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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 24. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. What are hormones and where are they produced?
  2. How do hormones bring about a response within the body?
  3. How does your body actively regulate the levels of glucose in the blood after you eat or during fasting?
  4. How are hormones involved in regulating the levels of calcium within your body?
  5. What hormones regulate sexual development and control the processes that occur during reproduction?
  6. What is the role of growth hormone in animals?
  7. How do hormones that act over very different time scales differ?
  8. What is metamorphosis and how do hormones regulate it in insects?

A Guide to the Reading

When exploring the content in Chapter 24 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

Regulation and Coordination of Physiological Processes

The human body contains organs and tissues that are separated by large distances, but yet they must still communicate, coordinate, and effectively work with each other.  This task is accomplished by the release of signaling molecules into the circulatory system by specific endocrine glands.  These signaling molecules are known as hormones and they are released into the blood and transported to specific target cells where they bring about a response.  This allows for thorough distribution of the signaling hormone to all parts of the body, ensuring they come in contact with the appropriate target cells.  Hormones produce a response in a specific target cell by either entering the target cell to act on specific genes or by stimulating receptors on the surface of the target cell to produce an internal response.  Once at the target cell, hormones circulating at very low concentrations bring about a large response because the target cell amplifies the processes being turned on within the cell.  The response to a hormone can occur over a short time span, as with calcium regulation by calcitonin and parathyroid hormone, over a medium to long time span, as with sex hormones, or over a long time span, as with the control of growth by growth hormone. 

For more information on this concept, be sure to focus on:

  • In Section 24.1, Hormones trigger a response in target cells
  • In Section 24.1, Target cells can amplify the hormonal signal
  • In Section 24.2, Calcium is regulated by hormones from the thyroid and parathyroid glands
  • Section 24.4, Regulating Long-term Processes:  Human Growth
  • Figure 24.1, Hormones Allow Cells to Communicate with One Another
  • Figure 24.2, Hormones Act More Slowly than the Nervous System

Regulation of Blood Glucose Levels           

Glucose is one of the basic energy sources used by an animal to produce the ATP needed to carry out cellular work.  Therefore, animals must actively regulate internal glucose levels to ensure adequate amounts are available.  The body regulates blood glucose levels with the help of four hormones: insulin, glucagon, epinephrine, and norepinephrine.   Both insulin and glucagon are produced in specialized islet cells in the pancreas.  Insulin is released in response to increased blood glucose levels and it stimulates the liver to store glucose in the form of glycogen.  Glucagon has the opposite effect and stimulates the conversion of glycogen to glucose when blood glucose levels are low, such as during fasting.  Both epinephrine and norepinephrine are released by the adrenal gland and work in concert with glucagon to stimulate the breakdown of glycogen into glucose.  The disease diabetes occurs in individuals who are unable to correctly control their blood glucose levels.  Type 1 diabetes is due to decreased production of insulin by the pancreas and Type 2 diabetes is due to a malfunction of the receptors in the liver that are stimulated by insulin to convert glucose into glycogen.  Both types of diabetes result in unhealthy levels of blood glucose. 

For more information on this concept, be sure to focus on:

  • In Section 24.2, Blood glucose levels are regulated by hormones from the pancreas and the adrenal glands
  • Figure 24.4, Balancing Levels of Glucose in the Blood
  • Figure 24.6, Compensating for a Defective Pancreas

Hormones Control Human Sexual Development and Reproduction

Sex hormones and the X and Y chromosomes are involved in the complex process of controlling the development of either a male or female.  The sex hormones are involved in signaling genes to target cells to produce a human fetus that is either a male or female.  Three hormones guide production of the male sex.  Testosterone and two other androgens direct the development of the sperm duct, prostate gland, and penis development in males.  In the developing female, three estrogens stimulate the development of the female reproductive tract.  Upon reaching puberty, the sex hormones control the development of adult characteristics such as facial and pubic hair, development of the penis and scrotum in males or breasts in females.  The gonadotropins, luteinizing hormone and follicle-stimulating hormone, are a class of sex hormones released by the pituitary gland that help coordinate the female menstrual cycle and male sperm development.  Changes in levels of the different gonadotropins and estrogen trigger ovulation, the release of the egg from the follicle in the female.  A part of the follicle remains in the ovary and begins to secrete progesterone that prepares the lining of the uterus for implantation of a fertilized egg.  Thus, sex hormones are actively involved in the development of sex characteristics and regulating reproduction during the entire life span of an animal. 

For more information on this concept, be sure to focus on:

  • In Section 24.3, Sex hormones play a role in sexual development before birth
  • In Section 24.3, Sex hormones coordinate sexual maturation at puberty
  • In Section 24.3, Sex hormones coordinate the menstrual cycle of human females
  • Figure 24.8, Sex-Specific Steroid Hormones           
  • Figure 24.9, Hormonal Control of the Menstrual Cycle in Human Females

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

Hormones Trigger a Response in Target Cells

  • Chapter 6 – Section 6.6, Signaling Molecules in Cell Communication
  • Chapter 6 – Figure 6.8, Receptors for Signaling Molecules
  • Chapter 6 – Figure 6.9, A Cell’s Response to a Steroid Hormone

Regulating Short-term Processes: Glucose and Calcium Homeostasis

  • Chapter 8 – Section 8.3, Glycolysis is the First Stage in the Cellular Breakdown of Sugars

Regulating Medium- and Long-Term Processes: Human Reproduction

  • Chapter 29 – Section 29.1, Human Reproduction and Development: A Brief Overview

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