Author: Julie Doll BSc, MSc•Reviewer: Dimitrios Mytilinaios MD, PhDLast reviewed: September 11, 2021Reading time: 19 minutes


A tissue is a group of cells, in near proximity, arranged to execute one or an ext specific functions.

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There are four an easy tissue species defined by their morphology and function: epithelial tissue, connective tissue, muscle tissue, and also nervous tissue.

Epithelial tissue creates protective boundaries and also is affiliated in the diffusion that ions and also molecules.Connective tissue underlies and also supports various other tissue types.Muscle tissue contracts to initiate motion in the body.Key facts around the organization types
Epithelial TissueFeatures - high cellularity, distinct sensory receptors, creates a barrier, avascular, innervatedSurfaces - basal (hemidesmosomes, basement membrane), apical (lumen, microvilli, cilia, stereocilia), lateral (adhering junctions, tight junctions, desmosomes, gap junctions)Types - squamous, cuboidal, columnar, simple, stratified, pseudostratified, specialized 
Connective TissueStructure - cells (structural, immunological, defense, power reservoirs), extracellular matrix (ground substance, protein fibers)Types of fibers - collagen, reticular, elasticClassification - ideal (dense, loose), embryonic (mesenchyme, mucous), dedicated (cartilage, adipose, bone, blood)
Muscle TissueFeatures - elastic, extensible, contractileTypes - skeletal, cardiac (gap junctions, intercalated discs), smooth, striated, nonstriated
Nervous TissueNeurons - soma, dendrites, axons, ganglia (PNS), nuclei (CNS)Glia - astrocytes, oligodendrocytes, Schwann cells, microglia - blood-brain barrier

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Epithelial tissue

Epithelial cell nuclei (histological slide)

Epithelial tissue is a highly cellular organization that overlies body surfaces, lines cavities, and also forms glands. In addition, specialized epithelial cells function as receptors for special senses (smell, taste, hearing, and also vision). Epithelial cells room numerous, exist in nearby apposition to each other, and also form devoted junctions to create a barrier between connective organization and cost-free surfaces. Complimentary surfaces that the body incorporate the outer surface of interior organs, lining of body cavities, exterior surface of the body, tubes and ducts. The extracellular matrix that epithelial tissue is minimal and also lacks extr structures. Although epithelial organization is avascular, it is innervated.

cabinet surfaces

The cells of epithelial tissue have actually three species of surfaces distinguished by their location and functional specializations: basal, apical, and also lateral.

Basal surface

The basal surface is nearest come the basement membrane. The basement membrane itself creates a thin barrier between connective tissues and the many basal layer of epithelial cells. Dedicated junctions referred to as hemidesmosomes for sure the epithelial cell on the basement membrane.

Apical surface

The apical surface of an epithelial cabinet is nearest to the lumen or cost-free space. Apical cell surfaces may display devoted extensions. Microvilli are small processes projecting from the apical surface to boost surface area. They are heavily connected in diffusion in the proximal convoluted tubule that the nephron and also in the lumen the the small intestines.

Cilia are small processes found in the respiratory tract tract and female reproductive tract. Their facility structure facilitates movement that brushes little structures with the lumen of either the trachea or Fallopian tubes. Stereocilia are comparable to cilia in size and also shape, but they room immotile and more frequently found in the epithelium of the male reproductive tract, particularly in the ductus deferens and the epididymis.

Lateral surfaces

The lateral surfaces of epithelial cells are situated between surrounding cells. The many notable lateral surface ar structures are junctions. Adhering junctions link the cytoskeleton of neighboring cells to create strength in the tissue. Desmosomes can be assumed of as spot-welding for epithelial tissues. They are usually located deep come adhering junctions and also are found in locations subject to stresses. For example in the stratified epithelium the the skin.

