Chapter 16 A

61
PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 16 The Endocrine System: Part A

Transcript of Chapter 16 A

Page 1: Chapter 16 A

PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

16The Endocrine System: Part A

Page 2: Chapter 16 A

Copyright © 2010 Pearson Education, Inc.

Endocrine System: Overview

• Acts with the nervous system to coordinate and integrate the activity of body cells

• Influences metabolic activities by means of hormones transported in the blood

• Responses occur more slowly but tend to last longer than those of the nervous system

• Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands

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Endocrine System: Overview

• Some organs produce both hormones and exocrine products (e.g., pancreas and gonads)

• The hypothalamus has both neural and endocrine functions

• Other tissues and organs that produce hormones include adipose cells, thymus, cells in the walls of the small intestine, stomach, kidneys, and heart

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Copyright © 2010 Pearson Education, Inc. Figure 16.1

Pineal glandHypothalamusPituitary gland

Parathyroid glands(on dorsal aspectof thyroid gland)Thymus

Thyroid gland

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

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Chemical Messengers

• Hormones: long-distance chemical signals that travel in the blood or lymph

• Autocrines: chemicals that exert effects on the 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 and will not be considered part of the endocrine system

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Chemistry of Hormones

• Two main classes

1.Amino acid-based hormones

• Amines, thyroxine, peptides, and proteins

2.Steroids

• Synthesized from cholesterol

• Gonadal and adrenocortical hormones

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Mechanisms of Hormone Action

• Hormone action on target cells

1. Alter plasma membrane permeability of membrane potential by opening or closing ion channels

2. Stimulate synthesis of proteins or regulatory molecules

3. Activate or deactivate enzyme systems

4. Induce secretory activity

5. Stimulate mitosis

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Mechanisms of Hormone Action

• Two mechanisms, depending on their chemical nature

1. Water-soluble hormones (all amino acid–based hormones except thyroid hormone)

• Cannot enter the target cells

• Act on plasma membrane receptors

• Coupled by G proteins to intracellular second messengers that mediate the target cell’s response

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Mechanisms of Hormone Action

2. Lipid-soluble hormones (steroid and thyroid hormones)

• Act on intracellular receptors that directly activate genes

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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

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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 the enzyme phosphodiesterase

• Intracellular enzymatic cascades have a huge amplification effect

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Copyright © 2010 Pearson Education, Inc. Figure 16.2

Hormone (1st messenger)binds receptor.

Receptoractivates Gprotein (GS).

G proteinactivatesadenylatecyclase.

cAMP acti-vates proteinkinases.

Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).

Receptor

G protein (GS)

Adenylate cyclase

Triggers responses oftarget cell (activatesenzymes, stimulatescellular secretion,opens ion channel,etc.)

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Inactiveprotein kinase

Extracellular fluid

Cytoplasm

Activeproteinkinase

GDP

GlucagonPTHTSHCalcitonin

1

2 3 4

5

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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 1

Hormone (1st messenger)binds receptor.

Receptor

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Extracellular fluid

Cytoplasm

GlucagonPTHTSHCalcitonin

1

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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 2

Hormone (1st messenger)binds receptor.

Receptoractivates Gprotein (GS).

Receptor

G protein (GS)

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Extracellular fluid

Cytoplasm

GDP

GlucagonPTHTSHCalcitonin

1

2

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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 3

Hormone (1st messenger)binds receptor.

Receptoractivates Gprotein (GS).

G proteinactivatesadenylatecyclase.

Receptor

G protein (GS)

Adenylate cyclase

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Extracellular fluid

Cytoplasm

GDP

GlucagonPTHTSHCalcitonin

1

2 3

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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 4

Hormone (1st messenger)binds receptor.

Receptoractivates Gprotein (GS).

G proteinactivatesadenylatecyclase.

Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).

Receptor

G protein (GS)

Adenylate cyclase

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Extracellular fluid

Cytoplasm

GDP

GlucagonPTHTSHCalcitonin

1

2 3 4

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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 5

Hormone (1st messenger)binds receptor.

Receptoractivates Gprotein (GS).

