Histology and Tissue Biology

Comprehensive vocabulary flashcards covering the four primary tissue types, embryonic germ layers, tissue preparation, cellular junctions, glandular structures, membranes, and wound healing concepts from the histology lecture notes.

Longitudinal section

A tissue cut along the longest direction of an organ, revealing a lengthwise appearance.

Cross section

A tissue cut perpendicular to the organ's length, showing a circular or transverse appearance of a tube.

Oblique section

A tissue cut made at an angle between a longitudinal and a cross section, producing a diagonal appearance.

Ectoderm

The outer primary embryonic germ layer that gives rise to the epidermis and nervous system.

Mesoderm

The middle primary embryonic germ layer that gives rise to muscle, bone, and blood.

Endoderm

The inner primary embryonic germ layer that gives rise to the mucous membrane lining of the gastrointestinal and respiratory systems, plus digestive glands.

Mesenchyme

A gelatinous embryonic tissue derived from mesoderm containing fibroblasts and delicate collagen fibers in a gel-like matrix, which gives rise to muscle, bone, and blood.

Avascular

Lacking blood vessels; a key characteristic of epithelial tissue where cells receive oxygen and nutrients solely by diffusion from underlying connective tissue.

Apical surface

The free surface of an epithelial cell that faces the outside of the body or the inside lumen of a hollow organ.

Basal surface

The bottom surface of an epithelial cell attached to the underlying basement membrane.

Lateral surface

The sides of an epithelial cell that contact neighboring cells.

Basement membrane

A thin, nonliving layer between epithelial tissue and underlying connective tissue that anchors epithelium, regulates material exchange, and provides structural foundation.

Simple squamous epithelium

A single layer of thin, flat cells that facilitates rapid diffusion and secretes serous fluid; located in lung alveoli, kidney glomeruli, endothelium, and serosa.

Simple cuboidal epithelium

A single layer of cube-shaped cells specialized for absorption and secretion; found in kidney tubules, thyroid gland, liver, mammary glands, salivary glands, and bronchioles.

Simple columnar epithelium

A single layer of tall, narrow cells with basal oval nuclei specialized for absorption, secretion, and mucus release; lines the GI tract, uterus, kidney, and uterine tubes.

Pseudostratified columnar epithelium

An epithelium where all cells contact the basement membrane but not all reach the apical surface, creating a staggered nucleus appearance; secretes and propels respiratory mucus.

Keratinized stratified squamous epithelium

Multiple layers of cells whose apical surface consists of dead, flat cells packed with keratin; forms the epidermis to resist physical injury and reduce water loss.

Nonkeratinized stratified squamous epithelium

Multiple layers of cells with nucleated, living surface cells providing a moist, friction-resistant lining; found in the tongue, oral mucosa, esophagus, and vagina.

Stratified cuboidal epithelium

Two or more layers of cells with cube-shaped surface cells that provide secretion and protection; located in sweat gland ducts and certain reproductive tubules.

Urothelium (transitional epithelium)

A stratified epithelium whose surface cells transition from rounded to flattened as the tissue stretches; lines the urinary bladder, ureters, and umbilical cord.

Goblet cells

Specialized, wineglass-shaped cells found among simple columnar and pseudostratified epithelia that secrete protective, lubricating mucus.

Fibroblasts

Connective tissue cells that synthesize and secrete protein fibers and ground substance.

Macrophages

Phagocytic cells that engulf foreign debris and participate in immune system activation.

Mast cells

Cells in connective tissue that release histamine (to dilate blood vessels and increase permeability) and heparin (to inhibit blood clotting).

Adipocytes

Fat cells specialized in storing triglycerides within a large central lipid droplet that pushes the nucleus against the cell membrane.

Chondroblasts

Immature cartilage cells that actively secrete the cartilage matrix.

Chondrocytes

Mature cartilage cells trapped within small matrix cavities called lacunae.

Osteoblasts

Bone cells that build and deposit new bone matrix.

Osteocytes

Mature bone cells that reside inside lacunae within mineralized matrix.

Osteoclasts

Specialized bone cells that dissolve and break down bone tissue.

Collagen fibers

Tough, flexible protein fibers highly resistant to stretching; prevalent in tendons, ligaments, and deep skin.

Reticular fibers

Thin, branching collagen fibers coated with glycoproteins that form the supportive stroma of lymphatic organs such as the spleen and lymph nodes.

Elastic fibers

Protein fibers composed of elastin that allow tissues such as the skin, lungs, and arteries to stretch and recoil.

Glycosaminoglycans (GAGs)

Negatively charged carbohydrates in ground substance (e.g., chondroitin sulfate, hyaluronic acid, heparin) that attract sodium, retain water, and regulate fluid balance.

Proteoglycans

Large, bottlebrush-shaped macromolecules in ground substance that trap water, enhance matrix viscosity, and bond cells to extracellular components.

Areolar tissue

Loose connective tissue with loosely arranged fibers and abundant ground substance; cushions organs, reduces friction, and supports epithelium.

Reticular tissue

Loose connective tissue consisting of a net-like framework of reticular fibers that forms the stroma of lymph nodes, spleen, thymus, and bone marrow.

Dense regular connective tissue

Connective tissue packed with parallel collagen fibers designed to withstand pulling forces in a single direction; forms tendons and ligaments.

