Chapter 5: Histology - Human Tissues and Membranes

Comprehensive vocabulary flashcards covering Chapter 5: Histology (Human Tissues and Membranes), detailing primary tissue classes, epithelial classifications, cellular junctions, glandular secretions, body membranes, connective tissue components, muscle, nervous tissue, wound repair, adaptation, and pathology.

Histology

The study of tissues and how they are arranged into organs; also known as microscopic anatomy.

Tissue

A group of similar cells and cell products working together to perform a specific structural or physiological role in an organ.

Organ

A structure with discrete anatomical boundaries that is composed of two or more primary tissue types.

Primary Tissue Classes

The four fundamental tissue categories in the adult human body: epithelial, connective, nervous, and muscular tissue.

Extracellular Matrix (ECM)

Extracellular material surrounding cells, composed of fibrous proteins and a clear hydrated gel called ground substance.

Ground Substance

The clear, gelatinous material filling the space between cells and fibers, also called tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel.

Ectoderm

The outermost primary germ layer that gives rise to the epidermis, nervous system, cutaneous glands, some cranial bones, pituitary gland, adrenal medulla, mouth lining, and anus.

Mesoderm

The middle primary germ layer that gives rise to connective tissues proper, bone, cartilage, blood, vascular endothelium, muscle, synovial and serous membranes, kidneys, and gonadal linings.

Endoderm

The innermost primary germ layer that gives rise to the mucosal lining of the airways and digestive tract (except the mouth and distal rectum/anal canal) and associated glands.

Tissue Sectioning Planes

The anatomical cutting orientations used in histology: longitudinal section (along the long axis), cross or transverse section (perpendicular to the long axis), and oblique section (cut at an angle).

Smear

A histological preparation technique in which a liquid or loose tissue sample, such as blood, is rubbed across a glass slide.

Spread

A histological preparation method in which thin membranes or cobwebby tissues, such as areolar connective tissue, are laid out flat on a slide.

Epithelial Tissue

A high-cellularity sheet of closely adhering cells, one or more layers thick, with an exposed apical surface and an anchored basal surface, that is avascular but innervated.

Apical Surface

The upper, unattached surface of an epithelial cell that faces away from the basement membrane toward an internal lumen or the external environment.

Basal Surface

The lower surface of an epithelial cell that is anchored to the underlying basement membrane.

Basement Membrane

An extracellular layer situated between an epithelium and underlying connective tissue, composed of collagen, reticular proteins, glycoproteins, and protein-carbohydrate complexes.

Simple Squamous Epithelium

A single layer of thin, flat cells with flattened nuclei specialized for rapid diffusion and filtration, found in lung alveoli, kidney glomeruli, endothelium, and serous membranes.

Simple Cuboidal Epithelium

A single layer of square or round cells with central, spherical nuclei specialized for secretion and absorption, found in kidney tubules, liver, and small gland ducts.

Simple Columnar Epithelium

A single layer of tall, rectangular cells with vertically oriented basal nuclei and apical microvilli or cilia, specialized for nutrient absorption and mucus secretion in the GI tract and uterine tubes.

Pseudostratified Columnar Epithelium

An epithelium that appears multilayered due to nuclei located at varied levels, though all cells touch the basement membrane; typically ciliated with goblet cells to propel mucus in the respiratory tract.

Goblet Cell

A specialized wineglass-shaped unicellular gland found interspersed in simple columnar and pseudostratified epithelia that synthesizes and secretes mucin.

Keratinized Stratified Squamous Epithelium

A multi-layered epithelium whose superficial layer consists of dead, flattened cells packed with keratin, specialized to resist abrasion, retard water loss, and block pathogen entry in the epidermis.

Nonkeratinized Stratified Squamous Epithelium

A multilayered epithelium lacking a surface layer of dead cells, maintaining living squamous surface cells to resist abrasion in moist regions like the mouth, esophagus, and vagina.

