Epithelial Tissue Overview

Study Notes

Epithelial Tissue

One of the four basic tissue types in the body (along with connective tissue, muscle, and nervous tissue).
Forms glands and lines the inside and outside of the body.
Epithelial cells are anchored to a basement membrane.
Epithelial tissue lacks extracellular matrix, meaning the cells are packed closely together.
Avascular, meaning it does not contain blood vessels. Receives nutrients and oxygen through diffusion from capillaries in the underlying connective tissue.

Classifications of Epithelium

Simple Squamous Epithelium:
- Single layer of flat, scale-like cells.
- Functions:
  - Diffusion
  - Filtration
  - Lubrication
- Locations:
  - Alveoli (for gas exchange)
  - Glomerulus (in the kidney, for filtration)
  - Lining of blood vessels (endothelial cells)
Simple Cuboidal Epithelium:
- Single layer of cube-shaped cells.
- Functions:
  - Absorption
  - Secretion
- Locations:
  - Nephron (tubules in the kidney)
  - Glands (e.g., sweat glands, liver, pancreas)
Simple Columnar Epithelium:
- Single layer of tall, thin cells.
- Functions:
  - Absorption
  - Secretion
  - May have cilia for moving fluid across apical surface
- Locations:
  - Gastrointestinal tract (stomach to anus)
  - Glands
  - Airways
  - Uterus and uterine tube
Stratified Squamous Epithelium:
- Multiple layers of cells, with the apical cells being flat.
- Function: Protection against abrasion
- Locations:
  - Epidermis (skin)
  - Esophagus
  - Vagina
- Two types:
  - Keratinized: Contains keratin, a tough protein, for added protection against water; apical cells lack nuclei.
  - Non-keratinized: Does not contain keratin; apical cells have nuclei.
Transitional Epithelium (Urothelium):
- Specialized stratified epithelium found only in the urinary system.
- Apical cells are dome-shaped and can stretch and distend.
- Function: Allows for the stretching and distension of the urinary system (e.g., bladder).
- Locations:
  - Urinary system (ureter, bladder, proximal urethra)
Pseudostratified Ciliated Columnar Epithelium (Respiratory Epithelium):
- Appears stratified, but all cells are anchored to the basement membrane.
- Ciliated, with cilia projecting from the apical surface.
- Function:
  - Secretion (mainly mucus)
  - Propulsion of mucus by cilia
- Location:
  - Respiratory system (trachea, proximal bronchi)

Cilia and Microvilli

Cilia:
- Hair-like projections located on the apical surface of cells.
- Function: Move liquid over the surface of the cell (like a crowd surfing at a concert)
Microvilli:
- Finger-like projections located on the apical surface of cells.
- Function: Increase surface area for absorption.

Surface Area & Absorption

Microvilli increase surface area for absorption in the jejunum
Brush border is a term for the appearance of the microvilli which resemble a hairbrush
The jejunum is where amino acids, simple sugars, and fats are absorbed

Epithelial Tissues

Simple squamous epithelium is one layer of flat cells (e.g., Bowman's capsule from the glomerulus)
Simple cuboidal epithelium is one layer of cube-shaped cells (the nucleus rounds out the cell)
Simple columnar epithelium is one layer of tall, thin cells (the tall nuclei are a key identifier)
Pseudostratified ciliated columnar epithelium is one layer of cells that appears stratified. The key identifier is the presence of cilia projecting from the cell surface (e.g., Respiratory epithelium)
Stratified squamous keratinized epithelium is multiple layers of cells with the top layer flat and no nuclei
Stratified squamous non-keratinized epithelium is multiple layers of cells with the top layer containing nuclei.
Nucleus is located typically in the center of cells.

Description

Explore the fundamental aspects of epithelial tissue, one of the four basic tissue types in the body. This quiz covers its classifications, functions, and locations, providing insights into simple squamous and cuboidal epithelium. Test your knowledge on how epithelial cells contribute to various physiological processes.