POL

1. Control by the Endocrine
and Nervous Systems
35.1-35.2

2. Chapter 35 Animal Hormones
Key Concepts
35.1 The Endocrine and Nervous Systems Play
Distinct, Interacting Roles
35.2 Hormones Are Chemical Messengers
Distributed by the Blood
35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
35.4 Hormones Regulate Mammalian Physiological
Systems
35.5 The Insect Endocrine System Is Crucial for
Development

3. Chapter 35 Opening Question
Why are the skeletal muscles under control of
both the nervous system and the endocrine
system?

4. 35.1
The Endocrine and Nervous
System Play Distinct,
Interacting Roles

5. Responding: Internal and External
The endocrine system is a system of ductless glands
that secrete chemical signals directly into the blood to
target tissue.
The nervous system is a system of neurons that
transmit “electrical” signals and release
neurotransmitters to target tissue.
The immune system is a system that responds to
invasion by pathogenic invaders that disrupt
homeostasis sometimes to the point of death.

6. Concept 35.1 The Endocrine and Nervous Systems Play Distinct,
Interacting Roles
Both nerve cells and endocrine cells are specialized for
control and coordination.
Endocrine cells secrete hormones into the blood.
Nerve and endocrine cells work together to ensure
proper functioning of an animal’s body.

7. Concept 35.1 The Endocrine and Nervous Systems Play Distinct,
Interacting Roles
Nerve and endocrine cells need to communicate with
other cells.
Most intercellular communication takes place by
means of chemical signals that travel to another cell,
the target cell.
The signal molecules bind to receptors on the target
cell, triggering a response.

8. Figure 35.1 Chemical Signaling by Nerve and Endocrine Cells
Describe the
differences in the
two pathways.

9. Concept 35.1 The Endocrine and Nervous Systems Play Distinct,
Interacting Roles
Nervous control is
• fast—nerve impulses
travel fast and end
quickly
• addressed—nerve
impulses are
delivered to highly
defined target cells
Endocrine control is
• slow—hormones
must travel to the
target in the blood,
may last a long time
in the blood, and
often alter gene
transcription
• broadcast—all cells
are potentially
exposed to a
hormone

10. Concept 35.1 The Endocrine and Nervous Systems Play Distinct,
Interacting Roles
The nervous and endocrine systems control different
functions:
Nervous system controls movement of skeletal
muscles, such as in a tennis player.
Endocrine system controls prolonged activities, such
as adolescent development.

11. Concept 35.1 The Endocrine and Nervous Systems Play Distinct,
Interacting Roles
The nervous and endocrine systems work closely
together.
Examples:
• The brain controls secretion of many hormones.
• Sex hormones affect brain development during
puberty.

12. Concept 35.1 The Endocrine and Nervous Systems Play Distinct,
Interacting Roles
Animals use chemical signaling over a broad range of
spatial scales.
• Paracrines—chemicals secreted by one cell that
affect neighboring cells.
• Autocrines—chemicals secreted into intercellular
fluids that diffuse to receptors on that very same cell.
• Hormones—carried throughout the body by blood
circulation.
• Neurotransmitters—move across the synaptic cleft;
secretion may be controlled by impulses that originate
far from the site of release.
• Pheromones—released into the environment and
affect other individuals.

13. Figure 35.2 Chemical Signaling Occurs over a Broad Range of Spatial Scales

14. 35.2
Hormones are Chemical
Messengers Distributed by
the Blood

15. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Exocrine glands—cells secrete substances into a
duct or a body cavity; for instance, mammary
glands, salivary glands.
Endocrine cells—secrete substances into the
blood.
• Cells may be dispersed in other tissues, or
aggregated to form a gland.

16. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Hormone—chemical substance, secreted into the
blood by endocrine cells, that regulates the
function of other cells
• They act at very low blood concentrations.
• Effects on target cells are initiated by
noncovalent binding of the hormone to
receptor proteins on target cells, giving them
specificity.

17. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Neurosecretory cells (neuroendocrine cells) resemble
neurons—they are excitable cells that propagate
action potentials.
• Cell bodies are in the CNS; the axon terminals
release hormones, often within neurohemal
organs.
• Provide a direct interface between nervous and
endocrine systems.
• Example: oxytocin (neurohormone from posterior
pituitary gland)

18. Figure 35.3 Two Types of Endocrine Cells

19. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Nonneural endocrine cells (epithelial endocrine cells)
are not excitable.
• Typically stimulated to secrete hormone by other
hormones.
• Examples: anterior pituitary gland, thyroid gland

20. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Hormones are classified into
three groups:
• Peptide and protein
hormones—water-
soluble and easily
transported in blood;
packaged in vesicles
and released to blood by
exocytosis; cannot cross
cell membranes, so
receptors are on the
exterior of target cells.
Peptide
-Insulin and ADH
Glycoproteins
-FSH and LH

21. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
• Amine hormones—modified amino acids; may be
lipid-soluble or water-soluble, receptors may be inside
target cell or on the exterior.
• Epinephrine and Melatonin

22. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
• Steroid hormones—synthesized from cholesterol;
lipid-soluble; bound to carrier proteins in blood;
receptors are inside target cells.
• Sex hormones (testosterone, progesterone),
aldosterone

23. Figure 35.4 The Three Principal Chemical Classes of Hormones (Part 3)
(A) Peptide hormones are composed of strings of amino acids. They include
proteins and small polypeptide molecules. Shown here are two proteins,
insulin and growth hormone. Each of these proteins consists of two
subunits, which are shown in different colors.
(B) Steroid hormones are modified from cholesterol molecules and all include
a characteristic set of four ring structures, here called the sterol backbone
and colored green. They include the corticosteroids produced by the
adrenal cortex and the sex steroids produced primarily by the gonads.
(C) Amine hormones are small molecules synthesized from single amino acid
molecules. Thyroxine and epinephrine are both made from the amino acid
tyrosine. The structures in B and C are in abbreviated form; not all carbon
(C) atoms are shown.
Create a chart comparing the
classes or hormones:
-solubility in water
-mode of transport
-effect on target cells
*see page 737 and the
previous slides

24. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Hormone receptor proteins on target cell surface:
• Hormone binds to the part of the receptor protein
that projects outside the cell membrane.
• Many receptors are G protein–linked receptors that
initiate second messenger signaling cascades
inside the target cell.

25. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Hormone receptors inside the target cell:
• Lipid soluble hormones can diffuse through the
cell membrane; receptors are in the cytoplasm;
the hormone–receptor complex moves into the
nucleus and alters gene expression.
• Example: Testosterone–receptor complex
activates transcription of genes that code for
enhanced synthesis of actin and myosin, which
increases muscle mass.

26. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Target cells can have receptors for more than one
hormone.
Negative or positive feedback can influence the
number of receptor proteins per cell.
Example: In type II diabetes mellitus, chronically high
levels of insulin lead to decreased production of
insulin receptors throughout the body, and the cells
become less sensitive to insulin.

27. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
One hormone can have different effects on different
types of cells.
Function of some hormones has changed over
evolutionary time because receptor systems can
change.
Example: Prolactin stimulates milk production in
mammals. Prolactin has been found in all vertebrate
phyla, but it has different functions, such as
stimulating nest-building in birds.

28. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Because target cells can have
different receptor systems, one
hormone can elicit different
responses from different target cells.
In the fight-or-flight response, the
adrenal medullary glands secrete
epinephrine (adrenaline) and
norepinephrine.
There are at least five types of G-
protein linked receptors for these
hormones in two categories: α-
adrenergic and β-adrenergic.

29. Figure 35.5 The Adrenal Gland Consists of Two Glands within One Gland

30. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Thus, the hormones bring about a range of responses
in various tissues:
• Faster and stronger heart beat
• Constriction of skin blood vessels
• Dilation of skeletal muscle blood vessels
• Breakdown of glycogen in the liver
• Decrease in blood flow and secretion of digestive
enzymes in the gut

31. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Timing of hormone release varies:
Peptide hormones are synthesized prior to use
and stored; they can be released quickly.
Steroid hormones are usually synthesized on
demand; initiation of secretion is relatively slow.

32. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Hormones must also be removed from the
blood.
Target cells or organs such as the liver and kidneys
can degrade hormones enzymatically, or
hormones may be excreted.
Removal terminates the hormone signal.

33. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Half-life of a hormone in the blood is the time
required for half the amount of secreted hormone
molecules to be removed.
Some half-lives are very short, such as epinephrine
(1–2 min).
Others are longer, such as antidiuretic hormone
(15 min), cortisol (1 hr), and thyroxine (1 week).

34. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Concentration of hormones in the blood is
stabilized by negative feedback.
If blood concentration rises above a set-point level,
secretion of the hormone is inhibited.
Hormones transported by carrier proteins in the
blood tend to have longer half lives.

