Author: Julie Doll BSc, MSc•Reviewer: Dimitrios Mytilinaios MD, PhDLast reviewed: September 30, 2021Reading time: 19 minutes


A organization is a team of cells, in close proximity, organized to perform one or an ext specific functions.

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There room four simple tissue varieties defined by your morphology and function: epithelial tissue, connective tissue, muscle tissue, and also nervous tissue.

Epithelial tissue create protective boundaries and is affiliated in the diffusion of ions and molecules.Connective tissue underlies and supports various other tissue types.Muscle tissue contract to initiate activity in the body.Key facts around the tissue types
Epithelial TissueFeatures - high cellularity, special sensory receptors, forms a barrier, avascular, innervatedSurfaces - basal (hemidesmosomes, basement membrane), apical (lumen, microvilli, cilia, stereocilia), lateral (adhering junctions, tight junctions, desmosomes, void junctions)Types - squamous, cuboidal, columnar, simple, stratified, pseudostratified, specialized 
Connective TissueStructure - cell (structural, immunological, defense, energy reservoirs), extracellular matrix (ground substance, protein fibers)Types that fibers - collagen, reticular, elasticClassification - proper (dense, loose), embryonic (mesenchyme, mucous), devoted (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 tissue that overlies body surfaces, lines cavities, and also forms glands. In addition, dedicated epithelial cells role as receptors for special senses (smell, taste, hearing, and vision). Epithelial cells are numerous, exist in near apposition to each other, and form devoted junctions to create a barrier between connective organization and totally free surfaces. Totally free surfaces the the body incorporate the outer surface of inner organs, lining of body cavities, exterior surface ar of the body, tubes and also ducts. The extracellular matrix of epithelial organization is minimal and also lacks extr structures. Back epithelial tissue is avascular, that is innervated.

cell surfaces

The cells of epithelial tissue have three varieties of surfaces identified by your location and functional specializations: basal, apical, and 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 great of epithelial cells. Dedicated junctions dubbed hemidesmosomes certain the epithelial cells on the basement membrane.

Apical surface

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

Cilia are small processes found in the respiratory tract tract and woman reproductive tract. Their facility structure facilitates activity that brushes small structures through the lumen of one of two people the trachea or Fallopian tubes. Stereocilia are similar to cilia in size and shape, however they room immotile and more frequently discovered in the epithelium that the male reproductive tract, specifically in the ductus deferens and also the epididymis.

Lateral surfaces

The lateral surface of epithelial cells are located between nearby cells. The many notable lateral surface structures room junctions. Adhering junctions attach the cytoskeleton of surrounding cells to develop strength in the tissue. Desmosomes have the right to be assumed of together spot-welding because that epithelial tissues. They are usually situated deep come adhering junctions and are uncovered in places subject come stresses. For example in the stratified epithelium of the skin.

Tight junctions form a solid barrier to prevent activity of molecules between adjacent epithelial cells. Tight junctions are uncovered in the simple columnar epithelium of the gut tube to regulate absorption of nutrients. Finally, void junctions perform the opposite function. Gap junctions allow tiny molecules and structures to pass freely in between cells. For example, gap junctions in cardiac muscle tissue permit for combination contraction the the heart.

an introduction of epithelial organization surfaces and also characteristics
qualities 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, void junctions

tissue structure

Two significant characteristics that epithelial tissue divide it right 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, found in capillary walls and also skin Columnar – cells space rectangular, cilia are frequently present, associated in absorption, secretion, protection, and lubrication, type the within lining the the gut tube


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

committed epithelial tissue

Keratinized stratified squamous epithelium – makes up the epidermis the skin Nonkeratinized stratified squamous epithelium – discovered in areas subject to abrasion, for instance oral mucosa and vaginal lining Pseudostratified ciliated columnar epithelium – lines the inner surface ar of the trachea Endothelium - currently the inner surface of blood vessels

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Connective tissue

Connective tissue is the many abundant tissue type in the body. In general, connective tissue consists of cells and an extracellular matrix. The extracellular matrix is consisted of of a ground substance and protein fibers. So, in a more detailed way, all connective organization apart from blood and lymph consists of three main components: cells, soil substance and also fibers.

