histology is the science that studies tissues: a set of cells similar in structure and function, it is a level of cellular organization assigned to
play a certain role within an organism. is closely linked to other branches such as:
- cytology: studies cellular structure
- pathological anatomy: studies histology for diagnostic purposes
- physiology: mechanisms of regulation and response of organisms
- embryology: tissue formation and embryonic processes
to distinguish and analyze the various tissues, the microscope is used which allows observation in detail and distinguishing the various
structures.
The tool varies according to the size of what I want to observe. The ability of the optical system to detect very small details is called
resolution power, it allows us to distinguish the details of extremely small structures in a very clear way.
optical microscope (micrometers -6) allows us to have an optimal resolving power. the complex lens system is referred to as an objective.
the maximum magnification level is 100x.
The minimum distance at which two points are seen as distinct is called the resolution limit.
The ability to zoom in on the image is a secondary feature to the resolution.
Lens and eyepiece work together to resolve the image (the eyepiece resolves the actual image resolved by the lens)
the different microscopes can operate with:
- bright field based on the property of the cell to absorb or scatter light, the samples must be stained
- darkfield (bright and dark differ by light source)
- phase contrast: allows you to observe live cells and samples, the light comes from below and allows you to observe live cells without dyes.
How are fabrics studied and observed?
block the autolysis process
- biopsy: taking a sample of an organ
objective: what I see on the slide must respect as much as possible the morphology that the tissue has in its biological location.
there must be no putrefaction process so I perform the...
- fixation (blocking the autolysis process) which can be chemical or physical
you have to set up the organic preparations
- arrange thin sections so that the light can pass through them. the tissue must be hard (with the fixation I make the sample hard in a
chemical way: I remove water, i.e. dehydrate and impregnate with paraffin wax)
- to make it visible I need dyes
I choose the coloring based on my study objective and the structures I want to detail and observe (e.g. I want to identify cell architecture)
dyes are divided into salts and acids/bases, the most important are:
- eosin affinity for basic structures (cytoplasm)
- hematoxylin affinity for acidic structures (nucleic acids and nuclei)
to identify other details there are other colors (e.g. membrane black) (base membrane fuchsia) (bacteria blue)
the different types of cells arrange and organize themselves to form 4 basic types of tissue:
1. EPITHELIUM OR EPITHELIAL TISSUE
the cells are very close, connected in various ways and immersed in a very scarce extracellular substance, they form cellular laminae or
solid clusters and rest on a basement membrane that separates it from the connective tissue, they are found on all internal and external
covering surfaces.
Epithelia cover the external and internal surfaces of the body (lining epithelia), line the internal surfaces of blood and lymphatic vessels,
form glands (glandular epithelia) performing different functions in relation to their different locations.
Epithelia are NOT vascularized and receive nutrients by diffusion from capillaries located in the surrounding connective tissue.
Epithelial tissue arises from all three germ layers:
from the ectoderm: the epidermis, which covers the external surface of the body, the epithelium of the cornea and the epithelium of the
mucosa which lines the oral cavity originate; the sebaceous and sweat glands attached to the skin and the mammary glands.
from the endoderm: formation of the epithelium of many of the mucous membranes that cover the internal surface of body cavities
communicating with the outside (for example, stomach, intestine, etc.) and give rise to the related glands (liver, pancreas, gastric glands
and intestinal, etc.)
from the mesoderm: the epithelium lining most of the urinary and genital tracts, the epithelium of the adrenal cortex and the epithelium lining
the ovary and serous cavities (pleura, pericardium and peritoneum) originate. The latter is commonly indicated with the term mesothelium;
the epithelium that lines blood and lymph vessels internally, called the endothelium.
COATING EPITHELIUM .
in most cases they are tissues that line the surfaces, cavities and ducts of the body.
It covers the external surfaces and the body cavities (tissue side, in contact with the underlying connective tissue), it also covers the luminal
side (side in contact with the organ cavity)
made up of laminae. one or more layers separated by poor matrix. cell junctions provide exchange mediation and mechanical strength.
