In today’s blog, we will begin to unravel the meaning behind Dr. Banting’s hypothesis by discussing the anatomy of the digestive system, microscopic structure of the pancreas and blood glucose regulation by the hormone insulin. During his 10-month stay here in London, Dr. Banting held a teaching position at the University of Western Ontario in the Department of Surgery and Physiology. In late October 1920, he was asked to prepare a lecture on the anatomical features of the pancreas and its role in carbohydrate metabolism. On the evening of October 30, 1920 Dr. Banting read an article written by Dr. Moses Baron, that discussed an autopsy report of a patient with diabetes whose pancreatic duct had been obstructed by stones (a condition called pancreatic lithiasis) and he had a eureka moment! He rose from his bed at 2 am on October 31, 1920 to jot down his 25-word hypothesis pertaining to the extraction of a hypothetical pancreatic hormone (later referred to as insulin).
His hypothesis read as follows:
Diabetus [sic]. Ligate pancreatic ducts of dog. Keep dogs alive till acini degenerate leaving islets. Try to isolate the internal secretion of these and relieve glycosurea [sic].
Sounds like a lot of scientific jargon, but what exactly does Dr. Banting’s hypothesis mean?
Pancreatic duct, acini and islets mentioned in the hypothesis are anatomical terms, so let’s start with the anatomy of the digestive system.
The digestive system consists of
The GI tract begins at the mouth and ends at the anus.
After you’ve chewed and swallowed your food, it travels down your esophagus before reaching your stomach. Food (now referred to as bolus) is partially digested by stomach/gastric acid before being pushed through a valve into the first part of the small intestine, the duodenum.
What happens in the duodenum?
In the duodenum (depicted as a pink structure on the left side of the diagram below), food (now referred to as chyme) is further digested by specialized proteins called enzymes. So where do these digestive enzymes come from?
Now, let’s take a closer look at the overall structure of the pancreas.
If you were to take a tissue sample of the pancreas, stain it and place it under the microscope you would notice
How are these structures organized inside the pancreas?
In a cross-section of the pancreas, we find cell clusters (lobules) called acini 3 (blue structures in the inset diagram above).
Acini surround lobules called islets of Langerhans (pink structures in the inset diagram above).
Islets of Langerhans consist of different cell types that are involved in regulating glucose levels.
How does insulin lower blood glucose?
Let’s suppose that your pancreas has released enzymes into the duodenum in order to digest a pretzel you’ve eaten into simple sugars/carbohydrates (e.g. glucose). At this point, glucose is absorbed across the walls of your small intestine into the bloodstream. This leads to an increase in blood glucose. The beta cells of your pancreas sense this increase and start producing insulin. Insulin then travels through your bloodstream and ends up targeting many tissues including liver, muscle and fat (or adipose tissue).
The end result is that glucose is removed from the bloodstream and blood glucose levels fall within a healthy range.
Insulin lowers blood glucose
Glucose is stored as
We will later take a closer look at insulin signaling, discuss what happens in patients with diabetes mellitus and conclude with a detailed explanation of Dr. Banting’s hypothesis.
1.Endocrine: relates to glands that release/secrete hormones directly into the bloodstream. These secretions are considered internal. Back
2. Exocrine: relates to glands that release/secrete their products into ducts instead of directly into the bloodstream. These secretions are considered external. Back
3. Acini is the plural form of acinus. Back
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