Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with

epithelial tissue Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

muscle tissue Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to contract. ...

, and

nervous tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...

. It develops mostly from the

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood, or bone. The interactions between mesenchyme and epithelium help to form nearly ever ...

, derived from the

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical ...

, the middle

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

nic

germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans (animals that are sister taxa to the sponges) produce tw ...

. Connective tissue is found in between other tissues everywhere in the body, including the

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

. The three

meninges In anatomy, the meninges (; meninx ; ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid spac ...

, membranes that envelop the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

and

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

, are composed of connective tissue. Most types of connective tissue consists of three main components:

elastic Elastic is a word often used to describe or identify certain types of elastomer, Elastic (notion), elastic used in garments or stretch fabric, stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rub ...

and

collagen fibers Type I collagen is the most abundant collagen of the human body, consisting of around 90% of the body's total collagen in vertebrates. Due to this, it is also the most abundant protein type found in all vertebrates. Type I forms large, eosinoph ...

ground substance Ground substance is an amorphous gel-like substance in the extracellular space of animals that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. Ground substance is active in the d ...

, and cells.

Blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

and

lymph Lymph () is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to be recirculated. At the ori ...

are classed as specialized fluid connective tissues that do not contain fiber. All are immersed in the

body water In physiology, body water is the water content of an animal body that is contained in the tissues, the blood, the bones and elsewhere. The percentages of body water contained in various fluid compartments add up to total body water (TBW). This ...

. The cells of connective tissue include

fibroblast A fibroblast is a type of cell (biology), biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework (Stroma (tissue), stroma) for animal Tissue (biology), tissues, and ...

adipocyte Adipocytes, also known as lipocytes and fat cells, are the cell (biology), cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through ...

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a p ...

s and

leukocyte White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...

s. The term "connective tissue" (in German, ) was introduced in 1830 by

Johannes Peter Müller Johannes Peter Müller (14 July 1801 – 28 April 1858) was a German physiologist, comparative anatomist, ichthyologist, and herpetologist, known not only for his discoveries but also for his ability to synthesize knowledge. The paramesonephri ...

. The tissue was already recognized as a distinct class in the 18th century.

Types

File:Illu connective tissues 1.jpg File:Illu connective tissues 2.jpg Connective tissue can be broadly classified into connective tissue proper, and special connective tissue. Connective tissue proper includes loose connective tissue, and dense connective tissue. Loose and dense connective tissue are distinguished by the ratio of ground substance to fibrous tissue. Loose connective tissue has much more ground substance and a relative lack of fibrous tissue, while the reverse is true of dense connective tissue.

Loose connective tissue

Loose connective tissue Loose connective tissue, also known as areolar tissue, is a cellular connective tissue with thin and relatively sparse collagen fibers. They have a semi-fluid matrix with lesser proportions of fibers. Its ground substance occupies more vol ...

includes

reticular connective tissue In cellular biology, reticular connective tissue is a type of connective tissue with a network of reticular fibers, made of type III collagen ('' reticulum'' = net or network). Reticular fibers are not unique to reticular connective tissue, but ...

, and

adipose tissue Adipose tissue (also known as body fat or simply fat) is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, Blood vessel, vascular endothel ...

Dense connective tissue

Dense connective tissue Dense connective tissue, also called dense fibrous tissue, is a type of connective tissue with fibers as its main extracellular matrix, matrix element. The fibers are mainly composed of type I collagen. Crowded between the collagen fibers are rows ...

also known as fibrous connective tissue is subdivided into dense regular and

dense irregular connective tissue Dense irregular connective tissue has fibers that are not arranged in parallel bundles as in dense regular connective tissue. Dense irregular connective tissue has less ground substance than loose connective tissue. Fibroblasts are the predomin ...

. Dense regular connective tissue, found in structures such as

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

s and

ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

s, is characterized by

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

fibers arranged in an orderly parallel fashion, giving it tensile strength in one direction. Dense irregular connective tissue provides strength in multiple directions by its dense bundles of fibers arranged in all directions.

