Principles: Histology

Principles: Histology

1. Anatomy Of The Cell

   • Eukaryotic cells
     • Outer membrane
     • Inner Cytosol - solution of proteins, electrolytes and carbohydrates
     • Cytoskeleton - determines shape and fluidity of cells
       • Made from thin, intermediate filaments and microtubules
     • Membrane bound organelles within the cytosol
   • Plasmalemma
     • Separates cytoplasm from outside environment
     • Phospholipid bilayer (ampiphatic
       • Hydrophillic head
       • Hydrophobic tail
     • Contains integral proteins
     • Can exocytose and endocytose material
     • Fluid mosaic
     • Selectively permeable
     • Contains embedded proteins
   • Organelles
     • Cytoplasm
       • Mitochondria = energy production
       • Rough ER = protein synthesis
       • Smooth ER = cholesterol and lipid synthesis/detoxification
       • Golgi apparatus = modification and packaging of secretions
       • Lysosomes = hydrolytic enzymes of intracellular digestion
       • Nucleus = contains genetic code
   • Cytoskeleton
     • Microfilaments = 7nm, composed of actin
     • Intermediate filaments = >10nm, composed of proteins
     • Microtubules = 25nm, composed of tubulin
       • Originate from organising centre called centrosome
       • Polar
       • Dyenin and kinesin attach to them and move along them
   • Nucleus
     • Enclosed by nuclear envelope - inner and outer membrane with nuclear pores
     • Outer nuclear membrane studded with ribosomes
     • Contains chromosomes
     • Site of RNA synthesis - mRNA, tRNA in nucleus, rRNA in nucleolus
   • Ribosomes
     • Formed in nucleolus
     • Small subunit which binds RNA and large subunit which catalyses formation of peptide bonds
   • Endoplasmic reticulum
     • Rough
       • Studded with ribosomes
       • Protein synthesis and initiation of glycoprotein formation
     • Smooth
       • Continues processing of proteins from rough ER
       • Site of lipid synthesis
   • Golgi Apparatus
     • Composed of a group of flattened membrane cound cisternae
     • Transport vesicles arrive at Golgi from SER
     • Modifies and packages macromolecules for SER
   • Intercellular junctions
     • Occluding junctions
       • Link cells to form diffusion barrier
       • Prevent diffusion
       • Also known as tight junctions
     • Anchoring junctions
       • Provide mechanical strength
       • Adherent junctions - link submembrane actin bundles of adjacent cells
       • Cadherin molecules bind to each other in extracellular space and to actin
       • Desmosomes link submembrane intermediate filaments of adjacent cells
       • Hemidesmosomes link submembrane intermediate filaments of cells to extracellular matrix through transmembrane proteins
     • Communicating junctions
       • Allow movement of molecules between cells
       • Often termed Gap Junctions
       • Each junction is circular patch studded with pores (produced by connexion proteins)
       • Found in epithelium, but also in smooth muscle and cardiac muscle
   • Endocytosis
     • Membrane invaginates, fuses and newly made endocytotic vesicle buds into cell
     • Often receptor mediated
   • Exocytosis
     • Works in reverse of endocytosis
   • Phagocytosis
     • Bacteria binds to cell surface, cell engulfs it to form phagosome, binds with lysosome containing digestive enzymes

