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© 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
© 2013 Pearson Education, Inc.
Endocrine System: Overview
• Controls and integrates– Reproduction– Growth and development– Maintenance of electrolyte, water, and
nutrient balance of blood– Regulation of cellular metabolism and energy
balance– Mobilization of body defenses
© 2013 Pearson Education, Inc.
Endocrine System: Overview
• Exocrine glands– Nonhormonal substances (sweat, saliva)– Have ducts to carry secretion to membrane
surface
• Endocrine glands– Produce hormones– Lack ducts
© 2013 Pearson Education, Inc.
Endocrine System: Overview
• Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands
• Hypothalamus is Neuroendocrine organ• Some have exocrine and endocrine
functions– Pancreas, gonads, placenta
• Other tissues and organs that produce hormones– Adipose cells, thymus, and cells in walls of
small intestine, stomach, kidneys, and heart
© 2013 Pearson Education, Inc.
Figure 16.1 Location of selected endocrine organs of the body.
Pineal glandHypothalamusPituitary gland
Thyroid glandParathyroid glands(on dorsal aspect of thyroid gland)Thymus
Adrenal glands
Pancreas
Gonads
• Testis (male)• Ovary (female)
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Chemistry of Hormones
• Two main classes– Amino acid-based hormones
• Amino acid derivatives, peptides, and proteins
– Steroids• Synthesized from cholesterol• Gonadal and adrenocortical hormones
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Mechanisms of Hormone Action
• Hormone action on target cells may be to– Alter plasma membrane permeability and/or
membrane potential by opening or closing ion channels
– Stimulate synthesis of enzymes or other proteins
– Activate or deactivate enzymes– Induce secretory activity– Stimulate mitosis
© 2013 Pearson Education, Inc.
Mechanisms of Hormone Action
• Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location1. 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
© 2013 Pearson Education, Inc.
Mechanisms of Hormone Action
2. Lipid-soluble hormones (steroid and thyroid hormones)• Act on intracellular receptors that directly activate
genes• Can enter cell
© 2013 Pearson Education, Inc.
Plasma Membrane Receptors and Second-messenger Systems
• cAMP signaling mechanism:1. Hormone (first messenger) binds to receptor
2. Receptor activates G protein
3. G protein activates adenylate cyclase
4. Adenylate cyclase converts ATP to cAMP (second messenger)
5. cAMP activates protein kinases that phosphorylate proteins
© 2013 Pearson Education, Inc.
Plasma Membrane Receptors and Second-messenger Systems
• cAMP signaling mechanism– Activated kinases phosphorylate various
proteins, activating some and inactivating others
– cAMP is rapidly degraded by enzyme phosphodiesterase
– Intracellular enzymatic cascades have huge amplification effect
© 2013 Pearson Education, Inc.
Slide 1Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.
Hormone(1st messenger)
Receptor G protein Enzyme 2ndmessenger
Adenylate cyclase Extracellular fluid
G protein (Gs)
GDP
Receptor
Hormone (1st messenger) binds receptor.
Receptor activates G protein (Gs).
G protein activates adenylate cyclase.
Adenylate cyclase convertsATP to cAMP (2nd messenger).
Inactiveproteinkinase
Triggers responses of target cell (activatesenzymes, stimulatescellular secretion,opens ion channel, etc.)
Activeproteinkinase
cAMP activates protein kinases.
Cytoplasm
cAMP
GTP
GTPGTP
ATP
1
2 3 4
5
© 2013 Pearson Education, Inc.
Slide 2Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.
Hormone(1st messenger)
Receptor G protein Enzyme 2ndmessenger Hormone (1st messenger)
binds receptor.1
Extracellular fluid
Receptor
Cytoplasm
© 2013 Pearson Education, Inc.
Slide 3Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.
Hormone(1st messenger)
Receptor G protein Enzyme 2ndmessenger
Extracellular fluid
Hormone (1st messenger) binds receptor.1
G protein (Gs)
GDP
Receptor
GTP
GTP
Receptor activates G protein (Gs).
2
Cytoplasm
© 2013 Pearson Education, Inc.
Slide 4Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.
