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
Describe the structure of mast cells.
Describe the function of mast cells.
Structure
- large, oval with centrally placed spherical nucleus
- basophilic granules in cytoplasm containing GAGs, histamine, and chemotactic mediators
- surface with IgE receptors
Function
- activation of mast cells with first exposure after plasma cells make IgE
- subsequent exposure antigen binds IgE causing cross linking
- cross linking causes degranulation
- histamine release can lead to shock
Describe the classifications of connective tissue based on composition and organization of cellular and extracellular components.
Embryonic connective tissue: present in embryo and umbilical cord
-mesenchyme
-mucous connective tissue (Wharton’s jelly)
Connective tissue proper: further divided based on relative amount of collagen type I
-loose connective tissue
- dense connective tissue (irregular and regular)
Specialized connective tissue: responsible for specific functions
-adipose tissue (white and brown)
Reticular connective tissue: loose connective tissue found in stroma of lymphoid organs, supported by reticular fibers in a network
Blood: liquid consisting of formed elements (RBCs, WBCs, and platelets) and plasma; transports oxygen and carbon dioxide, nutrients, and wastes; buffer; regulates temperature, hormones, pH, and osmotic pressure
Discuss the two types of embryonic connective tissue.
1. Mesenchyme
- found in embryo
- composed of mesenchymal cells forming 3D network
- few collagen/reticular fibers and abundent ground substance
2. Mucous connective tissue (Wharton’s Jelly)
- found in umbilical cord
- large amounts of hyaluronic acid with few collagen/reticular fibers
- gelatinous
Describe the types of connective tissues proper.
1. Loose connective tissue
- highly cellular with thin and sparse collage type I fibers, typically no bundles
- abundant ground substance with gel-like consistency
- most fibroblasts are active
- large number of transient cells
- typically located beneath epithelial and acts as filter
2. Dense connective tissue: large number of collagen type I fibers and bundles with fewer cells, little ground substance
irregular:
- fibers oriented in various directions and interwoven
- main cell present is fibroblast with scarce transient cells
- mostly inactive fibroblasts
- found in dermis and capsules of internal organs
regular:
- densely packed collagen bundles oriented in same direction
- very little space for ground substance and cells
- thin, sheet-like inactive fibroblasts located between collagen bundles with compressed heterochromatic nuclei
- found in tendons, ligaments, and aponeurosis
Describe the general characteristics of adipose tissue. Then compare and contrast the two types.
General adipose tissue
- connective tissue septa separate groups of adipocytes into lobules
- rich blood supply
- innervated by autonomic nervous system
- receptors for several hormones
White adipose tissue
- predominant type
- unilocular adipocytes
- receptors for growth hormone, insulin, and noradrenalin
- thermal insulation
shock absorption and keeps organs in place
Brown adipose tissue
- only in newbrons
- multilocular adipocytes
- large number of mitochondria and oxidize FA fast
- body heat
Describe reticular connective tissue.
Loose connective tissue in stroma of lymphoid organs
supported by network of reticular fibers
Describe blood as a connective tissue.
Describe the structure and function of each element
Consists of
Plasma: solution of nutrients and gases, 90% water and solutes like albumin, globulins, and clotting factors
Formed elements
1. Erythrocytes: a nuclear biconcave disks used for gas exchange, no organelles, just sacks of HGB pack mules for oxygen
2. Leukocytes: use blood to get to target, perform ameboid movement to move through tissue
neutrophils: most common, large with multilobed nuclei (PMNs), contains granules with bactericidal proteins, selective phagocytosis, produce IL1 which induces fever, makes pus
eosinophils: bilobed nucleus with eosinophilic granules containing cytotoxins that destroy protozoan and helminthic parasites, also break down histamine and inhibit mast cell degranulation (parasitic infections and allergic reactions)
basophils: smallest, lobed nucleus, full of basophilic granules containing histamine and heparin, similar to mast cells
Lymphocytes: second most common, large spherical or slightly indented heterochromatic nucleus, no granules
T lymphocytes: bone marrow to thymus to mature then renter blood. T-cell receptor (TCR) binding to antigen-MHC II presented by macrophage activated CD4 T cells which produce cytokines that recruit other immune cells. CD8 T cells recognize defective MHC I complexes and destroys
B lymphocytes: mature in bone marrow, surface immunoglobulin, reside in lymphoid and connective tissues to get viruses bacteria or other invaders, upon reaching target they proliferate into plasma cells which produce antibodies
Natural killer cells: large lymphocytes, kill certain virus infected cells and some tumor cells, also reject transplants
3. Monocytes: adhere to walls of blood vessels, on reaching tissue they become macrophages, large cells with bean nucleus, contains lysosomes and small mitochondria
4. Platelets: anucleate, lifespan of 8-10 days, contain few mitochondria, many granules with adhesion proteins and clotting factors