Transitional Epithelium (Urothelium)

A stratified epithelium characterized by rounded, dome-shaped surface cells that flatten under tension to permit stretching and distension in the urinary bladder, ureters, and renal pelvis.

Tight Junction

An intercellular junction that completely encircles an epithelial cell near its apical surface, fusing adjacent plasma membranes to prevent substances from passing between cells.

Desmosome

A patch-like cell junction anchored to intermediate filaments that holds neighboring cells together mechanically, resisting stretching and shear stresses.

Gap Junction

A communicating cell junction composed of ring-like transmembrane protein channels that allow ions, nutrients, and electrical signals to pass directly between adjacent cell cytoplasms.

Hemidesmosome

A half-desmosome junction that anchors the basal plasma membrane of an epithelial cell to the underlying basement membrane.

Cell Junctions

Specialized multiprotein structures that hold cells together, maintain tissue barrier integrity, and mediate intercellular communication.

Exocrine Gland

A gland that releases its secretory products through a tubular epithelial duct onto an external body surface or into the lumen of another organ.

Endocrine Gland

A ductless gland with high vascularity that secretes chemical messengers (hormones) directly into interstitial fluid and blood capillaries.

Modes of Glandular Secretion

The three mechanisms by which exocrine glands discharge products: merocrine (exocytosis), apocrine (apical cytoplasm pinching off), and holocrine (entire cell breakdown).

Merocrine Secretion (Eccrine)

The most common mode of secretion wherein gland cells release vesicles by exocytosis without losing cytoplasm or damaging the cell.

Holocrine Secretion

A secretory mechanism in which cells accumulate products until the entire cell disintegrates and ruptures, releasing oily secretion and cell debris (e.g., sebaceous glands).

Apocrine Secretion

A secretory mode in which the apical portion of the cell cytoplasm pinches off to release products such as milk fat droplets in mammary glands.

Serous Gland

An exocrine gland producing thin, watery fluids rich in enzymes, proteins, and electrolytes, such as tears, sweat, and parotid saliva.

Mucous Gland

An exocrine gland whose cells secrete the glycoprotein mucin, which absorbs water to form thick, sticky mucus.

Serous Demilune

A crescent-shaped cap of serous cells located on the end of a mucous acinus in a mixed exocrine gland.

Cutaneous Membrane

The skin; an epithelial membrane consisting of keratinized stratified squamous epithelium (epidermis) supported by dense irregular and areolar connective tissue (dermis).

Mucous Membrane (Mucosa)

A membrane lining tracts open to the exterior (digestive, respiratory, urinary, reproductive), consisting of an epithelium, an underlying lamina propria, and mucus-secreting cells.

Serous Membrane (Serosa)

A membrane lining closed internal body cavities (pleura, pericardium, peritoneum) consisting of a simple squamous mesothelium over areolar tissue that secretes lubricating serous fluid.

Synovial Membrane

A connective tissue membrane lacking epithelium that lines diarthrotic joint cavities and contains synoviocytes that secrete lubricating synovial fluid.

Fibroblast

The most common cell of connective tissue proper; a large, spindle-shaped cell that synthesizes collagen, elastic, and reticular fibers as well as ground substance.

Macrophage

A large phagocytic connective tissue cell derived from blood monocytes that engulfs foreign matter, bacteria, and dead cells, while activating the immune system.

Mast Cell

A connective tissue cell located along blood vessels that releases histamine to stimulate vasodilation and heparin to inhibit blood clotting during inflammatory responses.

Collagen Fibers

Tough, flexible, non-elastic extracellular fibers with high tensile strength made of collagen protein, predominant in tendons, ligaments, and bone.

Reticular Fibers

Thin, branching fibers composed of type III collagen coated with glycoproteins that form a supportive, sponge-like stroma in lymphoid organs.

Elastic Fibers

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

Glycosaminoglycans (GAGs)

Long unbranched polysaccharides composed of amino sugars and uronic acids that carry negative charges, attract water, and maintain fluid balance in the ground substance.