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

Connective organization cells

The cell originate native mesenchyme, a loosely arranged embryonic tissue featuring elongated cell in a viscous ground substance. Connective organization cells carry out not oppose every other however rather are 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 tissue fibers

The ground substance the connective tissue includes structural proteins referred to as fibers. There space three types of connective tissue fibers:

Collagen fibers space the most abundant fiber type. They have actually a high tensile strength however are also flexible. Collagen fibers are made up of countless subunits, dubbed collagen fibrils, that show up striated under electron microscopy. There are many types of collagen and also the collagen varieties present in a tissue provide it distinctive characteristics. Because that example, type i collagen gives resistance come stretch in bone tissue, when type IV collagen makes up the suprastructure that the basement membrane. Reticular fibers room thinner than collagen fibers. Castle are discovered in comprehensive networks and carry out structural support and also framework. Reticular fibers do not stain with constant H&E stain and a silver stain is essential to stain yarn black, making castle visible.

Connective organization classification

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

appropriate connective tissues

appropriate connective tissues include loosened connective tissue, regularly referred to as areolar tissue, and dense connective tissue. Loose connective tissue consists of thin, loosely arranged collagen fibers in a viscous floor substance.

Dense connective tissue deserve to be further classified right into dense consistent connective tissue and also dense irregular connective tissue. Dense continual connective tissue renders up tendons and ligaments. Fibers are densely packed and also organized in parallel to develop a solid tissue capable of withstanding the pull of muscle and bone in movement. Dense irregular connective tissue additionally contains numerous fibers yet lacks the directionality that dense regular connective organization fibers. The high number of fibers provides strength however the disorganized pattern of fibers permits for flexibility. Dense irregular tissue is connected the hollow organs that the cradle tract.

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Embryonic connective tissue

Embryonic connective tissue, obtained from mesoderm, is the precursor to numerous 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 are spindle shaped with processes extending from one of two people end. The cabinet processes connect to those of various other mesenchymal cells through gap junctions. Very thin, scattered collagen fibers room present, but they are not specifically strong mirroring the minimal stress put on the tissues of the developing embryo.

Mucous connective tissue is found in the umbilical cord. The cell of mucous connective tissue are spindle shame and reasonably sparse. A almost gelatinized ground substance referred to as Wharton’s jelly provides up most of the extracellular matrix between the cells and collagen fibers.

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

Details about dedicated connective tissues are detailed 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 also shape. The cell of muscle tissue are distinct in the they room contractile, or qualified of contraction. This contraction is a an outcome of sliding actin and myosin filaments. Muscle tissue is easily distinguishable by its extremely organized bundles of cells. Back there are three varieties of muscle organization with distinctive cell morphologies, the fiber bundles of each tissue kind are arranged in parallel oriented on the long axis and also are distinct from surrounding connective tissue. Muscle is classified according to the figure of the contractile cells.

review of muscle tissue
characteristics Extensible, elastic, contractile, organized into bundles
bones fast and solid contraction; large, cylindrical, elongated cells; syncytium; peripheral and ovoid nuclei; striated; current in voluntary skeletal muscles
Cardiac solid contraction; striated; solitary and centrally located nucleus, connected by void junctions and intercalated discs; syncytium; uncovered in the myocardium
Smooth Weak and also slow contractions; spindle shame cells; solitary and main nucleus; nonstriated; uncovered in involuntary muscles (viscera)

The three varieties of muscle organization are: skeletal muscle, cardiac muscle, and smooth muscle tissue.

skeleton muscle

Skeletal muscle is responsible for the voluntary movement of the body. For example, motion of the limbs, skin that the face, and orbits. Contraction of skeleton muscle organization is rapid and 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 skeletal muscle cells room peripheral and ovoid. When viewed under a microscope, the setup of actin and myosin provides skeletal muscle a striated appearance.

