Histology LC 1: Introduction to Histology

Cell Transport Mechanisms

• Simple diffusion transports small non-polar molecules (O2, N2) and small uncharged polar molecules (H2O, CO2, glycerol).
• Diffusion rate is proportional to the concentration gradient and shows little specificity.
• Lipophilic (fat-soluble) molecules pass easily through membranes, while water-soluble molecules diffuse slowly.
• Facilitated diffusion involves ion channels and carrier proteins, which have specificity for the transported molecules.

Membrane Proteins

Ion Channels

• Multi-pass transmembrane proteins create aqueous pores for specific small water-soluble molecules and ions.
• Passive transport occurs down electrochemical gradients, aided by proteins like aquaporins for water.

Carrier Proteins

• Carrier proteins assist in the transport of larger molecules across membranes.

Glycocalyx

• A sugar coat on the plasmalemma's outer surface, aiding cell recognition and interaction.

Rough Endoplasmic Reticulum (RER)

• Contains ribophorins for the binding of large ribosomal subunits.
• Abundant in secretory protein-synthesizing cells, organized into parallel arrays.
• Transitional elements form vesicles free of ribosomes, connected to the Golgi apparatus.

Mitochondria

• Rod-shaped organelles (0.2 µm wide, 7 µm long) synthesize membrane-bound proteins, lysosomal proteins, and secretory proteins.

Golgi Complex

• Composed of membrane-bounded cisternae (saccules) arranged in a stack, held by microtubules.
• Has distinct polarity with varying functions across regions.
• Contains enzymes for oxidizing fatty acids, synthesizing cholesterol, and detoxifying substances.

Lysosomes

• Types include multivesicular bodies formed by the fusion of endosomes, phagolysosomes fused with phagocytic vacuoles, and autophagolysosomes from autophagic vacuoles.
• Residual bodies are lysosomes expanded with undegraded material, often excreted from the cell.
• Examples of lysosomal enzymes include superoxide dismutase (SOD), glutathione oxidase, and catalase.

Peroxisomes

• Also known as microbodies, these spherical organelles are involved in oxidative reactions and contain catalase.

Glycogen and Lipid Droplets

• Glycogen appears as clusters in hepatocytes, serves as a glucose source for the bloodstream.
• Lipid droplets are storage forms of triglycerides and cholesterol, vary in size based on fixation methods.

Lipofuscin

• Membrane-bound, electron-dense material that accumulates with age in non-dividing cells, considered an "age pigment."

Centrosome

• Near the nucleus, consists of two centrioles and pericentriolar material.
• Centrioles are cylindrical (0.2 µm wide, 0.5 µm long) and composed of nine triplets of microtubules.

Nucleolus

• Involved in rRNA synthesis and ribosome assembly, has various particles including interchromatin and perichromatin granules.
• Sequesters nucleolar proteins for cell-cycle checkpoint signaling; regulator proteins are released when needed.

Nuclear Matrix

• Contains maturing ribosomal precursor particles, implicated in RNA processing and chromosomal interactions.

This quiz focuses on the basic principles of histology, particularly small molecule transport mechanisms such as simple diffusion. Understanding how non-polar and polar molecules move across cell membranes is crucial in the study of histology. Prepare to test your knowledge with questions on these foundational concepts.