Connective tissue 2 Dr. Maria Zahiri

Formation of Type I collagen  Within the cell  During translation, two types of peptide chains are formed on ribosomes along the RER. (the alpha-1 and alpha-2 chains)  These peptide chains (known as preprocollagen) have registration peptides on each end and a signal peptide.  The preprocollagen is then released into the lumen of the RER. Thereafter the signal peptides are cleaved inside the RER and the peptide chains are now called pro-alpha chains.  Hydroxylation of lysine and proline amino acids occurs inside the lumen. This process is dependent on ascorbic acid (Vitamin C) as a cofactor. Further glycosylation of specific hydroxylysine residues occurs.  Triple helical structure is formed inside the endoplasmic reticulum from each two alpha-1 chains and one alpha-2 chain. This is called procollagen.  Procollagen is transported into the golgi apparatus, where it is packaged and secreted by exocytosis. 2Dr. Maria Zahiri

3

Outside the cell  the registration peptides are cleaved and tropocollagen is formed by procollagen peptidase.  These tropocollagen molecules gather to form collagen fibrils, via covalent cross-linking by lysyl oxidase which links hydroxylysine and lysine residues. Multiple collagen fibrils form into collagen fibers.  Collagen may be attached to cell membranes via several types of protein, including fibronectin and integrin. 4Dr. Maria Zahiri

(a) Connective tissue proper: loose connective tissue, areolar Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some white blood cells. Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in inflammation; holds and conveys tissue fluid. Location: Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; surrounds capillaries. Photomicrograph: Areolar connective tissue, a soft packaging tissue of the body (300x). Epithelium Lamina propria Fibroblast nuclei Elastic fibers Collagen fibers 5

Dr. Maria Zahiri (d) Connective tissue proper: dense connective tissue, dense regular Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast. Function: Attaches muscles to bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction. Location: Tendons, most ligaments, aponeuroses. Photomicrograph: Dense regular connective tissue from a tendon (500x). Shoulder joint Ligament Tendon Collagen fibers Nuclei of fibroblasts 6

Dr. Maria Zahiri (e) Connective tissue proper: dense connective tissue, dense irregular Description: Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast. Function: Able to withstand tension exerted in many directions; provides structural strength. Location: Fibrous capsules of organs and of joints; dermis of the skin; submucosa of digestive tract. Photomicrograph: Dense irregular connective tissue from the dermis of the skin (400x). Collagen fibers Nuclei of fibroblasts Fibrous joint capsule 7

Dr. Maria Zahiri (f) Connective tissue proper: dense connective tissue, elastic Description: Dense regular connective tissue containing a high proportion of elastic fibers. Function: Allows recoil of tissue following stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration. Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes. Elastic fibers Aorta Heart Photomicrograph: Elastic connective tissue in the wall of the aorta (250x). 8

What kind of tissue does this represent? Where in the body can you find this tissue? delicate thin layers between tissues; present in all mucous membranes Loose (areolar) connective tissue Dr. Maria Zahiri9

What kind of tissue does this represent? Where in the body can you find this tissue? Adipose tissue fat Dr. Maria Zahiri10

What kind of tissue does this represent? Where in the body can you find this tissue? Dense connective tissue tendons; ligaments Dr. Maria Zahiri11

Dr. Maria Zahiri12

Classification of connective tissue Dr. Maria Zahiri  Emberyonic (mesenchyme)  Adult ( Loose- Dense)  Dense( Regular- Irregular) 13

Elastic Fibers Dr. Maria Zahiri  Staining (orsein) 1- oxytalan: microfibrils ( GP: fibromodolin, fibrilin) 2- Oxytalan+ elastin= elaunin 3- Elaunin + elastin in core= elastic  aa of elastin: Gly, Pro, Desmosin - isodesmosin  Disorders: marfan syndrom 14

Ground Substance Dr. Maria Zahiri An amorphous gel-like material it is not visible on slides, because it is removed during the preparation process composed of Glycosaminoglycans (GAG), Proteoglycans and multi adhesive Glycoproteins 15

Glycosaminoglycans (GAGs) or mucopolysaccharides Dr. Maria Zahiri  GAGs are negatively charged, long, rod-like chains of repeating disaccharides (hexosamine + uronic acid) that have the capability of binding large quantities of water(hydrophilic)  Hexosamine: Glocose amine or Galactose amine  uronic acid: glocoronic acid or iduronic acid 16

Different Types of GAGs Dr. Maria Zahiri17

Proteoglycan complex Dr. Maria Zahiri  Constitute a family of macromolecules each is composed of a protein core to which GAGs are covalently bonded  (heparin( mast cell), Agrecan(ECM), Syndecans and fibroglycan(cell surface)  They have large volume like a bottle brush  Function: -Cell Binding to ECM. 18

Glycoproteins Dr. Maria Zahiri  They have binding site for several components of extracellular matrix as well as for: integrin molecules of the cell membrane that facilitate the attachment of cells to the extracellular matrix  (Fibronectin, Laminin, Chondronectin, Osteonectin, Entactin, Tenascin) Fibronectin is a v-shaped macromolecule that has binding site for extracellular components integrins of cell membrane, 19

Dr. Maria Zahiri  Laminin is very large has three polypeptide chains, it is located in basal lamina and has binding site for:  heparan sulfate, type IV collagen, entactin and cell membrane 20

Dr. Maria Zahiri  Tenacin composed of 6 chains, it is distributed just in embryonic tissue and marks migratory pathway of some cells  Entactin bind to laminin and type IV collagen  Chondronectin and Osteonectin are similar to fibronectin and have binding sites for collagen type II and type I respectively 21

Integrins (Transmembrane Linkers) Dr. Maria Zahiri  Integrins are transmembrane proteins but unlike other cell surface receptors, they are linked to cytoskeleton and structural member of extracellular matrix such as collagen so they also called Transmembrane Linkers  Integrins are much more numerous than usual receptors  they bind to extracellular component by weak bonds 22

Fluid Dr. Maria Zahiri  Edeme phenomen 23

Specific connective tissue Dr. Maria Zahiri  Adipose tissue  Bone and cartilage  Blood 24

Adipose tissue (Fatty tissue) Dr. Maria Zahiri  A kind of connective tissue with many adipocytes  Forms one of the largest “organs” of body  15-20% of body weight in men  20-25% of body weight in women  Over 2 times as much stored energy as glycogen  Subcutaneous adipose shapes body  Shock absorber in soles of feet and palms  Thermal insulation  Fills space between organs 25

Two Types of Adipose Tissue Dr. Maria Zahiri  Yellow, White or unilocular  cells with one large fat droplet in cytoplasm  Brown or multilocular  cells with numerous smaller lipid droplets in cytoplasm and many mitochondria 26

Unilocular Adipose Tissue Dr. Maria Zahiri  White to dark yellow depending on diet  Most common form in adults  Cells mm diameter  Nuclei eccentric and flattened  Lipid droplet has no membrane  Heavily vascularized  Cell number constant after early postnatal period 27

Dr. Maria Zahiri28

Multilocular Adipose Tissue  multiple droplets  vascularization and many mitochondria,  Central nucleus  Has a lobular organization like glands  Production of body heat by many mitochondria  In human neonate, produces heat Dr. Maria Zahiri29

Dr. Maria Zahiri30

روزگارتان پر برکت 31Dr. Maria Zahiri