In the science of Histology, there are really some powerful dyes. Dyes are used for the identification of cells and tissues. So some dyes of histology below :
Tartrazine: This histology stain will stain cytoplasm, cartilage, and red blood cells yellow
Orcien Stain: A histology stain used for elastin fibers.
Masson Trichome: A trichrome histology stain is a mixture of three dyes. This histology stain can be helpful for differentiating cellular from extracellular items.
Golgi Stain: This histology stain for neurons
Giemsa Stain: this histology stain for peripheral blood smears and bone marrow and used to visualize parasites.
Cajal Stain: This histology stain is used on nervous tissue
Histology Dyes
Histology Topics and subjects
Peripheral Blood Cells
Tissues, Layers, and Organs
Epithelial Tissue, Surface Specializations, and Glands
Connective Tissue
Cartilage and Bone and Bone Histogenesis
Bone Marrow and Hemopoiesis
Nervous Tissue and Neuromuscular Junction
Muscle Tissue
Integument
Circulatory System
Lymphoid Tissues and Organs
Urinary System
Digestive System: Oral Cavity and Teeth
Digestive System: Alimentary Canal
Liver, Gall Bladder, and Pancreas
Endocrine System
Respiratory System
Male Reproductive System
Female Reproductive System (including Organs of Pregnancy)
Eye
Ultrastructure of the Cell (Electron Micrographs)
Histology power point slides and lectures
There are really good and very usefull histology lectures , notes and lectures about Histology. Histology subjects and ppt. power point presentation slides available below links:
The Cell histology
Histotechniques Lecture Notes histology
Epithelium histology
Loose Connective Tissues histology
Blood and Blood Vessels histology
Lymphatic System histology
Bone histology
Dense Connective Tissue and Cartilage histology
Muscle histology
Nervous System histology,
Sensory Systems histology
Integument histology
Digestive System I histology
Digestive System II histology
Respiratory System histology
Urinary System histology
Female Reproductive System histology
Male Reproductive System histology
Endocrine System histology
brain histology
l Nerve cells/neurons
Oligodendrocytes, Astrocytes, Ependymal cells,
Microglia Special glial cells - (CNS)
2 Glial cells|
Schwann cells, Satellite/Capsule cells,
Enteric (gut) glia - (PNS)
3 Blood vessels
4 Connective tissue enclosing sheaths
ELEMENTS OF NERVOUS SYSTEM
NEURONS : Pseudounipolar:one process branching into two a short way from the cell soma, e.g., dorsal-root ganglion cell
Bipolar cells processes come off from opposite poles of the cell, and the cell then assumes a spindle shape
Multipolar cells :
stellate or star-like, pyramidal with apical and basal dendrites, Purkinje with a plump body tapering to an espalier-oriented dendritic tree
NEURONS
Neuron , Axis-cylinder process = Axon
Protoplasmic processes = Dendrites
Body of the nerve cell = Soma
Nerve Cell
Neuron
Neuron
Body of the nerve cell = Soma
Soma contains a large central nucleus with little chromatin. The nucleolus is prominent because the neuron has to synthesize organelles and cytoplasm to fill its long processes
Around the nucleus is the perikaryon with:
(a) Nissl bodies/granules - basophilic, cytoplasmic structures are concentrations of granular ER.
(b) Neurofilaments - a variety of intermediate filament - are aggregated into neurofibrils visible in the cytoplasm after silver impregnations.
(c) Surrounding the nucleus are elements of the Golgi apparatus, mitochondria, lysosomes, and microtubules. Actin filaments move vesicles in the zone directly under the neuron's plasmalemma.
(d) Pigment is sometimes present, e.g., melanin in substantia nigra neurons, and lipofuscin in old neurons.
(e) Cell membrane has specialized receptive areas, the subsynaptic membranes of synapses.
