PowerLecture: Chapter 15

1
PowerLectureChapter 15

• The Endocrine System

2
Learning Objectives

• Know the general mechanisms by which molecules
  integrate and control the various metabolic
  activities in organisms.
• Understand how the neuro-endocrine center
  controls secretion rates of other endocrine
  glands and responses in nerves and muscles.
• Know the major endocrine glands and their
  secretions.

3
Learning Objectives (contd)

• Know how sugar levels are regulated by hormones.
• Differentiate the modes of action of steroid and
  nonsteroid hormones.

4
Impacts/Issues

• Hormones in the Balance

5
Hormones in the Balance

• Arsenic may be an endocrine disrupter, especially
  of glucocorticoids.
• Glucocorticoids in turn regulate genes that
  protect against cancer.
• This may be the link between the consumption of
  arsenic in water supplies and increased rates of
  bladder, lung, and skin cancers.

6
Hormones in the Balance

• Other endocrine disrupters are also coming under
  scrutiny.
• The herbicide atrazine has been widely used on
  crops and turf grasses.
• PCBs, used for many years as fluid insulation in
  electrical transformers, have been banned but
  still persist in the environment, where they are
  linked to reproductive disorders in humans and
  animals.
• Research is continuing on endocrine disrupters
  the jury is still out.

7
Useful References for Impacts/Issues

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• EPA Endocrine Disruptors Research Initiative
• InfoTrac New Report Points Up Growing Evidence
  of Endocrine Disrupters. European Report, May 4,
  2006.

8
How Would You Vote?

• To conduct an instant in-class survey using a
  classroom response system, access JoinIn Clicker
  Content from the PowerLecture main menu.
• Some pesticides may disrupt hormone function in
  humans and other animals. Should they remain in
  use while researchers study their safety?
• a. No, they could be dangerous until we know for
  sure, it is better to be safe than sorry.
• b. Yes, banning them because of potential harm
  isn't fair there should be solid evidence first.

9
Useful References for How Would You Vote?

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Endocrine Disruption Study on Atrazine
  Disputed. Pesticide Toxic Chemical News, Jan.
  13, 2003.
• Water Conserve 2.0 Chemical Affecting Frogs
  Sexuality Males Are Acquiring Female Attributes
  after Exposure to a Common Weedkiller, Study Says

10
Section 1

• The Endocrine System Hormones

11
The Endocrine System Hormones

• Hormones are signaling molecules that are carried
  in the bloodstream.
• Signaling molecules are hormones and secretions
  that can bind to target cells and elicit in them
  a response.
• Hormones are secreted by endocrine glands,
  endocrine cells, and some neurons.
• Local signaling molecules are released by some
  cells these work only on nearby tissues.
• Pheromones are signaling molecules that have
  targets outside the body and which are used to
  integrate behaviors.

12
The Endocrine System Hormones

• Hormone sources The endocrine system.
• The sources of hormones (hormone producing
  glands, cells, and organs) may be collectively
  called the endocrine system.
• Endocrine sources and the nervous system function
  in highly interconnected ways.

13
The Endocrine System Hormones

• Hormones often interact.
• In an opposing interaction the effect of one
  hormone opposes the effect of another.
• In a synergistic interaction the combined action
  of two or more hormones is necessary to produce
  the required effect on target cells.
• In a permissive interaction one hormone exerts
  its effect only when a target cell has been
  primed to respond by another hormone.

14
Animation Major Human Endocrine Glands
CLICKTO PLAY
15
Fig. 15.1a, p. 271
hypothalamus
pineal gland
pituitary gland
thyroid gland
parathyroid glands
thymus gland
adrenal glands
pancreatic islets
ovaries
testes
16
Useful References for Section 1

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Review of the Endocrine System. Deirdre
  G. Bauer. MedSurg Nursing, Oct. 2005.

17
Section 2

• Types of Hormones and Their Signals

18
Types of Hormones and Their Signals

• Hormones come in several chemical forms.
• Steroid hormones
• are lipids made from
• cholesterol.
• Amine hormones are
• modified amino acids.
• Peptide hormones are peptides of only a few amino
  acids.
• Protein hormones are longer chains of amino
  acids.

19
Types of Hormones and Their Signals

• All hormones bind target cells this signal is
  converted into a form that works in the cell to
  change activity.
• A target cells response to a hormone is
  dependent on two factors
• Different hormones activate different cellular
  response mechanisms.
• Not all cells have receptors for all hormones
  the cells that respond are selected by means of
  the type of receptor they possess.