Tight junctions kind a solid barrier to prevent movement of molecules between surrounding epithelial cells. Tight junctions are found in the an easy columnar epithelium that the gut tube to regulate absorption of nutrients. Finally, void junctions execute the the contrary function. Gap junctions allow tiny molecules and structures to pass freely between cells. For example, gap junctions in cardiac muscle tissue allow for coordinated contraction that the heart.

an overview of epithelial organization surfaces and characteristics
features extremely cellular, duty as receptors, form a barrier, minimal extracellular matrix, avascular, innervated,
Basal surface ar Basement membrane, hemidesmosomes
Apical surface Microvilli, cilia, stereocilia
Lateral surface ar Adhering junctions, desmosomes, chop junctions, space junctions

tissue structure

Two major characteristics the epithelial organization divide it into subclasses: the shape of the cells and the visibility of layers.

form of cells:

Squamous – cells space flattened, have the right to be keratinized or nonkeratinized, connected in protection and also diffusion, discovered in capillary walls and also skin Columnar – cells are rectangular, cilia are regularly present, associated in absorption, secretion, protection, and lubrication, kind the inner lining that the gut tube


Pseudostratified – simple epithelia that show up to it is in stratified when viewed in cross-section though they are just one great of cells

devoted epithelial tissue

Keratinized stratified squamous epithelium – provides up the epidermis of skin Nonkeratinized stratified squamous epithelium – found in areas subject come abrasion, for example oral mucosa and also vaginal lining Pseudostratified ciliated columnar epithelium – currently the inner surface of the trachea Endothelium - lines the inner surface of blood ship

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Connective tissue

Connective tissue is the most abundant tissue form in the body. In general, connective tissue consists of cells and an extracellular matrix. The extracellular procession is consisted of of a ground substance and also protein fibers. So, in a much more detailed way, every connective organization apart from blood and lymph is composed of three key components: cells, soil substance and fibers.

an introduction of connective tissue
Cell species Structural, immunological, defense, power reservoir
fibers Collagen, reticular, elastic
classification Proper: Loose; dense (regular, irregular) connective tissueEmbryonic: Mesenchymal; mucous connective tissueSpecialized: Cartilage; adipose; bone; blood

Connective tissue cells

The cells originate native mesenchyme, a loosely organized embryonic tissue featuring elongated cell in a viscous floor substance. Connective organization cells carry out not oppose every other yet rather room separated through a huge extracellular matrix.

cell Types:

Structural – fibroblasts, chondroblasts, osteoblasts, odontoblasts Immunological – plasma cell, leukocytes, eosinophils Defense – neutrophils, mast cells, basophils, macrophages Energy reservoir – adipose cells

Connective tissue fibers

The ground substance that connective tissue includes structural proteins called fibers. There are three types of connective tissue fibers:

Collagen fibers space the many abundant fiber type. They have a high tensile strength however are likewise flexible. Collagen yarn are comprised of countless subunits, dubbed collagen fibrils, that appear striated under electron microscopy. There are many types of collagen and the collagen varieties present in a tissue offer it unique characteristics. For example, type ns collagen provides resistance to stretch in bone tissue, when type IV collagen renders up the suprastructure the the basement membrane. Reticular fibers room thinner 보다 collagen fibers. Lock are found in extensive networks and administer structural support and framework. Reticular fibers execute not stain with regular H&E stain and a silver stain is essential to stain yarn black, making lock visible.

Connective organization classification

classification of connective tissue is based upon 2 characteristics: the composition of its cellular and also extracellular components and its function in the body. Tissues room either classified as proper, embryonic, or specialized.

suitable connective tissues

proper connective tissues include loosened connective tissue, often referred to together areolar tissue, and also dense connective tissue. Loose connective tissue is composed of thin, loosely arranged collagen yarn in a viscous soil substance.

Dense connective organization can be further classified into dense continuous connective tissue and also dense rarely often, rarely connective tissue. Dense continuous connective tissue makes up tendons and ligaments. Fibers room densely packed and organized in parallel to develop a strong tissue qualified of withstanding the pull of muscle and bone in movement. Dense rarely often, rarely connective tissue likewise contains plentiful fibers but lacks the directionality that dense continuous connective organization fibers. The high variety of fibers gives strength however the disorganized pattern of fibers allows for flexibility. Dense irregular tissue is connected the hole organs of the cradle tract.