Synapses
A junction that mediates information transfer from one neuron:
To another neuron
To an effector cell
Presynaptic neuron – conducts impulses toward the synapse
Postsynaptic neuron – transmits impulses away from the synapse
Cell to Cell Conduction: the Synapse
Cell to Cell Conduction: the Synapse
Electrical synapses: gap junctions
Very fast conduction
Example: cardiac muscle
Chemical synapses
Pre synaptic terminal
Synthesis of Neurotransmitters (L-glutamate, GABA, dopamine, serotonin, acetylcholine, noradrenaline and glycine OR "minor" transmitters such as cholecystokinin, endogenous opioids, somatostatin, substance P …)
Ca2+ releases Neurotransmitters
Synaptic cleft
Postsynaptic cell: Neurotransmitter receptors
Astrocytes :Protoplasmic astrocytes: large, star-shaped with many processes, some of which attach pedicels to blood vessels or the basal lamina under the pia mater; have cytoplasmic filaments and microtubules; are common in grey matter.
Fibrous astrocytes: similar to protoplasmic astrocytes, but have more filaments and glycogen, and lie in the white matter
Astrocytes
Fibrous Astrocytes (Objective 40x)
Astrocytes in BBB
Astrocytes:
Provide physical support to neurons
Clean up carcasses of dead neurons
Provide controlling chemicals to neurons
Play important role in providing nourishment to neurons
Oligodendrocytes
= oligodendroglia: plump cell body with fairly dense cytoplasm and a darker nucleus and fewer, shorter processes than an astrocyte; common in white matter, but some are perineuronal Provide physical support to neurons Produce myelin sheath that insulates axons
Microglia
(a) derived from mesenchyme via bone marrow;
(b) potentially phagocytic;
(c) dispersed throughout the brain;
(d) a small elongated cell with many short processes and a dark nucleus.This is the ramified or resting microglial cell, which becomes round and phagocytic as a reactive microglial cell (Gitter cell), when responding to damage
Clean up CNS debris
Play role of immune system in brain
(similar to microphages in blood)
Functions: Ependymal cells lining ventricles, and covering the choroid plexus, they are typically cuboidal and often have cilia
Ependymal cells : Form a relatively permeable barrier between CSF and the tissue fluid that surrounds the cells of the CNS. In certain region of the brain ependymal cells possess cilia, the beating of which help to circulate the CSF. Modified ependymal cells contribute to the formation of the choroids plexus which is a capillary knot that protrudes into a brain ventricle, and is involved in the synthesis of cerebrospinal fluid.
Cerebral neocortex :
The number of layers to be clearly seen depends on the particular area of the cerebral cortex and the criteria of the investigator. Thus Cajal worked with an 8-layered scheme, whereas Brodmann adopted 6 - today's choice. Even so, in the motor region only 5 are to be easily made out.
Cerebral Cortex
I: plexiform (molecular): dendrites and axons of cortical neurons making synapses; neuroglia and rare horizontal cells
II: outer granular: dense population small pyramidal cells and stellate cells [small neurons]; various axons and dendritec connections
III: (outer) pyramidal cell: moderate size; increasing size deeper
IV: inner granular: densely packed stellate cells
V: ganglionic or inner pyramidal: lg pyramidal cells (including Betz cells) and smaller numbers of stellate cells and small neurons
VI: multiform (fusiform) cell: numerous small neurons, small pyramidal cells, stellate cells, especially superficially and fusiform cells in deeper part.
Cerebral Cortex
I: plexiform
II: outer granular
III: (outer) pyramidal cell
IV: inner granular
V: ganglionic or inner pyramidal
VI: multiform (fusiform) cell
bone histology subjects
Bone Growth: Interstitial and Oppositional bone growht observed in histology science.
Bone Function: Mineral homeostasis and Hemopoiesis.
Key Special Words and simple definitons: Bones is a topic of Histology. If you learn histology, also you will learn something about bones tissue histology, and bone cell structure, bone layers.
Mineralization
Calcification
Ossification
Hardness
Tensile strength
Volkmann’s canal
Haversian canal
Lacunae
Osteon
Trabeculae
Epithelium
Epithelium
Types of epytheliums
The epithelia are tissues made from cells closely juxtaposed, without the interposition of fiber or ground substance (which distinguishes them from connective tissue). The cells are linked to each other through intercellular junctions. They are not vascularisés with the exception of vascular streaks (cochlea, the production of endolymph). The input of nutrients and export of waste is done in conjunction with connective tissue underlying through a basement membrane, which rests epithelium (if a fabric has joined cells but not basal, this is not an epithelium, such épendymocytes). In this type of tissue, cells are often polarized (the two opposite ends are different morphologically and biochemically), although there are some epithelia where this polarity is difficult to distinguish (liver tissue). There are the apical region of the cell and basal region which is attached to the basal lamina.
