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CYTOLOGY
The Cytoplasm
The cytoplasm contains
I-Living structures
i.e. Organelles.
II-non living substances i.e.
Inclusions.
III-Cytosol or matrix
Composed of soluble proteins,enzymes
and products of enzymatic reactions.
CYTOPLASM
(cytosol + organelles)
1-CYTOSOL –
Gel-like structure
2-ORGANELLESmall structure with a
specific function
The Cytoplasmic Organelles
The organelles may be divided into
membranous
non-membranous
(A) The membranous organelles
1- Cell membrane.
2- Mitochondria.
3- Rough endoplasmic reticulum. (rER.)
4- Smooth endoplasmic reticulum. (sER.)
5- Golgi apparatus.
6- Lysosomes.
7- Peroxisomes.
(B) The non-membranous organelles
1- Free ribosomes and polysomes.
2- Microtubles.
3- Centrioles, cilia and flagella.
4- Filaments.
1- Cell (Plasma) Membrane
By LM, the cell membrane is invisible except
when stained with silver or PAS techniques.
-By EM, it has a trilaminar appearance: two
outer and inner dark layers and a middle
light layer.
Cell (Plasma) Membrane
- It is very thin (65-100 A) perforated by even smaller
pores (7-10 A).
- It is composed of a phospholipid bilayer , proteins, and
carbohydrates.
- The cell membrane encloses the cellular contents and
regulates transport of substances (active or passive)
into and out of the cell.
-The cell membrane is composed of:
Lipids (30 %),
Proteins (60 %)
Carbohydrates (10 %).
-The lipid components are formed of
phospholipids and cholesterol.
The lipids are arranged as outer and inner
hydrophilic heads and middle hydrophobic
ends.
-The protein components are either intrinsic
(integral) or extrinsic proteins.
CELL MEMBRANE
Proteins that stick on the surface =
(either inside or outside of cell)
Proteins that stick INTO membrane =
(can go part way in or all the way through)
PERIPHERAL
INTEGRAL
CELL MEMBRANE
Cell membranes are made of
PHOSPHOLIPIDS
&
PROTEINS
The Cell Membrane
In 1997, Simon and Ikonen proposed the modern concept of cell membrane structure. It
is composed of a combination of protein receptors and glycosphingolipids organised in
glycolipoprotein microdomains, known as lipid rafts (Simons and Ikonen, 1997).
The new concept of lipid raft organisation. Area (1) is the standard lipid bilayer, whereas
area (2) is a lipid raft.
Intracellular space
Extracellular space
1- Non-raft membrane
2- Lipid raft
3- Lipid raft associated transmembrane protein
4- Non-raft membrane protein
5- Glycoproteins and glycolipids
6- GPI-anchored protein
7- Cholesterol
8- Glycolipid
(Korade and Kenworthy, 2008)
Functions of the cell membrane
1- Protect the structure integrity of the cell.
2- Regulating cell-cell interactions.
3- Recognition of antigens, foreign cells via
receptors.
4- Phagocytosis, pinocytosis, and exocytosis.
5- Controlling movements of substances in and
out of the cell (selective permeability).
6- Transport of substances across the
cell membrane is mediated through passive,
facilitated, active or bulk transport:
a- Passive transport:
It depends on concentration gradient
e.g.lipids and gases.
b-Facilitated transport:
It depends on concentration gradient
and the presence of carriers e.g.
glucose and amino acids.
c-Active transport:
It needs energy in the form of ATP e.g. the
passage of Na+ out of the cell i.e. sodium
pump. K+ is pumped into the cell.
7-The cell membrane may be modified in order to
perform a special function:
-Microvilli
Mainly in the columnar absorptive cells of the small
intestine to increase the surface area for absorption.
-Cilia
In the lining epithelium of the upper respiratory
passages. They beat in an upward direction in order
to move the mucous and foreign particles to the
outside.
-Flagella
In the tail of spermatozoa to facilitate their
movement.
2- Endoplasmic Reticulum (ER)
-A network of membrane enclosed channels.
– Cisternae are small spaces within the ER.
-Two types of ER predominate:
-Rough ER with attached ribosomes
(protein synthesis)
-Smooth ER without ribosomes that
function in lipid synthesis and special
functioning i.e., detoxification of liver cells,
release of Ca++ in muscle cells.
Endoplasmic Reticulum (ER)
-This was formally known as the basophilic
components of the cytoplasm.
-By LM, they can be detected as areas of
localized basophilia.
-By the EM, it is formed of a diffuse system of
membrane bound tubules, saccules and
flattened cisterns.
the surface of the endoplasmic reticulum is
studied with ribosomes giving it a rough or
granular appearance, hence the name rER
The basophilia of the rER resides not in the
canalicular passages but in the ribosomes
themselves.In cells specialized in synthesis
and secretion of protiens,
Increase in cells having high protein
secretion (pancreatic acini).
Functions of rER
- It is one of the cell organelles concerned with
protein synthesis the synthesis of protein
occurs in the ribosomes attached to the outer
surface of the rER.
-Storage and transport protein.
.
3- The Smooth Endoplasmic
Reticulum (sER)
By LM, the smooth endoplasmic reticulum
can not be seen.
By EM, it is formed of anastomizing
network of tubules pursuing tortuous
courses in the cytoplasm.
-Its cisternea are more tubular.
-It has no ribosomes attached to it.
Functions of sER
1-It is concerned with the synthesis of
lipids, lipoprotein and steroid
hormones.
2-It is concerned with detoxification of
certain drugs in liver cells.
3-Glycogen formation: sER contains the
enzymes required for glycogen
synthesis.
4-In cells characterized by contraction
e.g. striated and cardiac muscle, the
sER membrane contain enzymes that
pump Ca++ into the sER itself and
bind it with proteins.
5-In parietal cells of the stomach, the
sER is responsible for concentration of
Cl- in order to form HCI.
4- Ribosomes
-Small granular organelles that may be
unattached (free) or attached to the rough
ER.
-Ribosomes are held together to form
polysomes (polyribosomes).
-Produce proteins (from mRNA templates) for
use within the cell or for secretion for use
elsewhere in the body.
Ribosomes
•Not enclosed in a membrane.
•Made of two subunits.
•Composed of ribosomal RNA and protein.
•Carry out protein synthesis. Large numbers
occur in cells with high rates of protein synthesis,
e.g. pancreas cells – insulin secretion.
Ribosomes are intensely basophilic
because of rRNA.
There are three types of RNA
1- mRNA (messanger)
2- rRNA (ribosomal)
3- tRNA (transfer)
5- Golgi Complex
- Consists
of stacked membranous sacs
associated with the nucleus and the rough
ER.
-The “post office” of the cell.
The Golgi Apparatus
By LM and ordinary staining, it may appear
as pale area adjacent to the nucleus.
By EM, it appears as membrane bounded
flattened saccules arranged in parallel
arrays.
The stack has two surfaces:
1-The forming or immature face near
the nucleus and close to the rER
2-The mature surface which faces the
apex of the cell (the direction in which
secretion is delivered )
Function of Golgi Apparatus
1- Packaging and storage of proteins.
2- synthesis of CHO and glycoproteins.
3- Formation of secretory proteins.
4- Renewing of the cell membrane.
5- Formation of lysosomes.
6- Mitochondria
-They are responsible for energy production
needed by the cell.
- Usually found where metabolic activity is
high.
-They are considered as the powerhouse of
the cell cytoplasm.
-They can be stained by acid fuchsin, iron
haematoxylin.
Mitochondria
Using the EM, they are enclosed by two
membranes,.
The outer membrane is smooth but the inner
is thrown into projections or folds,
which are called cristae of the mitochondria,
to increase the surface area of the inner
surface.
The mitochondrial membranes delimit two
compartments:
a-The intercristal space, it contains the
mitochondrial matrix which contains
granules responsible for the regulation of
ionic environment of the mitochondria.
b- Intermembranal spaces, which is a
continuation of the intracristal space.
Functions of mitochondria
1-Mitochondria supply the cell with the
needed energy.
2-They breakdown glucose producing NADH
and ATP (powerhouse)
3-Mitochondria has a role in Ca++ level
regulation in the cell.
4-Mitochondria has the ability to divide since
they contain DNA.
7- Lysosomes
They are membranous organelles present in
almost all kinds of cells.
 Contain more than 40 hydrolytic enzymes
i.e. hydrolases such as acid phosphates,
proteases, nucleases, glycosidases, lipases
and certain sulfatases.
 Increase in cells with have phagocytic activity
(e.g. macrophages).