Dense irregular connective tissue

Connective tissue with randomly arranged, multidirectional collagen bundles that resist stress from many directions; found in the deep dermis and organ capsules.

Hyaline cartilage

Cartilage with a smooth, glassy matrix containing fine collagen fibers; reduces joint friction and supports the trachea, larynx, bronchi, and fetal skeleton.

Elastic cartilage

Cartilage containing an abundant network of elastic fibers that provides flexible, resilient support; found in the external ear and epiglottis.

Fibrocartilage

Cartilage characterized by coarse, parallel collagen bundles and rows of chondrocytes; provides shock absorption in the knee meniscus, intervertebral discs, and pubic symphysis.

Compact bone

Dense, solid osseous tissue organized into concentric lamellae surrounding central canals containing blood vessels and nerves.

Spongy bone

Porous osseous tissue constructed of delicate bony struts called trabeculae with marrow-filled spaces that reduce weight while offering multi-angle support.

Neurons

Large, excitable cells of the nervous system equipped with long cellular processes specialized to receive and transmit electrical signals.

Neuroglial cells

Smaller supporting cells of nervous tissue that protect, insulate, and assist neurons.

Dendrites

Branched neuronal processes that receive incoming electrical signals and carry them toward the soma.

Axon

A long nerve fiber process that conducts electrical impulses away from the neuron cell body toward other cells.

Skeletal muscle

Voluntary muscle tissue featuring long, cylindrical, unbranched fibers with visible striations and multiple peripherally located nuclei.

Cardiac muscle

Involuntary heart muscle composed of short, branched, striated cells with one central nucleus and intercalated discs.

Smooth muscle

Involuntary muscle tissue composed of non-striated, spindle-shaped (fusiform) cells, each containing a single central nucleus.

Intercalated discs

Specialized junctional connections between cardiac muscle cells that coordinate electrical transmission and synchronized contraction.

Tight junctions

Zipper-like protein fusions that encircle adjacent cells to seal the intercellular space and prevent fluid or solute leakage between cells.

Desmosomes

Spot-weld-like mechanical junctions attached to protein plaques and intermediate filaments that keep neighboring cells from pulling apart.

Hemidesmosomes

Asymmetric anchoring junctions that attach the basal surface of epithelial cells to the underlying basement membrane.

Gap junctions

Intercellular channels formed by transmembrane proteins that allow ions, sugars, and small molecules to pass directly from the cytoplasm of one cell to another.

Exocrine glands

Glands that release secretions into ducts leading to an epithelial surface or internal cavity.

Endocrine glands

Ductless glands that secrete hormones directly into the bloodstream.

Stroma

The supportive connective tissue framework of a gland, consisting of its outer capsule and internal septa.

Parenchyma

The functional cells of an organ or gland that perform its primary physiological work, such as secreting substances.

Acinus

A dilated sac-like cluster of secretory cells situated around a lumen that drains into an exocrine duct.

Merocrine secretion

A secretory mode in which products are discharged via exocytosis while leaving the secretory cell completely intact.

Holocrine secretion

A secretory mode in which accumulated products are released by the complete breakdown and disintegration of the secretory cell.

Cutaneous membrane

The skin; a dry, protective membrane consisting of keratinized stratified squamous epithelium overlying dense irregular and areolar connective tissues.

Mucous membrane

A moist internal membrane lining passages open to the external environment, composed of epithelium, an underlying lamina propria, and often a muscularis mucosae.

Serous membrane

A membrane lining closed internal body cavities (pleura, pericardium, peritoneum), composed of simple squamous mesothelium and areolar connective tissue that secretes lubricating fluid.

Synovial membrane

A joint-lining membrane composed purely of connective tissue without an epithelial lining, which produces lubricating synovial fluid.

Hyperplasia

Tissue growth through an increase in the total number of cells via cell division.

Hypertrophy

Tissue enlargement caused by an increase in the size of pre-existing cells rather than cell multiplication.

Neoplasia

Abnormal, unregulated tissue growth forming a benign or malignant tumor.

Anaplasia

A structural change in which cells revert to an unspecialized, less differentiated state, characteristic of malignant cancers.

Metaplasia

The reversible transformation of one mature, differentiated tissue type into another mature tissue type.

Atrophy

Reduction in tissue size resulting from a decrease in cell number or cell size due to disuse, aging, or lack of stimulation.

Necrosis

Pathological, premature cell and tissue death resulting from injury, infection, ischemia, or toxins, accompanied by inflammation.

Apoptosis

Genetically programmed, regulated cell suicide that eliminates surplus or aged cells without causing inflammation.

Regeneration

Tissue repair process wherein damaged cells are replaced with the same functional cell type, fully restoring original tissue architecture.

Fibrosis

Tissue repair process characterized by the replacement of damaged tissue with collagenous scar tissue, leaving compromised physiological function.

Granulation tissue

Vascular, soft repair tissue rich in newly formed capillaries and proliferating fibroblasts that develops during wound healing.

Totipotent

The developmental state of an early embryonic stem cell capable of giving rise to every cell type of both the embryo and placental tissues.

Pluripotent

Stem cells of the embryonic inner cell mass capable of differentiating into any cell type of the body proper.

Multipotent

Adult or developmental stem cells that can differentiate into a limited range of closely related mature cell lineages.

Unipotent

Stem cells possessing the capacity to generate only a single mature cell type, such as epidermal stem cells producing keratinocytes.