Pituitary Glands

7/31/2019 Pituitary Glands

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The Pituitary Gland


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MENU

Location & anatomy of the pituitary and hypothalamus

Posterior pituitary hormones

Anterior pituitary hormones

Control of the anterior pituitary

Clinical significance

This tutorial is designed as a single presentation, but if you wish to reviewa particular section, click one of the links below...


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Location of the Pituitary Gland

The pituitary gland controls the

functions of many of the otherendocrine glands.

Click on the pituitary gland to continue..

It is about the size of a pea !.


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Location of the pituitary and hypothalamus

Sella turcica

Anteriorpituitary

Opticchiasm

Mamillarybody

Hypothalamus

Posteriorpituitary

The hypothalamus islocated at the base of thebrain in the posterior part ofthe forebrain (diencephalon).

Pituitary stalkThe pituitary is locatedat the base of the brainwithin a bony cavitycalled the sella turcica.


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Sella turcica

Anteriorpituitary

Opticchiasm

Mamillarybody

Hypothalamus

Posteriorpituitary

Pituitary stalk

The pituitary gland itselfconsists of two main parts:

the anterior lobe(adenohypophysis)

the posterior lobe(neurohypophysis)

Location of the pituitary and hypothalamus


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Anatomy of the hypothalamus and pituitary gland

Anterior

pituitary

Posteriorpituitary

Infundibulum

Neurosecretoryneurones

Hypothalamus

The hypothalamus is theintegration centre for many

physiological processes in thebody


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Anterior

pituitary

Posteriorpituitary

Infundibulum


HypothalamusSupraoptic

nucleus

Paraventricularnucleus

Preopticnucleus


physiological processes in thebody.

It is made up of nervoustissue and contains

specialised neuronesarranged in groups callednuclei. These include thepreoptic, the supraopticandthe paraventricularnuclei.



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Anterior

pituitary

Posteriorpituitary

Infundibulum



nucleus



physiological processes in thebody.

These nuclei have axons,which terminate in the posteriorlobe of the pituitary.

It is made up of nervoustissue and contains groups

of specialised neuronescalled nuclei. These includethe preoptic, the supraopticand the paraventricularnuclei.

nerve axons

Preopticnucleus



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The anterior lobe islarger than the posteriorlobe and has three parts:

Posteriorpituitary

Infundibulum



nucleus


Anterior

pituitary

the pars distalis(the major part)

the pars tuberalis,

which forms a sleeveround the pituitarystalk

the pars intermedia,which adjoins theposterior lobe

Preopticnucleus



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To understand and remember how the pituitary gland works, it isimportant to understand how the pituitary is formed duringdevelopment.


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The two lobes of the pituitary develop from

different embryological tissues.

The POSTERIOR pituitary is neural tissuederived from primitive ectoderm. It develops as adowngrowth from the hypothalamus.

The ANTERIOR pituitary consists of epithelialtissueand develops upwards as an outgrowth fromthe roof of the mouth.

Development of the pituitary gland

Anteriorlobe

Posteriorlobe


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Development of the pituitary gland

Infundibulum growing downfrom the hypothalamus

Outgrowth of epithelial cellsgrowing up from the roof ofthe mouth

1. Outgrowths of tissue begin to appear from

the hypothalamus and the roof of the mouth

2. The two outgrowthsof tissue start to fusetogether

3. The immature anterior pituitary lobe

separates from the roof of the mouth

roof of mouth

Immature anteriorpituitary gland

4. The anterior and posterior pituitarylobes mature and the bony sellaturcica forms

anteriorlobeposteriorlobe

sella turcica


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In this photograph you can seethe lower part of thehypothalamus connected to theanterior pituitary by the pituitarystalk or infundibulum.

A network of blood capillaries inthe hypothalamus drain into largerportal blood vessels, which linkthe hypothalamus to the anteriorpituitary.

Connections between the hypothalamus and the anteriorpituitary gland

Portal

blood

vessels


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In this photograph you can seethe lower part of thehypothalamus connected to theanterior pituitary by the pituitarystalk or infundibulum.

neurones

Some of the neurones in the hypothalamus terminate close to the bloodcapillaries in the hypothalamus, but there is NO direct neural connection betweenthe hypothalamus and the anterior pituitary gland.

A network of blood capillaries inthe hypothalamus drain into largerportal blood vessels, which linkthe hypothalamus to the anteriorpituitary.

