Human Histology – Epithelial Tissue

Vocabulary flashcards covering key terms and definitions from the lecture on epithelial tissue, including embryonic origins, structural features, junctions, surface specializations, epithelial classifications, and glandular concepts.

Tissue

A group of structurally and functionally related cells sharing a common embryonic origin.

Epithelial Tissue

One of the four basic tissue types; forms coverings, linings, and glands.

Surface Epithelium

Epithelial layer that lines or covers external and internal body surfaces.

Glandular Epithelium

Epithelial cells specialized for secretion; forms exocrine and endocrine glands.

Connective Tissue

Basic tissue type that supports, binds, and protects organs; includes CT proper, bone, cartilage, blood.

Muscle Tissue

Basic tissue type specialized for contraction; skeletal, cardiac, and smooth forms.

Nervous Tissue

Basic tissue type specialized for rapid communication via electrical impulses.

Zygote

Fertilized egg cell; common origin of all body tissues.

Blastocyst

Early embryonic stage that develops from zygote before gastrulation.

Gastrula

Embryonic stage where three germ layers (ectoderm, mesoderm, endoderm) form.

Ectoderm

Outer germ layer; gives rise to epidermis, neurons, pigment cells.

Mesoderm

Middle germ layer; forms muscle, kidney tubules, red blood cells, etc.

Endoderm

Inner germ layer; forms alveolar cells, thyroid, pancreatic cells.

Basement Membrane

Extracellular layer beneath epithelium composed of basal lamina and reticular lamina.

Basal Lamina

Thin sheet of glycoproteins and collagen directly under epithelial cells.

Lamina Fibroreticularis (Reticular Lamina)

Collagen-rich layer attaching basal lamina to underlying connective tissue.

Apical Pole

Surface of an epithelial cell facing the lumen or free space.

Basal Pole

Surface of an epithelial cell in contact with the basement membrane.

Tight Junction (Zonula Occludens)

Most apical cell junction forming a water-tight seal between adjacent cells.

Adherens Junction (Zonula Adherens)

Belt-like junction linking actin filaments of neighboring cells.

Desmosome (Macula Adherens)

Spot junction providing strong adhesion via intermediate filaments.

Gap Junction (Nexus)

Communicating junction allowing passage of ions and small molecules between cells.

Hemidesmosome

Structure anchoring epithelial basal pole to the basal lamina.

Interdigitation

Finger-like lateral membrane infoldings that increase adhesion surface.

Microvilli

1 µm finger-like plasma-membrane extensions that increase apical surface area for absorption.

Cilia (Kinocilia)

7–10 µm motile apical projections specialized for moving mucus or fluid.

Stereocilia

Long, non-motile microvilli; increase surface area, found in epididymis and inner ear.

Flagella

~50 µm long whip-like projection propelling a cell, e.g., spermatozoon.

Basal Infoldings

Deep invaginations of basal plasma membrane enhancing ion transport and absorption.

Simple Epithelium

Single cell layer with all cells touching the basement membrane.

Stratified Epithelium

Two or more cell layers; only basal layer contacts basement membrane.

Simple Squamous Epithelium

Single layer of flat cells; lines alveoli, serous cavities (mesothelium), blood vessels (endothelium).

Simple Cuboidal Epithelium

Single layer of cube-shaped cells; forms kidney tubules, gland ducts, ovary surface.

Simple Columnar Epithelium

Single layer of tall cells; lines digestive tract, gallbladder; ciliated form in bronchi, uterine tubes.

Pseudostratified Epithelium

Single layer of varying-height cells that appear stratified; ciliated in trachea (respiratory epithelium).

Stratified Squamous Epithelium

Many layers; apical cells flat. Keratinized in skin, non-keratinized in mouth, esophagus, vagina.

Stratified Cuboidal Epithelium

2–3 layers of cuboidal cells; lines ducts of sweat, mammary, salivary glands.

Stratified Columnar Epithelium

Rare epithelium with columnar superficial cells; found in conjunctiva, large ducts.

Transitional Epithelium

Stratified epithelium with dome-shaped surface cells; stretches in ureter and bladder.

Gland

Organized epithelial tissue specialized for secretion.

Exocrine Gland

Gland that releases secretions onto an epithelial surface via ducts.

Endocrine Gland

Ductless gland that releases hormones into the bloodstream.

Unicellular Gland

Single secretory cell within epithelium; e.g., goblet cell.

Goblet Cell

Cup-shaped unicellular gland secreting mucin in respiratory and intestinal tracts.

Multicellular Gland

Gland composed of duct plus secretory units.

Simple Gland

Exocrine gland whose duct does not branch.

Compound Gland

Exocrine gland with branched duct system.

Tubular Secretory Unit

Glandular end piece shaped like a tube; may be straight, coiled, branched.

Acinar (Alveolar) Unit

Rounded secretory end piece resembling a sac; common in pancreas, parotid.

Tubuloacinar Gland

Gland containing both tubular and acinar secretory portions.

Mucous Acini

Secretory units producing viscous, glycoprotein-rich mucin that hydrates to mucus.

Serous Acini

Secretory units producing thin, enzyme-rich watery fluid; cytoplasm basophilic.

Mixed Acini

Secretory units containing both mucous and serous cells; may show serous demilunes.

Myoepithelial Cell

Contractile stellate cell surrounding secretory acini and ducts; aids in expelling secretions.

Merocrine Secretion

Exocytosis of secretory product with no loss of cell membrane or cytoplasm.

Apocrine Secretion

Release of apical cytoplasm together with secretory product; e.g., ceruminous glands.

Holocrine Secretion

Discharge of entire cell contents following cell destruction; e.g., sebaceous glands.

Artifact

Minor structural distortion in tissue sections caused by preparation steps.

Longitudinal Section (l.s.)

Tissue slice cut parallel to the organ’s long axis.

Cross / Transverse Section (c.s. or t.s.)

Tissue slice cut perpendicular to the long axis of the organ.

Oblique Section

Tissue slice cut at an angle between longitudinal and cross sections.