They rest on a shared structure called the basement membrane which provides anchorage, separates from the underlying connective tissue
and regulates metabolic exchanges between connective tissue and epithelium.
Epithelia depend on the diffusion of oxygen and metabolites from the underlying tissues as they are not vascularised
They form a protective waterproof barrier.
, functions are divided into
- defense, barrier, protect against external physical agents
- - mediate entry and exit of various substances, selective permeability
- secretion of mucus, hormones, enzymes
- absorption of various substances
- reception of sensibility, innervated by sensory nerves
The criteria according to which it is classified are based on: number of layers, shape of the cells, presence of morphological specializations
e.g. eyelash
SIMPLE EPITHELIA. a single layer of cells resting on the basement membrane.
it is always found at the level of surfaces with an absorption or secretion function. the cells have the same polarity. aligned cores
they have a poor selective capacity in filtering the passage of different substances.
we find an example of a very active simple epithelium in the small intestine, where we find tall cells so as to have space to host organelles
and specializations
simple or squamous squamous epithelium: Consists of a single layer of flat cells, in cross section appearing as thin ovals, in longitudinal
section appearing as a mosaic. These surfaces are not subjected to mechanical stress. Provided with a central, ovoid or spherical nucleus,
the margins are generally irregular and joined by junctions. Given their reduced thickness, it is found in tissues used for passive transport of
gas, e.g. lining the pulmonary alveoli, nephrons, tympanic membrane, mesothelium and endothelium of blood vessels.
- mesothelium: membrane that lines serous cavities (pleura, pericardium, peritoneum), acts as a lubricant and prevents rubbing between
organs
- endothelium: lines the innermost part of the blood vessels, forms the only layer in the capillaries. vessel permeability function.
simple cubic epithelium, Cells with secretory/absorptive activity. It is found in the stomach (glandular tubular epithelium), small intestine
(columnar epithelium with microvilli specialization on the top), the presence or absence of cilia identifies another type of epithelium
simple cylindrical columnar epithelium: tall cells, lines most of digestive tract, gallbladder and glandular ducts. Has specializations on its
apex (microvilli or cilia)
- entirocytes: non-ciliated, epithelium lining the intestinal mucosa, the mucosa invaginates forming the villi, has microvilli on the top,
increases the absorption surface
pseudostratified cylindrical epithelium, disordered distribution, but each cell touches the basement membrane, only a few the apex. Male
urethra, epididymis and large glandular excretory ducts
CUBICA O ffeso
STRATIFIED EPITHELIUM .
PAVIMENTOSE
stratified squamous epithelium (non-keratinized, no stratum corneum). Many layers of cells of various shapes; the deep layer that rests on
the basement membrane is composed of cubic or even cylindrical cells; one or more layers of cells with irregular polyhedral contours follow
towards the surface and finally layers of flattened elements, with a scaly appearance (the metabolism slows down, receives less nutrients
ISOPRISMATICA
and the cytoplasm flattens, andBATI PRISMAMICA
the cell tends to desquamate). The deep layer cells have an intense metabolic and proliferative activity and
are distinguished from the more superficial ones which are relatively metabolically inert. It performs functions similar to the keratinized one:
protection function, resistant to abrasion, not drying. We find it as a covering of humidified surfaces of the oral cavity, pharynx, esophagus,
uterine cervix, vagina.
stratified squamous epithelium (keratinized) It constitutes the epithelial layer of the skin, suitable for withstanding abrasion and drying to
which the surface of the body is subjected. During maturation, the epithelial cells undergo the keratinization process which involves the
formation of a thick layer of keratin K and from the remains of the degenerated cells. The superficial layers are eliminated with the growth of
the deep layers.
layers of the epidermis:
1. BASAL. keratinocyte cells (derives from etoderm sheet). Single layer of cubic or cylindrical cells. It is also called the germinal layer because
the keratinocytes that form it proliferate by mitosis (responsible for the continuous renewal of the epidermis.). The basal layer cells are
connected by desmosomes and rest directly on the basal lamina
2. thorny. The spinous layer consists of 4-8 layers of polyhedral basophilic cells that become flattened as they approach the surface. They are
firmly joined together by numerous desmosomes. Melanosomes are also present.
