Professor asastent of department histology, cytology and
embryology - KHODOROVSKA ALLA
Histology is the study of the tissues of the body and of how these
tissues are arranged to constitute organs. Each of the fundamental
tissues is formed by several types of cells and typically by specific
associations of cells and extracellular matrix. Histology is classed as
a subdiscipline of anatomy, because its methods involve dividing
tissues and organs into pieces and preparing them for microscopic
examination and chemical analyses.
Two aspects of the subject are distinguished;
special histology deals with the arrangement and special
adaptations of tissues in the various organs whereas
general histology deals with the components of the individual
Cytology is the science
about a cell.
The cell is the basic structural and functional unit of all
multicellular organisms, limited to an active cell
membrane, cytoplasm and nucleus. There are 2 basic cell
are typically small,
(bacteria) that lack a
The cytoplasm is a complex
colloidal system. The cytoplasm of a
cell consists of:
different polysaccharides and a
lot of enzymes. The colloid
system of hyaloplasm can be in a
liquid or gel consistence.
The cell membrane (plasmalemma) is an universal system which
form many structures of a cell. Each cell is bounded by a cell. The
plasmalemma includes 3 layer:
I. Glycocalyx (carbohydrates)
II. Lipid bilayer (lipid molecule and proteins)
III. Submembrane cortical layer (actin microfilaments and microtubules)
The structure of each membrane includes:
50-60% of its weight,
lipids 30-40 % and
following 3 groups:
Integral membrane proteins are tightly lodged in the lipid bilayer;
detergents are required to extract them. They are folded, with
their hydrophilic amino acids in contact with the phosphate groups
of the membrane phospholipids and their hydrophobic amino acids
in contact with the fatty-acid tails.
Тransmembrane proteins from onlyone membrane surface, while
others, penetrate the entire membrane and protrude from both
Peripheral membrane proteins
are more loosely associated
with the inner or outer
The inner and the outer dense line composed of a single layer of
phospholipids, between them settle some proteins. Carbohydrates
occur on plasma membranes mainly as oligosaccharide moieties of
membrane glycoproteins and glycolipids.
branching structure and
project from the cell's outer
superficial coat called the
glycocalyx that participates
in cell adhesion and
Structures of plasmalemma
The plasmalemma carry out some of the important functions:
The plasmalemma carry out some of the important functions:
•Barrier the plasmalemma separates a cell from an environment
and other cells; the nucleus is separated from cytoplasm,
membranes organelles from hyaloplasm.
•Receptor on a surface of plasmalemma. There are special
structures-receptors due to which the cell finds out different
chemical substances, physical factors, other cells, hormones and
•Transport-through a membrane of cell freely passes water, salts and
substances with low molecular weight. Such transport is called
•The transport against a gradient of concentration is called active.
water) can cross the
membrane in either
does not require
Certain molecules (e.g.,
glucose) cannot freely
diffuse across membranes
but must be helped across
facilitated diffusion is
often unidirectional, but it
follows a concentration
gradient and requires no
Some nondiffusible molecules can move into or out
of cell either along or against a concentration gradient.
Such movement requires energy, usually as ATP. An
example of this active transport is the sodium pump
(Na+/K+-ATPase), which can expel sodium ions from a cell
even when the external sodium concentration is higher
than the internal one.
Endocytosis сells engulf extracellular substances and bring
them into the cytoplasm in membrane-limited vesicles by
mechanisms described collectively a endocytosis.
Exocytosis removes substances from the cell. Cells use this
process both for secretion and for excretion of undigested material.
A membrane-limited vesicle or secretory granule fuses with the
plasma membrane and releases its contents into the extracellular
space, without disrupting the plasma membrane.
•In phagocytosis (“cell eating”), the cell engulfs insoluble
extracellular substances, such as large macromolecules or
entire bacteria. The vesicles formed are termed
•In pinocytosis (“cell drinking”), the cell engulfs small
amounts of intercellular fluid, which may contain a variety
of solutes. Pinocytotic vesicles are usually smaller than
Pinocytotic vesicles are usually smaller than phagosomes
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.
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 "beltlike" junction that encircles the
entire circumference of the cell.
These junctions act as barriers
that prevent the movement of
molecules into the intercellular
adhesion. This device surrounds the cell and
joins it to its neighbors.
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
Desmosomes are serving
to attach the basal cell
membrane to the basal
also called communicating junctions, are regions of
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.
Plasma membrane enfoldings of the
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.
- type of contact
between two nervous cells or
between a nervous cell and a
muscle. Through synapses pass
Cytoplasm structures can be divided into 3 groups:
enzymecontaining, permanent subcellular compatrments.