Proteoglycan

A massive macromolecule composed of a core protein linked to numerous GAG chains in a bottle-brush arrangement that forms a firm hydrated colloid to resist compression.

Areolar Connective Tissue

A loose connective tissue with loosely arranged fibers, abundant ground substance, high vascularity, and diverse cell types located beneath nearly all epithelia.

Adipose Tissue

A loose connective tissue dominated by adipocytes with large lipid droplets and peripherally displaced nuclei, functioning in energy storage, thermal insulation, and organ protection.

Reticular Tissue

A meshwork of reticular fibers and reticular fibroblasts forming the supportive structural stroma for lymphatic organs like the spleen, lymph nodes, and bone marrow.

Dense Regular Connective Tissue

A connective tissue composed of densely packed, parallel collagen bundles and compressed fibroblasts with minimal ground substance, adapted to withstand tensile pull in one direction (tendons, ligaments).

Dense Irregular Connective Tissue

A connective tissue containing randomly oriented, densely interwoven collagen fibers with few cells, specialized to resist unpredictable mechanical stresses in the deep dermis and organ capsules.

Dense Elastic Connective Tissue

A dense connective tissue containing prominent parallel elastic fibers and fibroblasts, found in the walls of large arteries (aorta) and vocal cords to allow recoil.

Chondrocyte

A mature cartilage cell residing within an isolated matrix cavity called a lacuna.

Chondroblast

A progenitor cartilage cell that actively synthesizes and secretes the surrounding cartilage matrix before becoming entrapped within a lacuna.

Perichondrium

A vascularized sheath of dense irregular connective tissue surrounding hyaline and elastic cartilage that supplies nutrients via diffusion and houses reserve chondroblasts.

Hyaline Cartilage

A glassy, smooth supportive tissue containing fine type II collagen fibers, chondrocytes in lacunae, and no blood vessels, providing friction-free joint movement and structural support in the trachea and costal cartilages.

Fibrocartilage

A tough cartilage with parallel, coarse bundles of type I collagen fibers and sparse chondrocytes, providing shock absorption in intervertebral discs, the pubic symphysis, and menisci.

Elastic Cartilage

A flexible cartilage containing an abundant meshwork of elastic fibers surrounded by a perichondrium, providing elastic support to the external ear and epiglottis.

Osteon (Haversian System)

The basic microscopic cylindrical unit of compact bone, composed of concentric lamellae of calcified matrix surrounding a central vascular canal.

Central Canal (Haversian Canal)

The longitudinal vascular channel at the center of an osteon through which blood vessels and nerves travel.

Concentric Lamellae

Concentric, onion-like rings of mineralized collagenous matrix arranged around the central canal of an osteon.

Canaliculi

Microscopic fluid-filled canals radiating through bone matrix that connect neighboring lacunae and allow osteocytes to communicate via gap junctions.

Osteocyte

A mature, nondividing bone cell located inside a lacuna that monitors mechanical stress and maintains the mineralized matrix.

Osteoblast

A bone-forming cell that synthesizes and secretes osteoid (unmineralized organic bone matrix) during bone growth and remodeling.

Osteoclast

A large, multinucleated bone-resorbing cell that breaks down bone matrix to remodel bone and release calcium into the blood.

Spongy Bone (Cancellous Bone)

Porous, lightweight bone tissue composed of an interconnecting latticework of trabeculae filled with bone marrow, found in epiphyses of long bones and inside flat bones.

Trabeculae

The thin plates, struts, and rods of calcified bone matrix that constitute the structural network of spongy bone.

Blood Plasma

The liquid ground substance of blood, accounting for approximately $55\%$ of whole blood, composed of $90\text{--}92\%$ water, dissolved proteins, electrolytes, and nutrients.

Formed Elements

The cellular components of blood making up approximately $45\%$ of whole blood volume, comprising erythrocytes, leukocytes, and platelets.

Erythrocyte

A biconcave, anucleated formed element filled with hemoglobin that transports oxygen ($\text{O}_2$) and carbon dioxide ($\text{CO}_2$).