They meet two physiological functions not exclusive of each other: function coating and glandular function.
The presence of specific intermediate filament Cytokeratin allows their identification by immunohistochemical methods.
histology topics
Quick study
For some operations still requires the surgeon during the operation on the information collected tissue for its further approach. In this case, a part of the sample in about 10 minutes as a quick cut processed.
Stabilization tissue by freezing (about -20 ° C), depending on fabric
Production of a 5-10 micron thick cut on cryostat
Pulling of the cut on a coated glass slides
DB-fast staining, Paragon staining or other quick-staining
Findings
histology and technic
Before a pathologist / biologist the fine details of a patient sample / evaluate an experiment may be the tissue processing a detailed assessment. These methods can take as Histotechnik together and are largely from laboratory histological biomedical analysts or (V) by MTA.
The tissue processing laboratory in histodiagnostischen includes the following terms:
Fixation to stabilize the tissue (Hauptfixans: 4% neutral buffered formaldehyde solution)
macroscopic examination of meaningful cut tissue districts. In the pathology and medical activities pertaining to the diagnostic process.
Drainage and impregnation of the fabric with liquid paraffin
Einblocken of the tissue in paraffin wax, paraffin cuboid is produced, which includes the tissue.
In modern Histologielaboren the Gewebsstückchen in so-called "Einbettkassetten" laid.
In these tissue sample through the drainage and Einparaffinierung. Then the cassette serves as a base block and can thus in the so-called quick-release frame, with the most modern microtomes are, to be fixed.
Manufacture of 2-5 microns thick slices on microtomes
Pulling on the cuts (coated) glass slides
Histologic staining
The processing of tissue FFPE (formalin-fixed paraffin-embedded tissue), including the Hämatoxylin-eosin staining, the world-wide routine method of Pathology and lasts an average of one to two days from adoption of the samples to the findings. In contrast to the clinical laboratory, many chemical steps carried out by hand. Especially the production cut at microtomes requires great skill.
History Of Histology
The electron microscope examination of tissue is also primarily in the research field. Here are 0,01-0,5 microns thick slices and with a high-resolution electron microscope examined.
Among the tasks of histopathology, the early diagnosis of tumors (eg gastric biopsy), classification of tumors (gut-/bösartig), detection of metabolic diseases, parasitic, bacterial, inflammatory diseases, assistance for the treatment choice and much more.
As a founder of histology is Marie Francois Xavier Bichat (1771-1802), without the microscope 21 tissue types in the human body as described. The emergence of histopathology write Johannes Peter Müller (1801-1858) to the 1838 book on the nature and structural properties of cancer published. As a father of histopathology is Rudolf Virchow (1821-1902) refers.
histology online
Histology
The histology (of Historic gr "tissue" and logos "lesson") is the science of biological tissues, and thus part of medicine and biology, specifically anatomy and pathology.
The histological / pathologist examined tissue samples. These are micrometer thin, colored Gewebsschnitte produced and judged at the microscope. They speak of morphological diagnosis, because the basis of appearance and behavior of färberischen tissue structures of the findings will be created. Probengut to work at the histological preparations include surgery (eg, stomach, intestine, kidney), Probeexzisionen (eg birthmark, tendons, cysts) and biopsies (eg stomach - colon, breast tissue biopsies). With the help of modern technology are already on tiny pieces of tissue (1-2 mm) Histological diagnoses create. These methods are mikroinvasiven for patient care and are often performed at screening.
basic histology topics
In this blog post, you will find to definition of these basic info., step by step you will learn lots of things about histology and biology science. IF you like biology, this is for you. Our topics:
nuclei
euchromatin and heterochromatin
nucleoli
mitotic figures
cytoplasm
simple columnar / cuboidal epithelium
stratified squamous epithelium
exocrine glands
smooth muscle
skeletal muscle
collagen fibers
fat
blood vessels
lymphatic vessels
red blood cells
neutrophils
lymphocytes
live histology, histology images, veterinary histology, skin histology, histology slides, histology quiz, bone histology, oral histology, tissue histology
sensory, contractility
Sensory: Many of the more complex sensory receptors of the nervous system are derived from specialized epithelia called neuroepithelia (e.g., the rods and cones of the retina, olfactory receptors of the nose, taste receptors on the tongue, etc.). Sensory receptors function by converting mechanical, chemical, or electromagnetic signals from the environment into nerve impulses which can be processed by the nervous system.