20
Types of Hormones and Their Signals

• Steroid hormones interact with cell DNA.
• Steroid hormones, such as estrogen and
  testosterone, are lipid-soluble and therefore
  cross plasma membranes readily.
• Once inside the cell, they penetrate the nuclear
  membrane and bind to receptors in the nucleus,
  either turning on or turning off genes.
• Switching genes on or off changes the proteins
  that are made by the cell, thus effecting a
  response.
• Some steroid hormones bind receptors in the cell
  membrane and change membrane properties to affect
  change to the target cells function.

21
Fig. 15.2a, p. 273
1 A steroid hormone molecule moves from the blood
into the fluid that bathes a target cell.
2 Being a lipid-soluable molecule, the steroid
hormone diffuses across the target cells plasma
membrane.
3 The hormone diffuses through the cytoplasm,
then on through the nuclear envelope. Inside the
nucleus, it will bind with a receptor molecule.
5 In the cytoplasm, the resulting protein
carries out the cells response to the hormone
signal.
receptor
4 Now the hormone-receptor complex triggers gene
activity in the DNA
hormone-receptor complex
change in cell activity
22
Video Mechanism of a steroid hormone
CLICKTO PLAY
23
Types of Hormones and Their Signals

• Nonsteroid hormones act indirectly, by way of
  second messengers.
• Nonsteroid hormones include the amine, peptide,
  and protein hormones.
• Nonsteroid hormones cannot cross the plasma
  membrane of target cells, so they must first bind
  to a receptor on the plasma membrane.
• Binding of the hormone to the receptor activates
  the receptor it in turn stimulates the
  production of a second messenger, a small
  molecule that can relay signals in the cell.
• Cyclic AMP (cyclic adenosine monophosphate) is
  one example of a second messenger.

24
1 A glucagon molecule diffuses from blood into
the fluid that bathes the plasma membrane of a
liver cell.
glucagon receptor at target cells membrane
Pi
cyclic AMP
ATP
2 Glucagon binds with the receptor, and the
binding activates adenylate cyclase. This enzyme
catalyzes the formation of cyclic AMP inside the
target cell.
3 The cyclic AMP now activates protein kinase A.
4 Protein kinase A converts phosphorylase kinase
to active form. This enzyme activates a
different enzyme, which breaks down glycogen to
its glucose monomers.
5 Protein kinase A also inhibits an enzyme
required for glycogen synthesis.
Fig. 15.2b, p. 273
25
Video Mechanism of a peptide hormone
CLICKTO PLAY
26
Useful References for Section 2

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Can PYY Cure Obesity? U.S. News World
  Report, Sept. 15, 2003.

27
Section 3

• The Hypothalamus and Pituitary Gland Major
  Controllers

28
The Hypothalamus and Pituitary Gland

• The hypothalamus and pituitary gland work jointly
  as the neural-endocrine control center.
• The hypothalamus is a portion of the brain that
  monitors internal organs and conditions.
• The pituitary is connected to the hypothalamus by
  a stalk.
• The posterior lobe consists of nervous tissue and
  releases two hormones made in the hypothalamus.
• The anterior lobe makes and secretes hormones
  that control the activity of other endocrine
  glands.

29
Fig. 15.1b, p. 271
hypothalamus
optic chasma
Location of the pituitary gland
pituitary stalk
anterior lobe
posterior lobe
membrane around brain
30
The Hypothalamus and Pituitary Gland

• The posterior pituitary lobe produces ADH and
  oxytocin.
• Neurons in the hypothalamus produce antidiuretic
  hormone (ADH) and oxytocin, which are released
  from axon endings in the capillary bed of the
  posterior lobe.
• ADH (or vasopressin) acts on the walls of kidney
  tubules to control the bodys water and solute
  levels by stimulating reabsorption.
• Oxytocin triggers uterine muscle contractions to
  expel the fetus and acts on mammary glands to
  release milk.

