CHAPTER 8 THE ENDOCRINE SYSTEM.ppt

8/9/2019 CHAPTER 8 THE ENDOCRINE SYSTEM.ppt

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THE ENDOCRINE SYSTEM


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OVERVIEW

Endocrine system organ are small and unipresive

Widely separated regions of the body

Role: Maintaining body homeostasis

System of ductless glands that secrete hormonesHormones are “messenger molecules”Circulate in the blood Act on distant target cellsTarget cells respond to the hormones for whichthey have receptors

The effects are dependent on the programmedresponse of the target cells

Hormones are just molecular triggers


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CATEGORY OF HORMONES

Amino acid based: modified amino acids (oramines), peptides (short chains of amino acids),and proteins (long chains of amino acids)

Steroids: lipid molecules derived from cholesterol


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HORMONES AND RECEPTORS


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PEPTIDE HORMONES

Peptide hormones do not enter the cell directly.

These hormones bind to receptor proteins in the

cell membrane.

When the hormone binds with the receptor

protein, a secondary messenger molecule

initiates the cell response.

Because peptide hormones are water soluble,

they often produce fast responses.


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(cytoplasm)

(nucleus)

peptide or aminoacid-derivedhormone(frst messenger)

(extracellular fuid)

cyclic AMP-synthesizingenzyme

cyclic AMP

ATP

inactiveenzyme

(second messenger)

activeenzyme

reactant

product

plasma membrane

nuclearenvelope

receptor

The hormone binds toa receptor on the plasmamembrane o a target cell

1

The activated enzymescatalyze specifc reactions

The secondmessenger activatesother enzymes

!

"ormone#receptor bindingactivates an enzyme that catalyzesthe synthesis o a second messenger$such as cyclic AMP

%


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STEROID HORMONES

Steroid hormones enter through the cell

membrane and bind to receptors inside of the

target cell.

These hormones may directly stimulate

transcription of genes to make certain proteins.

Because steroids work by triggering gene activity,

the response is slower than peptide hormones.


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gene

plasma

membrane ribosome

hormone receptor

steroid hormone

m&'A

(nucleus)

&'A polymerase

'A

(cytoplasm)

ne protein

(extracellular fuid)

A steroid hormonedi*uses through theplasma membrane

The hormone binds to areceptor in the nucleus or toa receptor in the cytoplasm

that carries it into the nucleus

The hormone#receptor

comple+ binds to 'A andcauses &'A polymerase tobind to a nearby promotersite or a specifc gene

&'A polymerase catalyzesthe transcription o 'A intomessenger &'A (m&'A)

The m&'A leaves thenucleus$ then attaches to aribosome and directs thesynthesis o a specifc proteinproduct

1

%

!

,

nuclearenvelope


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ENDOCRINE

ORGANS

Purely endocrine organsPituitary glandPineal glandThyroid glandParathyroid glands

Adrenal: 2 glandsCortexMedulla

Endocrine cells in other

organsPancreasThymusGonadsHypothalamus

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MECHANIS

MS OF

HORMONERELEASE

(a) Humoral: in response to changing levelsof ions or nutrients in the blood

(b) Neural: stimulation by nerves

(c) Hormonal: stimulation received fromother hormones

10


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11

Pituitary__________ (hypophysis)

Hypothalamus___________

"ypothalamusAnterior pituitary(adenohypophysis)

Posterior pituitary (neurohypophys

.earn the ! endocrine organs on this slide/"ypothalamusPituitary (hyophysis)Pineal


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Two divisions:

Anterior pituitary(adenohypophysis)

Posteriorpituitary(neurohypophysis)

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Sits in hypophyseal fossa: depression in sellaturcica of sphenoid bone