3. GRAINY. It consists of 3-5 layers of flattened cells containing large, intensely basophilic granules of irregular shape, not enveloped by a
membrane, called keratohyalin granules. These granules contain fiaggrin, a protein rich in histidine which has the ability to aggregate the
parallel bundles of keratin filaments into macrofibrils, giving the cell an elongated shape. Granular cells also synthesize loricrin, a protein
that is localized in keratohyalin granules and is then deposited on the inner surface of the plasma membrane, to contribute to the formation
of the cornified cell envelope. The adhesion molecules change: here there are tight junctions.
4. POLISHED. It is a transition layer located between the stratum granulosum and the stratum corneum, present in the epidermis of the palm
of the hand and the sole of the foot. It consists of a few layers of thickened and refractile acidophilic cells without nucleus and organelles,
which form a
, wavy line above the granular layer.
5. HORNY. Made up of flattened cells with no nucleus and other organelles (dead cells called corneocytes). Corneal cells are particularly
resistant to mechanical and chemical damage due to the presence, immediately below their plasma membrane, of a thick layer of material
called the cornified cell envelope. it is the layer that determines the thickness of the epithelial tissue
CORNEO
LUCIDO
GRANULOSO
SPINOSO
BASALE
stratified cubic epithelium. It is thin and is found in the major excretory ducts, salivary glands, pancreas and sweat glands.
stratified columnar epithelium. the cores are arranged on different levels
TRANSITIONAL EPITHELIUM (UROTHELIUM) . only in the urinary tract: bladder, ureter, urethra. is specialized in permeability and to
withstand strong strains and urine toxicity. Above the basal state are polyhedral cells, the most superficial cells having a roundish shape
(flattening as the bladder distends). This type of epithelium can be defined as plastic epithelium due to its ability to adapt to changes in the
volume of the organ.
POLARITY'. A fundamental property of epithelial cells is their morphological and functional polarity. Their apical end, facing the surface, in
fact differs from the basal end, oriented towards the underlying connective tissue. This property manifests itself in a different specialization
of the apical, basal and lateral cell surfaces and also in the non-uniform arrangement of the organelles inside the cell, which reflects the so-
called functional axis of the element.
Apical domain specializations: side facing the lumen or an external environment with respect to the epithelium, there are different structures
that allow the cell to communicate with the outside and perform functions of absorption and secretions, for this reason they have
specializations....
MICROVILLI, finger-shaped extrusions of the plasma membrane whose task is to increase the absorbent surface, 1 micrometre, supported
by actin filaments and transversally bound by vilin. they appear as a streaked border or brush border. numerous in the cells of the intestinal
mucosa
STEREOCIGLIA, supported by actin filaments such as microvilli, are longer than microvilli, about 100 actin units, elastic. they are found in
sensory cells and stimulus receptors at the level of the epididymis, cochlea of the ear and in the vas deferens (male reproductive system)
EYELASHES, unique endowed with the ability to move, diameter of 2 micrometers and length 7-10 micrometers.
The central axis consists of the axoneme, organized into 9 + 2 microtubule doublets. Each doublet is composed of
two subunits: subunit A is a complete microtubule composed of 13 protofilaments, subunit B, in the shape of an
incomplete circle, is formed by 10 protofilaments and is completed close to subunit A. With the exception of the
central pair which is complete.
Scourges. structure similar to those of the eyelashes, they differ in size (they reach up to 60 micro meters) the
only cells in the human body equipped with a flagellum are the spermatozoa.
Lateral domino specializations: Junctional complexes responsible for close contact between adjacent epithelial cells.
OCCLUDING JUNCTIONS (tight junctions). They allow the epithelium to function as a barrier, they waterproof the tissue. They are
peripheral junctions, located at the top, between two adjacent epithelial cells forming a seal that closes any intercellular space. They limit
the movement of H2O and other molecules in the intercellular space, allowing the maintenance of cell polarity. They regulate the passage of
substances between cells. Occluding zonules divide the plasma membrane into two distinct domains: apical and base-lateral.