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Embryonic connective tissue

Embryonic connective tissue, obtained from mesoderm, is the precursor to countless connective tissues in the adult body. It is categorized into two subtypes: mesenchyme and also mucous connective tissue. Mesenchyme is found within the embryo. Mesenchymal cells room spindle shaped with processes extending from one of two people end. The cabinet processes affix to those of other mesenchymal cell through gap junctions. Very thin, scattered collagen fibers space present, but they space not an especially strong showing the limited stress inserted on the tissues of the arising embryo.

Mucous connective tissue is uncovered in the umbilical cord. The cells of mucous connective tissue are spindle shame and relatively sparse. A virtually gelatinized soil substance referred to as Wharton’s jelly makes up most of the extracellular matrix in between the cells and also collagen fibers.

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Bone organization is distinct in the its extracellular procession is mineralized. Calcium phosphate, in the form of hydroxyapatite crystals, is responsible for the mineralization the bone and also creates a very strong tissue able to support and protect the body.Blood is a fluid connective organization that transports gases, nutrients, and wastes transparent the body. The fluid extracellular procession of blood is consisted of of plasma, which constitutes slightly much more than fifty percent of the tissue volume. The cell of blood tissue space classified as erythrocytes, leukocytes, and also thrombocytes. Erythrocytes, or red blood cells, lug oxygen and carbon dioxide through the cardiovascular system. Leukocytes, or white blood cells, space responsible because that the immune and allergic responses. Thrombocytes, or platelets, type clots and initiate the fix of injured blood vessels.

Details about committed connective tissues are listed below:

Muscle tissue

Muscle tissue is both extensible and also elastic, in various other words, it have the right to be stretched and returned to its initial size and shape. The cell of muscle tissue are distinctive in that they room contractile, or capable of contraction. This contraction is a an outcome of slide actin and myosin filaments. Muscle tissue is easily distinguishable through its very organized bundles of cells. Return there are three varieties of muscle organization with unique cell morphologies, the fiber bundles of each tissue kind are i ordered it in parallel oriented on the long axis and are unique from surrounding connective tissue. Muscle is classified follow to the illustration of the contractile cells.

an introduction of muscle tissue
characteristics Extensible, elastic, contractile, organized into bundles
skeletal rapid and strong contraction; large, cylindrical, elongated cells; syncytium; peripheral and ovoid nuclei; striated; current in voluntary skeletal muscle
Cardiac strong contraction; striated; single and centrally located nucleus, connected by space junctions and also intercalated discs; syncytium; discovered in the myocardium
Smooth Weak and also slow contractions; spindle shaped cells; single and main nucleus; nonstriated; uncovered in involuntary muscle (viscera)

The three types of muscle organization are: skeleton muscle, cardiac muscle, and smooth muscle tissue.

skeleton muscle

Skeletal muscle is responsible for the voluntary motion of the body. For example, motion of the limbs, skin that the face, and also orbits. Contraction of skeletal muscle tissue is rapid and also strong. Cells room large, cylindrical, and elongated. In embryonic development, myoblasts fuse with each other to kind one larger muscle cell, leading to syncytial, multinucleated cells. Nuclei of bones muscle cells room peripheral and ovoid. When viewed under a microscope, the arrangement of actin and myosin provides skeletal muscle a striated appearance.

Cardiac muscle

Cardiac muscle is discovered in the heart wall surface also recognized as myocardium. Choose skeletal muscle, actin and also myosin likewise give cardiac muscle a striated appearance. The motion that cardiac muscle cells carry out is involuntary and also coordinated by gap junctions. A major defining characteristics of cardiac muscle tissue is the existence of intercalated disks. Cardiac muscle cells room elongated and branched. Intercalated disks are present at the junctions between two cells. Although void junctions permit this tissue to duty as a syncytium, every cell has one, centrally situated nucleus.

Smooth muscle

Smooth muscle tissue is connected with arteries and tubular guts such as the intestinal tract. This type of tissue gives weak, slow involuntary movements. Smooth muscle cells room spindle shaped v one central nucleus. The contractile fibers that smooth muscle cells space arranged perpendicular to each other rather 보다 in parallel, because of this smooth muscle organization does not show up striated.

