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MBBS II ERS > L12 – Physiology of Pituitary Hormones > Flashcards

L12 – Physiology of Pituitary Hormones Flashcards

1
Q

Summarize the flow of neurohormones from hypothalamus to anterior pituitary?

A

dorsal medial, ventral medial, infundibular nuclei + PVN secrete neurohormones into
the Hypophyseal portal system:

primary capillary plexus @ median eminence
» secondary capillary plexus
» Adenohypophysis

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2
Q

Summarize the flow of neurohormones from hypothalamus to posterior pituitary?

A

paraventricular nucleus (PVN) and supraoptic nucleus (SON) secrete neurohormone

> > axon directly to posterior pituitary
stored in Herring bodies

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3
Q

Define the neurohormones secreted by the arcuate nucleus and their effect on anterior pituitary cells?

A

1) GH-releasing hormone (GHrH)&raquo_space; Somatotrophs&raquo_space; Growth hormone
2) Gonadotropin releasing hormone (GnRH)&raquo_space; Gonadotrophs&raquo_space; FSH and LH
3) (-) Dopamine&raquo_space; Lactotrophs&raquo_space; Prolactin

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4
Q

Define the neurohormones secreted by the PVN and their effect on anterior pituitary cells?

A

1) Corticotrophin releasing factor&raquo_space; corticotrophs&raquo_space; Adrenocorticotropic hormone
2) Thyrotropin releasing hormone&raquo_space; Thyrotrophs&raquo_space; TSH

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5
Q

Define the neurohormones secreted by the PVN

and SON and their effect on posterior pituitary cells?

A

PVN and SON:

Release Vasopressin and Oxytocin

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6
Q

Define the stimulating and inhibitng factors of Growth hormone/ somatotropin?

A

Stim = growth hormone-releasing hormone (GHRH) from arcuate nucleus&raquo_space; negative feedback to GHRH neuron

Inhibited by somatostatin (SS) from periventricular nucleus

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7
Q

Summarize the direct and indirect pathways for Growth hormone effect?

A

Directly activate GH-receptor:

i) Muscle = protein synthesis
ii) Adipose tissue = lipolysis
iii) Block GLUT-4 on diff. tissue = decrease glucose uptake

Indirect:
Activate GH-R on liver: produce IGF-1 to Bone, cartilage:
- Chondrocyte proliferation, bone growth

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8
Q

Which hormone has antagonistic action to growth hormone?

A

Insulin

Increased blood glucose suppresses GH secretion

OGTT can be suppression test for GH

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9
Q

Describe the feedback control of growth hormone release?

A

Increased GH&raquo_space; Increase stimulation of GH-R on liver&raquo_space; Increase IGF-1 production:

  • Suppress somatotrophs
  • Stimulate release of Somatostatin from PVN

> > feedback decrease GH secretion

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10
Q

Define the cause of GH hypersecretion, related symptoms?

A
  • Commonly tumour of somatotrophs in anterior pituitary
  • Hypersecretion of GH = Acromegaly and Gigantism:
  • Enlargement of organs
  • CVD
  • Hypertension
  • DM (GH antagonize Insulin)
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11
Q

Define the cause of GH hyposecretion, related symptoms and treatment?

A

Cause: damage to hypothalamus/ pituitary or mutation in GH secretion regulation

Result: Dwarfism:

  • Growth retardation
  • Hypoglycaemia&raquo_space; decreased energy
  • Low BMD, low muscle strength
  • Delayed puberty

Treatment: GH admin

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12
Q

Define the cause of GH unresponsiveness, treatment?

A

Laron Syndrome

Autosomal recessive: GH receptor mutation = insensitive to GH

Treatment = IGF-1 admin

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13
Q

Describe the rate of GnRH secretion from arcuate nucleus and the effects on gonadotropins?

A

GnRH = pulsatile secretion

High freq.= LH synthesis and secretion

Low freq. = FSH synthesis and secretion

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14
Q

Compare the effects of FSH and LH on gonads?

A

FSH = Gametogenesis (spermatogenesis and oogenesis)

LH = synthesis and secretion of sex steroids (Steriodogenesis)

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15
Q

Effect of FSH on male gonad? (3)

A

 Stimulates testosterone-binding protein in Sertoli cells to help spermatogenesis (permissive effect)

 Stimulates spermatogenesis

 Increase production, secretion of inhibin = negative feedback to FSH secretion in anterior pituitary

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16
Q

Effect of FSH on female gonad?

A

 Induces LH receptors expression on granulosa cells > ready for ovulation

 Stimulates oogenesis

 Increase production, secretion of inhibin = negative feedback to FSH secretion in anterior pituitary

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17
Q

Effect of LH on male gonad?

