Hp-Campling: Pituitary Hormones Essay

Front 1

Introduction - structure of anterior/posterior pituitary

Back 1

• Anterior – true endocrine gland made of glandular epithelium.

• Posterior – downgrowth of hypo and remains joined to the hypothalamo-hypophyseal nerve tract and secretes neurohormones made in hypothalamus.

Front 2

What is common in their synthesis? Preprohormone to prohmone

Back 2

• Peprohormone (large inactive protein from ribosome) contains copies of a peptide hormone, e.g. a signal sequence that directs protein to RER. N-terminal signal sequence cleaved and– prohormone – transported to ER for packaging.

Front 3

What is common in their synthesis? Prohormone to release

Back 3

• Golgi – packaged into membrane-bound secretory vesicles with proteolytic enzymes – cleaved to activate hormone – post-translational modification.

• Secretory vesicles containing peptides are stored in cytoplasm of endocrine cell until cell receives signal for secretion.

• Vesicles move to cell membrane and release their contents by Ca-dependent exocytosis.

• All peptide fragments released together into ECF – co-secretion.

Front 4

Explain the synthesis of posterior hormones

Back 4

• Synthesised in hypothalamus, packaged in granules with the transport protein neurophysin I (associated with ADH), II (associated with oxytocin)

Front 5

How are posterior hormones stored

Back 5

• Granules transported to terminals of axons in posterior and stored in axon terminals or Herring bodies along axon.

Front 6

How are posterior hormones released

Back 6

• Stimuli in form of nt released for hypo interneurons – neurones depolarise and propagate AP down axon, - granules secreted (along with neurophysin) by Ca-dep exocytosis and contents diffuse into adjacent capillaries as free hormones. Act on target – G protein-linked receptors.

Front 7

Explain the synthesis of thyroid hormones

Back 7

Hormones (T4 and T3) produced by follicular cells of thyroid

Coupling of iodinated tyrosine (iodination by thyroid peroxidase) to form thyroid.

Intracellular enzymes separate 3&4 – circulation.

Front 8

How is anterior hormones secretion regulated?

Back 8

• Hormone secretion controlled by hypothalamic neurohormones. All hormones except prolactin have another endocrine gland/cell as target – tropic. Trophic hormones – direcly affect growth – hyperplasia/hypertrophy.

Front 9

How are RH made and how do they travel from hypothalamus to anterior pituitary?

Back 9

• RHs synthesised in neurones of hypothalamus travel down axons and diffuse into primary plexus of hypophyseal portal system. Carried by hypophyseal portal veins to secondary plexus – distributed to target cells within anterior pituitary.

Front 10

Where are anterior synthesised, stored and secreted?

Back 10

Cells in anterior pituitary NOT hypothalamus.

Front 11

What is the structure of posterior hormones and their targets?

Back 11

Oxytocin (nonapeptide)– - Uterus, mammary glands

Vasopressin (nonapeptide dis. 1,6)- Kidneys or Arterioles

Front 12

Where are posterior hormones synthesised?

Back 12

Cell bodies of large neurones within supraoptic and paraventricular nuclei in hypothamalus

Front 13

What is the effect of oxytocin?

How is its action mediated?

Back 13

Smooth muscle contraction

Uterine contractions; lactation – contraction of myoepithelial cells lining duct of mammary gland – pos feedback

Mediated via specific receptors on target cells linked to IP3

Front 14

What is the effect of ADH?

Back 14

Stimulates water retention (V2 receptors, cAMP) in collectin ducts

Raises BP - vasoconstriction (acts on V1A receptors – via Ca, PLC and IP3)

induces male aggression

Front 15

What is the structure of anterior hormones, their targets and location of synthesis?

Back 15

Adrenocorticotropic hormone (ACTH)– Adrenal gland - Corticotrophs

Thyroid-stimulating hormone; Thyroid gland; Thyrotrophs

Follicle-stimulating hormone Gonads Gonadotrophs

Luteinizing hormone Gonads Gonadotrophs

Prolactin Ovaries, mammary glands Lactotrophs

Growth hormone Liver, adipose tissue Somatotrophs

Front 16

How is Oxytocin regulated?

Back 16

Activation of nerve endings in nipple/uterus stimulate release.

Neurogenic feedback - reflexes relayed to hypothamalus via spinothalamic tract

Front 17

How is ADH regulated?

Back 17

Increase in osmolality (osmoreceptors in hypothalamus)

Fall in ECV of >8%(pressure receptors), CCK secreted by SI

Decrease in arterial pp of O2 and increase CO2

Front 18

How is ACTH regulated?

Effect of hypersecretion

Back 18

Controlled by CRH from hypothalamus.

- circadian rhythm: Released episodically from corticotrophs

- stress: surgery and hypoglycaemia

- negative feedback control by cortisol.

Hypersecretion – Cushing’s. Hyper/hypo-responsiveness of target cell due to upregulation of receptors.

Front 19

How is TSH regulated?

Back 19

TSH from anterior pituitary. TSH secretion stimulated by TRH from hypothamalus. Thyroid hormone suppresses TSH secretion.

Front 20

How is FSH regulated?

Back 20

Secretion controlled by GnRH.

Front 21

How is LH regulated?

Back 21

Secretion controlled by GnRH.

Front 22

How is prolactin regulated?

Back 22

Controlled by Pit-1 Tf. Under inhibitory control of dopamine. Released episodically.

Thyrotropin-releasing hormone (TRH) has a stimulatory effect on prolactin release

Front 23

How is GH regulated?

Back 23

Release mediated through (+) GHRH and (-) somatostatin – CNS control.

Episodic secretion related to sleep-wake cycle. Peaks every 2-3 hrs.

Front 24

What are tropic hormones?

