DEPARTMENT OF HISTOLOGY,
CYTOLOGY, EMBRYOLOGY
Dr. Polinkevych Irina
 Histology (compound of the Greek words: ἱστός "tissue", and λογία -logia) is the study of the microscopic anatomy of cells and
tissues of plants and animals. It is commonly performed by
examining cells and tissues by sectioning and staining, followed
by examination under a light microscope or electron microscope.
 Cytology (from Greek κύτος, kytos, "a hollow"; and -λογία, -logia)
means "the study of cells". Cytology is that branch of life science,
which deals with the study of cells in terms of structure, function
and chemistry. Based on usage it can refer to:
Cytopathology: the study of cellular disease and the use of cellular
changes for the diagnosis of disease.
Cell biology: the study of (normal) cellular anatomy, function and
chemistry.
 Embryology (from Greek ἔμβρυον, embryon, "the unborn,
embryo"; and -λογία, -logia) is a science which is about the
development of an embryo from the fertilization of the ovum to
the fetus stage.
USES OF HISTOLOGY

Education - Histology slides are often used in teaching laboratories to help
students learn about the microstructures of human (and animal) biological tissues.

Diagnosis for treatment - Biological tissue samples taken from a patient (that is, a
specific person or animal's body) may be studied in detail to enable medical or
veterinary experts to learn more about the patient's condition and hence perhaps
understand its causes and make recommendations for treatment or management of
the condition.
Note: Although the study of the microstructure of diseased cells and tissues is an
aspect or use of histology because it uses histological techniques, study of
diseased tissues is more accurately called histopathology.

Forensic investigations - Forensic histology, immunohistochemistry and cytology
involving microscopic study of biological tissues using various stains can help
clarify the cause of sudden unexpected deaths and other issues in forensic science.

Autopsy - Biological tissues from a deceased person or animal can be studied
using histological techniques enabling experts (e.g. pathologists re. unexplained
death of a person) to learn about the circumstances and possibly cause of death.