A

Stimulates steroidogenesis (testosterone) in Leydig cells of testis

Increase plasma testosterone = negative feedback pn FSH, LH and GnRH secretion

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18
Q

Effect of LH on female gonad? (4)

A

 Stimulates steroidogenesis (testosterone) in theca cells of ovary&raquo_space; enzymatically modified by granulosa cells into estrogen

 Estrogen stimulates oogenesis, follicular development

 Terminates 1st meiosis = forms secondary oocyte

 Causes ovulation = forms corpus luteum (produces progesterone)

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19
Q

Describe how LH self regulates secretion in females?

A

Increase plasma estrogen = feedback inhibition on FSH, LH, GnRH

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20
Q

List 2 causes of hypergonadotropism?

A
  1. Pituitary tumor of gonadotropin

2. Ectopic GnRH-producing tumors of the lung and liver cell lines

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21
Q

List 2 causes of gonadotropin deficiency leading to hypogonadism?

A

1) Hyperprolactinemia&raquo_space; decrease GnRH production

2) Genetic mutation
i) GnRH neuron development (Kallman’s syndrome)
ii) GnRH receptor
iii) β-subunit of gonadotropin gene

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22
Q

Define the cause and effect of Kallmann syndrome?

A

X-linked / autosomal recessive

GnRH-secreting neurons are congenitally absent

No puberty, infertile

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23
Q

Which hormone secreted by the anterior pituitary is affected by dopamine differently than the rest?

A

Prolactin: Tonically Inhibited by dopamine from hypothalamus

24
Q

Describe the hypothalamic control to stimulate prolactin release?

A

1) Neurogenic stimuli (breast feeding) activate ANS&raquo_space; inhibit dopamine release at hypothalamus&raquo_space; Reduce tonic inhibition on lactotrophs to secrete prolactin
2) Physiological stimuli: high estrogen due to pregnancy&raquo_space; stimulate anterior pituitary directly&raquo_space; secrete prolactin

25
Q

Describe the effect of prolactin on mammary glands?

A

Prolactin bind to PRL-R (tyrosine kinase receptor)

> > receptor dimerize&raquo_space; activate JAK- STAT5 for gene transcription:

i) Growth and development of mammary gland for lactation
ii) Milk production by alveolar epithelial cells (galactopoiesis)

26
Q

Describe how prolactin inhibits lactating women from premature pregnancy?

A

Prolactin bind to receptors on afferent neurons of hypothalamic GnRH neurons

> > reduce stimulation of GnRH neurons
decrease GnRH = decrease FSH and LH from pituitary gonadotrophs

27
Q

List 3 pathological causes of hyperprolactinemia?

A

 Prolactinomas at pituitary

 Hypothalamic, pituitary stalk disorders: e.g. loss of dopamine inhibition on PRL

 Ectopic prolactin secretion from other tumors at other parts of body

28
Q

Effects of hyperprolactinemia on male and female?

A
  • Abnormal lactation (galactorrhea)
  • Hypogonadism, infertility (inhibit GnRH)

Female:
 Anovulation (lack of ovulation)
 Amenorrhea (lack of menstruation)

Male:
 Low testosterone level = lack of sex desire, erectile dysfunction
 Enlargement of breast tissue

29
Q

Treatment options for hyperprolactinemia?

A

Prolactin receptor blocker

Dopamine agonist

Vit B6

30
Q

Cause and effect of Sheehan syndrome?

A

blood loss and hypovolemic shock during and after childbirth

> > postpartum pituitary necrosis

> > cannot release prolactin/ breastfeed

31
Q

Define the precursor of ACTH?

A

proopiomelanocortin (POMC): cleaved into (not all):

  • ACTH
  • Endorphin
  • Melanocyte-stimulating hormone
  • Corticotropin-like intermediate peptide (CLIP)
32
Q

Describe the trigger and effect of ACTH?

A

Trigger = Corticotropin-releasing hormone from PVN&raquo_space; bind to CRH-R

Effect = increase production of POMC and release of ACTH at corticotrophs&raquo_space; stimulate adrenal cortex hormone production

33
Q

Describe the effect of ACTH on its target organ?

A

Binds to MC2R ( melanocortin receptors) at adrenal cortex» transcription of genes:

i) increase cholesterol uptake by adrenal cortical cells + cell growth
ii) Activate steroidogenic enzymes for steroidogenesis&raquo_space; make cortisol and androgens

34
Q

Describe the normal feedback regulation of ACTH?

A

ACTH > adrenal cortex > cortisol

1) Cortisol negatively feedback inhibit release of Corticotropin-releasing hormone (CRH) in hypothalamus
2) Suppress POMC production and ACTH release in corticotrophs at ant. pit.

35
Q

Describe the effects of extremely high plasma ACTH?