Back 24

Hormones that have other endocrine glands as their target (FLAT)
FSH - maturation of eggs and production of sperm
LH - stimulates release of steroid hormones in gonads - ovary and testes
ACTH - stimulates adrenal cortex to release glucocorticoids
TSH - stimulates thyroid gland to make and release thyroid hormone

Front 25

How does dopamine inhibit prolactin?

Back 25

Dopamine produced by neurons in the arcuate nucleus is secreted into the hypophyseal portal system of the median eminence, which supplies the pituitary gland.

Front 26

How is prolactin produced?

Back 26

In the absence of dopamine, secreted continuously.

Front 27

What is the solubility of thyroid hormones?

Back 27

Lipophilic

Front 28

Name the releasing hormones

Back 28

GnRH

TRH, CRG, SS, Dopamine, PRF

Front 29

How are RH secreted?

What is the effect of RH release?

Back 29

Pulsatile secretion, entrained to daily and seasonal rhythms through CNS input, signals transduced through Ca/cAMP

Stimulates synthesis of target anterior hormones at transcriptional level, modifies activity – post-transcriptional effects, hyperplasia/hypertrophy of target cells

Front 30

What are disorders of ADH secretion?

Back 30

SIADH – excessive release, hypervolemia results in dilutional hyponatremia. Treated with ADH antagonist


Undersecretion – can lead to DI

Front 31

What are the effects of over/undersecretion of prolactin?

Back 31

Oversecretion: benign tumour - pituitary adenoma. Spontaneous/lack of suppression in hypothalamic trophic hormone.

Overproduction– Overproduction– infertility. Treated by bromocriptine

Undersecretion – disconnection of axis (tumour), pituitary hypoplasia, pituitary destruction

Front 32

What other factor could cause prolactin release?

Back 32

Drugs - due to dopamine antagonist effects

Front 33

What is the effect of ACTH?

Back 33

Secretion of glucocorticoid(gluconeogenesis, suppress immune system), mineralocorticoid (ALDOSTERONE, Na/H2O retention,increase blood vol and bp) inadrenal cortex and androgens

Front 34

What is the effect of TSH?

Back 34

TSH stimulates cell metabolism, promotesa thropicresponse in cell size and activity

Causes increase in: TM ion fluxes, iodination of thyroglobulin, cellular metabolism, DNA synthesis, iodine flux into cell

T3 binds receptor. T4 deiodinated in target cells to T3. T4 binds to serum proteins.

Front 35

What is the effect of FSH?

Back 35

Growthof reproductive system

Front 36

What is the effect of LH?

Back 36

Sexhormone production

Front 37

What is the effect of Prolactin?

Back 37

Secretionof oestrogens/progesterone; milk production – neuronally mediated.

Front 38

What is the effect of GH?

Back 38

Promotes bone, soft tissue and viscera growth; lipid and carbohydrate metabolism

Indirect: stimulated liver toproduce somatomedins

Lipolysis

Front 39

What is the mechanism of action of thyroid hormones?

Back 39

Hydrophobic so pass through membrane

Receptors in nucleus of target cells

Forms homo/heterodimers with receptor - binds DNA upstream of regulated gene at hormone responsive element (HRE)

Front 40

Effect of thyroid hormone

Back 40

Determines BMR - increases conc. enzymes in catabolism, T3 interacts with catecholamines to increase HR and force of contractions

Regulates growth

Front 41

Other than GH, what hormones are involved in growth?

Back 41

· Thyroid hormone – hypersecretion not excessivegrowth

· Insulin – hyper – excessive growth

· Androgens – puberty, stimulate protein synth.Effect depends on GH

· Estrogens – effects growth prior to bonematuration

Front 42

What is the structure of the thyroid gland?

Back 42

· Highly vascularised

· Functional units – follicles – change appearanceaccording to activity

· Follicles – epithelial cells surround colloidfilled lumen, serves as EC storage for hormones

Front 43

Cause for ADH secretion?

Back 43

Vasopressin is secreted from the posterior pituitary gland in response to reductions in plasma volume, in response to increases in the plasma osmolality, and in response to cholecystokinin (CCK) secreted by the small intestine:

Front 44

Explain the stimuli for ADH release and the mechanism for its effect

Back 44

1) Most Potent: Osmolarity. Greater than 280 mOsM Hypothalamic osmoreceptors Interneurones in hypothalamus - synthesise AD. Released from pituitary. Collecting duct epithelium.

2) Low blood volume Decreased atrial stretch detected by stretch receptors. Sensory neuron to hypothalamus.

3) Decreased blood pressure. Carotid and aortic baroreceptors. Sensory neuron to hypothalamus.

Front 45

Oxytocin regulation

Back 45

neurogenicfeedback. Spinothalamic tract

Front 46

Cortisol regulation

Back 46

releasedby stress and circadian rhythm.

Front 47

Prolactin :

Back 47

oe/prosecretion, milk production, TSH/ACTH secretion. TRH stimulatory effect. Inhibitedby dopamine produced in arcuate nucleus into portal system of median eminence. Undersecretion – disconnection of axis, pituitaryhypoplasia

Front 48

GHregulation+ function

Back 48

+GHRH, Liver produces somatomedins stimulating somatostatin from hypothalamuswhich inhibit release of GH. Lipolysis.

Front 49

Trophichormones

Back 49

–induce hypertrophy or hyperplasia. TSH and ACTH

Front 50

RH

Back 50

pulsatile. Affect transcription

Front 51

Thyroid

Back 51

T3 interacts with catecholamines to increase HR and force ofcontractions.

Front 52

ADH

Back 52

plasmavolume – arterial stretch receptors, osmolarity (280 mOsM) by hypothalamicosmoreceptors, pressure – carotid/aortic baroreceptors. CCK from SI.