connective tissue

what is the connective tissue?

the tissue that creates the internal framework of the body, and connects organs with the rest of the body

how is connective tissue formed?

• formed by cells and molecules of extracellular matrix (ECM)

• differs from the epithelium, as it has a small number of cells and a large amount of extracellular matrix

what does the C.T develop from?

• the mesenchyme (multipotential cells of the embryo, which form which bone, cartilage, tendons, ligaments, capsules, blood and hematopoietic cells and lymphoid cells develop

where does mesenchyme mostly develop from?

the mesoderm, which is the middle embryonic germ layer, which almost all connective tissue, regardless of form, arise from.

functions of C.T

• establishing framework of the body

• transporting fluid and dissolved materials

• protecting organs

• supporting, surrounding and connecting other tissues

• storing energy

• defending the body from microorganisms

what are the structural elements of CT?

ECM and cells. tissue = ECM + cells

permanent residents (cells)

• cells that make up resident cell population are relatively stable, which includes:

  • fibroblasts, and myofibroblast, which is closely related

  • pigment cells

  • macrophages

  • adipocytes

  • mast cells

  • mesenchymal cells

transient (wandering) cells:

• consists primarily of cells that have migrated into the tissue from the blood in response to specific stimuli. these include:

  • lymphocytes

  • plasma cells

  • neutrophils

  • eosinophils

  • basophils

  • monocytes

what is the ECM?

• a major component of CT, unlike other tissue types, which mainly consist of cells mainly

how are protein fibers divided?

• collagen

• reticular

• elastic

what is ground substances?

• anionic marcomolecules

• multi adhesive glycoproteins

that stabilizes the ECM by binding to cells and to other ECM components

fibroblasts:

• most common CT cells

• synthesize ECM components:

  • collage

  • elastin

  • reticular fibers

  • glycosaminoglycans

  • proteoglycan

  • multi adhesive glycoproteins

• large active nuclei and eosinophilic cytoplasm

• spindle shaped nucleus

what are inactive fibroblasts called? how are they characterized in comparison to active fibroblasts?

• fibrocytes, which have scanty cytoplasm, organelles are few, and the nucleus may become heterochromatic

• active fibroblasts have abundant cytoplasm

when do fibroblasts become active?

when collagen needs to be laid down, such as in wound repair

what are myofibroblasts?

• modified fibroblasts that demonstrate characteristics similar to both fibroblasts and smooth muscle cells

• they can be contractile. in tissue repair, they help in retraction and shrinkage of scar tissue

pigment cells

• easily distinguished cells as they contain brown pigment (melanin) in their cytoplasm

• most abundant in CT of skin, choroid and iris of the eye, giving them their dark color

• variations in number of pigment cells and the amount of pigment in them accounts for difference in skin colors

• prevent light from reaching other cells, and protect deeper tissues from effects of lights (UV rays)

what are the pigment cells that are able to synthesize melanin?

• melanocytes, which are of neural crest origin. typically star-shaped (stellate) with long branching processes

• remaining cells are those that have engulfed pigment released by other cells, which are chromatophores and melanophores, and are modified fibroblasts

what are macrophages?

• phagocytic cells derived from monocytes and contain an abundant number of lysosomes

what are CT macrophages?

also know as tissue histiocytes, are derived from blood cells called monocytes

what are Macrophage cells of connective tissue are part of a large series of cells present in the body that have similar functions known as?

collectively form the mononuclear phagocyte system

where are macrophages diffusely scattered?

in the Ct, and in liver (Kupffer cells), spleen, lymph nodes (sinus histiocytes), lungs (alveolar macrophages), intraglomerular mesangial cells of kidneys and CNS (microglia)

what is the half-life of blood monocytes vs. tissue macrophages.

• 1 day for blood

• several months or years for tissue

what are mast cells?

• develop in bone marrow and differentiate in CT

• large, oval round CT cells

• cytoplasm is filled with basophilic secretory glands

• basophilic granules that store chemical substances that are known as mediators of inflammation

how are mediators of inflammation known as?

• heparin

  • sulfated glycos aminoglycan that acts locally as an anticoagulant

• histamine

  • promotes increase vascular permeability and smooth muscle contraction

what are pericytes?

