Author: Julie Doll BSc, MSc•Reviewer: Dimitrios Mytilinaios MD, PhDLast reviewed: October 28, 2021Reading time: 19 minutes


A tissue is a team of cells, in nearby proximity, arranged to carry out one or more specific functions.

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There are four straightforward tissue types defined by their morphology and also function: epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

Epithelial tissue creates protective boundaries and is associated in the diffusion the ions and also molecules.Connective tissue underlies and supports other tissue types.Muscle tissue contracts to initiate movement in the body.Key facts around the organization types
Epithelial TissueFeatures - high cellularity, special sensory receptors, develops a barrier, avascular, innervatedSurfaces - basal (hemidesmosomes, basement membrane), apical (lumen, microvilli, cilia, stereocilia), lateral (adhering junctions, chop junctions, desmosomes, void junctions)Types - squamous, cuboidal, columnar, simple, stratified, pseudostratified, specialized 
Connective TissueStructure - cells (structural, immunological, defense, energy reservoirs), extracellular procession (ground substance, protein fibers)Types the fibers - collagen, reticular, elasticClassification - ideal (dense, loose), embryonic (mesenchyme, mucous), committed (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 organization is a highly cellular organization that overlies human body surfaces, lines cavities, and forms glands. In addition, devoted epithelial cells role as receptors for unique senses (smell, taste, hearing, and vision). Epithelial cells are numerous, exist in close apposition to each other, and also form committed junctions to develop a barrier between connective organization and complimentary surfaces. Totally free surfaces that the body incorporate the external surface of internal organs, lining of body cavities, exterior surface of the body, tubes and ducts. The extracellular matrix the epithelial tissue is minimal and also lacks additional structures. Return epithelial tissue is avascular, the is innervated.

cell surfaces

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

Basal surface

The basal surface is nearest to the basement membrane. The basement membrane itself creates a thin barrier between connective tissues and also the most basal layer of epithelial cells. Committed junctions referred to as hemidesmosomes certain the epithelial cells on the basement membrane.

Apical surface

The apical surface of one epithelial cabinet is nearest come the lumen or complimentary space. Apical cell surfaces might display dedicated extensions. Microvilli are small processes projecting from the apical surface to rise surface area. They room heavily connected in diffusion in the proximal convoluted tubule that the nephron and also in the lumen of the small intestines.

Cilia are small processes found in the respiratory tract and mrs reproductive tract. Their complex structure facilitates activity that brushes little structures with the lumen of either the trachea or Fallopian tubes. Stereocilia are similar to cilia in size and also shape, however they space immotile and much more frequently discovered in the epithelium that the masculine reproductive tract, especially in the ductus deferens and the epididymis.

Lateral surfaces

The lateral surface of epithelial cells are situated between adjacent cells. The many notable lateral surface ar structures room junctions. Adhering junctions connect the cytoskeleton of bordering cells to produce strength in the tissue. Desmosomes can be believed of together spot-welding for epithelial tissues. They room usually situated deep come adhering junctions and also are found in places subject to stresses. For instance in the stratified epithelium of the skin.

Tight junctions type a solid barrier to prevent movement of molecule between adjacent epithelial cells. Chop junctions are found in the an easy columnar epithelium that the gut tube to control absorption that nutrients. Finally, space junctions do the opposite function. Gap junctions allow small molecules and structures to happen freely in between cells. For example, gap junctions in cardiac muscle tissue enable for coordinated contraction that the heart.

summary of epithelial tissue surfaces and characteristics
features extremely cellular, duty as receptors, type a barrier, minimal extracellular matrix, avascular, innervated,
Basal surface Basement membrane, hemidesmosomes
Apical surface ar Microvilli, cilia, stereocilia
Lateral surface ar Adhering junctions, desmosomes, chop junctions, void junctions

organization structure

Two major characteristics that epithelial tissue divide it into subclasses: the shape of the cells and also the presence of layers.

shape of cells:

Squamous – cells are flattened, have the right to be keratinized or nonkeratinized, involved in protection and diffusion, uncovered in capillary walls and skin Columnar – cells are rectangular, cilia are frequently present, connected in absorption, secretion, protection, and lubrication, type the inside lining the the gut tube


Pseudostratified – simple epithelia that show up to be stratified once viewed in cross-section despite they are only one layer of cells

dedicated epithelial tissue

Keratinized stratified squamous epithelium – provides up the epidermis the skin Nonkeratinized stratified squamous epithelium – found in regions subject to abrasion, for example oral mucosa and vaginal lining Pseudostratified ciliated columnar epithelium – lines the inner surface ar of the trachea Endothelium - lines the inner surface ar of blood vessels

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Connective tissue

Connective tissue is the many abundant tissue kind in the body. In general, connective tissue is composed of cells and also an extracellular matrix. The extracellular matrix is comprised of a ground substance and also protein fibers. So, in a more detailed way, all connective organization apart indigenous blood and lymph is composed of three main components: cells, floor substance and fibers.

