the matrix cells which are responsible for making the shaft and propelling the shaft upwards that's how hair grows and the bulb has melanocytes that imparts color to the growing shaft. Okay, let's move forward you will understand better with the histology picks okay so let's look at this clearer picture of a hair follicle you can distinctly see in fundibulum so this is the skin it goes inside a dermal papilla it goes out okay this is hair follicle goes inside the bulb and then come out just imagine just imagine the hair follicle pardon my Now till the end where you have the granular layer, the granular layer is the infundibulum.
So granular layer is actually a part of the epidermis. It's present here, it goes inside and it stops here. This granular layer presence is the part of infundibulum. Below the infundibulum you have the isthmus where the granular layer is absent. Here is absinthe.
Okay. And below that you have the stem. That is from the attachment of the erector pilari muscle to the suprapulbar region you have the stem.
Okay. So these are the histological parts of the hair follicle. This is how you see a hair follicle on a skin biopsy.
So let's revise again. Okay. You need to say it with me. This is the ostea. Ostia is the hole.
through which the hair actually comes out. Ostia means opening. This is the infundibulum. So you can see that the layers of the epidermis stops at the infundibulum. This is the isthmus that means from the part where the sebaceous gland opens to the rectal pilar muscle attachment which is I think roughly at this level is the isthmus or the neck of the hair follicle.
This is the supra bulb that is from the Adamson's ridge to the attachment of the rectal pilar. And then you have the bulb. So these are the parts of hair follicle roughly. Now this is the vertical long section of the hair follicle.
And you can easily see this is the shaft. The shaft has cortex and medulla. Then you have the inner root sheath.
the outer root sheath this is the bulbar area this this fringe that i'm told i was telling you about is the adamson fringe it is very important area histologically if you're analyzing the hair follicle it has the maximum number of stem cells and this whole part is the bulb here you can see the sebaceous glands this is the erector pylori so some people write it as Erectal pylori, some write it as erector pylori. This I think is the eccrine glands. Okay, so these are the vertical section of the hair follicle.
Now sebaceous glands. Let's discuss a bit about sebaceous glands. These are multi lobular structures. That means there are a lot of different lobules. Okay, these are all different separate lobules.
The labules are also known as acini. Acini means sac. So it looks like a sac in histology. All this acini drain into a common sebaceous duct.
Which is known as ductus seboglandularis. This is an old archaic term. Maybe they might ask in some viva or an MCQ. Ductus seboglandularis.
Now what essentially happens in a sebaceous gland? In the basal part of the sebaceous gland, you have small cuboidal nucleated highly mitotic sebocytes. And as the cell migrate from the basal part to the center part, the cells from initially cuboidal will gradually become large, swollen and filled with lipids or sebum.
As the cell migrates, from the basal part towards the center of the acini, it will become larger and accumulate a lot of lipids to form sebum. And when it reaches the center where the lumen is opening, so here you have the duct of the gland, and when it reaches the lumen, it will undergo holocrine secretion. Holocrine means the entire cell will burst and release its contents, and that is what happens when the cell of sebum or sebocytes secrete sebum.
So they start as cuboidal cells at the periphery of the acini and as they migrate towards the center, they will become larger, lipid accumulating and burst. And that is how sebum is released inside the duct and gradually this duct will open in the hair follicle. Hair follicle. And then from the ostea of the hair follicle, the sebum will come out. But there are four dye spots which are larger and they open directly on the skin.
They don't require a hair follicle. But most of the time, you will see the sebaceous gland with a hair follicle. And together, they are known as pylosebaceous unit.
Okay. They are known as pylosebaceous unit. That is hair plus sebum glands. So, look at this diagram. Okay.
Look at this histology. you can see large acini of sebum gland and individual sebocytes. But if you look at the periphery here, you will see these are flattened cuboidal, darkly staining cells, but as they move towards the center, they are larger now and they are more paler with a lot of lipid inside them, they are swollen.
And when they reach the lumen, they will burst and release the sebum inside the lumen. Now let's come to the eccrine sweat. glands.
Acrine sweat glands are derived from the primitive epidermal ridge. They have two portions. One is the secretory coil which is the glandular portion and then you have the ductal portion. So what actually acrine glands look like is they have a coiled structure and then a duct which opens to the epidermis.
So this is the ductal portion. and this is the secretory coil. Now, secretory coil has two types of cells, essentially three types of cells. You have clear cells, dark cells, and myoepithelial cells or myocytes.
Three types of cells. Let's learn about them. So, this secretory portion The secretory coil has three types of cells.
You have clear cells which are secretory in nature. They are located at the basement membrane. They have villi that means they have projections and they are responsible for secretion of the major part of sweat which is water and electrolytes. The dark cells are mucoid. Some people say they are goblet shaped but they are mucoid dark cells.
They are apical. Apical means towards the lumen, nearer to the lumen. They are smooth surface.
Clear cells are villi, dark cells are smooth surface. And as of now they have unknown function, but mostly people regard them as more of a regulatory function of sweat secretion. And then you have the myoepithelial cells at the basement membrane. These cells have actin filaments, they are contractile and they're responsible for pushing the sweat inside the lumen of the duct so that the sweat is excreted from the sweat ducts. Let's discuss the ductal part.
The ductal part has outer ring composed of peripheral basal cells and the inner ring in which they are called as luminal or cuticular cells. You need not remember this in detail. It's better to have a good understanding.
