Download CHAPTER 13: ENDOCRINE SYSTEM

UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
LEARNING OUTCOMES:
13.1
Introduction
1.
13.2
13.3
13.4
Distinguish between endocrine and exocrine glands.
General Characteristics of the Endocrine System
2.
Explain what makes a cell a target cell for a hormone.
3.
List some important functions of hormones.
Hormone Action
4.
Describe how hormones can be classified according to their chemical
composition.
5.
Explain how steroid and nonsteroid hormones affect their target cells.
Control of Hormone Secretion
6.
Describe how negative feedback mechanisms regulate hormone secretion.
7.
Explain how the nervous system controls hormone secretion.
13.5-3.10
Pituitary Gland – Other Endocrine Glands
8.
Name and describe the locations of the major endocrine glands, and list the
hormones that they secrete.
9.
Describe the actions of the various hormones and their contributions to
homeostasis.
10.
Explain how the secretion of each hormone is regulated.
13.11 Stress and Its Effects
11.
Distinguish between physical and psychological stress.
12.
Describe the general stress response.
13.12. Life-Span Changes
13.
Describe some of the changes associated with aging of the endocrine system.
13-1
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.1
INTRODUCTION
A.
The general function of the endocrine system is to integrate body systems (i.e.
maintain homeostasis), in conjunction with the nervous system. Recall that
glands are effectors or responsive body parts that are stimulated by motor
impulses from the autonomic nervous system. Some of these glands, endocrine
glands compose the endocrine system.
See Table 13.1, page 489, comparing the nervous and endocrine systems.
B.
13.2
Endocrine Gland versus Exocrine Gland
1.
Endocrine glands secrete hormones that travel through the bloodstream
and cause a response at a target site(s) or organ(s).
a.
Endocrine glands are ductless.
2.
Exocrine gland secrete substances into ducts which then either:
a.
leave the body (i.e. sweat/sebaceous glands) or
b.
secreted into an internal space or lumen (i.e. digestive glands).
c.
Exocrine glands are not part of the endocrine system
GENERAL CHARACTERISTICS OF THE ENDOCRINE SYSTEM
A.
HORMONE = a very powerful substance (or chemical messenger) secreted by an
endocrine gland into the bloodstream, that affects the function of another cell or
"target cell".
1.
B.
General Characteristics of hormones:
a.
needed in very small amounts (potent)
b.
produce long-lasting effects in the cells they target
c.
regulate metabolic processes (maintain homeostasis)
d.
are regulated by negative-feedback mechanisms
See Fig 13.3, page 489 to see an overview of the endocrine glands. They include
the following glands:
1.
2.
3.
4.
5.
hypothalamus
pituitary
pineal gland
thyroid
parathyroids
6.
7.
8.
9.
10.
thymus
adrenals
pancreas
testes
ovaries
13-2
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.3
HORMONE ACTION
A.
Chemistry of Hormones
Hormones may be steroid (produced from cholesterol = fat-soluble) or nonsteroid
(water-soluble), which are usually amino acid based. See Fig 13.4, page 491.
1.
2.
*
B.
A steroid hormone passes easily through the target cell membrane.
A nonsteroid hormone requires a receptor on the target cell membrane to
allow the hormone to enter the target cell.
See Tables 13.2, page 490 and Fig 3.3, page 491 re: Hormone Names and
Abbreviations and Types of Hormones, respectively.
Actions of Hormones
Hormones alter metabolic activity in a target cell.
1.
2.
3.
4.
C.
Up-regulation = increase in receptors due to decrease in hormones.
Down-regulation = decrease in receptors due to increase in hormones.
Steroid Hormones and Thyroid Hormones
a.
enter cell by diffusion directly through cell membrane
b.
bind to protein receptor
c.
Newly formed hormone-receptor complex alters gene expression.
d.
New proteins carry out function signaled by hormone.
e.
See Figure 13.5 and Table 13.4, page 492 re: Sequence of Steroid
Hormone Action.
*
See Clinical Application 13.1, page 493 re: Abusing Hormones to
Improve Athletic Performance.
Nonsteroid Hormones
a.
include amines, peptides, proteins, and glycoproteins
b.
Hormone binds outside of cell and acts as first messenger.
c.
Result is either increase or decrease in some second messenger.
d.
Second messenger activates protein cascade, leading to cellular
changes.
e.
Commonly G-protein regulated using cyclic AMP as the second
messenger.
f.
Fig 13.7 page 495, and Table 13.5, page 494 re: Sequence of
Actions of Nonsteroid Hormone Using CyclicAMP.
