histology lab

• Loose connective tissue


  • Sample specimen: Jejunum
  • Magnification: 1000x
  • Structures: Crypts of Lieberkühn, surrounded with loose connective tissue
  • Another example: connective tissue of the mesentery
• Dense irregular connective tissue


  • Sample specimen: Skin (thin section from Axillary area)
  • Magnification: 100x
  • Structures: Layer of keratinized cells above the stratified squamous epithelium (epidermis), below is the dermis with two sublayers - Papillary Layer (loose connective tissue) and Reticular Layer (dense irregular connective tissue)

  
• Dense regular connective tissue


  • Sample specimen: TENDON
  • Magnification: 1000x
  • Structures: Parallel arrangement of collagen fibers, made of Collagen Type I protein

  
• Adipose tissue


  • Sample specimen: Adipose tissue
  • At different magnifications, blood vessels can be appreciated in between areas of adipose tissue
  • The cytoplasm of each white adipose cell is occupied by a single, large, lipid droplet, pushing other organelles to the side, creating a signet ring appearance
  • The darker staining, thick, circular structures are blood vessels
• Mucoid tissue


  • Sample specimen: Umbilical cord
  • Magnification: 40x
  • Structures: 3 blood vessel structures (1 vein, 2 arteries), the surrounding area is occupied by Wharton's Jelly which is mucoid tissue

  
• Hyaline cartilage


  • Sample specimen: TRACHEA
  • Magnification: 40x, 100x, 1000x
  • Structures: Below the epithelial tissue layer is the hyaline cartilage, with territorial matrix, interterritorial matrix, and chondrocytes housed in lacuna (some isolated, some forming isogenous groups)

  
• Elastic cartilage


  • Sample specimen: EPIGLOTTIS
  • Magnective tissue: Elastic cartilage with darker-staining matrix and elastic fibers

  
• Spongy bone (cancellous bone)


  • Sample specimen: SPONGY BONE
  • Magnification: 40x, 100x, 400x, 1000x
  • Structures: Cavities housing bone marrow, lacuna containing osteocytes, canaliculi, trabeculae lined by endosteum
• Compact bone (cancellous bone)


  • Sample specimen: COMPACT BONE
  • Magnification: see labels
  • Structures: Haversian systems creating osteon units with central Haversian canal, surrounded by lamellar rings, also interstitial lamellae and circumferential lamellae

  
• Nervous system


  • Function: transmit nerve impulses
  • Anatomical division: Central nervous system, Peripheral nervous system
  • Functional division: Sensory division, Motor division
• Cerebrum


  Layers of cerebral cortex: Molecular layer, External granular layer, External pyramidal layer, Internal granular layer, Internal pyramidal layer, Multiform layer
• Cerebellum


  Layers of cerebellar gray matter: Molecular layer, Purkinje cells layer, Granular layer

  
• Spinal cord


  White matter (cortex), Gray matter (medulla)
• Connective tissue cells


  • Fixed cells: Mesenchymal cells, Fibroblasts/Fibrocytes, Reticular cells, Adipose cells, Mast cells, Resident macrophages
  • Wandering cells: Plasma cells, Leukocytes (Neutrophils, Eosinophils, Basophils, Monocytes, Lymphocytes), Wandering macrophages
• Mesenchymal cells


  Multipotent cells found in embryo and umbilical cord, rare in adults, stellate cells with long cytoplasmic processes, oval nuclei with distinct nucleolus
• Fibroblasts


  Most abundant cells in connective tissue, fibrocyte (inactive form) and fibroblast (active form), synthesize collagen, reticular, and elastic fibers, glycosaminoglycans, proteoglycans, and adhesive glycoproteins

  
• Reticular cells


  Fibroblasts specialized to synthesize precursor to type III collagen, slightly larger than fibroblasts, large and lightly-staining nucleus, long cytoplasmic processes that embrace reticular fibers, most numerous cell type in reticular tissue

  
• Adipose cells


  White adipose (fat) cells: Store fat as a single large droplet, nuclei pushed to the side ("signet ring")

  Brown adipose cells: Store fat as multiple lipid droplets (multilocular), found in hibernating animals & newborns, generate body heat
• Mast cells


  Function: local inflammatory response, tissue repair, innate immunity, oval to irregular shape, filled with basophilic granules that almost obscure the nucleus, located near small blood vessels and in tissue lining the digestive tract
• Leukocytes (WBCs)


  Neutrophils, Eosinophils, Basophils, Monocytes, Lymphocytes
• Macrophages


  Precursor cell: monocytes

  Resident and wandering macrophages, features: 10-30 μm, eccentrically located kidney or oval-shaped nucleus, function: phagocytic action, immune response, turnover of protein fibers
• Connective tissue fibers

