Endocrine System 1, Exocrine and endocrine glands

so in the body we have glands and the

gland is a cell or a structure that

produces a product and there's only two

types of gland in the body there's

exocrine and there's endocrine exocrine

and endocrine now EXO means out as in

exit endo means in as in endocardium the

inner layer and first of all we want to

think about what these two types of

glands do and we're going to start off

by thinking about the exocrine glands so

we're still thinking about glands but

we're thinking about exocrine glands

what is it that they do and what are

they well an EXO crying gland is

something that produces a product and

secretes it via a duct or secretes it

onto a surface so what do we mean by

that well for example we might think

about a sweat gland so here we have the

top layer of skin the epidermis and we

have sweat glands that go down deep down

into the skin that would be the layer of

the epidermis there and we see the sweat

gland is going down into the dermis and

it coils around like this it's a coiled

structure and there's actually two

components to this gland

well we actually have here this is the

duct so this is the ductal portion here

and then further in around about here

this bit is the glandular component so

this coil bit as they the glandular part

the part that actually produces the

sweat in this case so it's producing the

sweat and that sweat is rising up the

sweat line duct and it's being deposited

on the surface of the skin so it's a

product and it is being secreted via a


so sweat glands do this quite a few of

the glands in the gastrointestinal tract

are similar to this such as survivor II

glands or the gastric glands in the

stomach producing gastric juices or the

pancreas itself is actually an exocrine

gland lacrimal glands produce tears

sebaceous glands produce sebum mammary

glands produce milk just to give you a

few examples now we see that there are

actually many cells where we don't see

but this is a relatively macroscopic

structure it's small but it's made of

many cells so lining here there will be

many such individual secreting cells so

that's an example of a multicellular

exocrine gland but others are just a

single cell so for example we might

think of if we think of an epithelium

perhaps in the respire to attract this

could be a ciliated cell here and then

every so often and they aspire to mucosa

there's a different sort of cell and

it's kind of like this and when people

first looked at these they thought it

was a bit like an upside down drinking

goblet still have a nucleus in here of

course and do this phobia another more

normal looking cell next door to it the

ciliated cell there and because these

not like upside-down drinking goblets

they're called goblet cells and their

job is to produce mucus so they produce

mucus and that goes onto the surface and

is a very important part of the mucosa

Lurie clearance system so these are

exocrine glands they are producing

things and secreting them Viaduct

and we saw that one was multicellular

and of course that one is a

single-celled secretary gland there's

another group of glands in the body


still glanced so they're still glands

that these ones are the endocrine glands

so what are the endocrine glands

well the endocrine glands have also

cells they are secreting cells that

produce a product so here we have some

endocrine cells in an endocrine gland so

these are going to be multicellular

structures so these are endocrine glands

and within the endocrine glands normally

they'll be security vehicles and an

endocrine gland is a gland which

produces a hormone the chemical

messenger that is the product and they

could be in these microscopic vesicles

here producing this product now the

thing about endocrine glands is they are

very vascular they're very vascular so

they contain a lot of blood vessels and

going through here we have a capillary

and because their vascular is a blood

vessel fairly close by so there's not a

great amount of tissue fluid to get

through before the endocrine product can

be secreted into the bloodstream

now let's suppose that this is a blow-up

of the vesicle here and in this vehicle

there's going to be millions of

molecules of the individual endocrine

hormone and we see that for the purposes

of illustration this endocrine hormone

is spherical so this endocrine gland and

these endocrine cells that comprise the

endocrine gland will be releasing their

product directly into the blood

so that's the difference endocrine

glands release their product directly

into the blood exocrine glands release

their product via a duct so now we see

we have molecules of the secretory

product from the endocrine gland which

we call a hormone secreted directly into

the blood and in fact in the old days

the endocrine system used to be called

the ductless gland system because it was

a system of glands but he had no ducts

because the product is always secreted

directly into the bloodstream so here we

now see we have these endocrine

molecules that are in the blood they are

now in the systemic circulation they're

now in the systemic circulation in the

blood that means they'll go to all parts

of the body or parts of the body will be

reached by this endocrine product so

this is actually a messenger molecule

these are messenger molecules or if you

like signal molecules so you perhaps

know that the body communicates via

nervous messages very quickly but it

also communicates from one part of the

body to another part of the body to

control physiology to maintain

homeostasis via these endocrine plotted

products and these are signal molecules

now circulating in the blood and in the

