Unit 2: Connective Tissue Flashcards
Which tissue is the most diverse, abundant, widely distributed, and structurally varied?
Connective tissue
What is the function of connective tissue?
Provides structural and metabolic support and participates in defense and immune reactions
How do connective tissues vary?
In structure, function, and their content of cells and ECM
What kind of cells make up connective tissue?
“Stromal” cells - resident cells and transient cells
What makes up the ECM of connective tissue?
Protein fibers, ground substance
What kind of protein fibers are found in the ECM of connective tissue?
Collagen fibers
Reticular fibers
Elastic fibers
What is ground substance in the ECM of connective tissue?
Amorphous mixture of proteins and carbohydrates with variable amounts of salts and H2O
What are resident cells? What are the types?
Consistently present and consistent number
• Fibroblast / Fibrocyte
• Adipocyte
• CT specific cells (Chondrocyte, Osteocyte, etc…)
• Macrophage
• Mast cell
What are transient cells? What are the types?
Fluctuation in presence
• Plasma cell
• Lymphocyte
• Basophil
• Eosinophil
• Neutrophil
What connective tissue cells are hematopoietic in origin?
Resident cells: macrophages, mast cells
All transient cells
What is a fibroblast? What organelles does it contain?
Principle cell type of most connective tissue
Rich in rER & Golgi (↑ ECM protein synthesis)
Is a fibroblast active/inactive?
Active
How does a fibroblast stain?
Large, prominent, oval, pale staining nucleus
What is a fibrocyte? What organelles does it contain?
Minimal, acidophilic cytoplasm containing
Minimal rER & Golgi (↓ECM protein synthesis)
May be recruited following injury to regenerate fibroblast population
Is a fibrocyte active/inactive?
Inactive
How does a fibroblast stain?
Smaller darker, elongated nucleus
What kind of adipocytes are there?
White adipose, brown adipose
What does white adipose look like?
Large polyhedral or spherical cells
Contain a single lipid droplet per cell
Flattened, peripheral nucleus
What does white adipose provide?
Energy, insulation, protection, hormone production
What does brown adipose look like?
Smaller polygonal cells
Contain multiple lipid droplets per cell
What does brown adipose provide?
Abundant in newborns, limited distribution in adults
Used to generate heat
What is the origin of immune cells
Multipotent hematopoietic stem cell origin
What is the immune response of macrophages?
phagocytosis of bacteria or debris
What is the immune response of mast cells?
responses to allergens that bind IgE, secrete heparin, histamine, inflammatory mediators
What is the immune response of plasma cells?
Produce antibodies
What is the immune response of lymphocytes?
B and T cells involved in innate & acquired immunity
What is the immune response of basophils?
secrete heparin, histamine, inflammatory mediators
What is the immune response of eosinophils?
Anti-microbial
What is the immune response of neutrophils?
phagocytosis of bacteria or debris
How does the ECM function as an adhesive substrate?
Tracks to direct migratory cells
Concentration gradients for hapotatic migration
How does the ECM provide structure?
Defines tissue boundaries
Provides integrity and elasticity to developing organs
Degraded by invasive cells during development and disease
How does the ECM present growth factors to their receptors?
Controls spatial distribution of ECM-bound surface molecules
Facilitates crosstalk between growth factor receptors and ECM receptors
How does the ECM sequester and store growth factors?
Allows for spatio-temporal regulation of factor release
Organizes morphogen gradients
Mediates release of factors in the presence of appropriate cell-mediated forces of proteolytic degradation
How does the ECM sense and transduce mechanical signals?
Defines mechanical properties permissive/instructive to cell differentiation
Activates intracellular signaling through interaction with cell-surface receptors
Engages cytoskeletal machinery and synergizes with growth factor signaling
How many types of collagen are there and how?
29 different types of collagen via configuration of 42 types of α chains
What do collagen fibers provide?
strong, flexible, and high tensile strength
How much of the body is made of collagen
Make up 25% of all protein in the human body
What are collagen fibers composed of?
subunits called collagen fibrils…
• that are composed of collagen molecules…
• which are composed of polypeptide triple helix α chains
What are the types of collagen organization?
Fibrillar collagen
Sheet collagen
How do fibrillar collagen organize?
Extracellularly, collagen molecules align to form long fibrils
• Monomers associate head to tail in overlapping, staggered rows
How do sheet collagen organize?
Extracellularly, collagen molecules align form a meshwork
• Monomers associate head-to-head & tail to tail Form a meshwork, not a fibril
What is the composition of reticular fibers?
composed of type III collagen fibrils (3 α1 chains)
What are reticular fibers like in comparison to collagen?
are thinner (20nm vs up to 300nm) compared to collagen fibers
How do reticular fibers appear?
branched, forming a meshwork-like configuration, and usually not bundled
How do reticular fibers appear during staining?
Are not visible in H&E preparations, but stain with PAS (associated glycoproteins) and silver salts
Where are reticular fibers found?
organs with abundant spaces:
• Liver, lymph nodes, and spleen
What is the composition of elastic fibers?
composed of a central elastin core
• Elastin protein molecular structure allows for random coiling of the fiber
• Fibrillin glycoprotein acts as a substrate for the assembly of elastin proteins into an elastin core
What are elastic fibers like in comparison to collagen?
thinner and interwoven compared to collagen fibers
What is the purpose of elastic fibers?
branched and stretch and limit tissue tearing
• Allow structures such as blood vessels to stretch and relax
What is ground substance?
viscous substance of high-water content that occupies the space between cells and fibers
What does ground substance contain?
mixture of proteins and carbohydrates with variable amounts of salts
What are the components of ground substance?
Glycosaminoglycans (GAGs)
Proteoglycans (PG)
Multiadhesive glycoproteins (MAPs)
What are Glycosaminoglycans (GAGs)?
most abundant heteropolysaccharide components of ground substance
How are Glycosaminoglycans (GAGs) charged? How does this contribute to staining?
Negatively charged (hydrophilic and stain with basic dyes) due to sugar sulfate and carboxyl groups
How are Glycosaminoglycans (GAGs) bound? What is the exception?
most are post-translationally linked/bound to core proteins forming proteoglycans
Hyaluronan is an exception and presents as an extremely long free carbohydrate chain
attract water forming hydro-gels
What are Proteoglycans (PG)?
GAGs covalently bound to core proteins which facilitate ECM and cell-ECM organization
What are Multiadhesive Glycoproteins (MAPs)?
Small group of proteins facilitate ECM stabilization via binding sites for a variety of ECM proteins.
What are the types of connective tissue proper?
Loose connective tissue (fewer fibers, more ground substance)
Dense connective tissue (more fibers, less ground substance)
What are the types of loose connective tissue?
Areolar
Adipose
Reticular
What are the types of dense connective tissue?
Regular
Irregular
Elastic
