Unit 5

• Connective Tissue


  Tissue which provides general structure, mechanical strength, space filling, physical and metabolic support to more specialised tissues

  
• Connective Tissue


  • Prominent and abundant extracellular matrix (ECM) and only a few cells
  • Extracellular matrix produced and sustained by fibroblasts and myofibroblasts
  • Directly supplied by blood vessels, nerves and lymphatics

  
• Functions of Connective Tissue

  • Establishing a structural framework
  • Transporting fluids and dissolved materials
  • Protecting delicate organs
  • Supporting, surrounding and interconnecting tissues
  • Storing energy reserves
  • Defending the body from microorganisms
• Components of Connective Tissue

  • Cells
  • Extracellular Matrix

  
• Cells of Connective Tissue

  • Fibroblasts
  • Myofibroblsts
  • Adipocytes
  • Immune system Cells

  
• ECM of Connective Tissue


  • Ground Substance
  • Fibres
  • Collagen Fibres
  • Elastin Fibres

  
• Collagen


  • Main fibre in connective tissue and most abundant protein in human body
  • Provides tensile strength to resist pulling, stretching and tearing

  
• Elastin


  Arranged fibres/discontinuous sheets in the ECM that confers properties of stretching and elastic recoil
• Ground Substance


  • An amorphous transparent material with the physical character of semi-solid gel
  • Mixture of glycoproteins and carbohydrates with profound water binding ability
• Classification of Connective Tissues

  • Areolar Tissue
  • Dense Regular Connective Tissue
  • Dense Irregular Connective Tissue
  • Adipose Tissue
  • Reticular Tissue
  • Fluid Connective Tissue

  
• Adipose Tissue


  • Specialised tissue for fat storage
  • Composed of adipocytes
  • Fat in adipocytes are stored as triglycerides

  
• Adipose Tissue


  • Functions: Padding that cushions shocks
  • Provides insulation
  • Stores energy
  • Locations: Subcutaneous, Breasts, Gluteal area, Around the kidneys and eyeballs
• White Adipose Tissue


  Found in adults

  
• Brown Adipose Tissue


  • Found in newborn mammals - temperature regulation
  • Small amounts in adults

  
• Reticular Tissue


  • Consists of thin reticular fibers and reticular cells
  • Present in haemopoietic tissue and the spaces between the cells are filled with blood vessels and developing blood cells

  
• Areolar Tissue


  • Supports epithelia
  • Surrounds blood vessels and nerves
  • Connects various tissues and organs
  • Fibres run in random directions - mostly collagenous, but elastic and reticular fibres are also present

  
• Dense Regular Connective Tissue

  • Rich in modified fibroblasts with flat nuclei
  • Collagen fibers run parallel between them

  
• Dense Irregular Connective Tissue

  • Thick collagen fibers
  • Small amounts of amorphous ground substance and fibroblasts are present

  
• Haematopoiesis


  The production of blood cells and platelets
• Sites of Haematopoiesis


  • Prenatal: Yolk Sac (0-2 months), Spleen and Liver (2-7 months)
  • Childhood: All bone marrow is haemapoietic
  • Adulthood: Haematopoietic bone marrow is confined to the axial skeleton and proximal ends of the femurs and humeri
• Three parts of haemotopoiesis

  • Erythropoiesis: The production of Red Blood Cells
  • Myelopoiesis: The production of White Blood Cells
  • Thrombopoiesis: The production of Platelets
• Haematocrit


  The percentage of blood volume occupied by erythrocytes as they are packed down in a centrifuged blood sample
• Anemia


  Hematocrit is lower than normal caused by few circulating erythrocytes
• Polycythemia


  • Elevated hematocrit caused by excess circulating erythrocytes
  • Elevated hematocrit caused by dehydration of plasma
• Histology


  The study of tissues
• Four Types of Tissue

  • Epithelial Tissue
  • Connective Tissue
  • Muscle Tissue
  • Nervous Tissue
• Epithelium