Connections between the hypothalamus and the anteriorpituitary gland

Portal

blood

vessels


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You have now seen:

1. The anatomical structure of the pituitary gland

Lets now look at the posterior pituitary gland in moredetail.

2. Its spatial and anatomical relationship with the hypothalamus

3. How each pituitary lobe develops embryologically


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Posterior Pituitary Hormones


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Control of the posterior pituitary gland

Axons of hypothalamic-hypophyseal tract

Infundibulum

Anteriorpituitary

pituitary vein

Hypothalamus

Anteriorpituitary

Oxytocin

ADH

The posterior pituitary secretes2 important hormones :

Posterior pituitary

Anti-diuretic hormone (ADH),also called vasopressin

Oxytocin

kidney

breast and uterus

C l f h i i i l d


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Infundibulum

Supraopticnucleus


Anteriorpituitary

pituitary vein

Hypothalamus

Anteriorpituitary

Oxytocin

ADH

Both hormones are peptides,which are synthesised in the cell

bodies of neurones in theparaventricularand supraopticnuclei of the hypothalamus.


C t l f th t i it it l d


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Infundibulum

Anteriorpituitary

pituitary vein

Hypothalamus

Anteriorpituitary

Oxytocin

ADH


The hormones travel from thehypothalamus to the posterior

pituitary via axons in the pituitarystalk. This neuronal connection iscalled the hypothalamic-hypophysealtract.

Supraopticnucleus



C t l f th t i it it l d


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Infundibulum

Anteriorpituitary

pituitary vein

Hypothalamus

Anteriorpituitary

Oxytocin

ADH


The hormones are stored in theaxon terminals in the posterior

pituitary and can be secretedinto the bloodstream when nerveimpulses travel down theneurones

Supraopticnucleus




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What are the actions of the posterior pituitary hormones?

ADH increases waterreabsorption in the kidney andso modulates blood pressure

A deficiency in ADH causesdiabetes insipidus (polyuria,hypotension)

Anti-diuretic hormone (ADH)(vasopressin)

ADH

External stimuluse.g. low bloodpressure

Posteriorpituitary

ADH secretion is stimulated

by low blood pressure


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Oxytocin secretion isstimulated by stretching of thecervix during birth and sucklingof the baby at the breast

A deficiency of oxytocin causesa failure to progress in labourand difficulty with breast feeding

Oxytocin

Oxytocin

External stimuluse.g. stretching of

cervix or suckling

Oxytocin stimulates uterinecontractions during labour andthe milk ejection reflex after birth

Posteriorpituitary


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Now lets look at the anterior pituitary gland:

1. The cellular structure of the anterior pituitary gland.

2. What hormones does it secrete?

3. What are the effects of these hormones?


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Anterior Pituitary Hormones


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Cellular structure of the anterior pituitary gland

Somatotrophsproduce

growth hormone (GH)

ANTERIOR

PITUITARYsinusoid

The anterior pituitary is composed of groups of

epithelial cells surrounded by wide capillaries calledsinusoids.

Different populations of cells produce differenthormones.

For example:

GH

GH

GH

GH


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ANTERIOR

PITUITARYsinusoid




PRL

PRL

PRL

PRL

Lactotrophsproduce prolactin (PRL)


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ANTERIOR

PITUITARYsinusoid




TSH

TSH

TSH

TSH

Thyrotrophsproduce thyroid-stimulating hormone (TSH)


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ANTERIOR

PITUITARYsinusoid




Corticotrophsproduce bothadrenocorticotrophic hormone (ACTH) andmelanocyte-stimulating hormone (MSH)

MSHACTH

ACTH

MSH

MSH

ACTH


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ANTERIOR

PITUITARYsinusoid




LH

FSH

FSH

LH

FSH

Gonadotrophsproduce luteinising hormone (LH)and follicle-stimulating hormone (FSH)


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The following screens give a brief summary of what the anterior pituitaryhormones do.

Each hormone may be dealt with in more detail in other presentations.

