Connective Tissue Flashcards
Connective Tissue
- Provides structural and metabolic support
- Carries blood vessels; tissue repair
- Mediates exchange of nutrients/ metabolites/ waste products between tissue & circulation
where is primitive connective tissue-derived?
derived from mesodermal mesenchyme—contains stellate to spindle-shaped cells, jelly-like extracellular matrix, & occasional fibers
Mature connective tissue contains?
contains cells& extracellular material secreted by cells
Fibroblasts structure and function
- Structure: pointed, elongate, spindle-shaped cells
- Function: Synthesize & maintain proteinaceous ground substance & connective tissue fibers (collagen, elastin, & reticular fibers)
myofibroblasts
Fibroblasts with contractile ability
Reticular cells structure, synthesized, and function?
Structure: of lymph nodes & bone marrow; a type of fibroblast
Synthesized: reticular fibers (made of reticulin); by regular fibroblasts in some tissues
Function: may have a phagocytic function;
what are reticular cells morphologically similar to?
primitive mesenchymal cells; look like branched fibroblasts
Adipocytes structure and function
- Structure: Generally large, balloon-shaped, clear spaces filled with “lipid”
- Function: responsible for storage & metabolism of lipids
Extracellular organic matrix is also known as what?
ground substance
Extracellular material
- Various fibers embedded within matrix (e.g., collagen, reticulin, & elastin)
- Each type of fiber has different chemical make-up and characteristics
Collagen
- a glycoprotein; precursor proteins produced by fibroblasts
- at least 28 different types identified, based on AA sequence
- Principle fiber in extracellular matrix—provides tensile strength
Type I Collagen
- 90% of collagen in body
- Loose & dense connective tissue of skin, tendons, ligaments, bone & fibrocartilage
Type II collagen examples
hyaline and elastic cartilages
Type III collagen (made of reticulin fibers)
Reticulin fibers; thin, branching, net-like fibers
•For structural support in organs (e.g., liver, spleen, lymph nodes, bone)
•Produced by reticular cells in lymph nodes & bone marrow & by fibroblasts elsewhere
Argyrophilic
Seen in type III collagen, stains black with silver stain
Type IV collagen
found in basement membrane; doesn’t form fibers
Type V
cornea, placenta, dermo-epidermal junctions
what is the best-known collagenopathy?
Ehlers-Danlos syndrome= Affects Type V collagen; Characterized by hyperextension of joints, skin fragility, & poor wound healing
Collagen synthesis steps:
- synthesized as procollagen form triple helix
- Packed into secretory vesicles & secreted into ECS
- extracellular enzymatic modification to form tropocollagen monomers
- Polymerization of tropocollagen into final formation of collagen microfibrils
- Several microfibrils combine to form larger collagen fiber; several fibers make up collagen bundle
procollagen
composed of three alpha polypeptide chains
Elastin fibers structure and synthesized
Structure: Highly branched; random coiling pattern allows stretching; arranged in fibers & sheets; refractile
Synthesized: by fibroblasts as tropoelastin precursor; polymerizes in ECM to form elastin
what are the 2 components of elastic fibers
elastin and fibrillin
elastin
protein core similar to collagen, surrounded by microfibrils of fibrillin(structural glycoprotein)
Marfan’s syndrome
- Autosomal dominant condition resulting in abnormal elastic fibers
- Characterized by tall stature, long limbs, and long, thin fingers
- Enlarged aorta, with ↑ regurgitation and ↑ risk of developing a dissecting aneurysm
Glycoproteins
Fibrillin& fibronectinare structural glycoproteins—large polypeptides with branched polysaccharide side chains
Fibronectin location and function
Location: basement membrane
Function: aids in adhesion between cell membrane & extracellular matrix, via interaction of adhesion molecules known as integrins
Types of non-filamentous molecules (3)
- laminin
- entactin
- tenascin
laminin
sulfated glycoprotein; major component of basement membrane; produced by most epithelial & endothelial cells
entactin
sulfated glycoprotein; binds with laminin
tenascin
binds cells to extracellular matrix; thought to be important in cell migration in developing nervous system
Ground substance
- Amorphous, transparent material with properties of a semi-fluid gel
- Long, unbranched polysaccharide chains of repeating disaccharide units
One of the two sugars is always an amino sugar… what are they
either n-acetyl glucosamine or galactosamine
mucopolysaccharidoses
Non-functional or insufficient lysosomal enzymes => lysosomal storage diseases,
what is glucosaminoglycan(GAG) equalized to?
= mucopolysaccharide(MPS)
sulfated GAG examples
chondroitin sulfate, heparan sulfate
proteoglycans (= mucoproteins)
mostGAG’s covalently bind to protein molecules to form
5 types of GAG’s
- Hyaluronic acid
- Chondroitin sulfate
- keratan sulfate
- dermatan sulfate
- heparan sulfate
Hyaluronic acid (=hyaluronate)
- found in most connective tissue
- Predominant GAG in loose connective tissue
- Lacks sulfated side groups
- thousand sugars long
- Does not form proteoglycans itself, but can bind with them
- Ground substance is impervious barrier to microorganisms
Chondroitin sulfate
found in cartilage & bone
keratan sulfate
found in cartilage, bone, cornea & intervertebral disk
dermatan sulfate
found in dermis of skin, blood vessels, & heart valves
heparan sulfate
found in basement membrane, lung, liver
why dont GAG’s compact well?
- Negatively charged due to sulfate & carboxyl side groups => hydrophilic => gel formation
- Ground substance mostly GAG’s (1’ hyaluronic acid), proteoglycans, & water–Incompressibility of water provides turgor pressure of connective tissue
- Reinforced with fibrous proteins
what produces hyaluronidase?
pathogenic bacteria to destroy ground substance barrier and facilitate their spread
Forms of connective tissue (2)
- Loose
- Dense
Loose (areolar) connective tissue
- Sparse fibers & abundant ground substance => viscous, gel-like consistency
- Supportive function
- Located beneath epithelia & around Nn & vessels
Dense connective tissue
Provides structural support—abundant fibers, moderate # of cells, lesser ground substance
Types of dense connective tissue
- Regular
2. Irregular
Regular dense connective tissue
- collagen fibers oriented parallel to each other
- Densely packed fibers & cells arranged in fascicles(e.g., ligaments, tendons, & aponeuroses)
Irregular dense connective tissue
- collagen fibers oriented randomly
- Moderate number of fibers & few cells
what does specialized connective tissue include?
- bone, blood, cartilage, adipose tissue, hematopoietic tissue, & lymphatic tissue
- Also mesenchymal & mucus connective tissue (limited to embryo)
Adipose Tissue
- Contains adipocytes—cells derived from lipoblasts—primitive mesenchyme adapted for storing fat (1’ triglycerides)
- Fat energetically very active, has rich blood supply
- Function: energy storage, thermo regulation & shock absorber
White fat (=unilocular)
- distributed in dermis & around intraperitoneal organs
- Up to 20% of body wt in males, 25% in females
Brown fat (=multilocular)
- highly specialized
- present in infants & hibernating animals
- Used in thermoregulation to maintain body temperature
- In humans, located ~adrenals
- Large #’s of mitochondria => heat
