and proteoglycans. The presence of those sugars results in a negative
(polyanionic) charge on the luminal surface. Polarity of the epithelial cell is
based on these apical and basolateral specializations of the cell membrane
and is maintained by the zonula occludens of the junctional complex.
79.The answer is c.(Junqueira, p 83. Ross and Pawlina, pp 121, 131–132.)
Distal tubule cells of the kidney and striated duct cells of the submandibu-
lar glands possess prominent basal infoldings that are observed at the light
microscopic level as basal striations. Basal folds are modifications of the
basal region of the cell. These deep infoldings of the basal plasma mem-
brane increase surface area and compartmentalize numerous mitochondria
that provide energy for ionic and water transport. The primary (isotonic)
saliva(answer d)is formed by acinar cells and modified by the striated duct
cells which resorb Na+and excrete K+. Other activities listed (answers a, b
and e)are not directly associated with the basal folds.
80.The answer is a.(Young, pp 86–89. Junqueira, pp 68–70.)The struc-
ture labeled Din the transmission electron micrograph is the macula
adherens (desmosome). It forms a spot weld or rivet between the adjacent
cells and resists shearing forces on the epithelium. The transmission elec-
tron micrograph illustrates a junctional complex between two enterocytes
in the small intestine. Label Arepresents the microvilli, which constitute
the brush border. The brush border is covered by the glycocalyx and in the
small intestine contains enzymes involved in the degradation of food in the
lumen. The structure labeled Bis the zonula occludens, which provides a
tight seal between the epithelial cells. Label Cmarks the zonula adherens,
which interacts with actin which comprises the terminal web (label E).
81.The answer is b.(Alberts, pp 966–968, 1221. Young, p 90. Junqueira, pp 44,
50, 340, 425. Kierszenbaum, pp 7–8, 28–29.)The patient in the scenario presents
with Kartagener’s syndrome, also known as immotile cilia syndrome, and has
cilia that do not function normally. This leads to chronic infections (otitis
media) and infertility (immotile sperm or suboptimal oviductal ciliary function
in females). In that disorder, abnormalities occur in the organization of axone-
mal (ciliary) dynein arms (answer b)that bridge the nine outer doublet micro-
tubules(answer d)to each other. Dynein is a high-molecular-weight ATPase.
When dynein is activated, it produces the sliding motion of the microtubules
as it walks along the adjacent doublet. The protein nexin links the outer micro-
tubular doublets, creating a straplike arrangement of paired microtubules
166 Anatomy, Histology, and Cell Biology