Anterior pituitary hormones Growth Hormone


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1.Growth Hormone(GH) regulates growth

in the muscles and bones and opposes theaction of insulin

Somatotrophs in the anterior pituitarygland secrete GH

GH

Anterior pituitary hormones - Growth Hormone


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GH

Many body cells (chondrocytes, fat cells,muscle, but mainly the liver) respond to GHby secreting insulin-like growth factor (IGF)

+

IGF


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GH

Many body cells (chondrocytes, fat cells,muscle, but mainly the liver) respond to GHby secreting insulin-like growth factor (IGF)

+

IGF

Growth and cellular differentiationin bone, muscle and adipose cells

Therefore, GH acts indirectly via IGF toregulate body growth

Anterior pituitary hormones - LH and FSH


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2.Luteinising Hormone (LH)andFollicle Stimulating Hormone (FSH)

control both the ovaries and testes

Gonadotrophs in the anterior pituitary glandsecrete LH and FSH

LH FSH

p y


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ovary




In the female, LH and FSH stimulate

the ovary.

LH FSH

oestrogen progesterone

inhibin


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In the female, LH and FSH stimulate

the ovary.

The ovarian steroid hormones (oestradioland progesterone) have effects on many

other parts of the body (bone, brain,vascular tissue etc.), secondary sexualcharacteristics and behaviour.

LH FSH

Effects on bone, brain, vascular tissue etc.,behaviour

oestrogen progesterone

inhibin ovary


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FSHLH

testosteroneinhibin

testis

In the male, LH and FSH stimulatethe Leydig cells and the Sertoli cellsin the testis, respectively, to secretetestosterone and inhibin


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FSHLH

testosterone

Spermatogenesis, secondary sexualcharacteristics and behaviour

inhibin

testis

In the male, LH and FSH stimulatethe Leydig cells and the Sertoli cellsin the testis, respectively, to secretetestosterone and inhibin

Anterior pituitary hormones - Prolactin


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3.Prolactin (PRL) initiates lactation andpromotes the growth of the mammaryglands, ovaries and testes

Lactotrophs in the anterior pituitary glandsecrete PRL PRL

Anterior pituitary hormones Prolactin


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3.Prolactin (PRL) initiates lactation andpromotes the growth of the mammaryglands, ovaries and testes


Prolactin acts directly on the breast tostimulate milk production.

breast

Milkproduction


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3.Prolactin (PRL) initiates lactation andpromotes the growth of the mammary

glands, ovaries and testes


Prolactin acts directly on the breast tostimulate milk production.

Growth of mammary glands,ovaries and testes

breast

Milkproduction

Anterior pituitary hormones - Thyroid-stimulating hormone


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4.Thyroid-stimulating hormone (TSH)regulates the thyroid gland

Thyrotrophs in the anterior pituitary glandsecrete TSH

TSH


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4.Thyroid-stimulating hormone(TSH) regulates the thyroid gland

Thyrotrophs in the anterior pituitary glandsecrete TSH

TSHTSH acts on the thyroid gland to stimulate the

release of thyroid hormones (Thyroxine, T4,Tri-iodothyronine, T3.

thyroid

parathyroids

Thyroid hormones

Anterior pituitary hormones - Thyroid-stimulating hormone


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Thyrotrophs in the anterior pituitarygland secrete TSH

TSH


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release of thyroid hormones (Thyroxine, T4,Tri-iodothyronine, T3, and Calcitonin) as wellas changes to the thyroid gland

thyroid

parathyroids

Thyroid hormones


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release of thyroid hormones (Thyroxine, T4,Tri-iodothyronine, T3.

Metabolism, heat production,growth.

The thyroid hormones play an important role incontrolling control carbohydrate and fatmetabolism, and basal metabolic rate.

thyroid

parathyroids

Thyroid hormones

Anterior pituitary hormones - Adrenocorticotrophic hormone


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5.Adrenocorticotrophic hormone(ACTH) controls hormone secretion from

the adrenal cortex

Corticotrophs in the anterior pituitarygland secrete ACTH

ACTH


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the adrenal cortex


ACTHACTH acts on the adrenal cortex to stimulate therelease of glucocorticoids (mainly cortisol) and

adrenal androgens (mainly androstenedione anddehydroepiandrosterone (DHEA))

Adrenal cortex hormones

adrenalcortex


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the adrenal cortex


ACTHACTH acts on the adrenal cortex to stimulate therelease of glucocorticoids (mainly cortisol) and

adrenal androgens (mainly androstenedione anddehydroepiandrosterone (DHEA))

Metabolism, immune system, stressresponses, testosterone and oestrogen

Adrenal cortex hormones

adrenalcortex

Cortisol controls the metabolism of carbohydrates,fats and proteins, inflammatory and immuneresponses, and responses to stress

Anterior pituitary hormones - Melanocyte-stimulating hormone


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6.Melanocyte Stimulating Hormone (MSH)stimulates melanocytes in the skin