35. Concept 35.2 Hormones Are Chemical Messengers Distributed by
the Blood
Some hormones are converted to more active forms
after they are secreted (peripheral activation).
The thyroid secretes thyroxine (also called T4 or
tetraiodothyronine), which has four iodine atoms.
In peripheral tissues one iodine is removed, forming T3,
triiodothyronine, a more active form.

36. Apply the Concept – page 740
1. Use the data in the table to
estimate the half life of 600ug of
T4 in the bloodstream in this
experiment. (The concentration
at time 0 is the baseline).
2. If you were trying to correct a
hormone deficiency by
administering hormone therapy
and needed to keep the
hormone level in the blood
stream from falling too low, how
would your dosing differ for
hormones with different half-
lives.
One way to characterize the time
course of a hormone is to measure its
half-lie in the blood. A hormones
half-life can be measured in the lab
by injecting some of the hormone
and then determining the length of
time required for the blood level to
fall from its maximum level to
halfway back to its baseline level.

37. 35.3
The Vertebrate Hypothalamus
and Pituitary Gland Link the
Nervous and Endocrine
Systems

38. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The pituitary gland is the
“master gland,” it
secretes hormones that
control many other
glands.
The pituitary gland is
attached to the
hypothalamus of the
brain.
Two parts—anterior
pituitary and posterior
pituitary

39. • Hypothalamus is the “master
nerve control center”
– Receives information from
nerves around the body
about internal conditions
and regulates the release
of hormones from the
pituitary gland.
• Pituitary gland is the “master
gland”
– Secretes a broad range of
hormones regulating other
glands in the body.

40. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The posterior pituitary is an extension of the brain; the
hormones are synthesized and secreted by brain
neurosecretory cells.
The cell bodies are in the hypothalamus, the axons
extend into the posterior pituitary, forming a
neurohemal organ.
Different sets of neurosecretory cells secrete different
hormones.

41. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The hypothalamus secretes two peptide hormones
into the posterior pituitary:
• Antidiuretic hormone (ADH) (vasopressin)
controls water excretion by the kidneys.
• Oxytocin stimulates uterine contractions
during birth and milk flow from the breasts.
Brain signals control these secretions.

42. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The anterior pituitary is an endocrine gland; hormones are
synthesized by nonneural endocrine cells.
The four tropic hormones (tropins) control other
endocrine glands:
• Adrenocorticotropin hormone (ACTH) controls the
adrenal cortex
• Thyroid-stimulating hormone (TSH) controls the
thyroid gland
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
Both LH and FSH are gonadotropins and control the
gonads (ovaries and testes).

43. Figure 35.7 The Anterior Pituitary Gland

44. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The anterior pituitary also secretes:
• Growth hormone (GH)—acts on a wide
variety of tissues to promote growth
• Prolactin
• Melanocyte-stimulating hormone, named for its
action on skin-color cells in amphibians

45. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
Secretion of anterior pituitary hormones is controlled
by the hypothalamo–hypophysial portal system.
Neurosecretory cells in the hypothalamus secrete
hormones into blood capillaries in the hypothalamus.
The blood then flows to a second capillary bed in the
anterior pituitary.

46. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The neurohormones from the hypothalamus
are releasing hormones (RHs) and
inhibiting hormones (IHs).
Example: RH for growth hormone affects the
specific cells in the anterior pituitary that
secrete growth hormone, stimulating them to
secrete GH into the general circulation.

47. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
Endocrine cells act on each other in
sequences, forming an axis.
The hypothalamus–pituitary–adrenal cortex
(HPA) axis:
• In response to stress, cells in the
hypothalamus secrete corticotropin-
releasing hormone, which travels to the
anterior pituitary and stimulates release of
the tropic hormone ACTH.

48. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
• ACTH travels to the adrenal cortex, which
increases secretion of glucocorticoids
(cortisol).
Negative-feedback control: the concentration of
the hormones secreted by the target glands
provides information to the hypothalamus to
increase or decrease production of releasing
hormones.

49. Figure 35.8 Multiple Feedback Loops Control Hormone Secretion

50. Concept 35.3 The Vertebrate Hypothalamus and Pituitary Gland
Link the Nervous and Endocrine Systems
The neurosecretory cells in the hypothalamus
often secrete in pulses rather than
continuously.
Continuous secretion can lead target cells in
the pituitary to reduce numbers of RH or IH
receptor molecules and thus reduce
sensitivity.
Anterior pituitary hormones are also secreted
in pulses.

