Connective Tissue Flashcards
Connective tissue does what?
- Provides a matrix that supports and physically connects other tissues and cells together
- It’s interstitial fluid gives metabolic support to cells (Diffusion of nutrients and wastes products)
What does connective tissue consist of?
- Cells and extra cellular matrix (ECM)
What is ECM? (Extra cellular Matrix)
- Consists of fibers and ground substance
- Derived from embryonic mesenchyme which gives rise to the various connective tissues of the body
What is Mesenchyme?
- A tissue developing from the mesoderm (the middle layer of the embryo)
What are the 4 different types of permanent/resident CT cells?
- Fibroblasts
- adipocytes
- Macrophages
- Mast cells
What are Fibroblasts?
Principal and most prevalent connective tissue cell
What do fibroblasts Produce?
- They produce and maintain the Extra cellular matrix (ECM) - fibers and ground substance
- Synthesize and secret fibers like collagen, elastic, and reticular fibers.
- Also synthesizes the complex carbohydrates of ground substance (GAGS, Proteoglycans, and glycoproteins)
What is the most abundant fibers in the fibroblasts?
- Collagen
Active cells are called?
- Fibroblasts
Inactive cells that are smaller are called?
- Fibrocyte
What are Adipocytes?
- Fat cells, found in the connective tissues of many organs
- They are large cells derived from mesenchyme
- They are specialized for cytoplasmic storage of lipids (energy storage)
What do adipocytes do?
- They do the production of heat
They cushion and protect skin and other organs
What are Macrophages?
- Derived from monocytes (a type of white blood cell), sometimes referred to as tissue histiocytes
- They are capable of surrounding substances and pull them within the cell (Phagocytic cells)
- They remove all kind of debris
- They have golgi complexes
- IMPORTANT TO THE IMMUNE SYSTEM
- ALSO APC Antigen presenting Cell
What are Mast Cells?
- Large, ovoid heavily granulated connective tissue cells that develop in the bone marrow, and then migrate to connective tissue where they mature and differentiate to develop their characteristic granules
Where are Mast Cells found?
- They are numerous in the CT of skin and mucous membranes
- Surface has many Fc receptors for IgE antibodies; binding of IgE triggers mast cell activation and degranulation with release of granule content to the ECM
Mast cells are associated with what?
- allergic reactions known as immediate hypersensitivity reactions
- Some hypersensitivity reactions can be potentially fatal such as anaphylactic shock
What are some important secretory products of mast cell granules?
- Histamine
- Heparin
- Serine Proteases
- Eosinophil and neutrophil chemotactic factors
- Cytokines
What does histamine do?
Increases vascular permeability and smooth muscle contraction
What is Heparin?
- An anticoagulant
Serine Proteases
- Activates chemical mediators of inflammation
Eosinophil and Neutrophil Chemotactic Factors
Attract these leukocytes (WBC’s) to sites of inflammation
Cytokines
- Direct the activities of leukocytes and other cells of the immune system.
What are the 2 types of Wandering/Transient CT cells?
- Plasma Cells
- Other Leukocytes
What are Plasma Cells
- Physiologic function is an antibody producing cell which is derived from B Lymphocytes
- They are large ovoid cells with basophilic cytoplasm, large pale Golgi apparatus
- Nucleus eccentrically placed with compact peripheral regions of heterochromatin alternating with lighter areas of euchromatin giving a “Clock face” appearance
What do Other Leukocytes (WBC’s) do?
- If there is tissue injury and immune responses other leukocytes from the peripheral circulation may migrate between the endothelial cells of blood vessels to enter the connective tissues
Other Types of leukocytes (WBC’s) includes?
- Neutrophils
- Lymphocytes
- Eosinophils
- Basophils
Adult Stem Cells are?
- Tissue stem cells
- Niches of adult stem cells are located in various tissues and organs
- Typically limited to differentiating into lineage specific cells.
What are Myofibroblasts?
- Fibroblasts involved in wound healing
- Have a well developed contractile function; contain a form of actin similar to smooth muscle cells
What does the ECM contain?
- Connective tissue fibers
- Ground Substance
What are the types of connective tissue fibers?
- Collagen (most abundant)
- Reticular
- Elastic
What is Collagen?
- A family of proteins which form various extra cellular fibers, sheets and networks with strong resistance to shearing and tearing forces
- Most abundant protein in the body (30% of it’s dry weight)
- Collagen fibers are bundles of fine, thread like subunits called collagen fibrils
- Collagen synthesis may occur in other cell types but it is the specialty of the fibroblasts
Collagen Synthesis
- Pro-collagen at chains (polypeptides) produced in the RER
- In the ER, 3 a chains are aligned, stabilized by disulfide bonds, and folded as a triple helix
What is the triple helix in the collagen synthesis?
- The triple Helix undergoes exocytosis and cleaved into a procollagen molecule
What is a procollagen molecule in the triple helix?