Archaeology - Study of biological cells and tissues recovered from archaeological
sites can provide information about history, even ancient history. The state of
preservation of the biological material is critical, yet sometimes sufficient e.g. for
bone histology and dental histology.
THE FIVE MAIN STAGES IN THE
PREPARATION OF HISTOLOGY SLIDES ARE:
…
Fixing
…
Processing
…
Embedding
…
Sectioning
… Staining
COMMON HISTOLOGY STAINS
 There are many different histology stains. Histology stains are
normally selected according to the type of tissue to be observed.
Some stains are more widely used than others. Some stains are
only used to study very specific types of biological tissue.
 Hematoxylin and eosin (H&E stain) is the most commonly used
histology stain for light microscopy.
Hematoxylin stains the nuclei within cells blue (recall that the
cell structure of every biological includes a nucleus). Eosin
stains the cytoplasm of cells pink. It is because H&E is such a
common histology stain that so many histology slides seem to be
dominated by colours ranging from blue to pink - though of
course there are many exceptions due to the other stains used.
H&E is a permanent histology stain, as opposed to a temporary
stain.
OVERVIEW OF THE CELL AND CYTOPLASM
The cell is the basic structural and functional unit of all
multicellular organisms, limited to an active cell membrane
and consisting of cytoplasm and a nucleus. The cell is open,
automatically adjusting and self reproductive system.
1.
Cells are the basic structural and functional units of all multicellular organisms.
2.
Specific functions are identified with specific structural components and domains
within the cell.
3. Cells can be divided into two
major compartments: the
cytoplasm and the nucleus.
4. Organelles are described as
membranous (membrane limited)
or nonmembranous.
INTERCELLULAR CONNECTIONS
1.
Simple contact – membranes of two cells are on distance of 10-12 nm in such manner that glycocalyx one cell
adjoins with glycocalyx of another cell. The basic function is metabolism and information interchange between
cells.
2.
Zonulae occludentes — also called tight junctions. Zonula occludens are located between adjacent plasma
membranes most typically near the apices of epithelial cells. They form a "belt-like" junction that encircles the
entire circumference of the cell. These junctions act as barriers that prevent the movement of molecules into the
intercellular spaces.
3.
Zonular adherentes are band-like adhesion. This device surrounds the cell and joins it to its neighbors.
4.
Desmosomes (Maculae adherens). This is the most common type of tight junction between adjoining cells. A
desmosome is a small circumscribed area of attachment – attachment plaques. At the side of a desmosome the
plasma membrane (of each cell) is thickened because of the presence of dense layer of protein on inner surface.
Desmosomes are serving to attach the basal cell membrane to the basal lamina.
5.
Gap junctions, also called communicating junctions, are regions of intercellular communication. They are
widespread in epithelial tissues, in cardiac muscle smooth muscle cells and neurons. Gap junctions are built by
six closely packed transmembrane proteins connexins that assemble to from structures called connexons. The
two connexons fuse, forming the functional intercellular communication channel. The hydrophilic channel
permits the passage of ions, small molecules and hormones.
6.
Plasma membrane enfoldings of the basal plasma membrane increase the surface area available for transport.
The basal surface of some epithelia, especially those involved in ion transport, possesses multiple enfoldings of
the basal plasma membrane. These enfoldings partition the basal cytoplasm and many mitochondria into the
finger-like enfoldings.
7.
Synapse - type of contact between two nervous cells or between a nervous cell and a muscle. Through synapses
pass nervous impulses.
1. Cells are the basic structural and functional units of all multicellular
organisms.
The processes we normally associate with the daily activities of organisms—
protection, ingestion, digestion, absorption of metabolites, elimination of
wastes, movement, reproduction, and even death—are all reflections of
similar processes occurring within each of the billions of cells that
constitute the human body. To a very large extent, cells of different
types use similar mechanisms to synthesize protein, transform energy,
and move essential substances into the cell. They use the same kinds of
molecules to engage in contraction, and they duplicate their genetic
material in the same manner.
2. Specific functions are identified with specific structural components and
domains within the cell.
Some cells develop one or more of these functions to such a degree of
specialization that they are identified by the function and the cell
structures associated with them. For example, although all cells contain
contractile filamentous proteins, some cells such as muscle cells, contain
large amounts of these proteins in specific arrays. This allows them to
carry out their specialized function of contraction at both the cellular
and tissue level. The specialized activity or function of a cell may be
reflected not only by the presence of a larger amount of the specific
structural component performing the activity but also by the shape of
the cell, its organization with respect to other similar cells, and its
products.
3. Cells can be divided into two major compartments: the cytoplasm and
the nucleus.
 In general, the cytoplasm is the part of the cell located outside
the nucleus. The cytoplasm contains organelles (“little organs”)
and inclusions in an aqueous gel called the cytoplasmic matrix.
 The matrix consists of a variety of solutes, including inorganic
ions and organic molecules such as intermediate metabolites,
carbohydrates, lipids, proteins, and RNAs. The cell controls the
concentration of solutes within the matrix, which influences the
rate of metabolic activity within the cytoplasmic compartment.
 The nucleus is the largest organelle within the cell and contains
the genome along with the enzymes necessary for DNA
replication and RNA transcription.
 The cytoplasm and nucleus play distinct functional roles but also
work in concert to maintain the cell’s viability.
4. Organelles are described as membranous (membrane limited) or
nonmembranous.
Organelles include the membrane systems of the cell and the
membrane-limited compartments that perform the metabolic,
synthetic, energy-requiring, and energy- generating functions of
the cell, as well as nonmembranous structural components. All
cells have the same basic set of intracellular organelles, which
can be classified into two groups:
(1) membranous organelles with plasma membranes that separate
the internal environment of the organelle from the cytoplasm,
and
(2) nonmembranous organelles without plasma membranes.
Besides organelles, the cytoplasm contains
inclusions, structures that are not
usually surrounded by a plasma
membrane.
Inclusions contain products of metabolic
activity of the cell and consist largely of
pigment granules, lipid droplets, and
glycogen.
They are cytoplasmic or nuclear structures with
characteristic staining properties that are
formed from the metabolic products of cell.
They are considered nonmoving and
nonliving components of the cell. Some of
them, such as pigment granules, are
surrounded by a plasma membrane; others
(e.g., lipid droplets or glycogen) instead
reside within the cytoplasmic or nuclear
matrix.
THE MEMBRANOUS ORGANELLES INCLUDE:
The plasma (cell) membrane, a lipid bilayer that forms the cell
boundary as well as the boundaries of many organelles within the
cell;

rough-surfaced endoplasmic reticulum (rER), a region of
endoplasmic reticulum associated with ribosomes and the site of
protein synthesis and modification of newly synthesized proteins;

smooth-surfaced endoplasmic reticulum (sER), a region of
endoplasmic reticulum involved in lipid and steroid synthesis but
not associated with ribosomes;

