Beginning in May 1921 at the University of Toronto, Frederick Banting and Charles Best set out to isolate the hormone that would become insulin. Their method involved surgically tying off a duct in dogs before extracting tissue from the pancreas. Why did they tie off that duct first, and which pancreatic tissue were they trying to preserve?
- Tying off the duct redirected digestive enzymes into the bloodstream, which they needed in order to isolate insulin from the blood rather than from pancreatic tissue directly
- Tying off the duct stopped blood flow to the pancreas, causing the whole organ to shrink so it could be removed and studied more easily
- Tying off the duct triggered the pancreas to produce extra insulin as a stress response, giving them a larger sample to extract
- Tying off the duct caused the enzyme-producing tissue of the pancreas to atrophy from disuse while leaving the insulin-producing islets of Langerhans intact, since the two tissues have different vulnerabilities
Why D? And why not the others?
Correct answer: D. Tying off the duct caused the enzyme-producing tissue of the pancreas to atrophy from disuse while leaving the insulin-producing islets of Langerhans intact, since the two tissues have different vulnerabilities
Tying off the pancreatic duct blocked the outward flow of digestive enzymes, which caused the enzyme-producing tissue to waste away from disuse over several weeks, while the hormone-producing islets of Langerhans, which release their product directly into the bloodstream rather than through the duct, survived largely intact; this let Banting and Best extract an islet-rich tissue no longer contaminated by enzymes that would otherwise digest the hormone during extraction. By 1922, with colleagues James Collip and J.J.R. Macleod, they had refined this into the first usable insulin treatment for diabetes. The option describing enzymes redirected into the bloodstream is wrong because the duct ligation's purpose was to stop enzyme flow entirely, not reroute it into circulation. The option describing shrinkage from stopped blood flow is wrong because the ligation targets the duct carrying digestive secretions, not the pancreas's blood supply. The option describing a stress-induced surge in insulin production is wrong because no such stimulating effect occurs; the islets were simply protected from the atrophy affecting the surrounding enzyme-producing tissue, not stimulated to produce more.
Source: Britannica: Sir Frederick Grant Banting