1. Hormones and the Endocrine System
Chapter 45
Hormones and the Endocrine System

2. Overview: 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

3. Insect metamorphosis is regulated by hormones

5. Concept 45.1: 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

6. 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

7. 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

8. 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

9. Simple endocrine pathway
LE 45-2a
Pathway
Example
Low blood
glucose
Stimulus
Receptor
protein
Pancreas
secretes
glucagon ( )
Endocrine
cell
Blood
vessel
Target
effectors
Liver
Response
Glycogen
breakdown,
glucose release
into blood
Simple endocrine pathway

10. LE 45-2b Pathway Example Stimulus Suckling Sensory neuron
Hypothalamus/
posterior pituitary
Neurosecretory
cell
Posterior pituitary
secretes oxytocin
( )
Blood
vessel
Target
effectors
Smooth muscle
in breast
Response
Milk release
Simple neurohormone pathway

11. LE 45-2c Pathway Example Simple neuroendocrine pathway Stimulus
Hypothalamic
neurohormone
released in
response to
neural and
hormonal
signals
Sensory
neuron
Hypothalamus
Neurosecretory
cell
Hypothalamus
secretes prolactin-
releasing
hormone ( )
Blood
vessel
Anterior
pituitary
secretes
prolactin ( )
Endocrine
cell
Blood
vessel
Target
effectors
Mammary glands
Response
Milk production
Simple neuroendocrine pathway

12. Three major classes of molecules function as hormones in vertebrates:
Concept 45.2: 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

13. Signaling by any of these hormones involves three key events:
Reception
Signal transduction
Response

14. 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
Animation: Water-Soluble Hormone

15. LE 45-3 SECRETORY CELL SECRETORY CELL Hormone molecule Hormone
VIA
BLOOD
VIA
BLOOD
Signal receptor
TARGET
CELL
TARGET
CELL
Signal
transduction
pathway
Signal
receptor OR
Cytoplasmic
response
DNA
Signal
transduction
and response
mRNA
DNA
Nuclear
response
NUCLEUS
Synthesis of
specific proteins
NUCLEUS
Receptor in plasma membrane
Receptor in cell nucleus

16. 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

17. The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress

18. different cell responses
LE 45-4
Different receptors
different cell responses
Epinephrine
Epinephrine
Epinephrine
a receptor
 receptor
 receptor
Glycogen
deposits
Vessel
dilates
Glycogen
breaks down
and glucose
is released
from cell
Vessel
constricts
Intestinal blood
vessel
Skeletal muscle
blood vessel
Liver cell
Different intracellular proteins
different cell responses

19. 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
Animation: Lipid-Soluble Hormone

20. 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

21. Prostaglandins help regulate aggregation of platelets, an early step in formation of blood clots

23. Concept 45.3: The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system
The hypothalamus and the pituitary gland control much of the endocrine system

26. LE 45-6 Hypothalamus Pineal gland Pituitary gland Thyroid gland
Parathyroid glands
Adrenal glands
Pancreas
Ovary
(female)
Testis
(male)

27. Relation Between the Hypothalamus and Pituitary Gland
The hypothalamus, a region of the lower brain, contains neurosecretory cells
The posterior pituitary, or neurohypophysis, is an extension of the hypothalamus
Hormonal secretions from neurosecretory cells are stored in or regulate the pituitary gland

29. LE 45-7 Hypothalamus Neurosecretory cells of the hypothalamus Axon
Posterior
pituitary
Anterior
pituitary
HORMONE
ADH
Oxytocin
TARGET
Kidney tubules
Mammary glands,
uterine muscles

30. 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

31. LE 45-8 Neurosecretory cells of the hypothalamus Portal vessels
Tropic Effects Only
FSH, follicle-stimulating hormone
LH, luteinizing hormone
TSH, thyroid-stimulating hormone
ACTH, adrenocorticotropic hormone
Neurosecretory cells
of the hypothalamus
Nontropic Effects Only
Prolactin
MSH, melanocyte-stimulating hormone
Endorphin
Portal vessels
Nontropic and Tropic Effects
Growth hormone
Hypothalamic
releasing
hormones
(red dots)
Endocrine cells of the
anterior pituitary
Pituitary hormones
(blue dots)
HORMONE
FSH and LH
TSH
ACTH
Prolactin
MSH
Endorphin
Growth hormone
TARGET
Testes or
ovaries
Thyroid
Adrenal
cortex
Mammary
glands
Melanocytes
Pain receptors
in the brain
Liver
Bones