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

Connective organization cells

The cell originate indigenous mesenchyme, a loosely arranged embryonic organization featuring elongated cells in a viscous soil substance. Connective tissue cells do not oppose each other but rather space separated by 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 organization fibers

The ground substance that connective tissue includes structural proteins referred to as fibers. There room three types of connective organization fibers:

Collagen fibers are the most abundant fiber type. They have actually a high tensile strength however are likewise flexible. Collagen fibers are consisted of of many subunits, dubbed collagen fibrils, that show up striated under electron microscopy. There room many species of collagen and also the collagen varieties present in a tissue give it distinctive characteristics. Because that example, type i collagen offers resistance to stretch in bone tissue, if type IV collagen renders up the suprastructure of the basement membrane. Reticular fibers room thinner than collagen fibers. Lock are discovered in extensive networks and provide structural support and framework. Reticular fibers perform not stain with continuous H&E stain and also a silver stain is necessary to stain fibers black, making lock visible.

Connective organization classification

category of connective tissue is based upon two characteristics: the composition of that is cellular and extracellular components and also its duty in the body. Tissues space either classified as proper, embryonic, or specialized.

proper connective tissues

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

Dense connective tissue can be more classified right into dense consistent connective tissue and dense rarely often rare connective tissue. Dense regular connective tissue makes up tendons and ligaments. Fibers are densely packed and organized in parallel to create a solid tissue capable of withstanding the traction of muscle and also bone in movement. Dense rarely often, rarely connective tissue likewise contains abundant fibers however lacks the directionality that dense constant connective organization fibers. The high variety of fibers offers strength however the disorganized pattern of fibers permits for flexibility. Dense irregular tissue is linked the hollow organs of the cradle tract.

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Embryonic connective tissue

Embryonic connective tissue, derived from mesoderm, is the precursor to many connective tissues in the adult body. That is categorized right into two subtypes: mesenchyme and also mucous connective tissue. Mesenchyme is uncovered within the embryo. Mesenchymal cells space spindle shaped through processes extending from one of two people end. The cabinet processes connect to those of various other mesenchymal cell through space junctions. An extremely thin, scattered collagen fibers room present, yet they are not particularly strong reflecting the limited stress inserted on the tissues of the arising embryo.

Mucous connective tissue is found in the umbilical cord. The cells of mucous connective tissue space spindle shaped and relatively sparse. A nearly gelatinized ground substance called Wharton’s jelly provides up many of the extracellular matrix between the cells and collagen fibers.

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Bone organization is unique in that its extracellular matrix is mineralized. Calcium phosphate, in the type of hydroxyapatite crystals, is responsible for the mineralization of bone and also creates a very solid tissue able come support and also protect the body.Blood is a fluid connective tissue that transports gases, nutrients, and wastes throughout the body. The liquid extracellular matrix of blood is comprised of plasma, which constitutes slightly an ext than fifty percent of the organization volume. The cells of blood tissue space classified together erythrocytes, leukocytes, and thrombocytes. Erythrocytes, or red blood cells, carry oxygen and carbon dioxide with the cardiovascular system. Leukocytes, or white blood cells, room responsible for the immune and also allergic responses. Thrombocytes, or platelets, form clots and initiate the fix of injured blood vessels.

Details about dedicated connective organization are noted below:

Muscle tissue

Muscle tissue is both extensible and also elastic, in various other words, it have the right to be stretched and also returned come its original size and shape. The cells of muscle tissue are distinctive in the they room contractile, or qualified of contraction. This contraction is a result of slide actin and also myosin filaments. Muscle tissue is conveniently distinguishable by its highly organized bundles of cells. Return there are three varieties of muscle organization with distinct cell morphologies, the fiber bundles of each tissue kind are arranged in parallel oriented ~ above the lengthy axis and are unique from surrounding connective tissue. Muscle is classified according to the illustration of the contractile cells.

review of muscle organization
qualities Extensible, elastic, contractile, organized into bundles
skeleton rapid and solid contraction; large, cylindrical, elongated cells; syncytium; peripheral and also ovoid nuclei; striated; current in voluntary skeletal muscles
Cardiac strong contraction; striated; solitary and centrally situated nucleus, linked by gap junctions and also intercalated discs; syncytium; found in the myocardium
Smooth Weak and slow contractions; spindle shaped cells; solitary and central nucleus; nonstriated; discovered in involuntary muscle (viscera)

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

skeleton muscle

Skeletal muscle is responsible because that the voluntary motion of the body. Because that example, activity 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 also elongated. In embryonic development, myoblasts fuse with each other to type one larger muscle cell, bring about syncytial, multinucleated cells. Nuclei of skeleton muscle cells space peripheral and also ovoid. When viewed under a microscope, the arrangement of actin and also myosin offers skeletal muscle a striated appearance.

