Video Transcript
Insulin is secreted by the blank
and glucagon is secreted by the blank of the islets of Langerhans, and both have
blank on glucose levels in the blood. (A) 𝛼 cells, 𝛽 cells, similar
effects. (B) 𝛽 cells, 𝛼 cells, opposite
effects. (C) 𝛼 cells, 𝛽 cells, opposite
effects. Or (D) 𝛽 cells, 𝛼 cells, similar
effects.
The question tells us that insulin
and glucagon are secreted by the islets of Langerhans. And it asks us to identify the
cells that secrete insulin and glucagon, as well as their effect on blood glucose
levels.
You may remember that the islets of
Langerhans are the areas of endocrine tissue in the pancreas. Endocrine tissues secrete chemicals
directly into the bloodstream, rather than into ducts like exocrine tissue. There are several different
hormones secreted by the various cell types of the islets of Langerhans. But insulin and glucagon are the
primary hormones that regulate blood glucose. Controlling blood glucose levels is
critical because too much glucose has damaging effects on our tissues. But too little glucose can hinder
cellular respiration, leading to a lack of ATP.
To ensure that the body cells have
enough glucose for cellular respiration, 𝛼 cells in the islets of Langerhans
secrete glucagon when blood glucose levels fall below normal. Glucagon stimulates the breakdown
of glycogen, which is the form in which liver and muscle cells store glucose. This releases glucose into the
blood, raising the blood glucose back to a normal level.
When blood glucose rises above
normal, such as after a high-carbohydrate meal, 𝛽 cells in the islets secrete
insulin. Insulin signals cells to take up
excess glucose from the blood or, in the case of liver and muscle cells, to store it
as glycogen. As glucose is taken up and glycogen
is formed, the blood glucose level is lowered back to normal.
To summarize, insulin is secreted
by 𝛽 cells in the islets of Langerhans and helps to lower blood glucose. And glucagon is secreted by 𝛼
cells and helps to raise blood glucose. This means these two hormones have
opposite effects on glucose levels in the blood.
Now let’s return to our question to
select the option that correctly fills in the blanks. Based on what we have learned, we
can see that the correct answer choice is (B). And filling in the blanks gives us
the statement “Insulin is secreted by the 𝛽 cells and glucagon is secreted by the
𝛼 cells of the islets of Langerhans, and both have opposite effects on glucose
levels in the blood.”