Contractility: Some very specialized epithelial cells (myoepithelia) contain the contractile proteins myosin and actin similar to muscle. Myoepithelia are associated with the ducts of sweat, salivary, lacrimal, and mammary glands and assist in the secretory process.
Absorption
Epithelial cells are found in those organs (e.g., small intestine) which are involved in absorption of substances important for life. These cells often have microscopic projections on the apical surface of their plasma membranes called microvilli which increase cell surface area in order to facilitate absorption.
Groups of epithelial cells lining the small intestine are organized into larger finger-like structures called villi which project into the lumen of the gut to further increase its surface area and aid the process of nutrient absorption.
Functions and distribution:
Barrier: Epithelial tissue commonly functions as a covering or lining for organs and other tissues (e.g., skin, mucous membranes, intestinal tract, pleural cavity, etc.). In this way, epithelial cells serve as selective barriers between the environment and the internal structures of the body. They protect underlying tissues from drying, and from mechanical and chemical injury. Tight junctions between individual cells play an important role in the barrier function of epithelium. Some barrier epithelial cells have motile cilia that propel fluid or particulate matter over tissue surfaces (e.g., cells lining the bronchi).
Endocrine glands
Glandular tissues that have no ducts opening onto a surface or into a cavity. Most endocrine glands secrete their products (hormones) across basement membranes into connective tissues where they are absorbed by nearby blood vessels and transported to target organs (e.g., pituitary, and adrenal glands).
Exocrine glands can also be classified by their secretion mechanism.
Merocrine glands - Glands that secrete substances by the process of exocytosis (fusion of cytoplasmic vesicles with the plasma membrane resulting in the release of their contents into the extracellular space without compromising the integrity of the cell membrane). Sweat glands (eccrine sweat glands) and salivary glands are merocrine in nature. The lining of the respiratory and digestive tracts contain "goblet cells" - glandular epithelia that synthesize and secrete a complex glycoprotein called mucus. Mucus provides a protective function as well as serving as a lubricant.
Apocrine glands - Glands that secrete by shedding the apical portion of their cytoplasm into a duct (e.g., mammary glands). Sweat glands in the axillae, perianal region, and external genitalia are also apocrine in nature.
Holocrine glands - Glands that secrete by shedding entire cells from the lining of a duct (e.g., sebaceous glands).
8 types distinguished by morphology of secretory portion
8 types distinguished by morphology of secretory portion (tubular [coiled versus straight] versus acinar [simple versus compound]) and branching versus straight excretory portions (which may also secrete bicarbonate)
simple tubular: large intestine: single, straight; lined by goblet (mucous) cells
simple coiled tubular: sweat glands; terminal secretory portion lined by simple cuboidal epithelium; followed by nonsecretory (excretory) duct lined by stratified cuboidal epithelium
simple branched tubular: stomach; secretory portions converge into unbranched duct (wider diameter); lined by mucus-secreting cells.
