Microscopy and Cell Observation

Adjusting Light on a Microscope

Proper illumination is essential for clear microscopic observation. There are three main ways to adjust light on a microscope:

• Adjusting the diaphragm: The diaphragm controls the amount of light passing through the specimen. Opening it increases brightness; closing it increases contrast.

• Adjusting the condenser: The condenser focuses light onto the specimen. Raising or lowering it changes the intensity and focus of the light.

• Adjusting the light source (rheostat): The rheostat controls the voltage supplied to the light, altering its brightness.

Key Microscopy Terms

• Real Image: The actual image formed by the objective lens inside the microscope.

• Virtual Image: The image seen by the eye, formed by the ocular lens magnifying the real image.

• Total Magnification: The product of the magnification of the objective and ocular lenses.

• Resolution: The ability to distinguish two points as separate; higher resolution means finer detail can be seen.

• Parfocal: A feature where the microscope stays in focus when switching between objectives.

• Field (Field of View): The visible area seen through the microscope at a given magnification.

• Working Distance: The distance between the objective lens and the specimen.

• Depth of Field: The thickness of the specimen that remains in focus at one time.

Staining Cheek Cells

Staining enhances contrast, making cell structures visible. The typical procedure involves:

• Scraping the inside of the cheek to collect cells.

• Placing the sample on a slide and adding a drop of stain (e.g., methylene blue).

• Applying a coverslip and observing under the microscope.

Cheek cells appear as irregular, flat cells with a prominent nucleus when stained.

Cell Structures Visible with a Light Microscope

• Cell membrane

• Nucleus

• Cytoplasm

• Sometimes nucleoli and cell boundaries

The Cell: Structure and Function

Definitions and Functions of Cell Components

• Cell: The basic structural and functional unit of living organisms.

• Nucleus: The control center of the cell, containing genetic material (DNA).

• Plasma Membrane: The outer boundary of the cell, regulating entry and exit of substances.

• Cytoplasm: The cellular material outside the nucleus, containing organelles and cytosol.

• Chromatin: DNA and associated proteins in a loose, threadlike form.

• Chromosomes: Condensed chromatin visible during cell division.

• Nucleoli: Sites within the nucleus where ribosomal RNA is produced.

• Nuclear Envelope: Double membrane surrounding the nucleus.

• Nuclear Pores: Openings in the nuclear envelope allowing exchange of materials.

• Microvilli: Fingerlike extensions of the plasma membrane that increase surface area.

• Cytosol: The fluid portion of the cytoplasm.

• Ribosomes: Sites of protein synthesis; can be free or attached to rough ER.

• Smooth Endoplasmic Reticulum (SER): Synthesizes lipids and detoxifies substances.

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; synthesizes proteins for export.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosome: Contains digestive enzymes to break down waste and cellular debris.

• Peroxisome: Contains enzymes for detoxification and lipid metabolism.

• Mitochondria: The "powerhouse" of the cell; site of ATP production.

• Cytoskeletal Elements: Provide structural support and facilitate movement.

• Microtubules: Hollow tubes that maintain cell shape and aid in transport.

• Intermediate Filaments: Provide mechanical support for the cell.

• Microfilaments (Actin Filaments): Involved in cell movement and shape changes.

• Centrioles: Organize microtubules during cell division.

• Inclusions: Non-living substances in the cytoplasm (e.g., glycogen, lipid droplets).

Table: Functions of Major Cell Organelles

Mitosis and Cell Division

Mitosis is the process by which a cell divides to produce two genetically identical daughter cells. Key terms and structures include:

• Mitotic Spindle: Microtubule structure that separates chromosomes.

• Metaphase Plate: The central plane where chromosomes align during metaphase.

• Kinetochores: Protein structures on chromatids where spindle fibers attach.

• Sister Chromatids: Identical copies of a chromosome connected at the centromere.

• Centromere: The region where sister chromatids are joined.

The stages of mitosis are:

1. Prophase: Chromatin condenses into chromosomes; nuclear envelope breaks down; spindle forms.

2. Metaphase: Chromosomes align at the metaphase plate.

3. Anaphase: Sister chromatids separate and move to opposite poles.

4. Telophase: Nuclear envelopes reform; chromosomes decondense.

5. Cytokinesis: Division of the cytoplasm, resulting in two cells.

Cell Membrane Transport Mechanisms

Key Terms and Processes

• Selective Permeability: The property of the plasma membrane to allow some substances to pass while blocking others.

• Active Transport: Movement of substances against their concentration gradient, requiring energy (ATP).

• Passive Transport: Movement of substances down their concentration gradient, without energy input.

• Concentration Gradient: A difference in concentration of a substance across a space.

• Diffusion: The movement of molecules from high to low concentration due to kinetic energy.

• Kinetic Energy: The energy of motion that drives diffusion.

• Osmosis: The diffusion of water across a selectively permeable membrane.

• MWCO (Molecular Weight Cut-Off): The size limit of molecules that can pass through a membrane.

• Solute Pumps: Membrane proteins that move solutes against their gradient using ATP.

