72). THE CAROTID BODY

[Editor]

a) is more responsive to Pa02 than 02 content
b) responds to changes in pH
c) may respond to reduced perfusion
d) has chemoreceptor cells
e) has a lower blood flow per ml tissue when compared to the brain

[Editor]

ttttf

Carotid body-chemoreceptors above the carotid bifurcation on each side. Rate of discharge is increased by reduced O2 delivery (reduced PO2 or reduced cardiac output) or by impaired utilisation of O2 (e.g. due to cyanide poisoning). The rate of discharge increases greatly below arterial PO2 of 13.3kPa (100mmHg). Discharge is also increased by a rise in arterial PCO2 or fall in arterial pH. Each carotid body receives 0.04ml blood/min (2L/100g tissue/min), which is the highest blood flow per 100g tissue in the body. Because of this, dissolved O2 alone is not enough to provide the requirement for O2. As a result discharge is NOT increased by anaemia or CO poisoning where O2 carriage by Hb is reduced but arterial PO2 is not.