G proteinactivatesadenylatecyclase.

cAMP acti-vates proteinkinases.

Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).

Receptor

G protein (GS)

Adenylate cyclase

Triggers responses oftarget cell (activatesenzymes, stimulatescellular secretion,opens ion channel,etc.)

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Inactiveprotein kinase

Extracellular fluid

Cytoplasm

Activeproteinkinase

GDP

GlucagonPTHTSHCalcitonin

1

2 3 4

5

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Plasma Membrane Receptors and Second-Messenger Systems• PIP2-calcium signaling mechanism

• Used by some amino acid–based hormones in some tissues

• Involves a G protein

• G protein activates phospholipase C enzyme

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Plasma Membrane Receptors and Second-Messenger Systems• Phospholipase splits membrane phospholipid

PIP2 into two second messengers: diacylglycerol (DAG) and IP3

• DAG activates protein kinases; IP3 triggers release of Ca2+

• Ca2+ alters enzymes or channels or binds to the regulatory protein calmodulin

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Intracellular Receptors and Direct Gene Activation• Steroid hormones and thyroid hormone

1.Diffuse into their target cells and bind with intracellular receptors

2.Receptor-hormone complex enters the nucleus

3.Receptor-hormone complex binds to a specific region of DNA

4.This prompts DNA transcription to produce mRNA

5.The mRNA directs protein synthesis

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Copyright © 2010 Pearson Education, Inc. Figure 16.3

mRNA

New protein

DNA

Hormoneresponseelements

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

The receptor-hormone complex entersthe nucleus.

The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).

Binding initiatestranscription of thegene to mRNA.

The mRNA directsprotein synthesis.

Plasmamembrane

1

2

3

4

5

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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 1

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

Plasmamembrane

1

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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 2

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

The receptor-hormone complex entersthe nucleus.

Plasmamembrane

1

2

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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 3

DNA

Hormoneresponseelements

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

The receptor-hormone complex entersthe nucleus.

The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).

Plasmamembrane

1

2

3

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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 4

mRNA

DNA

Hormoneresponseelements

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

The receptor-hormone complex entersthe nucleus.

The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).

Binding initiatestranscription of thegene to mRNA.

Plasmamembrane

1

2

3

4

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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 5

mRNA

New protein

DNA

Hormoneresponseelements

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

The receptor-hormone complex entersthe nucleus.

The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).

Binding initiatestranscription of thegene to mRNA.

The mRNA directsprotein synthesis.

Plasmamembrane

1

2

3

4

5

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Target Cell Specificity

• Target cells must have specific receptors to which the hormone binds

• ACTH receptors are only found on certain cells of the adrenal cortex

• Thyroxin receptors are found on nearly all cells of the body

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Target Cell Activation

• Target cell activation depends on three factors

1. Blood levels of the hormone

2. Relative number of receptors on or in the target cell

3. Affinity of binding between receptor and hormone

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Target Cell Activation

• Hormones influence the number of their receptors

• Up-regulation—target cells form more receptors in response to the hormone

• Down-regulation—target cells lose receptors in response to the hormone

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Hormones in the Blood

• Hormones circulate in the blood either free or bound

• Steroids and thyroid hormone are attached to plasma proteins

• All others circulate without carriers

• The concentration of a circulating hormone reflects:

• Rate of release

• Speed of inactivation and removal from the body

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Hormones in the Blood

• Hormones are removed from the blood by

• Degrading enzymes

• Kidneys

• Liver

• Half-life—the time required for a hormone’s blood level to decrease by half

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Interaction of Hormones at Target Cells

• Multiple hormones may interact in several ways

• Permissiveness: one hormone cannot exert its effects without another hormone being present

• Synergism: more than one hormone produces the same effects on a target cell

• Antagonism: one or more hormones opposes the action of another hormone

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Control of Hormone Release

• Blood levels of hormones• Are controlled by negative feedback systems

• Vary only within a narrow desirable range

• Hormones are synthesized and released in response to

1. Humoral stimuli

2. Neural stimuli

3. Hormonal stimuli

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Humoral Stimuli

• Changing blood levels of ions and nutrients directly stimulates secretion of hormones