Hormone(1st messenger)
Receptor G protein Enzyme 2ndmessenger
Adenylate cyclase Extracellular fluid
G protein (Gs)
GDP
Receptor
Hormone (1st messenger) binds receptor.
Receptor activates G protein (Gs).
G protein activates adenylate cyclase.
Cytoplasm
GTP
GTPGTP
1
2 3
© 2013 Pearson Education, Inc.
Slide 5Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.
Hormone(1st messenger)
Receptor G protein Enzyme 2ndmessenger
Adenylate cyclase Extracellular fluid
G protein (Gs)
GDP
Receptor
Hormone (1st messenger) binds receptor.
Receptor activates G protein (Gs).
G protein activates adenylate cyclase.
Adenylate cyclase convertsATP to cAMP (2nd messenger).
Cytoplasm
cAMP
GTP
GTPGTP
ATP
1
2 3 4
© 2013 Pearson Education, Inc.
Slide 6Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.
Hormone(1st messenger)
Receptor G protein Enzyme 2ndmessenger
Adenylate cyclase Extracellular fluid
G protein (Gs)
GDP
Receptor
Hormone (1st messenger) binds receptor.
Receptor activates G protein (Gs).
G protein activates adenylate cyclase.
Adenylate cyclase convertsATP to cAMP (2nd messenger).
Inactiveproteinkinase
Triggers responses of target cell (activatesenzymes, stimulatescellular secretion,opens ion channel, etc.)
Activeproteinkinase
cAMP activates protein kinases.
Cytoplasm
cAMP
GTP
GTPGTP
ATP
1
2 3 4
5
© 2013 Pearson Education, Inc.
Plasma Membrane Receptors and Second-messenger Systems
• PIP2-calcium signaling mechanism
– Involves G protein and membrane-bound effector – phospholipase C
– Phospholipase C splits PIP2 into two second messengers – diacylglycerol (DAG) and inositol trisphosphate (IP3)
• DAG activates protein kinase; IP3 causes Ca2+ release
• Calcium ions act as second messenger
© 2013 Pearson Education, Inc.
Plasma Membrane Receptors and Second-messenger Systems
– Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin
– Calcium-bound calmodulin activates enzymes that amplify cellular response
© 2013 Pearson Education, Inc.
Other Signaling Mechanisms
• Cyclic guanosine monophosphate (cGMP) is second messenger for some hormones
• Some work without second messengers– E.g., insulin receptor is tyrosine kinase
enzyme that autophosphorylates upon insulin binding docking for relay proteins that trigger cell responses
© 2013 Pearson Education, Inc.
Intracellular Receptors and Direct Gene Activation
• Steroid hormones and thyroid hormone1. Diffuse into target cells and bind with
intracellular receptors2. Receptor-hormone complex enters nucleus;
binds to specific region of DNA3. Prompts DNA transcription to produce
mRNA4. mRNA directs protein synthesis5. Promote metabolic activities, or promote
synthesis of structural proteins or proteins for export from cell
© 2013 Pearson Education, Inc.
Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones. Slide 1
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
1
5
The receptor-hormone complex enters the nucleus.
The receptor- hormone complex binds a specific DNA region.
Binding initiates transcription of the gene to mRNA.
The mRNA directs protein synthesis.
New protein
Nucleus
mRNA
DNA
ReceptorBinding region
Receptor-hormonecomplex
Receptorprotein
Steroidhormone Plasma
membraneExtracellularfluid
Cytoplasm
2
3
4
© 2013 Pearson Education, Inc.
Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones. Slide 2
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
1
Nucleus
Receptorprotein
Steroidhormone Plasma
membraneExtracellularfluid
Cytoplasm
Receptor-hormonecomplex
© 2013 Pearson Education, Inc.
Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones. Slide 3
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
1
The receptor-hormone complex enters the nucleus.
Nucleus
Receptor-hormonecomplex
Receptorprotein
Steroidhormone Plasma
membraneExtracellularfluid
Cytoplasm
2
© 2013 Pearson Education, Inc.
Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones. Slide 4
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
1
The receptor-hormone complex enters the nucleus.
The receptor- hormone complex binds a specific DNA region.
Nucleus
DNA
ReceptorBinding region
Receptor-hormonecomplex
Receptorprotein
Steroidhormone Plasma
membraneExtracellularfluid
Cytoplasm
2
3
© 2013 Pearson Education, Inc.
Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones. Slide 5
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
1
The receptor-hormone complex enters the nucleus.
The receptor- hormone complex binds a specific DNA region.
Binding initiates transcription of the gene to mRNA.
Nucleus
mRNA
DNA
ReceptorBinding region
Receptor-hormonecomplex
Receptorprotein
Steroidhormone Plasma
membraneExtracellularfluid
Cytoplasm
2
3
4
© 2013 Pearson Education, Inc.
Slide 6Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones.
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
1
5
The receptor-hormone complex enters the nucleus.
The receptor- hormone complex binds a specific DNA region.
Binding initiates transcription of the gene to mRNA.
The mRNA directs protein synthesis.
New protein
Nucleus
mRNA
DNA
ReceptorBinding region
Receptor-hormonecomplex
Receptorprotein
Steroidhormone Plasma
membraneExtracellularfluid
Cytoplasm
2
3
4
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Humoral Stimuli
• Changing blood levels of ions and nutrients directly stimulate secretion of hormones
• Example: Ca2+ in blood– Declining blood Ca2+ concentration stimulates
parathyroid glands to secrete PTH (parathyroid hormone)
– PTH causes Ca2+ concentrations to rise and stimulus is removed
© 2013 Pearson Education, Inc.
Figure 16.4a Three types of endocrine gland stimuli. Slide 1
Humoral Stimulus
Hormone release caused by alteredlevels of certain critical ions ornutrients.
Stimulus: Low concentration of Ca2+ incapillary blood.
Parathyroidglands
Parathyroidglands
Capillary (low Ca2+
in blood)
Thyroid gland(posterior view)
PTH
Response: Parathyroid glands secreteparathyroid hormone (PTH), whichincreases blood Ca2+.
© 2013 Pearson Education, Inc.
Figure 16.4a Three types of endocrine gland stimuli. Slide 2
Humoral Stimulus
Hormone release caused by alteredlevels of certain critical ions ornutrients.
Parathyroidglands
Parathyroidglands
Capillary (low Ca2+
in blood)
Thyroid gland(posterior view)
© 2013 Pearson Education, Inc.
Figure 16.4a Three types of endocrine gland stimuli. Slide 3
Humoral Stimulus
Hormone release caused by alteredlevels of certain critical ions ornutrients.
Stimulus: Low concentration of Ca2+ incapillary blood.
Parathyroidglands
Parathyroidglands
Capillary (low Ca2+
in blood)
Thyroid gland(posterior view)
PTH
Response: Parathyroid glands secreteparathyroid hormone (PTH), whichincreases blood Ca2+.
© 2013 Pearson Education, Inc.
Neural Stimuli
• Nerve fibers stimulate hormone release– Sympathetic nervous system fibers stimulate
adrenal medulla to secrete catecholamines
© 2013 Pearson Education, Inc.
Figure 16.4b Three types of endocrine gland stimuli. Slide 1
Neural Stimulus
Hormone release caused by neural input.
Stimulus: Action potentials in preganglionicsympathetic fibers to adrenal medulla.
CNS (spinal cord)
Preganglionicsympatheticfibers
Medulla ofadrenal gland
Capillary
Response: Adrenal medulla cells secreteepinephrine and norepinephrine.
© 2013 Pearson Education, Inc.
Figure 16.4b Three types of endocrine gland stimuli. Slide 2
Neural Stimulus
Hormone release caused by neural input.
CNS (spinal cord)
Preganglionicsympatheticfibers
Medulla ofadrenal gland
Capillary
© 2013 Pearson Education, Inc.
Figure 16.4b Three types of endocrine gland stimuli. Slide 3
Neural Stimulus
Hormone release caused by neural input.
Stimulus: Action potentials in preganglionicsympathetic fibers to adrenal medulla.
CNS (spinal cord)
Preganglionicsympatheticfibers
Medulla ofadrenal gland
Capillary
Response: Adrenal medulla cells secreteepinephrine and norepinephrine.
© 2013 Pearson Education, Inc.
