Lecture 6: Connective Tissue Flashcards
Definition of Tissue?
- Plentiful extracellular matrix surrounding scattered cells
- (Connective Tissue is one of the 4 types of basic tissues [others are epithelium, muscle, and nervous])
4 types of connective tissue?
1) Blood
2) Supportive Connective Tissue (cartilage and bone)
3) Adipose Tissue
4) Connective Tissue Proper
6 Functions of Connective Tissue?
1) Support
2) Packing
3) Diffusion Medium
4) Defense
6) Storage
How does connective tissue function as a Diffusion Medium?
- Nutrients pass from capillaries to tissues via connective tissue (can be a filter)
- Metabolites pass from tissues back to capillaries
How does connective tissue function for defense?
- Bacteriostatic (stops movement of bacteria w/in tissues)
- Inflammatory responses (battleground for body’s defense system)
2 major components of Connective Tissue Proper?
- Expanded Extracellular Matrix (broth and noodles)
- Resident Cells (chicken)
3 major components of the Expanded Extracellular Matrix (ECM)?
- Amorphous Intracellular Ground Substance (broth)
- Adhesive Glycoproteins
- Fibers (noodles)
What is Amorphous Intracellular Ground Substance in general?
- colorless semi-fluid gell
- fills spaces between cells and fibers
- indistinguishable with light microscopy
- Contain proteoglycans and glycoprotens
- capacity to retain a large amount of tissue fluid
What does Amorphous Intracellular Ground Substance contain?
- Proteoglycan monomer
- GAGs
- Cations (Na+, K+, Ca++)
- Hyaluronic acid
What is a proteoglycan momomer in ECM?
single polypeptide with covalently attached GAGs
What are Glycosaminoglycans (GAGs) and what are their functions in ECM?
- chains of repeated disacharides
- one sugar is uronic acid, and other is amino sugar
- many amino sugars sulfated (strong - charge)
- bind cations (Na+, K+, Ca++) and water to make ground substance hydrated and viscous
What is Hyaluronic acid and what is its function in ECM?
- single very long GAG chain
- non-covalently binds proteoglycan monomers to form proteoglycan aggregate
- aggregate occupies large space in ECM, binds collagen fibers to maintain integrity of ECM gel
- Hyaluronidase released by some bacteria, breaks down ECM
What are Adhesive Glycoproteins’ general function in ECM?
- Important in Binding ECM fibers and cells together
- Present in relatively small amounts
- Have wide distribution
What makes up the Adhesive Glycoprotein part of ECM?
- Fibronectin
- Laminin
- Integrins
What is Fibronectin and what is its function in ECM?
- large multifunctional protein
- Domains(distinct polypeptide regions) of fibronectin are recognition sites for cell surface receptors, GAGs, and collagens
What is Laminin and what is its function in ECM?
- adhesive glycoprotein present in basal laminae
- 3 molecules twisted around eachother
- contains sites for binding integrins, proteoglycans, and collagens
- recognition of laminin by cell surface integrins binds cells to basal laminae (crosslinker)
What are integrins and what are their functions in ECM?
- transmembrane proteins, are cell surface receptors for fibronectin and other ECM components
- bind to basal laminae
- their cytoplasmic domain links to the cytoskeleton and several enzymes
- Enzyme locations and activities regulate cellular behaviors
- Metastatic movements of cancer cells depend on these integrins and interactions with adhesive glycoproteins. Cell movements through basal laminae and along ECM fibers
What are Fibers in ECM?
- elongated, formed extracellular protein structures
- 4 types: collagen, reticular fibers, basal lanimae, and elastic fibers
What is collagen and what is its function in ECM generally?
- Long thin protein-containing extracellular fibers stain blue with triple stain, and pink with H&E
- form chief proteins in bone, tendon, and skin
- Collagenase synthesized by many tumor cells and bacteria, inc invasiveness in CT
Most abundant collagens in ECM?