51. Figure 35.9 Effectiveness of Gonadotropin-Releasing Hormone (GnRH) Depends on a Pulsatile
Pattern of Release (Part 1)

52. Figure 35.9 Effectiveness of Gonadotropin-Releasing Hormone (GnRH) Depends on a Pulsatile
Pattern of Release (Part 2)

53. Figure 35.9 Effectiveness of Gonadotropin-Releasing Hormone (GnRH) Depends on a Pulsatile
Pattern of Release (Part 3)

54. 35.4
Hormones Regulate
Mammalian Physiological
Systems

55. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems
The thyroid gland has two cell types that
produce thyroxine (T4) and calcitonin.
T4 is synthesized from the amino acid tyrosine
and iodine. T4 is converted to T3, which is more
active. Both forms are called thyroid
hormones.
They are vital to growth and development:
promote protein synthesis and gene
transcription. Insufficient amounts can impair
mental and physical development.

56. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems
In areas where soils lack iodine, it
can be supplied in the diet by
iodized salt.
Lack of dietary iodine can cause
goiter, an enlarged thyroid gland.
• When the thyroid does not
produce enough hormone,
feedback to the hypothalamus
increases TSH production,
which stimulates the thyroid
gland to grow larger – forming
a goiter.

57. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems
The gonads produce sex steroids.
• Androgens—masculinizing steroids (e.g.,
testosterone)
• Estrogens and progesterone—feminizing steroids
Both sexes make both types, in varying levels.

58. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems
During embryonic development, sex hormones
determine the sex of fetus.
If the embryo is XY, the SRY gene on the Y
chromosome causes gonads to develop into testes,
and they begin to produce testosterone.
High testosterone levels cause external structures to
develop into male forms. Without testosterone,
female forms develop.

60. Figure 35.13 Sex Steroids Direct the Prenatal Development of Human Sex Organs (Part 1)

61. Figure 35.13 Sex Steroids Direct the Prenatal Development of Human Sex Organs (Part 2)

62. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems
At puberty, the anterior pituitary is stimulated by
gonadotropin-releasing hormone (GnRH) from the
hypothalamus to produce the gonadotropins (FSH
and LH).
In males, LH stimulates production of testosterone,
which alters gene expression in many areas, resulting
in hair growth, deeper voice, increase in muscle
mass, and growth of penis and testes. Increased FSH
stimulates sperm production.

63. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems
In females, increased LH stimulates production of
estrogen, which results in growth of breasts,
vagina, and uterus; hips enlarge, menstrual
cycles begin.
Increased FSH stimulates maturation of ovarian
follicles, necessary for production of mature eggs.

64. Concept 35.4 Hormones Regulate Mammalian Physiological
Systems

66. 35.5
Insect Endocrine System

67. Concept 35.5 The Insect Endocrine System Is Crucial for
Development
In arthropods, hormones control molting and
metamorphosis.
The rigid exoskeleton must be shed
periodically to allow growth (molting or
ecdysis), and must then be replaced.
The molting process is connected to both
growth and morphological development
(development of form).

68. Figure 35.14 Key Structures and Hormones in the Control of Insect Development

69. Concept 35.5 The Insect Endocrine System Is Crucial for
Development
Hormones regulate molting:
• PTTH (prothoracicotropic hormone) is secreted by
the brain; it stimulates the prothoracic gland to
secrete ecdysone.
• Ecdysone undergoes peripheral activation and
stimulates epidermal cells to secrete enzymes that
loosen the exoskeleton.
• The epidermal cells then synthesize a new
exoskeleton.

70. Concept 35.5 The Insect Endocrine System Is Crucial for
Development
Juvenile hormone is also released from the
brain and controls body form as the insect
molts.
If JH is at high concentrations when the insect
molts, it retains the larval body form. If
concentration is low, the insect develops into
the pupal and then adult form.

71. Figure 35.15 Hormonal Control of Molting and Metamorphosis in a Moth

72. Answer to Opening Question
Muscles need to be controlled on two scales of spatial
definition and two scales of time.
The nervous and endocrine systems are suited to
exerting control on these different scales— evolution
has favored control by both systems.
The nervous system is suited to controlling muscle
movement; the endocrine system is suited to
controlling muscle development.
Why are the skeletal muscles under control of
both the nervous system and the endocrine
system?