The document discusses the endocrine system and hormone function. It covers topics such as: - The main endocrine glands that release hormones and their functions in controlling cell activity and metabolism. - The two main mechanisms by which hormones act - through membrane receptors or by directly interacting with DNA. - How hormones bind to target cells and cause changes through second messengers or gene transcription. - Negative feedback loops help control hormone release by inhibiting upstream glands from producing more hormones.

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Chapter 15 Part I Overview
Hormone types
Hormone activity

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Endocrine System Function
• Control cell activity
• metabolism
• Release hormones
• Slower control than CNS/PNS
• Endocrine glands: pituitary, thyroid,
parathyroid, adrenal, and pineal glands

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Endocrine System: Overview
• Some organs have endocrine and exocrine
function
• pancreas and gonads
• adipose cells, thymus, small intestine,
stomach, kidneys, and heart
• Hypothalamus has neural and endocrine
functions

4. Copyright © 2011 Pearson Education, Inc. Figure 15.1
Pineal gland
Hypothalamus
Pituitary gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)

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Chemical Messengers
• Hormones: Long ranging chemical signals,
travel through blood or lymph
• Autocrine: chemicals affect the cells that
secretes them
• “self stimulating”
• Paracrine: locally acting chemicals that affect
other cells

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Hormone Action
• How hormones cause change:
1. Open or close ion channels
2. Stimulate synthesis of proteins
3. Activate or deactivate enzymes
4. Induce secretion
5. Stimulate mitosis

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Chemistry of Hormones
• Two main classes
1. Amino acid-based hormones
• Water soluble
• ex. Proteins… such as tryptophan
2. Steroids
• Non-water soluble
• Made from cholesterol
• ex. Estrogen & testosterone

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Mechanisms of Hormone Action
Two mechanisms, depends on chemical makeup
1. Water-soluble hormones (amino acid–based)
• Cannot enter target cells
• Can’t pass through plasma membrane
• Bind to receptors on cell surface
• Initiate chain reactions inside cell

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Membrane Receptors and
Second-Messengers
• Hormone signaling mechanism
1. Hormone (primary messenger) binds to
surface receptor
2. Receptor activates internal
signals(secondary messengers)
3. Triggers change in the cell
• Increased mitosis
• Protein production

10. Copyright © 2011 Pearson Education, Inc. Figure 15.2, step 1
Hormone (1st messenger)
binds receptor.
Receptor
Hormones that
act via cAMP
mechanisms:
Epinephrine
ACTH
FSH
LH
Extracellular fluid
Cytoplasm
Glucagon
PTH
TSH
Calcitonin
1
Figure 15.2, step 2
Hormone (1st messenger)
binds receptor.
Receptor
activates G
protein (GS).
Receptor
G protein (GS)
Hormones that
act via cAMP
mechanisms:
Epinephrine
ACTH
FSH
LH
Extracellular fluid
Cytoplasm
GDP
Glucagon
PTH
TSH
Calcitonin
1
2
Figure 15.2, step 3
Hormone (1st messenger)
binds receptor.
Receptor
activates G
protein (GS).
G protein
activates
adenylate
cyclase.
Receptor
G protein (GS)
Adenylate cyclase
Hormones that
act via cAMP
mechanisms:
Epinephrine
ACTH
FSH
LH
Extracellular fluid
Cytoplasm
GDP
Glucagon
PTH
TSH
Calcitonin
1
2 3
Figure 15.2, step 4
Hormone (1st messenger)
binds receptor.
Receptor
G protein (GS)
Adenylate cyclase
Hormones that
act via cAMP
mechanisms:
Epinephrine
ACTH
FSH
LH
Extracellular fluid
Cytoplasm
GDP
Glucagon
PTH
TSH
Calcitonin
1
2 3 4
Figure 15.2, step 5
Hormone (1st messenger)
binds receptor.
cAMP acti-
vates protein
kinases.Receptor
G protein (GS)
Adenylate cyclase
Triggers responses of target cell (activates enzymes,
stimulates cellular secretion, opens ion channel,etc.)
Hormones that
act via cAMP
mechanisms:
Epinephrine
ACTH
FSH
LH
Inactive
protein
Extracellular fluid
Cytoplasm
Active
protein
GDP
Glucagon
PTH
TSH
Calcitonin
1
4
5
• cAMP is a common second messenger.