Special connective tissue

Special connective tissue consists of

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

and

. Other kinds of connective tissues include fibrous, elastic, and

lymphoid The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphoid organs, lympha ...

connective tissues. Fibroareolar tissue is a mix of fibrous and areolar tissue. Fibromuscular tissue is made up of fibrous tissue and muscular tissue. New vascularised connective tissue that forms in the process of wound healing is termed

granulation tissue Granulation tissue is new connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process. Granulation tissue typically grows from the base of a wound and is able to fill wounds of almost any size ...

. All of the special connective tissue types have been included as a subset of

fascia A fascia (; : fasciae or fascias; adjective fascial; ) is a generic term for macroscopic membranous bodily structures. Fasciae are classified as superficial, visceral or deep, and further designated according to their anatomical location. ...

in the ''fascial system'', with blood and lymph classed as ''liquid fascia''. Bone and cartilage can be further classified as supportive connective tissue. Blood and lymph can also be categorized as fluid connective tissue, and ''liquid fascia''.

Membranes

Membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

s can be either of connective tissue or

. Connective tissue membranes include the

(the three membranes covering the

and

) and

synovial membrane Synovial () may refer to: * Synovial fluid * Synovial joint A synovial joint, also known as diarthrosis, joins bones or cartilage with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer bou ...

s that line joint cavities.

Mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

s and

serous membrane The serous membrane (or serosa) is a smooth epithelial membrane of mesothelium lining the contents and inner walls of body cavity, body cavities, which secrete serous fluid to allow lubricated sliding (motion), sliding movements between opposing ...

s are epithelial with an underlying layer of loose connective tissue.

Fibrous types

Fiber types found in the

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix (ICM), is a network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and bio ...

are

elastic fibers Elastic fibers (or yellow fibers) are an essential component of the extracellular matrix composed of bundles of proteins (elastin) which are produced by a number of different cell types including fibroblasts, endothelial, smooth muscle, and air ...

, and reticular fibers.

Ground substance Ground substance is an amorphous gel-like substance in the extracellular space of animals that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. Ground substance is active in the d ...

is a clear, colorless, and viscous fluid containing glycosaminoglycans and

proteoglycan Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to w ...

s allowing fixation of Collagen fibers in intercellular spaces. Examples of non-fibrous connective tissue include

(fat) and

. Adipose tissue gives "mechanical cushioning" to the body, among other functions. Although there is no dense collagen network in adipose tissue, groups of adipose cells are kept together by collagen fibers and collagen sheets in order to keep fat tissue under compression in place (for example, the sole of the foot). Both the ground substance and proteins (fibers) create the matrix for connective tissue.

Type I collagen Type I collagen is the most abundant collagen of the human body, consisting of around 90% of the body's total collagen in vertebrates. Due to this, it is also the most abundant protein type found in all vertebrates. Type I forms large, eosinop ...

is present in many forms of connective tissue, and makes up about 25% of the total protein content of the mammalian body.

Function

Connective tissue has a wide variety of functions that depend on the types of cells and the different classes of fibers involved.

Loose Loose may refer to: Places * Loose, Germany * Loose, Kent, a parish and village in southeast England People * Loose (surname) Arts, entertainment, and media Music Albums * ''Loose'' (B'z album), a 1995 album by B'z * ''Loose'' (Crazy Horse album ...

and

, formed mainly by

s and

collagen fiber Type I collagen is the most abundant collagen of the human body, consisting of around 90% of the body's total collagen in vertebrates. Due to this, it is also the most abundant protein type found in all vertebrates. Type I forms large, eosinop ...

s, have an important role in providing a medium for oxygen and nutrients to diffuse from

capillaries A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the in ...

to cells, and carbon dioxide and waste substances to diffuse from cells back into circulation. They also allow organs to resist stretching and tearing forces.

Dense regular connective tissue Dense regular connective tissue (DRCT) provides connection between different tissues in the human body. The collagen fibers in dense regular connective tissue are bundled in a parallel fashion. DRCT is divided into white fibrous connective tissue ...

, which forms organized structures, is a major functional component of

s and

aponeuroses An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

, and is also found in highly specialized organs such as the

cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...

