Intro to Histology and Microscopy

Introduction to Histology and Microscopy

• Histology is the study of tissues.

Cell Theory

• The cell is the basic structural and functional unit of all living organisms.
• All organisms are made up of one or more cells.
• Cells arise from preexisting cells.

Cell Types

• The basic unit of life is the cell, it represents the simplest collection of matter that can live.
• Living organisms can be unicellular or multicellular.
• Cells can be prokaryotic or eukaryotic.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells are 0.5-5um in size, while eukaryotic cells are >10um.
• Prokaryotic cells lack a nuclear membrane; they have a nucleoid region in the cytosol. Eukaryotic cells have a membrane-bound nucleus.
• Prokaryotic cells have circular DNA complexed with RNA, while eukaryotic cells have linear DNA complexed with histones and proteins.
• Prokaryotic cells lack membrane-bound organelles, while eukaryotic cells have them.
• Energy generation occurs in the cell membrane of prokaryotic cells, and in the mitochondria of eukaryotic cells.
• Prokaryotic cells divide through binary fission, while eukaryotic cells divide through mitosis and meiosis.

Plasma Membrane

• The plasma membrane, also known as the cell membrane or plasmalemma, envelopes cell contents and serves as the boundary and supports the structure.
• It regulates the movement of material into and out of the cell and plays a role in cellular communication.

Cytoplasm

• The cytoplasm is the gelatinous substance that fills the inside of the cell.
• It is enclosed by the plasma membrane, located external to the nuclear membrane.
• Cytosol is the substance in which the organelles are suspended.

Cytoskeleton

• The cytoskeleton provides structural support to cells, assists with cell motility, and facilitates the movement of materials throughout the cell.
• Main components include microtubules, microfilaments, and intermediate filaments.

Mitochondria

• Mitochondria are the powerhouse of the cell, serving as the site of energy production in the form of ATP.
• They comprise of a double-membrane bound organelle and contain their own DNA.

Ribosomes

• Ribosomes are the site of protein synthesis.
• Consist of 2 subunits (large and small).

Endoplasmic Reticulum (ER)

• The ER is a convoluted, membranous network of intercommunicating channels called cisterns.
• Rough ER modifies, transports, and stores proteins.
• Smooth ER handles detoxification and lipid biosynthesis.

Golgi Apparatus

• The Golgi apparatus serves as a packaging center and completes modifications of proteins produced in the Rough ER (RER).
• This organelle packages and addresses proteins made by the RER to their proper destinations.

Vesicles

• Vesicles are spherical, membrane-bound organelles, transporting cellular material.
• These are generated by the cell membrane.

Lysosomes

• Lysosomes are spherical, membrane-bound organelles that contain enzymes for digestion.
• Known as "suicidal bags" and produced by the Golgi apparatus.

Peroxisome

• Peroxisomes are spherical, membrane-bound organelles that handle beta oxidation of lipids.
• Responsible for detoxification of harmful substances.
• They form by budding from the ER.

Nucleus

• The nucleus houses the genetic material (DNA) of the cell, which directs protein synthesis.
• The nucleolus consists of RNA and protein for ribosome assembly.
• A nuclear envelope acts as the boundary between cytoplasm and nuclear contents.

Cell Transport Processes

• Passive transport involves the movement of substances across a membrane without the requirement of energy.
• Active transport needs energy to move subsances.
• Vesicular transport brings materials across the cell membrane via creating or losing vesicles.

Passive Transport: Simple Diffusion

• A passive transport process, involving unassisted movement of solutes across a semipermeable membrane from high to low concentration
• This does not require energy.

Passive Transport: Facilitated Diffusion

• Needs carrier proteins to facilitate movement of solutes across a membrane from high to low concentration.
• This does not require energy.

Passive Transport: Osmosis

• Osmosis is the movement of water across a semipermeable membrane, flowing from low to high concentration of solutes.
• Since this is passive energy is not required.

Active Transport

• Protein pumps facilitate the movement of solutes across a semipermeable membrane, moving from low to high concentration (against the concentration gradient).
• active energy is required.

