I. Introduction to Epithelium –provides a barrier between internal and external environments for protection of internal environment against changing environment. Epithelium is ideal due to its unique design.
II. Tissues– a group of cells that work together to perform a function
A. Histology– the study of tissues
B. Epithelial tissue– covers and lines organs; glands
C. Connective tissue– the most abundant tissue that connects, supports, fills spaces and transports materials (e.g. blood).
D. Muscle tissue– contraction and movement
E. Neural tissue– communication, transmits information
III. Location and general function of epithelium
A. Covering body surfaces, lining organs, lining body cavities and passageways
B. Protects underlying structures
C. Some epithelia are impermeable barriers, some are easily crossed, and some are absorptive surfaces
IV. Cellular features of epithelium
A. Tight junctions– region in which adjacent cells are bound together by fusion of the outer phospholipid layer of their cell membranes. It is like a tight zipper that makes it nearly impossible for some substances to pass between cells.
B. Apical (free) and base (attached) surfaces
C. Avascular tissue
D. Regeneration ability
E. Basement membrane –between base of epithelium and underlying connective tissue
V. Solute and water movement across/between epithelial cells; Four features of transport epithelium:
A. Asymmetric distribution of transporters –different membrane proteins at apical vs. basal layers
B. Tight junctions –governs movement between cells
C. Epithelial tissue is diverse –many types specialized to function such as absorption, structural support….
D. Numerous mitochondria –provide energy for high demands of energy involved with transport
E. Transcellular transport– this is when solutes,or water, move across epithelial tissue by traveling through the epithelial cell
F. Paracellular transport– this is when solutes, or water, move between adjacent cells. Tight junctions can only allow smaller molecules (ions, water) to pass through the protein connections
G. Leaky epithelium– these are tissues that frequently permit paracellular transport. Found in kidney, small intestine
H. Tight epithelium– these are tissues that conduct minimal paracellular transport through tight junctions.
I. Water movement follows osmotic forces.Water moves by transcellular and paracellular transport.