1. Chapter 45
Hormones: The Body’s Long-
Distance Regulators
• Animal hormones are chemical signals that are
secreted into the circulatory system and
communicate regulatory messages within the body
• Hormones reach all parts of the body, but only
target cells are equipped to respond. Why?
3. • Remodeling
• Replacement (respecification)
• New structures
• Death
Larva function: dispersal (sea urchin) or growth
(amphibians)
4. Eye migration and associated neuronal changes during
metamorphosis of Xenopus laevis
Axons cross midline in early Axons do not cross in late
Eyes move
from prey
mode to
predator
mode (in
front for
bifocal
vision)
7. In the wild remains in
juvenile stage because
thyroid does not
release thyrotropin
Give the hormone in
the lab and get adult
form that is never
seen in the wild.
Here neoteny = retention of juvenile form
with adult gametes
8. The endocrine system and the nervous
system act individually and together in
regulating an animal’s physiology
• Animals have two systems of internal communication
and regulation: the nervous system and the endocrine
system
• The nervous system conveys high-speed electrical
signals along specialized cells called neurons
• The endocrine system secretes hormones that
coordinate slower but longer-acting responses
9. Overlap Between Endocrine and
Nervous Regulation
• The endocrine and nervous systems function
together in maintaining homeostasis,
development, and reproduction
• Specialized nerve cells known as neurosecretory
cells release neurohormones into the blood
• Both endocrine hormones and neurohormones
function as long-distance regulators of many
physiological processes
10. Control Pathways and Feedback Loops
• There are three types of hormonal control
pathways: simple endocrine, simple
neurohormone, and simple neuroendocrine
• A common feature is a feedback loop
connecting the response to the initial stimulus
• Negative feedback regulates many hormonal
pathways involved in homeostasis
11. LE 45-2a
Target
effectors
Response
Simple endocrine pathway
Glycogen
breakdown,
glucose release
into blood
Liver
Blood
vessel
Pancreas
secretes
glucagon ( )
Endocrine
cell
Low blood
glucose
Receptor
protein
Stimulus
Pathway Example
12. LE 45-2b
Target
effectors
Response
Simple neurohormone pathway
Stimulus
Pathway Example
Suckling
Milk release
Smooth muscle
in breast
Neurosecretory
cell
Blood
vessel
Posterior pituitary
secretes oxytocin
( )
Hypothalamus/
posterior pituitary
Sensory
neuron
13. LE 45-2c
Target
effectors
Response
Simple neuroendocrine pathway
Stimulus
Pathway Example
Milk production
Blood
vessel
Hypothalamus
Sensory
neuron
Mammary glands
Endocrine
cell
Blood
vessel
Anterior
pituitary
secretes
prolactin ( )
Hypothalamus
secretes prolactin-
releasing
hormone ( )
Neurosecretory
cell
Hypothalamic
neurohormone
released in
response to
neural and
hormonal
signals
14. Hormones and other chemical signals bind to
target cell receptors, initiating pathways that
culminate in specific cell responses
• Hormones convey information via the
bloodstream to target cells throughout the body
• Three major classes of molecules function as
hormones in vertebrates:
– Proteins and peptides
– Amines derived from amino acids
– Steroids
15. • Signaling by any of these hormones involves
three key events:
– Reception
– Signal transduction
– Response
16. Cell-Surface Receptors for Water-
Soluble Hormones
• The receptors for most water-soluble hormones
are embedded in the plasma membrane,
projecting outward from the cell surface
18. • Binding of a hormone to its receptor initiates a
signal transduction pathway leading to
responses in the cytoplasm or a change in gene
expression
• The same hormone may have different effects
on target cells that have
– Different receptors for the hormone
– Different signal transduction pathways
– Different proteins for carrying out the response
19. LE 45-4
Different receptors different cell responses
Epinephrine
α receptor
Epinephrine
β receptor
Epinephrine
β receptor
Vessel
constricts
Vessel
dilates
