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Epithelial cell shape classifications

Squamous (flattened)
Cuboidal (roughly cube-shaped)
Columnar (pillar-shaped)


Epithelial cell layering classifications

Simple - single layer
Stratified - multi-layered


Epithelial cell classifications

Simple squamous
Simple cuboidal
Simple columnar
Stratified squamous


Explain the pseudostratified classification

- Falsely stratified
- Looks multi-layered but surface cells have contact with basal lamina


Two forms of cell-cell junctions

Zonulae (belts)
Maculae (spots)


Types of junction

Tight junctions
Adhesion belts
Gap junctions


Features of tight junctions

- Occluding junction
- Seals paracellular pathways
- Prevents molecules moving through space between cells
- Junction type closest to apex of cell
- Allows cells to establish and maintain apical-basolateral polarity by preventing mixing of proteins/lipids between different plasma membrane compartments


Features of adhesion belts

- Adherens junction
- Usually formed just basal to apical tight junction
- Transmembrane adhesion molecule is cadherin
- Cadherins associate with the actin cytoskeleton
- Controls assembly of other junctions
- "Master junction"


Cadherin properties

Part of a family of Ca2+ ion-dependent cell adhesion molecules


Features of desmosomes

- Spot junction
- Found at multiple points between adjacent cell membranes
- Linked to intermediate filament cytoskeleton
- Provides mechanical continuity between cells


Features of gap junctions

- Spot junction
- Clusters of pores
- Each pore formed of 6 identical subunits in membrane
- Pores are continuous with pores in adjacent cell membrane
- Allow passage of ions and small molecules between cells
- Opening and closing pores controls intercellular communication


Role of polarity in epithelial cells

Polarity in these cells allows functions to be unidirectional.
Difference in polarity between apical and basolateral domain allows direction to be established


Functions of epithelial cells

- Secretion (endocrine/exocrine)
- Fluid and solute transport
- Absorption
- Protection


Process of exocrine secretion

Secretory granules in apical domain move to and fuse with apical membrane to release contents into lumen or duct
- Golgi apparatus in middle of cell
- Extensive rough ER in basal cytoplasm


Process of endocrine secretion

Secretory granules in basolateral domain move to and fuse with apical membrane to release contents into bloodstream
- Golgi apparatus in middle of cell
- Extensive rough ER in the apical cytoplasm


Adaptations of epithelial cells for fluid and solute transport

- Passive transport of water and ions through ion and water channels in apical membrane
- Basal membrane has active transport transporters
- Many mitochondria in basolateral domain to supply energy to active transporters
- Transport direction apical to basal towards blood vessel


Adaptations of epithelia cells for absorption

- Microvilli increase SA
- Villi on small intestine surface increase SA
- Villi covered with intestinal epithelial cells
- Nutrient-transporting carriers found in microvillous brush-border membranes


Polarisation of fluid and transporting epithelia

- Ion pumps and channels have apical-basolaterla polarisation in plasma membrane
- Polarisation of transporter allows directional flow of fluids and ions
- Flow differs depending on function of cell (blood vessel to extracellular or other way round)


Polarisation of secretory epithelial cells

- Secretion polarised to ensure that secreted products are delivered to correct tissue compartment
- Unpolarised cells would have vesicles fusing and secreting their contents from nearest membrane regardless of function


Small intestinal epithelial cell turnover rate

Turnover every 3-5 days


Colon epithelial cell turnover rate

Turnover every 5-7 days


Epidermis (epithelium of the skin) turnover rate

48 days but dependent on region


Division process of epithelial cells in small intestine

- Cells lost from villus tip
- New cells produced by crypt stem cells


Differences between villus and Crypt of Leiberkhun

Villus - fold of cells of epithelia that extends out into lumen of small intestine
Crypt of Leiberkhun - Opposite of villus, epithelia invaginates away from lumen of small intestine lined with stem cells that produce new epithelial cells


Relationship of cell loss and cell production when cell turnover is steady

Cell loss = cell production


Relationship of cell loss and cell production when cell turnover causes a reduction in tissue mass

Cell loss > cell production


Relationship of cell loss and cell production when cell turnover causes and increase in tissue mass

Cell loss < cell production


Nerve cell types and their functions

Neurones - Excitable cells involved in communication
Astrocytes - Support neurones, involved in cell repair and neurotransmitter reuptake
Oligodendrocytes - Myelin production for CNS cells
Schwann cells - Myelin production for peripheral nerve cells
Microglial cells - Perform immune functions in CNS
Ependymal cells - Regulate production and movement of cerebrospinal fluid (CSF)


Neurone components



Intercellular communication process in neurones

- Occurs at synapses
- Arrival of action potential at axon terminal triggers Ca2+ influx, triggers exocytosis of vesicles containing neurotransmitter molecules
- Neurotransmitters released into synaptic cleft and bind to receptors located on postsynaptic membrane
- Neurotransmitter broken down in synapse or recycled into pre-synaptic knob


Process by which the resting membrane potential of a neurone is established

- High extracellular Na+
- High intracellular K+
- Established by Na+/K+ pump
- Depolarisation occurs = Na+ flows in through open voltage-gated sodium channels
- Repolarisation occurs = K+ flows out through open voltage-gated potassium channels
- Resting membrane potential restored


What is an action potential

A depolarisation of a nerve cell leading to the transmission of a signal


By what methods are action potentials propagated along axons?

Cable transmission
Saltatory conduction