12.11.3 Endocrine Function: Oscillations in Hormone Levels

Question 1

Endocrine Function: Oscillations in Hormone Levels

Answer 1

• The body’s hormone levels oscillate to maintain homeostasis.
• High blood-glucose levels (such as after a meal) stimulate the pancreas to release insulin into the blood. Insulin causes body cells and the liver to take up glucose, thus lowering the blood sugar level.
• Low blood glucose levels stimulate the pancreas to release glucagoninto the blood. Glucagon stimulates the liver to release glucose, raising the blood sugar level.

Question 2

note

Answer 2

• The diagram to the left illustrates the hormonal control of blood glucose levels.
• Beginning on the left side of the diagram, high blood glucose levels stimulate the pancreasto release the hormone insulin. Insulin causes the liver to take up glucose and store it as glycogen and causes cells of the body to take up glucose for use as an energy source (1 and 2).
• Blood glucose levels decrease in response to the uptake of glucose into the liver and body cells (3). Low glucose levels in the blood trigger the pancreas to release the hormone glucagon, which stimulates the liver to release glucose into the blood (4 and 5). Blood glucose levels rise and the cycle continues (6).
• The chart to the left illustrates the oscillation in glucose, insulin, and glucagon levels over time. The first line represents glucose levels, the second, insulin levels, and the third, glucagon levels.
• After a high sugar meal, blood glucose levels rise (1). In
  response to increasing glucose levels, insulin levels rise (2). As insulin levels rise, blood glucose levels plummet (3). As glucose levels drop below normal, glucagon is released and causes the liver to release more glucose into the blood (4). Eventually blood glucose levels increase in response to glucagon (5). Over time, blood glucose and hormone levels achieve a normalized state (see bottom figure).

Question 3

Immediately after a meal, __________ levels would be expected to increase, while __________ levels would decrease due to the __________ levels of glucose in the blood.

Answer 3

• insulin, glucagon, increasing

Question 4

Hormone levels in the blood stream tend to

Answer 4

• rise and fall according to internal and external conditions.
• be regulated by negative feedback.

Question 5

Insulin lowers blood glucose levels by

Answer 5

• increasing glucose uptake by body cells.

Question 6

When blood glucose levels are high, the pancreas releases __________. When blood glucose is low, the pancreas releases __________.

Answer 6

• insulin; glucagon

Question 7

Insulin acts at the liver to promote

Answer 7

• the production of glycogen

Question 8

True or false?

Because of homeostasis, hormone levels in the body are always constant.

Answer 8

• false

Question 9

An example of regulation through the antagonistic effects of two hormones is

Answer 9

• the regulation of blood glucose levels with insulin and glucagon.