Corticotrophs in the anterior pituitary glandalso secrete MSH

MSH


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Corticotrophs in the anterior pituitary glandsecrete MSH

MSH

MSH acts on melanocytes in the epidermis ofthe skin to stimulate the secretion of melanin

Melanin

melanocytesin the skin


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Corticotrophs in the anterior pituitary glandsecrete MSH

MSH

MSH acts on melanocytes in the epidermis ofthe skin to stimulate the secretion of melanin

Skin pigmentation

MelaninMelanin controls pigmentation in the skin

melanocytesin the skin

Summary of hormones secreted by the anterior pituitary gland


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Adrenocorticotrophic Hormone (ACTH) controls hormone secretion from the adrenal cortex

Growth Hormone(GH) regulates growth in muscles and bones and opposes the action of insulin

Prolactin initiates lactation and promotes the growth of the mammary glands, ovaries and testes

Thyroid Stimulating Hormone (TSH) regulates the thyroid gland

So the anterior pituitary secretes at least 7 important hormones:

Melanocyte Stimulating Hormone (MSH)stimulates melanocytes in the skin

Luteinising Hormone (LH) and

Follicle Stimulating Hormone (FSH)

control both the ovaries and the testes

Essentials in


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Biomedical Science

Kings College London

Date last modified:26/09/2001Stuart Milligan

Victoria Pocock



Control of the Anterior Pituitary

B t h t t l th diff ti l ti f th t i it it


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But what controls the differential secretion of the anterior pituitarygland hormones?

The following screens will show:

1. How the hypothalamus controls the anterior pituitary gland

2. The importance of negative feedback control of the hypothalamic-pituitaryaxis.

Hypothalamic control of the anterior pituitary hormones


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These hypothalamicneurones releaseneurosecretoryhormones into theportal blood vessels

We have already seen thatmany neurones terminate inthe base of the hypothalamusin close association with theportal blood vessels.

hypothalamic

neuronesHypothalamus

Anterior

pituitary

NEUROSECRETORYHORMONES

portal bloodvessels

The hypothalamic hormonescontrol the release of anteriorpituitary hormones



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Let us look at how thehypothalamic hormonescontrol the release of anteriorpituitary hormones using

thyroid stimulating hormone(TSH)as an example..

In the cold, specificneurones in thehypothalamus secrete the neurosecretory

Only certain neurones in thehypothalamus can secreteTRH Other hypothalamic


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hypothalamicneurones

Hypothalamus

hormone Thyrotrophin Releasing Hormone(TRH)

Anterior

pituitary

TRH

Lowtemperature

+

TRH. Other hypothalamicneurones secrete differentneurosecretory hormonesunder different conditions.


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Hypothalamus

TRHstimulates thethyrotrophs in theanterior pituitary to

secrete thyroidstimulatinghormone (TSH)Anterior

pituitary

TRH

Lowtemperature

+

TSH then stimulates the thyroid to releasethyroid hormones, which subsequentlycause an increase in body temperature

thyrotrophsTSH

Thyroid

Thyroidhormones

Increased body

temperature

Hypothalamic hormones that control the anterior pituitary


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Growth Hormone Releasing Hormone (GHRH)

Somatostatin

The hypothalamus secretes several hormones that control thesecretion of anterior pituitary hormones:

GH+



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Somatostatin


Corticotrophin Releasing Hormone (CRH) + ACTH



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Somatostatin


Corticotrophin Releasing Hormone (CRH)

Gonadotrophin Releasing Hormone (GnRH) LHFSH

+



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Somatostatin

Thyrotrophin Releasing Hormone (TRH)



Gonadotrophin Releasing Hormone (GnRH)

TSH+



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Somatostatin

Dopamine

Thyrotrophin Releasing Hormone (TRH)

Prolactin Releasing Factors (PRF),one of which is TRH



Gonadotrophin Releasing Hormone (GnRH)

-PRL

+


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The hypothalamic hormones are the

primary hormones controlling thesecretion of the anterior pituitaryhormones.

However, many other factors feed intothe control of the hypothalamic-pituitary

axis..

Lets look at some of these ..

Specific stimuli


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Hypothalamus

Pituitary

We have already seen that specificstimuli (e.g. cold in the case ofTSH) feed into the hypothalamiccontrol system

Specific stimuliCircadian changes


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Hypothalamus

Pituitary

SLEEP

GH levels

24 hrs

In addition, many hormones showdaily rhythms.

