General and Systematic Histology for Radiography

Practice flashcards covering the microarchitecture of human tissues, their histological preparation, and their specific relevance to radiological imaging as discussed in the lecture notes.

Histology

The study of the microarchitecture of cells and tissues.

Fixation

The multi-step process of immersing tissue in a chemical fixative, most commonly $10\%$ Neutral Buffered Formalin, to terminate metabolic processes and prevent autolysis.

Microtome

A precision instrument using an ultra-sharp steel blade to slice tissue sections into thicknesses of $4$ to $6\,\mu\text{m}$.

Hematoxylin

A basic dye with a net positive charge that binds to basophilic (anionic) components like DNA and RNA, staining them deep blue or purple.

Eosin

An acidic dye with a net negative charge that binds to acidophilic (cationic) components like cytoplasmic proteins, staining them pink or red.

Artifact

Any artificial structural feature introduced during preparation or image acquisition that does not exist in living tissue, such as shrinkage or beam hardening.

Hydropic Degeneration

Cellular swelling caused by the failure of the $\text{Na}^+/\text{K}^+$ ATPase pump due to ATP deprivation, often visible as bright hyperintensity on Diffusion-Weighted Imaging (DWI).

Rough Endoplasmic Reticulum (rER)

A network of membranous sacs studded with ribosomes that displays intense basophilia due to high concentrations of rRNA.

Heterochromatin

Tightly coiled, condensed, and transcriptionally inactive DNA that aggregates at the nuclear periphery and stains deeply with basic dyes.

Euchromatin

Loosely uncoiled, transcriptionally active DNA that appears pale and dispersed under microscopic evaluation.

Indirect Action (Radiation)

Damage caused by ionizing radiation interacting with water molecules to produce highly reactive free radicals, such as the hydroxyl radical ($\text{OH}^*$), which then attack DNA.

Law of Bergonié and Tribondeau

The principle stating that cells are highly radiosensitive if they have a high mitotic rate, a long mitotic future, and are least differentiated.

M (Mitosis) Phase

The most radiosensitive phase of the cell cycle, during which chromatin is condensed and DNA-repair mechanisms are halted.

Basement Membrane

An acellular structural sheet consisting of the basal lamina and reticular lamina that anchors epithelial cells to underlying connective tissue.

Simple Squamous Epithelium

A single layer of flattened, scale-like cells that forms the endothelium of vessels and the mesothelium of serous membranes.

Transitional Epithelium (Urothelium)

A stratified tissue unique to the urinary tract featuring superficial 'umbrella cells' that allow for massive organ distension.

Microvilli

Tiny, non-motile cytoplasmic projections with an actin filament core that form a brush border to expand surface area for absorption.

Cilia

Motile, hair-like projections containing a $9+2$ microtubule axoneme that utilize ATP to move mucus and pathogens out of the respiratory tract.

Metaplasia

A reversible, adaptive transformation where one adult epithelial type replaces another to withstand chronic stress, such as squamous metaplasia in the trachea of smokers.

Ground Substance

A semi-fluid gel composed of Glycosaminoglycans (GAGs), Proteoglycans, and Glycoproteins that acts as a hydrostatic shock absorber in connective tissue.

Type I Collagen

The most abundant protein in the human body, providing high tensile strength and staining bright pink/red with eosin.

Fibroblast

The resident permanent cell of connective tissue proper responsible for synthesizing the fibers and ground substance of the extracellular matrix.

White Adipose Tissue

Unilocular tissue where each cell contains a single massive lipid droplet that compresses the nucleus into a 'signet ring' appearance.

Hounsfield Units (HU)

The scale used in CT to measure physical density; white adipose tissue typically ranges from $-60\,\text{HU}$ to $-120\,\text{HU}$.

Hyaline Cartilage

A support tissue with a smooth, amorphous matrix containing fine Type II collagen fibers, found on articular surfaces and in the trachea.

Hydroxyapatite

The inorganic mineral component of bone matrix with the chemical formula $\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2$.

Osteon (Haversian System)

The structural unit of compact bone consisting of concentric lamellae of calcified matrix surrounding a central Haversian canal.

Sarcomere

The functional contractile unit of striated muscle bounded between two Z-lines, containing alternating A-bands (myosin) and I-bands (actin).

Intercalated Discs

Specialized junctional complexes in cardiac muscle containing desmosomes for adhesion and gap junctions for electrical continuity.

Nissl Bodies

Clumps of rough endoplasmic reticulum and free ribosomes in the neuronal soma that stain intensely with basic dyes.

Blood-Brain Barrier (BBB)

A selective triad consisting of continuous endothelial cells with tight junctions, a continuous basal lamina, and perivascular astrocyte foot processes.

Tunica Media

The middle layer of blood vessel walls, composed primarily of smooth muscle and elastic fibers; it is thicker in arteries than in veins.

Vasa Vasorum

A miniature blood supply network located within the tunica adventitia of large blood vessels.

Type II Pneumocytes

Cuboidal cells in the alveolar septum that produce pulmonary surfactant to lower surface tension and prevent lung collapse.

Blood-Air Barrier

The thin interface for gas exchange consisting of Type I pneumocyte cytoplasm, fused basal laminae, and capillary endothelial cytoplasm.

Kupffer Cells

Resident macrophages located within the leaky sinusoidal capillaries of the liver lobules.

Glomerular Filtration Barrier

A three-layer filter consisting of fenestrated capillary endothelium, the glomerular basement membrane (GBM), and podocyte filtration slits.

Stratum Funktionale

The dynamic inner mucosal layer of the endometrium that undergoes cyclic changes and is shed during menstruation.