Full transcript
0:00welcome to module 2 tissues
0:03while this information may be a little
0:05less intuitive than the other modules
0:07the information is important to help you
0:08build your understanding of things that
0:09we're going to be discussing later on in
0:11the course
0:12more so in the second half
0:15recall from the last module the tissues
0:17are groups of cells that are similar in
0:19structure and perform a common or
0:20related function remember that while
0:23often the cells that make up tissues are
0:25the same
0:26these cells don't have to be the same
0:27within a given tissue
0:29histology
0:30is how we study tissues
0:32typically it's done with slices under
0:34the microscope so if you like what you
0:36see today you're likely interested in
0:38histology
0:39there are four main types of tissues in
0:41the human body
0:42the epithelial tissue which in general
0:44provides protection connective tissue
0:47which provides support to other tissues
0:49as well as attaching things together
0:51muscle tissue which moves us which is
0:53relatively obvious
0:55and nervous tissue which is responsible
0:56for control because nervous tissue
0:58includes the brain spinal cord plus all
1:00of the nerves that come off of these
1:01main structures and run everywhere else
1:03in the body
1:05there are two types of epithelial tissue
1:07covering and lining epithelium
1:10which you can see here the cells are
1:12lined up forming a barrier because of
1:14this row of cells
1:15typically we talk about it with respect
1:17to the skin as the skin is made up of
1:19lining epithelial
1:20which makes sense because it protects
1:22our
1:23our skin protects us from the outside
1:24world but you'll also see lining or
1:26covering epithelial cells in the in the
1:29wall of an organ for example in the
1:32lining of our stomach it protects the
1:35muscle of the stomach from the contents
1:37inside the stomach so the food in the
1:39stomach acid so the epithelial cells
1:41lining that organ are a barrier between
1:44what's inside the pouch of the organ and
1:46the structure of the organ
1:48the second type is glandular epithelium
1:51and these form the glands in our body
1:54and you can see here that the epithelial
1:56cells form a circle together with an
1:58opening in the middle and these cells
2:00are going to work together to make
2:02something and push it into this opening
2:04which will either connect with a tunnel
2:06or into the bloodstream and and i give
2:08you some more detail on some later
2:10slides coming up
2:11so an easy example is the salivary gland
2:14which produces saliva it will the cells
2:17of the salivary gland will produce
2:18saliva push it into this tunnel that
2:20ends up into your mouth
2:22regardless of which type of epithelia
2:25they are forming boundaries between
2:27different environments so they're lining
2:29between inside outside a glandular
2:31boundary between the tunnel or inner
2:33part versus the rest of the body and
2:36really it's deciding what gets to cross
2:39this boundary so that's the role of the
2:41epithelium
2:43almost all substances that enter or
2:45leave our body or body cavities must
2:47pass through epithelium so whether it's
2:50skin the lining of the bladder the
2:51lining of the stomach etc
2:55the epithelium has functions many
2:57functions based on its location and
2:59specialization of the group of cells
3:01that make up that particular layer of
3:03epithelium
3:04and these four functions are physical
3:06protection absorption sensation and
3:09secretion
3:12so the first function of physical
3:14protection
3:15in this example here you can see
3:18this key function of epithelia
3:21using the urinary bladder as an example
3:23so we can see there's a
3:25portion of cells here from the bladder
3:27there's your tissue slide and if we
3:29zoom in a little bit further you can see
3:31them lined up cells forming that
3:33epithelial tissue tissue layer providing
3:36physical protection between the lumen of
3:39the bladder where the urine would be
3:40stored and the remaining structure of
3:43the organ or the bladder and what this
3:46physical protection does is it stops
3:47harmful substances from entering body
3:50the body or
3:51these particular organs
3:55which brings us to the next function
3:57absorption
3:58epithelial tissues can form a selective
4:01barrier through which some things can
4:02pass and some some things cannot so
4:05absorption is just the term used to
4:07describe when things cross over or in
4:09and out of the of the epithelial barrier
4:13or whether it's the organ or the glands
4:15that are taking things in
4:16so for example an epithelial layer will
4:18allow food products to be absorbed in
4:20the small intestine
4:22in this example here you can see some
4:24cells taken from a portion of the
4:25tubules in the kidney where fluid
4:28absorption occurs basically constantly
4:30and don't worry we'll cover more
4:33detail on the on the kidney and the
4:34urinary system but very briefly you can
4:37see in this tissue slide section of the
4:39kidney here
4:40these
4:41rings of
