Histology - Connective Tissue Flashcards
Mesenchyme
Abundant cells, euchromatic nuclei & with lots of cytoplasmic processes. Abundant ground substance. Few, if any, reticular fibers.
Mucous Connective Tissue
Scattered cells with heterochromatic nuclei. Fair amt ground substance. Clearly visible fibrils and fibers.
Connective Tissues Proper Types
- Loose (areolar) (LCT) 2a. Dense irrecular 2b. Dense regular 3. Reticular tissue
Loose (areolar) connective tissue (LCT)
Primarily beneath epithelium, LOTS of cells, fair amt of ground substance. Loosely arranged ECM, “woven mat”. Site of immune responses.
Dense Irregular Connective Tissue (DiRCT)
Clear spaces, multidirectional. Fewer cells, much less ground tissue. Large bundles of collagen fibers oriented in multiple directions.
Dense Regular Connective Tissue (DRCT)
Fewer cells, box car nuclear arrangement, unidirectional. Little ground substance. Collagen fibers: Large bundles oriented in one direction.
Reticular Tissue Location
Stroma of liver, spleen, bone marrow, lymph nodes, endocrine organs
Reticular Tissue Features
LOTs of cells, Meshwork of delicate specifically stained, black fibers (silver-stained). LOTs of open spaces for lymph, blood, or cells to move through. “Chicken-wire” appearance.
Adipose tissues
Highly cellular, packed, surrounded by delicate ECM of reticular fibers. Not polarized or joined by tight junctions, not contractile, and do not conduct impulses. Mesenchymal origin.
White Adipose Tissue
Throughout body, large round oval cells, appear white. Long term energy homeostasis.
Brown Adipose Tissue
Multilocular adipocytes that are smaller and appear vacuolated. Heat-generation. Found mostly in infants (back, neck, shoulders) and adults around organs.
Conective Tissue Support Functions
structural framework, harnesses muscle contraction into movement, scaffolding of gland and organs, medium for metabolic exchange, protection, fat storage.
Ground substance
Clear, gel-like substance of varying density depending on water content that occupies the space between the cells & fibers. Usually lost with histological processing, so appears empty. Composed of Glycosaminoglycans, Proteoglycans and their aggregates, and multiadhesive glycoproteins.
Glyscosaminoglycans (GAGs)
Repeating, mostly sulfated, disaccharide units.
Proteoglycans (PGs)
Core protein (I) + GAGs (-). Sulfated GAGs give them a high negative charge that attracts Na+ and thus water, forming a hydration shell. Present in ALL CTs, purposeof hydrating ECM.
Proteoglycan Aggregates
A core component of cartiledge ECM. Individual PG’s indirectly bound to hyaluronan (re-enforced by link protein) creating giant macromolecules that attract large volumes of water, giving ECM gel-like “shock- absorbers”.
Primary function of GAGs & PGs in BM
Charge-based filtration barrier
Multiadhesive glycoproteins (MGPs)
Multidomain and multifunctional molecules that stabilize the ECM assembly and link it to the CT.
Multiadhesive glycoprotein examples
Fibronectin, Laminin, Tenascin, Osteopontin, Entactin/Nidogen
ECM Fiber Types
Elastic, Collagen, Reticular
Elastic fibers
Typically thinner than collagen fibers and often arranged in a branching patter. Look like “rubber bands” that have stretched then recoiled. Permit tissues to be stretched and then recoil. Found in skin, large blood vessels, lung walls.
Specific stain for elastic fibers
Orcein (stain elastic fibers brown or black). Broken rubber band appearance. Smaller than collagen fibers.
Fibrillin microfibrils
Surround and permeate elastic fibers, helping to organize their growth.
Collagen
Most abundant structural component (30% of dry weight of the body). Imparts tensile strength to tissues. Flexible but not elastic.
Collagen types
Fibrillar (I, II, III), Sheet-forming (IV), Anchoring (VII).
Fiber bundle assembly
All fibrillar collagens mature to fibril stage, but not all go on to form fibers or fiber bundles. Tropocollagen molecule to fibril to fiber to fiber bundle.
Tropocollagen molecule
mature collagen molecule
Fibril
orderly alignment of tropocollagen molecules
Type I Collagen
90% of collagen, provides tensile strength and is only fibrillar collagen that can form fibrils, fibers & bundles. Widely distibuted (dermis, bone, ligaments, tendons, joint capsules, muscle, nerve, sclera of eye, scar tissue).
Type II Collagen
Less common, found in cartilage and vitreous humor. Provides tensile strength and restrains PG aggregate expansion.
Type II Collagen TEM appearance
slender fibrils, no bundling.
Type III Collagen: Reticular fibers
Heavily glycosylated. Fibrils only. First collagen laid down in embryo and after an injury.
Reticular fiber distribution
Surround: Adipocytes, smooth muscle fibers, prepheral nerve fibers, small blood & lymph vessels (microcirculation). Also a major component of the reticular lamina that underlies the basal lamina.
Reticular fiber function
Forms a delicate latticework (network) providing support for organs that: 1. filter blood or lymph (spleen, lymph nodes) 2. Have rich microvasculature (liver, GI tract, encocrine organs) and 3. Have rapidly changin populations of proliferating cells (bone marrow).
Type IV Collagen (basal lamina)
Monomers form flat sheet-like meshwork. No fibrils (no periodicity). Found in basal lamina (epithelium) and external lamina (muscle & nerve). Provides support (epithelium) and filtration.
Type VII collagen
Anchoring, non-fibrillar. Anchors basal lamina to reticular lamina.
Connective Tissue Embryonic Origins
From mesenchyme, which is sourced from mesoderm and neural crest. Mesenchyme-like cells, retained in adult CTs are source of stem cells.
CT Cell Types
Fribroblast, Chondrocyte, Adipocyte
Adipocyte Tumor (benign and malignant)
Benign: lipoma. Malignant: Liposarcoma
Chondrocyte Tumor (benign and malignant)
Benign: Chondroma. Malignnant: Chondrosarcoma
Fibroblasts
Principal CT cell. Synthesizes & secretes all ECM components.
Fibroblast (activated)
Numerous cells in close proximity, cell structure reflects intense synthetic activity, gwoth or repair within 2 hours after injury. Secrete type III collagen. Later replace type II with type I.
Fibrocyte
Quiescent fibroblast. Fewer cells, more widely dispersed. Reduced activity, ECM maintenance.
Myofibroblasts
Protein-secreting cell containing bundles of actin filaments (contractile). Most active during 1st week (2nd week: undergo apoptosis). Generate & maintain steady contractile force (approximate tissues) Assist with synthesis & secretion initial ECM (quick repair).
Macrophages
Arise from monocytes (white blood cell) after migration from blood into CT, whereafter they are considered resident CT cells.
Macrophage functions
- Host response to injury: Inflammation. 2. Host defense.
Macrophage LM appearance
Large cells, eccentric nuclei, pften appear vacuolated
Macrophage TEM appearance
Features of a phagocytic cell
Foreign Body Giant Cells
When macrophages encounter large foreign bodies, they may fuse to form a very large cell. These very large cells engulf or “wall-off” the foreign body.
Mast cells
Preformed chemical mediators of inflammation. Secrete Cytokines & Leukotrienes. Skin, Respiratory & GI systems.
Heparin
Anticoagulant mast cell. (a GAG).
Histamine
A mast cell that promotes increased vascular permeability, intense smooth muscle contraction, and mucus secretion by nasal & bronchial glands.
Unilocular Adipocytes
Most common type of fat cell. Large, spherical cells with eccentric nucleus and thin rim of cytoplasm that synthesize and store lipids as TAGs for energy and secrete hormones, growth factors, and cytokines.
Multilocular Adipocytes
(brown) fat cells located in brown adipose tissue. Function: Heat generation (thermogenesis)
Transient Cells
- Develop elsewhere (bone marrow) 2. Migrate into CT’s to perform their functions 3. Short-lived: White blood cells and Plasma cells
Plasma cells: LM Appearance
Oval-shaped cell (tear drop), Eccentric nucleus, Prominent nucleolus, Heterochromatin distributed in “Clock-face or Cartwheel” pattern.
Parenchyma
Comprises the functional parts of an organ. Liver = hepatocytes.
Stroma
The connective, supportive framework of a biological cell, tissue, or organ.
Mucosa
Epithelium + Lamina propria
Epithelium
Simple columnar with brush border + goblet cells
what types of connective tissue come from embryonic CT?
Mesenchyme
Mucous
Loose Areolar location?
Lies immediately deep to epithelium surrounds blood vessels
dense Regular collagenous location?
Tendons
Ligaments
Aponeuroses