Intestinal blood
vessel
Skeletal muscle
blood vessel
Liver cell
Different intracellular proteins different cell responses
Glycogen
deposits
Glycogen
breaks down
and glucose
is released
from cell
The hormone epinephrine has multiple effects in
mediating the body’s response to short-term stress
20. Intracellular Receptors for Lipid-Soluble
Hormones
• Steroids, thyroid hormones, and the hormonal
form of vitamin D enter target cells and bind to
protein receptors in the cytoplasm or nucleus
• Protein-receptor complexes then act as
transcription factors in the nucleus, regulating
transcription of specific genes
21. Paracrine Signaling by Local Regulators
• In paracrine signaling, nonhormonal chemical
signals called local regulators elicit responses in
nearby target cells
• Types of local regulators:
– Neurotransmitters
– Cytokines and growth factors
– Nitric oxide
– Prostaglandins
22. • Prostaglandins help regulate aggregation of
platelets, an early step in formation of blood clots
23. • The hypothalamus and the pituitary gland
control much of the endocrine system
27. LE 45-7
Mammary glands,
uterine muscles
Hypothalamus
Kidney tubules
OxytocinHORMONE
TARGET
ADH
Posterior
pituitary
Neurosecretory
cells of the
hypothalamus
Axon
Anterior
pituitary
28. • Other hypothalamic cells produce tropic hormones,
hormones that regulate endocrine organs
• Tropic hormones are secreted into the blood and
transported to the anterior pituitary, or
adenohypophysis
• The tropic hormones of the hypothalamus control
release of hormones from the anterior pituitary
29. LE 45-8
Neurosecretory cells
of the hypothalamus
Endocrine cells of the
anterior pituitary
Portal vessels
Pituitary hormones
(blue dots)
Pain receptors
in the brain
Endorphin Growth hormone
BonesLiver
MSH
Melanocytes
Prolactin
Mammary
glands
ACTH
Adrenal
cortex
TSH
ThyroidTestes or
ovaries
FSH and LH
TARGET
HORMONE
Hypothalamic
releasing
hormones
(red dots)
Tropic Effects Only
FSH, follicle-stimulating hormone
LH, luteinizing hormone
TSH, thyroid-stimulating hormone
ACTH, adrenocorticotropic hormone
Nontropic Effects Only
Prolactin
MSH, melanocyte-stimulating hormone
Endorphin
Nontropic and Tropic Effects
Growth hormone
30. Posterior Pituitary Hormones
• The two hormones released from the posterior
pituitary act directly on nonendocrine tissues
• Oxytocin induces uterine contractions and milk
ejection
• Antidiuretic hormone (ADH) enhances water
reabsorption in the kidneys
Anterior Pituitary Hormones
• The anterior pituitary produces both tropic and
nontropic hormones
31. Tropic Hormones
• The four strictly tropic hormones are
– Follicle-stimulating hormone (FSH)
– Luteinizing hormone (LH)
– Thyroid-stimulating hormone (TSH)
– Adrenocorticotropic hormone (ACTH)
• Each tropic hormone acts on its target
endocrine tissue to stimulate release of
hormone(s) with direct metabolic or
developmental effects
32. Nontropic Hormones
• Nontropic hormones produced by the anterior
pituitary:
– Prolactin: stimulates lactation in mammals but has
diverse effects in different vertebrates
– Melanocyte-stimulating hormone (MSH) influences
skin pigmentation in some vertebrates and fat
metabolism in mammals
– β-endorphin: inhibits pain
33. Growth Hormone
• Growth hormone (GH) has tropic and nontropic
actions
• It promotes growth directly and has diverse
metabolic effects
• It stimulates production of growth factors
35. Thyroid Hormones
• The thyroid gland consists of two lobes on the
ventral surface of the trachea
• It produces two iodine-containing hormones:
triiodothyronine (T3) and thyroxine (T4)
38. • Calcitonin stimulates Ca2+
deposition in bones and
secretion by kidneys, lowering blood Ca2+
levels
• PTH, secreted by the parathyroid glands, has the
opposite effects on the bones and kidneys, and
therefore raises Ca2+
levels
• PTH also has an indirect effect, stimulating the
kidneys to activate vitamin D, which promotes
intestinal uptake of Ca2+
from food
39. LE 45-11
STIMULUS:
Rising blood
Ca2+
level
Thyroid gland
releases
calcitonin.