4:44epithelial cells you can see the lumen
4:46of the opening of the tubes you can see
4:50the arrangement
4:52of these cells and if you were to draw a
4:553d cartoon of that cellular arrangement
4:57you can see the sheet of the epithelial
4:59cells you can see the basement name
5:01membrane and you can see the connective
5:03tissue
5:05the third function is sensation so
5:07epithelial tissue
5:09also forms some specialized sensory
5:11receptors
5:13here we're looking at the sensory
5:14reception it can be done in several ways
5:17but shown here is the eye and
5:19photoreceptors so in the eye we've got
5:21specialized epithelia of rods and cones
5:25and
5:26you know another example would be taste
5:27buds in our tongue in our respiratory
5:30system sensation is a common function of
5:32the epithelial respiratory system as the
5:34epithelial cells will have a hair-like
5:37extensions that can detect changes in
5:39temperature chemical composition if
5:41there's too little oxygen or if
5:43something big comes through that tube
5:46and then you'll choke because you feel
5:49something passing so when those hairs
5:51those extensions off of this epithelial
5:53tissue are bent
5:55uh it sends some sensory responses
5:58and says hey this isn't good to your
6:00brain
6:02start coughing to get this out of your
6:03airway so
6:05sensation is also an important function
6:07of epithelial tissue
6:10the last function of epithelial tissue
6:11is secretion and secretion occurs in
6:13glands and this is where you've got a
6:15group of one or more modified epithelial
6:17cells that make or secrete a particular
6:20substance and there are two types of
6:22glands the first is endocrine and
6:25endocrine glands secrete products
6:27directly into the bloodstream so some
6:30examples are like your thyroid and your
6:31pituitary hormones so if you put a
6:34substance in the blood it can go
6:36anywhere into the whole body
6:38another example of an endocrine gland is
6:40the pancreas which produces insulin
6:43the other type of gland is an exocrine
6:46gland and these secrete their product
6:48into ducts or channels or tunnels that
6:51take products to a desired and one
6:54specific location in the body and the
6:56salivary glands that i spoke to earlier
6:58they only secrete the saliva to
7:00particular areas of the mouth
7:02your sweat glands we do have a lot of
7:04these but they have specific ducts to
7:06take the sweat to specific areas of the
7:09skin so they can only have a localized
7:11impact
7:12looking at the structure of the exocline
7:14an endocrine excuse me gland more
7:16closely
7:17and remember endocrine glands make the
7:20substance and get it directly into the
7:22bloodstream
7:23that function is reflected in the
7:25structure that you can see a thyroid
7:27gland here and if you want to try to
7:29find that if you just put your fingers
7:31about fingers width below your adam's
7:33apple and pinch the two sides and hum
7:36lightly you'll feel the area vibrate
7:38you're in the right spot and the humming
7:40isn't coming from
7:41the gland it's coming from the larynx in
7:44like in behind the gland
7:45um
7:46but the thyroid gland just wraps around
7:48that area so you're able to to feel the
7:50vibration of the vocal cords in in the
7:52in the structures in behind so if we
7:55look at the slice of this thyroid gland
7:57we can see our purple epithelial cells
8:00here
8:01forming a ring
8:03and they're surrounding this follicle so
8:05these cells are producing thyroid
8:07hormone they're secreting it into this
8:10area and then it can diffuse across
8:13into the bloodstream when needed so you
8:15can see how closely associated they are
8:18these endocrine glands that produce the
8:20hormone passing directly through that
8:22outer epithelial layer into the nearby
8:23blood vessels you can see how close they
8:26are arranged with the blood vessels and
8:28the follicles together
8:30you can see that very thin layer of
8:32basement membrane which we'll discuss in
8:34detail in a few more slides it is
8:36present in endocrine gland cells but but
8:38it is thin and so because these products
8:41have to get
8:43through your your to your bloodstream
8:45they can exert control over whole body
8:47activities like metabolism so your
8:49thyroid gland for example and thyroid
8:52hormones they drive growth and
8:53metabolism which you need all over your
8:55body so as soon as you see something
8:58later on when you when you take some
9:00physiology classes and whatnot where
9:02there's an impact of a hormone that is
9:05across the body you know it's coming
9:07from an endocrine gland it has to
9:10because that's the only way you can have
9:12such a widespread effect
9:15exocrine glands on the other hand
9:17secrete their products that they make
9:18into ducts to be carried to the target
9:20location and some examples of these
9:22types of glands include the sweat glands
9:24that i spoke to on an earlier slide but
9:27also like your pancreas which will
9:29create and secrete digestive enzymes and
9:32they secrete those into your duodenum
9:34there's the salivary glands that secrete