ANCHOR JOINTS. are localized junctions. They include both cell-cell adhesions and cell-matrix adhesions.
play a certain role within an organism. is closely linked to other branches such as:
- cytology: studies cellular structure
- pathological anatomy: studies histology for diagnostic purposes
- physiology: mechanisms of regulation and response of organisms
- embryology: tissue formation and embryonic processes
to distinguish and analyze the various tissues, the microscope is used which allows observation in detail and distinguishing the various
structures.
The tool varies according to the size of what I want to observe. The ability of the optical system to detect very small details is called
resolution power, it allows us to distinguish the details of extremely small structures in a very clear way.
optical microscope (micrometers -6) allows us to have an optimal resolving power. the complex lens system is referred to as an objective.
the maximum magnification level is 100x.
The minimum distance at which two points are seen as distinct is called the resolution limit.
The ability to zoom in on the image is a secondary feature to the resolution.
Lens and eyepiece work together to resolve the image (the eyepiece resolves the actual image resolved by the lens)
the different microscopes can operate with:
- bright field based on the property of the cell to absorb or scatter light, the samples must be stained
- darkfield (bright and dark differ by light source)
- phase contrast: allows you to observe live cells and samples, the light comes from below and allows you to observe live cells without dyes.
How are fabrics studied and observed?
block the autolysis process
- biopsy: taking a sample of an organ
objective: what I see on the slide must respect as much as possible the morphology that the tissue has in its biological location.
there must be no putrefaction process so I perform the...
- fixation (blocking the autolysis process) which can be chemical or physical
you have to set up the organic preparations
- arrange thin sections so that the light can pass through them. the tissue must be hard (with the fixation I make the sample hard in a
chemical way: I remove water, i.e. dehydrate and impregnate with paraffin wax)
- to make it visible I need dyes
I choose the coloring based on my study objective and the structures I want to detail and observe (e.g. I want to identify cell architecture)
dyes are divided into salts and acids/bases, the most important are:
- eosin affinity for basic structures (cytoplasm)
- hematoxylin affinity for acidic structures (nucleic acids and nuclei)
to identify other details there are other colors (e.g. membrane black) (base membrane fuchsia) (bacteria blue)
the different types of cells arrange and organize themselves to form 4 basic types of tissue:
1. EPITHELIUM OR EPITHELIAL TISSUE
the cells are very close, connected in various ways and immersed in a very scarce extracellular substance, they form cellular laminae or
solid clusters and rest on a basement membrane that separates it from the connective tissue, they are found on all internal and external
covering surfaces.
Epithelia cover the external and internal surfaces of the body (lining epithelia), line the internal surfaces of blood and lymphatic vessels,
form glands (glandular epithelia) performing different functions in relation to their different locations.
Epithelia are NOT vascularized and receive nutrients by diffusion from capillaries located in the surrounding connective tissue.
Epithelial tissue arises from all three germ layers:
from the ectoderm: the epidermis, which covers the external surface of the body, the epithelium of the cornea and the epithelium of the
mucosa which lines the oral cavity originate; the sebaceous and sweat glands attached to the skin and the mammary glands.
from the endoderm: formation of the epithelium of many of the mucous membranes that cover the internal surface of body cavities
communicating with the outside (for example, stomach, intestine, etc.) and give rise to the related glands (liver, pancreas, gastric glands
and intestinal, etc.)
from the mesoderm: the epithelium lining most of the urinary and genital tracts, the epithelium of the adrenal cortex and the epithelium lining
the ovary and serous cavities (pleura, pericardium and peritoneum) originate. The latter is commonly indicated with the term mesothelium;
the epithelium that lines blood and lymph vessels internally, called the endothelium.
COATING EPITHELIUM .
in most cases they are tissues that line the surfaces, cavities and ducts of the body.
It covers the external surfaces and the body cavities (tissue side, in contact with the underlying connective tissue), it also covers the luminal
side (side in contact with the organ cavity)
made up of laminae. one or more layers separated by poor matrix. cell junctions provide exchange mediation and mechanical strength.
They rest on a shared structure called the basement membrane which provides anchorage, separates from the underlying connective tissue
and regulates metabolic exchanges between connective tissue and epithelium.
