around the central microtubule doublet. The radial spokes (answer c)restrain
the sliding movement of the outer doublets, so those doublets are held in place
and sliding is limited lengthwise. The inner sheath (answer a)surrounds the
central microtubule doublet (answer e).The basal body that anchors the
microtubules also plays an essential role in converting the sliding of the outer
microtubules into the bending of the cilium.
Bronchiectasis is the irreversible, abnormal dilation of one or more
bronchi associated with various lung conditions, commonly accompanied by
chronic infection. In Kartagener’s syndrome it has been found that uncoordi-
nated dyskinesia is more prevalent than immotile cilia. There is therefore a
movement in the literature to call this syndrome primary ciliary dyskinesia
(PCD), and Kartagener’s syndrome would be a subclassification of that group
of disorders. Dextrocardia (cardiac apex to the right) occurs in mild cases and
situs inversus in more severe cases. In situs inversus, the morphologic right
atrium is on the left, and the morphologic left atrium is on the right. Pul-
monary structures (i.e., right and left lungs) as well as abdominal organs may
also be reversed in a mirror image of normal. The development of right-left
asymmetry is at least partially regulated by ciliary beat at Hensen’s node.
The saccharin test is a test of nasal mucociliary clearance. It is carried
out by placing a small amount of saccharin behind the anterior end of the
inferior turbinate. In the presence of normal mucociliary action, the sac-
charin will be swept backward to the nasopharynx and a sweet taste per-
ceived. Failure of sweetness to be detected within about 20 minutes
indicates delayed mucociliary clearance.
82.The answer is e.(Kierszenbaum, pp 7–8, 28–29. Alberts, pp 966–968,
Junqueira, pp 44, 46. Ross and Pawlina, pp 104–106.)Nexin, the radial spokes,
and the basal body all play a role in restricting the sliding motion and con-
verting it to the bending of the axoneme in relation to the basal body. 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
(answer a).The basal body (answer b)anchors the microtubules and also
plays an essential role in converting the sliding of the outer microtubules into
the bending of the cilium. The basal bodies resist the sliding movement gen-
erated by dynein activation. Nexin (answer c)links the outer microtubular
doublets, creating a strap-like arrangement of paired microtubules around the
central microtubule doublet. The radial spokes hold the microtubule doublets
in place, and sliding is limited lengthwise. The radial spokes (answer d)are
rigid and do not slide against nexin.
Epithelium Answers 167