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cells of the nervous system are highly committed to transmit electric impulses about the body. There space two main types of cells found in worried tissue: neurons and glia.

Neurons often tend to have a large cell body, or soma, and also long projections supplied in transmitting information. This projections are referred to as axons or dendrites. Axons send impulses far from the soma and also dendrites lug incoming information. Neurons are many easily determined by your axons in either longitudinal or cross-sectional slide. Groups of neurons are described as ganglia in the peripheral nervous system and as nuclei in the central nervous system.

review of nervous tissue
Neurons Function: transmission of electrical impulsesStructure: soma (cell body), axons (transmit impulses far from soma), dendrites (transmit just arrived impulses)Organization: ganglia (PNS) and also nuclei (CNS)
Glia Function: support and also nourish neuronsAstrocytes: assistance synapses, kind a protective barrier roughly blood vesselsOligodendrocytes: insulate axons and increase impulse estimate in the CNSSchwann cells: oligodendrocytes equivalents in the PNSMicroglia: defend the nervous device

Glia space the sustaining cells of nervous tissue and also significantly outnumber neurons. This cells differ by an ar of the nervous system. Astrocytes assistance neurons, especially near synapses, and provide a protective barrier surrounding blood vessels. Oligodendrocytes are found in the white matter of the main nervous system. Large projections from this cells wrap approximately the axon of a neuron insulating that to permit for much faster projection of impulses.

In the peripheral worried system, Schwann cells achieve the same task. Oligodendrocytes and Schwann cells are valuable in identify nervous tissue because the sheathing they provide appears as a thick layer neighboring a tubular axon. Microglia are the macrophages of the nervous system. This cells constantly survey nervous tissue to destroy invaders and clear cabinet debris.

Nervous tissue exhibits a fluid-filled extracellular space v which ions and neuromediators take trip to transmit impulses. Since the generation of action potentials requires a particular concentration of ions, the extracellular setting is highly regulated by glia. Capillaries passing through nervous tissue are completely surrounded by glia to kind the blood brain barrier.

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A organization is a group of cells, in near proximity, organized to do one or more specific functions. There are four simple tissue species defined by their morphology and function:

epithelial tissueconnective tissuemuscle tissuenervous tissue

Epithelial tissue

Epithelial organization is a highly cellular organization that overlies human body surfaces, present cavities, and also forms glands. It is avascular but innervated. Epithelial cell exist in near apposition, creating a obstacle between connective tissues and totally free surfaces. Their surfaces challenge basally, apically and laterally, through each having distinctive features. Specialized epithelial tissue likewise exists.

Connective tissue

Connective organization is the most abundant tissue type in the body. It is composed of cells, the originate from mesenchyme, and also an extracellular matrix. The extracellular matrix is made up of a ground substance and protein fibers. There are several necessary cell types and three main fibers: collagen, reticular and also elastic. Classification of connective tissue into three broad types is based top top the composition of the cellular and also extracellular components and its role in the body.

Muscle tissue

Muscle tissue is both extensible and elastic. The cells space contractile and are very organized into fiber bundles. Muscle is classified follow to the illustration of the contractile cells, right into three types: skeletal, cardiac and also smooth. The first two species have a striated appearance as result of the parallel orientation the the fiber bundles.

Nervous tissue

Cells of the nervous device are highly specialized to transmit electrical impulses roughly the body. There space two key types: neurons and glia. Neurons tend to have a large cell body and projections carrying details to (dendrites) and from (axons) the cell body itself. Groups of neurons are described as ganglia (PNS) and also nuclei (CNS). Glia room the supporting cells of worried tissue. Castle consist of astrocytes, oligodendrocytes/Schwann cells and microglia.



M. H. Ross: Histology: A Text and Atlas, 6th edition, Lippincott Williams & Wilkins (2011), p. 98-101; 159-172S. G. Waxman: Clinical Neuroanatomy, 27th edition, McGraw-Hill education (2013), p. 7-14

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