32. 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

33. Anterior Pituitary Hormones
The anterior pituitary produces both tropic and nontropic hormones

34. 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

35. Nontropic Hormones
Nontropic hormones produced by the anterior pituitary:
Prolactin
Melanocyte-stimulating hormone (MSH)
-endorphin

36. Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates
MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals
Endorphins inhibit pain

37. 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

38. Concept 45.4: Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior
Many nonpituitary hormones regulate various functions in the body

39. 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)

41. The hypothalamus and anterior pituitary control secretion of thyroid hormones through two negative feedback loops

42. LE 45-9
Hypothalamus
TRH
Anterior
pituitary
TSH
Thyroid T3 T4

43. Thyroid hormones stimulate metabolism and influence development and maturation
Hyperthyroidism, excessive secretion of thyroid hormones, can cause Graves’ disease in humans

45. The thyroid gland also produces calcitonin, which functions in calcium homeostasis

46. Parathyroid Hormone and Calcitonin: Control of Blood Calcium
Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin, play the major role in calcium (Ca2+) homeostasis in mammals

48. LE 45-11 Calcitonin Thyroid gland releases calcitonin. Reduces
Ca2+ uptake
in kidneys
Stimulates
Ca2+ deposition
in bones
STIMULUS:
Rising blood
Ca2+ level
Blood Ca2+
level declines
to set point
Homoeostasis:
Blood Ca2+ level
(about 10 mg/100 mL)
Blood Ca2+
level rises
to set point
STIMULUS:
Falling blood
Ca2+ level
Stimulates
Ca2+ release
from bones
Parathyroid
gland
PTH
Increases
Ca2+ uptake
in intestines
Active
vitamin D
Stimulates Ca2+
uptake in kidneys

49. 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

50. 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

52. LE 45-12 Body cells take up more glucose. Insulin Beta cells of
pancreas
release insulin
into the blood.
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)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Alpha cells of pancreas
release glucagon into
the blood.
Liver breaks
down glycogen
and releases
glucose into the
blood.
Glucagon

53. 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

54. Glucagon increases blood glucose levels by
Stimulating conversion of glycogen to glucose in the liver
Stimulating breakdown of fat and protein into glucose

55. 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

56. 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

57. 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

59. 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

60. 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

61. LE 45-13 Stress Nerve signals Spinal cord (cross section) Hypothalamus
Releasing
hormone
Nerve
cell
Anterior pituitary
Blood vessel
Nerve cell
ACTH
ACTH
Adrenal
gland
Kidney
Short-term stress response
Long-term stress response
Effects of epinephrine and norepinephrine:
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Glycogen broken down to glucose;
increased blood glucose
1. Retention of sodium
ions and water by
kidneys
1. Proteins and fats
broken down and
converted to glucose,
leading to increased
blood glucose
2. Increased blood pressure
3. Increased breathing rate
2. Increased blood
volume and blood
pressure
4. Increased metabolic rate
5. Change in blood flow patterns, leading to
increased alertness and decreased
digestive and kidney activity
2. Immune system may
be suppressed

62. Gonadal Sex Hormones
The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins

64. The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system
Testosterone causes increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks

66. Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics
In mammals, progestins, which include progesterone, are primarily involved in preparing and maintaining the uterus

67. Melatonin and Biorhythms
The pineal gland, located in the brain, secretes melatonin

69. Light/dark cycles control release of melatonin
Primary functions of melatonin appear to relate to biological rhythms associated with reproduction

70. Concept 45.5: Invertebrate regulatory systems also involve endocrine and nervous system interactions
Diverse hormones regulate homeostasis in invertebrates
In insects, molting and development are controlled by three main hormones:
Brain hormone stimulates release of ecdysone from the prothoracic glands
Ecdysone promotes molting and development of adult characteristics
Juvenile hormone promotes retention of larval characteristics

71. LE 45-15_3 Brain Neurosecretory cells Brain hormone (BH) Corpus
cardiacum
Corpus
allatum
Low JH
Prothoracic
gland
Ecdysone
Juvenile
hormone
(JH)
EARLY
LARVA
LATER
LARVA
PUPA
ADULT