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Yara shwabkeh

Osama Alkhader

Heba Kalbouneh

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CELL OVERVIEW

-Note ; the important thing is to know how the organelles appear under the microscope

- the stains we usually use in Histology are composed of acidic dye and basic dye

- Acidic dye interacts with basic part of the cell & Basic dye reacts with the acidic

part of the cell

- The nucleus of the cell contains Nucleic Acid (DNA and ribosomal RNA ) , so it

reacts with the basic dye which is called Hematoxylin , so we call it Basophilic

structure .

Philic means love so it loves to interact with the base

- The cytoplasm contains organelles swimming inside it,

The net charge of proteins in the cytoplasm is positive so the cytoplasm reacts

with the acidic dye with is called Eosin , and we call the cytoplasm Acidophilic

Nucleus Cytoplasm

Blue color Pinkish color

Basophilic (because it contains nucleic acid) Acidophilic (eosinophilic)

Stained with hematoxylin Stained with eosin

Hematoxylin Eosin

Basic dye Acidic dye

Stains the nucleus Stains the cytoplasm

Positive charged dye

Negative charged dye

Stains acidic parts (so they are basophilic ) and these parts are negative

Stains basic parts (so they are acidophilic ) and these parts are positive

Nuclei of the cell

(colored with blue

color)

Cytoplasm ( pinkish

color )

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Sections cut through a curved tube

There are 3 kinds of tissue sections :

1) Cross section : tissue is cut perpendicularly to the long axes of the tube 4 shapes of cross sections ( understand them but don't memorize )

a) Cross section,In the middle, there is a circular rounded shape lumen, And the lines are made of cells Note: this is the hardest type of histology because we are studying a 2D

structure from 3D structure b) Cross section at the edge of the tube : no lumen is present only an oval shape

block of cells c) Cross section from the curved area of the tube: oval structural lumen d) More deeper cross section from the curve area: two circular centers connected by

a group of cells

2) Longitudinal section: tissue is cut parallel to the long axes of the tube

a. At the middle of the tube : two columns of cells b. At the edge of the tube : square area with no lumen filled with cells

Cross section

perpendicul-ar

to the long axes

of the tube

At the edge of

tube Curved area

of the tube

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3) Oblique section : tissue cut an angle between a cross and Longitudinal sections so we have at the center a circular lumen but oval in shape

Cross

section

Edge of the

tube

(Tangential)

Oblique section At the deep

curve area

of the tube Note: the blue circles are the nuclei

of the cells and the pinkish color is

the cytoplasm, the white central

oval circle is the lumen

- in this picture it is a cell , if we took a longitude plane which is labeled with B , we will see the nucleus and the cytoplasm of the cell

- But if we have another plane which is away from the nucleus which is A , we won’t see the nucleus ,but this doesn’t mean that the cell doesn’t have a nucleus

- We need to study more than one section to understand the 3D shape of the structure

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- - in this picture it is a cell , if we took a longitude plane which is labeled with B , we

will see the nucleus and the cytoplasm of the cell - But if we have another plane which is away from the nucleus which is A , we

won’t see the nucleus ,but this doesn’t mean that the cell doesn’t have a nucleus - We need to study more than one section to understand the 3D shape of the

structure

Nucleus: - The nucleus is surrounded by a nuclear membrane - The nuclear membrane has the same structure as the cell membrane

(phospholipids bilayer) , but in the nuclear membrane there is two membranes each with the same structure as the cell membrane .

- Outer nuclear membrane and inner membrane and the space between them is called perinuclear space

- also there is nuclear pores which are important for the materials to pass from the cytoplasm to the nucleus and visa versa

- Nucleolus is the site for the synthesis of RNA (mRNA , tRNA , rRNA ) and ribosomes

- Nucleoplasm is filled with genetic materials ( chromatin )

the DNA inside the cytoplasm has 2 forms: 1- Light area 2- dark area

Each nucleus represents a cell

each cell is different in shape

and size from other cells

(this a LM image)

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- The DNA is in two forms:

1) Active form of DNA means that it is doing transcription of mRNA , the light area is the active form and it is called euchromatin which is the uncondensed form of DNA

2) Non active form the dark area which is called Heterochromatin which is the condensed From the chromatin, we can know if the cell is active or not.

