Download 16 - Brazosport College

PowerPoint® Lecture Slides
prepared by
Barbara Heard,
Atlantic Cape Community
Ninth Edition
College
Human Anatomy & Physiology
CHAPTER
16
The Endocrine
System: Part 1
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
Endocrine System: Overview
• Acts with nervous system to coordinate
and integrate activity of body cells
• Influences metabolic activities via
hormones transported in blood
• Response slower but longer lasting than
nervous system
• Endocrinology
– Study of hormones and endocrine organs
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Endocrine System: Overview
• Exocrine glands
– Nonhormonal substances (sweat, saliva)
– Have ducts to carry secretion to membrane
surface
• Endocrine glands
– Produce hormones
– Lack ducts
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Figure 16.1 Location of selected endocrine organs of the body.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Gonads
• Ovary (female)
• Testis (male)
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Chemical Messengers
• Hormones: long-distance chemical
signals; travel in blood or lymph
• Autocrines: chemicals that exert effects
on same cells that secrete them
• Paracrines: locally acting chemicals that
affect cells other than those that secrete
them
• Autocrines and paracrines are local
chemical messengers; not considered part
of endocrine system
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Chemistry of Hormones
• Two main classes
– Amino acid-based hormones
• Amino acid derivatives, peptides, and proteins
– Steroids
• Synthesized from cholesterol
• Gonadal and adrenocortical hormones
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Mechanisms of Hormone Action
• Though hormones circulate systemically
only cells with receptors for that hormone
affected
• Target cells
– Tissues with receptors for specific hormone
• Hormones alter target cell activity
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Mechanisms of Hormone Action
• Hormones act at receptors in one of two
ways
1. Water-soluble hormones (all amino acid–
based hormones except thyroid hormone)
•
•
•
Act on plasma membrane receptors
Act via G protein second messengers
Cannot enter cell
2. Lipid-soluble hormones (steroid and thyroid
hormones)
•
•
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Act on intracellular receptors that directly activate
genes
Can enter cell
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Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 1
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone Receptor G protein Enzyme
2nd
(1st messenger)
messenger
1 Hormone (1st messenger)
binds receptor.
Extracellular fluid
Adenylate cyclase
G protein (Gs)
Receptor
5 cAMP activates
protein kinases.
cAMP
GTP
GTP
ATP
GDP
Inactive
protein
kinase
GTP
Active
protein
kinase
Triggers responses of
target cell (activates
enzymes, stimulates
cellular secretion,
opens ion channel, etc.)
Cytoplasm
2 Receptor
activates G
protein (Gs).
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3 G protein
activates
adenylate
cyclase.
4 Adenylate
cyclase converts
ATP to cAMP (2nd
messenger).
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Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones.
Extracellular
fluid
Steroid
hormone
Plasma
membrane
Cytoplasm
Receptor
protein
Nucleus
Slide 1
1 The steroid hormone
diffuses through the plasma
membrane and binds an
intracellular receptor.
Receptorhormone
complex 2 The receptorhormone complex enters the
nucleus.
Receptor
Binding region
DNA
mRNA
3 The receptor- hormone
complex binds a specific DNA
region.
4 Binding initiates
transcription of the gene to
mRNA.
5 The mRNA directs protein
synthesis.
New protein
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Target Cell Specificity
• Target cells must have specific receptors
to which hormone binds, for example
– ACTH receptors found only on certain cells of
adrenal cortex
– Thyroxin receptors are found on nearly all
cells of body
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Target Cell Activation
• Target cell activation depends on three
factors
– Blood levels of hormone
– Relative number of receptors on or in target
cell
– Affinity of binding between receptor and
hormone
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Target Cell Activation
• Hormones influence number of their
receptors
– Up-regulation—target cells form more
receptors in response to low hormone levels
– Down-regulation—target cells lose receptors
in response to high hormone levels
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Control of Hormone Release
• Blood levels of hormones
– “Controlled” by negative feedback systems
– Vary only within narrow, desirable range
• Endocrine gland stimulated to synthesize
and release hormones in response to
– Humoral stimuli
– Neural stimuli
– Hormonal stimuli
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Figure 16.4a Three types of endocrine gland stimuli.
Slide 1
Humoral Stimulus
Hormone release caused by altered
levels of certain critical ions or
nutrients.
Capillary (low Ca2+
in blood)
Thyroid gland
(posterior view)
Parathyroid
glands
Parathyroid
glands
PTH
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Stimulus: Low concentration of Ca2+ in
capillary blood.
Response: Parathyroid glands secrete
parathyroid hormone (PTH), which
increases blood Ca2+.
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Figure 16.4b Three types of endocrine gland stimuli.
Slide 1
Neural Stimulus
Hormone release caused
by neural input.
CNS (spinal cord)
Preganglionic
sympathetic
fibers
Medulla of
adrenal gland
Capillary
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Stimulus: Action potentials in preganglionic
sympathetic fibers to adrenal medulla.