Pituitary secretes 9 hormonesThe Pituitary

1. TSH2. ACTH. !SH". #H$. %H

&. P'#(. )SH

*. A+H ,antidiuretic hormone- or /asopres9. 0ytocin

_________________________________________________________________

The rst our are “tropic”hormones, they regulatethe unction o otherhormones

________


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WHAT THE LETTERS STAND FOR…

TSH: thyroid-stimulating hormone

ACTH: adrenocorticotropic hormone

FSH: follicle-stimulating hormone

LH: luteinizing hormone

GH: growth hormonePRL: prolactin

MSH: melanocyte-stimulating hormone

ADH: antidiuretic hormone

Oxytocin13


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HYPOTHALAMUS CONTROLS

ANTERIOR PITUITARY HORMONE

RELEASEReleasing hormones (releasing factors)Secreted like neurotransmitters from neuronalaxons into capillaries and veins to anteriorpituitary (adenohypophysis)

TRH-----turns on TSHCRH-----turns on ACTH

GnRH (=LHRH)---turns on FSH and LH

PRF-----turns on PRL

GHRH----turns on GHInhibiting hormones

PIF-----turns off PRL

GH inhibiting hormone---turns off GH14


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WHAT THE LETTERS MEAN…Releasing hormones (releasing factors) ofhypothalamus

Secreted like neurotransmitters from neuronal axons into capillaries

and veins to anterior pituitary (adenohypophysis)TRH (thyroid releasing hormone) -----turns on* TSH

CRH (corticotropin releasing hormone) -----turns on ACTH

GnRH (gonadotropin releasing hormone) ---turns on FSH andLH

PRF (prolactin releasing hormone) -----turns on PRLGHRH (growth hormone releasing hormone) ----turns on GH

Inhibiting hormones ofhypothalmusPIF (prolactin inhibiting factor) -----turns off PRL

GH (growth hormone) inhibiting hormone---turns off GH

The hypothalamus controls secretion of hormones which intheir turn control the secretion of hormones by the thyroid gland, the adrenal cortex and gonads: in this way the brain

controls these endocrine glands

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3ote: 4turns on5 means causes to be released


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SO WHAT DO THE PITUITARY

HORMONES DO?

TSH stimulates the thyroid to produce thyroidhormone

ACTH stimulates the adrenal cortex to produce

corticosteroids: aldosterone and cortisolFSH stimulates follicle growth and ovarianestrogen production; stimulates spermproduction and androgen-binding protein

LH has a role in ovulation and the growth ofthe corpus luteum; stimulates androgensecretion by interstitial cells in testes

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The four tropic ones re6ulate the function of other horm


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THE OTHERS FROM THE ANTERIOR

PITUITARY…

GH (aka somatrotropic hormone) stimulates growth of

skeletal epiphyseal plates and body to synthesize

protein

PRL stimulates mammary glands in breast to make

milk

MSH stimulates melanocytes; may increase mental

alertness

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FROM THE POSTERIOR PITUITARY

(NEUROHYPOPHYSIS)STRUCTURALLY PART OF THE BRAIN

ADH (antidiuretic hormone AKA vasopressin) stimulates

the kidneys to reclaim more water from the urine, raises

blood pressure

Oxytocin prompts contraction of smooth muscle in

reproductive tracts, in females initiating labor and ejection

of milk from breasts

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TSH ti l t th th id t d


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TSH: thyroid7stimulatin6 hormoneACTH: adrenocorticotropic hormone!SH: follicle7stimulatin6 hormone

#H: luteini8in6 hormone%H: 6roth hormoneP'#: prolactin)SH: melanocyte7stimulatin6hormone

A+H: antidiuretic hormone0ytocin

T&" (thyroid releasing hormone)turns on TSH

0&" (corticotropin releasinghormone)turns on ACTHn&" (gonadotropin releasinghormone) turns on !SH and #HP&2 (prolactin releasing hormone)

turns on P'#"&" (groth hormone releasinghm)turns on %H

TSH stimulates the thyroid to producethyroid hormoneACTH stimulates the adrenal corte toproduce corticosteroids: aldosteroneand cortisol

!SH stimulates follicle 6roth ando/arian estro6en productionstimulates sperm production andandro6en7bindin6 protein#H has a role in o/ulation and the6roth of the corpus luteum

stimulates andro6en secretion byinterstitial cells in testes%H ,a;a somatrotropic hormone-stimulates 6roth of s;eletalepiphyseal plates and body tosynthesi8e proteinP'# stimulates mammary 6lands inbreast to ma;e mil;

)SH stimulates melanocytes mayincrease mental alertnessA+H ,antidiuretic hormone or/asopressin- stimulates the ;idneysto reclaim more ater from the urineraises blood pressure0ytocin prompts contraction of

smooth muscle in reproducti/e tracts

a n w e p u t i t a l l to g e t h e r ?