Epithelia depend on the diffusion of oxygen and metabolites from the underlying tissues as they are not vascularised
They form a protective waterproof barrier.
, functions are divided into
- defense, barrier, protect against external physical agents
- - mediate entry and exit of various substances, selective permeability
- secretion of mucus, hormones, enzymes
- absorption of various substances
- reception of sensibility, innervated by sensory nerves
The criteria according to which it is classified are based on: number of layers, shape of the cells, presence of morphological specializations
e.g. eyelash
SIMPLE EPITHELIA. a single layer of cells resting on the basement membrane.
it is always found at the level of surfaces with an absorption or secretion function. the cells have the same polarity. aligned cores
they have a poor selective capacity in filtering the passage of different substances.
we find an example of a very active simple epithelium in the small intestine, where we find tall cells so as to have space to host organelles
and specializations
simple or squamous squamous epithelium: Consists of a single layer of flat cells, in cross section appearing as thin ovals, in longitudinal
section appearing as a mosaic. These surfaces are not subjected to mechanical stress. Provided with a central, ovoid or spherical nucleus,
the margins are generally irregular and joined by junctions. Given their reduced thickness, it is found in tissues used for passive transport of
gas, e.g. lining the pulmonary alveoli, nephrons, tympanic membrane, mesothelium and endothelium of blood vessels.
- mesothelium: membrane that lines serous cavities (pleura, pericardium, peritoneum), acts as a lubricant and prevents rubbing between
organs
- endothelium: lines the innermost part of the blood vessels, forms the only layer in the capillaries. vessel permeability function.
simple cubic epithelium, Cells with secretory/absorptive activity. It is found in the stomach (glandular tubular epithelium), small intestine
(columnar epithelium with microvilli specialization on the top), the presence or absence of cilia identifies another type of epithelium
simple cylindrical columnar epithelium: tall cells, lines most of digestive tract, gallbladder and glandular ducts. Has specializations on its
apex (microvilli or cilia)
- entirocytes: non-ciliated, epithelium lining the intestinal mucosa, the mucosa invaginates forming the villi, has microvilli on the top,
increases the absorption surface
pseudostratified cylindrical epithelium, disordered distribution, but each cell touches the basement membrane, only a few the apex. Male
urethra, epididymis and large glandular excretory ducts
CUBICA O ffeso
STRATIFIED EPITHELIUM .
PAVIMENTOSE
stratified squamous epithelium (non-keratinized, no stratum corneum). Many layers of cells of various shapes; the deep layer that rests on
the basement membrane is composed of cubic or even cylindrical cells; one or more layers of cells with irregular polyhedral contours follow
towards the surface and finally layers of flattened elements, with a scaly appearance (the metabolism slows down, receives less nutrients
ISOPRISMATICA
and the cytoplasm flattens, andBATI PRISMAMICA
the cell tends to desquamate). The deep layer cells have an intense metabolic and proliferative activity and
are distinguished from the more superficial ones which are relatively metabolically inert. It performs functions similar to the keratinized one:
protection function, resistant to abrasion, not drying. We find it as a covering of humidified surfaces of the oral cavity, pharynx, esophagus,
uterine cervix, vagina.
stratified squamous epithelium (keratinized) It constitutes the epithelial layer of the skin, suitable for withstanding abrasion and drying to
which the surface of the body is subjected. During maturation, the epithelial cells undergo the keratinization process which involves the
formation of a thick layer of keratin K and from the remains of the degenerated cells. The superficial layers are eliminated with the growth of
the deep layers.
layers of the epidermis:
1. BASAL. keratinocyte cells (derives from etoderm sheet). Single layer of cubic or cylindrical cells. It is also called the germinal layer because
the keratinocytes that form it proliferate by mitosis (responsible for the continuous renewal of the epidermis.). The basal layer cells are
connected by desmosomes and rest directly on the basal lamina
2. thorny. The spinous layer consists of 4-8 layers of polyhedral basophilic cells that become flattened as they approach the surface. They are
firmly joined together by numerous desmosomes. Melanosomes are also present.