Response: Adrenal medulla cells secrete
epinephrine and norepinephrine.
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Figure 16.4c Three types of endocrine gland stimuli.
Slide 1
Hormonal Stimulus
Hormone release caused by another
hormone (a tropic hormone).
Hypothalamus
Anterior
pituitary
gland
Thyroid
gland
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Adrenal Gonad
cortex (Testis)
Stimulus: Hormones from hypothalamus.
Response: Anterior pituitary gland secretes
hormones that stimulate other endocrine
glands to secrete hormones.
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Nervous System Modulation
• Nervous system modifies stimulation of
endocrine glands and their negative
feedback mechanisms
– Example: under severe stress, hypothalamus
and sympathetic nervous system activated
•  body glucose levels rise
• Nervous system can override normal
endocrine controls
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Hormones in the Blood
• Hormones circulate in blood either free or
bound
– Steroids and thyroid hormone are attached to
plasma proteins
– All others circulate without carriers
• Concentration of circulating hormone
reflects
– Rate of release
– Speed of inactivation and removal from body
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Interaction of Hormones at Target Cells
• Multiple hormones may act on same target
at same time
– Permissiveness: one hormone cannot exert
its effects without another hormone being
present
– Synergism: more than one hormone
produces same effects on target cell 
amplification
– Antagonism: one or more hormones
oppose(s) action of another hormone
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Amino Acid based hormones
•
•
•
•
•
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Water soluble
May be stored and release later
Most are free – metabolized quickly
Shorter half-live
Example – Amino acid based hormones
except Thyroxin
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Steroid Homones
•
•
•
•
•
•
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Lipid-soluble
Cannot be stored
Transported by plasma proteins
Half life is longer
Less fluctuation in blood
Example: Estrogen, progesterone,
testosterone, aldosterone, corticol
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The Pituitary Gland and Hypothalamus
• Pituitary gland (hypophysis) has two
major lobes
– Posterior pituitary (lobe)
• Neural tissue
– Anterior pituitary (lobe)
(adenohypophysis)
• Glandular tissue
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Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 1
Paraventricular nucleus
Hypothalamus
Posterior lobe
of pituitary
Optic
chiasma
Infundibulum
(connecting stalk)
Hypothalamichypophyseal
tract
Supraoptic
nucleus
Inferior
hypophyseal
artery
Axon terminals
2 Oxytocin and ADH are
transported down the axons of
the hypothalamic- hypophyseal
tract to the posterior pituitary.
3 Oxytocin and ADH are
stored in axon terminals in
the posterior pituitary.
Posterior lobe
of pituitary
Oxytocin
ADH
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1 Hypothalamic neurons
synthesize oxytocin or
antidiuretic hormone (ADH).
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4 When hypothalamic neurons
fire, action potentials arriving at
the axon terminals cause
oxytocin or ADH to be released
into the blood.
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Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 1
Hypothalamus
Anterior lobe
of pituitary
Superior
hypophyseal
artery
2 Hypothalamic hormones
travel through portal veins to
the anterior pituitary where
they stimulate or inhibit
release of hormones made in
the anterior pituitary.
3 In response to releasing
hormones, the anterior
pituitary secretes hormones
into the secondary capillary
plexus. This in turn empties
into the general circulation.
GH, TSH, ACTH,
FSH, LH, PRL
Hypothalamic
neurons synthesize
GHRH, GHIH, TRH,
CRH, GnRH, PIH.
1 When appropriately stimulated,
hypothalamic neurons secrete
releasing or inhibiting hormones
into the primary capillary plexus.
Hypophyseal
portal system
• Primary capillary
plexus
• Hypophyseal
portal veins
• Secondary
capillary plexus
A portal
system is
two
capillary
plexuses
(beds)
connected
by veins.
Anterior lobe
of pituitary
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Posterior Pituitary and Hypothalamic
Hormones
• Oxytocin and ADH
– Each composed of nine amino acids
– Almost identical – differ in two amino acids
• What are the actions of Oxytocin?
• How about ADH?
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ADH (Vasopressin)
• Inhibits or prevents urine formation
• Primary purpose water balance –
osmolarity of body fluids – normal 285 –
300 milliosmols
• Targets kidney tubules  reabsorb more
water
• Release also triggered by pain, low blood
pressure, and drugs
• Inhibited by alcohol, diuretics
• High concentrations  vasoconstriction
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Determining Osmolality
• Osmolality = concentration based on #
solutes/liter
• Lab reports do not show osmolality – show
electrolyte concentration – need to double
Na+ concentration
• Hypertonicity = >300 mOsm
• Edema = <285 mOsm
• Osmoreceptors respond to change in
osmolality of plasma
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ADH
• Diabetes insipidus
– ADH deficiency due to hypothalamus or
posterior pituitary damage
– Must keep well-hydrated
• Syndrome of inappropriate ADH
secretion (SIADH)
– Retention of fluid, headache, disorientation
– Fluid restriction; blood sodium level
monitoring
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