Connective Tissue Flashcards
What are the functions of connective tissue?
- Provide structural support (most important)
- Used for storage of metabolites
- Play important role in defense and protection by mediating immune, inflammatory, and allergic responses
- Used to repair other tissues and organs through fibrosis
Describe the fibrillar components of collagen and how they are organized into fibrils, fibers, and bundles.
- Most abundant protein in human body
- Flexible and have high tensile strength
- Produced principally by fibroblasts
- Structure:
- Fibers composed of fibrils
- Molecule measues ~ 300 nm
- Consists of 3 polypeptide chains that form a triple helix
- Molecules polymerize laterally head → tail to form Collagen Fibrils
- Fibrils CANNOT be visualized in light microscope
- Have distinctive banding in electron microscope
- Due to small gaps b/t collagen moleclues that absorb stain
- Collagen Fibrils assemple into Collagen or Reticular Fibers
- Type I Collagen Fibers can assemble into Collagen Bundles
Describe the major types of collagen and where they are found.
- Over 20 different types
- Four Major Types:
- Type I
- Principal type
- Found in dermis of skin, tendons, ligaments, fascia, bone, and most connective tissues proper (Loose CT, Dense Regular/Irregular CT)
- Fibrils → Fibers that can be assembled → Bundles
- Type II
- Found in cartilage
-
Only forms fibrils
- Gives cartilage “glassy” appearance
- Type III (Reticular Fibers)
- Found in cells of various tissues and organs
- Loose CT
- Walls of blood vessels
- Lymphoid Tissues
- Bone Marrow
- Smooth Muscle
- Nerves
- Lung
- Fibrils → Reticular Fibers
- Form supporting framework for cells
- Found in cells of various tissues and organs
- Type IV
- Does NOT form banded fibrils
- Forms sheet-like meshwork of beaded filaments
- Found in the basal lamina
- Type I
Describe the fibrillar components of elastin and fibrillin and how they are organized into fibrils, fibers, and bundles.
- Elastic Fibers
- Elastin
- Contains hydrophobic domain that causes the molecules to coil in aqeous environments
- Elastin molecules are cross-linked by covalent bonds
- Form either fibers of variable length or form lamellar layers (blood vessels)
- Responsible for elasticity because they passively return to their normal configuration after stretch or deformation
- Fibrillin
- A glycoprotein that forms thin microfibrils
- Surround developing elastic fibers
- Provide substrate for their assembly
- Organize elastin into elastic fibers
- Elastin
List the major components of the ground substance.
- Glycosaminoglycans (GAGs)
- Proteoglycans
- Multiadhesive Glycoproteins
Describe glycosaminoglycans and their role in the extracellular matrix.
- Most abundant component of ground substance
- Long-chain, unbranched, highly neagatively charged polysaccharides
- Makes them hydrophilic
- Can bind water which forms a highly hydrated gel
- Helps resist compression/deformation
- Allows quick diffusion of water-soluble particles
- Several types of GAGs found in CT:
- Hyaluronic Acid (Hyaluronan)
- Always present in ECM
- Different form other GAGs in having a much longer molecule that doesn’t contain sulfer
- Does NOT form proteoglycans
- Chondroitin Sulfate, Dermatan Sulfate, Keratan Sulfate, Heparan Sulfate
- Some of the more common types of GAGs
- Attach to proteins to form proteoglycans
- Hyaluronic Acid (Hyaluronan)
Describe proteoglycans and their role in the extracellular matrix.
- Composed of GAGs covalently attache to a core protein
- GAGs extend perpendicularly from the core protein
- GAGs repel each other form a brush-like structure
- GAGs extend perpendicularly from the core protein
- Form giant aggregates by non-covalently attaching to hyaluronic acid via a link protein
- Aggregates are hydrophilic
- Responsible for gel state of ECM
- Account for ability of CT (esp. cartilage) to resist compression w/o losing flexibility
- Aggregates are hydrophilic
Describe multiadhesive glycoproteins and their role in the extracellular matrix.
