Exocrine Glands – Histology | Lecturio


in this lecture I'm going to provide an

overview of the structure of exocrine

glands in the body and some indication

of the function of these glands but I'm

also going to deal with them in more

detail where appropriate when I review

the organ systems in later lectures

exocrine glands are very important in a

number of different organ systems and

it's important that first of all you

understand what a gland is and know that

basically these glands form two major

categories they're either serous

secreting or mucous secreting you need

to also understand the way in which

glands secrete the components that they

have made and how we classify glands or

name them and most importantly also it's

important to have some understanding of

the duct system of these glands because

these ducts with in some glands modify

the secretion product produced by the

secretory cells now there are a number

of different types of glands as I

explained I'm mainly going to

concentrate in today's lecture on the

exocrine glands they're glands that

synthesize then secrete their products

onto the surface they do so either

directly such as we see in goblet cells

lining some epithelia or they secrete

their product via a tube called a duct

or a con jute and as I mentioned earlier

some of these ducts modify the secretion

of the glands there are also endocrine


these are glands that synthesize their

products but then they secrete them into

the extracellular space around the

glands because during development

when the epithelium invaginate it into

underlying connective tissue the

connection between the surface of the

epithelium and the secretory invaginate

adapt ethereal cells is lost and so

there is nowhere for these glands to

secrete their products so therefore they

secrete them into extracellular space

and then those secretory products move

into the bloodstream and delivered to

target organs often a long way away from

where these glands actually synthesized

the material another way in which glands

are classified or named is because often

some cells can secrete products that

affect their neighbors and these are

called para kind plans these para kline

plans secrete their products into the

underlying interstitial space and that

diffuses to nearby cells and affects

their function will do with those in

another lecture so basically the types

of glands are really classified on the

way in which they secrete their products

and also the way in which those products

reach their target tissues either

through a duct as in exocrine glands or

via the blood in endocrine glands or

just via diffusion along local

interstitial space to affect neighboring

cells it's important to understand how

glands release their secretary products

and as I said earlier in this lecture

we're going to concentrate only on

exocrine glands well there are three

ways in this diagram there are three

representations of the way in which

exocrine glands or secrete resells

secrete their products firstly there is

maricon secretion now this is a crease

this form of secretion this mechanism of

secretion is probably the most common

the secretory cells make their products

and they store their products within

little membrane-bound granules at the

apex of the cell and when they're

stimulated to secrete these little

granules containing the secretory

product moves to the apical surface of

the cell the membrane fuses with the

cell membrane and the product is

released into the luminal space by a

process we call exocytosis

so that's merocrine secretion another

way in which the cell gets rid of its

products is by apocrine secretion

apocrine secretion is where often the

secretion product is stored at the

apical surface but then that apical

surface or a component of that apical

service breaks off and so what is

released into the luminal space is the

secretion product but also a small part

of the cytoplasm of the cell and this is

common in some of the glands in the

eyelid and probably in the mammary gland

and the remaining form of secretion the

remaining way in which cells release

their product is called holocrons

secretion this is where the cell

synthesizes its product accumulates a

product within the cell cytoplasm but

then undergoes programmed cell death so

the whole cell is lost into the luminal

space holocron secretion we will see

when we look at skin when we look at the

sebaceous gland in skin where her

leckrone secretion occurs now there are

different ways in which exocrine glands

are named or classified first of all if

you look at the epithelial surface shown

on the left

and slide the image of an epithelium in

the gut you can see single glands or

single secretory cells called goblet

cells they look like a wine goblet

they're shaped like a wine goblet and

these are called goblet cells they

secrete mucus they're an example of a

unicellular gland a single cell sitting

in an epithelial surface all on its own

although there are clusters of these

cells all the way along the epithelial

surface if you look at the image on the

right hand side this is an example of a

multicellular gland here is a sheet of

epithelial cells that are secretely

forming a number of layers and if you

look very carefully at this stomach

mucosa these layers of epithelial

secretory cells you can see that they

stain differently the surface ones are

very clear staining in the middle you

can see some cells that have a pink

reddish stain and down the base of these

epithelial layers of cells you can see

bluish stain cells and that indicates

that in this sheet of secretory

epithelial cells there are three

different sorts of secretory products so

that is an example of a multicellular

gland now I want you to remember the

word mucosa that I've shown you on this


stomach mucosa the word mucosa is a word

a term I'm going to use in a number of

lectures particularly when we look at

the organ system so please remember that

word because later on towards the end of

the lecture I'm going to explain what a

mucosa is I won't do it now because it's

more important and more appropriate

towards the end but just remember that

word mucosa okay

these multicellular glands can be get

far more complex than just a sheet of

cells that you saw in that stomach

mucosa they can acquire a duct rather

than dis secreting onto the surface like

a goblet cell or like these cells in the

stomach mucosa during development when

the epithelium invaginate s-- into the

underlying lamina propria the portion

that connects the invaginate 'add

epithelial cells to the surface is

retained and that forms the conjured or

adapt the deeper epithelial cells that

have invaginate it into the lamina

propria become the secrete resells the

busy cells that make the secretion

products and so we can further classify

multicellular glands of having ducts and

if the ducts don't branch we call it a

simple gland but if the duct branches

like you see in the three diagrams down

in the bottom of this slide we call it a

compound gland now the classification

can go further if you look at the nature

or the shape or the structure of the

secretory product and I'm not going to

go through all the names listed here and

I certainly don't want to emphasize

these names or I certainly wouldn't

expect you to be able to recall these

names because in reality when you look

at sections through multicellular glands

it's very difficult to appreciate the

3-dimensional structure and therefore be

able to name the grounds like you see

listed here it's very different though

to needing to remember the way in which

epithelia are named and classified