31
Animation Posterior Pituitary Function
CLICKTO PLAY
32
a Secretory neurons in the hypothalamus
synthesize ADH or oxytocin.
b The ADH Oxytocin moves downward inside the
axons of the secretory neurons and accumulates in
the axon endings.
d The hormone molecules move into the general
circulation.
c Action potentials trigger the release of these
hormones, which enter blood capillaries in the
posterior lobe of the pituitary.
oxytocin
ADH
kidney nephrons
muscles in uterus wall
mammary glands
Fig. 15.3, p. 274
33
The Hypothalamus and Pituitary Gland

• The anterior pituitary lobe produces six other
  hormones.
• Corticotropin (ACTH) stimulates the adrenal
  cortex.
• Thyrotropin (TSH) stimulates the thyroid gland.
• Follicle-stimulating hormone (FSH) causes ovarian
  follicle development and egg production.

34
The Hypothalamus and Pituitary Gland

• Luteinizing hormone (LH) also acts on the ovary
  to release an egg.
• Prolactin (PRL) acts on the mammary glands to
  stimulate and sustain milk production.
• Somatotropin (STH), also known as growth hormone
  (GH), acts on body cells in general to promote
  growth.
• Most of these hormones are releasers that
  stimulate target cells to secrete other hormones
  other hormones from the hypothalamus are
  inhibitors and block secretions.

35
Animation Anterior Pituitary Function
CLICKTO PLAY
36
Fig. 15.4, p. 275
a Cell bodies of different secretory neurons in
the hypothalamus secrete releasing and
inhibiting hormones.
b The hormones are picked up by a capillary bed
at the base of the hypothalamus.
c The bloodstream delivers hormones to a
capillary bed in the anterior lobe of pituitary.
e Hormones from anterior lobe cells enter small
blood vessels that lead to the general
circulation.
d Molecules of the releasing or inhibiting
hormone diffuse out of capillaries and act on
endocrine cells in the anterior lobe.
ACTH
TSH
FSH
LH
PRL
STH(GH)
most cells (growth-promoting effects)
thyroid gland
adrenal glands
mammary glands
testes in males, ovaries in females
37
(No Transcript)
38
Video Hypothalamus and Pituitary
CLICKTO PLAY
39
Useful References for Section 3

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• The Pituitary Society
• InfoTrac The Scent of Trust. Prevention, Oct.
  2005.

40
Section 4

• Factors That Influence Hormone Effects

41
Factors That Influence Hormone Effects

• Problems with control mechanisms can result in
  skewed hormone signals.
• Endocrine glands in general only release small
  quantities of hormones and control the frequency
  of release to make sure there isnt too much or
  too little hormone.

42
Factors That Influence Hormone Effects

• Abnormal quantities of hormones can lead to
  growth problems.
• Gigantism results from an
• oversecretion of growth
• hormone in childhood.
• Pituitary dwarfism
• results from an
• undersecretion of GH.

Figures 15.5a and 15.14
43
Factors That Influence Hormone Effects

• Acromegaly is a condition resulting from an
  oversecretion of GH in adulthood leading to
  abnormal thickening of tissues.
• Diabetes insipidus occurs when ADH secretions
  fall or stop, leading to dilute urine and the
  possibility of serious dehydration.

Figure 15.5b
44
Factors That Influence Hormone Effects

• Hormone interactions, feedback, and other factors
  also influence a hormones effects.
• At least four factors influence the effects of
  any given hormone.
• Hormones often interact with one another.
• Negative feedback mechanisms control secretion of
  hormones.
• Target cells may react differently to hormones at
  different times.
• Environmental cues can affect release of
  hormones.
• Hormones throughout the body are affected in
  similar ways.

45
(No Transcript)
46
Video Hormone Replacement Therapy

• This video clip is available in CNN Today Videos
  for Anatomy Physiology, 2003, Volume VII.
  Instructors, contact your local sales
  representative to order this volume, while
  supplies last.

47
Useful References for Section 4

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Acromegaly. Ana Pokrajac-Simeunovic and
  Peter Trainer. Chemist Druggist, Nov. 19, 2005.

48
Section 5

• The Thymus, Thyroid, and Parathyroid Glands

49
The Thymus, Thyroid, and Parathyroid Glands

• Thymus gland hormones aid immunity.
• Thyroid hormones affect metabolism, growth, and
  development.
• The thyroid gland secretes thyroid hormone (TH),
  which has effects on metabolism, growth, and
  development the thyroid gland also secretes
  calcitonin, which helps regulate calcium levels
  in the blood.

