Epithelial Tissue Structure and Development

Composed of tightly packed cells with minimal intercellular substance
Cells are connected by specialized junctions (e.g. tight junctions, adherens junctions, desmosomes)
Apical surface: exposed to outside environment or lumen of an organ
Basal surface: attached to basement membrane
Lateral surface: adjacent to neighboring cells

Cancer: abnormal cell growth and proliferation, often originating from epithelial cells (e.g. carcinomas)
Epithelial dysplasia: abnormal cell growth and differentiation
Epithelial-mesenchymal transition (EMT): epithelial cells acquire mesenchymal characteristics, often associated with cancer progression and fibrosis

Barrier function: protection from external environment and regulation of ion and water transport
Secretion and absorption: production and uptake of substances (e.g. hormones, enzymes, nutrients)
Sensory function: reception of stimuli (e.g. light, sound, touch)
Exocrine function: production and secretion of substances (e.g. sweat, saliva, mucus)

Simple epithelium: single layer of cells, often lining cavities and glands
- Squamous epithelium: flat, scale-like cells (e.g. skin, lungs)
- Cuboidal epithelium: cube-shaped cells (e.g. kidney tubules)
- Columnar epithelium: tall, column-shaped cells (e.g. intestine)
Stratified epithelium: multiple layers of cells, often providing additional protection
- Stratified squamous epithelium: multiple layers of flat cells (e.g. skin, vagina)
- Transitional epithelium: multiple layers of cells that can stretch (e.g. bladder)
Pseudostratified epithelium: single layer of cells with nuclei at different heights, giving a layered appearance
- Pseudostratified ciliated epithelium: cilia and microvilli on surface (e.g. respiratory tract)
Specialized epithelium: modified to perform specific functions
- Keratinized epithelium: thickened, keratinized cells (e.g. skin)
- Neuroepithelium: specialized for sensory reception (e.g. retina, cochlea)

Epithelial cells are tightly packed with minimal intercellular substance
Specialized junctions (tight junctions, adherens junctions, desmosomes) connect cells
Cells have distinct apical, basal, and lateral surfaces

Epithelial tissue develops from all three primary germ layers: ectoderm, endoderm, and mesoderm
Embryonic ectoderm and endoderm give rise to epithelial tissue
Signaling pathways and transcription factors influence epithelial development during embryogenesis

Cancer originates from abnormal epithelial cell growth and proliferation
Epithelial dysplasia: abnormal cell growth and differentiation
Epithelial-mesenchymal transition (EMT) is associated with cancer progression and fibrosis

Epithelial tissue provides a barrier function, regulating ion and water transport
It facilitates secretion and absorption of substances (e.g., hormones, enzymes, nutrients)
Epithelial tissue has sensory functions, receiving stimuli (e.g., light, sound, touch)
Exocrine function involves production and secretion of substances (e.g., sweat, saliva, mucus)

Simple Epithelium
- Squamous epithelium: flat, scale-like cells (e.g., skin, lungs)
- Cuboidal epithelium: cube-shaped cells (e.g., kidney tubules)
- Columnar epithelium: tall, column-shaped cells (e.g., intestine)
Stratified Epithelium
- Stratified squamous epithelium: multiple layers of flat cells (e.g., skin, vagina)
- Transitional epithelium: multiple layers of cells that can stretch (e.g., bladder)
Pseudostratified Epithelium
- Pseudostratified ciliated epithelium: cilia and microvilli on surface (e.g., respiratory tract)
Specialized Epithelium
- Keratinized epithelium: thickened, keratinized cells (e.g., skin)
- Neuroepithelium: specialized for sensory reception (e.g., retina, cochlea)

Epithelial tissue is composed of tightly packed cells with minimal intercellular substance
Cells are connected by specialized junctions such as tight junctions, adherens junctions, and desmosomes
The apical surface of epithelial cells is exposed to the outside environment or lumen of an organ
The basal surface of epithelial cells is attached to the basement membrane
The lateral surface of epithelial cells is adjacent to neighboring cells

Epithelial tissue is derived from all three primary germ layers: ectoderm, endoderm, and mesoderm
Epithelial tissue develops from embryonic ectoderm and endoderm
Signaling pathways and transcription factors play a crucial role in the development of epithelial tissue during embryogenesis

Cancer often originates from epithelial cells, characterized by abnormal cell growth and proliferation
Epithelial dysplasia is a condition characterized by abnormal cell growth and differentiation
Epithelial-mesenchymal transition (EMT) is a process where epithelial cells acquire mesenchymal characteristics, often associated with cancer progression and fibrosis

Epithelial tissue provides a barrier function, protecting the body from the external environment and regulating ion and water transport
Epithelial tissue is involved in secretion and absorption, producing and taking up substances such as hormones, enzymes, and nutrients
Epithelial tissue has a sensory function, receiving stimuli such as light, sound, and touch
Epithelial tissue has an exocrine function, producing and secreting substances such as sweat, saliva, and mucus

Simple epithelium is a single layer of cells, often lining cavities and glands
- Squamous epithelium is composed of flat, scale-like cells, found in tissues such as skin and lungs
- Cuboidal epithelium is composed of cube-shaped cells, found in tissues such as kidney tubules
- Columnar epithelium is composed of tall, column-shaped cells, found in tissues such as the intestine
Stratified epithelium is composed of multiple layers of cells, often providing additional protection
- Stratified squamous epithelium is composed of multiple layers of flat cells, found in tissues such as skin and vagina
- Transitional epithelium is composed of multiple layers of cells that can stretch, found in tissues such as the bladder