3. GRAINY. It consists of 3-5 layers of flattened cells containing large, intensely basophilic granules of irregular shape, not enveloped by a
membrane, called keratohyalin granules. These granules contain fiaggrin, a protein rich in histidine which has the ability to aggregate the
parallel bundles of keratin filaments into macrofibrils, giving the cell an elongated shape. Granular cells also synthesize loricrin, a protein
that is localized in keratohyalin granules and is then deposited on the inner surface of the plasma membrane, to contribute to the formation
of the cornified cell envelope. The adhesion molecules change: here there are tight junctions.
4. POLISHED. It is a transition layer located between the stratum granulosum and the stratum corneum, present in the epidermis of the palm
of the hand and the sole of the foot. It consists of a few layers of thickened and refractile acidophilic cells without nucleus and organelles,
which form a
, wavy line above the granular layer.
5. HORNY. Made up of flattened cells with no nucleus and other organelles (dead cells called corneocytes). Corneal cells are particularly
resistant to mechanical and chemical damage due to the presence, immediately below their plasma membrane, of a thick layer of material
called the cornified cell envelope. it is the layer that determines the thickness of the epithelial tissue
CORNEO
LUCIDO
GRANULOSO
SPINOSO
BASALE
stratified cubic epithelium. It is thin and is found in the major excretory ducts, salivary glands, pancreas and sweat glands.
stratified columnar epithelium. the cores are arranged on different levels
TRANSITIONAL EPITHELIUM (UROTHELIUM) . only in the urinary tract: bladder, ureter, urethra. is specialized in permeability and to
withstand strong strains and urine toxicity. Above the basal state are polyhedral cells, the most superficial cells having a roundish shape
(flattening as the bladder distends). This type of epithelium can be defined as plastic epithelium due to its ability to adapt to changes in the
volume of the organ.
POLARITY'. A fundamental property of epithelial cells is their morphological and functional polarity. Their apical end, facing the surface, in
fact differs from the basal end, oriented towards the underlying connective tissue. This property manifests itself in a different specialization
of the apical, basal and lateral cell surfaces and also in the non-uniform arrangement of the organelles inside the cell, which reflects the so-
called functional axis of the element.
Apical domain specializations: side facing the lumen or an external environment with respect to the epithelium, there are different structures
that allow the cell to communicate with the outside and perform functions of absorption and secretions, for this reason they have
specializations....
MICROVILLI, finger-shaped extrusions of the plasma membrane whose task is to increase the absorbent surface, 1 micrometre, supported
by actin filaments and transversally bound by vilin. they appear as a streaked border or brush border. numerous in the cells of the intestinal
mucosa
STEREOCIGLIA, supported by actin filaments such as microvilli, are longer than microvilli, about 100 actin units, elastic. they are found in
sensory cells and stimulus receptors at the level of the epididymis, cochlea of the ear and in the vas deferens (male reproductive system)
EYELASHES, unique endowed with the ability to move, diameter of 2 micrometers and length 7-10 micrometers.
The central axis consists of the axoneme, organized into 9 + 2 microtubule doublets. Each doublet is composed of
two subunits: subunit A is a complete microtubule composed of 13 protofilaments, subunit B, in the shape of an
incomplete circle, is formed by 10 protofilaments and is completed close to subunit A. With the exception of the
central pair which is complete.
Scourges. structure similar to those of the eyelashes, they differ in size (they reach up to 60 micro meters) the
only cells in the human body equipped with a flagellum are the spermatozoa.
Lateral domino specializations: Junctional complexes responsible for close contact between adjacent epithelial cells.
OCCLUDING JUNCTIONS (tight junctions). They allow the epithelium to function as a barrier, they waterproof the tissue. They are
peripheral junctions, located at the top, between two adjacent epithelial cells forming a seal that closes any intercellular space. They limit
the movement of H2O and other molecules in the intercellular space, allowing the maintenance of cell polarity. They regulate the passage of
substances between cells. Occluding zonules divide the plasma membrane into two distinct domains: apical and base-lateral.
ANCHOR JOINTS. are localized junctions. They include both cell-cell adhesions and cell-matrix adhesions.
