Histology Basics Quiz

Histology

• Histology is the study of the microscopic structure of normal tissues. It helps understand how tissues are built to perform their functions.
• Tissues are collections of cells with similar characteristics.
• Cell size ranges from 10-30 micrometers.
• Microscopes are used to study cells.

Light Transmission Microscopy

• Uses visible light to examine a sample.
• Objective lenses enlarge and project the image to the eyepiece.
• Common magnifications are X4, X10, and X40.
• The sample needs to be transparent.

Tissue Preparation

• Fixation: Preserves tissue structure using chemicals that cross-link proteins and inactivate enzymes.
• Dehydration: Removes water from the tissue using alcohol solutions (e.g., moving from 65% to 100% alcohol).
• Clearing: Tissue is transferred to organic solvents that are miscible with both alcohol and paraffin to make it transparent.
• Infiltration: Tissue is immersed in melted paraffin until fully infiltrated (absorbed by paraffin).
• Embedding: The tissue is placed in molds filled with melted paraffin. Once solidified the specimen forms paraffin block.
• Trimming: The block is trimmed to expose the tissue for sectioning. Freezing with liquid nitrogen is an alternative to paraffin embedding for tissue sectioning.
• Staining: Highlights specific tissue structures and components. H&E staining is common (nuclei stain blue, cytoplasm stains pink/red). PAS stain is used for carbohydrates.

Microscopy Techniques

• Phase-contrast microscopy: Used to observe unstained samples, useful for live cells that would be killed under staining.
• Confocal microscopy: Allows observation of a single plane of a sample, useful for 3D-imaging.
• Stereomicroscopy: A microscope that magnifies an object without thin-sectioning the specimen.
• Electron microscopy: Uses electrons, in two kinds of configurations, Transmission electron microscope (TEM) or Scanning electron microscope (SEM). TEM can give a 3D picture (in a 2D arrangement) while SEM gives a 3D surface rendering.

Immunochemistry

• Uses antibodies (produced by B-lymphocytes) to identify specific proteins/molecules.
• Antibodies have a variable domain (paratope) that attaches to the specific protein/molecule (antigen).
• The epitope is the part of the antigen that the antibody recognizes.

The Cell

• The basic unit of life, and composed of plasma membrane, the encircling membrane surrounding the cell.
• Phospholipids create a bi-layer with hydrophobic tails facing inward and hydrophilic heads facing outward.
• Cholesterol is found between the phospholipids affecting membrane fluidity and flexibility.
• Proteins perform various functions, some face outward, some inward, and others span the membrane.
• Glycocalyx: a sugar layer surrounding the membrane, bonded with proteins and phospholipids. It plays a role in recognition and cell-cell interactions.
• Hyaluronic acid: creates a jelly-like layer around cells, which retains water.

Membrane Transport

• Simple diffusion: Lipophilic molecules and small, uncharged molecules pass through easily.
• Channel/facilitated diffusion: Membrane proteins act as channels to allow passage of specific molecules(usually charged).
• Carrier/pump: Larger molecules/charged molecules transported against their concentration gradient, requiring energy., often using ATP as energy source.

Cytoskeleton

• Microfilaments: Composed of actin.
• Microtubules: Composed of tubulin required for mitosis and other cellular needs.
• Intermediate filaments: Provide structural support.

Organelles

• Ribosome: Synthesize proteins based on instructions from mRNA. They have three sites (A, P, and E) to perform protein synthesis.
• Endoplasmic Reticulum (ER): Rough ER (RER) has ribosomes and synthesizes proteins for transport/secretion. Smooth ER (SER) synthesizes lipids and other molecules.
• Golgi Apparatus: Modifies and packages proteins and lipids for secretion or use within the cell.
• Lysosomes: Contain digestive enzymes to break down waste and molecules.
• Mitochondria: Produce ATP through cellular respiration.
• Peroxisomes: Contain enzymes to break down fatty acids into smaller molecules.
• Cellular inclusion: Accumulation of substances like lipids or glycogen, storing energy in some cells.
• Nucleus: Contains DNA, controls cellular activities, including protein production, and contains the nucleolus where ribosomes assemble.

Cell Cycle

• Interphase: period of cell growth and DNA replication. Divided in G1, S, and G2 phases.

Mitochondria

• Produce ATP
• Metabolism of amino acids and lipids
• Act as a sensor for the health of the cell
• Cells can undergo apoptosis (programmed cell death)

Cell Division

• Mitosis: Process of cell division, resulting in two identical daughter cells.
• Cytokinesis: Division of the cytoplasm.
• Stem cells: Undifferentiated cells that can divide indefinitely and differentiate into specialized cell types.
• Types of stem cells include embryonic and adult stem cells.

Types of tissues

• Epithelial: Covers body surfaces, lines cavities, forms glands responsible for secretions.
• Connective: Supports, connects, and separates different tissues and cells. Forms extracellular matrix.
• Muscular: Responsible for movement, contracts.
• Nervous: Transmits information via nerve impulses.

Bone

• Compact bone: Dense bone tissue organized into osteons. Each osteon is around a central canal.
• Spongy bone: A framework of trabeculae.
• Epiphysis: Ends of the long bone.
• Diaphysis: Shaft of the bone.
• Osteoblasts: Bone-forming cells.
• Osteocytes: Mature bone cells.
• Osteoclasts: Bone-resorbing cells. -Periosteum: Membrane covering bone. Contains cells that produce new bone tissue, which has a key role in bone growth and fracture healing. -Endosteum: Membrane lining the internal surfaces of the bone. Contains cells that produce new bone tissue, which has a key role in bone growth and bone remodeling.

Blood

• Consists of a suspension of cells (red blood cells, white blood cells, platelets) within a fluid matrix called plasma.
• Function is to transport substances throughout the body.

Connective Tissue

• Connective tissue is characterized by an abundance of extracellular matrix that is largely composed of protein fibers (collagen, elastic) embedded in a ground substance.
• Types include loose (areolar) connective tissues, dense regular connective tissue, dense irregular connective tissue, reticular connective tissue.
• Specialized connective tissues include cartilage, bone, and blood.

Glands

• Glands are epithelial tissue; they produce and secrete substances. Glands can be exocrine (secrete through ducts) or endocrine (secrete into the bloodstream).

Special epithelia structures

• Cilia: hair-like extensions of the cell membrane that can beat, move substances.
• Stereocilia: (also called static cilia), extensions of the cell membrane that do not beat or move.
• Microvilli: finger-like projections that increase surface area for absorption.