Epithelial Tissue Types

• There are eight types of epithelium

Simple Squamous Epithelium

• It consists of a single layer of flat, thin cells
• Found lining blood vessels, air sacs, and the heart
• This epithelium allows diffusion, filtration, and secretion

Stratified Squamous Epithelium

• Characterized by multiple cell layers with surface cells being flat
• Keratinized type is located in the epidermis of the skin
• Non-keratinized type is located in the esophagus, mouth, and vagina
• Protects against abrasion, pathogens, and dehydration

Simple Cuboidal Epithelium

• It consists of a single layer of cube-shaped cells
• Found in kidney tubules, thyroid gland, and ovary
• It functions in secretion and absorption

Stratified Cuboidal Epithelium

• Made up of multiple layers of cube-shaped cells
• Present in sweat glands, mammary glands, and salivary glands
• It functions in protection and secretion

Simple Columnar Epithelium

• It consists of a single layer of tall, rectangular cells, often with microvilli or cilia
• Non-ciliated type is located in the digestive tract (stomach, intestines)
• Ciliated type is located in uterine tubes and bronchioles
• It functions in absorption, secretion of mucus by goblet cells, and movement of mucus

Stratified Columnar Epithelium

• Characterized by multiple layers with columnar cells on the surface
• Found in the male urethra, conjunctiva of the eye, and large ducts of some glands
• Functions in protection and secretion

Transitional Epithelium

• Consists of multiple layers where cells can change shape, rounded when relaxed and flattened when stretched
• Located in the urinary bladder and ureters
• Stretching to allow urine storage is the main function

Pseudostratified Columnar Epithelium

• Appears stratified but is a single layer; all cells touch the basement membrane and are often ciliated
• Ciliated type is found in the trachea and upper respiratory tract
• Non-ciliated type is found in male reproductive ducts
• It functions in secretion and movement of mucus (with cilia)

Cilia and Microvilli

• Cilia consists of microscopic, hair-like structures that extend from the surface of certain cells, aiding in movement of substances or fluid across the cell surface
• Villi are finger-like projections of the mucous membrane in the small intestine, which increase surface area for nutrient absorption
• Microvilli are tiny, finger-like extensions of the plasma membrane found on epithelial cells, increasing surface area for absorption and secretion

Epithelial Functions

• Protection
• Absorption
• Secretion
• Excretion
• Filtration
• Sensation
• Transport

Birefringence

• The optical property of a material that splits light into two refracted rays with different velocities when passing through an anisotropic substance

Birefringence of Amyloid

• Amyloid fibers show apple-green birefringence under polarized light when stained with Congo red dye

Fluorochrome

• A fluorescent dye binds to specific molecules and emits light when excited by a specific wavelength
• Used in microscopy to visualize structures or molecules

Resolution

• The ability to distinguish between two points or structures
• Higher resolution mean clearer, more detailed images

TEM (Transmission Electron Microscopy)

• A type of electron microscopy where electrons pass through a sample
• Provides high-resolution, 2D images of internal structures

SEM (Scanning Electron Microscopy)

• A type of electron microscopy where electrons scan the surface of a sample
• Produces 3D images of its surface features

Immunofluorescence

• A technique that uses fluorescently labeled antibodies to detect specific proteins or antigens in cells or tissues

Direct Immunofluorescence

• Fluorescently labeled antibody directly binds to the target antigen

Indirect Immunofluorescence

• A secondary fluorescent antibody binds to the primary antibody
• Amplifies the signal

Health

• A state of complete physical, mental, and social well-being, not merely the absence of disease or infirmity

Disease

• A condition that disrupts the normal functioning of the body or mind, often caused by infection, genetic factors, or environmental influences

Necessary Causes

• Factors that must be present for a disease to occur (e.g., bacteria causing infection)

Subsidiary Causes

• Additional factors that contribute to the development or severity of a disease but are not essential (e.g., poor diet, stress)

Cell Injury Types

• Reversible Injury: Cells can recover
• Irreversible Injury: Cells can't recover, leading to death
• Necrosis: Uncontrolled cell death with inflammation
• Apoptosis: Controlled, programmed cell death
• Hypoxic Injury: Damage from lack of oxygen
• Chemical Injury: Damage from toxins or chemicals
• Physical Injury: Damage from physical forces or extreme conditions

Grossing

• The initial examination and dissection of tissue samples
• It involves cutting the tissue into smaller pieces for further processing

Purpose of Fixation

• Fixation preserves tissue structure and prevents degradation
• Keeps the tissue in a life-like state by halting enzymatic activity and preventing bacterial growth

Factors Affecting Fixation

• pH (acidity or alkalinity) affects the effectiveness of the fixative, with pH 7.0-7.4 being optimal for best preservation
• Higher temperatures speed up fixation, while low temperatures slow it down
• Inadequate fixation time can lead to incomplete preservation
• Different fixatives (e.g., formalin, alcohol) are used depending on the tissue and the desired outcome

Processing Steps

• Dehydration: Removing water from the tissue using alcohol
• Clearing: Replacing alcohol with a substance (like xylene) that is miscible with both alcohol and embedding medium
• Embedding: The tissue is infiltrated with wax or resin, hardening it to allow sectioning
• Sectioning: Thin slices of tissue are cut for examination under a microscope

Frozen Section and Instrument

• A rapid tissue processing method where tissue is frozen, cut into thin sections, and stained quickly
• Often used in surgeries to provide immediate results
• A microtome or cryostat is used for sectioning the tissue

H&E Stain and Its Action on Nucleus and Cytoplasm

• Hematoxylin (H) stains the nucleus blue/purple by binding to DNA and RNA
• Eosin (E) stains the cytoplasm pink by binding to proteins in the cell