Answered: Based on the information provided,…

1st Edition

ISBN:9781938168130

Author:Kelly A. Young, James A. Wise, Peter DeSaix, Dean H. Kruse, Brandon Poe, Eddie Johnson, Jody E. Johnson, Oksana Korol, J. Gordon Betts, Mark Womble

Publisher:Kelly A. Young, James A. Wise, Peter DeSaix, Dean H. Kruse, Brandon Poe, Eddie Johnson, Jody E. Johnson, Oksana Korol, J. Gordon Betts, Mark Womble

Chapter17: The Endocrine System

Section: Chapter Questions

Problem 37RQ: In the elderly, decreased thyroid function causes ________. increased tolerance for cold decreased...

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Question

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts

releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons (H+) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

The Esp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp mutation that prevented the production of a functional Esp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Based on the information provided, which of the following best justifies the claim that osteocalcin is a

hormone?

a.The activation of the osteocalcin by a bone cell is pH dependent.

b.The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.

c.The phosphorylation of the insulin receptor causes a response in osteoblast bone cells.

d.The change in expression of Esp changes the insulin receptor activity of the osteoblast.

Q
1.27
Normal
Mutant
1.0-
0.8-
0.6-
0.4-
-----
0.2+
40
Minutes After Glucose Injection
20
60
Figure 2: Blood insulin levels in normal mice and Esp mutant mice after exposure to glucose
Blood Insulin (ng/mL)

Insulin
Östeocalcin
Receptor
Insulin-Secreting
Cells of
the Pancreas
Osteoclast
Osteoblast
LInsulin Receptor
Esp
Protein
OPG
H*H*
H H*
'H*
Bone
pH s 4.5
Active
Osteocalcin
Inactive
Osteocalcin
Figure 1. Pathway activated by insulin binding to the insulin receptor

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