• Example: Ca2+ in the blood

• Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone)

• PTH causes Ca2+ concentrations to rise and the stimulus is removed

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Copyright © 2010 Pearson Education, Inc. Figure 16.4a

(a) Humoral Stimulus

Capillary (lowCa2+ in blood)

Parathyroidglands

Thyroid gland(posterior view)

PTHParathyroidglands

1 Capillary blood containslow concentration of Ca2+,which stimulates…

2 …secretion ofparathyroid hormone (PTH)by parathyroid glands*

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Neural Stimuli

• Nerve fibers stimulate hormone release

• Sympathetic nervous system fibers stimulate the adrenal medulla to secrete catecholamines

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Copyright © 2010 Pearson Education, Inc. Figure 16.4b

(b) Neural Stimulus

CNS (spinal cord)

Medulla ofadrenalgland

Preganglionicsympatheticfibers

Capillary

1 Preganglionic sympatheticfibers stimulate adrenalmedulla cells…

2 …to secrete catechola-mines (epinephrine andnorepinephrine)

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Hormonal Stimuli

• Hormones stimulate other endocrine organs to release their hormones • Hypothalamic hormones stimulate the 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 the final target organs inhibit the release of the anterior pituitary hormones

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Copyright © 2010 Pearson Education, Inc. Figure 16.4c

(c) Hormonal Stimulus

Hypothalamus

Thyroidgland

Adrenalcortex

Gonad(Testis)

Pituitarygland

1 The hypothalamus secreteshormones that…

2 …stimulatethe anteriorpituitary glandto secretehormonesthat…

3 …stimulate other endocrineglands to secrete hormones

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Nervous System Modulation

• The nervous system modifies the stimulation of endocrine glands and their negative feedback mechanisms

• Example: under severe stress, the hypothalamus and the sympathetic nervous system are activated

• As a result, body glucose levels rise

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The Pituitary Gland and Hypothalamus

• The pituitary gland (hypophysis) has two major lobes

1. Posterior pituitary (lobe):

• Pituicytes (glial-like supporting cells) and nerve fibers

2. Anterior pituitary (lobe) (adenohypophysis)

• Glandular tissue

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Pituitary-Hypothalamic Relationships

• Posterior lobe• A downgrowth of hypothalamic neural tissue

• Neural connection to the hypothalamus (hypothalamic-hypophyseal tract)

• Nuclei of the hypothalamus synthesize the neurohormones oxytocin and antidiuretic hormone (ADH)

• Neurohormones are transported to the posterior pituitary

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Copyright © 2010 Pearson Education, Inc. Figure 16.5a

1

2

3

4

Hypothalamicneuronssynthesize oxytocin and ADH.

Oxytocin and ADH aretransported along the hypothalamic-hypophyseal tract to the posterior pituitary.

Oxytocin and ADH arestored in axon terminals in the posterior pituitary.

Oxytocin and ADH are released into the blood when hypothalamic neurons fire.

Paraventricularnucleus Supraopticnucleus Optic chiasma

Hypothalamus

Inferiorhypophyseal artery

OxytocinADH

Infundibulum (connecting stalk)Hypothalamic-hypophysealtract

Axon terminalsPosteriorlobe ofpituitary

(a) Relationship between the posterior pituitary and the hypothalamus

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Pituitary-Hypothalamic Relationships

• Anterior Lobe:

• Originates as an out-pocketing of the oral mucosa

• Hypophyseal portal system

• Primary capillary plexus

• Hypophyseal portal veins

• Secondary capillary plexus

• Carries releasing and inhibiting hormones to the anterior pituitary to regulate hormone secretion

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Copyright © 2010 Pearson Education, Inc. Figure 16.5b

1

2

3

When appropriatelystimulated, hypothalamic neurons secrete releasing and inhibiting hormones into the primary capillary plexus.

Hypothalamic hormones travel through the portal veins to the anterior pituitary where they stimulate or inhibit release of hormones from the anterior pituitary.

Anterior pituitaryhormones are secreted into the secondary capillary plexus.