Functions of Lysosomes
1-They maintain the health of normal cells, by
getting rid of worn-out organelles.
2-Important in the defense of the body against
certain bacterial invaders.
3-They can contribute in causing certain
inflammatory lesions.
4-In liver cells, they are responsible for
breakdown of glycogen and in thyroid gland
for breakdown of thyroglobulin.
The formation and function of lysosomes
8- Perioxisomes
- Membranous
organelles resembling
lysosomes and containing enzymes.
- Promote the breakdown of fats to yield
hydrogen peroxide.
- Also contains catalase, an enzyme that
breaks down excess hydrogen peroxide.
- These are abundant in liver and kidney cells.
Function of Peroxisomes
9- Centrosome and Centrioles
- Centrosome is a nonmembranous mass near
the nucleus.
– Found only in cells capable of mitosis
– Mature muscle and nerve cells lack a
centrosome.
- Centrioles are paired rodlike structures within
the centrosome.
– Composed of 9 bundles of 3 microtubules .
– During mitosis, centrioles diverge to either
CENTRIOLES
Appear during cell division to pull
chromosomes apart
CENTRIOLES
Made of PROTEINS called MICROTUBULES
10- Cilia and Flagella
-Cytoplasmic projections that contain cytoplasm and
microtubules bounded by cell membrane.
-Cilia are numerous short projections (multiple processes
with 2-10 um in length) and are interspersed with goble
cells.
- Flagellum is single possess with 100-200 um in length,
sperm a single whip-like flagellum for propulsion.
Cilia and Flagella
-9 + 2 arrangement
-9 pairs of microtubules and 2 single central
tubules.
-Protein dynein is the “motor” molecule that
help in the motility.
- Lack of dynein protein lead to immotile
cilia(respiratory infection and infertility).
CILIA
Motion of cilia