Vesicular Transport: Endocytosis

• Bulk movement of substances INTO the cell by vesicles forming at the plasma membrane.
• Endocytosis includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Vesicular Transport: Exocytosis

• Is the bulk movement of a substance OUT OF the cell through fusion of secretory vesicles with the plasma membrane.

The Cell Cycle

• There are 2 phases of the cell cycle: interphase and M phase (mitosis).

Cell Cycle: Interphase

• Divided into G1, S, and G2 phases
• During G1, cells accumulate needed enzymes and nucleotides for DNA replication.
• The S phase involves DNA replication.
• During G2, cells grow in preparation for mitosis.

Cell Cycle : Prophase & Metaphase

• In prophase, chromosomes condense and become visible, centrosomes move toward opposite poles, spindle fibers emerge from centrosomes, and the nuclear envelope breaks down.
• In metaphase, chromosomes line up at the metaphase plate, and each sister chromatid is attached to a spindle fiber originating from opposite poles.

Cell Cycle: Anaphase and Telophase and Cytokinesis

• During anaphase, centromeres split in two, sister chromatids are pulled toward opposite poles, and certain spindle fibers begin to elongate the cell.
• In telophase, chromosomes arrive at opposite poles and begin to decondense, nuclear envelope material surrounds each set of chromosomes, and the mitotic spindle breaks down.
• Cytokinesis; in animal cells- a cleavage furrow separates the daughter cells, and in plant cells- a cell plate (new cell wall precursor) grows to separate the daughter cells.

Compound Microscope Parts: Magnifying

• Objective lens and ocular lenses which magnify samples

Compound Microscope Parts: Illuminating

• Substage condenser, iris diaphragm, and light source which illuminate samples.

Compound Microscope Parts: Mechanical

• Base, c-shaped arm and stage - which allow the sample to be mounted on a microscope.

Mechanical Parts: Base

• This holds the various parts of the microscope.

Mechanical Parts: Arm

• The arm is the part used for holding the microscope.

Mechanical Parts: State

• A rigid platform on which specimen to be viewed is placed on.

Illuminating Parts: Substage Condenser

• Controls the intensity of the light.

Illuminating Parts: Diaphragm

• Controls the amount of light reaching the object.

Illuminating Parts: Illuminator

• The light source.

Illuminating Parts: Coarse Adjustment Knob

• Allows objective lenses to be moved towards or away from the specimen.

Illuminating Parts: Fine Adjustment Knob

• Used for fine tuning and high resolution focusing.

Magnifying Parts: Eyepiece

• The final image is viewed through this part.

Magnifying Parts: Objective Lens

• Lenses through which the samples are viewed: Scanner, Low Power, HIgh Power and Oil Imersion

Microscope Magnification

• Scanner (Low Magnification)
• LPO (Low Power Objective Magnification)
• HPO (High Power Objective Magnification)
• OIO (Oil Immersion Objective Magnification)

Caring for the Microscope

• Carry holding the C-shaped arm with one hand and other hand under the base.
• Cover the Microscope and never allow direct light when not in use.
• When using oil immersion objective, do not adjust the coarse screw.
• After using Oil Immersion, clean the immersion objective by wiping with soft cotton cloth or lens paper.
• Keep Objectives Dry and never let dry objectives come in contact with oil.
• Return to Default Position when switching objectives.
• Store microscopes in a safe dry place and when being stored, orient the C-shaped arm toward the entrance for easy reach.

Summary

• All living organisms are made up of cells.
• Prokaryotic cells are primitive cells with no defined nucleus and no membrane-bound organelles.
• Eukaryotic cells are have different membrane-bound organelles, which perform specific functions that help maintain the life of the cell.
• Cells can transport materials passively along a concentration gradient or through the pumps with use of energy.
• Cells arise from preexisting cells as the cell cycle proceeds.
• Important to understand the parts of microscope when observing cells and tissues, and there are proper handling procedures.