Light area Dark area

Called euchromatin Called heterochromatin

Uncondensed form of DNA (lightly stained)

Condensed DNA (deeply stained)

Active form of DNA Not active

Electron lucent (light area) Electrodense (back area)

Electron microscope

Dark area

Light area

Nuclear envelope

Inactive DNA

Active DNA

Nucleolus

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this cell here as an active cell because it is full with euchromatin, but for an example if we have a dark cell, we can know that it is inactive because it contains a lot of heterochromatin.

The nuclear pores are guarded by a special type of proteins called Nucleoporins -and under the nuclear membrane there’s a network of intermediate filaments called Nuclear lamina to support the nucleus and gives a shape . - the outer nuclear membrane is continuous with the rough ER .

Barr body *note : we can have more than one nucleus in single nucleus * more number of nucleoli the more the cell is active in the synthesis of ribosomes ( protein synthesis )

- Female XX the first X chromosome is spread as a form of euchromatin and heterochromatin, the second X is usually condensed and attached to the inner nuclear membrane

- From this way, we can distinguish the female cell from the male cell by seeing a small dense mass of heterochromatin attached to outer membrane.

- In males, this isn’t presented because the Y chromosome is a small chromosome with limited number of genes.

Cytoplasm Contains:

1) Organelles 2) Inclusions 3) Cytoskeleton to support the cell

- Inclusions isn’t essential for vitality of the cell

It is a stored material in the cell *example: skin cells store melanin pigment for the skin color but not all cells in the body have this material so the melanin is considered as an inclusion.

Cytoplasmic organelles: 1) Membranous:

a. Cell membrane

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b. Mitochondria c. ER d. Golgi e. Vesicles f. Lysosomes

2) Non-membranous a. Ribosomes b. Centrioles important for cell division

1) Cell membrane

- Composed of phospholipids bilayer

- In addition to lipids the membrane is also composed of proteins. two types of membranous protein: 1. Integral protein (transmembrane): spans the layer thickness if the membrane 2. Peripheral protein : associated with the extra cytoplasmic or cytoplasmic side

The thickness of the membrane is 7.5 – 10 nm: Light microscope we can’t view it because the resolution power of LM is 0.2 µm Electron microscope we can see it, appears as 2 dark lines, separated by a light one, this is called trilaminar appearance of cell membrane

- Another important thing is called glycocalyx

- Glycocalyx a sugar chain branched from the outer surface of the plasma

membrane attached to a proteins (glycoprotein)

Hydrophilic polar head

Hydrophobic non-polar tail

Tri 3

Laminar layer

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or to phospholipids (glycolipids)

- Function of glycocalyx: recognition and adhesion

*note: the more number of unsaturated fatty acid the more the fluidity of the

membrane

Types of transport: 1) simple diffusion: according to the concentration gradient, it’s for small

uncharged hydrophobic particles

2) facilitated diffusion: a channel or a carrier protein, for hydrophilic materials or

charged ions

3) active transport: which needs energy because it transports molecules against

their concentration gradient

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Endocytosis (general name of eating / drinking of the cell)

1) phagocytosis:

-eating of the cell

-for solid materials

-cell membrane do a thing called pseudopodium in order to engulf certain

materials

2) pinocytosis:

-drinking of the cell

-liquid material

3) receptor-mediate:

-for certain hormones (such as insulin) and molecules

2) mitochondria

- it is the site of ATP production

- example: if we are studying a certain motile cell (a moving cell ) we should know that

for the cell movement it needs ATP and by that we know that this cell has in its

cytoplasm a high concentration of mitochondria

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- mitochondria is rod in shape

- its membrane is composed of 2 layers : outer (smooth) membrane , and inner (cristae)

membrane .

- LM : the mitochondria doesn’t appear under LM in HE stain

But in order to view it under LM we use a especial stain that stains the

mitochondrial enzyme.