- Assemble into thin fibrils
- Serve as cross-links b/t collagen, ECM, and cells
- Play important role in stabilizing the ECM
- Bind ECM to transmembran proteins from integrin family
- Hemidesmosomes
- Focal adhesions
- Bind ECM to transmembran proteins from integrin family
- Two Types:
- Fibronectin
- Most abundant glycoprotein in CT
- Molecule composed of a dimer
- Contains binding domains that interact with diff. ECM molecules
- Type I, II, III Collagen, GAGs, Fibrin, Integrin, and others
- Contains binding domains that interact with diff. ECM molecules
- Laminin
- Present in the basal lamina
- Binding sites for Type IV Collagen, Integrin, and others
- Fibronectin
List the resident cells found in connective tissue.
- Fibroblasts
- Adipocytes
- Macrophages
- Mast Cells
Describe fibroblasts.
- Principal resident cell of CT
- Responsible for producing components of ECM:
- Collagen
- Elastic Fibers
- Elastin
- Fibrillin
- GAGs
- Proteoglycans
- Multiadhesive Glycoproteins
- Have different appearances in different types of CT
- Usually reside in close proximity to collagen fibers
- Four Main Types:
- Active Fibroblasts
- Present in actively growing CT or during wound repair
- Abundant cytoplasm w/ many thin processes
- Contiains abundant RER and Golgi Apparatus
- Oval-shaped Nucleus
- Pale, Euchromatic
- One or more well-expressed nucleoli
- Commonly found in Loose CT
- Inactive Fibroblasts
- Present in Dense CT
- Have more limited cytoplasm
- Contains less develope RER and Golgi
- More elongated nucleus
- Dark, Heterochromatic
- Myofibroblasts
- Display properties of both fibroblasts and smooth muscle
- Contain bundles of actin filaments and dense bodies similar to smooth muscle cells (ability to contract)
- NOT a type of smooth muscle
- Don’t have an external lamina
- Often numerous at wound sites
- Thought to be important for closure of wound
- Display properties of both fibroblasts and smooth muscle
- Mesenchymal Cells
- Present in Embryonic CT
- Superficially resemble Active Fibroblasts
- Pale, Euchromatic Nuclei
- Well develope RER and Golgi
- Pluripotent
- Give rise to fibroblasts, chondroblasts, osteoblasts, and adipocytes
- Active Fibroblasts
Describe adipocytes.
- CT specialized for storing fat and producing a variety of hormones
- Two Types:
- Uniloculuar
- Most common
- Aggregate to form white adipose tissue
- Large spherical cells
- Single large lipid droplet
- Cytoplasm and flattened nucleus form thin rim around lipid droplet
- Multilocular
- Rare in adult humans
- Found within brown adipose tissue of newborns around the root of the aorta and renal arteries
- Help sustain body temp.
- Found within brown adipose tissue of newborns around the root of the aorta and renal arteries
- Characterized by:
- Multiple lipid droplets
- Round nuclei
- Large number of mitochondria (give tissue brown color)
- Metabolize lipid to produce heat
- Rare in adult humans
- Uniloculuar
Describe macrophages.
- Phagocytic cells derived from monocytes
- Originate from precursor in bone marrow → circulate through blood → migrate into connective tissue → become macrophages
- One in CT can undergo mitosis and increase their number
- Ways to identify: (Both features can be difficult to see)
- Presence of ingested material in the cytoplasm
- Kidney-shaped nucleus
- Functions:
- Phagocytosis of bacteria, senescent cells, and tissue clean up
- Have MHC II on cell surface, which allows them to present antigens to other cells of the immune system (including T-cells)
- Produce cytokines that activate cells of the immune system
- Mononuclear Phagocytic System
- Histiocytes (CT)
- Alveolar (Lungs)
- Kupffer (Liver)
- Osteoclasts (Bone)
- Langerhans (Skin)
- Dendritic (Lymphoid- lymph nodes, tonsils, and spleen)
- Microglial (CNS) - Associated w/ Alzheimers)
Describe mast cells.