Elastic fiber Elastic fibers (or yellow fibers) are an essential component of the extracellular matrix composed of bundles of proteins (elastin) which are produced by a number of different cell types including fibroblasts, endothelial, smooth muscle, and ai ...

s, made from

elastin Elastin is a protein encoded by the ''ELN'' gene in humans and several other animals. Elastin is a key component in the extracellular matrix of gnathostomes (jawed vertebrates). It is highly Elasticity (physics), elastic and present in connective ...

and fibrillin, also provide resistance to stretch forces. They are found in the walls of large blood vessels and in certain ligaments, particularly in the ligamenta flava. In

hematopoietic Haematopoiesis (; ; also hematopoiesis in American English, sometimes h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. In a healthy adult human, roughly ten ...

and

lymphatic Lymph () is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to be recirculated. At the origi ...

tissues, reticular fibers made by reticular cells provide the stroma—or structural support—for the

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

(that is, the bulk of functional substance) of the organ.

Mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood, or bone. The interactions between mesenchyme and epithelium help to form nearly ever ...

is a type of connective tissue found in the developing organs of an

that is capable of differentiation into all types of mature connective tissue. Another type of relatively undifferentiated connective tissue is the mucous connective tissue known as Wharton's jelly, found inside the

umbilical cord In Placentalia, placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord i ...

. This tissue is no longer present after birth, leaving only scattered mesenchymal cells throughout the body. Various types of specialized tissues and cells are classified under the spectrum of connective tissue, and are as diverse as

brown Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing and painting, brown is usually made by combining the colors Orange (colour), orange and black. In the ...

and

white adipose tissue White adipose tissue or white fat is one of the two types of adipose tissue found in mammals. The other kind is brown adipose tissue. White adipose tissue is composed of monolocular Adipocyte, adipocytes. In humans, the healthy body fat percent ...

and

. Cells of the immune system—such as

plasma cell Plasma cells, also called plasma B cells or effector B cells, are white blood cells that originate in the lymphoid organs as B cells and secrete large quantities of proteins called antibodies in response to being presented specific substances ca ...

s, and eosinophils—are found scattered in loose connective tissue, providing the ground for starting inflammatory and immune responses upon the detection of

antigen In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

Clinical significance

There are many types of connective tissue disorders, such as: * Connective tissue neoplasms including

sarcoma A sarcoma is a rare type of cancer that arises from cells of mesenchymal origin. Originating from mesenchymal cells means that sarcomas are cancers of connective tissues such as bone, cartilage, muscle, fat, or vascular tissues. Sarcom ...

s such as hemangiopericytoma and malignant peripheral nerve sheath tumor in nervous tissue. * Congenital diseases include

Marfan syndrome Marfan syndrome (MFS) is a multi-systemic genetic disorder that affects the connective tissue. Those with the condition tend to be tall and thin, with dolichostenomelia, long arms, legs, Arachnodactyly, fingers, and toes. They also typically ha ...

and Ehlers-Danlos Syndrome. * Myxomatous degeneration – a pathological weakening of connective tissue. * Mixed connective tissue disease – a disease of the autoimmune system, also undifferentiated connective tissue disease. *

Systemic lupus erythematosus Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...

(SLE) – a major autoimmune disease of connective tissue *

Scurvy Scurvy is a deficiency disease (state of malnutrition) resulting from a lack of vitamin C (ascorbic acid). Early symptoms of deficiency include weakness, fatigue, and sore arms and legs. Without treatment, anemia, decreased red blood cells, gum d ...

, caused by a deficiency of

vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits, berries and vegetables. It is also a generic prescription medication and in some countries is sold as a non-prescription di ...

which is necessary for the synthesis of collagen. * Fibromuscular dysplasia is a disease of the blood vessels that leads to an abnormal growth in the arterial wall.

Notes and references

External links

Overview, University of Kansas

Heritable disorders of connective tissue
US National Institute of Arthritis and Musculoskeletal and Skin Diseases
Connective tissue photomicrographs
{{DEFAULTSORT:Connective Tissue

Types

Loose connective tissue

Dense connective tissue

Special connective tissue

Membranes

Fibrous types

Function

Clinical significance

See also

Notes and references

External links