Hormones are chemical messengers that are classified into three main groups: amino acid-based hormones like proteins, peptides, and amines; steroids derived from cholesterol; and local hormones like prostaglandins. Hormones are specific to target cells that have receptors, and binding alters the target cell's activity in a lock-and-key mechanism. This can cause changes like increased membrane permeability, protein synthesis, or enzyme activation. Steroid hormones directly enter the nucleus and activate genes, while non-steroid hormones signal through second messengers like cAMP. Endocrine glands can be stimulated by other hormones, circulating ions, or nerves.

1. THE CHEMISTRY OF HORMONES AND
HORMONE ACTION
Pages 309-312

2. THE CHEMISTRY OF HORMONES
 Hormones are chemical messengers
 Three classifications:
 Two main groups:
1. Amino acid–based:
 Proteins
 Peptides (chains of amino acids; smaller than proteins)
 Amines (a derivative of ammonia)
2. Steroids—made from cholesterol (lipid based)
 Local Hormones:
3. Prostaglandins— made from highly active lipids that are
released from almost all cell membranes
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3. HORMONE SPECIFICITY
 Hormones are specific
 Target a cell or organ
 Target cells must have specific protein receptors
 Hormone binding alters cellular activity
 The act of a hormone binding to its target cell
is very similar to that of an enzyme and its
substrate- like a lock and key mechanism
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4. HORMONE ACTION
Hormones can cause:
1. Changes in membrane permeability or
electrical state
2. Synthesis of proteins, such as enzymes
3. Activation or inactivation of enzymes
4. Stimulation of mitosis
5. Promotion of secretory activity
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5. HORMONE DELIVERY
 The chemical structure of a hormone
determines how it is delivered to its target
 Two mechanisms:
1. Direct gene activation
• Steroids
• Ex: hormones of the adrenal cortex: corticosteroids
2. Indirect delivery: Second-messenger system
(a middle man)
1. Water soluble, non-steroids (protein/peptide
hormones)
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6. STEROID HORMONE ACTION
1. Diffuse directly through cell membrane
2. Enter the nucleus
3. Bind to a receptor protein within the nucleus
4. This hormone-receptor complex binds to
specific sites on the cell’s DNA
5. Certain genes are activated to synthesize new
proteins
http://highered.mheducation.com/sites/0072943696/student_view0/chapter
10/animation__mechanism_of_steroid_hormone_action__quiz_1_.html
© 2015 Pearson Education, Inc.

7. FIGURE 9.1A MECHANISMS OF HORMONE ACTION.
Steroid
hormone
Cytoplasm Nucleus
Receptor
protein
Hormone-receptor
complex
DNA
mRNA
New
protein
Plasma
membrane
of target
cell
1
(a) Steroid hormone action
2
3
4
5
6
Slide 1

8. SECOND-MESSENGER SYSTEM (non-steroids)
1. Hormone (first messenger) binds to a membrane
receptor
2. Activated receptor sets off a series of reactions that
activates an enzyme
3. Enzyme catalyzes a reaction to produce a second
messenger
4. Second messenger manage additional intracellular
changes to promote a specific response in the target
cell
https://www.youtube.com/watch?v=Nt2r5R0ZO5U
© 2015 Pearson Education, Inc.

9. FIGURE 9.1B MECHANISMS OF HORMONE ACTION.
(b) Nonsteroid hormone action
Plasma
membrane
of target cell
Receptor
protein
Nonsteroid
hormone (first
messenger)
Cytoplasm
Enzyme
ATP
cAMP
Second
messenger
Effect on cellular function,
such as glycogen
breakdown
1
2
3
4
Slide 1

10. ENDOCRINE GLAND STIMULI
 Three mechanisms for stimulus of glands:
1. Hormonal (most common)
• Endocrine organs are activated by other hormones
• Ex: anterior pituitary secretes hormones that stimulate other glands to
release hormones
2. Humoral
• Changing blood levels of certain ions and nutrients stimulate
hormone release
• Ex: PTH/calcitonin released in response to Ca⁺⁺ levels
3. Neural
• Nerve impulses stimulate hormone release
• Ex: sympathetic division stimulates release of
epinephrine/norepinehprine by the adrenal medulla
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11. USEFUL LINKS TO ANIMATIONS
 Hormonal Communication
 http://highered.mheducation.com/sites/0072495855/student_view0/c
hapter20/animation__hormonal_communication.html
 Hormone function summarized with animation for both
chemical types of hormones
 https://www.youtube.com/watch?v=TgNwxF3aQpE