-EM : it appears under EM ( typical appearance )

3) Endoplasmic Reticulum (ER)

1) ribosomes attached to it (granular in appearance) rough ER

2) no ribosomes attached to it smooth ER

*another difference between rER and sER is the profile for each one , rER has flat

sacs cisternae and sER is more rounded

-function of rER : protein synthesis

- WE CAN SEE THE ER UNDER THE LIGHT MICROSCOPE, as we mentioned earlier;

cytoplasm is acidophilic and appears in pinkish color so all the organelles in it are

also acidophilic EXCEPT FOR rER because it is studded with ribosomes and

ribosomes contains ribosomal RNA and rRNA contains nucleic acid so it is

basophilic and appears as blue areas in the pinkish cytoplasm

*note : rER doesn’t appear in all cells only in cells with prominent rRNA , meaning

that the cell is active in protein synthesis more ribosomes more rRNAmore

nucleic acid more blue spots in the cytoplasm

- function of sER : detoxification

The liver is the organ that is responsible on detoxification in our body , so the liver

cells will have prominent sER .

Another example is in muscle cells which are the storage site for calcium so these

cells have prominent sER .

- LM : the sER doesn’t appear under light microscope

EM : appears

4) Golgi apparatus

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They are slightly curved and the edges are a little bit swollen , there isn’t

ribosomes attached to it

- Golgi apparatus is associated with many vesicles because its function is

modification of proteins that have been synthesized in rER , after modification

they’re going to be transformed via vesicles called secretary vesicles , they are

called secretary because proteins that are synthesized in rER and packed in golgi ,

are destined for export ( outside the cell )

*an important note : free ribosomes synthesis proteins for the use inside the

cell .

Attached ribosomes Free ribosomes

Synthesis proteins for the outside of the cell (export)

Synthesis proteins for the use inside the cell

-LM : we need to use a especial stain otherwise we can’t view the Golgi under LM

The meaning of “where the Golgi was “:

The Golgi apparatus is phospholipids (because it’s membranous) and by the use of

paraffin wax technique, we used an organic solvent xylene, which dissolve lipids.

-even though the Golgi doesn’t dissolve it won’t be stained by eosin because eosin is an

aqueous solvent.

5) secretory granules

-LM: acidophilic area

-EM: secretory vesicles from Golgi they look as electron dense rounded structure with

homogenous materials

6) lysosomes

- contains hydrolytic enzymes

This hallow white area is

where the golgi was

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EM : electron dense homogenous , the same concept as secretory granules

Lysosome comes from Golgi rER synthesis the hydrolytic enzymes then they

move to golgi for modification then we have lysosome.

_ phagosome from phagocytosis will fuss with lysosome and the materials inside

the phagosome will be digested

Primary lysosome lysosome before fussing with phagosome

Secondary lysosome after fussing with phagosome

*note: the remained material which is the material that the lysosome can’t

Residual body digest , we call it the

- this is very important because cells with aging accumulates very large amounts

to (related age pigmentand this produce certain pigment called body,of residual

age )

Residual body Secondary lysosome Primary lysosome

Undigested material only Hydrolytic enzyme + digested material

Contains only hydrolytic enzymes

*how to differentiate between primary lysosome and secretory granular ?

- both of them are rounded in shape and homogenous, But if we took a section from a phagocytic cell it is lysosome Another section from gland secretory vesicles

Secondary lysosome , particulate

appearance which is the digested

material and the background is the

hydrolytic enzyme

Primary lysosome , because it

appears homogenous

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7 ) Ribosomes - Composed of large and small subunits - LM : if we have prominent ribosomes they appear basophilic (rER) - EM : electron dense areas - Free ribosomes usually form groups called polysomes

Connected by a strand of mRNA

8) cytoskeleton - cytoskeletal elements in the cell not only to give shape and support, they are tracks or highways for the movement of organelles within the cell - there is 2 types of motor proteins : 1) dynein : walk in one direction 2) kinesin -organelles such mitochondria and secretory vesicles don’t swim in the cytoplasm, there are tracks of these cytoskeletal elements, to move these structures within the cell .

Refer to the slides for more pictures Good luck guys <3 Yara Al-shwabkeh