Summary: In vertebrates, short-term imbalances in blood pressure are
regulated by reflex changes in cardiac output and peripheral
resistance, the so-called cardiac limb and peripheral limb of the
baroreflex, respectively. Van Vliet and West (1994) reason that
without this feedback controller the cardiovascular system
would be vulnerable to acute hypertension that could result in
vascular lesions, increased capillary pressures and oedema and
impaired flow autoregulation among other problems.
Baroreflex responses have been identified in many vertebrate
species (see review by Bagshaw, 1985). In reptiles, the anatomy
of baroreceptive fibres as well as their functional responses have
been studied in turtles, lizards and snakes (Stephens et al. 1983;
Millard and Moalli, 1980; Berger et al. 1980; Backhouse et al.
1989). Little is known in crocodilians, although the existence
of a functional baroreflex response is hardly disputed.
In mammals, and probably birds, the existence of myelinated
baroreceptors (with thresholds well below normal arterial
pressures) permits compensation for acute hypotension. This
is believed to protect the tissues from ischaemia, which could
result from a drop in the driving pressure and the high