Introduction to Cytology and Microscopes

Introduction to Cytology and Genetics

• Cytology and genetics were introduced.
• Cell membrane, mitochondrion, cytoplasm, nucleus, DNA, endoplasmic reticulum, lysosome, ribosome, and Golgi apparatus are cellular components.

Microscopes

• Microscopes are optical devices used to observe microscopic objects (less than 70µm).
• The goal of the chapter is to explain microscope types, design, operation, and biomedical microscopic techniques.

Types of Microscopes

• Microscopes are categorized by the type of radiation used (light or electron).

Light Microscopes

• Light microscopes use white or UV light (sunlight, bulb, or vapor lamp).
• Optical components are made of glass.
• The resolution is 0.2 µm and maximum theoretical magnification is 2,000 times.
• Practical magnification is up to 1,000 times.
• Routine observation uses transmitted light.
• Fluorescent and inverted microscopes utilize light from above the slide.

Light Microscope Components

• The diagram displays microscope parts (eyepieces, observation tube, objective lens, stage, condenser lens, light source, base) and controls (neck, coaxial stage controls, course focus, fine focus, switch, rheostat).

Electron Microscopes

• Electron microscopes utilize a stream of electrons emitted by a cathode as radiation.
• Optical components use electromagnetic lenses.
• Resolution is 0.2 nm and maximum magnification is 1,000,000 times.
• Samples need preparation (fixation, staining, contrasting).
• Transmission electron microscope (TEM) visualizes samples by passing an electron beam through them.
• Scanning electron microscope (SEM) observes the sample surface with the electron beam.

Types of Electron Microscopes

• Transmission electron microscope (TEM) creates high-resolution images of internal cell structures by passing electrons through the sample.
• Scanning electron microscope (SEM) creates three-dimensional images of the specimen surface using a scanning electron beam.

Types of Light Microscopes

• Stereomicroscopes (dissecting microscopes) use light from two slightly different angles to view specimens in three dimensions.
• Low-power magnification is typically less than 100x.

Inverted Microscope

• This microscope type reverses the optical path, placing the optics below the slide and the light source above.
• It is useful for observing cell cultures growing on the bottom of Petri dishes.

Fluorescence Microscope

• For specific samples, a special type of light microscope uses UV (ultraviolet) radiation to illuminate the specimen, leading to light emission at longer wavelengths (visible light).
• Special fluorescent dyes, called fluorochromes, are used in this type of observation.
• The fluorescence microscopy is a useful technique for cytogenetic analysis (like FISH)

Polarized Microscope

• A polarized microscope uses polarized light generated by special Nicol prisms to observe structures like chitin, and crystalline cell inclusions.

Recommended Procedure for Microscopic Observation

• Quadrants, concentric circles, and clock face orientations aid in identifying specimen positions within the microscope's field of view.

Types of Slide Preparations

• Impression preparations press a clean slide against a tissue surface, facilitating cell observation.
• Smear preparations spread a drop of a cellular suspension across a slide.
• Covered slides comprise a sample, supported by a cover slip.

Native Slides

• Used to detect physiological cell behaviors like movement, division, and ingestion, but not good for intracellular structure analysis.
• Phase and dark-field microscopy are often used for observations requiring higher detail.

Fixation

• Fixation halts cellular processes and autolysis.
• Chemical or physical fixation methods are used, including heating and drying, and chemical solutions.

The Cell

• Cells are the functional and structural unit of all organisms.
• Cytology is the study of cells, including their basic life processes (metabolism, growth, reproduction, and irritability).

Cell Theory

• In 1838, Schleiden and Schwann defined plant and animal cells as elemental components of all living organisms.
• In 1855, Virchow revised the cell theory with the concept that all cells arise from existing cells.

Cell Types

• Prokaryotic cells (e.g., bacteria, archaea) are simple, small, and lack a nucleus or membrane-bound organelles.
• Eukaryotic cells (e.g., protozoa, fungi, plants, animals) are complex, larger, possess a nucleus, and have membrane-bound organelles.

Eukaryotic Cell

• Eukaryotic cells form unicellular or multicellular organisms.
• Organisms categorized by their nutritional pattern (autotrophic or heterotrophic).
• They undergo processes like differentiation to specialize.

Shape and Size of Cells

• Cell size and shape are specific to their locations and functions in the body.
• Cells exhibit various shapes like spherical, biconcave disc, squamous, cuboidal, polygonal, spindle-shaped, and multi-polar.

Cells According to Size

• Cells can be classified as small (e.g., erythrocytes, lymphocytes), medium-sized (e.g., plasma cells, chondrocytes), or large (e.g., human ova, megakaryocytes, motor neurons).

Molecular Structure of Cell Membranes

• Cell membranes (biomembranes) are essential components of all cells.
• Their discovery was closely tied to the development of transmission electron microscopy.
• Detailed observation reveals typical trilaminar structure.
• Chemical composition differences reflect cell specialization.

Function of Cell Membrane

• The cell membrane separates intracellular from extracellular spaces.
• It's a dynamic equilibrium boundary, maintaining the internal environment.
• It contains vital components like enzymes, receptors, and transport proteins, playing roles in substance intake and interactions.

Main Components of Cell Membranes

• Phospholipids are main cell membrane components, arranged in a double layer (bilayer).
• Polar heads face the aqueous environment, while non-polar tails face inward.
• These phospholipids are not chemically bound, therefore they can move laterally.

Cell Membrane Proteins

• Integral proteins penetrate or traverse the phospholipid bilayer.
• Peripheral proteins are situated on the surface of the bilayer.
• Proteins have various roles: transport of ions and substances, signal reception (hormones, neurotransmitters), and catalytic activity (enzymes).

Cell Junction Types

• Descriptions of cell junction types (tight junctions, adherens junctions, desmosomes, gap junctions) are included.