50
Fig. 15.6a, p. 278
thyroid cartilage (Adams apple)
blood vessel
thyroid gland
trachea (windpipe)
51
Animation Thyroid Hormone Action
CLICKTO PLAY
52
Fig. 15.6b, p. 278
Stimulus Blood level of thyroid hormone falls
below a set point.
Response

Hypothalamus
TRH
Anterior Pituitary
Rise in the blood level of thyroid hormone
inhibits secretion of TRH and THS.
TSH
Thyroid Gland
Thyroid hormone is secreted.
53
Fig. 15.6b, p. 278
Stimulus Blood level of thyroid hormone falls
below a set point.
Stepped Art
54
The Thymus, Thyroid, and Parathyroid Glands

• Iodine-deficient diets interfere with proper
  synthesis of thyroid hormones.
• Simple goiter is an enlargement
• of one or both lobes of the thyroid
• gland in the neck enlargement
• follows low blood levels of thyroid
• hormones (hypothyroidism).
• Graves disease and other forms of
• hyperthyroidism result from too
• much thyroid hormone in the blood.

Figure 15.7
55
The Thymus, Thyroid, and Parathyroid Glands

• PTH from the parathyroids is the main calcium
  regulator.
• Humans have four parathyroid
• glands, which secrete
• parathyroid hormone (PTH),
• the main regulator of blood
• calcium levels.
• More PTH is secreted when blood calcium levels
  drop below a certain point less is secreted when
  calcium rises.
• Calcitonin contributes to processes that pull
  calcium out of the blood.

56
Fig. 15.8, p. 279
Decrease in calcium ion concentration in blood
Parathyroid glands
PTH
stimulates
Calcium ion level increases
Osteoclasts release calcium ions from bone
Kidney tubules increase calcium ion reabsorption
Intestine increases calcium ion absorption
57
Fig. 15.8, p. 279
Decrease in calcium ion concentration in blood
Osteoclasts release calcium ions from bone
Kidney tubules Increase calcium ion reabsorption
Intestine Increases calcium ion absorption
Stepped Art
58
The Thymus, Thyroid, and Parathyroid Glands

• Rickets in children arises from a vitamin D
  deficient diet vitamin D is needed to aid
  absorption of calcium from food.
• Hyperparathyroidism sees so much calcium being
  withdrawn from a persons bones that the bone
  tissue is dangerously weakened.

59
Useful References for Section 5

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• The American Thyroid Association
• InfoTrac Primary Hyperparathyroidism (The
  Effective Physician). William E. Golden Robert
  H. Hopkins. Internal Medicine News, Dec. 1, 2005.

60
Section 6

• Adrenal Glands and Stress Responses

61
Adrenal Glands and Stress Responses

• The adrenal cortex produces glucocorticoids and
  mineralocorticoids.
• One adrenal gland is located on top of each
  kidney the outer part of each gland is the
  adrenal cortex, the site of production for two
  major steroid hormones.

62
Adrenal Glands and Stress Responses

• Glucocorticoids raise the level of glucose in the
  blood.
• The main glucocorticoid, cortisol, is secreted
  when the body is stressed and blood sugar levels
  drop cortisol promotes gluconeogenesis, a
  mechanism for making glucose from amino acids
  derived from protein breakdown.
• Cortisol also dampens the uptake of glucose from
  the blood, stimulates the breakdown of fats for
  energy, and suppresses inflammation.
• Hypoglycemia can result when the adrenal cortex
  makes too little cortisol this results in
  chronically low glucose levels in the blood.

63
Animation Control of Cortisol Secretion
CLICKTO PLAY
64
Fig. 15.9, p. 281
Response
Stimulus
Hypothalamus
a Blood level of cortisol falls below a set
point
b
CRH
Anterior Pituitary
adrenal cortex
f Both the hypothalamus and pituitary detect
rise in blood level of cortisol and slow its
secretion.
ACTH
adrenal medulla
Adrenal Cortex
Cortisol is secreted, with these effects
c Cell uptake of glucose from blood slows in
many tissues, especially muscles (not the
brain). d Proteins are broken down in many
tissues, muscles especially. The amino acids are
converted to glucose, and used in the assembly or
repair of cell structures. e Fats in adipose
tissue are broken down to fatty acids that enter
blood as an alternative energy source, indirectly
conserving glucose for the brain.
kidney
65
Adrenal Glands and Stress Responses

• Mineralocorticoids regulate the concentrations of
  minerals such as K and Na in the extracellular
  fluid aldosterone is one example that works in
  the nephrons of the kidneys.
• The adrenal cortex also secretes sex hormones in
  the fetus and at puberty.