body we have our untold numbers of cells

70 or 80 trillion cells and we've noted

that this endocrine product is spherical

now here's a cell in the body and we

notice that on the surface of this cell

there are triangular shape to receptors

it wouldn't literally triangular-shaped

is diagrammatic but what they are these

are specific proteins specific receptor

sites for specific signal molecules that

will be circulating around the body and

that one's triangular

and this one here this cell here has

square receptor size on its cell surface

again specific code tenacious molecules

designed to interact with a particular

molecule what's called a ligand molecule

it one comes along and here we have

another cell and this one's got rounded

spherical receptors on his surface so

here's our endocrine hormones our signal

molecule and it's going through thee

through this systemic circulation so

there's a another systemic capillary and

we notice that these body cells are in

close proximity with the systemic


they'll be bathed in tissue fluid of

course and what will happen is that

these signal molecules these endocrine

molecules will go into the tissue fluids

and they will diffuse throughout the

tissue fluids and when that circular

signal molecule comes to that triangular

receptor site is it going to fit in well

of course not but it will keep diffusing

and when it comes to the square receptor

site is it going to fit it of course not

but can you see when it comes to its

specific receptor molecule site is going

to fit in I'm going to fit in to that

receptor site and that means we'll have

a combination between the receptor

molecule protein and the signal molecule

so something like this lock and key idea

isn't it the UM the receptor site will

be the lock and the signal molecule

would be the key that goes into that

lock and when the signal molecule

combines with the receptor protein there

is a chemical bonding between the two

there is a physical chemical bond which

is formed

and that chemical bond will be a signal

that goes into the cell to other parts

of the cell - so we're going to other

parts of the cell so we could do a

blow-up of this cell so here's the

here's the cell with the receptor sites

and our signal protein is now bound into

these receptor sites and the combination

of the signal and the receptor brings

about changes inside the cell and the

changes it brings about inside the cell

are described as secondary messenger

systems secondary messenger systems so

by this way of thinking

the primary messenger system is going to

be the hormone circulating around to the

tissue cells and the second messenger

system is going to be the biochemical

changes that are triggered inside the

cell and these secondary messenger

systems are going to trigger changes

inside the cell so for example if this

was thyroid hormone which is bound into

a thyroid receptor that's going to

trigger secondary messenger systems

inside the cell and that's going to

affect in muscle cells or liver cells

several hundred of these mitochondria

which are the powerhouses of the cells

and these mitochondria need to produce

the right amount of energy so that the

cell itself has the right amount of

energy to facilitate its physiological

processes and if there's more thyroid

hormone bound into the receptor site the

secondary messenger systems will

increase the activity of the

mitochondria increasing metabolism more

food will be used more oxygen will be

consumed more energy will be generated

more ADP will be converted into ATP

more energy will be made and the

metabolic rate of the cell will increase

conversely if there's less thyroid

hormone in the receptor sites they'll be

less to stimulate the mitochondria and

the metabolic activity in the cell will

go down but alternatively we might have

been talking about insulin so this could

be an insulin molecule of course insulin

is a is a proteinaceous endocrine

hormone and when the insulin binds on to

the insulin receptors that will bring

about changes in the cell membrane it

will actually allow something called a

glucose transporter molecule to go to

the surface of the cell membrane and

that will actually make a physical hole

in the surface of the cell membrane and

that's good because that will allow the

the glucose molecules now are in the

tissue fluid these glucose molecules

this shape to go through the hole into

the cell and of course they can go to

the mitochondria as well where they can

be used in the production of energy so

the glucose molecule c6h12o6 will be

dated into the cell but if the insulin

had not bound with its receptor side had

not triggered the secondary messenger

system which caused the glucose

transporter molecules to go to the

surface then the glucose will be left in

the tissue fluids in the blood and not

getting into the cell which of course is

the irony in diabetes there's too much

glucose in the blood and tissue fluid

but none in the cells that's that's why

we are we find our patients go katatak

but again the point is the insulin has

triggered second messenger systems

inside the cell facilitating

physiological change and we can see that

this is aimed at maintaining homeostasis

in the case of the thyroid hormone the

homeostasis of metabolism and energy

production in the case of the insulin

molecule homeostasis of glucose all of

things which are needed to regulate and


trol the cellular environment of the

body so that all the body cells are

working together in a coordinated way as

a whole organism not as individual unis

being conducted and coordinated by the

release of endocrine hormones in just

the right amount at just the right time

to control just the right amount of

physiological process