Prostaglandins
1.
2.
3.
4.
5.
6.
locally acting signals (paracrine)
potent and needed in small amounts
not stored; produced just prior to release; rapidly inactivated
variety of effects
sometimes alter other hormones
See box on page 496 re: many synthetic prostaglandin uses.
13-3
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.4
CONTROL OF HORMONAL SECRETIONS
A.
Introduction
1.
B.
C.
The body must be able to turn processes on and off.
a.
Recall destruction of ACh in neuromuscular junction.
Half Life – time it takes for half of hormone to be removed from the plasma
1.
Short half life – quick acting and turn off quickly
2.
Long half life – longer lasting effects
a.
Thyroid and steroid hormone effects may last for days.
Control Sources: See Fig 13.8, page 496.
1.
2.
Generally one or any combination of 3 types of control:
a.
hormonal control by tropic hormones of hypothalamus
b.
nervous control by autonomic nervous system
c.
hormonal control by regulating blood levels
See Figures 13.10 and 13.11 page 498 for set point and negative feedback.
The overall scheme for the release of most hormones is presented in Figure 13.15, page
500. First the HYPOTHALAMUS secretes "releasing hormones" that target the anterior
pituitary gland, which in turn secretes hormones. See Fig 13.13, page 499.
13.5
PITUITARY GLAND
A.
Introduction: See Fig 13.9, page 497 and Fig 13.12, page 499.
1.
2.
3.
The pituitary gland (hypophysis), at the base of the brain is about 1 cm in
diameter.
It is attached to the hypothalamus by the pituitary stalk called the
infundibulum. Fig 13.9, page 497.
a.
Hypophyseal portal system exists.
o
Blood vessels to the anterior pituitary allow tropic
hormones direct access to the pituitary.
b.
Nerve axons
o
Axons from the hypothalamus extend to the posterior
pituitary.
o
They release 2 hormones.
The pituitary gland is composed of two major parts:
a.
Anterior pituitary gland
b.
Posterior pituitary gland
13-4
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.5
PITUITARY GLAND
B.
Anterior Pituitary Hormones
The Anterior Pituitary Gland (APG) hangs from the base of the brain and sits
in the sella turcica. See Fig 13.9, page 497. The APG secretes 6 different
hormones. See Fig 13.15, page 500.
1.
Human Growth Hormone (GH)
a.
controls growth of the body
b.
targets bone, muscle, and adipose tissue
c.
See Clinical Application 13.2, page 501 re: Growth Hormone Ups
and Downs.
2.
Prolactin (PRL)
a.
b.
3.
Thyroid stimulating hormone (TSH)
a.
b.
c.
4.
stimulates the production of milk by the mammary glands
targets the mammary glands
controls the secretion of hormones by the thyroid gland
targets thyroid gland
See Fig 13.16, page 500.
Adrenocorticotropic Hormone (ACTH)
a.
b.
controls the secretion of hormones by the adrenal cortex
targets the outer portion of the adrenal gland (cortex).
5.
Follicle Stimulating Hormone (FSH)
a.
response depends upon sex:
o
In females, FSH stimulates maturation of an ovarian follicle
and ovum.
o
In males, FSH stimulates the maturation of sperm in the
testes.
b.
A gonadotropin, which targets primary sex organs (ovary and
testes).
6.
Luteinizing Hormone (LH)
a.
response depends upon sex:
o
In females, LH causes ovulation.
o
In males, LH causes secretion of testosterone.
b.
A gonadotropin, which targets ovaries and testes.
13-5
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.5
PITUITARY GLAND
C.
Posterior Pituitary Hormones:
The Posterior Pituitary Gland
1.
2.
3.
4.
is located behind the anterior pituitary gland
is continuous with nerve fibers (supraopticohypophyseal tract) of the
hypothalamus
does not actually produce hormones (they are produced by the
hypothalamus), but stores them until it is stimulated to release them
secretes 2 hormones:
a.
Antidiuretic Hormone (ADH):
o
o
o
o
b.
o
c.
targets distal convoluted tubules (of kidney)
causes DCT’s to reabsorb water back into the bloodstream,
and therefore controls water balance and (increases) blood
pressure.
Also called vasopressin
See boxes on page 502 re: alcohol’s inhibition of ADH
secretion and diabetes insipidus.
Oxytocin (OT):
o
o
*
See Fig 13.12, page 499.
targets uterine smooth muscle and breasts
causes uterine muscle contraction and milk release from
suckled nipples
See box on page 503 re: induction of labor using OT.