66
Adrenal Glands and Stress Responses

• Hormones from the adrenal medulla help regulate
  blood circulation.
• The inner part of the adrenal gland, the adrenal
  medulla, secretes epinephrine and norepinephrine.
• Secretion by the adrenal medulla influences these
  molecules to behave like hormones to regulate
  blood circulation and carbohydrate use during
  stress.

67
Adrenal Glands and Stress Responses

• Long-term stress can damage health.
• Stress triggers the fight-flight response and the
  release of cortisol, epinephrine, and
  norepinephrine constant release of these
  molecules can contribute to hypertension and
  cardiovascular disease.
• Excess cortisol suppresses the immune system,
  making individuals susceptible to disease.
• Social connections for support and exercise for
  health can reduce the effects of stress.

68
Video Peanut Allergies

• This video clip is available in CNN Today Videos
  for Anatomy Physiology, 2004, Volume VIII.
  Instructors, contact your local sales
  representative to order this volume, while
  supplies last.

69
Useful References for Section 6

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• InfoTrac Prenatal Exposure to Stress and Stress
  Hormones Influences Child Development. Elysia
  Poggi Davis Curt A. Sandman. Infants Young
  Children, JulySept. 2006.

70
Section 7

• The Pancreas Regulating Blood Sugar

71
The Pancreas Regulating Blood Sugar

• The pancreas has both exocrine and endocrine
  functions the endocrine cells are located in
  clusters called pancreatic islets.

72
Fig. 15.10, p. 282
stomach
pancreas
small intestine
73
The Pancreas Regulating Blood Sugar

• Each pancreatic islet secretes three hormones
• Alpha cells secrete glucagon, which causes
  glycogen stored in the liver to be converted to
  glucose, which then enters the bloodstream.
• Beta cells secrete insulin, which stimulates the
  uptake of glucose by liver, muscle, and adipose
  cells to reduce levels in the blood, especially
  after a meal.
• Delta cells secrete somatostatin, which can
  inhibit the secretion of glucagon and insulin.

Figure 15.9
74
Animation Hormones and Glucose Metabolism
CLICKTO PLAY
75
Fig. 15.10a, p. 282
Stimulus Increase in blood glucose
Stimulus Decrease in blood glucose
a
f
PANCREAS
c
beta cells
alpha cells
b
beta cells
alpha cells
g
h
_
_


x
x
glucagon
insulin
glucagon
insulin
d
Body cells, especially in muscle and adipose
tissue, take up and use more glucose. Cells in
skeletal muscle and liver store glucose in the
form of glycogen.
i
Cells in liver break down glycogen faster. The
released glucose molecules enter blood.
Response Increase in blood glucose
j
e
Response Decrease in blood glucose
76
Useful References for Section 7

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• Journal of the Pancreas
• InfoTrac Perfecting a Pancreas Scientists
  Fine-Tune a Device to Be Used by Diabetics. Jamie
  Talan. Newsday, May 15, 2006.

77
Section 8

• Disorders of Glucose Homeostasis

78
Disorders of Glucose Homeostasis

• Diabetes mellitus is a
• disease resulting from the
• secretion of too little insulin.
• Without insulin, cells cant
• remove glucose from the
• blood the kidneys remove the excess in urine,
  creating imbalances in water-solute
  concentrations.
• Metabolic acidosis, a lower than optimal blood
  pH, can result because of this imbalance.

Figure 15.11
79
Disorders of Glucose Homeostasis

• In type 1 diabetes (also known as juvenile-onset
  diabetes) the insulin is no longer produced
  because the beta cells have been destroyed by an
  autoimmune response.
• Only about 1 in 10 diabetics have this form of
  diabetes.
• Treatment is by insulin injection.

80
Disorders of Glucose Homeostasis

• Type 2 diabetes is a global health crisis.
• In type 2 diabetes the insulin levels are near
  normal but the target cells cannot respond to the
  hormone.
• Beta cells eventually break down and produce less
  and less insulin.
• Excess glucose in the blood damages capillaries.
• Cardiovascular disease, stroke, heart attack, and
  other serious complications arise.