3lue is rom hypothalamus3lac4 is rom pituitary


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20

Pituitary__________ (hypophysis)

Hypothalamus___________

'o try and remember the anatomy


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THE THYROID GLAND

Anterior neck ontrachea just inferior tolarynx

Two lateral lobes and

an isthmusProduces two hormonesThyroid hormone:tyrosine based with 3 or4 iodine molecules

T4 (thyroxine) and T3Calcitonin involved withcalcium and phosphorusmetabolism

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Thyroid is composed of spherical folliclesFollicle cells: produce thyroglobulin, the precursor of thryoid

hormone (thyroxin)

Colloid lumen is of thyroglobulin

Parafollicular “C” cells: produce calcitonin

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AN EXAMPLE OF A FEEDBACK

LOOP

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A certain item in the blooddecreases

A certain area of the brainsenses this decrease

A certain hormone isreleased

This hormone stimulatesthe release of anotherhormone

This other hormone

stimulates the release ofthe hormone which wassensed to be decreased inthe first place, causing it tobe increased to desiredlevel

Thyroxine (thyroid hormone)

Hypothalamus

TRF from the hypothalamus

TSH from anterior pituitary

Thyroxine from the thyroid

(TSH has caused cleavage ofthryroglobulin into thyroxine)

generic particular example: thyroid hormon


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SOME EFFECTS OF THYROID

HORMONE

(THYROXINE)Increases the basal metabolic rateThe rate at which the body uses oxygen to

transform nutrients (carbohydrates, fats and

proteins) into energy

Affects many target cells throughout the

body; some effects areProtein synthesis

Bone growthNeuronal maturation

Cell differentiation24


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THE EFFECTS OF

CALCITONIN

Secreted from thyroid parafollicular (C) cells

when blood calcium levels are high

Calcitonin lowers Ca++ by slowing the calcium-

releasing activity of osteoclasts in bone and

increasing calcium secretion by the kidney

Acts mostly during childhood

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THE PARATHYROID

GLANDS

Most people have four

On posterior surface of thyroid

gland

(sometimes embedded)

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PARATHYROIDS

(TWO TYPES OF

CELLS)Rare chief cells

Abundant oxyphil cells

(unknown function)

Chief cells produce PTHParathyroid hormone, or

parathormone

A small protein hormone

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FUNCTION OF PTH(PARATHYROID HORMONE OR

“PARATHORMONE”) Increases blood Ca++ (calcium) concentration when it gets too low

Mechanism of raising blood calcium

1. Stimulates osteoclasts to release more Ca++ frombone

2. Decreases secretion of Ca++ by kidney

3. Activates Vitamin D, which stimulates theuptake of Ca++ from the intestine

Unwitting removal during thyroidectomy waslethal

Has opposite effect on calcium ascalcitonin (which lowers Ca++ levels) 28


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ADRENAL (SUPRARENAL) GLANDS(“SUPRARENAL” MEANS ON TOP OF THE

KIDNEY)Each is really two endocrine glands Adrenal cortex (outer) Adrenal medulla (inner)

Unrelated chemicals but all help with extreme situations

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ADRENAL GLAND

Adrenal cortexSecretes lipid-based steroid hormones, called “corticosteroids” –

“cortico” as in “cortex”MINERALOCORTICOIDS

Aldosterone is the main one

GLUCOCORTICOIDS

Cortisol (hydrocortisone) is the main one

Adrenal medulla

Secretes epinephrine and norepinephrine

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ALDOSTERONE, THE MAIN

MINERALOCORTICOID

Secreted by adrenal cortex in response to adecline in either blood volume or blood pressure(e.g. severe hemorrhage)Is terminal hormone in renin-angiotensin mechanism