• also called adventitial or perivascular cells

• found surrounding endothelial cells and small venules

• pericytes express a cohort of proteins similar to those of stem cells in the bone marrow

• possess characteristics of endothelial cells and smooth muscle cells

• believed to be contractile cells, which assist in the regulation of blood flow through capillaries

adipocytes:

• also called fat cells

• although some fats may be present in cytoplasm, including fibroblasts, some cells store an abundant amount of fat and become distended with it. these are called fat cells, adipocytes and lipocytes

• aggregations of fat cells compose adipose tissue

plasma cells

• major cell type present during inflammation

• derived from lymphocytes (B cells) and are responsible for synthesis and release of humoral antibodies

ECM of CT

composed of fibers, ground substance and extracellular fluid

what are protein fibers?

CT fibers are present in varying amounts, depending on structural needs or functions of CT. each type of fiber is produced by fibroblasts and composed of protein consisting of long peptide chain. the three types are

1. collagen

2. reticular

3. elastic

collagen fibers:

• large family of proteins that form fibers or networks

• most abundant protein in human body, representing 30% of its dry weight

• collagen is produced by fibroblasts

• collagen type i is most abundant and widespread

what are the major collagen types?

• type I — CT, bone

  • bones, tendons, organ capsules, dentin

• type II __ hyaline, elastic cartilage

• type III — reticular fibers

  • often associated with type I

• type IV — placenta and is associated with type I

• type VIII — attaching basal lamina to lamina reticularis

reticular fibers

• now known as to be one of the types of collagen fiber

• consists mainly of collagen type III

• forms networks of very thin fibers in certain organs

embryonic CT

• mesenchymal

• mucous

• limited to embryo

adult CT proper

• loose (areolar)

• reticular

• adipose

• dense irregular

• dense regular

  • collagenous

  • elastic

mesenchymal CT

• only present in early weeks of embryo life

• disappears when its cells undergo differentiation, which all types of CT are derived

• some mesenchymal cells remain mature supporting tissues and act as stem cells

• mesenchymal cells are often used as a source of pluripotential stem cells for tissue repair and transplantation because they can develop into other cell types

mucous CT

• more viscous in consistency

• major component of mucoid tissue is jelly-like ground substance rich in hyaluronic acid

• its ground substance is frequently referred to as wharton’s jelly

• contains collagen bundles and numerous star-shaped fibroblasts

• found deep to the fetal skin and in the umbilical cord

loose (areolar) CT

• fills in the spaces of the body just deep to the skin

• characterized by loosely arranged fibers (collagen, reticular, elastics) and abundant cells of various types

• loose CT of mucous membrane is called lamina propria

dense CT

• less flexible and far more resistant to stress than loose CT

• adapted to offer resistance and protection

types of dense CT

• irregular

  • coarse, almost haphazardly arranged bundles of collagen fibers interlaced with few elastic and reticular fibers

  • chief cellular constituents are fibroblasts, macrophages and occasional mast cells

  • often closely associates with loose CT; found in dermis of skin, sheath of nacres and capsules of internal organs

• regular

  • fibers are arranged in parallel array and are densely packed and composed of either:

    • collagenous fibers: tendons ligaments and aponeuroses

    • elastic fibers: large arteries, suspensory ligament of penis

the cellular components of both regular and irregular elastic CT are almost strictly limited to what?

fibroblasts

reticular CT

• form a network of thin reticular fibers (type III collagen) in loose ground substance

• produced by specialized fibroblasts called reticular cells

• location:

  • liver

  • spleen

  • kidney

  • lymph nodes

  • tonsils

  • appendix

  • bone marrow

adipose tissue

• specialized type of CT in which adipocytes (fat cells) predominate

• represent approx. 20% of body weight of normal, higher when obese

functions of adipose tissue

• largest repository of energy

• adipocytes release hormones and a number of important factors.

• Fills up spaces between other tissues and helps to keep some organs in place, such as the kidneys

what are the two types of adipose tissues

• white (unilocular))

• brown (multilocular)

white (unilocular)

• more common type

• serve as storage tissue for lipid (energy reserve)

• during development, lipid accumulates lipid droplets, which coalesce to form a large central droplet (unilocular)

• cell takes on a signet-ring appearance - cytoplasm (ring), flattened nucleus on periphery

• whitish-yellow fat in cytoplasm, giving it its color

brown (multilocular)

• less common type

• contains multiple lipid droplets (multilocular), central nucleus

• high number of mitochondria

• brown color from high concentration of cytochrome in mitochondria

• functions in thermogenesis

• obesity is excessive formation of adipose tissue