simple acinar: rounded secretory unit; pockets in epithelial surface; secretory cells (e.g., mucus-secreting glands of penile urethra)
simple branched acinar: several acini emptying into single excretory duct (stratified epithelium); sebaceous gland
compound branched tubular: = duct branched; secretory portions tubular and branched; duodenal (Brunner's) glands
compound acinar: secretory units are acinar and drain into branched ducts; pancreas; branched excretory ducts of increasing diameter lined by simple cuboidal epithelium
compound tubulo-acinar: 3 types secretory units: branched tubular; branched acinar (serous cells); branched tubular (mucous cells) with acinar end pieces ([serous] demilunes); submandibular salivary gland
myoepithelial cells: sometimes embedded in basement membrane; may aid secretion of acinus glands
striated ducts: striations due to mitochondria lined up along folds of basal membrane; transport Na and bicarbonate; cells high cuboidal to columnar
intercalated ducts come between acini or acini and striated ducts; cells low cuboidal
Exocrine glands
Glandular tissue that have ducts that open onto a body surface or into a body cavity. Examples include sebaceous, sweat, and mammary glands. Salivary glands and certain glandular structures of the pancreas that secrete digestive enzymes are examples of exocrine glands secreting into a body cavity. The secretions of exocrine glands can be mucous (viscous), or serous (thin, watery). The ducts of exocrine glands may be simple straight tubes, or can be arranged as more complex branching tubes. Some of the more complex branching duct systems may terminate in multiple sac-like structures called acini giving them a "bunches of grapes" appearance.
Glandular Epithelium
Glandular Epithelium Columnar epithelium basic histology with goblet cells is called glandular epithelium. Some parts of the glandular epithelium consist of such a large number of goblet cells that there are only a few normal epithelial cells left. Columnar and cuboidal epithelial cells often become specialised as gland cells which are capable of synthesising and secreting certain substances such as enzymes, hormones, milk, mucus, sweat, wax and saliva. Basic histology Unicellular glands consist of single, isolated glandular cells such as the goblet cells. Sometimes a portion of the epithelial tissue becomes invaginated and a multicellular gland is formed. Multicellular glands are composed of clusters of cells. Most glands are multicellular including the salivary glands.
Transitional epithelium
Transitional epithelium in basic histology blog - Also called uroepithelium. Stratified epithelial tissue with unique dome-shaped surface cells giving it a cobblestoned appearance. Found exclusively in the urinary system (lining of bladder and ureter). They serve as a barrier preventing the exposure of underlying tissues to urine. They are also able to stretch in response to bladder filling. Basic histology
Pseudostratified epithelium
Pseudostratified epithelium - basic histology Intermediary between simple and stratified epithelium. Consists of one layer of irregularly shaped and sized cells attached to a basement membrane. Because these cells vary in height, their nuclei are at different levels, giving the appearance (under the microscope) of more than one layer of cells. Found in lining of the trachea, bronchi, pharynx, nasal cavity, and urethra in basic histology blog
Stratified Epithelium
Stratified epithelim in basic histology Where body linings have to withstand wear and tear, the epithelia are composed of several layers of cells and are then called compound or stratified epithelium. The top cells are flat and scaly and it may or may not be keratinised (i.e. containing a tough, resistant protein called keratin). The mammalian skin is an example of dry, keratinised, stratified epithelium. The lining of the mouth cavity is an example of an unkeratinisied, stratified epithelium.
Ciliated Columnar Epithelium
Ciliated Columnar Epithelium These are simple columnar epithelial cells, but in addition, they posses fine hair-like outgrowths, cilia on their free surfaces. These cilia are capable of rapid, rhythmic, wavelike beatings in a certain direction. This movement of the cilia in a certain direction causes the mucus, which is secreted by the goblet cells, to move (flow or stream) in that direction. Ciliated epithelium is usually found in the air passages like the nose. It is also found in the uterus and Fallopian tubes of females. The movement of the cilia propel the ovum to the uterus.
Squamous (pavement) epithelium
Squamous cells have the appearance of thin, flat plates. The shape of the nucleus usually corresponds to the cell form and help to identify the type of epithelium. Squamous cells, for example, tend to have horizontall flattened, elliptical nuclei because of the thin flattened form of the cell. They form the lining of cavities such as the mouth, blood vessels, heart and lungs and make up the outer layers of the skin.
Priority of this kind of tissue is to allow rapid exchange by diffusion or filtration
Simple Cuboidal Epithelium:
As their name implies, cuboidal cells are roughly square or cuboidal in shape. Each cell has a spherical nucleus in the centre. Cuboidal epithelium is found in glands and in the lining of the kidney tubules as well as in the ducts of the glands. They also constitute the germinal epithelium which produces the egg cells in the female ovary and the sperm cells in the male testes.
