Objectives and Introduction

This study guide covers the identification and function of cell organelles as seen under electron microscopy, with a focus on histological techniques and the interpretation of micrographs. Understanding these concepts is essential for students of Anatomy & Physiology, as it bridges the gap between cellular structure and function.

• Recognize organelles and cell ultrastructure on electron micrographs.

• Describe the function of major organelles.

• Explain how pathologists prepare tissues for examination.

• Analyze micrographs for abnormalities.

Histotechnology: Preparing Tissues for Observation

Gross Examination of Tissue

When a tissue sample is removed during surgery, it is sent to the pathology department for examination. The first step is the gross examination, where the specimen is visually inspected and marked for orientation.

• Fixation: The tissue is preserved in a fixative (commonly formalin) to maintain its natural state and prevent decay.

• Sectioning: The tissue is embedded in paraffin wax and sliced into thin sections for microscopic analysis.

• Staining: Sections are stained to highlight different cellular components. Hematoxylin and eosin (H&E) is a common stain.

• Mounting: The stained sections are placed on glass slides for examination under a microscope.

Example: A tumor biopsy is fixed, embedded, sectioned, stained, and then examined for cancerous cells.

Purpose of Histotechnology

• Allows visualization of cellular and tissue structures.

• Enables diagnosis of diseases based on microscopic appearance.

Organelle Identification and Electron Micrographs

Electron Microscopy

The electron microscope uses a beam of electrons to create highly detailed images of cell structures, far surpassing the resolution of light microscopes.

• Transmission Electron Microscope (TEM): Electrons pass through thin sections of the specimen, revealing internal structures.

• Scanning Electron Microscope (SEM): Electrons scan the surface, providing detailed surface images (not covered in detail here).

Electron Micrograph: The resulting image from an electron microscope, showing organelles and cell ultrastructure.

Generalized Eukaryotic Cell Structure

A typical eukaryotic cell contains various organelles, each with specific functions. Recognizing these on micrographs is essential for understanding cell biology.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Nucleolus: Site of ribosome synthesis.

• Mitochondria: Powerhouse of the cell; site of ATP production.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; Smooth ER synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for waste breakdown.

• Ribosomes: Sites of protein synthesis.

• Plasma Membrane: Regulates entry and exit of substances.

Detailed Structure of the Nucleus

Nuclear Envelope

• Double membrane structure surrounding the nucleus.

• Outer membrane: Continuous with rough ER.

• Inner membrane: Lines the nuclear interior.

Nuclear Pores

• Gaps in the nuclear envelope.

• Function: Allow movement of molecules (e.g., RNA, proteins) in and out of the nucleus.

Nucleoplasm

• Gel-like substance inside the nucleus.

• Contains nucleotides, enzymes, and ions.

• Suspends chromatin and nucleolus.

Nucleolus

• Dense region within the nucleus.

• Composed of RNA and proteins.

• Function: Manufactures ribosomal subunits (rRNA).

DNA Organization

• Chromatin: DNA-protein complex; exists in two forms:

  • Euchromatin: Lightly stained, extended, and accessible for transcription.

  • Heterochromatin: Dark-stained, condensed, and transcriptionally inactive.

• Chromosome: Condensed form of DNA, visible during cell division.

• Centromere: Point of attachment between replicated DNA strands (sister chromatids).

Table: Comparison of Chromatin Types

Key Terms and Definitions

• Organelle: Specialized structure within a cell that performs a specific function.

• Micrograph: Photograph or digital image taken through a microscope.

• Histology: Study of tissues at the microscopic level.

• Pathologist: Medical specialist who examines tissues for disease diagnosis.

Summary and Applications

• Understanding cell structure and organelle function is fundamental for interpreting tissue samples and diagnosing diseases.

• Electron microscopy provides the resolution needed to study organelles in detail.

• Recognizing the appearance of organelles and chromatin types on micrographs is a key skill in anatomy and pathology.

Additional info: For further study, refer to Table 5.1 in your lab manual for detailed images and functions of each organelle, and review Chapter 3 of Saladin's "Anatomy and Physiology: Unity of Form and Function" for more electron micrograph examples.