Note that GH is released in pulsesduring the hours of sleep.



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Pituitary

Pulse generator

Pulses of GnRH

LH levels

24 hrs

The secretion of GnRH seemsto be governed by a

hypothalamic pulse generator.

24 hour profile of LH levels in ayoung adult.

Note the pulses of LH markedby arrows.


Pulses?


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Hypothalamus

Pituitary

Feedback from peripheral signals

(usually negative feedback)e.g. thyroid hormones, gonadal steroids

And a very important control formost the the anterior pituitaryhormones is feedback control.


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Lets use TSH as an example for looking at

feedback control.

Negative feedback controls of the hypothalamic-pituitary axis


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Specific external signals,e.g. low temperature,stimulate the secretion ofTRH by the

hypothalamus.

+hypothalamicneurones

Hypothalamus

Anteriorpituitary

TRH

Lowtemperature

thyrotrophsTSH

TRH stimulates thesecretion of TSH by theanterior pituitary.



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TSH stimulates thethyroid to releasethe thyroidhormones, T3 andT4.

+hypothalamicneurones

Hypothalamus

Anteriorpituitary

TRH

Lowtemperature

thyrotrophsTSH

Thyroid

T4

T3



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The thyroid hormonesfeedback onto thehypothalamus and theanterior pituitary tosuppress further TSHproduction. This is anegative feedback effect.


Hypothalamus

Anteriorpituitary

TRH

thyrotrophsTSH

Thyroid

T4

T3



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So high levels ofthyroid hormonessuppress TRH andTSH secretion.


Hypothalamus

Anteriorpituitary

thyrotrophs

Thyroid

T4

T3

(TRH)

(TSH)



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However, when there arelow levels of thyroidhormones, TRH andTSH secretion will be

high.


Hypothalamus

Anteriorpituitary

TRH

thyrotrophsTSH

Thyroid

T4

T3

Essentials in

Biomedical Science


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Biomedical Science

Kings College LondonDate last modified:

26/09/2001Stuart Milligan

Victoria Pocock

TO VIEW THIS PRESENTATION FULLSCREEN, CLICK RIGHT HANDBUTTON ON MOUSE AND SELECT

FULL SCREEN OPTIONTo navigate between pages: use Page Up/Page Downkeys, or click mouse on navigation controls

Clinical significance

Because the control of the hypothalamic-pituitary axis involves a number of steps


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pituitary axis involves a number of steps,problems of under-secretion or over-

secretion of hormones can arise fromdifferent physiological defects in thecontrol pathway.

Using growth hormone (GH) as anexample, we will now look now howproblems might arise.

But first a reminder of the controls of GH...

Control of Growth Hormone


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Hypothalamus

somatotrophsAnteriorpituitary

Liver

SomatostatinGHRH

+

GH

GHRH stimulatessecretion of GH bythe anterior pituitary

GH stimulates secretionof insulin-like growth

factors (IGF) by theliver.

IGFs stimulate growthin bones, muscles andfat IGF

Whereassomatostatininhibits GHsecretion

Control of GH secretionBlood glucose

ExerciseSleep


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But other factors such assleep, exercise, stress,

food intake and bloodsugar levels also influencethe release of thesehormones

Hypothalamus

Pituitary

GH

Liver

IGF-1

FoodStress

SomatostatinGHRH +


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Given the understanding of the normal control of GH, well now

look at how it can go wrong..

Hypothalamus

Hypersecretion of GH


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Pituitary

GH

Liver

IGF-1

In a few people, the pituitary continues tosecrete GH independently of the normal

regulatory mechanisms.

The levels of GH increase above normal,leading to excess bone growth and organenlargement.

The hypersecretion of GH alsocauses changes in sugar and lipidmetabolism and can cause diabetes.

Excess bone growth

Organ enlargement

Diabetes

GHRH + Somatostatin


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Understanding how the system

works also gives us an insightinto where the controlmechanisms can break down

Lets look at a growth disorders

such as short stature as an

example.

HypothalamusWhat could cause short stature?

Problems can occur in the hypothalamuse.g. defects in GHRH production


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Pituitary

GH

Liver

GHRH

+Somatostatin

IGF-1

e g de ects G p oduct o

Problems can occur in the pituitarye.g. defects in GH secretion or bioactivity

Problems can occur in the abilityof cells to produce IGF.

Problems can occur in the target organse.g. defects in growth response

So there is a

complex,

hierarchical

control system and problems

can occur at any

of the levels

Lets now look at how the function of


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hypothalamic-pituitary axis be tested...