Hypothalamus

Hypothalamic neuroncell bodies

Hypophysealportal system

Superiorhypophyseal artery

(b) Relationship between the anterior pituitary and the hypothalamus

Anterior lobeof pituitaryTSH, FSH, LH, ACTH, GH, PRL

• Primary capillary plexus• Hypophyseal portal veins• Secondary capillary plexus

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Anterior Pituitary Hormones

• Growth hormone (GH)

• Thyroid-stimulating hormone (TSH) or thyrotropin

• Adrenocorticotropic hormone (ACTH)

• Follicle-stimulating hormone (FSH)

• Luteinizing hormone (LH)

• Prolactin (PRL)

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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 the secretory action of other endocrine glands)

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Growth Hormone (GH)

• Produced by somatotrophs

• Stimulates most cells, but targets bone and skeletal muscle

• Promotes protein synthesis and encourages use of fats for fuel

• Most effects are mediated indirectly by insulin-like growth factors (IGFs)

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Growth Hormone (GH)

• GH release is regulated by

• Growth hormone–releasing hormone (GHRH)

• Growth hormone–inhibiting hormone (GHIH) (somatostatin)

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Actions of Growth Hormone

• Direct action of GH

• Stimulates liver, skeletal muscle, bone, and cartilage to produce insulin-like growth factors

• Mobilizes fats, elevates blood glucose by decreasing glucose uptake and encouraging glycogen breakdown (anti-insulin effect of GH)

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Homeostatic Imbalances of Growth Hormone• Hypersecretion

• In children results in gigantism

• In adults results in acromegaly

• Hyposecretion

• In children results in pituitary dwarfism

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Copyright © 2010 Pearson Education, Inc. Figure 16.6

Growth hormone

Feedback Inhibits GHRH releaseStimulates GHIHreleaseInhibits GH synthesisand release

Anteriorpituitary

Liver andother tissues

Indirect actions(growth-promoting)

Direct actions(metabolic,anti-insulin)

Insulin-like growthfactors (IGFs)

ExtraskeletalSkeletal Fat Carbohydratemetabolism

Increased cartilageformation and

skeletal growth

Increased proteinsynthesis, andcell growth and

proliferation

Increasedfat breakdown

and release

Increased bloodglucose and otheranti-insulin effects

EffectsEffects

Produce

Hypothalamussecretes growthhormone—releasinghormone (GHRH), andsomatostatin (GHIH)

Initial stimulusPhysiological responseResult

Increases, stimulatesReduces, inhibits

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Thyroid-Stimulating Hormone (Thyrotropin)

• Produced by thyrotrophs of the anterior pituitary

• Stimulates the normal development and secretory activity of the thyroid

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Thyroid-Stimulating Hormone (Thyrotropin)

• Regulation of TSH release

• Stimulated by thyrotropin-releasing hormone (TRH)

• Inhibited by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus

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Copyright © 2010 Pearson Education, Inc. Figure 16.7

Hypothalamus

Anterior pituitary

Thyroid gland

Thyroidhormones

TSH

TRH

Target cellsStimulatesInhibits

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Adrenocorticotropic Hormone (Corticotropin)• Secreted by corticotrophs of the anterior

pituitary

• Stimulates the adrenal cortex to release corticosteroids

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Adrenocorticotropic Hormone (Corticotropin)• Regulation of ACTH release

• Triggered by hypothalamic corticotropin-releasing hormone (CRH) in a daily rhythm

• Internal and external factors such as fever, hypoglycemia, and stressors can alter the release of CRH

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Gonadotropins

• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

• Secreted by gonadotrophs of the 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 the gonadotropin-releasing hormone (GnRH) during and after puberty

• Suppressed by gonadal hormones (feedback)

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Prolactin (PRL)

• Secreted by lactotrophs of the anterior pituitary

• Stimulates milk production

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Prolactin (PRL)

• Regulation of PRL release

• Primarily controlled by prolactin-inhibiting hormone (PIH) (dopamine)

• Blood levels rise toward the end of pregnancy

• Suckling stimulates PRH release and promotes continued milk production