Page 349 - Color Atlas of Biochemistry

340 Tissues and organs

Bone and teeth B. Teeth
The illustration shows a longitudinal section
The family of connective-tissue cells includes
fibroblasts, chondrocytes (cartilage cells), and through an incisor, one of the 32 permanent
teethinhumans. The majority ofthe tooth
osteoblasts (bone-forming cells). They are spe-
cialized to secrete extracellular proteins, par- consists of dentine. The crown of the tooth
extends beyond the gums, and it is covered in
ticularly collagens, and mineral substances,
which they use to build up the extracellular enamel. By contrast, the root of the tooth is
coated in dental cement.
matrix (see p. 346). By contrast, osteoclasts
dissolve bone matter again by secreting H + Cement, dentin, and enamel are bone-like
and collagenases (see p. 342). substances. The high proportion of inorganic
matter they contain (about 97% in the dental
enamel) gives them their characteristic hard-
A. Bone ness. The organic components of cement,
dentin, and enamel mainly consist of collagens
Bone is an extremely dense, specialized form
of connective tissue. In addition to its suppor- and proteoglycans; their most important min-
eral component is apatite, as in bone (see
tive function, it serves to store calcium and
phosphate ions. In addition, blood cells are above).
A widespread form of dental disease, ca-
formed in thebonemarrow. Themost impor- ries, is caused by acids that dissolve the min-
tant mineral component of bone is apatite,a
form of crystalline calcium phosphate. eral part of the teeth by neutralizing the neg-
atively charged counter-ions in apatite (see
Apatites are complexes of cationic Ca 2+
2–
–
2–
matched by HPO 4 ,CO 3 ,OH ,orF – as A). Acids occur in food, or are produced by
microorganisms that live on the surfaces of
anions. Depending on the counter-ion, apatite the teeth (e. g., Streptococcus mutans).
can occur in the forms carbonate apatite
The main product of anaerobic degradation
Ca 10 (PO 4 ) 6 CO 3 ,as hydroxyapatite Ca 10 (PO 4 ) 6 of sugars by these organisms is lactic acid.
(OH) 2 ,or fluoroapatite Ca 10 (PO 4 ) 6 F 2 .In addi-
tion, alkaline earth carbonates also occur in Other products of bacterial carbohydrate me-
tabolism include extracellular dextrans (see
bone. In adults, more than 1 kg calcium is
stored in bone. p. 40)—insoluble polymers of glucose that
Osteoblast and osteoclast activity is con- help bacteria to protect themselves from their
stantly incorporating Ca 2+ into bone and re- environment. Bacteria and dextrans are com-
moving it again. There are various hormones ponents of dental plaque, which forms on in-
2+
salts
adequately cleaned teeth. When Ca
that regulate these processes: calcitonin in- and other minerals are deposited in plaque
creases deposition of Ca 2+ in thebonematrix,
while parathyroid hormone (PTH) promotes as well, tartar is formed.
The most important form of protection
2+
the mobilization of Ca ,and calcitriol im-
proves mineralization (for details, see p. 342). against caries involves avoiding sweet sub-
stances(foodscontaining saccharose, glucose,
The most important organic components of
bone are collagens (mainly type I; see p. 344) and fructose). Small children in particular
and proteoglycans (see p. 346). These form should not have very sweet drinks freely
available to them. Regular removal of plaque
the extracellular matrix into which the apa-
tite crystals are deposited (biomineralization). by cleaning the teeth and hardening of the
dental enamel by fluoridization are also im-
Various proteins are involved in this not yet portant. Fluoride has a protective effect be-
fully understood process of bone formation,
including collagens and phosphatases. Alka- cause fluoroapatite (see A)is particularly re-
sistant to acids.
line phosphatase is found in osteoblasts and
acid phosphatase in osteoclasts. Both of these
enzymes serve as marker enzymes for bone
cells.

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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