  The sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands
• Epithelial tissues


  • Derived from all germ layers
  • Ectoderm (epidermis)
  • Endoderm (lining of the gastrointestinal tract)
  • Mesoderm (linings of body cavities)
• General Characteristics of Epithelium

  • Cellularity - Epithelia tissue consists almost entirely of cells with little extra cellular matrix, closely bound cells (cell junctions)
  • Polarity - apical and basal surfaces differ, Many specializations of cell membrane (cell junctions, microvilli, cilia)
  • Attachment - To the basal lamina
  • Avascularity - lack blood vessels
  • Restricted thickness - due to avascularity
  • Regeneration - high rate of cell division, no blood vessels
• Apical cell surface


  Microvilli - Finger-like projections that increase surface area for absorption, Cilia - Tiny hair like structures on the surface of the cell that sweep hair, mucus, trapped dust and bacteria
• Basal lamina/basal membrane


  Felt-like sheet of extracellular material that epithelium attaches to, Lamina lucida (clear layer closer to the epithelium), Lamina densa (granular deeper layer), Germinative cells (stem cells) replace short-lived epithelial cells
• Two groups of epithelia

  • Covering epithelia - Cover the external surfaces (skin, lungs, gut) and line the internal cavities (blood and lymphatic vessels, pleura)
  • Glandular epithelia - A gland is one or more cells that produce and secrete a specific product, The product is always a water-based fluid (aqueous) and usually contains proteins (the product is referred to as a secretion)
• Classification of Covering Epithelium

  • Number of Cell Layers - Simple epithelia (one cell layer thick), Stratified epithelia (two or more cell layers thick), Pseudostratified epithelium (an intermediate type that appears stratified but really is one cell layer thick)
  • The shape of epithelial cells - Squamous Cells (Flat top cells), Cuboidal Cells (Cube like), Columnar Cells (Cylindrical Cells)
• Summary on Different Types of Epithelium

  • Simple - Number of cell layers (1), Cell shape (Squamous, Cuboidal, Columnar)
  • Pseudostratified - Number of cell layers (Varies), Cell shape (Columnar, Ciliated or un-ciliated)
  • Stratified - Number of cell layers (Varies), Cell shape (Squamous, Cuboidal, Columnar, Transitional)
• Diagrammatic representation of a Pseudostratified ciliated columnar epithelia
• Epithelium


  • A: Stratified squamous epithelium of the tongue
  • B: Keratinized stratified squamous epithelium of the skin
  • A: Simple columnar epithelium
  • B: Finger-like projection (villi) of columnar cells with its brush border (cilia or C) at the luminal surface
  • A: Simple cuboidal epithelium of the kidney tubules
  • Stratified columnar epithelium of the male urethra
  • A & B: Transitional epithelium of the urinary bladder
• Cell adhesion


  The process by which cells interact and attach to a surface, substrate or another cell, mediated by interactions between molecules of the cell surface
• Three types of cell junctions

  • Tight junctions
  • Gap junctions
  • Desmosomes
• Desmosomes


  Also called Zonula Adherens, Intercellular junctions that provide strong adhesion between cells, They link intracellularly to the intermediate filament cytoskeleton, They form the adhesive bonds in a network, Gives mechanical strength to tissues, Desmosomes anchor together two adjacent non touching cells, Consists of two components: A pair of dense cytoplasmic thickenings knows as plaques, Strong glyco- protein filament containing cadherins that extend across the space between the two cells and attach to the plaque on both sides
• Tight Junctions


  Also called Zonula Occludens, Binds adjacent cells together that are in direct contact, Form protective and functional barriers, Primarily located in sheets of epithelial tissue as epithelium function as highly selective barriers between two compartments, The major types of proteins in junctions are the claudins and the occludins, Each strand is formed from a row of transmembrane proteins embedded in both plasma membranes, with extracellular domains joining one another directly, Tight junctions are impermeable to molecules or ions, Any material must, therefore, pass through the cell by diffusion/ active transport