Most cuboidal cells in this kind of tissue are involved in secretion, filtration and absorption
Simple Columnar Epithelium:
Columnar epithelial cells occur in one or more layers. The cells are elongated and column-shaped. The nuclei are elongated and are usually located near the base of the cells. Columnar epithelium forms the lining of the stomach and intestines. Some columnar cells are specialised for sensory reception such as in the nose, ears and the taste buds of the tongue. Goblet cells (unicellular glands) are found between the columnar epithelial cells of the duodenum. They secrete mucus or slime, a lubricating substance which keeps the surface smooth.
Many columnar cells in this kind of tissue are involved in secretion and absorption
Those that are ciliated are involved in movement of particles
Simple epithelium
Simple epithelium can be subdivided according to the shape and function of its cells.
1. Shape of the cells “Squamous”
Cells are thin and flat
Often display many angular outlines when viewed from above
“Cuboidal”
Cells are approximately as tall as wide
“Columnar”
Cells are definitely more taller than wide
2. The number of cell layers present “Simple”
Only one layer of cells
All cells touch the basement membrane
“Stratified”
There is more than one layer of cells
Only the lowest cells rest on the basement membrane
Other cells are stacked upon each other in various configuration making up the "layers"
All cells arise from cell division by the lowest cells
Depending on the number of layers, displacement of the cells upwards into the different layers causes them to change shape
Types of Epithelial Tissue
Epithelial tissue can be divided into two groups depending on the number of layers of which it is composes. Epithelial tissue which is only one cell thick is known as simple epithelium. If it is two or more cells thick such as the skin, it is known as stratified epithelium.
Germ Cell Origin: Epithelial tissues are derived from all three primary germ cell layers.
Ectoderm: The epithelial cells of the skin and oral cavity (epidermis) are derived from ectoderm. Epithelial cells covering the cornea and lens, as well as sensory receptors of the eyes, ears, and nose, are also ectodermal in origin.
Mesoderm: The epithelial lining of blood vessels (endothelium) is derived from mesoderm. The epithelial lining of the pleural and peritoneal cavities (mesothelium) also originate from mesodermal cells.
Endoderm: The epithelial lining of the respiratory system and digestive tracts - as well as the functional cells (parenchyma) of the liver, pancreas, gallbladder, thyroid, and parathyroid, are derived from endoderm.
General Characteristics Of Epithelial Tissue
There are many characteristics common to all epithelial tissue making it easy to recognize. However, students sometimes still find a way to misidentify epithelial tissue. Therefore pay close attention to the following major elements that characterize this type of tissue.
Epithelial tissue covers surfaces and lines internal passage ways . As such epithelial tissue is found in 3 major places
–outer surface of the body
–surface of organs
–internal surface lining of tubules, vessels and hollow organs
The fact that Epithelial Tissue covers or lines means that most epithelial tissues have a free surface which does not contact other cells or extracellular material. This surface is called the apical surface. The opposite side is called the basal surface. On histological slides, this apical surface is the most easiest to recognize. It is at the interface where empty space (usually a vast area of white space) meets tissue.
Example of a typical epithelium layer
The picture on the right shows the epithelial layer sandwiched between the two green arrows. The obvious free empty space is located on top and the sharp point of the arrow thus points at the apical surface of the epithelium. The sharp point of the lower arrow meets up with the basal surface. The green line marks the boundary between the epithelium layer and the underlying tissue and is the site where the basement membrane can be located.
Cells of Epithelial Tissue fit closely together and form sheets of cells. There is hardly any extracellular material that separates the cells from each other.
The Basal surface of the cells are attached to a basement membrane which provides an anchor for attachment to underlying tissues such as connective tissue. NO BLOOD VESSELS PENETRATE THE BASEMENT MEMBRANE TO REACH THE EPITHELIAL LAYER.
And finally take note that most glands are composed primarily from epithelial cells.
Junctions
Adherens Junctions
Adherens junctions provide strong mechanical attachments between adjacent cells.
They hold cardiac muscle cells tightly together as the heart expands and contracts.
They hold epithelial cells together.
They seem to be responsible for contact inhibition.
Some adherens junctions are present in narrow bands connecting adjacent cells.
Others are present in discrete patches holding the cells together.
