Download lecture 3 - JU Med: Class of 2019

# The epithelium #
part 1 
we will talk about the general features of the epithelium  BUT before that we should know
several points 
# The human body is composed of only four basic types of tissues ( epithelial tissue – muscular
tissue – nervous tissue – connective tissue ) which all contain cells and molecules of the ECM
(extracellular matrix) .
these tissue exist in association with one another and in variable proportions and morphologies
forming the different organs of the body .
- Note : Morphology is a branch of biology dealing with the study of the form and
structure of organisms and their specific structural features .
# Epithelial tissues are composed of closely aggregated polyhedral cells with strong
adhesion to one another and attached to a thin layer of ECM .
# Epithelia are cellular sheets that line the cavities of organs and cover the body
surface .
# The principle functions of epithelial (epi : upon / thele: nipple ) tissues are :
1) covering , lining and protecting surfaces ( ex: the epidermis is stratified
squamous epithelium )
2) absorption ( ex : the intestinal lining )
3) secretion ( ex :parenchyma cells of glands )
- Note : Because epithelial cells line all external and internal surfaces of the body ,
all substances that enter or leave tissues and organs must cross an epithelium .
 Remember :histology is a two dimensional study of three dimensional reality
- Note : we knew that the epithelium lines and covers the organs , " accurately it covers the top
of organs "
---- therefore, any structure we see under the microscope , the top layer of this structure is
epithelial cells 
- The substructures in the body ( internal organs ) are sandwiched between two sheets of
epithelial cells ( Outer sheet and inner sheet )  the outer sheet of stomach is covered
by peritoneum " it is a smooth membrane that forms the lining of the abdominal cavity " >>>>
this peritoneum is part of the mesothlium>>>>> this mesothlium surrounds the Stomach from
the outer  >>>> and internally another layer of epithelium surrounds the Stomach  .
- If we look a tube such as ( urinary tract or GI tract ) we will find them covered from inside by a
epithelium layer >>>> and we should know that the epithelium changes from type to another in
response to the characteristics of the areas that it covered them 
________________________________________________________________________________
The characteristics of the epithelial cells
1) They line cavities or cover surfaces >>>> this means that any substances entering or leaving
the organ should pass through epithelium " this info is reported later  "
2) They are originated from any of the three embryonic layers :
- The embryo starts in 3rd week with process of Gastrulation " Forming the 3 layers : ectoderm –
endoderm – mesoderm ) .
- The tissues are formed from the last three layers >>>> But we should know that the tissues
formed from one layer differ from that formed from another layer >>>> for example : the
tissues formed from ectoderm differ from the tissues that formed from mesoderm .
‫ يعني أنّ األنسجة التي تتكون من إحدى الطبقات تختلف عن األنسجة التي تتكون من طبقات أخرى ولذلك لكل طبقة من‬#
‫ وبالتالي تتميّز األنسجة بالخصوصية التامة مع العلم أنّه لو أنتجت طبقة نوع من‬ ‫الطبقات الثالثة أنسجتها الخاصة بها‬
‫األنسجة مثالً ال يمكن ألي طبقة أخرى أن تنتج نفس‬
 ‫النوع التي أنتجته الطبقة األولى وهذا نوع من الخصوصية أيضا‬
3) Because they are present on the surfaces of the organs >>>> they are closely packed , forming
sheets >>> therefore NO spaces between epithelial cells .
- If we assume presence of spaces between epithelial cells >>>> any substance can pass between
them ( means the substance passes through the spaces between epithelial cells NOT through
the epithelial cells >>> AND this is wrong 
- But without the spaces , the cells determine what should pass through them ( MEANS >>> the
cells play a main role of activation , absorption and secretion .
- NOTE : with the exception of some endocrine glands , all epithelial cells have one free surfaces.
4) They rest on a basement membrane or a basal lamina
5) They are " avascular " means without vessels  >>> They depend in their nutrition on the
Connective tissues "C.T" that stay under them .