See Fig 13.17, page 502, comparing the structures of ADH and OT.
See Table 13.6, page 503, Hormones of the Pituitary Gland.
13-6
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.6
THYROID GLAND
A.
Structure of the Gland
1.
2.
B.
13.7
The thyroid gland is located below the larynx and around trachea.
See Fig 13.18, page 504.
is composed of follicles involved in iodine uptake, in order to produce
thyroxine (T4) & triiodothyronine (T3) below.
See Fig 13.19, page 504.
Thyroid Hormones
Three hormones are secreted by the thyroid: See Table 13.7, page 505.
1.
Thyroxine (T4) &
2.
Triiodothyronine (T3):
a.
increase basal metabolic rate by stimulating cellular oxygen use to
produce ATP
b.
regulate metabolism
c.
T3 is the more potent form, however 90% of circulating hormone is
T4.
d.
See hormone structures in Fig 13.20, page 505.
e.
See Table 13.8 and Figures 13.21-13.23, page 506 re: Disorders of
the Thyroid Gland.
3.
Calcitonin:
a.
release is triggered by an increase in blood calcium levels
b.
targets bone cells (stimulates osteoblast activity and inhibits
osteoclast activity) and distal convoluted tubules (causes secretion
of excess calcium into urine)
c.
Therefore, causes a decrease in blood calcium (and phosphate)
levels back to normal.
PARATHYROID GLANDS
A.
Structure of the Glands
1.
consist of 4 small glands
2.
are located within the thyroid gland, usually on the posterior surface
See Fig 13.24, page 507.
B.
Parathyroid Hormone (PTH):
1.
Release of PTH is stimulated by decreased blood calcium levels.
2.
PTH targets bone cells (activates osteoclasts to resorb bone), proximal
convoluted tubules (causes PCT’s to reabsorb calcium back into
bloodstream), and activates Vitamin D to calcitriol which effects the small
intestine (promotes calcium absorption).
See Fig 13.26, page 507.
3.
Therefore, PTH causes an increase in blood calcium (and phosphate) and
brings levels back to normal.
C.
PTH and calcitonin together maintain the homeostasis of Ca2+ in the blood.
See Fig 13.26, page 507 and Fig 13.27, page 508.
D.
See Table 13.9, page 508, re: Disorders of the Parathyroid Glands.
13-7
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.8
ADRENAL GLANDS
A.
Structure of the Glands: See Fig 13.28, page 509.
1.
are located atop the kidneys and are retroperitoneal
2.
are divided into an outer adrenal cortex and an inner adrenal medulla.
B.
Hormones of the Adrenal Glands
1.
Hormones of the Adrenal Medulla (AM):
a.
The AM is located in the central portion of the adrenal glands.
b.
produces 2 closely related catecholamine hormones, which
function in the sympathetic division of the autonomic nervous
system:
1.
epinephrine
2.
norepinephrine
See Fig 13.30, page 509, and Table 13.10, page 510.
These hormones target:
a.
the heart (SA Node to increase heart rate)
b.
smooth muscle:
o
peripheral
arterioles
(vasoconstriction,
which increases blood pressure)
o
terminal
bronchioles
(bronchodilation,
which increases depth of breathing)
c.
the diaphragm (increased breathing rate)
c.
See Section 13.11, Stress and Its Effects below.
2.
Hormones of the Adrenal Cortex (AC):
a.
The AC is located in the outer portion of the adrenal glands.
b.
produces many steroid hormones when stimulated by ACTH:
See Fig 13.32, page 511 and Table 13.11, page 512.
1.
Aldosterone targets distal convoluted tubules (in the
kidney), causing reabsorption of electrolytes and water back
into the blood (increases blood pressure).
a.
See Fig 13.31, page 511.
2.
Cortisol targets all cells, where it regulates glucose
metabolism (along with T3 and T4).
a.
See Fig 13.33, page 512.
b.
See box on page 513 re: cortisol used as drug to
reduce inflammation.
3.
Supplemental sex hormones (estrogens and androgens) that
target secondary sex organs.
a.
Female androgens are responsible for sex drive, hair
growth in the axillary and inguinal region at puberty
and maintenance of all secondary sex organs
following menopause.
c.
See Clinical Application 13.3, page 513 re: Disorders of the
Adrenal Cortex.
13-8
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.9
PANCREAS
A.
Structure of the Gland
1.
is located behind the stomach on the left side of abdomen. See Fig 13.34,
page 513.
2.
functions as a mixed gland. (i.e. both an exocrine gland (digestion) and
endocrine gland (see below)
a.