Calcitonin
Stimulates
Ca2+
deposition
in bones
Reduces
Ca2+
uptake
in kidneys
Blood Ca2+
level declines
to set point
Homoeostasis:
Blood Ca2+
level
(about 10 mg/100 mL)
STIMULUS:
Falling blood
Ca2+
level
Blood Ca2+
level rises
to set point
Stimulates
Ca2+
release
from bones
PTH
Parathyroid
gland
Stimulates Ca2+
uptake in kidneys
Active
vitamin D
Increases
Ca2+
uptake
in intestines
40. Insulin and Glucagon: Control of Blood
Glucose
• The pancreas secretes insulin and glucagon,
antagonistic hormones that help maintain
glucose homeostasis
• Glucagon is produced by alpha cells
• Insulin is produced by beta cells
41.
42. Target Tissues for Insulin and Glucagon
• Insulin reduces blood glucose levels by
– Promoting the cellular uptake of glucose
– Slowing glycogen breakdown in the liver
– Promoting fat storage
• Glucagon increases blood glucose levels by
– Stimulating conversion of glycogen to glucose in the
liver
– Stimulating breakdown of fat and protein into
glucose
43. LE 45-12
Beta cells of
pancreas
release insulin
into the blood.
Insulin
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Rising blood glucose
level (for instance, after
eating a carbohydrate-
rich meal)
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
Liver breaks
down glycogen
and releases
glucose into the
blood.
Body cells
take up more
glucose.
Alpha cells of pancreas
release glucagon into
the blood.
Glucagon
44. Diabetes Mellitus
• Diabetes mellitus is perhaps the best-known
endocrine disorder
• It is caused by a deficiency of insulin or a
decreased response to insulin in target tissues
• It is marked by elevated blood glucose levels
• Type I diabetes mellitus (insulin-dependent) is an
autoimmune disorder in which the immune system
destroys pancreatic beta cells
• Type II diabetes mellitus (non-insulin-dependent)
involves insulin deficiency or reduced response of
target cells due to change in insulin receptors (old
age, sigh)
45. Adrenal Hormones: Response to Stress
• The adrenal glands are adjacent to the kidneys
• Each adrenal gland actually consists of two
glands: the adrenal medulla and adrenal cortex
46. Catecholamines from the Adrenal
Medulla
• The adrenal medulla secretes epinephrine
(adrenaline) and norepinephrine
(noradrenaline)
• These hormones are members of a class of
compounds called catecholamines
• They are secreted in response to stress-
activated impulses from the nervous system
• They mediate various fight-or-flight responses
47. Stress Hormones from the Adrenal
Cortex
• Hormones from the adrenal cortex also function
in response to stress
• They fall into three classes of steroid hormones:
– Glucocorticoids, such as cortisol, influence glucose
metabolism and the immune system
– Mineralocorticoids, such as aldosterone, affect salt
and water balance
– Sex hormones are produced in small amounts
48. LE 45-13
Stress
Hypothalamus
Anterior pituitary
Blood vessel
ACTH
ACTH
Releasing
hormone
Nerve
cell
Nerve cell
Long-term stress response
Effects of
mineralocorticoids:
1. Retention of sodium
ions and water by
kidneys
2. Increased blood
volume and blood
pressure
Effects of
glucocorticoids:
1. Proteins and fats
broken down and
converted to glucose,
leading to increased
blood glucose
2. Immune system may
be suppressed
Short-term stress response
Effects of epinephrine and norepinephrine:
1. Glycogen broken down to glucose;
increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood flow patterns, leading to
increased alertness and decreased
digestive and kidney activity
Nerve
signalsSpinal cord
(cross
section)
Adrenal
gland
Kidney
