162
Epithelium
Answers
73.The answer is b.(Young, p 91. Junqueira, pp 68–70, 72.)The child in
the vignette suffers from microvillous inclusion disease (MID) which
results in the absence of microvilli in the small intestinal absorptive cell
(enterocyte) brush border (apical structure labeled between the arrows in
the photomicrograph). MID is associated with an inability to absorb even
simple nutrients; the disease presents as refractory diarrhea in the newborn
period with chronic dependency on total parenteral nutrition. In MID,
microvilli are found as inclusions in the apical enterocyte. Microvilli
increase surface area for specialized uptake of molecules by pinocytosis,
receptor-mediated endocytosis, and phagocytosis. The microvilli also con-
tain the brush border enzymes such as lactase and alkaline phosphatase.
Microvilli are supported by a core of microfilaments and are capable of
movement; however, cilia (answer a)function in the movement of sub-
stances, such as mucus and foreign material, over the surface. Cell move-
ment is controlled by interactions between the cytoskeleton and the
extracellular matrix (answer c),while microtubules facilitate organellar
movement within the cytoplasm (answer d).Transitional epithelium char-
acteristic of the urinary system facilitates distensibility and stretch (answer e).
A table listing functions and locations of epithelia is provided below.
Simple
Simple squamous Endothelium of blood vessels Transport, absorption, secretion
Simple cuboidal Collecting ducts of kidneys Transport, reabsorption, secretion
Simple columnar Epithelium of the gut: stomach, Absorption, protection,
intestines lubrication (mucus)
Stratified
Stratified cuboidal Sweat ducts Transport
Stratified columnar Excretory ducts of salivary Transport
glandsEPITHELIAL TYPES, LOCATION,AND FUNCTION
Epithelial Type Location Function(Continued)