• Pinocytosis: "Cell drinking"; the cell engulfs extracellular fluid.

• Phagocytosis: "Cell eating"; the cell engulfs large particles or cells.

PhysioEx Experiment 5B

This experiment typically investigates osmosis and diffusion using artificial membranes. Key findings include:

• Only molecules smaller than the MWCO can pass through the membrane.

• Water moves to balance solute concentrations (osmosis).

• Active transport requires energy, while passive transport does not.

Additional info: PhysioEx 5B often demonstrates the principles of dialysis and the effect of solute size on membrane permeability.

Histology: The Study of Tissues

Primary Tissue Types

• Epithelial Tissue

• Connective Tissue

• Muscle Tissue

• Nervous Tissue

All four tissue types are found in most organs. For example, the skin contains epithelial (epidermis), connective (dermis), muscle (arrector pili), and nervous (sensory receptors) tissues.

Epithelial Tissue Classification

• Based on cell shape: Squamous (flat), Cuboidal (cube-shaped), Columnar (tall).

• Based on arrangement: Simple (one layer), Stratified (multiple layers).

• Surfaces: Apical (free) surface and basal surface (attached to basement membrane). Naming stratified epithelium: Based on the shape of the apical surface cells.

• Special types: Transitional (stretchable, found in bladder), Pseudostratified (appears layered but all cells touch the basement membrane).

Key Histology Terms

• Histology: The study of tissues.

• Basement Membrane: Thin layer anchoring epithelium to connective tissue.

• Endocrine Gland: Ductless gland that secretes hormones into the blood.

• Exocrine Gland: Gland that secretes substances through ducts to a surface.

• Extracellular Matrix: Non-cellular material surrounding cells in connective tissue.

• Ground Substance: Gel-like component of the extracellular matrix.

• Mesenchyme: Embryonic connective tissue.

• Neuron: Nerve cell that transmits electrical signals.

• Neuroglia: Supporting cells in nervous tissue.

• Striation: Alternating light and dark bands in muscle tissue.

• Intercalated Discs: Specialized connections between cardiac muscle cells.

Identifying Tissue Types and Fibers

• Epithelial Tissue: Look for closely packed cells with little extracellular matrix.

• Connective Tissue: Abundant extracellular matrix; may contain collagen, elastic, and reticular fibers.

• Muscle Tissue: Long, striated or smooth cells; may have multiple nuclei.

• Nervous Tissue: Large neurons with branching processes and smaller neuroglia.

• Fibers: Collagen (thick, strong), Elastic (thin, stretchy), Reticular (fine, branching).

The Integumentary System

Functions of the Skin

• Protection from mechanical, chemical, and biological damage

• Prevention of water loss

• Regulation of body temperature

• Sensory reception

• Excretion of wastes

• Synthesis of vitamin D

Skin Structure

• Epidermis: Outermost layer; composed of stratified squamous epithelium.

• Dermis: Deeper layer; composed of connective tissue, contains blood vessels, nerves, glands.

Layers of the Epidermis (from deep to superficial)

• Stratum Basale: Single row of stem cells; site of mitosis.

• Stratum Spinosum: Several layers of keratinocytes; provides strength.

• Stratum Granulosum: Cells contain granules; begin to die.

• Stratum Lucidum: Thin, clear layer found only in thick skin (palms, soles).

• Stratum Corneum: Outermost, many layers of dead, keratinized cells.

Note: The stratum lucidum is only present in thick skin.

Cells of the Epidermis

• Keratinocytes: Produce keratin, a protective protein.

• Melanocytes: Produce melanin, which protects against UV radiation.

• Langerhans (Dendritic) Cells: Immune defense.

• Merkel Cells: Sensory receptors for touch.

Layers of the Dermis

• Papillary Layer: Superficial, areolar connective tissue; contains dermal papillae and capillaries.

• Reticular Layer: Deep, dense irregular connective tissue; provides strength and elasticity.

Skin Color and Melanin

• Melanin: Pigment produced by melanocytes; determines skin color and provides UV protection.

• Other factors: Carotene (yellow-orange pigment), hemoglobin (redness from blood flow).

Hair and Hair Follicle Structure

• Root Sheaths: Layers surrounding the hair root, providing support.

• Matrix: Growth zone of the hair; cells divide to produce hair.

Thick vs. Thin Skin

• Thick Skin: Found on palms and soles; has all five epidermal layers, including stratum lucidum; no hair follicles.

• Thin Skin: Covers most of the body; lacks stratum lucidum; contains hair follicles.

Glands of the Skin

• Sebaceous Glands: Secrete sebum (oil) into hair follicles; found everywhere except palms and soles.

• Sudoriferous (Sweat) Glands: Two types: Eccrine (most common, for thermoregulation) and Apocrine (in axillary and genital areas, active after puberty).

Fingerprints

• Formed by dermal papillae in the papillary layer of the dermis.

• Patterns include loops, whorls, and arches.

Additional info: Identification of tissue types and skin structures under the microscope is a key laboratory skill in Anatomy & Physiology.