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Connective Tissue - Coggle Diagram
Connective Tissue
Types of Connective Tissues
Loose Connective Tissue
Main components include collagen fibers (especially types I and III), elastic fibers, hyaluronic acid, and decorin.
Functions encompass serving as a structural framework for organs (interstitium), attaching epithelia to underlying tissue, allowing independent movement, and providing elasticity and strength in tissues and organs (e.g., skin).
This form of connective tissue is the most abundant and is found in the interstitium.
Dense Connective Tissue
Main components include collagen fibers, especially type I, which provide tensile strength, especially in tissues under mechanical stress.
This collagen type is found in dense regular connective tissues like tendons, ligaments, and aponeurosis, as well as in dense irregular connective tissues such as the dermis (stratum reticulare), fascia, duramater, sclera, cornea, and organ and joint capsules.
Reticular Connective Tissue
Main components include reticular fibers, fibronectin, and fibroblastic reticular cells.
Their function lies in forming a network where stem cells from blood and the immune system mature.
This network is found in bone marrow and secondary lymphoid organs.
Elastic Ligaments
Main components include elastic fibers, which dominate over collagenous fibers.
Their function is to provide ligaments with a high level of elasticity.
These elastic fibers are found in the yellow ligament (ligamentum flavum) and the nuchal ligament.
Mucous Connective Tissue
Main components include fine collagen fibers, hyaluronic acid, and water forming Wharton jelly.
Its function is to protect and insulate umbilical cord vessels.
Wharton jelly is found in the umbilical cord.
Stroma of Ovary
Main components include few reticular fibers and numerous spindle-shaped cells.
Their function is in follicle formation in the ovaries.
Specialized Connective Tissue
Occurs in ligaments, tendons, fascia, cartilage, and bone tissue.
Cartilage
Adaptive connective tissue, essential for mechanical movement, consists of chondrocytes and a specialized extracellular matrix.
Types of Cartilage
Elastic Cartilage
(e.g., in the auricle)
Fibrocartilage
(e.g., in intervertebral
discs)
Hyaline Cartilage
The most
predominant type (e.g., in the nasal
septum).
Avascular tissue receiving nutrients through diffusion, either from a cartilaginous membrane (perichondrium) or joint fluid (synovial fluid).
Cartilage Cells
Chondroblasts
Formed from mesenchymal progenitor cells, chondroblasts, capable of cell division and matrix secretion.
Chondroblasts mature into chondrocytes as they are enclosed in cavities (lacunae) within the extracellular matrix they generate.
Chondrocytes
Derived from chondroblasts, chondrocytes create and preserve the extracellular matrix (ECM).
Housed within lacunae in the ECM, they lose the ability to divide.
Chondrocytes play a crucial role in endochondral ossification, influencing fetal skeletal development, longitudinal bone growth, and bone healing post-fracture.
Hyaline Cartilage
Hyaline cartilage, the most prevalent and fragile type, provides resilience to friction.
Chondrocytes, residing in lacunae, characterize its histology.
Examples include the cartilaginous rings of the trachea, nasal septum, and the cartilaginous precursor of bones.
Fibrocartilage
Fibrocartilage, with thick layers of dense collagen fibers and minimal chondrocytes, is tough and inelastic, providing resilience to tensile forces.
Examples include the menisci, intervertebral discs, and pubic symphysis.
Elastic Cartilage
Elastic cartilage is flexible and resilient, featuring an extracellular matrix with elastic fibers.
Examples include the auricle, external auditory canal, and epiglottis.
Chondrogenesis
Chondrogenesis is the formation and renewal of cartilage, driven by mechanical and chemical factors like load, pressure changes, fibroblast growth factors, thyroid hormones, and cytokines.
Process
Mesenchymal osteoprogenitor cells transform into chondroblasts.
Chondroblasts multiply, producing the cartilage ECM.
Cartilage model forms through chondrocyte proliferation and ECM secretion.
Fibroblasts, from the periphery, create a connective tissue capsule.
Undifferentiated perichondrium cells can become chondroblasts.
Cartilage grows through appositional growth or regeneration of damaged chondrocytes.
Regeneration
Cartilage regeneration occurs from undifferentiated precursor cells of the perichondrium.
Articular and fibrocartilage lack a perichondrium and cannot regenerate.
In late adolescence, chondrocytes lose cell division ability, leading to limited cartilage regeneration in adults.
Muscle
Muscle tissue consists of long fibers with the unique ability to contract, achieved through the coordinated interaction of myofilaments actin and myosin within myocytes.