•Cytoplasmic inclusions are structures, membranebound or not, that are generally more transient than
organelles and less actively involved in cell metabolism.
•Cytoplasmic matrix the cytoskeleton is composed of
proteinaceous elements that form a supporting network
within the cytoplasm; some of these elements
(microtubules) also form discrete cytoplasmic structures
such as centrioles.
Organelles constantly present in a cell are described as
membranous and nonmembranous.
The membranous organelles include:
endoplasmic reticulum (rER and sER)
The nonmembranous organelles include:
filaments (different varieties)
Membranous organelles are the most part of organelles
of a cell.
The largest of the cytoplasmic organelles, mitochondria are the
energy providers of the cell. The size to bacteria (usually 2-6 mm
in lenght and 0.2 mm in diameter but quite variable) and have
varios shapes: spheric, ovoid, filamentous. Each mitochondrion is
bounded by 2 unit membranes.
The outer mitochondrial membrane has a smooth contour and
forms a continuous but relatively porous covering. It is freely
permeable to various small molecules.
membrane is less porous and is
therefore semipermeable. It has
numerous infoldings, or cristae, that
project into the mitochondrion’s
interior. The mitochondrial cristae
of most cells are shelflike, but those
typically more tubular.
The mitochondrial membranes create 2 membrane-limited spaces. The
intermembrane space is located between the inner and outer membranes and is
continuous with the interacristal space that extends into the cristae. The
intercristal space, or matrix space, is enclosed by the inner membrane and
contains the mitochondrial matrix.
The mitochondrial matrix contains
water, solutes, and large matrix
granules, believed to be concerned
concentrations. It also contains
circular DNA and mitochondrial
ribosomes similar to those of bacteria.
The matrix contains numerous
soluble enzymes involved in such
specialized mitochondrial functions as
the Krebs cycle cycle, tricarboxylic acid cycle),
b-oxidation of lipids, and
Function the provide of cell with the energy for chemical and
mechanical work by storing energy generated from cellular
metabolites in the high-energy bonds of ATP.
Mitochondria are found in nearly all eukaryotic cells, and in most
they are dispersed throughout the cytoplasm.
However, they accumulate in the
highest concentrations in cell types and
intracellular regions with the highest
Cardiac muscle cells are notable for
the abundance of their mitochondria.
Epithelial cells lining the kidney
tubules have abundant mitochodria
interdigitated between basal plasma
membrane infoldings where active
transport of ions and water occurs.
The ribosomes are protein-synthesizing organelles. Each type of
ribosome has 2 unequal ribosomal subunits. Cytoplasmic ribosomes
are composed of ribosomal RNA (rRNA) synthesized in the nucleos
and associated proteins synthesized in the cytoplasm.
They are intensely basophilic. Light microscopy reveals cytoplasmic
accumulations of ribosomes as basophilic patches, formerly termed
ergastoplasm in grandular cells and Nissl bodies in neurons. In
electron micrographs, ribosomes appear as small, electron-dense
Cytoplasmic ribosomes occur in 2 forms.
Free ribosomes are individual ribosomes dispersed in cytoplasm.
Polysomes are groups of ribosomes evenly distributed along a
single strand of messenger RNA (mRNA), an arrangement that
permits synthesis of multiple copies of a protein from the same
message. Polysomal ribosomes read (translate) the mRNA code and
thus play a critical role in assembling amino acids into specific
proteins, are found free in the cytoplasm (free polysomes) and
attached to membranes of the rER.
Free polysomes are involved in the
synthesis of structural proteins and
enzymes for intracellular use.
Polysomes of the rER are involved
in synthesizing proteins that are
The endoplasmic reticulum (ER) is a complex organelle involved in the
synthesis, packaging, and processing of various cell substances. It is a
freely anastomosing network (reticulum) of membranes that form vesicles,
or cisternae; these may be elongated, flattened, rounded, or tubular.
Transfer vesicles (transitional
vesicles) are small, membranelimited vesicles that bud from
the ER and cross the
intervening cytoplasm to reach
the Golgi complex for further
processing or packaging of
ER occurs in 2 forms:
Rough endoplasmic reticulum (rER)
The also called granular endoplasmic reticulum, is studded with
ribosomes, many of them in polysomal clusters.
flattened, and elongated,
specialized for protein
acinar cells, plasma cells).
The ribosomes give rER
The fine structure of
rER (membranes and
individual ribosomes) is visible only with the
Rough endoplasmic reticulum (RER)
rER is mainly concerned with the synhtesis of proteins for
sequestration from the rest of the cytoplasm, ie, secretory proteins
such as collagen, proteins for incorporation into cell membranes,
and lysosomal enzymes (separated from the rest of the cytoplasm to
RER in protein-secreting
epithelial cells often lies in
membrane and the nucleus.