Cardiac muscle

Cardiac muscle is discovered in the heart wall also recognized as myocardium. Prefer skeletal muscle, actin and also myosin additionally give cardiac muscle a striated appearance. The activity that cardiac muscle cells provide is involuntary and coordinated by gap junctions. A major defining characteristics of cardiac muscle tissue is the presence of intercalated disks. Cardiac muscle cells are elongated and also branched. Intercalated disks are present at the junctions in between two cells. Although space junctions enable this organization to function as a syncytium, each cell has one, centrally located nucleus.

Smooth muscle

Smooth muscle organization is connected with arteries and also tubular organs such as the minister tract. This kind of tissue provides weak, slow-moving involuntary movements. Smooth muscle cells space spindle shaped v one main nucleus. The contractile fibers of smooth muscle cells space arranged perpendicular to each other rather than in parallel, therefore smooth muscle organization does not show up striated.

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cells of the nervous device are highly specialized to transmit electric impulses about the body. There are two main varieties of cells found in concerned tissue: neurons and glia.

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

review of nervous organization
Neurons Function: infection of electrical impulsesStructure: soma (cell body), axons (transmit impulses away from soma), dendrites (transmit just arrive impulses)Organization: ganglia (PNS) and also nuclei (CNS)
Glia Function: support and also nourish neuronsAstrocytes: support synapses, form a safety barrier approximately blood vesselsOligodendrocytes: insulate axons and increase impulse forecast in the CNSSchwann cells: oligodendrocytes equivalents in the PNSMicroglia: defend the nervous device

Glia room the sustaining cells of worried tissue and also significantly outnumber neurons. This cells differ by an ar of the nervous system. Astrocytes support neurons, particularly near synapses, and carry out a protective barrier surrounding blood vessels. Oligodendrocytes are found in the white matter of the main nervous system. Large projections from these cells wrap about the axon of a neuron insulating it to allow for faster projection the impulses.

In the peripheral worried system, Schwann cells attain the very same task. Oligodendrocytes and Schwann cells are advantageous in identifying nervous tissue since the sheathing they carry out appears together a thick layer neighboring a tubular axon. Microglia are the macrophages of the nervous system. These cells constantly survey nervous organization to ruin invaders and clear cell debris.

Nervous organization exhibits a fluid-filled extracellular space v which ions and neuromediators take trip to transmit impulses. Because the generation of action potentials requires a specific concentration that ions, the extracellular environment is extremely regulated through glia. Capillaries passing through nervous organization are fully surrounded by glia to type the blood mind barrier.

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A tissue is a group of cells, in nearby proximity, organized to execute one or an ext specific functions. There are four simple tissue types defined by their morphology and function:

epithelial tissueconnective tissuemuscle tissuenervous tissue

Epithelial tissue

Epithelial organization is a extremely cellular tissue that overlies body surfaces, currently cavities, and forms glands. It is avascular but innervated. Epithelial cells exist in near apposition, developing a obstacle between connective organization and free surfaces. Your surfaces confront basally, apically and also laterally, with each having distinctive features. Specialized epithelial tissue also exists.

Connective tissue

Connective organization is the many abundant tissue type in the body. It is composed of cells, the originate from mesenchyme, and an extracellular matrix. The extracellular matrix is consisted of of a ground substance and protein fibers. There space several essential cell species and three key fibers: collagen, reticular and elastic. Classification the connective tissue into three broad varieties is based upon the composition of that is cellular and extracellular components and also its function in the body.

Muscle tissue

Muscle tissue is both extensible and elastic. The cells room contractile and also are extremely organized into fiber bundles. Muscle is classified according to the appearance of the contractile cells, into three types: skeletal, cardiac and smooth. The an initial two types have a striated appearance as result of the parallel orientation the the fiber bundles.

Nervous tissue

Cells that the nervous device are highly devoted to transmit electrical impulses roughly the body. There room two main types: neurons and glia. Neurons often tend to have actually a huge cell body and also projections carrying info to (dendrites) and from (axons) the cell human body itself. Groups of neurons are described as ganglia (PNS) and also nuclei (CNS). Glia room the supporting cells of concerned tissue. Lock consist that astrocytes, oligodendrocytes/Schwann cells and microglia.



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

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