FOH 2014:epithelia

Section I: The anatomy of the cell       
#1 Cellular organization        #2 Membranes & surfaces        #3: Cytoskeleton        #4: Cell contacts       
#5: The cytoplasm & its organelles        #6: Nucleus, cell cycle, turnover & death       
Section II: General histology       
#7: Skin deep (and beyond) – epithelia        #8: Keeping it all together – connective tissues       
#9: Think about it – neural tissues        #10: Make a muscle       

#7: Skin deep (and beyond) – epithelia

Surface epithelia
Today's main learning objective was to identify features characteristic of epithelia, specifically of surface epithelia, and relate those morphological features to the respective functions. During the practical class we looked at five different slides:

• renal papilla
  
• cornea
  
• epidermis (finger)
  
• respiratory epithelium (pharynx)
  
• urothelium (urinary bladder).
  

Renal papilla
Locate a collecting duct (wide lumen), and note the one-layered cubic (iso-prismatic) epithelium. These cells sit atop a basal lamina (not visible by light microscopy; only its correlate, the basal membrane [basal lamina + lamina fibroreticularis] can be seen). Collecting ducts participating in regulating urinary excretion and content. ADH (adiuretin) = vasopression secreted from the dorsal pituitary lobe hormonally regulates the water conduction ability of the apical plasma membrane. Other single-layered epithelia ("epithelium simplex") can be found in some renal tubuli and in the mesothelium covering the ovary.

Cornea
Corneal EPIthelium (toward the outside world) regenerates within 7 days. While it is multi-layered, one needs to be able to see through, so obviously it is non keratinizing epithelium. The corneal ENDOthelium (single layer; toward the anterior chamber of the eye) does not regenerate. Aquaporins in corneal endothelium regulate the water content of the stroma. The stroma is the layer in between the corneal epithelium and the endothelium, more precisely between the Bowman membrane (under epithelium) and the Descemet membrane (under endothelium). The Descemet membrane mainly consists of collagen type VIII. Increased water content of the stroma (e.g. due to relatively less corneal endothelial cells due to aging) results in turbidity/ loss of transparency of the cornea, potentially requiring corneal transplants.

Epidermis (finger)
Corneal

Respiratory epithelium (pharynx)
Corneal Corneal

Urothelium (urinary bladder)
Corneal

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