Hormonal Stimuli
• Hormones stimulate other endocrine organs to release their hormones – Hypothalamic hormones stimulate release of
most anterior pituitary hormones– Anterior pituitary hormones stimulate targets
to secrete still more hormones– Hypothalamic-pituitary-target endocrine organ
feedback loop: hormones from final target organs inhibit release of anterior pituitary hormones
© 2013 Pearson Education, Inc.
Figure 16.4c Three types of endocrine gland stimuli. Slide 1
Hormonal Stimulus
Hormone release caused by anotherhormone (a tropic hormone).
Stimulus: Hormones from hypothalamus.
Anteriorpituitarygland
Thyroidgland
Adrenalcortex
Gonad(Testis)
Hypothalamus
Response: Anterior pituitary gland secreteshormones that stimulate other endocrine glands to secrete hormones.
© 2013 Pearson Education, Inc.
Figure 16.4c Three types of endocrine gland stimuli. Slide 2
Hormonal Stimulus
Hormone release caused by anotherhormone (a tropic hormone).
Anteriorpituitarygland
Thyroidgland
Adrenalcortex
Gonad(Testis)
Hypothalamus
© 2013 Pearson Education, Inc.
Figure 16.4c Three types of endocrine gland stimuli. Slide 3
Hormonal Stimulus
Hormone release caused by anotherhormone (a tropic hormone).
Anteriorpituitarygland
Thyroidgland
Adrenalcortex
Gonad(Testis)
Hypothalamus
© 2013 Pearson Education, Inc.
Figure 16.4c Three types of endocrine gland stimuli. Slide 4
Hormonal Stimulus
Hormone release caused by anotherhormone (a tropic hormone).
Stimulus: Hormones from hypothalamus.
Anteriorpituitarygland
Thyroidgland
Adrenalcortex
Gonad(Testis)
Hypothalamus
Response: Anterior pituitary gland secreteshormones that stimulate other endocrine glands to secrete hormones.
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Hormones in the Blood
• Hormones removed from blood by– Degrading enzymes– Kidneys– Liver
• Half-life—time required for hormone's blood level to decrease by half
– Varies from fraction of minute to a week
© 2013 Pearson Education, Inc.
Onset of Hormone Activity
• Some responses ~ immediate
• Some, especially steroid, hours to days
• Some must be activated in target cells
© 2013 Pearson Education, Inc.
Duration of Hormone Activity
• Limited– Ranges from 10 seconds to several hours– Effects may disappear as blood levels drop– Some persist at low blood levels
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
The Pituitary Gland and Hypothalamus
• Pituitary gland (hypophysis) has two major lobes
– Posterior pituitary (lobe)• Neural tissue
– Anterior pituitary (lobe) (adenohypophysis)• Glandular tissue
© 2013 Pearson Education, Inc.
Pituitary-hypothalamic Relationships
• Posterior pituitary (lobe)– Downgrowth of hypothalamic neural tissue– Neural connection to hypothalamus
(hypothalamic-hypophyseal tract)– Nuclei of hypothalamus synthesize
neurohormones oxytocin and antidiuretic hormone (ADH)
– Neurohormones are transported to and stored in posterior pituitary
© 2013 Pearson Education, Inc.
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 1
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
Oxytocin and ADH are stored in axon terminals in the posterior pituitary.
When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.
1
2
3
4OxytocinADH
Posterior lobeof pituitary
Opticchiasma
Infundibulum(connecting stalk)
Hypothalamic-hypophyseal
tract
Axon terminals
Posterior lobeof pituitary
Paraventricular nucleus
Hypothalamus
Supraopticnucleus
Inferiorhypophysealartery
Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.
© 2013 Pearson Education, Inc.
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 2
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
1
Posterior lobeof pituitary
Opticchiasma
Infundibulum(connecting stalk)
Axon terminals
Paraventricular nucleus
Hypothalamus
Supraopticnucleus
Inferiorhypophysealartery
Hypothalamic-hypophyseal
tract
Posterior lobeof pituitary
© 2013 Pearson Education, Inc.
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 3
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
1
2
Posterior lobeof pituitary
Opticchiasma
Infundibulum(connecting stalk)
Axon terminals
Paraventricular nucleus
Hypothalamus
Supraopticnucleus
Inferiorhypophysealartery
Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.Hypothalamic-
hypophysealtract
Posterior lobeof pituitary
© 2013 Pearson Education, Inc.