9:36the saliva directly into areas of your
9:38mouth and the general structure of
9:40exocongres glands are that they are
9:42ring-shaped just like endocrine but
9:44instead of having a closed follicle
9:47here that you would then have to diffuse
9:50or transport across the product into
9:53nearby blood vessels that was endocrine
9:55exocrine
9:57this lumen will actually form a duct to
10:00take the product into a specific
10:02location
10:03so on the slide here you can see
10:05we have a sweat gland and in this
10:07histological steam slice of the
10:09epithelial cells you can see that these
10:11aluminum are sometimes
10:13excuse me the layers of the epithelial
10:16cells are sometimes in a single layer
10:18sometimes they are stratified cuboidal
10:20so you can see here in the cartoon you
10:22got stratified which just simply means
10:23more than one layer
10:25and if you compare these two
10:28endocrine glands you can actually see
10:29that thicker basement membrane you can
10:31see it much more clearly in the exocrine
10:33and endocrine which makes some sense
10:36when you consider that the endocrine has
10:38to have that
10:40secretion or diffusion across the cells
10:42into the nearby blood vessels whereas
10:44exocrine doesn't really want the product
10:46to leave the gland into any nearby
10:49tissue it wants the product to travel
10:51through
10:52the duct
10:54sweat glands are also exocrine glands
10:57and they will pass the sweat to the
11:00lumen hair to the duct to a specific
11:03area of the outside skin
11:05typically exocrine glands are more
11:08important than what would call local
11:10control because they only can impact a
11:13specific targeted area
11:16and speaking of sweat you may be
11:17familiar with the work by dr spreet from
11:20the university of guelph he's worked
11:22with gatorade for years to analyze sweat
11:24and urine and a few other things from
11:26from canada's national team and in some
11:29other levels of athletes and oftentimes
11:30you'll see them on television during
11:32commercials of the world juniors but dr
11:35richardson did her phd with dr spreed
11:37and her phd while it was not sweat it
11:39was on the translocation of fatty acid
11:42transport proteins to the plasma
11:43membrane in human and rat skeletal
11:45muscle during moderate intensity
11:47exercise so this is very much in her
11:49wheelhouse
11:51next we need to talk about the structure
11:53of epithelial tissue and we're going to
11:55start at the apical or free surface side
11:57this is the side that's exposed to the
11:59external environment or the cavity of
12:01the organ when we're talking about our
12:02skin it's the side of that epithelial
12:05layer that faces the outside world if
12:07we're talking about our stomach it's the
12:09side of the lining that is exposed to
12:11the food in the stomach acid
12:13if the epithelial tissue has hairs or
12:15extensions called microvilli or cilia
12:17these have to be located on the apical
12:19surface so that they can do their
12:22functions which in the case of the
12:23intestines is to help move things along
12:25the inside of the tube in the case of
12:27respiratory and skin its sensory
12:29functions so this apical surface being
12:32the exposed surface applies to all
12:34epithelia whether it's the lining
12:36covering or glandular type
12:40the basal surface of epithelial tissue
12:42is the anchored bottom surface of the
12:44cells and it's attached to the basal
12:47lamina which is part of the basement
12:49membrane when the epithelial tissue is
12:52connected with connective tissue
12:54this basal lamina acts essentially like
12:57a filter it's going to decide what can
12:59and cannot travel into or out of the
13:02epithelial layer of that tissue
13:05when the epithelial tissue is connected
13:08to connective tissue
13:10the basement membrane is also made up of
13:12the reticular lamina and together these
13:15basal and reticular lamina the basement
13:17membrane decide what's going to pass
13:19between these two tissues
13:23some fun and important facts about
13:24epithelial tissue is that you're going
13:26to find that they they always fit
13:29together closely to make these
13:31continuous sheets it's just how they
13:34assemble themselves even if you're
13:35talking about a gland where they're
13:37wrapped in a circle they're still in a
13:39sheet you rarely see an epithelial cell
13:41on its own
13:43connective tissue will often provide
13:44protection on its structural support to
13:46epithelial tissue because while
13:48epithelial tissue can be a barrier and
13:50do secretion absorption sensory
13:52functions they still do usually need
13:54some sort of support which often comes
13:57from connective tissue
13:59these tissues are avascular which means
14:02that blood vessels arteries and veins do
14:05not go directly to them therefore they
14:07are a vascular
14:10so how do they get their nutrients well
14:12they do it from nearby blood vessels and
14:15when they
14:16are anchored to connective tissue the
14:19blood vessels in the connective tissue
14:21is where their nutrients come from