Adherens junctions are built from:
cadherins — transmembrane proteins (shown in red) whose
–extracellular segments bind to each other and
–whose intracellular segments bind to
catenins (yellow). Catenins are connected to actin filament
One of the oncogenes that is frequently found in colon cancer appears to be the mutated version of a protein that normally interacts with catenins. Loss of functioning adherens junctions may also lead to tumor metastasis.
What is Histology -2-
The plasma membranes of adjacent epithelial cells frequently contain transmembrane proteins called junctional complexes (also called intercellular junctions) that link cells together. Several types of junctional complexes exist:
Anchoring junctions (desmosomes, adherens junctions, hemidesmosomes) - Proteins embedded in, and spanning, the plasma membranes of adjacent cells allowing epithelia to adhere to one another forming structural units of cells - i.e., allowing individual cells to function as a solid sheet rather than as isolated cells. Fibers attached to anchoring junctions within cells help them to resist stretching forces. This is particularly important in those areas of the body that are subject to mechanical stresses (e.g., epidermis of the skin).
Tight junctions - These are junctional complexes that serve as barriers to the free diffusion of molecules across epithelial surfaces. By fusing the plasma membranes on their lateral surfaces, tight junctions prevent molecules from moving between the cells. This means that any substance absorbed across a layer of epithelial cells has to pass through the cells - not around them. This provides a mechanism by which epithelial tissue can control absorption (selective permeability), and keep tissue compartments with different chemical compositions separate from one another.
Gap junctions - These junctional complexes contain channels which permit ion flow and the passage of small molecules between contiguous cells. Cells with gap junctions are able to communicate and coordinate their activity.
Histology Definition
Epithelial tissues are physically separated from underlying connective tissues by a basement membrane (also called the basal lamina). The portion of an epithelial cell attached to the basement membrane is called its basal surface. The opposite side - facing the external environment, or lumen of a body cavity, is its apical surface. Basement membranes are composed of a special type of collagen and a substance called laminin (see below). The basement membrane helps epithelial cells orient themselves in relation to other tissues. After epithelial injury (e.g., an abrasion), the basement membrane serves as a scaffolding upon which new cells attach themselves during healing.
Epithelium: Surface and Glandular
Epithelium is one of the primary tissues. Typically it consists of cells that are closely opposed to one another and occur in various morphological types, thus producing tissues with rather scanty intercellular substance. The epithelial tissues are divided into two major groups: namely, the covering and lining epithelial membranes and second the glandular epithelium.
Maximum cell-to-cell contact; minimum extracellular material; cell junctions; supported by basement membrane (basal lamella); not penetrated by blood vessels; derived from all embryonic germ layers, including mesoderm (endothelia and mesothelia)
Polarity: basal vs apical (luminal); lateral; specialized plasmalemma, appendages and junctional complexes
glycocalyx (apical) vs basement membrane (bm: basal lamina secreted by epithelium + lamina reticularis secreted by connective tissue)
Epithelia: thelia = nipple; epithelia = upon the nipple (convex [surface layer: epidermis, intestinal lining]); endothelia = within the nipple (concave [lining blood and lymph vessels and heart; cornea]); mesothelia = epithelia derived from splanchnic and somatic mesoderm lining body cavity (peripheral serosa) and covering organs (visceral serosa) within peritoneal, plural- and cardiac cavities.
Maximum cell-to-cell contact; minimum extracellular material; cell junctions; supported by basement membrane (basal lamella); not penetrated by blood vessels; derived from all embryonic germ layers, including mesoderm (endothelia and mesothelia)
Polarity: basal vs apical (luminal); lateral; specialized plasmalemma, appendages and junctional complexes
glycocalyx (apical) vs basement membrane (bm: basal lamina secreted by epithelium + lamina reticularis secreted by connective tissue)
Epithelia: thelia = nipple; epithelia = upon the nipple (convex [surface layer: epidermis, intestinal lining]); endothelia = within the nipple (concave [lining blood and lymph vessels and heart; cornea]); mesothelia = epithelia derived from splanchnic and somatic mesoderm lining body cavity (peripheral serosa) and covering organs (visceral serosa) within peritoneal, plural- and cardiac cavities.
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