Anatomy and Physiology: Chapter 05 Histology Review

A comprehensive collection of vocabulary terms covering histology basics, epithelial and connective tissues, excitable tissues, cell junctions, and tissue growth/repair based on the Chapter 05 lecture outline.

Histology

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

Organ

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

Matrix

The extracellular material of a tissue, composed of fibrous proteins and a clear gel called ground substance or tissue fluid.

Ectoderm

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

Endoderm

The inner primary germ layer that gives rise to the mucous membrane lining the digestive and respiratory tracts and digestive glands.

Mesoderm

The middle primary germ layer that becomes a gelatinous tissue called mesenchyme, eventually giving rise to cartilage, bone, and blood.

Fixative

A chemical such as formalin used to prevent decay and preserve histological specimens.

Longitudinal Section ($l.s.$ )

A tissue specimen cut on its long axis.

Cross Section ($c.s.$ or $x.s.$ )

A tissue specimen cut perpendicular to the long axis of an organ; also called a transverse section ($t.s.$ ).

Simple Epithelium

A tissue consisting of only one layer of cells, where every cell touches the basement membrane.

Stratified Epithelium

A tissue consisting of $2$ to $20$ or more layers of cells, where some cells rest on top of others and do not touch the basement membrane.

Goblet Cells

Wineglass-shaped mucus-secreting cells found in simple columnar and pseudostratified epithelia.

Basement Membrane

The layer between an epithelium and the underlying connective tissue that anchors the epithelium.

Keratinized Stratified Squamous Epithelium

A tissue found on the skin surface covered with a layer of compact, dead squamous cells to resist abrasion and retard water loss.

Transitional Epithelium

A multilayered epithelium with surface cells that change from round to flat when stretched, allowing the filling of the urinary tract.

Fibroblasts

Large, flat cells in fibrous connective tissue that produce the fibers and ground substance of the matrix.

Macrophages

Cells that arise from monocytes to phagocytize foreign material and activate the immune system when they sense antigens.

Collagenous Fibers

Tough, flexible, and stretch-resistant fibers made of the body's most abundant protein ($25\%$ ).

Glycosaminoglycans (GAGs)

Long polysaccharides that regulate water and electrolyte balance in tissues; examples include chondroitin sulfate and heparin.

Areolar Tissue

A loose connective tissue with loosely organized fibers and abundant blood vessels that underlies nearly every epithelium.

Reticular Tissue

A mesh of reticular fibers and fibroblasts that forms the supportive stroma (framework) for lymphatic organs.

Dense Regular Connective Tissue

Tissue with densely packed, parallel collagen fibers found in tendons and ligaments.

Adipose Tissue

A tissue in which adipocytes (fat cells) are the dominant cell type, serving as the body's primary energy reservoir.

Chondroitin Sulfate

The most abundant GAG in the matrix of cartilage, responsible for its stiffness.

Lacunae

Small cavities in the matrix of cartilage or bone that house chondrocytes or osteocytes.

Perichondrium

A sheath of dense irregular connective tissue that surrounds elastic and most hyaline cartilage.

Osteon

A structural unit of compact bone consisting of a central canal and its surrounding concentric lamellae.

Canaliculi

Delicate canals radiating from each lacuna in bone, allowing osteocytes to contact each other.

Formed Elements

The cellular components of blood, including erythrocytes ($RBCs$ ), leukocytes ($WBCs$ ), and platelets.

Neurosoma

The cell body of a neuron which houses the nucleus and other organelles.

Intercalated Discs

Electrical and mechanical connections that join cardiomyocytes end to end in cardiac muscle.

Tight Junction

A linkage between adjacent cells by transmembrane cell-adhesion proteins that seals off the intercellular space.

Desmosome

A patch-like cell junction that holds cells together to resist mechanical stress, similar to a clothing snap.

Exocrine Glands

Glands that maintain contact with the body surface or a cavity by way of a duct.

Endocrine Glands

Ductless glands that secrete hormones directly into the blood.

Parenchyma

The cells of a gland that perform the actual tasks of synthesis and secretion.

Merocrine Secretion

A mode of secretion using vesicles that release their products by exocytosis; also called eccrine secretion.

Holocrine Secretion

A mode of secretion where cells accumulate a product until they disintegrate, releasing a mixture of cell fragments and substance.

Hyperplasia

Tissue growth achieved through cell multiplication (increasing the number of cells).

Differentiation

The development of a more specialized form and function by unspecialized tissue.

Metaplasia

The process of changing from one type of mature tissue to another.

Totipotent Stem Cells

Embryonic stem cells with the potential to develop into any type of fully differentiated human cell, including accessory organs of pregnancy.

Regeneration

The replacement of dead or damaged cells by the same type of cell as before, restoring normal function.

Fibrosis

The replacement of damaged cells with scar tissue, which holds organs together but does not restore function.

Atrophy

The shrinkage of a tissue through a loss in cell size or number, often due to aging or disuse.

Necrosis

Pathological tissue death due to trauma, toxins, or infections.

Apoptosis

Programmed cell death for cells that have completed their function; involves the activation of the Fas receptor.