Prompts distal and collecting tubules in kidney toreabsorb more sodiumWater passively followsBlood volume thus increases

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CORTISOL,THE MOST IMPORTANT

GLUCOCORTICOID

(GLUCOCORTICOID RECEPTORS ARE FOUND IN THE CELLS OF MOS

VERTEBRATE TISSUES)

It is essential for lifeHelps the body deal with stressful situationswithin minutes

Physical: trauma, surgery, exercisePsychological: anxiety, depression, crowdingPhysiological: fasting, hypoglycemia, fever, infection

Regulates or supports a variety of important

cardiovascular, metabolic, immunologic, andhomeostatic functions including water balance

32People with adrenal insuciency these stresses can cause

hypotension, shoc! and death must gi"e glucocorticoids, eg orsurgery or i ha"e inection, etc#


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CORTISOL, CONTINUED

Keeps blood glucose levels high enough to supportbrain’s activityForces other body cells to switch to fats and aminoacids as energy sources

Catabolic: break down proteinRedirects circulating lymphocytes to lymphoidand peripheral tissues where pathogens usuallyare

In large quantities, depresses immune andinflammatory responseUsed therapeuticallyResponsible for some of its side effects 33


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HORMONAL STIMULATION OF

GLUCOCORTICOIDS HPA AXIS(HYPOTHALAMIC/PITUITARY/ADRENAL AXIS)

With stress, hypothalamus sends CRH toanterior pituitary (adenohypophysis)

Pituitary secretes ACTH

ACTH goes to adrenal cortex where stimulatesglucocorticoid secretionSympathetic nervous system can also stimulate it

Adrenal cortex also secretes DHEA

(dehydroepiandrosterone)Converted in peripheral tissues to testosterone andestrogen (also steroid hormones)

Unclear function in relation to stress 34

=n 6eneral:


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Steroid-secreting cells

have abundant smooth

ER As opposed to rough ER in

protein-secreting cells

Steroids directly diffuse

across plasmamembraneNot exocytosis

Abundant lipid dropletsRaw material from which

steroids made

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=n 6eneral:


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ADRENAL

MEDULLA

Part of autonomicnervous system

Spherical chromaffincells are modified

postganglionicsympathetic neuronsSecrete epinephrineand norepinephrine

Amine hormonesFight, flight, fright Vesicles store thehormones

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THE PINEAL GLAND

At the end of a short stalk on the roof of thediencephalon

Pinealocytes with dense calcium particlesCan be seen on x-ray (because of Ca++)Melatonin helps regulate the circadium rhythmThe biological clock of the diurnal (night/day) rhythmComplicated feedback via retina’s visual input

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THE PANCREAS

Exocrine and endocrine cells

Acinar cells (forming most of the pancreas) Exocrine function

Secrete digestive enzymes

Isletcells (of Langerhans) Endocrine function

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PANCREATIC


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PANCREATIC

ISLET

ENDOCRINE

CELLS

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Alpha cells/ secrete glucagonraises blood sugarmostly in periphery

3eta cells/ secrete insulinloers blood sugarcentral part (are more

abundant)Also rare elta cells/secretesomatostatin

inhibits glucagon


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THE GONADS (TESTES AND OVARIES)

MAIN SOURCE OF THE STEROID SEX HORMONES Testes Interstitial cells secrete androgens Primary androgen is testosterone

Maintains secondary sex characteristics Helps promote sperm formation

Ovaries Androgens secreted by thecal folliculi

Directly converted to estrogens by follicular granulosa cells Granulosa cells also produce progesterone Corpus luteum also secretes estrogen andprogesterone 40


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ENDOCRINE CELLS IN VARIOUS

ORGANS

The heart: atrial natriuretic peptide (ANP)Stimulates kidney to secrete more salt

Thereby decreases excess blood volume, high BP and high blood

sodium concentration

GI tract & derivatives: Diffuse neuroendocrine system(DNES)