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Mechanisms of Hormone Action
2. Lipid-soluble hormones (steroids)
• Can pass through plasma membrane
• Bind to intracellular receptors
• Directly activates gene
• Receptor + hormone binds to DNA
• Promotes transcription of mRNA
• mRNA then translated into protein

12. Copyright © 2011 Pearson Education, Inc. Figure 15.3, step 1
Receptor-
hormone
complex
Receptor
protein
Cytoplasm
Nucleus
Extracellular fluid
Steroid
hormone
The steroid hormone
diffuses through the plasma
membrane and binds an
intracellular receptor.
Plasma
membrane
1
Figure 15.3, step 2
Receptor-
hormone
complex
Receptor
protein
Cytoplasm
Nucleus
Extracellular fluid
Steroid
hormone
The steroid hormone
diffuses through the plasma
membrane and binds an
intracellular receptor.
The receptor-
hormone complex enters
the nucleus.
Plasma
membrane
1
2
Figure 15.3, step 3
DNA
Hormone
response
elements
Receptor-
hormone
complex
Receptor
protein
Cytoplasm
Nucleus
Extracellular fluid
Steroid
hormone
The steroid hormone
diffuses through the plasma
membrane and binds an
intracellular receptor.
The receptor-
hormone complex enters
the nucleus.
The receptor- hormone
complex binds a hormone
response element (a
specific DNA sequence).
Plasma
membrane
1
2
3
Figure 15.3, step 4
mRNA
DNA
Hormone
response
elements
Receptor-
hormone
complex
Receptor
protein
Cytoplasm
Nucleus
Extracellular fluid
Steroid
hormone
The steroid hormone
diffuses through the plasma
membrane and binds an
intracellular receptor.
The receptor-
hormone complex enters
the nucleus.
The receptor- hormone
complex binds a hormone
response element (a
specific DNA sequence).
Binding initiates
transcription of the
gene to mRNA.
Plasma
membrane
1
2
3
4
Figure 15.3, step 5
mRNA
New protein
DNA
Hormone
response
elements
Receptor-
hormone
complex
Receptor
protein
Cytoplasm
Nucleus
Extracellular fluid
Steroid
hormone
The steroid hormone
diffuses through the plasma
membrane and binds an
intracellular receptor.
The receptor-
hormone complex enters
the nucleus.
The receptor- hormone
complex binds a hormone
response element (a
specific DNA sequence).
Binding initiates
transcription of the
gene to mRNA.
The mRNA directs
protein synthesis.
Plasma
membrane
1
2
3
4
5

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Target Cell Activation
• Target cell activation depends on:
1. Presence of receptor
• Target cells must have specific hormone receptors
• Receptors are often limited to specific tissues
1. Hormone concentration
2. Number of receptors on cell
3. binding of receptor and hormone

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Target Cell Activation
• Hormones can influence receptor numbers
• Up-regulation —more receptors
• Down-regulation — lose receptors

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Control of Hormone Release
• Negative feedback loops
• Help control hormone release
• Hormones produced inhibit upstream
glands
• ex. To make hormone 3 you need
hormones 1 and 2.
• Negative feedback loop is hormone 3
inhibits production of hormones 1 and 2.
• Prevents overproduction of hormones

16. Copyright © 2011 Pearson Education, Inc. Figure 15.4c
Hypothalamus
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
Pituitary
gland
1 The hypothalamus secretes
hormones that…
2 …stimulate
the anterior
pituitary gland
to secrete
hormones
that…
3 …stimulate other endocrine
glands to secrete hormones
Negative
feedbackNegative Feedback Loop