Golgi apparatus, a membranous organelle composed of multiple
flattened cisternae responsible for modifying, sorting, and
packaging proteins and lipids for intracellular or extracellular
transport;

endosomes, membrane-bounded compartments interposed within
endocytotic pathways that have the major function of sorting
proteins delivered to them via endocytotic vesicles and redirecting
them to different cellular compartments for their final destination;

lysosomes, small organelles containing digestive enzymes that are
formed from endosomes by targeted delivery of unique lysosomal
membrane proteins and lysosomal enzymes;

transport vesicles—including pinocytotic vesicles, endocytotic
vesicles, and coated vesicles—that are involved in both endocytosis
and exocytosis and vary in shape and the material that they
transport;

mitochondria, organelles that provide most of the energy to the cell
by producing adenosine triphosphate (ATP) in the process of
oxidative phosphorylation; and

peroxisomes, small organelles involved in the production and
degradation of H 2 O 2 and degradation of fatty acids.
THE NONMEMBRANOUS ORGANELLES INCLUDE:

microtubules, which together with actin and intermediate filaments
form elements of the cytoskeleton and continuously elongate (by
adding tubulin dimers) and shorten (by removing tubulin dimers), a
property referred to as dynamic instability;

filaments, which are also part of the cytoskeleton and can be
classified into two groups—actin filaments, which are flexible chains
of actin molecules, and intermediate filaments, which are ropelike
fibers formed from a variety of proteins—both groups providing
tensile strength to withstand tension and confer resistance to
shearing forces;

centrioles, or short, paired cylindrical structures found in the center
of the microtubule-organizing center (MTOC) or centrosome and
whose derivatives give rise to basal bodies of cilia; and

ribosomes, structures essential for protein synthesis and composed of
ribosomal RNA (rRNA) and ribosomal proteins (including proteins
attached to membranes of the rER and proteins free in the
cytoplasm).
PLASMA MEMBRANE
The plasma membrane is a lipid-bilayered structure visible with
transmission electron microscopy.
The plasma membrane bounds the cell. It controls the movement of
materials into and out of the cell. It's a complex double layer made up
of phospholipids and proteins. Phosopholipids are a special class of
lipids that contain two fatty acid "tails" and one negatively charged
phosphate "head."
The two fatty acid "tails" are hydrophobic
(water hating) and the phosphate "head" is
hydrophilic (water loving). The plasma
membrane is made up of two layers of
phospholipids. The hydrophobic fatty acid tails
face inwards and the hydrophilic phosphate
heads face outwards.
Analogy: The door and exterior of the
university would represent the plasma
membrane because they control who and what
enters the university.
CYTOSKELETON:
 The shape of the cell is determined by
a network of fibers called the
cytoskeleton. The two main fibers
involved are microtubules and
microfilaments. Microtubules are made
of the protein tubulin and participate
in cell division and movement.
Microfilaments are also important in
cell movement. They are thin, rod-like
structures composed of the protein
actin.
 Analogy: The cytoskeleton could be
represented by steal or wooden beams
that hold the structure of the school
together.
RIBOSOMES:
 Ribosomes are sites of protein
synthesis; their only function is to
build proteins for the entire cell.
They're round structures composed
of RNA and proteins. They can be
either free floating in the cell or
attatched to another structure called
the endoplasmic reticulum (ER).
 Analogy: The classrooms of the
university could represent the
ribosomes of the cell. Just as the
ribosomes are the sites where
proteins are made (food for the cell),
the classrooms are the sites where
"brain food" or knowledge is made.
CENTRIOLES:
 These are small, paired cylindrical structures that hang out near
the nucleus. As animal cells prepare for cell division these two
centrioles separate and go to opposite ends of the cell. They
produce fibers called microtubules, which pull the chromosomes
apart and move them to opposite ends of the cell. They are
common in animal cells, but not found in plant cells. These will be
discussed in more detail when we learn about cell reproduction.
ENDOPLASMIC RETICULUM (ER):
 Endoplasmic reticulum is a network of
folded membranes that extend through
the cytoplasm to the nuclear
membrane. There are two kinds of ER:
rough and smooth. Rough ER has
ribosomes associated with it, while
smooth has no ribosomes. The basic
function of ER is transport, proteins
produced by the ribosomes are
transported to regions of the cell where
they are need or they are transported
to the Golgi body for export from the
cell.
 Analogy: The ER could be represented
by a teacher. The ER is responsible for
transporting proteins just as a teacher
is in charge of transporting knowledge.
The teacher is in control of the
classroom (ribosome).
GOLGI BODIES:
 The function of Golgi apparatus is twofold: modification of lipids and proteins
and storage and packaging of materials
that will be exported from the cell. The
Golgi apparatus is often called the
"shipping department" of the cell. The
vesicles that pinch off from the Golgi
apparatus move to the cell membrane
and the material in the vesicle is
released to the outside of the cell.
 Analogy: In a way, parents or guardians
could be used as a representative for the
Golgi body since they pick up where the
ER left off. The Golgi bodies modify,
process, and sort the protein products.
In a similar way, parents or guardians
are responsible for their children once
they leave the responsibility of their
teacher (ER). Parents or guardians can
also become involved in modifying the
information the teacher tries to teach
the students.
LYSOSOMES:
 These are tiny sacs that carry
digestive enzymes, which they
use to break down old, worn out
organelles, debris, or large
ingested particles. They are the
cleanup crew.
 Analogy: The custodial crew of
the school would represent the
lysosomes. They are
responsible for keeping the
university clean.
VACUOLES:
 Vacuoles store water and a
number of other things, such as
food, wastes, salts, or pigments.
There are a wide variety of
vacuoles, containing a wide
variety of substances.
 Analogy: Storage areas of the
school, such as closets that hold
books or other supplies, could
represent vacuoles.
NUCLEUS:
 The nucleus is considered the control
center of the cell. It is usually the
largest organelle. It not only directs
what goes on in the cell, it is also
responsible for the cell's ability to
reproduce. It's the home of the
hereditary information, DNA, which is
bunched into large structures called
chromosomes. The nucleolus is visible
in the nucleus, and it makes another
cell organelle called the ribosomes. The
nucleus is bound by the nuclear
envelope, a phosopholipid bilayer
similar to that of the plasma
membrane.
 Analogy: The principal of the school
would represent the nucleus because
he or she would be in control of what
goes on throughout the entire school.
MITOCHONDRIA:
 The mitochondria is the powerhouse of
the cell. They're responsible for
converting the energy from organic
molecules into useful energy for the
cell. The basis of energy in the cell is
ATP. Mitochondria are usually shaped
like stubby cigars sometimes they are
round. They have a double membrane
consisting of an outer membrane and a
highly folded inner membrane. The
inner mitochondrial membrane forms
folds called cristae. Most of the
production of ATP is done in the cristae.
 Analogy: The university cafeteria could
represent the mitochondria. The
cafeteria would be where all of the
employees and students of the
university get energy to function
through the day by eating food.
THE CELL THEORY STATES:
o
All living organisms are composed of cells. They may be unicellular or
multicellular.
o
The cell is the basic unit of life.
o
Cells arise from pre-existing cells.
The modern version of the Cell Theory includes the ideas that:

All known living things are made up of one or more cells.

All living cells arise from pre-existing cells by division.

The cell is the fundamental unit of structure and function in all living
organisms.

The activity of an organism depends on the total activity of independent cells.

Energy flow (metabolism and biochemistry) occurs within cells.

Cells contain hereditary information (DNA) which is passed from cell to cell
during cell division.

All cells are basically the same in chemical composition in organisms of similar
species.
CELL CYCLE
 The reproduction cycle of a cell is
termed the cell cycle.
 For renewing cell populations
and growing cell populations
including embryonic cells, cells in
tissue culture and even tumor
cells a cell cycle may be described
that two principal phases mitosis
(M phase) and interphase which
include three phases G1, S and
G2 .
 G1 phase (presynthesis, gap 1) of interphase is usually a period of
cell growth and may last only a few hours in a rapidly dividing cell
or may last a lifetime in a nondividing cell. The cell that leaves the
cycle in G1, to begin “terminal” differentiation is considered to
begin the G0 phase “0” for outside the cycle.
 During the S (synthesis) phase DNA of the cell is doubled. The
centrioles often self-duplicate during this stage.
 During G2 phase (postsynthesis, gap 2) the final preparations for
cell division occur; these include repair of damaged DNA,
synthesis of tubulin for the spindle apparatus and ATP
accumulation for the energy-expensive mitosis.
MITOSIS
Mitosis follows the G2 phase and consists of four phases:

-prophase

-metaphase

-anaphase

-telophase
Mitosis is a cell division process that produces two daughter cells with the same
chromosome number and DNA content as the original cell.
During prophase chromatin coils form chromosomes. The nuclear membrane and
nucleolus start to disappears. The mitotic spindle apparatus begins to assembly
between the centriole pairs. The two centriole pairs migrate to opposite poles of
the cell.

During metaphase chromosomes becomes shorter, thicker and line up at the cell
equator between the centriole pairs, and each chromosome has a centromere to
which microtubules of the spindle apparatus attach.

During anaphase , which begins with the centromere region, the sister
chromatids separate and move to opposite poles of the now elliptical cell along
the mitotic spindle.

During telophase the chromosomes begin to uncoil. Telophase is marked by the
reconstitution of a nuclear envelope around the chromosomes at each pole. The
nucleoli reappear and the cytoplasm divides to form two daughter cells.