- The basic subunit from which all fibers or sheets are assembled (AKA Tropocollagen)
- Different combinations of procollagen a chains produce the various types of collagen with different structures and functional properties
What are Reticular Fibers?
- They are the supporting stroma of hemopoeitic (bone marrow) and lymphatic tissue forming an extensive network called a RETICULUM
- In these tissues reticular fibers are produced by reticular cells (fibroblasts) which surrounds the fiber with it;s cytoplasm, thus isolating it from other tissue components
Where are Reticular fibers found?
- They are found in delicate loose connective tissue found at the boundary of CT and epithelium, surrounding adipocytes, small blood vessels, nerves, and muscle cells
- They are abundant in embryonic tissue ‘
Reticular fibers are what type of collagen?
- They are mostly type 3 Collagen
What are elastic fibers produced by?
- They are produced by fibroblasts, composed of fibrilin which forms a network of micro fibrils embedded in a large mass of cross linked elastin.
What do the elastic fibers do?
- allow tissues to respond to stretch and distension
- Thinner than collagen fibers (type 1), interspersed with networks of collagen bundles
- In large blood vessels, elastin also occurs in fenestrated (discontinuous) sheets called elastic lamellae
- They do not stain well with H&E
What is the ground substance?
- The part of the ECM that occupies spaces between the cells and fibers.
- Highly hydrated, transparent complex mixture consisting of 3 MAJOR MACROMOLECULES
- Glycosaminoglycans
- Proteoglycans
- Multiadhesive Glycoproteins
What are Glycosaminoglycans (GAG’s)?
- Major GAG’s (Hyaluronic acid, chondroitin,/dermatan sulfates, keratin sulfates, and heparin sulfate)
- Responsible for the physical properties of ground substance, space filling, cushioning, and lubricant functions. E
Proteoglycans are?
- Composed of GAG’s covalently attached to core proteins; associate with collagen fibers and other ECM components
What are multiadhesive glycoproteins?
- Plays an important role in stabilizing the ECM and linking it to the cell surfaces.
- Uses Fibronectin
what are the 3 types of connective tissue proper?
- Loose Connective Tissue (Areolar Tissue)
- Dense Irregular Connective Tissue
- Dense Regular Connective Tissue
What is Loose connective tissue (Areolar Tissue)?
- Characterized by fewer loosely arranged fibers (mostly type 1 collagen) and abundant cells
- Primarily located beneath the epithelia that cover the body surfaces and line the internal surfaces of the body.
Associated with the epithelium of glands and surrounds small blood vessels - Always irregular (random) in it’s arrangement of fibers
What is Dense Irregular Connective Tissue?>
- Characterized by abundant fibers (mostly type 1 collagen) and few cells (mostly fibroblasts)
- Provides significant strength, allows organs and tissues to withstand stretching and distension forces
- Collagen bundles appear randomly interwoven
Location of Dense Irregular Connective Tissue?
- Dermis of the skin
- submucosa of hollow organs
- Capsules surrounding most organs
What is dense Regular Connective Tissue?
- Characterized by ordered and densely packed arrays of fiber and cells
- Mostly Type 1 Collagen and fibroblasts aligned in parallel rows, offers great resistance to prolonged or repeated stress.
- Contains very little ECM, very few blood vessels
Examples of Dense Regular Connective Tissue?
- Tendons (Connect muscle to bone)
- Ligaments (Connects Bone to Bone)
- Aponeuroses (Sheet Like Tendons)
What are the 3 types of Specialized connective tissue?
- Embryonic connective tissues (2 types: Mesenchyme and Mucoid (mucous CT))
- adipose Tissue (2 types: White and Brown)
- Reticular Tissue
What is the Mesenchyme embryonic CT?
- Primarily found in the embryo
- Contains undifferentiated cells capable of differentiating into all the connective tissues (proper and specialized/supportive: cartilage and bone)
- Also includes stem cells for other tissues (blood and muscle)
What is the Mucoid (Mucous) embryonic CT?
- Present in the umbilical cord
- Wharton’s Jelly: specialized ground substance (jelly like)
- Fewer cells (fibroblasts) than mesenchyme and wispy fibers
- also found in the nucleus pulposus of the intervertebral disc
What is the White Adipose tissue?
- Uniocular: contains single large droplets of triglycerides (lipid) which displaces the nucleus to the periphery
- Appear spherical when isolated, it polyhedral when closely packed (“Chicke Wire”) appearance
- Specialized for long term energy storage
- Lipid removed by solvents used in routine histologic techniques; appear empty with standard light microscopy
What is the Brown Adipose Tissue?
- 2-5% of newborn body weight ; mostly back, neck, and shoulders
- Greatly reduced during childhood and adolescence
- Multiocular: contain multiple lipid droplets, abundant mitochondria, nucleus more centrally located
- Mainly function to produce heat
What is thermogenesis?
- Numbers of brown adipocytes increase during cold adaptation