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Biomedical subjects

A G Richards

Publications and source records attributed to A G Richards.

18 recordsLinked to original sources
PubMed1977

Ultrastructural changes in intersegmental cuticle during rotation of the terminal abdominal segments in a mosquito.

The terminal abdominal segments of male Aedes aegypti rotate 180 degrees within 24 hr after adult emergence, rotation occurring in the intersegmental membrane between abdominal segments VII and VIII. The ultrastructure of this rotating membrane is compared with non-rotating intersegmental membranes at different developmental stages. The deposition of cuticle in both the rotating and non-rotating intersegments appears ultrastructurally similar, and follows the sequential pattern described for the insects. Shortly after adult emergence, however, disruptive changes occur in the membrane cuticle that are more pronounced in non-rotating intersegments. This disruption occurs initially 1 hr after adult emergence and becomes maximal within 3 hr. Disruption appears to occur by the addition of fluid to the cuticle and results in a ten-fold increase in cuticle thickness in non-rotating intersegments but only a two-fold increase in thickness in the rotating intersement. While in the disrupted condition, the non-rotating intersegmental membranes become extensively folded whereas the cuticle in the rotating intersegment becomes stretched. During rotation, strain forces in the rotating intersegment result in a reorientation of microfibers in the cuticle from parabolic to parallel. This reorientation is presumably brought about by plastic flow.

Abdomen↗
PubMed1976

Dynamic tomography.

Dynamic tomography is a radiographic procedure that allows details in a thin layer within the patient to be examined. This layer can be moved at will throughout the patient. Thus, details lying in an infinite number of layers can be scrutinized one layer at a time. Eight underexposed radiographs are made under rigid controls. Each film receives one fourth of a normal exposure. The "in focus" layer of details is about 0.5 mm. thick. Various future applications of the technique are discussed.

Humans↗
PubMed1976

Ultrastructure of the atypic muscles associated with terminalial inversion in male Aedes aegypti (L).

Two sets of opposed, crossed muscles are present in the rotating region of the abdomen in male A. aegypti. These muscles undergo changes during rotation of the genitalia that suggest they function as the driving force for rotation. During this rotation, one muscle of each set contracts and the opposed one becomes elongated. The contracting muscles are atypic physiologically. They contract from 300 mum to about 69 mum, and this requires a period of 18 to 24 hours. They shorten only once and those muscle fibers still present after the completion of rotation remain in a contracted condition at least for two weeks. The elongated muscles never shorten; they become stretched to approximately 2.5 times their original length and disappear soon after rotation is completed.

Aedes↗