Cardiac muscle

Cardiac muscle is uncovered in the heart wall surface also known as myocardium. Like skeletal muscle, actin and also myosin additionally give cardiac muscle a striated appearance. The movement that cardiac muscle cells administer is involuntary and also coordinated through gap junctions. A significant defining properties of cardiac muscle organization is the existence of intercalated disks. Cardiac muscle cells are elongated and also branched. Intercalated disks are existing at the junctions between two cells. Although void junctions enable this tissue to function as a syncytium, every cell has actually one, centrally located nucleus.

Smooth muscle

Smooth muscle organization is connected with arteries and tubular guts such together the minister tract. This type of tissue gives weak, slow involuntary movements. Smooth muscle cells room spindle shaped with one main nucleus. The contractile fibers of smooth muscle cells room arranged perpendicular to each various other rather 보다 in parallel, therefore smooth muscle organization does not show up striated.

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cell of the nervous system are highly committed to transmit electrical impulses approximately the body. There are two main varieties of cells found in worried tissue: neurons and also glia.

Neurons often tend to have actually a huge cell body, or soma, and also long projections provided in transmitting information. This projections are described as axons or dendrites. Axons send impulses away from the soma and dendrites lug incoming information. Neurons are many easily established by your axons in one of two people longitudinal or cross-sectional slide. Groups of neurons are referred to as ganglia in the peripheral nervous system and as nuclei in the central nervous system.

an overview of nervous tissue
Neurons Function: transmission of electrical impulsesStructure: soma (cell body), axons (transmit impulses far from soma), dendrites (transmit incoming impulses)Organization: ganglia (PNS) and nuclei (CNS)
Glia Function: support and also nourish neuronsAstrocytes: assistance synapses, type a safety barrier roughly blood vesselsOligodendrocytes: insulate axons and increase impulse projection in the CNSSchwann cells: oligodendrocytes equivalents in the PNSMicroglia: defend the nervous system

Glia room the sustaining cells of concerned tissue and also significantly outnumber neurons. These cells different by an ar of the concerned system. Astrocytes support neurons, specifically near synapses, and carry out a protective obstacle surrounding blood vessels. Oligodendrocytes are discovered in the white matter of the main nervous system. Large projections from this cells wrap about the axon of a neuron insulating the to permit for faster projection of impulses.

In the peripheral nervous system, Schwann cells attain the same task. Oligodendrocytes and also Schwann cell are advantageous in identify nervous tissue because the sheathing they provide appears as a special layer surrounding a tubular axon. Microglia room the macrophages that the concerned system. This cells constantly inspection nervous tissue to destroy invaders and clear cabinet debris.

Nervous tissue exhibits a fluid-filled extracellular space through which ions and also neuromediators travel to transmit impulses. Because the generation of activity potentials requires a specific concentration the ions, the extracellular atmosphere is extremely regulated by glia. Capillaries passing v nervous organization are fully surrounded through glia to type the blood brain barrier.

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A tissue is a team of cells, in near proximity, arranged to execute one or an ext specific functions. There room four basic tissue varieties defined by their morphology and also function:

epithelial tissueconnective tissuemuscle tissuenervous tissue

Epithelial tissue

Epithelial tissue is a highly cellular organization that overlies body surfaces, present cavities, and forms glands. That is avascular but innervated. Epithelial cells exist in nearby apposition, forming a barrier between connective organization and totally free surfaces. Their surfaces confront basally, apically and laterally, v each having distinctive features. Specialized epithelial tissue likewise exists.

Connective tissue

Connective organization is the most abundant tissue kind in the body. It is composed of cells, the originate native mesenchyme, and also an extracellular matrix. The extracellular matrix is consisted of of a ground substance and also protein fibers. There room several important cell species and three key fibers: collagen, reticular and also elastic. Classification the connective tissue into three broad varieties is based ~ above the composition of the cellular and also extracellular components and its duty in the body.

Muscle tissue

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

Nervous tissue

Cells that the nervous system are highly devoted to transmit electrical impulses approximately the body. There space two main types: neurons and also glia. Neurons have tendency to have actually a huge cell body and also projections carrying details to (dendrites) and from (axons) the cell human body itself. Groups the neurons are referred to as ganglia (PNS) and also nuclei (CNS). Glia are the supporting cells of worried tissue. They consist the astrocytes, oligodendrocytes/Schwann cells and also microglia.



M. H. Ross: Histology: A Text and Atlas, sixth 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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