2. Diversity of Cells And Their Function

   • Stains
     • H&E Stain = Haematoxylin and Eosin
       • Eosin = acidic dye, negatively charged, dyes basic things pink
       • Haematoxylin = basic dye, positively charged, dyes acidic things purple
   • Tissue types
     • Epithelium
       • Covers surfaces of body, lines hollow organs, forms glands
       • All have basal lamina
       • Non - vascular
       • Usually polarised - apical and basal sides differ
       • Functions
         • Mechanical barrier
         • Chemical barrier
         • Absorption
         • Secretion
         • Containment
         • Locomotion
       • Classification
         • Cell shape
           • Squamous = flattened
           • Cuboidal = cube
           • Columnar = tall and thin
         • Number of layers
           • Simple = one layer
           • Stratified = two or more layers
           • Pseudostratified = looks like multiple layers but is actually only one
         • Cell surface, tissue surface specialisations
           • Prominent microvilli
           • Cillia
           • Keratinised
         • Presence of specialised cell types
           • Goblet cells
       • Glandular epithelium
         • Endocrine = product secreted towards basal end of cell
           • Distributed by vascular system
           • Ductless glands
         • Exocrine = product secreted towards apical end of cell
           • Ducted glands
     • Connective tissue
       • Forms framework of body, dynamic role in development, growth and homeostasis of tissues, and energy storage (fat)
       • 3 types
         • Soft connective tissue
           • Loose
           • Tendons, ligaments, mesentery, stroma of organs, dermis of skin
           • Dense irregular if fibres run in many directions
           • Dense regular if fibres run in the same direction
         • Hard connective tissue
           • Bone and cartilage
           • Strong, flexible, compressable, semi-rigid tissue
           • Cartilage
             • Hyaline = articular surface, tracheal rings, costal cartilage
             • Elastic
             • Fibrocartilage
           • Bone
             • Outer shell of cortical bone makes up shaft - diphysis
             • Cancellous/trabecular bone occupies end - epiphyses
         • Blood and lymph
       • Consists of...
         • Extracellular matrix
           • Fibres - collagen, reticular and elastic fibres
           • Ground substance
           • Tissue fluid
         • Cells
           • Fibroblasts = synthesises ECM, collagen and stroma of animal tissue
           • Adipose cells = fat cells
           • Osteocytes = cells in bone
           • Chondrocytes = secretes matrix of cartilage and becomes embedded in it
     • Muscle
       • Specialised to generate force by contraction
       • Force is movement of actin fibres over myosin fibres
       • 3 types
         • Smooth = involuntary and non-striated
         • Skeletal = voluntary and striated, multinucleated
           • Nuclei are elongated and located at cell periphery
         • Cardiac = involuntary and striated
           • Have intercalated discs which contain multiple intercellular junctions to maintain mechanical integrity
     • Nervous Tissue
       • Consists of neurons and their supporting cells (glia)
       • Control function and allows for rapid communication between different parts of the body
       • Surrounded by connective tissue coat
         • Meninges in CNS
         • Epineurum in PNS
       • Glia
         • Astrocytes = support and ion transport
         • Oligodentricytes (CNS) = produce myelin
         • Microglia = provide immune surveillance
         • Schwann Cells (PNS) = produce myelin and support axons

3. Organisation of cells into tissues and organs

   • GI tract
     • Salivary glands
       • Parotid, submandibular, sublingual
       • Striated ducts
     • Oesophagus to anal canal = 4 major layers
       • Mucosa
         • Epithelium - sits on basal lamina
         • Lamina Propria - loose connective tissue
         • Muscularis mucosae - thin layer of smooth muscle
       • Submucosa = loose connective tissue
       • Muscularis externa = 2 thick layers of smooth muscle, inner circular and outer longitudinal
       • Serosa or adventita = outer layer of connective tissue that either suspends digestive tract or attaches to other organs
   • Protective mucosa
     • Non - keratinised stratified squamous epithelium
       • Oral cavity
       • Pharynx
       • Oesophagus
       • Anal canal
   • Absorptive mucosa
     • Simple columnar epithelium with villi and tubular glands
       • Small intestine
   • Secretory
     • Simple columnar epithelium with extensive tubular glands
       • Stomach
   • Protective and absoprtive
     • Simple columnar epithelium with tubular glands
       • Large intestine
         • In large intestine, the outer longituduinal smooth muscle is not continuous - found in 3 muscular strips called teniae coli
   • Kidney
     • Thousands of nephrons
   • Digestive tract nervous system
     • Enteric nervous system
       • Ganglia between 2 muscle layers that make up muscularis externa
   • Respiratory System
     • Trachea
       • Airway
       • Respiratory epithelium
       • Lamina propria
       • Seromucous gland in submucosa
       • hyaline cartilage of tracheal ring
     • Bronchi vs bronchioles
       • Bronchus = large diameter airways with hyaline cartilage
       • Bronchioles = small airways, no cartilage, mainly smooth muscle
     • Alveoli
       • Lined by simple squamous epithelium
   • Liver
     • Lobules = livers functional units
   • • Exocrine (pancreatic digestive enzymes) and endocrine gland (islets of Langerhans produce insulin)
   • Blood and blood vessels
     • Blood
       • 55% plasma, 45% cells
       • RBC = no nucleus
         • Lifespan = 4 months
       • WBC
         • Neutrophils
         • Eosinophils
         • Basophils
         • Monocytes
         • Lymphocytes
     • Blood vessels
       • Artery
         • Tunica intima = extends to internal elastic membrane
           • Endothelial cells
         • Tunica media
           • smooth muscle
         • Tunica adventita
           • Supporting connective tissue
       • Simple squamous epithelium of blood vessels is called endothelium
       • Arteriole
         • 1 or 2 layers of smooth muscle in tunica media and almost no adventita
       • Capillaries
         • Endothelial cells and a basal lamina
         • Have pericytes - connective tissue cells with contractile properties
         • 3 types
           • Continuous
             • Muscle
             • Nerve
             • Lung
             • Skin
           • Fenestrated
             • Have pores
             • gut mucosa
             • Endocrine glands
             • Kidney
           • Sinusoidal
             • Have large gaps
             • Liver
             • Spleen
             • Bone marrow
       • Venules
         • Endothelium
         • Pericytes
       • Veins
         • Tunica intima
         • Thin, continuous tunica media
         • Few layers of smooth muscle cells
         • Large veins have thick tunica adventita