Endocrine portions are the Pancreatic Islets (of Langerhans).
See Fig 13.35, page 514, and Table 13.12, page 515.
b.
Hormones of the Pancreatic Islets:
1.
glucagon:
o
is produced by Alpha cells (α-cells) in Islets of
Langerhans
o
Secretion is stimulated by decreased blood glucose
levels (i.e. fasting).
o
increases blood glucose levels (i.e. causes
breakdown of glycogen and release of glucose into
bloodstream).
2.
insulin:
o
is produced by Beta cells (β-cells) in Islets of
Langerhans
o
Secretion is stimulated by increased blood glucose
levels (i.e. after eating).
o
decreases blood glucose levels (i.e. moves glucose
from bloodstream into cells and promotes glycogen
formation in liver and skeletal muscle).
3.
See Fig 13.36, page 514 to review how these two hormones
regulate glucose homeostasis in the blood.
3.
See Clinical Application 13.4, page 516, Diabetes Mellitus.
4.
See From Science to Technology 13.1, page 517, Treating Diabetes.
13.10 OTHER ENDOCRINE GLANDS: See Fig 13.3, page 490.
A.
PINEAL GLAND
1.
is attached to the thalamus of the brain stem
2.
secretes a hormone called melatonin:
a.
production is stimulated by daylight (circadian rhythm)
b.
affects moods, emotions, etc.
c.
See box on page 516 re: jet lag.
B.
THYMUS GLAND
1.
is located in the mediastinum region behind sternum
2.
produces a hormone called thymosin that affects the maturation of
lymphocytes (T-cells)
3.
plays an important role in lymphatic system and immunity
4.
decreases in size as we age
13-9
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.10 OTHER ENDOCRINE GLANDS
C.
OVARIES
1.
An ovarian follicle (and ovum) start to mature each month following
puberty under the influence of follicle stimulating hormone (FSH).
a.
2.
D.
(will be discussed in greater detail in Chapter 22)
The developing follicle secretes estrogen:
o
Estrogen develops female secondary sexual characteristics
(at puberty) and maintains them throughout life.
o
Estrogen targets:
1.
mammary glands (development) within breasts
(enlargement)
2.
genitalia (growth and enlargement)
3.
adipose tissue in hips, thighs, and buttocks (growth)
Luteinizing hormone (LH) causes the mature follicle to rupture, releasing
the ovum (ovulation).
a.
The follicle then becomes the corpus luteum.
o
The corpus luteum secretes progesterone:

Progesterone prepares the uterine lining for
implantation of the zygote.
TESTES
(will be discussed in greater detail in Chapter 22)
1.
FSH targets the testes and causes the production of sperm.
2.
LH targets the testes and causes the production of testosterone:
a.
Testosterone develops male secondary sexual characteristics at
puberty and maintains them throughout life.
b.
Testosterone targets:
o
hair follicles in facial, pectoral, axillary, inguinal regions
(hair growth)
o
genitalia (enlargement)
o
muscle and bone (growth and strengthening)
o
vocal cords in larynx (thicken resulting in deeper voice)
13-10
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
E.
HORMONE SUMMARY TABLE (Keyed at the end of this outline)
HORMONE
SECRETED BY
WHAT
GLAND?
TARGET(S)?
EFFECT(S) AT
TARGET SITE
Growth Hormone
Thyroid Stimulating Hormone
(TSH)
Prolactin (PRL)
Adrenocorticotropic Hormone
(ACTH)
Luteinizing Hormone (LH)
Follicle Stimulating Hormone
(FSH)
Triiodothyronine (T3) and
Thyroxine (T4)
Aldosterone
Cortisol
Estrogen
Progesterone
Testosterone
Antidiuretic Hormone (ADH)
Oxytocin (OT)
Parathyroid Hormone (PTH)
Calcitonin
Insulin
Glucagon
Epinephrine/ Norepinephrine
Melatonin
Thymosin
13-11
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
13.11 STRESS AND ITS EFFECTS
A.
Types of Stress
1.
Physical
a.
Injury = accidental.
b.
Exercise = purposeful.
2.
Psychological
a.
Emotions = automatic.
b.
Overloaded = can be self induced.
B.
Responses to Stress
1.
General Stress Syndrome is the hypothalamic response to stress. See Fig
13.37, page 518 and Table 13.13, page 519.
a.
Activates adrenal medulla via sympathetic nervous system – short
term
b.
Activates adrenal cortex (cortisol) release in long term stress
c.
