Search PubMed⌕ Search

Biomedical subjects

A Bennett

Publications and source records attributed to A Bennett.

At least 271 records · Page 15Linked to original sources
PubMed1975

The intrinsic innervation of the human alimentary tract and its relation to function.

The intrinsic innervation of the human gut has been studied in strips of circular and longitudinal muscle removed at operation. Electrical stimulation of the nerves at a wide range of frequencies (0-1 to 128 Hz) can evoke a variety of responses due to activation of four types of nerves. There is evidence for cholinergic, adrenergic, non-adrenergic inhibitory, and non-cholinergic excitatory fibres, which may be stimulated at different frequencies. The various regions of the alimentary tract, and even the muscle layers within a region, may respond differently to nerve stimulation. This is most marked at 4 Hz and the observed differences correlate with the function of each part and its dependence on extrinsic innervation. The stomach is relatively insensitive to electrical stimulation, and this is consistent with its reliance on vagal innervation. The dominant excitatory responses in the longitudinal muscle of the oesophagus and ileum correlate with their high motility and propulsive function, whereas the dominant inhibitory responses in the colon correlate with its lower motility and storage function.

Acetylcholine↗
PubMed1973

Complementary chromatic adaptation in a filamentous blue-green alga.

Fluorescent and red light environments generate greatly different patterns of pigmentation and morphology in Fremyella diplosiphon. Most strikingly, red-illuminated cultures contain no measurable C-phycoerythrin and have a mean filament length about 10 times shorter than fluorescent-illuminated cultures. C-phycoerythrin behaves as a photoinducible constituent of this alga. Spectrophotometric and immunochemical procedures were devised so that C-phycoerythrin metabolism could be studied quantitatively with [(14)C]-phenylalanine pulse-chased cultures. Transfer of red-illuminated cultures to fluorescent light initiates C-phycoerythrin production by essentially de novo synthesis. C-phycoerythrin is not degraded to any significant extent in cultures continuously illuminated with fluorescent light. Transfer of fluorescent-illuminated cultures to red light causes an abrupt cessation of C-phycoerythrin synthesis. The C-phycoerythrin content of cultures adapting to red light decreases and subsequently becomes constant. Loss of C-phycoerythrin is not brought about by metabolic degradation, but rather by a decrease in mean filament length which is effected by transcellular breakage. In this experimental system, light influences intracellular C-phycoerythrin levels by regulating the rate of synthesis of the chromoprotein.

Adaptation, Physiological↗
PubMed1973

Prostaglandin E2 and gastric acid secretion in man.

1. Extracts of human stomach homogenized in Krebs solution had more PGE(2)-like activity than tissue homogenized in acid/ethanol or in the presence of indomethacin, indicating that the tissue can synthesize PGE(2).2. The distribution and synthesis of PGE(2)-like substance in human stomach was determined by extracting frozen sections cut parallel to the mucosal surface. Peak levels usually occurred at a depth of 0-600 mum in the mucosa.3. Small amounts of a PGE(2)-like substance were present in basal gastric juice, and its concentration was usually even lower in secretion stimulated by pentagastrin or histamine.4. Submaximal acid secretion produced by I.V. infusion of pentagastrin generally fell slightly when indomethacin was administered rectally to inhibit PG synthesis.5. These experiments, together with the findings that orally administered PGE compounds do not inhibit human gastric acid secretion, seem to argue against a possible inhibitory role for PGE(2) in gastric acid secretion in man.6. If this is so, it would follow that gastric bleeding caused by aspirin-like drugs is not due to increased acid secretion. A hypothesis is presented that tissue damage following vasoconstriction and ischaemia, due to inhibition of PG synthesis in blood vessels, contributes to the bleeding.

Gastric Juice↗