These tests are often calledChallenge testsbecause they aredesigned to challenge the normaloperation of the system..

1. Hypothalamic releasing factors, e.g. TRHand GnRH, are useful to identifyspecific functional cell types in the anterior pituitary (thyrotrophs and

d h ) b hi b d f di i f h i i i

Challenge Tests


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gonadotrophs), but this test cannot be used for diagnosis of hypopituitarism orhyperpituitarism.

Time (minutes)

0 20 60 90-15

2

4

6

8

FSH mU/L

GnRH200 g IV

20

Time (minutes)

0 20 60 90-15

10

LH U/L

GnRH200 g IV

Note the rapid FSH response when

GnRH is given to normal subjects

And the same dose of GnRHresults in similar rapid rises in LH

2. Synthetic drugs can be given to investigate whether the negative feedback controlof the anterior pituitary is working properly ( e.g. dexamethasone(suppresses ACTH)and metyrapone (blocks cortisol secretion))

Challenge Tests


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Plasma ACTH = 2 pmol/L

and metyrapone(blocks cortisol secretion))

Cortisol

ACTH

-

Normal negative feedback

control of ACTH by cortisolsecreted by the adrenal cortex

Cortisol

-

ACTH

Metyrapone

Metyrapone blocks cortisol

secretion from the adrenalcortex

Plasma ACTH = 10 pmol/L

Cortisol

-

ACTH

DEX

Dexamethasone suppresses

ACTH secretion by the anteriorpituitary

Plasma ACTH = 37 pmol/L+

Note the increased level of ACTH due toblockage of cortisol secretion and thereforeremoval of negative feedback control

Note the reduced level of ACTHdue to suppression bydexamethasone

3. The use of a physiological stimulus,e.g. insulin-induced hypoglycaemia,(insulin tolerance test) can be used to

Challenge Tests

HypopituitaryNormal


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( )help define defects in the system

For example, in normal patients,insulin-induced hypoglycaemiaactivates hypothalamic neuronesto stimulate pituitary secretion of

corticotrophin, GH and prolactin.

But, in subjects with hypopituitarism,plasma cortisol and and serum GH

levels are far below normal levels.

0 30 60 90 12

Time (minutes)

Insulin

0.15 U/kg

Hypopituitary

5

3

1

800

600

400

200

20

10


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Understanding the normal control of thehypothalamic-pituitary axis allows the system tobe manipulated to achieve different aims

Lets use the control of reproduction by GnRH,LH, FSH and ovarian hormones as anexample..

Control ofreproduction

Hypothalamus


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The basic operation of the

hypothalamic-pituitary-gonadalsystem is shown opposite.

Understanding this system allowed formsof contraception to be developed ..

Pituitary

LHFSH

Ovary

Oestradiol

GnRH

+

+GnRH drives FSH productionfrom the pituitary, and FSHstimulates follicle growth.

Oestradiol produced by thefollicle provides negativefeedback.

Control ofreproduction

Hypothalamus


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The negative feedback control

of oestrogens was the originalbasis of the oral contraceptivepill

Pituitary

LHFSH

Ovary

GnRH

High doses of oestrogens act onthe hypothalamic-pituitary axis tosuppress LH and FSH secretionand so suppress follicle growthand prevent ovulation

Oestradiol

Oral oestrogens


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But we can also use our

understanding to stimulate

reproduction

Stimulation ofovarian function

HypothalamusI t t t f i f tilit it i


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One method is give pulses ofGnRH: these will stimulate thepituitary to secrete more LH andFSH.

GnRH

Pituitary

LHFSH

Ovary

(pulses)

In some treatments for infertility, it isnecessary to stimulate the ovaries

Growth of more follicles

Oestradiol

Stimulation offollicular growth

Hypothalamus


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Or: an alternative is togive FSH to stimulate theovary directly

GnRH

Pituitary

FSH

Ovary


Oestradiol

Hypothalamus

Stimulation offollicular growth


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Pituitary

LHFSH

Ovary

Oestradiol

GnRH

Or another wayis to give an anti-

oestrogen (e.g. clomiphene). Theanti-oestrogen blocks the negativefeedback of oestradiol, sogonadotrophin levels rise!

Clomiphene

Therefore, clomiphene is often used

as a fertility treatment for women toincrease the number of folliclesgrowing and ovulating



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Pituitary Glands