welcome to the da vinci academy histology video course the entire video course is available on youtube and covers all of the fundamental principles of histology and relevant cell biology you can find all the videos from the course by clicking the histology playlist link in the description below and then you can access the corresponding practice questions and histology lab videos by going to our website which is also linked in the description below this part of the epithelial lecture series is dedicated to a more detailed overview of glandular epithelia and the classification scheme for the glands and now we have the glandular epithelium the glands or glandular epithelia they derive from the covering epithelial tissue where some of the covering epithelial cells start to divide at a higher mitotic rate and the crowding daughter cells start to kind of invaginate into the underlying connective tissue and that happens without the breach of the basal lamina or the basement membrane and here's that process a little further along and now we have a much larger column of epithelial cells that have invaded or invaginated into the underlying connective tissue this column of cells can either organize themselves into an exocrine gland or an endocrine gland we'll look at the exocrine gland first and these glands are characterized by the fact that they're still communicating or continuing with the covering epithelium here and here's the glandular epithelium down here and then covering here as well so same things happening here covering and glandular as for the lumen or lumina that develop in the middle of such an such a glandular epithelium they communicate with the external environment as well the deeper portion of the exocrine glands the cells will differentiate into the secretory cells so these are the cells that are producing the secretory products and then releasing them into the lumen and likewise here and the glandular cells themselves can either organize themselves into this spherical structure called asynus in singular or asyni in plural or into a test tube shape like this which we call the tubule or tubules and then the upper portion of the glandular epithelia typically become the duct where the cells are typically smaller and their functions are to essentially drain the lumen into the external environment so that's exocrine glands now what about endocrine glands let's go back to this column of cells up here should this column of cells lose their connection to the covering epithelium let's say some of these cells up top here start to undergo apoptosis and leaving behind a collection of epithelial cells just embedded in the connective tissue that's the case where we have an endocrine gland where it has lost its connection to the covering epithelium and access to the external environment in this case this group of cells will either organize themselves into cords of cells or plates of cells shown here in green color like so or they can organize themselves into a spherical structure sometimes with or without a space in the middle where the secretory products can be secreted and stored there until they're ready to be released in terms of releasing the secretory products the secretory products are being released into the nearby capillary or vasculature not into any duct or external environment so endocrine glands are typically associated with lots of capillary beds within that endocrine gland let's look at some common features of the secretory cells in the glandular epithelia we'll start with the mucus secreting cells these cells are typically associated with the exocrine glands these are the columnar cells that resemble a goblet and we call them goblet cells and identified them before in a tissue like this here's the respiratory epithelium and at this point you're welcome to pause the video and see if you can identify some goblet cells based on what you saw before and perhaps you were able to identify these three there's at least three more here's one here's another here's another this might be another goblet cell there too so these are the goblet cells and they're called a goblet cells because the cytoplasmic content and the organelles including the nuclei are typically kind of pulled towards the base of the cell or the basal compartment and then most of the apical compartment is just packed full of mucin-filled vesicles that are ready to be secreted and what stains with h and e are the cytoplasmic content outlining this empty space in the middle hence the goblet so the apical compartment this is where the mucin is stored and mucin being a carbohydrate-rich molecule that doesn't attract h nor e it appears as a pale staining region with hne but with pas pas reacting well with carbohydrate-rich content it'll turn that apical compartment of a goblet cell a lovely fuchsia color like so here's another here's another incidentally this epidemiol tissue has microvilli with brush border and a lot of glycocalyx being carbohydrate rich material it reacts with pas and it shows up as this lovely pink color or fuchsia colored outline up there when number of these mucous secreting cells line up together and invaginate into the underlying connective tissue to form an exocrine gland they tend to form a tubule like morphology as opposed to a spherical morphology so we're seeing lots of mucus secreting cells lining up together embedded within the connective tissue down here so that's a exocrine glandular tubule another type of secretory cells in the exocrine glands are the serous secreting cells these are the cells that produce more of a proteinaceous fluids as opposed to mucin and such cells are cuboidal to pyramidal in shape or pyramid-like and i might even argue that serous cells are more pyramid shaped rather than cube shaped and when you look at such cells they have really interesting and peculiar staining pattern with h and e in that nucleus tends to kind of pull towards the basal compartment and of course nucleus being rich with acid dna it stains well with hematoxylin the bluish color and the basal compartment of the cytoplasm too tends to stain well with hematoxylin so kind of bluish to purple hue in the basal compartment has a lot to do with the rich rna content in there associated with ribosomes which suggests that there's a lot of translation going on in this cell and then the apical compartment of the exact same cell contains a lot of secretory vesicles that are filled with proteins which stain well with eosin so in a single cell we have basal compartment that stains well with bluish hued hematoxylin and the apical compartment that stains pinkish with the eosin and that's exactly what we see here and before we go on imagine kind of aligning a number of these pyramidal cells right up next to each other several of them and you can already see that number of these serous secreting cells would form a spherical secretory unit as opposed to a tubule and that is exactly what we're seeing here here is a spherical aciness and within it here's the lumen and here is a pyramidal cell the serous secreting cell and as promised here's the basal compartment here's the basement membrane or the lamp basal lamina here's the nucleus you can see that the basal compartment of the cell is