Smooth endoplasmic reticulum (SER)
The smooth endoplasmic reticulum (SER) lacks ribosomes
and thus appears smooth in electron micrographs.
SER cisternae are more
tubular or vesicular than those
SER stains poorly, if at all, so
with the light microscope it is
indistinguishable from the rest
of the cytoplasm.
Because it lacks ribosomes, the
SER cannot synthesize proteins.
It has many enzymes, important
in lipid metabolism, steroid
hormone synthesis, glycogen
(glucose-6phosphatase), and detoxification.
Smooth endoplasmic reticulum (SER)
The sER is suspended in the
cytoplasm of many cells and
is especially abundant in cells
hormones (cells of the adrenal
cortex, gonads in liver cells
“hepatocytes”, where it is
involved in glycogen synthesis
and drug detoxification).
sarcoplasmic reticulum is
found in striated muscle cells,
where it helps to regulate
sequestering and releasing
The Golgi complex (Golgi apparatus) participates in many activities,
particularly those associated with secretion. It has an essential role
in coordinating membrane flow and vesicle traffic among organelles.
The composed of 3 major
conspicious stack of 3-10
discrete, slightly curved,
numerous small vesicles
peripheral to the stack;
a few large vacuoles,
condensing vacuoles, at
the concave surface of the
The cis face (convex face,
forming face) of the stack is
usually closest to adjacent
dilated ER cisternae and is
surrounded by transfer
vesicles. Its cisternae stain
more darkly with osmium.
The trans face (concave
face, maturing face) often
harbors several condensing
vacuoles and generally faces
away from the nucleus.
Lysosomes are spheric, membrane-limited vesicles that
may contain more than 50 enzymes each and function as
the cellular digestive system. Their characteristic enzyme
activities distinguish them from other cellular granules.
The enzyme most widely exploited for their identification
is acid phosphate, because it occurs almost exclusively in
lysosomes. Other enzymes common in lysosomes are
ribonucleases, deoxyribonucleases, cathepsins, sulfatases,
b-glucoronidase, and phospholipases and other proteases,
glucosidases, and lipases.
Lysosomal enzymes usually occur as glycoproteins
and are most active at an acidic pH. Lysosomes
occur in various sizes and electron densities,
depending on their level of activity.
Primary lysosomes are small (5-8 nm), with electron-dense
contents; they appear as black circles in electron micrographs. They
are the storage form of lysosomes, and their enzymes are mostly
inactive. Lysosomes enzymes synthesized and coreglycosylated in the
RER are transferred to the Golgi complex for further glycosylation;
it is uncertain whether their final packaging as primary lysosomes
occurs in the Golgi complex. The primary lysosomes disperse
through the cytoplasm.
They are found in most cells
but are most abundant in
phagocytic cells (macrophages,
Secondary lysosomes are larger and less electron-dense and have a
mottled appearance in electron micrographs. They are formed by
the fusion of one or more primary lysosomes with a phagosome.
Their primary function is the digestion of products of heterophagy
and autophagy; when the lysosomal enzymes mix with the
phagosome contents, they become active.
Lysosomal enzymes also catabolize certain products of cell synthesis,
thus regulating the quality and quantity of secretory material.
Secondary lysosomes occur
throughout the cytoplasm in
many cells, in numbers that
reflect the cell’s lysosomal
and phagocytic activity.
membranelimited inclusion of
varying size and
associated with the
terminal phases of
materials such as
and certain lipids.
Peroxisomes are membrane-limited, enzyme-containing vesicles
somewhat larger than primary lysosomes. Peroxisomes function in
hydrogen peroxide metabolism. They contain urate oxidase,
hydroxyacid oxidase, and d-amino acid oxidase, which produce
hydrogen peroxide capable of killing bacteria; they also contain
catalase, which oxidizes various substrates and uses the hydrogen
removed in the process to convert the toxic hydrogen peroxide to
gluconeogenesis by assisting in the boxidation of fatty acids. They are found
dispersed in the cytoplasm or in
association with the SER.
Microtubules are the thickest components of the cytoskeleton, with
diameters of 24 nm. They are fine tubular structures of variable
lenght, with dense walls (5 nm thick) and a clear internal space (14
nm in internal diameter). The walls are composed of subunits called
tubulin heterodimers, each of which consists of one a-tubulin and
one b-tubulin protein molecule. The tubulin heterodimers are
arranged in protofilaments.
Thirteen of these threadlike b-tubulin
polymers of a- and b-tubulin
align parallel to one another to
form the wall of each
increase in length by adding
new heterodimers to one end,
called the nucleation site.