- Originate in bone marrow → migrate into CT → proliferate and differentiate
- Structure:
- Largest cells in CT (20-30 µm)
- Oval
- Centrally placed spherical nucleus
- Lage number of large basophilic granules
- Contain histamine, heparin sulfate or chondroitin sulfat, and chemotactic mediators
- Surface contains receptors for IgE
- Similar to basophils but differ in nuclear morphology
- Function:
- Activation occurs when first exposure of antigen results in and increase in IgE that binds to the surface of the cell
- Subsequent exposure → antigen binds to surface bound IgE
- Causes cross-linking of IgE → Degranulation
- Degranulation → release of histamine which results in:
- Vasodilation and Increased Vascular Permeability that promotes emigration of WBCs into tissue)
- Bronchochonstriction and Increased Mucus Production (caused by several other agents too)
- Chemotactic Mediators attract WBCs, Eosinophils, and Neutrophils
- These reactions are usually mild and local, but can be serious and life threatening
List the transient cells found in connective tissue.
- Plasma cells
- Leukocytes
Describe plasma cells.
- Anti-body producing cells derived from B-lymphocytes
- Most numerous in areas of inflammations and where foreign particls and microorganisms have entered tissue
- Characteristics
- Prominent RER and Golgi
- Dark Heterochromatin alternates with pale euchromatin
- Creates “clock-face” pattern
Describe leukocytes.
- Otherwise known as white blood cells (WBCs)
- Found in CT, especially in areas of inflammation
List and describe the types of embryonic connective tissue.
- Composed of:
- Mesenchyme
- Mucous connective tissue
- Mesenchyme
- Found in the embryo
- Composed of mesenchymal cells
- Pluripotent
- Form 3-D network
- Very few fibers
- Abundant ground substance
- Mucous connective tissue
- Found only in the umbilical cord
- Contains large amounts of hyaluronic acid
- Very few fibers
- Gelatin-like appearance (Wharton’s Jelly)
List and describe the connective tissues proper.
- Subdivisions:
- Loose (areolar) Connective
- Dense Connective
- Dense Irregular
- Dense Regular
-
Loose (areolar) connective tissue
- Highly cellular w/ thin and relatively sparse Type I Fibers
- Usually don’t contain bundles
- Abundant ground substance
- Most fibroblasts are active
- Contain large number of transient cells (plasma cells and leukocytes)
- Located beneath epithelia that cover internal surfaces of the body (e.g. lamina propria of intestine)
- Acts as filter tissue
- Also surrounds blood and lymphatic vessels and nerves, excretory ducts
- Highly cellular w/ thin and relatively sparse Type I Fibers
-
Dense Connective Tissue
- Contain larger amounts of Collagen Type I fibers and bundles
- Little ground substance and fewer cells than in Loose CT
-
Dense Irregular
- __Fibers oriented in various directions
- Main type of cell is fibroblast
- Most are inactive
- Transient cells (plasma cells and leukocytes) are scarce or absent
- Fine networks of elastice fibers scattered around collagen
- Found:
- Dermis of skin
- Capsule of internal organs
- Spleen
- Testis
-
Dense Regular
- Densely packed collagen bundles
- Oriented in same direction
- Inactive fibroblasts
- Thin, sheet-like
- Located in b/t bundles
- Compressed, heterochromatic nuclei
- Found:
- Tendons
- Ligaments
- Aponeuroses
- Densely packed collagen bundles
List and describe specialized connective tissues.
-
Adipose Tissue
- Largest respository of energy via triglycerides
- Connective tissue septa separate groups of adipocytes into lobules
- Receive rich blood supply
- Innervated by autonomic system
- Contains several receptors for several hormones
-
White adipose tissue
- Composed of unilocular adipocytes
- Accumulates energy
- Contains receptors for GH, Insulin, and noradrenalin
- Poor heat conductor
- Attributes to insulation of body
- Visceral adipose helps to keep organs in place and plays important role in shock-absorption
-
Brown adipose tissue
- Not present in human, but found in newborns
- Composed of multilocular adipocytes
- Contain large amounts of mitochondria
- Oxidize fatty acids up to 20 times the rate of white adipose tissue
- Increasing body heat production threefold
List the main components of blood.
- Plasma
- Formed Elements
- Erythrocytes
- Neutrophils
- Eosinophils
- Basophils
- Lymphocytes
- Monocytes
Describe the structure and function of plasma.
- Structure:
- Solution of nutrients and gases
- More than 90% water
- Various solutes
- Albumin
- Globulins
- Clotting Factors
Describe the abundance, structure, and function of erythrocytes.
