Connective Tissue Flashcards
Describe the common feature of all connective tissues.
What are the 4 main functions of connective tissues?
Common feature: all have relatively few cells with a large amount of extracellular matrix
Functions
- Structural support
- Storage of metabolites
- Defense and protection by mediating immune responses
- Repair other tissues with fibrous scars
What are the two basic substances that make up the extracellular matrix?
fibers and ground substance
What are the 3 types of fibers found in the extracellular matrix of connective tissues?
What fibrillar proteins make up these fibers?
- Collagen fibers - formed by collagen
- Reticular fibers - formed by collagen
- Elastic fibers - formed by elastin and fibrillin
Where is collagen produced?
Describe the structure of collagen.
Collagen is produced in fibroblasts.
Collagen molecules consist of 3 polypeptide chains that form a triple helix
Collagen molecules polymerize laterally and head-to-tail to form collagen fibrils (have distinctive banding when viewed with electron microscope)
Collagen fibrils then assemble into collagen or reticular fibers
Type I collagen can actually assemble collagen fibers into larger collagen bundles, but that is only type I.
Describe Collagen I-IV and where these can be found
Type I Collagen
- found in dermis, tendons, ligaments, fascia, bone, and most connective tissues proper
- fibrils to fibers to bundles
Type II Collagen
- found in cartilage
- fibrils (not visualized in light microscope, but appears glassy)
- no fibers or bundles
Type III Collagen
- found in loose connective tissue, walls of blood vessels, lymphoid tissue, bone marrow, smooth muscle, nerves, lungs, etc.
- fibrils into reticular fibers (mesh work)
Type IV Collagen
- found in basal lamina
- sheet like mesh work of beaded filaments
- no fibrils
What is Ehlers-Danlos syndrome (EDS)?
What molecule mutation causes this?
How does this present?
Congenital disorder, impaired extracellular modification of collagen resulting in defective fibers
Present with: skin hyper elasticity; loose, unstable joints, low muscle tone/weakness, osteopenia, deformities of spine…
Describe the structures of elastic fibers.
Thinner than collagen fibers, arranged in branching patterns.
Made of two fibrillar proteins: elastin and fibrillin
Elastin:
- hydrophobic domain causes coiling in aqueaous environments
- cross linked by covalent bonds
- can form fibers or lamellar layers
- passively return to normal configuration after stretching
Fibrillin:
-glycoprotein that forms thin microfibrils that surroun developing elastic fibers to provide substrate for assembly
What mutation causes Marfan’s syndrome?
Fibrillin mutation, the glycoprotein component of elastic fibers that form the extracellular matrix in connective tissue
Results in CV, skeletal, and ocular defects including mitral valve prolapse, arachnodactyly and rupture of elastic arteries
Where is ground substance found in connective tissue?
What are the 3 main components of ground substance?
Found between fibers of extracellular matrix
1. Glycosaminoglycans (GAGs)
- most abundant component of ground substance
- long-chain, negatively charged (hydrophilic) polysaccharides
- hydrophilicity results in binding of water and formation of a gel-like substance which resists compression and allows quick diffusion of water soluble particles
2. Proteoglycans
- consist of GAGs covalently bound to core proteins like a brush
- attach noncovalently to long chains of hyaluronic acid to form aggregates
- aggregates responsible for gel state of ECM
3. Multi adhesive glycoproteins
- cross link between collagen, ECM, and cells to stabilize ECM
- bind ECM through transmembrane proteins from integrin family (associated with hemidesmosomes and focal adhesions)
What are some common types of GAGs? Do they all form proteoglycans?
Hyaluronic acid
- always present in ECM
- much longer molecule than other GAGs, does not contain sulfate
- does not form proteoglycans
Chondroitin sulfate, dermatan sulfate, keratin sulfate, and heparin sulfate
-attach to proteoglycans
Describe two types of multiadhesive glycoproteins.
1. Fibronectin: most abundant
- dimer that contains binding domains that interact with different ECM molecules like Type 1-III collagen, GAGs, fibrin, integrin, and more
- can assemble into thin fibrils
2. Laminin
- present in basal lamina
- binds collagen type IV, integrin, and others
Connective tissue cells can be divided into 2 categories.
List these categories and give examples.
1. Resident Cells (fixed cells): undergo mitosis within connective tissue and spend most of life in connective tissue
- fibroblasts: produce components of ECM including collagen and elastic fibers, GAGs, proteoglycans, multiadhesive proteins, etc.
- adipocytes: store fat and produce hormones
- macrophages: (derived from monocytes) phagocytosis, antigen presenter cell, produce cytokines,
- mast cells: mediate inflammatory and hypersensitivity reactions
2. Transient Cells: derived from precursors in bone marrow, involved in immune response
- plasma cells: antibody producing cells derived from B-lymphocytes (clock face pattern)
- leukocytes: WBC found in areas of inflammation
Describe the basic function of fibroblasts and give the four types of fibroblasts.
Function: producing components of ECM
Active fibroblasts
- present in actively growing connective tissue or during wound repair, commonly found in loose connective tissue
- abundant cytoplasm with many RER and Golgi
- nucleus is oval-shaped and pale and euchromatic with one or more obvious nucleoli
Inactive fibroblasts (fibrocytes)
- present in dense connective tissues that aren’t growing
- limited cytoplasm with less developed RER and Golgi
- nucleus is more hetochromatic, dark, and elongated
Myofibroblasts: properties of both fibroblasts said and smooth muscle cells
- contains bundles of actin filaments and dense bodies
- can contract, but not a type of smooth muscle
- numerous at wound sites
Mesenchymal cells
- present in embryonic connective tissue
- pale, euchromatic nuclei
- well developed RER and Golgi
- multipotent giving rise to other connective tissue cells including fibroblasts, chondroblasts, osteoblasts, and adipocytes
What are the basic functions of adipocytes?
Where are they derived?
What are the two types?
Function: storing fat and producing hormones
Derived: mesenchymal cells
1. unilocular adipocytes: most common
- found either singularly in loose connective tissue or forming aggregates called white adipose tissue
- large, spherical, with a single large lipid droplet
- cytoplasm and flattened nucleus form a thin rim around the fat droplet
2. multilocular adipocytes: mostly found in newborns
- found within brown adipose tissue typically around root of aorta
- multiple fat droplets with a lot of mitochondria giving brown color
- nucleus is centrally placed, not flattened
- metabolism of this generates heat
What are the functions of macrophages?
Where are macrophages derived from?
Macrophages have different nomenclature based on location. List these plz.
Functions:
1. Phagocytosis of bacteria and old cells and tissue
- Antigen presenting
- Cytokine production
Origin:
Monocytes in bone marrow
Mononuclear phagocytic system
Connective tissue: histiocytes
Lung: alveolar macrophages
Liver: Kupffer cells
Bone: Osteoclasts
Skin: Langerhans cells
Lymphoid organs: Dendritic cells
CNS: Microglial cells