A

bind with low affinity to activate MC1R expressed in melanocytes of skin, hair follicles

produce, dispense brown/black melanin pigment&raquo_space; hyperpigmentation (skin darkening)

36
Q

Define difference between primary and secondary adrenal insufficiency?

A

Primary = Adrenal cortex is dysfunctional: high ACTH and CRH

Secondary = Either hypothalamus or Pituitary is dysfunctional

37
Q

Define ACTH deficiency?

A

Failure of hypothalamus to stimulate pituitary ACTH production: Low CRH and ACTH

Classify as secondary adrenal insufficiency

38
Q

Which 2 conditions mimic the symptoms of ACTH deficiency (secondary adrenal insufficiency)?

A

 Primary adrenal insufficiency (i.e. Addison’s disease)

 Hereditary Mutation in the MC2R gene

39
Q

High CRH, ACTH, but low cortisol. Which type of adrenal insufficiency?

A

Primary

40
Q

High CRH, Low ACTH, Low cortisol .Which type of adrenal insufficiency?

A

Secondary, pituitary disease

41
Q

Low CRH, Low ACTH, Low cortisol .Which type of adrenal insufficiency?

A

Secondary, hypothalamus diease

42
Q

List 2 causes of over-production of ACTH?

A

 Adenoma of corticotrophs at pituitary

 Ectopic CRH/ACTH production in some fastgrowing tumors (e.g. oat cell carcinoma of the lung)

43
Q

Diff. between Cushing disease and Cushing syndrome?

A

Disease = excessive secretion of ACTH from the anterior pituitary gland (secondary disorder)

Syndrome = primary disorder in adrenal cortex = symptoms that occur due to high cortisol levels

44
Q

Compare structure of glycoprotein hormones secreted by anterior pituitary?

A

FSH, LH, TSH

Common a- subunit
specific B- subunits

45
Q

Describe the trigger and effect of TSH release?

A

PVN&raquo_space; Tyrotropin-releasing hormone (TRH)&raquo_space; Pituitary thyrotropes&raquo_space; TSH

TSH receptor on thyroid follicular cells&raquo_space; thyroidal gene expression:

1) Thyroid cell growth and differentiation
2) T3, T4 production

46
Q

Describe the TSH regulation?

A

TSH > thyroid follicular cells > T3,T4

i) T3 inhibit pituitary thyrotrope: decrease synthesis of TSH β subunit, TSH secretion
ii) T3 inhibit TRH synthesis in hypothalamus

47
Q

Compare the structure between Vasopressin and Oxytocin?

A

Both 9a.a. long, only differing in 2 a.a.

48
Q

Source of Vasopressin and Oxytocin?

A

Magnocellular neurons of PVN and SON

> > hypothalamo/ hypophyseal tract to the posterior pituitary, carry by neurophysin

> > Stored in Herring Bodies at terminal axon

49
Q

Describe the release mechanism of Vp and Oxytocin?

A

Stimuli > depolarize magnocellular neuron

> > AP propagate down hypophyseal tract to terminal axon

> > Depolarization = open Ca channels to increase [Ca] intracellular

> > Exocytosis of Herring bodies and release Vp/ oxytocin into fenetrated capillary

50
Q

Summarize the effects of Vp?

A

Receptor = GPCR:

1) V1aR is coupled to Gαq protein: vascular smooth muscle&raquo_space; vasoconstriction
2) V2R is coupled to Gαs protein: Renal collecting ducts: Trafficking of AQP2 to apical membrane for water reabsorption

51
Q

Summarize the effects of Oxytocin?

A

1) Positive feedback on uterus myometrium contraction during labor
2) Contraction of myoepithelial cells in mammary gland for milk let-down during breastfeeding

52
Q

Disease caused by Vp insufficiency?

A

diabetes insipidus

Kidney cannot concentrate urine adequately

53
Q

Diff. between central and nephrogenic Diabeter insipidus?

A

A. Central diabetes insipidus (CDI): defect of vasopressin production / release

B. Nephrogenic diabetes insipidus (NDI): kidney cannot respond to vasopressin by producing concentrated urine

54
Q

What causes Nephrogenic diabetes insipidus (NDI)?

A

a. Mutation in V2R

b. Genetic defect in the AQP2 gene

55
Q

3 causes of excessive vasopressin?

A

Inappropriate ADH secretion:

1) Certain cancers with ectopic Vp production
2) Heart failure with aberrant baroreceptor activity
3) Diseased hypothalamus with slow leakage of Vp

56
Q

Symptoms and signs of Excessive Vp?

A
  • hypotonic / dilutional hyponatremia
  • Mild to moderate: headache, nausea, muscle weakness
  • Advanced: cerebral edema = confusion, hallucination
  • Grave: seizures, coma, death

MBBS II ERS (37 decks)

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