Each cilium executes a propulsive power stroke, followed
by a recovery stroke
This sequence ensures that fluid is moved in one direction
only
Cilia and Flagella
Made of PROTEINS
called MICROTUBULES
(9 + 2 arrangement)
FLAGELLA
Help in cell movement
Cilia and Flagella
11- CYTOSKELETON
1- Gives cell shape & support Help move organelles around
2- Made of PROTEINS called
MICROFILAMENTS & MICROTUBULES
Cytoskeleton
1- Microtubules - hollow tubes consisting of
13 columns of the protein tubulin: alpha-tubulin
& beta-tubulin (keep the cell shape).
2- Microfilaments (Thin) - two intertwined
strands of actin filaments(help in moving
cytoplasmic components. And help in
cleavage of mitotic cell).
3- Intermediate Filaments - fibrous proteins
supercoiled into thicker cables(Keratins,
Vimentin, and Desmin)
11- Cell Nucleus
-Near the center of the cell.
Skeletal muscle fibers are multinucleate
– Erythrocytes lack nuclei
-Enclosed by a nuclear envelope.
– Lipid bilayer perforated by pores
– Nucleolemma cisternae is the space between the
two layers
-Intra-nuclear structures:
– Nucleoli (within nucleus)
 composed of protein and RNA; produces
ribosomes
–
NUCLEUS
Largest organelle in animal cells
NUCLEAR PORES Openings to allow molecules
to move in and out of nucleus
The Nucleus - cellular control center
1.Nuclear Membrane

encloses contents of nucleus separating its contents
from the cytoplasm

continuous in spots with endoplasmic reticulum

double membranes which are fused at the nuclear
pores

lined by the nuclear lamina, a array of fibers that
maintain nuclear shape
The nucleus and its envelope
2. Nuclear Pores
- regulate the entrance and exit of
macromolecules into and out of the nucleus
3. Karyoplasm
-contents of the nucleus
-matrix is a colloid much like the cytosol
The nucleus and its envelope
4. Nucleolus
- Storage site for ribosomal RNA
- Ribosomes assembled here
- Number varies from species to species but is constant
within cells of some species
5. Chromatin
- Threads of genetic material
- Composed of DNA and highly specialized proteins
called histones
- Condense to form chromosomes at the time of cell
division