Basic goal is to increase available nutrients to fight off stress.
13.12 LIFE-SPAN CHANGES
A.
Endocrine glands shrink with age, and accumulate fibrous connective tissue, fat,
and lipofuscin, but hormone levels usually remain within normal levels.
1.
Decreasing levels of calcitonin and PTH increase osteoporosis risk.
2.
Muscle, liver, and fat cells may develop insulin resistance.
3.
Changes in melatonin secretion affect body clock.
4.
Thymosin production declines, hampering infectious disease resistance.
OTHER INTERESTING TOPICS:
A.
Human Pheromones in Sweat and Tears? See Introduction on page 488.
B.
McCune-Albright syndrome. See box on page 494
C.
Intermediate lobe and melanin production in fetuses. See box on page 498.
D.
Hypophyseal portal system. See box on page 498.
E.
Diabetes Insipidus. See box on page 503..
F.
ACE Inhibitors. See box on page 511.
G.
Hypoglycemia. See box on page 515.
INNERCONNECTIONS OF THE ENDOCRINE SYSTEM. See page 520.
CHAPTER SUMMARY – see pages 521-523.
CHAPTER ASSESSMENTS – see pages 523-524.
INTEGRATIVE ASSESSMENTS/ CRITICAL THINKING – see pages 520-524.
13-12
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
HORMONE SUMMARY TABLE
HORMONE
Growth Hormone (GH)
SECRETED BY
WHAT GLAND?
anterior pituitary
Thyroid Stimulating Hormone
(TSH)
Prolactin (PRL)
anterior pituitary
Adrenocorticotropic Hormone
(ACTH)
anterior pituitary
Luteinizing Hormone (LH)
anterior pituitary
anterior pituitary
TARGET(S)?
bone, muscle,
fat
thyroid
mammary
glands
adrenal cortex
Follicle Stimulating Hormone
(FSH)
anterior pituitary
In males:
interstitial cells
in testes
in females:
mature ovarian
follicle
males: seminiferous
tubules of
testes
females:
primordial
ovarian follicle
Triiodothryronine (T3) &
Thyroxine (T4)
Aldosterone
thyroid
all cells
adrenal cortex
Cortisol
adrenal cortex
distal
convoluted
tubules
all cells
Estrogen
ovarian follicle
secondary sex
organs
EFFECT(S) AT
TARGET SITE
growth of tissues
secrete hormones
T3 & T4
gland development
secrete hormones
cortisol and
aldosterone
males: testosterone
secretion
females: ovulation
males: sperm
production
females:
follicle/ovum
maturation
regulates rate of
metabolism
reabsorption of Na+
and water (increases
blood pressure)
rate of glucose
metabolism
development at
puberty and
maintenance
throughout life ‘til
menopause
13-13
UNIT 3 - CHAPTER 13: ENDOCRINE SYSTEM
HORMONE
SECRETED BY
WHAT GLAND?
corpus luteum of
ovary
TARGET(S)?
Testosterone
interstitial cells of
testes
secondary sex
organs
Anti-Diuretic Hormone (ADH)
posterior pituitary
distal
convoluted
tubule (DCT)
Oxytocin (OT)
posterior pituitary
Parathyroid Hormone (PTH)
parathyroids
uterine smooth
muscle and
suckled nipples
proximal
kidney tubules,
osteoclasts,
intestine
contraction during
labor and release of
milk
reabsorption of Ca2+
into blood, bone
resorption, dietary
Ca 2+ absorption
(increases blood
Ca2+)
Calcitonin
thyroid
distal
convoluted
tubules and
osteoblasts
secretion of Ca2+
into urine, bone
formation (decreases blood Ca2+)
Insulin
β-cells of pancreatic
Islets
all cells, liver
and skeletal
muscle
allows glucose into
cells from blood,
glycogen formation
(decreases blood
glucose)
Glucagon
α-cells of pancreatic
Islets
liver and
skeletal muscle
breakdown of
glycogen (increase
in blood glucose)
Epinephrine/Norepinephrine
adrenal medulla
cardiac muscle,
arteriole and
bronchiole
smooth muscle,
diaphragm, etc
increases heart rate
and blood
pressure...
Melatonin
pineal
limbic system
Thymosin
thymus
t-lymphocytes
circadian rhythm,
emotions/behavior
maturation
Progesterone
uterine
endometrium
EFFECT(S) AT
TARGET SITE
preparation for
implantation
(thickens, etc)
development at
puberty and
maintenance
reabsorption of
water ( increases
blood pressure)
13-14