and at times the diverticulum remains attached to the umbilicus by a
connective tissue stalk, as is mostly likely the case here. The diverticu-
lum generally extends 2 inches from the ileum; about 2 ft from the ileo-
cecal valve and usually manifests itself by bleeding prior to the first 2
years of life. There may be two types of ectopic tissue present in the
diverticulum: either acid secreting epithelium (stomach; detected with
radioactive technetium injected into the venous blood stream which
then accumulates within the diverticulum) or pancreatic epithelium.
(The rule of “2” helps remind you of the characteristics of Meckel’s
diverticulum.) The appendix (answer a)is a diverticulum off the
cecum,notthe ileum. Diverticuli (answer c)can cause blood in the
stool but would be extremely rare in a toddler. Internal hemorrhoids
(answer d)would generally be detected in a rectal exam, especially in a
toddler and is notassociated with “currant jelly” stools. The blood would
more likely be black if a duodenal ulcer (answer e)were present, which
would also be very rare in a toddler.
391.The answer is b.(Sadler, pp 229–231.)The kidney forms in three
stages. The pronephric, metanephric, and mesonephric kidneys all form from
the urogenital ridge, an extension of intermediate mesoderm into the
coelomic cavity. Mesoderm derived from the somites (somatic; answer a)
gives rise to components of the axial skeleton and associated muscle and
connective tissues. Splanchnic lateral plate mesoderm (answer c)gives rise
to the smooth muscle and connective tissue tunics of the abdominal viscera.
Somatic lateral plate mesoderm (answer d)contributes substantially to the
skeleton, connective tissue, and muscle mass of the appendages. Neural
crest (answer e)forms the sensory and sympathetic chain ganglia and
other structures.
392.The answer is a.(Moore and Dalley, pp 63–64, 320.)The adrenal
medulla is innervated from thoracic levels of the spinal cord mediated by
preganglionic sympathetic nerve fibers traveling in the lesser and least
splanchnic nerves, with some contribution from the greater splanchnic
and lumbar splanchnic nerves [thus not (answer b)]. Because both the
adrenal medulla and postganglionic sympathetic neurons are adrenergic
and derived from neural crest tissue, the homology of the chromaffin
cells and postganglionic sympathetic neurons is apparent. There appears
to be noparasympathetic innervation (answers c and d)to the adrenal
522 Anatomy, Histology, and Cell Biology