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 4
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
Oxytocin and ADH are stored in axon terminals in the posterior pituitary.
1
2
3
Posterior lobeof pituitary
Opticchiasma
Infundibulum(connecting stalk)
Axon terminals
Paraventricular nucleus
Hypothalamus
Supraopticnucleus
Inferiorhypophysealartery
Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.Hypothalamic-
hypophysealtract
Posterior lobeof pituitary
© 2013 Pearson Education, Inc.
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 5
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
Oxytocin and ADH are stored in axon terminals in the posterior pituitary.
When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.
1
2
3
4OxytocinADH
Posterior lobeof pituitary
Opticchiasma
Infundibulum(connecting stalk)
Axon terminals
Paraventricular nucleus
Hypothalamus
Supraopticnucleus
Inferiorhypophysealartery
Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.Hypothalamic-
hypophysealtract
Posterior lobeof pituitary
© 2013 Pearson Education, Inc.
Pituitary-hypothalamic Relationships
• Anterior Lobe:– Originates as out-pocketing of oral mucosa– Vascular connection to hypothalamus
• Hypophyseal portal system– Primary capillary plexus– Hypophyseal portal veins– Secondary capillary plexus – Carries releasing and inhibiting hormones to anterior
pituitary to regulate hormone secretion
© 2013 Pearson Education, Inc.
Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 1
Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary.
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
Anterior lobeof pituitary
When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.
Hypophysealportal system
• Primary capillary plexus• Hypophyseal portal veins• Secondary capillary plexus
Superiorhypophyseal
artery
Anterior lobeof pituitary
Hypothalamus Hypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.
A portal system is two capillary plexuses (beds) connected by veins.
12
3
© 2013 Pearson Education, Inc.
Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 2
GH, TSH, ACTH,FSH, LH, PRL
Anterior lobeof pituitary
When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.
Hypophysealportal system
• Primary capillary plexus• Hypophyseal portal veins• Secondary capillary plexus
Superiorhypophyseal
artery
Anterior lobeof pituitary
Hypothalamus Hypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.
A portal system is two capillary plexuses (beds) connected by veins.
1
© 2013 Pearson Education, Inc.
Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 3
Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary.
GH, TSH, ACTH,FSH, LH, PRL
Anterior lobeof pituitary
When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.
Hypophysealportal system
• Primary capillary plexus• Hypophyseal portal veins• Secondary capillary plexus
Superiorhypophyseal
artery
Anterior lobeof pituitary
Hypothalamus Hypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.
A portal system is two capillary plexuses (beds) connected by veins.
12
© 2013 Pearson Education, Inc.
Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 4
Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary.
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
Anterior lobeof pituitary
When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.
Hypophysealportal system
• Primary capillary plexus• Hypophyseal portal veins• Secondary capillary plexus
Superiorhypophyseal
artery
Anterior lobeof pituitary
Hypothalamus Hypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.
A portal system is two capillary plexuses (beds) connected by veins.
12
3
© 2013 Pearson Education, Inc.
Posterior Pituitary and Hypothalamic Hormones
• Oxytocin and ADH– Each composed of nine amino acids– Almost identical – differ in two amino acids
© 2013 Pearson Education, Inc.
Oxytocin
• Strong stimulant of uterine contraction
• Released during childbirth
• Hormonal trigger for milk ejection
• Acts as neurotransmitter in brain
© 2013 Pearson Education, Inc.
ADH (Vasopressin)
• Inhibits or prevents urine formation
• Regulates water balance
• Targets kidney tubules reabsorb more water
• Release also triggered by pain, low blood pressure, and drugs
• Inhibited by alcohol, diuretics
• High concentrations vasoconstriction
© 2013 Pearson Education, Inc.
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
© 2013 Pearson Education, Inc.
Anterior Pituitary Hormones
• Growth hormone (GH)
• Thyroid-stimulating hormone (TSH) or thyrotropin
• Adrenocorticotropic hormone (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin (PRL)
© 2013 Pearson Education, Inc.