- NOTE : If we assume that the epithelial cells contain a blood vessels ( veins and arteries ) 
>>>> Then any simple wound will make an immediate bleeding  >>>>> So that the epithelial
cells do not contain any type of blood vessels 
6) They are richly innervated (free nerve endings can be seen among epithelial cells )
# If we stimuli the skin with pin ( e3ni Dboos :P ) >>>> the skin will be harder " form a trauma "
"  ‫ " وقت يبسمر وييبس الجرح‬ ‫يعني أنّه قد ت ّم تغيّر نوع النسيج الطالئي تِبعا ّ لإلصابة‬
# Through the epithelium we recognize the taste by taste cells that covered by epithelium , smell
by smell cells that covered by epithelium , sound and a lot of things in similar route 
>>>>> The main result is : The epithelium teaches the CNS the recognizing of the sounds , tastes
, smells ----- etc 
# For-example : the baby recognizes a tastes of food in the beginning of life By the epithelium
covering the oral cells >>>> and after a period he will be able to recognize a lot of tastes of food
and refuse or accept it " btblsh el zana5a :P "
# For-example : we can recognize the smell of people by the olfactory cells covered by
epithelium 
7) They have a high regenerative power
- the liver is exposed daily to many foreign or harmful chemical substances such as medications
 >>> these substances damage a lot of liver cells >>>> BUT because the liver cells have a high
regenerative power " they are covered by epithelial cells " >>>> the unaffected cells repair the
damage and regenerate new cells instead of the damaged cells 
- Note : in the general when we are injured and the wounds appear on the skin >>> The
epithelial cells of each side of skin start to divide and differentiate to connect the two sides of
the wound  therefore the wound will heal after nearly 24 hours 
>>> But the function of the surgeon when he sews the wound that to decrease the distance
between the two sides of the wound , therefore decreasing the time wanted to heal the wound
- But we should know that " the healing of epithelium does not mean that the wound becomes
stronger and the patient is able to participate all the harder activations such as the sports
(NO!!!) >>>> The heal of the epithelium means healing the wound outwardly 
‫(ويجب أن نالحظ أن المريض يأتي بعد فترة للطبيب يعاني من ألم في منطقة في الجرح وذلك نتيجة ضعف الجرح وهذا دليل‬
‫على أن الجرح غير قوي لدرجة أن‬
‫ وهنا ي قوم الطبيب بإزالة الصديد الموجود مكان الجرح وينظف الجرح ليزول‬, ‫يمارس المريض األنشطة المرهقة مثل الرياضة‬
) ً‫األلم قليال‬
- Note : we should know that the regenerative power of the epithelial cells differs from area to
another area in the body (e3ni mosh kol el parts of the body zay ba39` )
8) Epithelial cells are one example of a polarized cells " featuring distinct " apical " , " lateral"
and " basal " plasma membrane domains >>>> epithelial cells connect to one another via their
lateral side to form epithelial sheets that line cavities and surfaces through the body .
Each plasma membrane domain " basal and apical " has a distinct protein composition , giving
them distinct proprieties and allowing directional transport of molecules across the epithelial
sheet , how epithelial cells generate and maintain polarity remains unclear ( BUT the points that
mentioned later are the main reasons to consider the epithelial cells polarized cells  ) .
9) Epithelium may undergo "Metaplasia"
- Note : This characteristic is not special of the epithelial cells because a lot of cells in the body
have metaplasia process 
- Metaplasia : is reversible change from one type of epithelium to another in response to
stimulus ( means when removal the stimulus , the epithelium will return to first type    ) .
# CONCENTRATE OK ! (very important )
- in the respiratory tract we find a type of epithelium called " ciliated pseudo-stratified columnar
epithelium " that lines the respiratory tract >>> when the polluted air (smoking – car fumes )
enters this tract , it touches these epithelial cells ((((>>>>> AND the example that we will study
here is Nicotine as a polluted substance inside the respiratory tract >>>>>))))      
- On the surfaces of the epithelial cells in the respiratory tract we find the Cilia " it directs the
polluted substances that enter inside this tract (Toward the top ) means it directs these
substances to oral and nasal cavities " >>>>> subsequently we will cough or sneeze to get rid of
these substances 
- In order to work the cilia , it needs protein called "Dynein " ( without this protein , the cilia will
not work  )
- Nicotine is the inhibitor of this protein >>>> therefore the cilia of the smokers do not work 
>>>> the cilia will degrade after a period of time  >>>>> therefore the polluted substances will
accumulate in the respiratory tract .