Classification
Nonstriated
Smooth muscles lacking a specific filament arrangement.
Striated
Skeletal and cardiac muscles with organized sarcomeres.
Muscle contraction involves excitation-contraction coupling and the sliding filament mechanism.
Skeletal muscles are under voluntary control, while smooth muscles respond involuntarily to the autonomic nervous system and external stimuli.
Smooth muscles are highly elastic and are found in hollow organs, vessels, and respiratory and urinary tracts.
Cardiac muscles, forming the myocardium, contract involuntarily under the control of cardiac pacemaker cells.
Fascia
Separates muscles and organs from surrounding structures.
Supports and protects muscles and internal organs.
Minimizes friction, well-innervated for proprioception and nociception.
Types
Deep Fascia
Surrounds muscles, creating compartments.
Visceral Fascia
Supports and encloses organs in their cavities.
Superficial Fascia
Thin layer beneath the skin, composed of loose connective tissue.
Tendons
A dense connective tissue band attaching muscles to bone.
Components include collagen fibril bundles forming fibers, fascicles forming tendon fascicles, and bundles of fascicles forming the tendon.
Endotenon
Thin connective tissue around individual tendon fascicles.
Epitenon
Loose connective tissue around tendon fascicles and endotenon.
Paratenon
Loose connective tissue septae radiating from epitenon, containing nerves and blood vessels between tendon fascicles.
Cells
Tenocytes
Produce extracellular matrix, arranged longitudinally along the tendon.
Tenoblasts
Immature tenocytes involved in tissue repair.
Extracellular Matrix
Collagen types I, III, IV
Noncollagenous components, including elastin and proteoglycans.
Functions
Links bones to skeletal muscles.
Transmits muscle force to bones and joints for movement.
Ligaments
Poorly elastic connective tissue strands from dense collagen fibers, inserting into the joint body or capsule.
Types: Intracapsular (Type 1) and Extra-articular (Type 2) ligaments.
Functions include guiding, limiting, and strengthening joint motion.
Occurs in synovial joints.
Bone Tissue
Mineralized Extracellular
Matrix
Collagen Fibrils
Hydroxyapatite Crystals
Bone Cells
Osteoclasts
Multinucleated phagocytes derived from monocyte and macrophage precursors, possessing calcitonin receptors, involved in bone remodeling and resorption.
Found in Howship lacunae and bone multicellular units.
Osteocytes
Star-shaped osteoblasts involved in bone remodeling, located within lacunae, connected to neighboring osteoblasts and osteocytes through gap junctions in the bone canaliculi.
Osteoblasts
On free bony surfaces of the
periosteum and endosteum.
An osteoblast “walled in” by a new osteoid layer is called an
osteocyte.
Osteoblasts, formed from osteoprogenitor cells, produce osteoid, influenced by TGF-β and bone morphogenic proteins.
They require an alkaline environment, produce bone alkaline phosphatase, and regulate osteoid mineralization, contributing to bone remodeling.
Osteoprogenitor Cells
Osteoprogenitor cells, originating from mesenchyme, can differentiate into osteoblasts and replace them. Under low oxygen pressure, they may also become chondrogenic cells.
They are found in the periosteum and endosteum.
Definition
Ossification begins with mesenchymal or cartilage framework, forming woven bone that is later replaced by lamellar bone.
Distinguishable layers exist in the outer cortex and trabecular center.
Function
Supportive
Protective
Storage (calcium and phosphorus reservoir)
Hematopoiesis
Types of Bone
Long Bones
Metaphysis
Area between the epiphysis and
the diaphysis.
Diaphysis
Central region of a long bone, containing compact bone and a medullary cavity for bone marrow storage.
Epiphysis
Contains compact and trabecular bone with aligned trabeculae along lines of stress.
Linear bone growth occurs at the epiphyseal plate in the epiphysis, housing the articular surface.
Apophysis
Large bony projections where
ligaments and tendons attach.
Short Bones
Include tarsal and carpal bones.
Flat Bones
The axial skeleton, consisting of bones like the scapulae, sternum, ribs, and most skull bones, is characterized by two layers of compact bone surrounding trabecular bone and bone marrow.
Sesamoid Bones
Sesamoid bones, like the patella, develop within tendons to reduce friction and minimize wear on the tendon.
Irregular Bones
The axial skeleton, comprising bones like the sacrum, coccyx, vertebrae, mandible, palatine, hyoid, and temporal bones, functions in muscle attachment and protection (e.g., vertebrae safeguarding the spinal cord).