Leukocyte

A nucleated white blood cell (neutrophil, eosinophil, basophil, lymphocyte, or monocyte) that functions in immune defense against infection and foreign antigens.

Platelet

A small, anucleated cell fragment pinched off from a megakaryocyte in red bone marrow that mediates hemostasis and blood clotting.

Nervous Tissue

Excitable tissue specialized for rapid electrochemical communication, consisting of functional neurons and supportive neuroglial cells.

Neuron

The structural and functional conducting cell of nervous tissue, possessing a soma, dendrites, and an axon.

Dendrite

A branched cellular process of a neuron specialized to receive electrochemical signals from environment or other neurons and transmit them toward the soma.

Axon

A single long nerve fiber that conducts electrical impulses (action potentials) away from the neuron cell body toward effector cells or synaptic targets.

Neuroglia

The supporting, non-conducting cells of nervous tissue (including astrocytes, microglia, oligodendrocytes, and ependymal cells) that protect, insulate, and nourish neurons.

Muscle Tissue Types

Contractile excitable tissues specialized for movement, categorized into skeletal muscle (striated, voluntary), cardiac muscle (striated, involuntary), and smooth muscle (non-striated, involuntary).

Intercalated Disc

A specialized cross-band junction between cardiomyocytes containing desmosomes and gap junctions that allows mechanical coupling and synchronized electrical conduction.

Hyperplasia

An increase in the total mass or size of a tissue resulting from an increase in the number of cells via cell division.

Hypertrophy

An increase in tissue or organ size resulting from the enlargement of preexisting cells rather than cell multiplication.

Atrophy

The shrinkage of a tissue or organ due to a reduction in cell size or cell number, often triggered by disuse, aging (sarcopenia), or loss of nerve supply.

Metaplasia

A reversible change in which one mature, differentiated tissue type transforms into another mature tissue type, typically in response to chronic irritation.

Dysplasia

Disordered cellular growth and proliferation characterized by abnormal cell size, shape, organization, and loss of tissue architecture; a precancerous state.

Carcinoma in Situ (CIS)

A severe dysplasia where full-thickness epithelial cellular abnormalities are present, but the basement membrane remains completely intact with no invasion.

Invasive Carcinoma

A malignant epithelial neoplasm where cancer cells breach the basement membrane and invade the underlying vascularized connective tissue stroma.

Regeneration

The repair of injured tissue via replacement of damaged cells with the same functional cell type, fully restoring original physiological architecture and function.

Fibrosis

The repair of damaged tissue through replacement with nonfunctional fibrous connective tissue (scar tissue), maintaining structural continuity but not function.

Granulation Tissue

The soft, vascular pink tissue formed during early wound repair, composed of proliferating capillary sprouts (angiogenesis), fibroblasts, and temporary type III collagen.

Myofibroblast

A modified fibroblast displaying contractile properties that pulls the edges of a healing wound inward during wound contraction.

Tissue Repair (Wound Healing)

The five-step physiological response to tissue injury: 1. Clot formation, 2. Inflammatory response, 3. Granulation tissue, 4. Maturation and remodeling, 5. Wound contraction.

Necrosis

Premature, pathological tissue death resulting from trauma, toxins, severe infections, or ischemia, accompanied by cellular swelling and inflammation.

Infarction

Sudden localized tissue death resulting from an abrupt, severe loss of arterial blood supply, commonly caused by a thrombus or embolus.

Gangrene

Extensive tissue necrosis resulting from severe arterial ischemia, subdivided into dry gangrene (shriveled, black, ischemic) and wet gangrene (superimposed bacterial infection).

Decubitus Ulcer

A pressure-induced bed sore or form of dry gangrene where prolonged pressure over bony prominences cuts off cutaneous blood flow, producing necrosis.

Apoptosis

Programmed, non-inflammatory cell death in which a cell shrinks, condenses chromatin, undergoes membrane blebbing, and fragments into apoptotic bodies for macrophage clearance.