- Abundance:
- 600 erythrocytes for every 1 leukocyte
- Structure:
- Anucleated biconcave disks
- 8 x 2.5 µm
- NO organelles
- Sacks of hemoglobin
- Function:
- Carry oxygen
- Biconcave shape allows more surface area for gas exchange
- Deacreases distance oxygen must diffuse through the cell
Describe the abundance, structure, and function of neutrophils.
- Abundance:
- Most common leukocyte (55-70% of leukocytes)
- Structure:
- Fairly large cells (10-12 µm)
- Multilobed nuclei
- Cytoplasm contains granules
- Bactericidal proteins
- Fairly large cells (10-12 µm)
- Function:
- Selectively phagocytize bacteria
- Produce IL-1
- Increases body temperature and causes fever
- Dead neutrophils and cell debris form pus
Describe the abundance, structure, and function of eosinophils.
- Abundance:
- Rare (2-4% of Leukocytes)
- Structure:
- Slightly larger thatn neutrophils (11-14 µm)
- Bilobed nucleus
- Cytoplasm contains eosinophilic granules
- Cytotoxins designed to destroy protozoan and helminthic parasites
- Function:
- Destroy protozoan and helminthic parasites
- Most common in blood during parasitic infections and allergic reactions
- Modulate allergic response
- Break down histamine
- Inhibit mast cell degranulation
- Destroy protozoan and helminthic parasites
Describe the abundance, structure, and function of basophils.
- Abundance:
- Rarest leukocytes (0.5-1.5% of all leukocytes)
- Structure:
- Smallest of granulocytes (8-10 µm)
- Lobed nucleus
- Cytoplasm contains basophilic granules
- Contain histamine and heparin
- Function:
- Produce histamine
- Very similar to mast cells
Describe the abundance, structure, and function of lymphocytes.
- Abundance:
- Second most common (20-30% of all leukocytes)
- Structure:
- Large spherical
- Slightly indented hetorchromatic nucleus
- Tiny rim of cytoplasm
- NO granules
- Function:
- 3 Main Populations
- T-Cells
- Arise from bone marrow and hemopoietic organs → transmit through blood into thymus → mature and multiply → reenter blood stream
- Characterized by T-cell receptor (TCR) on cell surface
- Binds to antigen-MHC-II complexes
- Activates CD4+ T cells
- Produce cytokines
- Activates CD4+ T cells
- Binds to MHC-I complexes
- Activates CD8+ T cells
- Recognize defective MHC-I complexes and destroys cells and destroys them
- Activates CD8+ T cells
- Binds to antigen-MHC-II complexes
- B-lymphocytes
- Arise and mature in the bone marrow
- Characterized by surface immunoglobulins bound to plasma membrane
- Reside in lympoid and connective tissues (spleen and lymph nodes)
- Where they are programmed for viruses, bacteria, or other foreign particles
- When they reach target tissue → proliferate into plasma cells → produce antibodies
- Natural Killer Cells
- Large lyphocytes
- Programmed to kill certain virus infected cells and some types of tumors
- Play important role in transplant rejection
- T-Cells
- 3 Main Populations
Describe the abundance, structure, and function of monocytes.
- Abundance:
- 4-6% of all leukocytes
- Structure:
- Large cells (12-20 µm)
- Bean/Kidney shaped nucleus
- Cytoplasm contains lysosomes and small mitochondria
- Function:
- Circulate through peripheral blood → adhere to walls of blood vessels → use ameboid movement to reach target → become macrophages
Describe the abundance, structure, and function of platelets.
- Abundance:
- 200,000-300,000 per mm3
- Structure:
- Biconvex discoid particles
- Diameter of 2-4 µm
- Contain:
- Few mitochondria
- Many granules
- Adhesion proteins and clotting factors
- Have lifespan of 8-10 days
- Biconvex discoid particles
Describe the composition and function of blood.
- Composed of:
- RBC’s
- WBC’s
- Platelets
- Plasma
- Function:
- Transport System for:
- O2
- CO2
- Nutrients
- Wastes
- Maintains homeostasis by acting as a buffer
- Regulates temp., hormone levels, pH, osmotic pressure
- Clots if exposed to air/collagen
- Transport System for: