Connective Tissue (1).docx

**Connective Tissue** ===================== *Definition* - a diverse group of tissues that share a common origin, the mesenchyme (mesoderm) of the embryo. Connective tissue is composed of (1) **fibers**, (2) **cells**, and (3) **ground substance.** ***1. Connective Tissue Fibers*** ==============...

**Connective Tissue** ===================== *Definition* - a diverse group of tissues that share a common origin, the mesenchyme (mesoderm) of the embryo. Connective tissue is composed of (1) **fibers**, (2) **cells**, and (3) **ground substance.** ***1. Connective Tissue Fibers*** ================================= *A. Collagen* ------------- Characteristics of collagen fibers ================================== - 0.5 --10 μm in diameter ----------------------- - unbranched but flexible ------------------------- - indefinite length & variable width ------------------------------------ - provides tensile strength --------------------------- - acidophilic: stains pink with eosin, blue with Mallory, green with Masson's ----------------------------------------------------------------------------- \- when stained with osmium or a heavy metal (for electron microscopy), collagen exhibits a banding pattern that repeats every 68 nm along its length. This pattern reflects the structure and arrangement of the collagen molecule (tropocollagen) to form a fibril. Examples of some collagen types and their properties (from Table 6.2 of text). *Note: You are responsible for knowing the tissue distribution and properties of collagen types I through IV.* +-----------------+-----------------+-----------------+-----------------+ | | TYPE | Polymerized For | Tissue Distribu | | | ==== | m | tion | | | | =============== | =============== | | | | = | ==== | +-----------------+-----------------+-----------------+-----------------+ | Fibril-forming | ### | fibril | bone, skin, | | -------------- | | ------ | tendon, | | | ### I | | ligaments, | | (fibrillar) | | fibril | cornea, | | | ### II | | internal | | *-typical & | | fibril | organs(accounts | | most common* | ### III | | for 90% of body | | | | *(reticular | collagen) | | *-rope-like | ### | fibers)* | | | structure* | | | cartilage, | | | ### V | fibril (with | intervertebral | | *-clearly | | type I) | disc, | | visible with | ### XI | | notochord, | | em* | | fibril (with | vitreous humor | | | | type II) | of the eye | | *-can also be | | | | | seen with the | | | skin, blood | | light | | | vessels, | | microscope* | | | internal organs | | | | | | | | | | (*stroma of the | | | | | spleen, lymph | | | | | nodes & bone | | | | | marrow)* | | | | | | | | | | as for type I | | | | | | | | | | as for type II | +-----------------+-----------------+-----------------+-----------------+ | Fibril-associat | ### IX | lateral | cartilage | | ed | | association | | | --------------- | ### XII | | tendon, | | -- | | lateral | ligaments, | | | | association | other | +-----------------+-----------------+-----------------+-----------------+ | Network-forming | ### | sheet like | basal laminae | | --------------- | | network | | | | ### IV | | beneath | | | | anchoring | stratified | | | ### VII | fibrils | squamous | | | | | epithelia | +-----------------+-----------------+-----------------+-----------------+ ***B. Reticular Fibers*** ========================= a. Characteristics ------------------ - thin fibers; 0.5 - 2 μm in diameter ------------------------------------- - consists of Type III collagen ------------------------------- - coated with proteoglycans --------------------------- - stains with silver salts or PAS --------------------------------- - synthesized by fibroblasts and reticular cells and also by Schwann cells and smooth muscle cells of blood vessels and alimentary canal ---------------------------------------------------------------------------------------------------------------------------------------- b. Locations and functions ========================== (1) reticular organs - supporting framework for spleen, lymph nodes, and bone marrow; produced by reticular cells in these tissue --------------------------------------------------------------------------------------------------------------------------------- (2) between smooth muscle cells -- produced by smooth muscle cells ------------------------------------------------------------------ (3) surround acini of glands, adipocytes, small blood vessels, muscle & nerve -- produced by fibroblasts -------------------------------------------------------------------------------------------------------- (4) boundary between epithelia and connective tissue -- provide attachment of epithelial cells to underlying connective tissue ------------------------------------------------------------------------------------------------------------------------------ ***C. Elastic Fibers*** ======================= - smaller diameter than collagen -------------------------------- - branch -------- - form a loose 3-D networks, fenestrated sheets or parallel bundles ------------------------------------------------------------------- - staines with orcein or resorcin-fuchsin ----------------------------------------- - composed of two structural components: ---------------------------------------- *1.* *elastin* - main component ------------------------------- - amorphous core when viewed with em ------------------------------------ 2. *microfibrils* -- within and at the periphery of fiber --------------------------------------------------------- - electron dense when viewed with em ------------------------------------ - contains the glycoprotein fibrillin ------------------------------------- - fibrillin microfibrils organize the growing elastic fiber ----------------------------------------------------------- - - \- each elastin molecule can expand and retract - throughout the body but mostly in organs than must stretch and then return to their original shape: ----------------------------------------------------------------------------------------------------- (1) elastic arteries (i.e., aorta) -- forms fenestrated sheets in concentric layers between layers of smooth muscle cells; microfibrils are not found in lamellae; elastic material is produced by smooth muscle cells ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- (2) dermis of skin ------------------ (3) lung -------- ***Clinical Aspect*** - - - - - ***\ *** ***2. Ground Substance*** ========================= - occupies the space between the cells and fibers ----------------------------------------------- - contains proteoglycans and multiadhesive glycoproteins ------------------------------------------------------ *A. Functions* -------------- - #### mechanical support; withstands compressive forces - #### rapid diffusion of water-soluble molecules - #### regulate activities of various growth factors and other secreted proteins by binding to them - #### regulates molecular (and other types of) trafficking in the extracellular matrix *B. Components* --------------- \(1) [Glycosaminoglycans] (GAGs) \- form part of a proteoglycan molecule (core protein covalently bound to GAGs) (see below) - highly negatively charged --------------------------- - GAGs include: --------------- #### Hyaluronic acid\* Heparin sulfate #### Chondroitin sulfate Heparin #### Dermatan sulfate Keratan sulfate #### \*Hyaluronic acid differs from the others in that it is not bound to protein, i.e., does not form a proteoglycan ================================================================================================================  ====================== *(3) [Multiadhesive Glycoproteins ]* ================================================ *Functions:* \- stabilizes the extracellular matrix (ECM) \- links cells to components of the ECM \- regulates cell movement \- stimulates cells proliferation and differentiation *Some examples:* a. Fibronectin -------------- b. Laminin ---------- ***\ *** ***3. Connective Tissue Cells*** ================================ *a. Fibroblasts* ================ - principle connective tissue cells ----------------------------------- - synthesize collagen, elastic and reticular fibers and components of the ground substance ------------------------------------------------------------------------------------------ - contain rER, a prominent Golgi apparatus, nucleolus. When inactive, the cytoplasm is eosinophilic; when active, i.e., wound healing, the cytoplasm is basophilic ------------------------------------------------------------------------------------------------------------------------------------------------------------------ - under appropriate conditions can differentiate into other cell types ---------------------------------------------------------------------- *b. Macrophages* ================ - also known as tissue *histiocytes* ------------------------------------ - have an indented, kidney-shaped nucleus ----------------------------------------- - abundant lysosomes, phagocytic vesicles, rER, Golgi and secretory vesicles ---------------------------------------------------------------------------- \- derived from blood monocytes - functions include phagocytosis, antigen presentation, secretion, tissue remodeling, inflammation and fever, lymphocyte activation, tissue reorganization and damage, microbicidal and tumoricidal activities -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- *\ * *c. Mast Cells* =============== - develop in the bone marrow ---------------------------- - spherical nucleus ------------------- - metachromatic granules containing histamine, SRS-A (slow reacting substance of anaphylaxis), ECF-A (eosinophil chemotactic factor of anaphylaxis), and heparin ---------------------------------------------------------------------------------------------------------------------------------------------------------------- - IgE receptors (receptors that bind to antibody class E) present on plasma membrane ------------------------------------------------------------------------------------ - present in vicinity of small blood vessels; numerous in the connective tissue of skin and mucous membranes; not present in the brain or spinal cord ----------------------------------------------------------------------------------------------------------------------------------------------------- - functions: hypersensitive reactions, anaphylaxis, allergies ------------------------------------------------------------- [Mast cell functions] *d. Plasma Cells* - large ovoid cell (20 μm) -------------------------- - basophilic cytoplasm (ergastoplasm) and eccentrically placed nucleus ---------------------------------------------------------------------- - prominent nucleolus and peripherally placed clumps of heterochromatin ----------------------------------------------------------------------- - derived from B-lymphocytes ---------------------------- - produce antibodies -------------------- - located in GI and respiratory tract as well as salivary glands, lymph nodes and hemopoietic tissue ---------------------------------------------------------------------------------------------------- *e. Reticular Cells* ==================== - stellate cells with pale staining nuclei and prominent nucleolus ------------------------------------------------------------------ - located in lymphatic organs, bone marrow and adipose tissue ------------------------------------------------------------- - produce the reticular fibers in hemopoietic and lymphatic organs (except thymus) ---------------------------------------------------------------------------------- - cytoplasm surrounds fibers thereby maintaining a unique relationship with fibers ---------------------------------------------------------------------------------- - may be phagocytic in some organs ---------------------------------- *f. Adipocytes* =============== - fat-storing cells (specialized for the synthesis & storage of lipid) ---------------------------------------------------------------------- - lipid accumulation results in a 'signet-ring' appearance (flattened nucleus & cytoplasm surrounding large fat droplet) ------------------------------------------------------------------------------------------------------------------------ - tend to concentrate around small blood vessels ------------------------------------------------ - form adipose tissue --------------------- * * === **III. Types of Connective Tissue** **I. Connective Tissue Proper** **II. Connective Tissue with Special Properties** **I. Connective Tissue Proper** ##### ***A. Loose (Areolar) Connective Tissue*** \- site of immune reactions, gas and nutrient exchange \- supports the epithelial parenchyma of major organs \- tissue where blood vessels are distributed \- underlies the mesothelium lining the pleural and peritoneal cavity ***B. Dense Connective Tissue*** ================================ *a. Dense Irregular Connective Tissue* -------------------------------------- - sparse cell population compared to loose CT --------------------------------------------- - little ground substance ------------------------- - consists mostly of fibers (mostly collagen with elastic interspersed) ----------------------------------------------------------------------- - bundles of fibers are oriented in various directions to resist stretching/pulling ----------------------------------------------------------------------------------- *b. Dense Regular Connective Tissue* ------------------------------------ - orderly arrangement of fibers as occurs in tendons, ligaments, aponeurosis, and the cornea -------------------------------------------------------------------------------------------- - fibers are oriented in the direction best suited to resist stress ------------------------------------------------------------------- Example: tendons - - - **II. Connective Tissue with Special Properties** ***A*** ***. Reticular Tissue*** - loose connective tissue where reticular fibers (Type III collagen) predominate -------------------------------------------------------------------------------- - forms the stroma of bone marrow, spleen, and lymph nodes ---------------------------------------------------------- ***B. Elastic Tissue -- Ligaments*** ==================================== - a form of dense connective tissue in that it has a predominance of fibers (mostly elastic), little ground substance and few cells ----------------------------------------------------------------------------------------------------------------------------------- - elastic fibers are interspersed with collagen fibers ------------------------------------------------------ - location: where elastic fibers outnumber collagen fibers; examples: --------------------------------------------------------------------- ligamenta flava of the vertebral column -- gives spinal cord flexibility ------------------------------------------------------------------------ ligamentum nuchae of the neck ----------------------------- elastic ligaments of vocal folds (larynx) ----------------------------------------- elastic arteries (aorta for example) ------------------------------------ ***C. Adipose Tissue*** ======================= - a form of connective tissue specialized for lipid storage; plays a key role in energy homeostasis --------------------------------------------------------------------------------------------------- - some locations: ----------------- hypodermis (paniculis adiposus) ------------------------------- omentum ------- mesentery --------- retroperitoneal space --------------------- breast ------ around kidney and eyeball, palms of hands and soles of feet -- in these areas fat forms a cushion and is maintained during reduced caloric intake - two types of adipose tissue: ============================== *a. White Adipose Tissue* ========================= - closely packed white fat cells containing a single large lipid droplet (unilocular); can be 120 μm in diameter ---------------------------------------------------------------------------------------------------------------- - found in subcutaneous tissue; its distribution is influenced by age and sex: ------------------------------------------------------------------------------ - found in the omentum, mesenteries and retroperitoneal areas in both sexes; amount of lipid decreases with fasting ------------------------------------------------------------------------------------------------------------------- - found in the orbit of the eye, major joints, palms and soles of feet; amount of lipid does not change with fasting because fat serves as a cushion ---------------------------------------------------------------------------------------------------------------------------------------------------- 1. ***Leptin -- inhibits food intake; stimulates metabolic rate*** =============================================================== 2. Angiotensinogen -- causes hypertension in obesity 3. Resistin -- contributes to insulin resistance; increases in obesity 4. Adiponectin -- opposes resistin; anti-inflammatory; decreases in obesity 5. IL-6, TNF-α -- contributes to chronic, low-grade inflammation that underlies heart disease, type 2 diabetes 6. Steroid hormones *\ * *b. Brown Adipose Tissue* ========================= - cells are smaller than that of white adipose tissue; the cytoplasm contains many lipid droplets (multilocular) and the nucleus is spherical and eccentric in position ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- - brown fat has a lobular organization and is highly vascular ------------------------------------------------------------- - specialized for heat production --------------------------------- - found in newborns and species that hibernate. In adult humans, the appearance of multilocular brown fat cells gradually disappears and cells resemble white fat cells. Recent evidence suggests that brown fat persists in adult humans throughout life and may be linked to resistance to obesity. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Thermoregulation in Infants: **Exposure to cold** **Skin sensory receptors** **Impulses to temperature regulating centers in brain** **Sympathetic pathway to brown fat** **To blood vessels to increase blood flow To fat cells** **release of norepinephrine** **breakdown of triglycerides to fatty acids and glycerol** **fatty acid oxidation** **HEAT**