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ENDOCRINECELLSINVARIOUSORGANS


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ENDOCRINE CELLS IN VARIOUS ORGANS

CONTINUEDThe heart: atrial natriuretic peptide (ANP)Stimulates kidney to secrete more salt

Thereby decreases excess blood volume, high BP and high bloodsodium concentration

GI tract & derivatives: Diffuse neuroendocrine system(DNES)

The placenta secretes steroid and protein hormonesEstrogens, progesteroneCRHHCG

The kidneysJuxtaglomerular cells secrete renin

Renin indirectly signals adrenal cortex to secrete aldosteroneErythropoietin: signals bone marrow to increase RBC production

The skinModified cholesterol with uv exposure becomes Vitamin D precursor Vitamin D necessary for calcium metabolism: signals intestine to

absorb CA++

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PATHOLOGY

PituitaryGigantism –too much GH in childhood Acromegaly – too much GH in adulthoodPituitary dwarfs – too little GH in childhoodDiabetes insipidus - too much ADH

PancreasDiabetes mellitus – one type of insulin (not enough)

ThyroidHyperthyroidism, commonest is Grave’s disease

(autoimmune)Hypothyroidism

In childhood leads to cretinismEndemic goiter from insufficient iodine in diet Adult hypothyroidism (myxedema): autoimmune

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5+ophthalmos orave6s disease

5nlarged

thyroid(goiter) romiodinedefciency


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PATHOLOGY, CONTINUED

Adrenal glandCushing’s syndrome (see next pic)Usually caused by an ACTH-secreting pituitary tumorRarely by tumor of adrenal cortexIatrogenic

Addison’s diseaseHyposecretion (under secretion) of adrenal cortexUsually involves cortisol and aldosterone: low blood glucose andsodium, severe dehydration, fatigue, loss of appetetie, abdominalpain

(Jane Austin)

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BEFOREANDAFTERONSETOFCUSHING’S


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BEFORE AND AFTER ONSET OF CUSHING’S

DISEASE

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After>efore


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HOMEOSTASIS AND HORMONES

Examples:Thyroid and temperature control

Thyroid, Parathyroid, and calcium

Pancreas and glucose control


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Knowing the following:The thyroid produces thyroxine, which increases

metabolism.

Thyroid-stimulating hormone is released by the

pituitary.Sketch a negative feedback loop that controls

body temperature regulation.

78&9

T

85T"5

&


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TEMPERATURE CONTROL


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Knowing the following:

Calcitonin from the thyroid inhibits calcium

release from the bones.

Parathyroid hormone stimulates release of calciumfrom the bones.

Sketch a negative feedback loop that controls

blood calcium level.

78&9

T

85T"5

&


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BLOOD CALCIUM


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Knowing that:

Insulin from the pancreas lowers blood glucose by

stimulating body cells to take up glucose.

Glucagon from the pancreas increases blood sugar by

stimulating the liver to break down glycogen into

glucose.Sketch a negative feedback loop that controls

blood sugar.

78&9

T

85T"5

&


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BLOOD SUGAR CONTROL


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OTHER HORMONE ROLES

Controlling sleep cycles (melatonin)

Controlling reproductive cycles (melatonin, sex

hormones)

Growth (growth hormone)

Responding to stress or emergencies

(epinephrine and other hormones)


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HORMONES EVERYWHERE!

Many other organs besides the endocrine glands

produce hormones.

Kidneys produce several hormones that regulate

blood pressure, which is essential for kidney

function.The digestive system produces several hormones

that regulate appetite.


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Low body fat stimulates leptin production, which stimulates appetite. The mouse

is obese because its low leptin levels give it an enormous appetite. Leptin

injections return the mouse’s weight to normal. Humans sometimes have a leptin

issue, too, but the problem is a bad leptin receptor on body cells. Alas, leptin

injections won’t cure that.

The obese mouse on the

left does not produce

enough leptin, a hormone

produced by fat cells.

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CHAPTER 8 THE ENDOCRINE SYSTEM.ppt