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Chapter 34
Endocrine Control
34.2 The Vertebrate Endocrine System
• Animal cells communicate with one another by way of a
variety of short-range and long-range chemical signals
• Animal cells communicate with adjacent cells through gap
junctions and by releasing molecules that bind to receptors in
or on other cells
Mechanisms of Intercellular Signaling
• Many cells secrete local signaling molecules – such as
prostaglandins released by injured cells – which affect only
neighboring cells
• Animal hormones are secreted into interstitial fluid, enter the
blood, and are distributed throughout the body
Hormones and the Endocrine System
• Internal secretions carried by the blood that influence the
activities of specific body organs are called hormones
• Endocrine glands and other structures that secrete hormones
make up an animal’s endocrine system
• Some of the major endocrine glands also have functions
unrelated to hormone secretion
Hypothalamus
Pineal gland
Parathyroid glands
Pituitary gland
Thyroid gland
Thymus gland
Adrenal glands
Pancreas
Gonads
Figure 34-2 p587
ANIMATED FIGURE: Major human
endocrine glands
34.3 The Nature of Hormone Action
• For a hormone to have an effect, it must bind to protein
receptors on or inside a target cell
• Hormone action involves three steps:
1. A hormone activates a target cell receptor
2. The signal is transduced (changed into a form that affects
target cell behavior)
3. The cell makes a response
From Signal Reception to Response
Signal
Reception
Signal
Transduction
Cellular
Response
Table 34-1 p588
Intracellular Receptors
• Steroid hormones are made from cholesterol and can diffuse
across the plasma membrane
• Most steroid hormones form a hormone-receptor complex that
binds to a promoter inside the nucleus and alters the
expression of specific genes
1 A steroid hormone
molecule is moved from
blood into interstitial fluid
bathing a target cell.
2 Being lipid
soluble, the
hormone
easily
diffuses
across the
cell’s plasma
membrane.
3 The hormone
diffuses through the
cytoplasm and nuclear
envelope. It binds with
its receptor in the
nucleus.
5 The
resulting
mRNA moves
into the
cytoplasm and
is transcribed
into a protein.
gene product
receptor
hormone–
receptor
complex
4 The
hormone–
receptor
complex
triggers
transcription of a
specific
gene.
Figure 34-3a p589
Receptors at the Plasma Membrane
• Large amine, peptide and protein hormones bind to a receptor
at the plasma membrane
• Binding triggers formation of a second messenger (molecule
that relays signal into cell)
• Enzyme converts ATP to cAMP
• cAMP activates a cascading series of reactions
A peptide hormone
1 molecule,
glucagon,
diffuses from blood into
interstitial fluid bathing
the plasma membrane
of a liver cell.
unoccupied glucagon
receptor at target cell’s
plasma membrane
ATP
cyclic
AMP
+ Pi
2 Glucagon binds
with a receptor.
3 Cyclic AMP
Binding activates an
activates another
enzyme that catalyzes enzyme in the cell.
the formation of
cyclic AMP from ATP
inside the cell.
4 The enzyme activated by
cyclic AMP activates another
enzyme, which in turn
activates another kind that
catalyzes the breakdown of
glycogen to its glucose
monomers.
5
The enzyme
activated by
cyclic AMP
also inhibits
glycogen
synthesis.
Figure 34-3b p589
Receptor Function and Diversity
• Only cells with appropriate and functional receptor proteins
can respond to a hormone
• Gene mutations that alter receptor structure can prevent or
change cell response to a hormone
• Examples:
• Androgen insensitivity syndrome
• Variations in ADH receptors
Take-Home Message: How do hormones exert
their effects on target cells?
• Hormones exert their effects by binding to protein receptors,
either inside a cell or at the plasma membrane.
• Steroid hormones often enter a cell and act by altering the
expression of specific genes.
• Peptide and protein hormones usually bind to a receptor at
the plasma membrane. They trigger formation of a second
messenger, a molecule that relays a signal into the cell.
• Variations in receptor structure affect how a cell responds to a
hormone.
ANIMATION: Hormones and target cell
receptors
34.4 The Hypothalamus and Pituitary Gland
• The hypothalamus is the main center for control of the
internal environment – it connects structurally and functionally
with the pituitary gland
• The pituitary gland has two parts:
• The posterior lobe secretes hormones made in the
hypothalamus
• The anterior lobe makes its own hormones
• The hypothalamus signals the pituitary by way of secretory
neurons that make hormones
Control of Anterior Pituitary
• Hormones from the hypothalamus control the release of
anterior pituitary hormones
• Releasing hormones encourage secretion of hormones by
target cells
• Inhibiting hormones reduce secretion of hormones by target
cells
• Releasing and inhibiting hormones are secreted into the stalk
that connects the hypothalamus to the pituitary
Feedback Controls of Hormone Secretion
• Positive feedback mechanisms
• Response increases the intensity of the stimulus
• Example: Oxytocin and childbirth contractions
• Negative feedback mechanisms
• Response decreases the stimulus
Take-Home Message: How do the
hypothalamus and pituitary gland interact?
• Some secretory neurons of the hypothalamus make
hormones (ADH, OT) that move through axons into the
posterior pituitary, which releases them.
• Other hypothalamic neurons produce releasers and inhibitors
that are carried by the blood into the anterior pituitary. These
hormones regulate the secretion of anterior pituitary
hormones (ACTH, TSH, LH, FSH, PRL, and GH).
34.6 Sources and Effects
of Other Vertebrate Hormones
• In addition to the hypothalamus and pituitary gland, endocrine
glands and endocrine cells secrete hormones
• The gut, kidneys, and heart are among the organs that are
not glands, but include hormone-secreting cells
Table 34-3 p593
Multiple Hormone Receptors
• Most cells have receptors for multiple hormones, and the
effect of one hormone can be enhanced or opposed by
another one
• Example: Skeletal muscle hormone receptors
• Glucagon, insulin, cortisol, epinephrine, estrogen
testosterone, growth hormone, somatostatin, thyroid
hormone and others
Take-Home Message: What are the sources
and effects of vertebrate hormones?
• In addition to the pituitary gland and hypothalamus, endocrine
glands and endocrine cells secrete hormones.
• The gut, kidneys, and heart are among the organs that are
not considered glands, but do include cells that secrete
hormones.
• Most cells have receptors for multiple hormones, and the
effect of one hormone can be enhanced or opposed by that of
another.