of the intestinal and aortic walls. There are errors in the transcription of
type III collagen mRNA or in translation of this mRNA. Hyperextensible
skin(answer b)occurs in Ehlers-Danlos type VI disorder, in which prob-
lems with the hydroxylation of the amino acid lysine and subsequent cross-
linking result in enhanced elasticity. Type VII Ehlers-Danlos disorder
involves a specific deficiency in an amino terminal procollagen peptidase.
This results from a genetic mutation that alters the propeptide sequence in
such a way that the molecular orientation and cross-linking are adversely
affected. The result is hypermobility (answer c) of synovial joints.
Increased degradation of proteoglycans occurs in osteoarthritis (answer d).
Type I collagen is found in dentin (answer e).
94.The answer is c.(Junqueira, pp 123, 125–127.)The photomicrograph
illustrates the microscopic structure of brown fat. Both types of fat tissue
(brown and white) are highly vascularized and function in protection from
the cold. Brown fat specifically is involved in heat production, whereas white
fat is a true thermal insulator. Brown adipose tissue is multilocular and is
found in the human fetus and neonate. Brown fat is involved in nonshiver-
ing thermogenesis and generates heat (answer c),probably as a protective
device for developing organs in the fetus and neonate. White adipose tissue
is specialized for lipid storage and functions as a thermal insulator (answer b)
and shock absorber. White adipose tissue is unilocular, and the cells have a
single, large lipid droplet in the cytoplasm that provides the “signet-ring”
appearance often described for fat cells. Brown adipose tissue has a multiloc-
ular appearance and is brown because of numerous mitochondria.
In fat, norepinephrine activates the cyclic AMP (answer d)cascade
through adenylate cyclase. Cyclic AMP activates hormone-sensitive lipase,
which removes triglycerides from the stored lipid and hydrolyzes free fatty
acids. In white adipocytes, the released fatty acids and glycerol are
exported from the cells. In brown adipose tissue, the fatty acids are used
within the cell (answer a).However, the electron transport system is
uncoupled from oxidative phosphorylation, which results in the produc-
tion of heat (answer c)instead of ATP. Heat is transferred to the blood by
the extensive capillary networks found in brown adipose tissue.
Shivering(answer e)initiates the mobilization of lipid in white adi-
pose tissue because shivering requires energy.
Connective Tissue Answers 185