Microfilaments are the thinnest cytoskeletal components (5-7 nm
wide). They are usually composed of one of several types of actin
protein. In striated muscle cells, actin filaments form a stable
paracrystalline array in association with filaments of myosin. Actin
filaments in other cells are less stable and can dissociate and
reassemble. These changes are regulated in part by calcium ions and
cyclic AMP and by actin-binding proteins in the cytoplasm.
Microfilaments are contractile, but to contract, they usually interact
with myosin. In muscle cells, myosin forms thick filaments. In
nonmuscle cells, it exists in soluble form.In nonmuscle cells,
microfilaments are generally distributed as an irregular meshwork
throughout the cytoplasm.
A centriole is a cylindric group of microtubules, 150 nm in overall
diameter and 350-500 nm long, containing 9 microtubule triplets in a
pinwheel array. Each microtubule in a triplet shares a portion of the
wall of the neighboring microtubule.
An interphase (nondividing)
cell has a pair of adjacent
centrioles with perpendicular
long axes, each surrounded by
satellites, or pericentriolar
from the pericenriolar
bodies and radiate into the
Centrioles are the structural organizers of the cell. Centriole
duplication is a prerequisite for cell division, and during mitosis
the centrioles organize the microtubules of the mitotic spindle.
Location. Between cell divisions,
centrioles are near the nucleus, often
surrounded by Golgi complexes. The
centrioles and associated Golgi
cytocenter, which appears as a clear
zone near the nucleus. During the S
phase of interphase, each centriole
duplicates by giving rise to a
procentriole that grows at right
angels to the original. During mitosis,
the new centriole pairs migrate to
opposite cell poles to organize the
Prominent among inclusions serving as storage depots are spheric
lipid droplets, which differ in appearance depending upon the type
of histologic preparation.
Glycogen granules are inclusions that are PAS-positive in light
microscopy and appear in electron micrographs as rosettes of
electron-dense particles. Both lipid droplets and glycogen granules
lack a limiting membrane.
Melanin is a brownish pigment widely distributed in vertebrates,
often found in electron-dense, membrane-limited granules termed
melanosomes. It is particularly abundant in epidermal cells and in
the pigment layer of the retina.
Nuclei vary in appearance from tissue to tissue and cell to cell, but
they generally have a:
one to several nucleoli
The nuclear contents are set apart from the cytoplasm by a double
membrane called the nuclear envelope and a narrow (40-70 nm)
intermembrane space called the perinuclear space.
The nuclear envelope is often considered an exctension of the
RER, because its outer surface is often peppered with ribosomes and
shows occasional continuities with the RER.
The inside of the inner
membrane is lined with the
fibrous lamina, a layer
consisting of proteins called
The envelope is perforated by many nuclear pores,
each of which has a diameter of about 70 nm and is
8 globular subunits
called annular proteins,
octagonal appearance in
Each pore is covered
The pores provide a channel
important molecules between
the nucleus and cytoplasm.
nucleic acids synthesized in the
nucleus and used in the
cytoplasm (mRNA, rRNA,
synthesized in the cytoplasm
and used in the nucleus
The nucleoplasm is the matrix in which the other
intranuclear components are embedded. It is composed of
enzymatic and nonenzymatic proteins, metabolites, ions,
It includes the nuclear
matrix – a fibrillar
that appears to bind
Nuclear chromatin is an intensely basophilic substance
consisting of DNA and associated histone and nonhistone
Nuclei containing highly coiled chromatin, termed
heterochromatin, stain darkly with basic dyes.
Chromatin is a complex of DNA and proteins. It
is responsible for the characteristic basophilia of
condensed chromatin called
heterochromatin and the
lightly staining material is a
The chromosomes, the most highly condensed form of
chromatin, are visible during mitosis. In females, only one
X chromosome (either of the 2) is used by each cell;
The inactive X chromosome is often visible as a clump of
heterochromatin termed sex chromatin, or the Barr body.
In most cells, the Barr
body is attached to the
inner surface of the
nuclear envelope. In a
it may appear as a
During interphase (between mitoses), each nucleus
usually has at least one (or2) intensely basophilic body
called a nucleolus. Nucleoli are the synthesis sites for
most ribosomal RNA (rRNA).
mitosis and reappears
The term nucleolonema is used by light microscopists to refer to a
threadlike basophilic substructure of the nucleolus. The nucleolonema
contains 2 rRNA-rich components distinguishable by electron microscopy.
The pars fibrosa consists of densely packed ribonucleoprotein fibers, 510 nm in diameter. These fibers consist of the newly synthesized primary
transcripts of the rRNA genes and associated proteins.
The pars granulosa
contains dense granules,
15-20 nm in diameter,
that represent maturing
export to the cytoplasm.