Epithelial tissues are composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin extracellular matrix
Epithelial tissues form cellular sheets that line the cavities of organs and body surfaces, with functions including covering, lining, protection, absorption, and secretion
Types of epithelia include covering or lining epithelia and secretory or glandular epithelia
Classification of lining epithelia is based on the number of cell layers and the shape of the cells
Shapes of cells in epithelia:
Squamous: flattened
Cuboidal: cube-shaped
Columnar: column-like
Examples of epithelial types:
Simple squamous epithelium: lines vessels (endothelium) and serous lining of cavities like pericardium, pleura, peritoneum (mesothelium)
Simple cuboidal epithelium: found in renal collecting tubules and ducts
Simple columnar epithelium: present in renal collecting ducts and lining of the gallbladder
Stratified epithelium types:
Stratified squamous epithelium (keratinized): found in the skin
Stratified squamous epithelium (nonkeratinized)
Stratified cuboidal epithelium: in sweat glands
Stratified columnar epithelium
Pseudostratified columnar epithelium is found lining the human trachea
Brown Adipose Tissue (BAT) contains cells with multiple lipid droplets interspersed among abundant mitochondria
Connective tissue consists of cells like fibroblasts, mast cells, macrophages, plasma cells, leukocytes, and adipocytes
Extracellular matrix (ECM) of connective tissue includes protein fibers and ground substance
Types of protein fibers in ECM:
Collagen
Elastic
Reticular
Ground substance of ECM includes glycosaminoglycan, proteoglycan, and glycoproteins
Two general classes of connective tissue proper:
Loose (Areolar) Connective Tissue
Dense Connective Tissue
Regular Connective Tissue
Irregular Connective Tissue
Specialized Connective Tissue types:
White Adipose Tissue: more common type specialized for fat storage
Brown Adipose Tissue: contains cells with multiple lipid droplets interspersed among abundant mitochondria
Reticular Connective Tissue
Adipose Tissue
Cartilage
Bone
Blood
DifferenceInterferenceContrast Microscope (DIC): also known as Nomarski Interference Contrast Microscope, similar to phase contrast microscope, forms nearly 3Dshadowed images under oblique illumination, works using 2 coherent beams of light from the same source and prisms
Fluorescence Microscope: uses fluorophores to generate fluorescence in biological samples, components include xenon arc or mercury vapor lamps, excitation filter, dichroic mirror, and emission filter
Confocal Microscope: similar to fluorescencemicroscope, uses fluorescent dyes, pinhole focuses light onto a specific spot in the sample and rejects out-of-focus glare
Electron Microscopes:
Fundamental types of microscopes:
Light Microscopes:
Bright Field Microscope: most commonly used, illumination from tungsten light passed through the condenser
Dark Field Microscope: effective for observing live and unstained biological samples, uses an opaque disc under the condenser, specimen appears brightly lit against a dark background, used to identify Treponema pallidum
Phase Contrast Microscope: preferred for translucent and colorless specimens, annular ring at the substage condenser front focal plane, converts differences in specimen components into brightness or contrast differences in the image, first accurate method in manual counting of platelets
Transmission Electron Microscope (TEM): uses electrons transmitted through a specimen to produce a 2D image, specimen is often an ultrathin section of less than 100nm thick, essential systems include electron gun and condenser, image producing system, and image recording system
ScanningElectronMicroscope (SEM): designed for studying surfaces of solid objects, narrow beams of electrons scattered or emitted from the specimen surface produce a 3D character of the surface, essential parts include source of electrons, electromagneticlenses, electron detector, sample chamber, computer, and display
Difference between light and electron microscopes:
Light microscopes use light for illumination and are suitable for live samples, while electron microscopes use electrons and are ideal for studying surfaces of solid objects
Histology is the study of tissues, relying on microscopy to reveal cell, tissue, and organ structure
Goals of Histology include understanding tissue structure not visible to the naked eye, the relationship between tissue structure and function, and providing a basis for treating diseased and injured tissues
Tissues are groups of differentiated cells of similar structure and function, consisting of cells and extracellular matrix (ECM)
Four basic types of tissues found in the human body are connective tissue, epithelial tissue, muscle tissue, and nervous tissue
Methods of study in Histology include tissue processing, microscopy, and preparation of tissue slides for study
Tissue processing involves steps like fixation, dehydration, clearing, infiltration, embedding, trimming, section cutting, staining, and mounting
Fixation in tissue processing aims to avoid autolysis and preserve cell and tissue structure, using compounds like Phosphate Buffered Formalin, Formal Calcium, and Formal Saline
Dehydration in tissue processing replaces water in the tissue with organic solvent, commonly using acetone or alcohols
Clearing in tissue processing involves immersing tissue in a series of clearing agent-alcohol mixtures, with commonly used reagents like Amyl Acetate and Methyl Benzoate
Infiltration in tissue processing involves immersing cleared tissue in a series of clearing-embedding medium mixtures at medium-high temperature
Embedding in tissue processing positions infiltrated tissue in a mold filled with embedding medium, commonly using paraffin wax for light microscopy
Section cutting in tissue processing involves slicing the hardened tissue block with a microtome into extremely thin sections
Staining in tissue processing uses dyes to selectively color tissue components, with common stains like hematoxylin and eosin (H&E)
Mounting in tissue processing involves placing a protective glass coverslip on the slide with clear adhesive before microscopic observation