Chapter 4 Homeostatic Mechanisms • MHR 1214.3 Regulating Blood Sugar
Imagine that you go to bed on Sunday night, and
in the middle of the night you wake up and need to
use the bathroom. You wake up the next morning
feeling thirsty and go to the bathroom again. All
Monday seems to be spent quenching your thirst
and battling a constant need to urinate. After a few
days spent like this you decide to see your doctor,
and by the end of the week you are in a hospital.
You are diagnosed as having insulin-dependent
diabetes. Given the current state of technology, this
means that you could be giving yourself injections
of insulin for the rest of your life.
Diabetes is a malfunction of one of the major
homeostatic systems in the body — the endocrine
system. This system controls the levels of sugar
(usually glucose) in the blood. Normally, blood
sugar level stays around 100 mg/mL, although
it fluctuates somewhat during the day. These
fluctuations are controlled by a homeostatic
mechanism called antagonistic hormones. Chapter
6 explains hormones and the endocrine system in
greater detail, but for now you can think of
hormones as molecules produced by glands to
trigger certain reactions in other parts of the body.
Blood sugar is controlled by two hormones, insulin
and glucagon, which are produced in an organ
called the pancreas.
When studying the digestive system, you learned
that the pancreas is also responsible for the
production of many of the enzymes necessary for
the digestion of food. Scattered among the cells
that produce these enzymes are groups of cells
called the islets of Langerhans(see Figure 4.14).
Within these islets, cells called alpha cells produce
the hormone glucagon, while beta cells produce
insulin. Both of these hormones are secreted directly
into the blood vessels located in the pancreas.
Insulin is a hormone that lowers blood sugar
levels. It accomplishes this by making the cell
membranes with which it comes in contact more
permeable to glucose. In addition, insulin triggers
changes within the cells to increase their rate
of metabolism and thus consume increased
amounts of glucose.Figure 4.14Glucagon and insulin are produced by clusters
of cells within the pancreas called islets of Langerhans
(stained dark in this preparation).The release of insulin is controlled by a negative
feedback system similar to those that exist
elsewhere in the body. In this case, the receptor,
integrator, and effector are all found in each beta
cell of the pancreas. Each of these cells has
specialized receptors on its cell membrane that
respond to glucose molecules. The more glucose
in the blood and surrounding fluid, the greater the
number of receptors that are activated.Canadian researchers Frederick Banting and Charles Best
are famous as the co-discoverers of a method for isolating
insulin for the treatment of diabetes. In 1923, they won the
Nobel Prize for medicine, sharing the prize with Dr. J.J.R.
Macleod and J.B. Collip. Although it was Banting’s and Best’s
research in the summer of 1921 that led to the breakthrough,
Macleod and Collip did much of the work to make insulin
useful medically. By 1923, over 25 000 patients were being
treated with insulin in Canada and the United States.BIO FACT
EXPECTATIONS
Describe the role of the pancreas in controlling blood sugar in the human
body, and the factors that contribute to Type 1 and Type 2 diabetes.
Detail the contributions made by Banting and Best to the discovery of the
role of insulin in controlling blood sugar.