14:24interestingly these are these cells are
14:26actually innervated so they aren't
14:28directly
14:30vascularized there's no direct arteries
14:32or veins but there is direct contact
14:34with
14:34nerves meaning they attach directly to
14:37it so that means that the epithelial
14:39tissue can pass information from this
14:41tissue layer to the
14:42brain the last point is that these
14:45tissues have a high regenerative
14:47capacity
14:48and
14:50it's handy because epithelial tissue is
14:52often damaged by friction or toxic
14:54substances like the sun or smoke or in
14:56terms of your stomach like the acid
14:58but as long as they receive adequate
15:00nutrition they can replace lost cells by
15:02cell division
15:04so for example if you cut your skin on
15:06your hand the skin will heal but a lot
15:09of other parts of the body if you cut it
15:10as deep as you could as you could cut
15:12the skin and it would still heal
15:15that other part of the body wouldn't it
15:16heal nearly as well or as quickly and
15:19this is really not typical for a tissue
15:22with no direct blood supply because the
15:23number one thing you need for repair is
15:25nutrients which comes from the blood so
15:28this diffusion across is really quite
15:30efficient to support that high
15:32regenerative capacity of the epithelial
15:35tissue
15:38we need to learn the classification of
15:40epithelial tissue so because epithelial
15:42tissue is found all over the body
15:44but it has different shapes and cell
15:47uh different arrangement of layers and
15:48different cell shapes it's how we use it
15:50to classify and talk about the different
15:53types of epithelia so the first is the
15:56arrangement of layers is it a single
15:58layer which is simple or is it in
16:00multiple layers which is called
16:01stratified so here you can see the
16:03multiple single layers stacked together
16:05to form a stratified epithelial tissue
16:08we also have something called
16:09pseudostratified which is where
16:12the tissue may look like it's in
16:13multiple layers but it actually isn't
16:16every cell does contact that basement
16:18membrane so it's it's actually pseudo
16:20meaning not really or false stratified
16:23the cell shape is squamous which is thin
16:26flat wide cuboidal which literally the
16:30cells are cube shaped kind of like
16:31little rubik's cubes all approximately
16:33the same size
16:34and same
16:36size on all the sides you can also have
16:39columnar where they're tall and thin
16:41rectangular face shaped like columns and
16:44you can have a mix and match of the
16:45types within a tissue so you can have
16:48different cell shapes and different
16:49arrangement of layers within any given
16:51tissue rules of thumb for epithelial
16:54tissue are that if there are more layers
16:56you have more protection so if you have
16:57an area where you need greater
16:59protection you're going to have more
17:00layers of epithelial tissue it will be
17:03stratified so you will have stratified
17:05epithelia
17:07single layers mean that it's easier for
17:09substances to pass through that
17:10epithelial tissue so if you have a
17:13simple epithelium it usually means
17:15you're going to have absorption
17:16secretion going on in that area
17:19more layers equals thicker equals
17:21greater protection
17:23less layers thinner crossing of
17:25substances
17:27cilia are often very helpful in moving
17:29substances or they're involved in
17:31sensation cilia and even somewhat
17:33microvilli can sense but really their
17:36main function is to move things along
17:37like a food bolus through your esophagus
17:41we need to now go through the basic
17:43types of the epithelia so within that
17:46basic classification system we have more
17:48specific types the first is a simple
17:51squamous and this is a very thin and
17:54delicate layer of tissue
17:56it's specialized for moving molecules
17:58across it i think everybody can
17:59appreciate how quickly and easily
18:01something could pass through here the
18:02cross section of the tissue slide here
18:04is from the small intestine where
18:06absorption is really critical
18:08also in blood vessel walls you'll have
18:10this simple squamous that has a special
18:12name called endothelium you'll get it in
18:14the lining of the abdominal cavity where
18:16it's called mesothelium and then you'll
18:18also have it in your alveoli in your
18:19lungs that's critical for gas exchange
18:22so again simple squamous is going to be
18:24located wherever you need to have
18:27absorption and or secretion the second
18:29we're going to discuss is simple cuboid
18:32and this is for absorption of fluids as
18:34opposed to larger molecules and here you
18:36can see it's in the lining the nephron
18:40tubules of the nephron in the kidney
18:42which the kidney is responsible for
18:44blood filtration because it maintains
18:46the water level within the blood too
18:48right so here we can have a nice passing
18:50of fluids as opposed to larger molecules
18:53by this simple cuboidal cell shape when
18:56we look at our simple columnar so a
