osteogenesis imperfecta with mutations in type I collagen; children with type
I have typical blue sclerae with defects in bone and dentin.
The structure labeled Bis dentin, which consists of mineralized colla-
gen synthesized by odontoblasts. Odontoblasts are derived from the neural
crest. The pulp of a mature tooth (labeled Din the diagram) consists pri-
marily of loose connective tissue rich in vessels and nerves. Odontoblasts
lie at the edge of the pulp cavity and secrete collagen and other molecules,
which mineralize to become dentin (B).Mineralization of the matrix
occurs around the odontoblast processes and forms dentinal tubules.
Ameloblasts, which are ectodermal derivatives, lay down an organic matrix
and secrete enamel, initially onto the surface of the dentin. As hydroxyap-
atite crystals form at the apices of ameloblast (Tomes’) processes, rods of
enamel grow peripherally, and the ameloblasts resorb the organic matrix so
that the enamel layer (A)is almost entirely mineral. It contains nocollagen,
but has unique proteins such as the amelogenins and enamelins.
On eruption of the tooth, enamel deposition is complete and the
ameloblasts are shed. Cementum (E)has a composition similar to that of
bone, is produced by cells similar in appearance to osteocytes, and covers
the dentin of the root. The periodontal ligament (C)consists of coarse col-
lagenous fibers running between the alveolar bone and the cementum of
the tooth and separates the tooth from the alveolar socket. Although the
periodontal ligament suspends and supports each tooth, the ligament per-
mits physiologic movement within the limits provided by the elasticity of
the tissue. It is a site of inflammation in diabetic patients and is affected in
scurvy (recall the image of the 18th century British sailor).
220.The answer is a. (Young, pp 254–257. Junqueira, p 294. Kumar, pp
639–642.)The woman in the scenario suffers from pernicious anemia
resulting from autoantibodies to the parietal cells, which are responsible
for the production of intrinsic factor as well as HCl. The abnormal stage I
Schilling test is indicative of a deficiency in intrinsic factor. Chief cells and
parietal cells are found in the fundus (region A).Chief cells synthesize
pepsinogen and parietal cells produce HCl and intrinsic factor. The gastric
(fundic) glands contain mucous cells, chief cells, and parietal cells. Intrin-
sic factor is required for absorption of vitamin B 12 from the small intestine.
The diagram shows the anatomic relationship between the esophagus,
stomach, and duodenum. The esophagus (C)joins the stomach in the car-
diac region (D).The pylorus (F)contains shorter glands with deeper pits
338 Anatomy, Histology, and Cell Biology