81
Disorders of Glucose Homeostasis

• Metabolic syndrome is a warning sign.
• Prediabetes describes individuals with slightly
  elevated blood sugar levels that have an
  increased risk for developing type 2 diabetes
  about 20 million Americans fall into this
  category and do not know it.

82
Disorders of Glucose Homeostasis

• A composite of features collectively called
  metabolic syndrome also describe risk for
  diabetes these features include apple shaped
  waistline, elevated blood pressure, low levels of
  HDL, and elevated glucose and triglycerides.
• Type 2 diabetes can be controlled with a
  combination of improved diet, exercise, and
  sometimes drugs.

83
(No Transcript)
84
Video Gene Therapy for Diabetes

• This video clip is available in CNN Today Videos
  for Genetics, 2005, Volume VII. Instructors,
  contact your local sales representative to order
  this volume, while supplies last.

85
Useful References for Section 8

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• American Diabetes Association
• CDC Diabetes
• InfoTrac Pancreas and Islet Transplantation in
  Type 1 Diabetes. Diabetes Care, April 2006.
• InfoTrac Preventing Diabetes. Kathy Doheny.
  Natural Health, April 2004.

86
Section 9

• Some Final Examples of Integration and Control

87
Some Final Examples ofIntegration and Control

• Light/dark cycles influence the pineal gland,
  which produces melatonin.
• Located in the brain, the pineal gland is a
  modification of a primitive third eye and is
  sensitive to light and seasonal influences this
  gland secretes the hormone melatonin.
• Melatonin is secreted in the dark, and levels
  change with the seasons.
• The biological clock seems to tick in synchrony
  with day length and is apparently influenced by
  melatonin.

88
Some Final Examples of Integration and Control

• Seasonal affective disorder (SAD) affects persons
  during the winter and may result from an
  out-of-sync biological clock melatonin makes it
  worse exposure to intense light helps.
• Melatonin levels may potentially be linked to the
  onset of puberty.

89
Some Final Examples of Integration and Control

• Hormones also are produced in the heart and GI
  tract.
• Atrial natriuretic peptide (ANP) produced by the
  heart atria regulates blood pressure.
• Gastrin and secretin from the GI tract stimulate
  release of stomach and intestinal secretions.

90
Some Final Examples of Integration and Control

• Prostaglandins have many effects.
• More than 16 prostaglandins have been identified
  in tissues throughout the body.
• When stimulated by epinephrine and
  norepinephrine, prostaglandins cause smooth
  muscles in blood vessels to constrict or dilate.
• Allergic responses to dust and pollen may be
  aggravated by the effects of prostaglandins on
  airways in the lungs.
• Prostaglandins have major effects on menstruation
  and childbirth.

91
Some Final Examples of Integration and Control

• Growth factors influence cell division.
• Hormonelike proteins called growth factors
  influence growth by regulating the rate of
  cellular division.
• Epidermal growth factor
• (EGF) influences the growth
• of many cell types, as does
• insulinlike growth factor (IGF).
• Nerve growth factor (NGF)
• promotes growth and survival
• of neurons in the developing
• embryo.

92
Some Final Examples of Integration and Control

• The current list of growth factors is expanding
  rapidly many of these factors may have
  applications in medicine.
• Pheromones may be important communication
  molecules in humans.
• Pheromones are released outside of the body by
  several animals to serve as sex attractants,
  territory markers, and communication signals.
• Recent studies suggest that humans also may
  communicate using pheromones.

93
Some Final Examples of Integration and Control

• Are endocrine disrupters at work?
• Endocrine disrupters are proposed to be
  environmental substances that interfere with
  reproduction or development.
• Sperm counts in
• males in Western
• countries declined
• about 40 between
• the years 1938 and
• 1990, possibly due
• to exposure to estrogens in the environment.

Figure 15.13
94
Useful References for Section 9

• The latest references for topics covered in this
  section can be found at the book companion
  website. Log in to the books e-resources page at
  www.thomsonedu.com to access InfoTrac articles.
• National Research Center for Women Families
  Are Pretty Products Causing Early Puberty?
• Howard Hughes Medical Institute The Matters
  Biological Clockworks
• InfoTrac Drug of Darkness Can a Pineal Hormone
  Head Off Everything from Breast Cancer to Aging?
  Science News, May 13, 1995.
• InfoTrac The Chemistry of Love. Sanjay Gupta.
  Time, Feb. 18, 2002.

95
Video Hormone-Induced Adjustments
CLICKTO PLAY