Bone Composition
Bone Matrix
Composed of organic
and inorganic components.
Bone Membranes
Cover the inner
and outer surface of the bone.
Bone Marrow
Either actively
involved in hematopoiesis (red
bone marrow) or primarily replaced by adipose cells (yellow
bone marrow).
Bone Cells
Build and remodel
bones.
Resident Cells
Fibroblasts
Most common cell type in connective tissue.
Origin: Derived from mesenchymal stem cells.
Function: Synthesis and organization of the
ECM.
Histological features
Spindle-shaped cells arranged in a
branching pattern.
Euchromatin-rich
Abundant in rough ER
Prominent Golgi apparatus
Fibrocytes
Fibroblast with low metabolic activity
Fibrocytes and fibroblasts describe the same type of cell in two different states
(dormant and active).
Myofibroblasts
Contractile hybrid cells with features of both
fibroblasts and smooth muscle cells
Function: Synthesize ECM components and are involved in the proliferative phase of wound
healing.
Histological features: Indistinguishable from fibroblasts under the light microscope without immunohistochemical staining e.g., actin or desmin.
Chondroblasts and chondrocytes
Function: Produce and maintain the
ECM in cartilage.
Definition
Connective tissue is the most abundant type in the body, providing support and connection for various tissues.
It is comprised of cells, mainly fibroblasts, and an extracellular matrix (ECM)
The specific composition of the ECM determines the biochemical properties of the connective tissue, and there are various types, with loose and dense connective tissue being the most common.
Extracellular Matrix (ECM)
Definition
Composed of various macromolecules.
Arranged in a three-dimensional structure.
Specific composition determines the biochemical properties of the connective tissue.
Components
ECM fibers
Collagen Fibers
Fibroblasts synthesize collagen, the most abundant protein, organizing and providing strength and elasticity to the extracellular matrix.
Collagen types include fibril-forming (e.g., type I, II, III, V, XI) and non-fibril-forming (e.g., type IV, VIII, X).
Degradation is carried out by specific collagenases.
Distribution
Type I
Constitutes 90% of body collagen, found in bone, skin, tendons, ligaments, and various tissues.
Type II
Present in cartilage, the vitreous humor of the eye, and intervertebral discs.
Type III
Forms reticular fibers in skin, blood vessels, granulation tissue, and uterus.
Type IV
Component of basement membranes and the lens.
Type V
Found in bone, skin, fetal tissue, and placenta.
Reticular Fibers
Composed of type III collagen.
Secreted by reticular cells.
Reticular fibers crosslink to form a fine
meshwork (reticulin).
This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic
system.
Elastic Fibers
Major component of elastic fibers.
Rich in the nonhydroxylated amino
acids glycine, proline, and lysine.
Provides tissue with elasticity.
Spontaneous, disorganized spatial
structure (relaxed conformation) that
temporarily adopts an orderly arrangement only when stretched.
Synthesis
Crosslinks form extracellularly with transglutaminase and lysyl oxidase.
Elastin synthesis involves crosslinking molecules into bundles with fibrillin, aided by desmosine.
Elastin degradation occurs enzymatically via elastase.
Occurence
Found in tissues requiring high elasticity and the ability to recoil after transient stretch, elastic fibers are present in large arteries (e.g., aorta), lungs, skin, vocal folds, and elastic ligaments like the ligamenta flava, connecting vertebrae.
Glycosaminoglycans (GAGs)
Polysaccharide chains in the extracellular matrix, like hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate, carry negative charges and bind water, acting as a cushion.
Proteoglycans
Proteoglycans, proteins with glycosaminoglycan side chains, serve in shock absorption, support (e.g., resisting compression in articular cartilage), and forming cell-cell or cell-matrix junctions.
They also have signaling roles by binding molecules.
Examples include Aggrecan for shock absorption in cartilage and Decorin for regulating collagen fibril assembly.
Glycoproteins
Proteins with short carbohydrate side chains contribute to ECM organization by providing specific binding sites for cells and other matrix molecules.
Examples include Fibronectin, involved in cell-matrix interactions and embryogenesis, and Laminin, a major component of the basal lamina that binds collagens, integrins, and proteoglycans.
Transient Immune Cells
Number of immune cells found in
connective tissue varies depending on local and pathophysiological conditions.
Lymphocytes
Plasma cells
Macrophages
Mast cells