  • Collagen fibers, Reticular fibers, Elastic fibers
• Ground substance


  Transparent, amorphous, homogenous, gel-like material, components: water, glycosaminoglycans, proteoglycans, multiadhesive glycoproteins, function: medium for exchange of nutrients, oxygen, and waste
• Loose collagenous (areolar) connective tissue


  High vascularity, loose, irregular arrangement of sparse CT fibers, abundant ground substance, forms a layer beneath epithelial lining, fills spaces between muscle and nerve

  
• Dense collagenous connective tissue


  Few blood vessels, densely packed collagen fibers, less ground substance, provides strength and support
• Ordinary Connective Tissue


  • Loose Collagenous (Loose Connective Tissue; aka Areolar Connective Tissue)
  • Dense Collagenous (Dense Connective Tissue)
  • Mucoid Connective Tissue
  • Reticular Connective Tissue
  • Adipose Tissue

  
• Loose Collagenous (Loose Connective Tissue; aka Areolar Connective Tissue)


  • More prevalent in the body than the dense CT
  • High vascularity vs Dense CT
  • Loose, irregular arrangement (haphazardly) of sparse CT fibers
  • Abundant ground substance that surrounds cells and fibers (relatively same amount of these 3 components)
  • Forms a layer beneath epithelial lining of many organ; filling the spaces between muscle and nerve
  • Location: papillary layer of dermis, submucosa of the bowel (lamina propria), muscle fascia, mesentery

  
• Dense Collagenous (Dense Connective Tissue)


  • Few blood vessels
  • Scanty ground substance
  • Abundant CT fibers
  • Fewer cells vs loose CT
  • Classification based on arrangement of fibers: Dense Irregular CT (fibers run in various directions or randomly interwoven) and Dense Regular CT (fibers run parallel to each other or in a definite pattern)

  
• Mucoid Connective Tissue


  • Abundant amorphous jelly-like ground substance with few collagen, elastic or reticular fibers
  • The GS is mainly hyaluronic acid
  • Cellular elements are also few, mainly mesenchymal cells and fibroblasts
  • Locations: Umbilical cord (Wharton's Jelly); dental pulp of young teeth

  
• Reticular Connective Tissue


  • Predominant cell: reticular cells
  • Most abundant fiber: reticular fibers (Collagen Type III)
  • The reticular cells are usually seen attached to the fibers
  • Function: supporting framework of organs; meshwork for passage of leukocytes in lymphoid tissues
  • Location: stroma of liver, myeloid tissue, pancreas, lymph nodes, spleen

  
• Types of Cartilage


  • Hyaline Cartilage
  • Elastic Cartilage
  • Fibrocartilage

  
• Hyaline Cartilage


  • Most abundant type of cartilage in the body
  • Appear glistening, white, smooth in fresh tissue
  • Consists of cells (chondrocytes) inside cavities (lacunae) that are dispersed in intercellular substance (cartilage matrix)
  • Cells are isolated or form isogenous groups
  • Intervening matrix interterritorial matrix
  • Matrix immediately surrounding the cells territorial matrix
  • Location: skeleton of the fetus in-utero, articular surface of movable joints, sternal end of ribs, epiphyseal plate of long bones, large respiratory passages (trachea, external nose, larynx, bronchi)

  
• Elastic Cartilage


  • More flexible than hyaline cartilage
  • Appear yellowish in fresh tissue
  • Contains elastic fibers aside from Collagen type II fibrils
  • Function: maintains shape while allowing flexibility
  • Location: auricle, external acoustic meatus, auditory tube, epiglottis, some parts of the larynx

  
• Fibrocartilage


  • Can withstand greater stress than hyaline and elastic cartilage
  • Appear white in fresh tissue
  • Transitional stage between hyaline cartilage and dense CT; Collagen type I
  • Cells occur isolated or in aligned isogenous aggregates
  • Location: intervertebral discs, pubic symphysis, surface layers of tendons and ligaments that press on bone (knee, jaw)

  
• Cells of Bone Tissue

  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteoprogenitor cells


  • Fusiform cells; line periosteum and endosteum
• Osteoblasts


  • Synthesizes organic constituents of bone GS, and precursors of collagen fibers in the bone tissue; growth factors; cytokines that direct osteoclast activity
  • Have receptors for parathyroid hormone
  • Form: large, round and polygonal or cuboidal in shape with numerous cytoplasmic processes
• Osteocytes


  • Osteoblasts that get trapped in the developing matrix
  • Little secretory capability, enough to maintain the bone matrix that surrounds them
• Osteoclasts


  • Multinucleated cells; ruffled border where bone resorption happens
  • Function: Bone resorption
  • Housed in HOWSHIP's lacunae areas of resorbed bone
• Periosteum


  • Covers external surface of bone
  • Layers: Outer - fibrous; dense irregular CT, Inner - cellular; osteoprogenitor cells and/or osteoblasts