Intro to Histology

Study Notes

Cells are the basic structural and functional units of all living organisms.
Approximately 40 trillion cells exist in the human body, which may be eukaryotic or prokaryotic.
Most cells possess one nucleus; however, some can be multinucleated.
Protoplasm, the living part of a cell, consists of the nucleus and cytoplasm, surrounded by a plasma membrane.
Internal cell structure is often modified to reflect specific functions.

Differentiation begins with the zygote, which undergoes divisions leading to blastomeres and embryonic stem cells.
Cell differentiation occurs in the fetus and is influenced by gene expression.
Specific gene sets mediate cytoplasmic activities, positioning cells into specialized tissues.

Four fundamental tissue types exist:
- Epithelial Tissue: Covers surfaces, lines cavities, and forms glands.
- Connective Tissue: Provides structural and functional support to other tissues, distinguished by its extracellular matrix.
- Muscle Tissue: Composed of contractile cells, enabling movement.
- Nervous Tissue: Responsible for receiving, transmitting, and integrating information, controlling body activities.

Tissue preparation involves creating thin slices or sections for visual examination via transmitted light.
Key steps in tissue preparation:
- Fixation: Preserves structure and prevents degradation; commonly involves buffered formaldehyde or glutaraldehyde for electron microscopy.
- Dehydration: Gradual extraction of water through increasing ethanol solutions.
- Clearing: Replacement of ethanol with an organic solvent that mixes with both alcohol and embedding media.
- Infiltration: Cleared tissue is immersed in melted paraffin at 52°-60°C, evaporating the clearing solvent.
- Embedding: Tissue is allowed to harden in paraffin at room temperature.
- Trimming: The hardened block is trimmed for microtome sectioning, typically at thicknesses of 3-10 micrometers for light microscopy.