Anterior Pituitary Hormones
• All are proteins
• All except GH activate cyclic AMP second-messenger systems at their targets
• TSH, ACTH, FSH, and LH are all tropic hormones (regulate secretory action of other endocrine glands)
© 2013 Pearson Education, Inc.
Growth Hormone (GH, or Somatotropin)
• Produced by somatotropic cells
• Direct actions on metabolism– Increases blood levels of fatty acids;
encourages use of fatty acids for fuel; protein synthesis
– Decreases rate of glucose uptake and metabolism – conserving glucose
Glycogen breakdown and glucose release to blood (anti-insulin effect)
© 2013 Pearson Education, Inc.
Growth Hormone (GH, or Somatotropin)
• Indirect actions on growth
• Mediates growth via growth-promoting proteins – insulin-like growth factors (IGFs)
• IGFs stimulate– Uptake of nutrients DNA and proteins– Formation of collagen and deposition of bone
matrix
• Major targets—bone and skeletal muscle
© 2013 Pearson Education, Inc.
Growth Hormone (GH)
• GH release chiefly regulated by hypothalamic hormones– Growth hormone–releasing hormone (GHRH)
• Stimulates release
– Growth hormone–inhibiting hormone (GHIH) (somatostatin)
• Inhibits release
• Ghrelin (hunger hormone) also stimulates release
© 2013 Pearson Education, Inc.
Homeostatic Imbalances of Growth Hormone
• Hypersecretion– In children results in gigantism– In adults results in acromegaly
• Hyposecretion– In children results in pituitary dwarfism
© 2013 Pearson Education, Inc.
Figure 16.6 Growth-promoting and metabolic actions of growth hormone (GH).
Hypothalamussecretes growthhormone–releasinghormone (GHRH), andGHIH (somatostatin)
Anteriorpituitary
Inhibits GHRH release
Stimulates GHIH release
Inhibits GH synthesisand release
Feedback
Indirect actions(growth-promoting)
Liver andother tissues
Insulin-like growthfactors (IGFs)
Produce
Effects
Skeletal ExtraskeletalFat
metabolismCarbohydratemetabolism
Direct actions(metabolic,anti-insulin)
Effects
Growth hormone (GH)
Increased cartilageformation and
skeletal growth
Increased proteinsynthesis, andcell growth and
proliferation
Increasedfat breakdown
and release
Increased bloodglucose and otheranti-insulin effects
Increases, stimulates
Initial stimulus
Reduces, inhibits
Physiological response
Result
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Figure 16.7 Disorders of pituitary growth hormone.
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Thyroid-stimulating Hormone (Thyrotropin)
• Produced by thyrotropic cells of anterior pituitary
• Stimulates normal development and secretory activity of thyroid
• Release triggered by thyrotropin-releasing hormone from hypothalamus
• Inhibited by rising blood levels of thyroid hormones that act on pituitary and hypothalamus
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Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroidhormones
Target cellsStimulates
Figure 16.8 Regulation of thyroid hormone secretion.
Inhibits
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Adrenocorticotropic Hormone (Corticotropin)
• Secreted by corticotropic cells of anterior pituitary
• Stimulates adrenal cortex to release corticosteroids
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Adrenocorticotropic Hormone (Corticotropin)
• Regulation of ACTH release– Triggered by hypothalamic corticotropin-
releasing hormone (CRH) in daily rhythm– Internal and external factors such as fever,
hypoglycemia, and stressors can alter release of CRH
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Gonadotropins
• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Secreted by gonadotrophs of anterior pituitary
• FSH stimulates gamete (egg or sperm) production
• LH promotes production of gonadal hormones
• Absent from the blood in prepubertal boys and girls
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Gonadotropins
• Regulation of gonadotropin release– Triggered by gonadotropin-releasing hormone
(GnRH) during and after puberty– Suppressed by gonadal hormones (feedback)
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Prolactin (PRL)
• Secreted by prolactin cells of anterior pituitary
• Stimulates milk production
• Role in males not well understood
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Prolactin (PRL)
• Regulation of PRL release– Primarily controlled by prolactin-inhibiting
hormone (PIH) (dopamine)
• Blood levels rise toward end of pregnancy
• Suckling stimulates PRL release and promotes continued milk production
• Hypersecretion causes inappropriate lactation, lack of menses, infertility in females, and impotence in males