Video Transcript
It was previously thought that the
secretions of the pancreas were controlled by nervous stimulation. How did Ernest Starling and William
Bayliss demonstrate otherwise? (A) They monitored the transmission
of nervous impulses from the pancreas and observed that they did not travel to the
brain. (B) They cut off the nerve supply
to the pancreas and observed that pancreatic juice was still released. (C) They identified and isolated a
group of enzymes that controlled the secretion of the pancreas.
Ernest Starling and William Bayliss
are two scientists who made great strides in understanding not just the function of
the pancreas, but also were responsible for coining the term “hormone.” The question is asking us to
determine how their experiments demonstrated that pancreatic secretions were not
controlled by nervous stimulation.
To do this, let’s first take a
quick look at the pancreas itself before we delve into their research in more
detail. The pancreas is a gland that makes
up part of the human endocrine system and also acts as an accessory gland in the
human digestive system. This means that while food does not
pass through the pancreas as it makes its way through the digestive tract, this
gland is incredibly important in the digestion of food due to the enzymes it
secretes as a part of pancreatic juice. We can see the location of the
pancreas among some other organs of the digestive system here. It’s located just behind the
stomach.
The pancreas is often described as
a mixed gland, as it is capable of behaving both as an endocrine gland, by secreting
hormones like those that control our blood sugar levels, and also as an exocrine
gland, by secreting pancreatic juice into the duodenum, which makes up the first
part of the small intestine.
Starling and Bayliss tried to
determine whether these exocrine pancreatic secretions of pancreatic juice were a
result of nervous stimulation as was believed at the time or something else
entirely. When they cut off the nerve supply
to the pancreas, they observed that it still secreted pancreatic juice into the
duodenum immediately after food arrived there.
The scientists found that before
the pancreas releases the pancreatic juice, the mucosa cells that line the duodenum
and the jejunum, the first two parts of the small intestine, release chemicals. They called these chemicals
secretin. Secretin then entered the
bloodstream and was transported to the pancreas. This stimulated pancreatic juice
and the digestive enzymes it contains to be secreted into the duodenum so efficient
digestion of food could occur. As they had cut off the nerve
supply to the pancreas, they concluded that it could not possibly have been nervous
stimulation that causes the secretion of pancreatic juice, but rather these chemical
secretions that they named hormones.
This provides us with enough
information to answer the question. The way that Starling and Bayliss
demonstrated that the secretions of the pancreas were not controlled by nervous
stimulation is (B). They cut off the nerve supply to
the pancreas and observed that pancreatic juice was still released.