- In response to this case >>>> the number of goblet cells will increase inside the respiratory
tract " the function of the goblet cells is secretion of mucous to modify the air entered the
respiratory tract  " >>>>> But when the mucus and polluted substances accumulate inside the
respiratory tract ( zadet el 6een balleh    ) the cilia try to expose these substances but they
cannot    >>>> the mucus accumulates and covers the cells to save them from polluted
substances  >>> But after a period of time (( after the water is evaporated or absorbed from
the mucus substances )) the mucus will become more solid ( more viscous ) >>>> therefore the
smoker will not able to expose them out of the respiratory tract    >>>> the viscous mucus
substance that covers the cells start rubbing with cells and it changes the surfaces of the cells
from their type of epithelium to stratified squamous epithelium MEANS ( we have risk    )
- Note : when the epithelium changes its type from any type TO stratified squamous epithelium
( here we have risk )
# Note : If the smoker stops the smoking , the epithelium will return to first type ( the type
before changing )   
>>>>> BUT if the smoker continues the smoking >>>> the metaplasia will develop to neoplasia
means Cancer ( tumor )   
# Note : the time expectancy of the lung cancer is 2 year But 40% of people will live all this
period ( 60% of people will die before all this period ) .
# Note : when the smoker stops the smoking , the cilia will return to original state and all the
degenerated cilia are replaced with new cilia   
10) They are modified to perform special functions (ex: sensory – secretary ) .
11) The nuclear form - of the epithelial cells – corresponds roughly to the cell shapes .
12) The boundaries between the cells are frequently indistinguishable with L.M
________________________________________________________________________________
The basement membrane and the basal lamina 
# The doctor will discuss the electron paragraph in P.75 figure (4-3)
Notes :
- Before 1930 ( before invention of EM ) when the scientists studied the specimen of
trachea with PAS stain >>>> the result is positive >>>> means the specimen contains a
carbohydrate  >>>> Then they found an area under the epithelium " 100 nm thickness "
>>>> and they found another areas under the epithelium " 20 – 40 nm thickness "
>>>>and we called these areas ( basement membrane ) and they defined it as ( the area
that present under the epithelium with ( 20 – 100 nm thickness ) .
- The reason of difference of thickness of basement membrane that the L.M used is
inadequate to show the real or accurate thickness of specimen 
- The basement membrane is described as scaffold   
- in the 1930 ( with invention of E.M )
>>> Notice that the gray area in the figure (4-3) is called ( lamina lucida )
Remember : in the E.M , the area that appears ( gray to white ) color is called "electron
lucent" because it allows the electrons passing among it
>>> Notice that the darkish layer " under the lamina lucida " is called lamina densa ,
because it reflects the electrons 
# The basal lamina has two parts ( lamina lucida " upper " + lamina densa " lower " )
### Question : What is the area that gives PAS positive reaction ???
>>>> the area that under the lamina densa contains Reticular fibers ( the reticular fibers
are collagen type 3 that contains carbohydrate ) >>>>> this area is called Lamina
reticularis >>>>> this area that appeared in L.M and gave us PAS positive reaction    .
- Note : when we talk the basal lamina >>>>> means ( the electron microscopy structure )
and consists of lamina lucida and lamina densa 
-Note : when we talk basement membrane >>>> means the area that present in the C.T
that gave us PAS positive reaction .
# We should know that that basal lamina By E.M is basal lamina ( that consists of two
lamina ) But By L.M is basement membrane ( that contains collagen type 3 >>> that gives
PAS positive reaction ).