Cell Processes Lecture 23 Flashcards
Epithelial tissues can be arranged in
single or multiple layers
Epithelial cells form the boundary
between the body’s organs or between the body and the external environment
Epithelial tissue are subject to physical breakdown so
undergo constant and rapid renewal process
Functions of the epithelial tissue
- protection
- filtration
- secretion
- absorption
- excretion
- neuroendocrine function
Glandular Epithelium
- develop from epithelial cells that sink below the epithelium surface during development
- secreting portion of glands
Structure of exocrine glands
- simple or branched structure
- end pieces contain secretory or acini cells
- openings are made of ductile cell (transport properties)
Glandular secretion
Contain 2 types
i) Acinar cells which create a primary secretion rich in organic molecules
ii) Duct cells which modify the composition o the primary secretion by either absorbing or secreting specific ions
What separates epithelial cells from their neighbours
lateral intercellular space
The laminal edges of epithelial cells are held together at
laminal edges
Tight Junctions are composed of
thin bands that encircle the cell and make contact with thin bands from adjacent cells
Tight Junctions act as
A barrier (which restricts the movement of substances through the intercellular spaces between cells) and a fence (which prevents the membrane proteins from diffusing in the plane of the lipid bilayer)
Tight juncions separate epithelial cells into
Apical membrane (faces lumen of the organ or cavity) and Basolateral membrane (that adheres to the adjacent basement membrane and interfaces with the blood)
What are the two ways transport can occur across the cell
Transcellular and Paracellular
What is paracellular transport governed by
laws of diffusion and tightness of junction
What can be measured during paracellular transport
electrical resistance to ion flow through tight junctions (the higher the more tight junctions)
Epithelial tissue can be classifieed as
Leaky epithelium - paracellular transport dominates and Tight epithelium - transcellular transport dominates`
From Proximal —> Distal
- Leaky to tight epithelium
- low to high electrical resistance
- low to high number of strands
- para (bulk) to transcellular (hormonally controlled)
Transcellular transport
primary and secondary active transport in combination with passive diffusion through ion channels to produce transport across the epithelial tissue
Transport can either be
Absorption (lumen to blood) or Secretion ( blood to lumen)
Transepithelial transport can be broken down into
1) entry and exit steps - for absorption entry is apical but for secretion it is the basolateral)
2) electrochemical gradient (entry or exit —> passive or active)
3) electroneutrality (movement of positive or negative ion will attract a counter ion)
4) osmosis