Types I, II, III, and IV
What is type I collagen and where is it found?
- regular or irregularly arranged bundles and layers in dense CT
- have high tensile strength
- do not stretch, tough to break
- synthesized by the fibroblast
- found in dermis, fascia, bone, ligaments and tendons
What does type II collagen form and where?
- Fibrils (not fibers) in hyaline and elastic cartilage
What does Type III collagen form and where?
- form reticular fibers
- found in skin, blood vessels, glands, lymphoid tissues
Where is type IV collagen found?
- basal and exterminal laminae of epithelia, muscle, fat and nerve tissues
What does extracellular processing of collagen include?
- proteolysis of end peptides
- spontaneous assembly of fibrils of tropocollagen
- enzymatic crosslinking of tropocollagen by lysine oxidase
What is the order of parts (smallest to largest) that make up collagen?
- Fibrils: are regular arrays of long tropocollagen molecules. bind with eachother and other ECM proteins to form:
- Collagen Fibers
- Collagen bundles
What are Reticular Fibers made of and where are they found in ECM?
- Contain type III collagen fibrils and glycoproteins
- thin fibers stained by silver stains
- lie beneath basal lamina and surround muscle and other cells
- support and bind cells
What does the Basal Laminae consist of and what is its function?
- contain collagen type IV (doesn’t assemble into fibrils, assemble into an open network that is 2D scaffold for assembly of other proteins into basal laminae)
- support all epithelia and in external laminae surrounding muscle fibers and Schwann cells
- along with the underlying reticular lamina, make up the Basement membrane
What do Elastic Fibers contain and what is their function in ECM?
- highly refractile
- branch and contain protein, elastin (gives them their elasticity
- stain yellow-orange with triple stain
What does Elastin contain and what is its function?
- contain many hydrophobic amino acids
- when stretched, avoid aqueous environment, and fold back when tension is released (elasticity)
What are the 3 resident cells (non-motile) of Connective Tissue Proper?
- Fibroblasts
- Mast cells
- Fat cells (store fat)
What do Fibroblasts do in ECM?
- most common cell
- involved in synthesis of CT fibers and ground substance
- structural function
What do Mast Cells do in ECM?
- secretes pharmacologically potent mediators when stimulated (histamine and heparin)
- important in allergic responses (defense function)
- resemble blood basophil in structure
What are the 4 Immigrant Cells of Connective Tissue Proper?
- Macrophages
- Plasma Cells
- Neutrophils
- Other blood cells (lymphocytes, eosiniphils [stain intense red])
What are Macrophages’ role in ECM?
- arise from blood monocytes
- involved in phagocytosis, play critical role in immunity (defense)
What does phagocytosis involve?
- involves extension of cytoplasmic projections
- surround a target, incorporate it into a vesicle that fuses with granules and lysosomes containing lytic enzymes
What are Plasma Cells’ role in ECM?
- Found in subepithelial connective tissue
- derived from B-lymphocytes
- produce antibodies (immunologic function)
What are Neutrophil’s role in ECM?
- other phagocytic cell of the immune system (defense function)
- most numerous
- most important cellular component of innate immune response
What are the 3 subtypes of Irregularly Arranged Adult Connective Tissue Proper?
- Loose Connective Tissue (ex. areolar)
- Dense Connective Tissue
- Special Connective Tissue
What is the most widely distributed irregularly arranged connective tissue?
Loose Connective Tissue
(more cells, less fibers)
Where is Dense Irregular Connective Tissue found?
- found in organ capsules, dermis of skin, joint capsules, and aponeuroses
- (more fibers[thicker], less cells)
What are the two types of Special Irregular Connective Tissue?
- Adipose (loose CT, fat cells predominate)
- Reticular (reticular fibers abundant)
What is a well organized (fibers arranged in same direction) type of connective tissue where fibers predominate, and where is it found?
- Regularly Arranged Dense Connective Tissue
- found in tendons and ligaments
