CT Flashcards
What makes up connective tissue cells?
Resident cells and wandering cells
What 2 things make up the extracellular matrix?
Fibers and ground substance
What is connective tissue?
Comprises a diverse group of cells within a tissue-specific extracellular matrix (ECM)<br></br><img></img><img></img>
What makes up the resident cells?
Fibroblasts
Macrophages
Adipocytes
Mast cells
Adult stem cells
What makes up wandering cells?
Lymphocytes
Plasma cells
Neutrophils
Eosinophils
Basophils
Monocytes
What makes up fibers in the extracellular matrix?
Collagen fiber system (collagen fibers, reticular fibers)Elastic fiber system
What makes up ground substance?
GAGs
Proteoglycans
Structural glycoproteins (fn, laminin)
Water
Functions of connective tissues
Support: provides support and connections, (e.g. tendons and ligaments)
Defense: the site of inflammatory and immune reactions, physical barrier
Nutrition:
resevoir for water & electrolytes,
stores energy as triglycerides (adipocytes),
supports blood vessels,
passageway for nutrients and gases
Types of connective tissue
Embryonic CT (disappears after birth)
CT proper - divides into loose CT and dense CT (dense CT divides into regular and irregular)
Specialized CT (bone, cartilage, adipose tissue)
Loose/Areolar CT
Loosely arranged cells/ground substance (more)/ fibers
Supports epithelial tissue, surrounds blood vessels, fills spaces between muscles.
Diffusion of oxygen/carbon dioxide and nutrients/wastes, inflammatory and immune reactions, provides structural support
Dense CT
Prominent fibers, little ground substance
Very dense fibers, shows up red (collagen) in H&E
Dense regular CT
Fibers arranged in orderly parallel bundles
Tendons, ligaments, cornea
Transmit force of muscle contraction
Attach muscles to bones
Protection
Dense irregular CT
Collagen is randomly ordered
Seen in the skin, GI tract
Provides tensile strength
Protection
Collagen fiber system includes what?
Collagen fibers
Reticular fibers
Both of these won’t stain will in H&E staining, and will use a special staining
Collagen is the thicker line, elastic fibers are the thinner blue line
Details about collagen fibers
Most abundant type
Flexible yet high tensile strength
Wavy structures
Variable width
Collagen synthesis
Mainly in fibroblast cells
Transcription: The gene for collagen is transcribed in the nucleus, producing mRNA.
Polypeptide Synthesis: mRNA is translated into a collagen polypeptide (procollagen) in the rough ER (RER). It includes repetitive Gly-X-Y sequences, with post-translational modifications like hydroxylation, which requires Vitamin C.
Golgi Apparatus: The procollagen is further modified and assembled into larger structures.
Extracellular Processing: Procollagen is secreted outside the cell and processed into tropocollagen.
Collagen Fiber Formation: Tropocollagen aggregates to form collagen fibers and networks, providing structure to tissues.
Scurvy
Vitamin C (ascorbic acid) is a required cofactor for the addition of hydroxyl groups to proline and lysine residues
A deficiency of water-soluble vitamin C leads to the development of scurvy, characterized principally by bone disease in growing children and by hemorrhages and healing defects in both children and adults
Structure of collagen fibers
Procollagen Subunit: Collagen begins as smaller units called procollagen, which have overlapping and gap regions.
Collagen Fibril: Procollagen subunits come together to form collagen fibrils. These fibrils have a repeating pattern, which is why you see gaps and overlaps.
Collagen Fiber: Several collagen fibrils bundle together to form thicker collagen fibers, which give tissues their strength.
Collagen fibers are thicker than elastic fibers because of the bundling of fibers
Reticular fibers
Very fine type III collagen fibers form a 3D network ratherthan a thick bundle for support.
Support hematopoietic (bone marrow) and lymphoid organs (except thymus). Produced by reticular cells
Stained with silver salts due to the high content of sugar chains
Structurally support backgruond cells
What is type 1 collagen?
Found in dermis, tendon, bone, fibrocartilage
Fibril forming collagen
Resistance to tension
What is type II collagen
found in hyaline cartilage, intervertebral disc
resistance to pressure
fibril forming collagen
type III collagen
<ul><li>Maintenance of expansible organs</li><li>reticular connective tissue</li><li>fibril forming collagen</li></ul>
type IV collagen
<ul><li>Basal lamina</li><li>support delicate structures and filtration</li><li>network forming collagen</li></ul>
Elastic fibers
<ul><li>Responsible for elasticity, resilience, & shape control. Allow tissues to respond to stretch and distension.</li><li>Typically thinner than collagen fibers.</li><li>Synthesized by fibroblasts (in skin and tendons), chondroblasts (inelastic cartilage), and smooth muscle cells (in large blood vessels)</li><li>the branching pattern of these fibers form a 3D network interwoven with collagen fibers</li><li>Aorta: elastic fibers help stretch and recoil</li><li><img></img></li></ul>
Elastic fiber composition
<div><ul><li>Core of the protein elastin.</li><li>Mature elastin has 2 unique AAs, desmosine and isodesmosine, covalently linking elastin monomers together.</li><li>Enable their stretch and recoil like rubber bands.</li></ul></div>
Osteogenesis imperfecta
Caused by defective synthesis of collagen (most frequently type 1)
Results in brittle bones, blue sclera
Ehler-danlos syndrome
<div><ul><li>Defects in collagen synthesis or assembly.</li><li>Fragile, hyperextensible skin vulnerable to trauma, hypermobile joints.</li><li>Poor wound healing</li></ul></div>
Marfan syndrome
<ul><li><div>Caused by a mutation in FBN1 gene for fibrillin, resulting in a lack of resistance in tissues rich in elastic fibers.</div></li><li><div>Tall stature, long fingers, bilateral subluxation of lens, mitral valve prolapse, aorticdissection</div></li></ul>
Ground substance
part of the ECM
Colourless, hydrated (high water content)
Fills the space between cells and fibers)
Functions of ground substance
<div><ol><li>Lubricant bc of viscosity</li><li>Diffusion of water-soluble molecules</li><li>Anchors cells via cell-ECM adhesion</li><li>Path for cell migration</li><li>Binds & retains growth factors</li><li>Transmits info across plasma membrane via cell adhesion molecules</li></ol></div>
Glycosaminoglycans (GAG)
Macromolecule of ground substance
Dermatan sulfate mediate wound repair, fibrosis
Keratan sulfate related to cell motility, axonal guidance & embryo implantation
Hyaluronic acid very important in development bc major component of mucous CT found in umbilical cord. Major component of cartilage (resists compression, promotes flexibility, shock absorber)
Proteoglycans
Macromolecule of ground substance
Aggrecan related to hydration of ECM cytoskeleton
Syndecan facilitated interaction between the proteins of ECM and the actin
Glycoproteins
Macromolecule of ground substance
Integrin binds cells to ECM
Fibronectin binds many ECM components, attach to integrins
Laminin mediates attachment to basement membrane
important molecules of ground substance
Glycosaminoglycans (GAGs) - Unbranched polysaccharide chains
Multiadhesive glycoproteins - stabilize ECM & link to cell surface(s)
Proteoglycans - large macromolecules with protein core
GAGs + core proteins = proteoglycan monomers
hyaluronic acid
Present as a free carbohydrate chain
Effective insulator, preventingdiffusion through the dense network
Found in cartilage and important in immobilizing molecules like growth factors.
Proteoglycans indirectly bind to HA by linker proteins, forming giant aggregates
Not covalently bound to protein
What do glycoproteins do for attachment?
Multi-adhesive glycoproteins facilitate attachment between cell-CT element or attach CT elements
Hyaluronidases
Enzymes that degrade hyaluronic acid
lowers the viscosity of the CT, increasing tissue permeability
Important in:
drug delivery
Bacterial infection
Metastatic potential of tumors
Matrix mettalloproteinases
Tissue remodeling and degradation of ECM
Tumor invasion, metastasis, and tumor angiogenesis require the participation of MMPs
Expression increases in association with tumorigenesis
Fibroblasts
Component of resident cells
Spindle shaped cells with elliptic nucleus, thin cytoplasm
Make precursors of groundsubstance, collagen, and elastic fibers
Most common cell type
Rarely divide, but capable in response to injury and inflammation. (specialized fibroblast: myofibroblast)
Active have large, euchromatic nuclei, while inactive fibroblasts are smaller with more heterochromatic nuclei
Macrophages
Phagocytic: contains lysosomes and residual bodies
Secrete hydrolytic enzymes (eg. collagenase)
Initiate immune responses (release cytokines, present antigens to lymphocytes)
Identification: dyes in staining will be engulfed by macrophages
Lysososmes for break down of phagocytic material
Oval or kidney shaped nucleus (hard to identify in H&E staining)
Numerous phagocytic vesicles for transient storage of ingested material
Mast cells
Arise from multipotent hematopoietic stem cells in the bone marrow
Oval to round cells with microvilli
Central nucleus, surface express IgE receptors
Cytoplasm filled with dense secretory granules containing heparin, histamine, vasoactive mediators & chemotactic factors.
Adipose tissue (specialized connective tissue)
Resident cells in CT - has blood vessels
Depot for triglycerides—main energy stores
Insulates body against the heat loss
Fat stored as triglycerides - high-density energy
Fills space between tissues - Cushions for certain anatomical parts behaving as shock absorbers (e.g. the soles of feet, around kidney, in orbit around eye)
Paracrine and endocrine substances: secretes Leptin, acting on hypothalamus to regulate food intake & energy consumption
Types of adipocytes (resident cells in CT)
Unilocular/white adipocytes (Metabolic energy storage, insulation, cushioning, hormone production)
Multilocular/brown adipocytes (heat production/thermogenesis)
Unilocular (white) adipocytes
Contain one large lipid droplet surrounded by a ring of cytoplasm
The nucleus is flattened and located on the periphery
Secretes reticular fibers that surround the adipocyte
Doesn’t show up very well on H&E staining, filled in on sudan black staining
Multilocular (brown) adipocytes
Fetal life and first decade after birth
Multiple lipid droplets. Eccentric nucleus
Numerous mitochondria
Plasma cells
Lymphocyte-derived, antibody-producing cells.
Oval cell, eccentric nucleus
Clock face” or “wheel” nucleus
RER»_space; Basophilic cytoplasm → Golgi “ghost” (golgi gets washed out)
Has a small amount of cytoplasm, nucleus is usually on one side of the cell
How do leukocytes (WBC) get into connective tissue?
Diapedesis: WBC leave blood by migrating between the epithelial lining of capillaries to enter CT.
This process increases during inflammation.
