Introduction to Histology Cell Structures Dr. Rebecca A. Code Summer Scholars 2007

Histology – the study of cellular structures of the body Anatomy at the microscopic level (microanatomy) Cells---tissues---organs---organ systems 1015 cells in the human body 200+ cell types in the body Observation – the key to identifying cell types

Nucleus – present in almost all cells, stains well with hematoxylin. Size Shape Location Number Nucleolus – site of rRNA synthesis Density Euchromatic – light staining nucleus due to regions of chromosomes that are less coiled, indicating that the DNA is actively transcribing mRNA. Heterochromatic – dense, darkly staining nucleus due to tightly coiled chromatin, presumably not transcriptionally active.

Cytoplasmic organelles – other clues to differentiate cell types and function Ribosomes Mitochondria Golgi apparatus Endoplasmic reticulum Microfilaments Secretory vesicles Pigment granules Lipid droplets

Cell Specializations Microvilli – found on many epithelial cells; 1-2 mm long extensions of cell membrane; increase surface area (15-20X) for absorption; lots of microvilli = brush border Cilia – 7-10 mm long; motile structures stabilized by microtubules; function to move fluid over cells; found in trachea, bronchi, oviducts, flagella of sperm. Stereocilia –very long microvilli, non-motile; for absorption; in epidydimus and on hair cells of inner ear.

Microvillus Cilium

Cell Adhesions/Junctions Nearly all cells are connected to neighboring cells by cell junctions Occluding junctions join cells together to form impermeable barrier Adhering junctions provide mechanical attachment between cells. Communicating junctions permit movement of ions or molecules between cells

Cell Junctions Occluding – the most apical junction Zonula occludens, tight junctions Adhering – 2 types: Zonula adherentes Macula adherens = desmosomes Communicating Gap junctions

Histology = 2 dimensional image A section is a slice of tissue Orientation when sectioned affects what you see.

Section of Round Solid Object A B B A

Sections cut through a curved tube

Light Microscope = tool of the histologist Oculars (eyepieces) Stage Objective Lens Condenser Light source Focus knobs

Specimen Preparation Fixation, dehydration, embedding Sectioning Staining: most common is H&E Hematoxylin: cationic dye (+ charge) that binds to negatively charged (acidic) structures in the cell. Example: nucleus = blue Eosin: anionic dye (- charge) adheres to basic structures in the cell. Example: amine groups (NH3+) on proteins make cytoplasm pink.

Kidney cells

Heterochromatic and Euchromatic Nuclei

Golgi Apparatus in Nerve Cells

Mitochondria and Myofibrils

Microvilli of Intestinal Epithelial Cells

Cilia of Tracheal Epithelial Cells

False Intercellular Bridges (Desmosomes)