So we are just discussing that. The proximal part of duct has major activity as compared to distal part. So if let's say this is the secretory coil and this is the duct.
So if you remember your physiology of sweat production, the proximal part. the proximal part and distal part. The proximal part is more active as compared to distal part.
So, when the sweat is formed, it is rich in water and sodium and as it moves towards the duct, the sodium is reabsorbed in the ductal part and the sweat which comes out is hypotonic. That means it has more water and that water gets evaporated which further cools the body which is the major function of sweat. So this is a pictographic representation of a sweat gland and M stands for the myoepithelial cells. They are responsible for contraction of these lumen contraction of the secretory coil. So the sweat is eventually propelled out of the glands.
The C are the clear cells which are secretory in nature. They are rich in mitochondria because they have a lot of activity going on. They are forming the sweat.
And the D1 here, the D1 are the goblet shaped dark cells. They look like a goblet, like a cup. So these are cobble shaped dark cells.
So dark cells are more towards the lumen. Here is the lumen of the duct. So dark cells are more of the lumen while the clear cells are more towards the basement membrane.
They rest on the basement membrane. You can see the contact with the basement membrane here. So this is a pictographic representation of a ecran gland.
So in this histomicrograph, you can easily see the ecran glands. you can see that they are multicellular lined structures. These structures are lined together and they're clumped together. So what has happened is, the ecrain gland is like this, a coil. And when you cut them in a biopsy, in a sectioning, all you can see are the lumens.
And that is what you're seeing here. You are seeing lumen. So this is the ecrain gland.
And mostly you see ecrain glands adjacent to hair follicles, but they open directly into the skin. as opposed to apocrine glands which secrete their contents inside the hair follicle. Okay, let's move forward. Now this is an eccrine duct.
So this part is an eccrine gland while this is the ductal part of the eccrine gland. Okay, the apocrine sweat glands are seen in the axilla, anogenital region, areola and nipple complex. the eyelids where they are known as the moles gland and the external auditory meatus. Their development is predominantly at the time of puberty. They are derived from primarily epithelial germ layer.
It is again like the ecran glands has two parts. You have secretory part and a short duct which opens in the infundibulum of the hair follicle. So you have a secretory portion which is located at the level of deep dermis or subcutis.
and then you have a short duct which is two layered cuboidal cell and this duct opens into the infundibulum of the hair follicle. This is an important question. The duct of the apocrine gland opens into the infundibulum of hair follicle while the duct of the eccrine gland opens directly into the skin. The secretion is majorly apocrine type and a little bit of mirocrine type.
So what do we mean by that? In apocrine, this is a cell the contents are at the top and the cell will gradually pinch off the top and this part will be excreted this is known as apocrine apocrine mode of secretion while in mirocrine it forms little little vesicles secrete out the major pattern of secretion of apocrine sweat is sorry in in apocrine sweat glands is as a name suggests apocrine So here you can see an apocrine sweat glands. Now remember how the ecrain gland looks inside a microscope.
They are thicker walled, the lumen is smaller, it is multicellular line while in the apocrine the lumen is larger. You can see the cells have a very undulating or a wavy appearance like this. Okay.
I mean look at here, look at here. You can see this is a jagged appearance. Why?
Because the top part has been pinched off. Okay, so that is known as apocrine secretion. Let's zoom it up to see it a bit better. So, here you can appreciate the pinching of the apical part of the apocrine cells.
And that is how the apocrine sweat is secreted. The top part is pinched off. Okay, let's move forward. So with that we end the third part of this lecture these special structures and with this this video lecture on the histology of normal dermis is finished. We will meet again next week when we will discuss different dermal reaction pattern, we will discuss ghrelinomatous pattern, we will discuss mixed cell infiltrate pattern, we will discuss sclerosing pattern, we will discuss leprosy patterns in next week's video.
Now these two books we have already mentioned previously in the video on the epidermal histology that these two books are very good and you can easily understand you may start with this and then you you should read this i will just put the metropathology and then furthermore to fine-tune your knowledge you can read mackey's dermatopathology or livers or weed and dermatopathology but remember always see the slides. Okay. If you are just reading the books and not looking at the slides, you will never learn dermatopathology.
You can do the opposite. You see a lot of slides, you read a few books. That's a much better approach. But if you are just going to read books and not look at the slides, you will not be able to learn dermatopathology to that extent that you should actually. So go start with these two books and then gradually migrate to higher books.
So the reading recommendations, although you don't require, if you have gone through this video, is Readings, Fundamental of Pathology of Skin, IDville textbook on Dermatopathology. Now, Pathology Outlines is a good online source to look at different slides. They have good quality slides. They have good descriptions. You can go through them.
McKinsey Dermatopathology, Fitzpatrick Dermatology, 9th edition and Rooks 10th edition are the books that I have referred. And with that, I will conclude this lecture. before lecture and if you have seen both the parts together kudos to you it took a bit of time to make this lecture and that is why last week there was no video but i think this larger video i hope it makes up for it and if you have any issues any clarifications any doubts you are free to email me at my email id although i prefer if you write in the comment section with the timestamp you may comment any doubts suggestions any queries any suggestion for different videos then i do take them i do reply to them i do take some time to reply but i do eventually reply okay and next week we'll see we'll have a video on dermal reaction patterns and till then adios and enjoy your weekend