The volume of the carotid body and periadventitial type I and type II cells in the carotid bifurcation region of the fetal cat and kitten.

The bilateral distribution of carotid body type I cells was investigated in 6 fetuses (gestational age 95%) and 9 newborn kittens (aged 1 day to 4 days) by serially sectioning the carotid bifurcation regions. In most specimens type I cells occurred in close proximity to the wall of the occipital artery or one of its small proximal branches within a division of connective tissue with definable but irregular borders. This combination of type I cells and connective tissue constituted the principal mass of the carotid body. Using an interacting image analysis system, the area of the carotid body in each serial section was measured by accurately contouring its perimeter. The volume of the carotid body was calculated by multiplying the sum of the areas of the serial sections by the thickness of the section. The volume of the carotid body was 0.052 +/- 0.018 mm3 in the fetuses and 0.025-0.117 mm3 in the 1-4 day old kittens. A degree of symmetry in the values for the volume of the right and left carotid body was found. Caudally, and separate from the principal mass of carotid body type I cells, isolated groups of periadventitial type I cells were noted in the connective tissues around the occipito-ascending pharyngeal trunk, origin of the occipital artery and rostral end of the common carotid artery in 7 out of 12 specimens from fetal cats and 11 out of 18 specimens in newborn kittens. The volumes of the periadventitial groups of cells ranged between 25-1,365 micron3 in fetuses and 10-1,351 micron3 in kittens.