staining a little more bluish to purplish hue here's another cell with bluish to purplish hue and the apical compartment has a lot of this kind of granular structure that is staining pink so this is the eosinophilic or acetophilic apical compartment filled with proteinaceous fluids that's ready to be secreted so to summarize serous secreting cells are really unique in that they have this two-toned staining pattern with h and e with basophilic basal compartment and the acetophilic pink apical compartment and number of these serious secreting cells lining up next to each other will tend to form an acins as opposed to a tubule the third type of secretory cells in the glandular epithelia are the steroid hormone secreting type of cells and such cells are typically associated with endocrine organs and in terms of their morphology these are large polygonal cells with equally large nuclei that are spherical and euchromatic for the most part which means that a lot of the chromatins are in their unspooled form for transcriptional activity and within the nuclei there are typically punctate or very much distinctive nucleolus or two even which suggests a lot of ribosomal assembly activity that's taking place and in terms of the cytoplasm although we will not see a lot of protein-filled vesicles there may be some small vesicles filled with poorly stained steroid hormone-containing type of vesicles as well as a lot of smooth er if we were to look at these cells under transmission electron microscopy as mentioned earlier these type of secretory cells are arranged in cores or follicles and endocrine glands and we do have a separate endocrine systems lecture later on in this curriculum so we'll spend a lot of time focusing a little more on the exocrine glands for the rest of this lecture an interesting thing about the glandular epithelial cells or more specifically the secretory cells is the fact that some of these cells can actually occur within the covering epithelium as opposed to being a part of the proper exocrine or endocrine units and that's okay and we've actually seen this before with the mucous secreting cells or the goblet cells in the respiratory epithelium here this is a covering epithelium of the upper respiratory tract we saw that there were some goblet cells that were interspersed in this epithelium and likewise in the small intestine in the gut tube there are some endocrine cells that solitarily occur within the lining epithelium like the enteroendocrine cells and here's the covering epithelium with a lovely brush border here and incidentally we can see a nice kind of comparison between the cilia versus the brush border the microvilli and another incidental note there are these goblet cells interspersed in this covering epithelium as well at any rate right next door we're actually seeing this cell and note that in the basal compartment here closer to the basement membrane we're seeing this eosinophilia in the cytoplasm which indicates some protein-rich secretory vesicles that are ready to be secreted not into the external environment or the lumen but into the connective tissue into our body so that's an endocrine cell here's another example of endocrine cell that is embedded within the lining or covering epithelium and when some of these secretory cells occur solitarily in the covering epithelium those cells are sometimes classified or called the unicellular exocrine or endocrine glands depending on whether they're excreting out into the external environment or into the connective tissue into our body here's a quick summary of how to distinguish between the exocrine versus the endocrine glands with the unicellular glands we just need to be sure where the secretory vesicles are stored within the cell because the apical compartment storage indicates exocrine secretion but the basal compartment storage indicates endocrine secretion with the proper multicellular glands we just need to search for the direct connection or lack thereof of the glandular epithelia with the covering epithelia and search for ducts if they're a duct we're talking about the exocrine glands let's turn our attention now to the exocrine gland classification we have a lot of exocrine glands in our body that secrete things and they have many different morphologies and functions and similar to the covering epithelial tissue classification exocrine gland classification uses morphological observation of two criteria one is to count the number of ducts that drain the secretory unit if there is a single duct we call that a simple exocrine gland but if there are more than one duct then we call that the compound exocrine gland and then the second morphological category or criteria is the shape of the secretory units the parts that are actually producing and secreting things we could have a tubular shaped secretory unit especially if they're made up of columnar cells then we could have a test tube shaped secretory unit so that's tubular exocrine gland we could have branched tubular exocrine gland if there are two test tubes that are draining into a single duct for example like this then we could call this a branched tubular exocrine gland then we have coiled tubular we have exceptionally long tubule that ends up kind of coiling like a yarn like this deep down in the connective tissue we could have acenar secretory units where typically with pyramidal cells that line up right next to each other like this form instead of a test tube a sphere an asynus so that's an acenar exocrine gland we could also have branched acenar exocrine glands so we could have two or even more of these spherical secretory units draining into a single duct for example in which case that's a branched acenar exocrine gland then we could have a mix of both tubule or tube and asiness or sometimes we could have a tube that ends in an asynus like so so that's tubulo-acenar exocrine gland and as you can imagine in a gland like this we could have tubule that is lined with goblet cells that produce mucin and spheres or the acinus that produce more of a proteinaceous serous secretion so glands like these will typically have mixed secretions you may have guessed already but there's formula for exocrine gland classification as well that is to essentially add the number of ducts with the shape of the secretory unit and end with the gland type that is either exocrine or endocrine in terms of the number of ducts there are only two options simple or compound secretory unit morphology there are actually six options that is tubular branch tubular coil tubular acenar branched asynar or tubuloacenar and all of these classification criteria all of course go with the exocrine gland and this is a super duper generalization but tubular glands tend to be composed of the mucous secreting columnar cells whereas the acenar glands are typically composed of the serous secreting pyramidal cells although there will be some exceptions these are good generalizations for the time being thank you for watching this video from the davinci academy histology video course which is completely available on youtube to access the corresponding practice questions and histology lab videos go to our website using the link in the description below [Music] oh [Music] you