18:58single layer of calmer now cells they
19:01come in two varieties
19:03the first is non-ciliated so here you
19:06would have microvilli on the surface to
19:08increase the surface area so they've got
19:10lots of little bumps on them you can see
19:12here it's coming from the small
19:13intestine you may have some goblet cells
19:15in there to produce some mucus to
19:17provide a slippery surface for things to
19:18move across typically you'll see these
19:20in your like your digestive system and
19:22you can see how the tissue slice looks a
19:24lot like the little cartoon they're
19:26highly structured um tissue is very
19:29consistent but you can see that single
19:31layer of columnal cells all attached to
19:33the basement membrane and
19:35and over top of the connective tissue
19:38the other type is ciliated simple
19:40columnar cells so here we still have a
19:42single layer of column shaped cells but
19:45on the top they are covered with these
19:46cilia so hair-like structures on the
19:48surface this type of
19:50tissue will typically also have goblet
19:52cells it also might need some mucus
19:54production this example here is coming
19:56from the uterine ii fallopian tube where
19:59the cilia are going to help move the
20:01eggs along
20:03but this this type of tissue would also
20:05still do absorption and secretion
20:07the stratified squamous here
20:10you can see
20:11the many many many layers okay so
20:13stratified multiple layers uh we've got
20:15our squamous it's very thick it's found
20:17in areas where protection is important
20:19this you would also see this in your
20:21skin
20:22the
20:23tissue from the bottom to top you can
20:25see that the bottom layers have nuclei
20:28but the top layers don't that's because
20:30those top cells are dead and you'll just
20:32slough those off and if you needed more
20:34layers they're going to grow from the
20:36basal surface up
20:37so this stratified tissue again it's
20:40going to
20:41regenerate from below pushing the cells
20:44up if you were to exfoliate your skin
20:47you're sloughing off these
20:49top layers of the skin and yes it will
20:52look more radiant because you are
20:53getting rid of these old cells and it
20:55doesn't hurt the tissue you don't have
20:57to go to the hospital if you exfoliate
21:00because the tissue is still able to
21:01provide the proper protection
21:03without
21:04a compromise when it slips off those
21:06cells so if you sand or scratch off
21:09enough skin you'll get through enough
21:11layers that you would bleed because
21:13you're hitting that that underlying
21:15connected tissue layer
21:18stratified cuboidal on the other hand
21:20you've got layers of these cuboidal
21:22cells they still offer protection but
21:23not nearly as well as that squamous that
21:26i just showed you the layers are thicker
21:28simply because of the cuboidal shape but
21:31the layers don't overlap as well
21:33as a squamous does so here i'm showing
21:36a section in the esophagus
21:38it's an esophagus gland duct but
21:41you can also have it in the lining of
21:43sweat glands and salivary glands
21:46if we look at stratified calmer it's
21:47similar to the cuboidal and that it
21:49still offers protection but not as well
21:51as the squamous because you just you
21:53don't get the same overlap even though
21:55the layers are thicker the examples of
21:57where you can find this type of tissue
21:59is in the male urethra or the
22:01conjunctiva of the eyeball which is just
22:03the front layer of your eyeball
22:05and shown in the picture here is just
22:07the lining of the pharynx and again you
22:09can see how those tissue slides and even
22:11the microscopic zoom ins look very much
22:13like the cartoons
22:16the pseudoscenarified columnar is the
22:19tissue where the cells appear to be in
22:21layers but they really aren't because
22:22every single solitary tissue is hitting
22:24that basement membrane
22:26and um you can see it in the cartoon as
22:28well usually the ciliated uh certified
22:31stratified polymer is ciliated usually
22:33it has goblet cells oftentimes you're
22:35going to find this in your respiratory
22:36system to simply help move things along
22:38the walls and what's being shown here is
22:40the epithelium in your trachea
22:44a transitional epithelium you'll see
22:46these stratified layers of cells that
22:48change in shape depending on where they
22:50are
22:51and also in what loads are applied to
22:54them so the example here is from the
22:55bladder and when your bladder is full
22:58these inner layers of cells are going to
22:59flatten to make more space inside your
23:01bladder so you can hold more urine but
23:03when you empty your bladder the cells
23:05sort of bounce back and look more
23:07cuboidal so this type of transitional
23:09epithelium allows stretchy structures to
23:12expand from within which is quite useful
23:14if you think about some of the things we
23:16have in our body
23:18this is the end of module two part a of
23:21the epithelial tissues the other types
23:23of tissues will be covered up covered in
23:25part b in the upcoming module