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Y1 LCRS Endo > Pituitary > Flashcards

Pituitary Flashcards

Adenohypophysis; Neurohypophysis

1
Q

Where is the adenohypophysis located?

A

Front of pituitary

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2
Q

How is blood supplied to the adenohypophysis?

A

Supplied by the hypophysial artery that enters and forms a fenestrated plexus @ the median eminance
Long portal veins carry blood to 2° plexus
Drains to the cavernous sinus and then jugular veins

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3
Q

What are the 6 adenohypophysical hormones?

A 
Somatotrophins
Prolactins
Thyroid Stimulating Hormone
LH
FSH
ACTH
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4
Q

Where do neurones terminate in the adenohypophysis?

A

@ the Median Eminence

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5
Q

Where is the neurohypophysis located?

A

Back of pituitary

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6
Q

How is blood supplied to the neurohypophysis?

A

Inferior hypophysial artery
No fenestration or plexus in median eminence
Drains to jugular veins

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7
Q

What hormones are produced by the neurohypophysis?

A

none

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8
Q

What hormones are secreted by the neurohypophysis?

A

Oxytocin and vasopressin (ADH)

Produced in the hypothalamic neurones

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9
Q

Where do neurones terminate in the neurohypophysis?

A

Posterior pituitary gland

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10
Q

What are the 5 main types of adenohypophysial cells and what hormones do they produce?

A

Somatotrophs - growth hormone
Lactotrophs - prolactin
Thyrotrophs - thyroid stimulating hormone
Gonadotrophs - LH and FSH
Corticotrophs - ACTH adrenocorticotrophic hormone

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11
Q

What is the hypothalamo-adenohypophysial axis regarding growth?

A

Growth hormone releasing hormone (stim)/Somatostatin (inhib)→Somatotrophin→Somatomedins (IGF-1)

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12
Q

What is the hypothalamo-adenohypophysial axis regarding lactation?

A

Thyrotrophin releasing hormone (stim)/Dopamine (inhib)→prolactin→breasts

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13
Q

What is the hypothalamo-adenohypophysial axis regarding thyroid stimulation?

A

Thyrotrophin releasing hormone (stim)→Thyroid stimulating hormone→T3 and T4 in thyroid gland

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14
Q

What is the hypothalamo-adenohypophysial axis regarding gonad stimulation?

A

Gonadotrophin releasing hormone (stim)→LH and FSH→testosterone, progesterone and oestrogen in gonads

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15
Q

What is the hypothalamo-adenohypophysial axis regarding adrenal gland stimulation?

A

Corticotrophin releasing hormone (stim)/Vasopressin (stim)→ACTH→cortisol in adrenal gland

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16
Q

What is the general structure of the steps of the hypothalamo-adenohypophysial axis?

A

1) Hormones from hypothalamic nuclei are released to the 1° plexus
2) Hormones act on anterior pituitary target cells
3) Adenohypophysial hormones released from 2° plexus into the general circulation
4) Hormones act on target organs
5) Negative feedback from target organ hormone

17
Q

What stimulates somatotrophin production?

A 
Sleep
Stress
Oestrogen
Exercise
Fasting
Amino acids
Ghrelin
18
Q

What supresses hypothalamic dopaminergic neurones in the prolactin pathway?

A

Suckling

19
Q

What are the two types of neurones found in the posterior pituitary?

A

Supraoptic neurones - above optic chiasm

Paraventricular neurones - next to 3rd ventricle

20
Q

What are features of supraoptic neurones?

A

All are magnocellular (pass dwon to neurohypophysis)
∴Have herring bodies along axon
Originate in hypothalamic supraoptic nuclei
Terminate in the neurohypophysis
Either vasopressinergic or oxytocinergic

21
Q

What are features of paraventricular neurones?

A

Magnocellular (pass down to neurohypophysis) and parvocellular (neurones pass to other parts of the brain)
Originate in paraventricular nuclei
Either vasopressinergic or oxytocinergic

22
Q

What differentiates vasopressin from oxytocin?

A

AVP has phenylalanine and arginine in place of isoleucine and leucine in oxytocin

23
Q

What are the similarities between vasopressin and oxytocin?

A

Nonapeptides

Initially prohormones that are cleaved to form hormone

24
Q

What is the principle action of vasopressin?

A

ADH anti diuretic hormone

acts on kidney to promote water retention

25
Q

Where are vasopressin receptors found?

A

V1a:
-Arterial/arteriolar smooth muscle (vasoconstriction)
-Hepatocytes (glycogenolysis)
-CNS neurones (Behavioural and other effects)
V1b:
-Corticotrophs (ACTH production)
V2:
-Collecting duct cells (water reabsorption)
-Other effects (endothelial cells, factor VIII and von Willbrandt factor)

26
Q

What is the vasopressin dependent aquaporin?

A

Aquaporin 2

27
Q

How is vasopressin synthesised?

A

1) Pre-provasopressin translated in the hypothalamic nuclei comprised as SS-HORMONE-NP-GP
2) Signal sequence directs the pre-prohormone to the golgi for packaging into a vesicle containing the pre-prohormone and an enzyme that can cleave the sections to release the hormone
3) Vesicles travel down neurone, by time it reaches end it has been cleaved
4) Vasopressin released to the posterior pituitary where it can enter blood stream

28
Q

How is oxytocin synthesised?

A

1) pre-prooxytocin translated with a signal sequence and a neurophysin
2) Signal sequence directs pre-prohormone to golgi for packaging
3) Golgi packages it into vesicles with enzyme that can cleave the sections to release the hormone
4) Vesicle travels down neurone and is hormone is cleaved before it reaches the end
5) Oxytocin released to posterior pituitary and can enter blood stream

29
Q

What is the purpose of the neurophysin in the translation of hormones?

A

Protects the hormone from degradation as it travels down the axon
Carrier protein that transports hormones to the neuropophysis

30
Q

What is the purpose of Herring bodies?

A

Allow movement and storage of hormones

31
Q

How does vasopressin promote water retention?

A

1) Binds to V2 receptor of collecting duct cells (receptor is linked to a G protein with GaS subunits that activate adenyl cyclase)
2) cAMP produced from ATP using adenyl cyclase to activate PKA
3) Aquaporin 2 molecules are synthesised to vesicles due to vasopressin, which also causes their movement to and insertion into the apical membrane
4) Allows water to diffuse out of lumen

32
Q

What are the major therapeutic advantages of oxytocin?

A 
Uterus
-Rhythmic contraction
-Cervix dilation
-increased local prostanoid production
Mammary gland
-contraction of myoepithelial cells for milk ejection
33
Q

What are the minor unwanted effects of oxytocin?

A 
CVS
-Transient vasodilation
-Tachycardia
-Constriction of umbilical arteries and veins
Kidneys
-Anti-diuresis
-2° hyponatraemia
34
Q

What are the effects of oxytocin on the CNS?

A

‘tend and befriend’ behaviour
maternal behaviour
social recognition

35
Q

How is vasopressin controlled by osmoreceptors?

A

1) Increased plasma osmolarity causes shrinkage of hypothalamic osmoreceptors as water leaves the cells∴stimulating neurones that lead to stimulating vasopressin secretion
2) Additional neurones travel to brain to stimulate thirst
3) Vasopressin travels to kidneys to increase water absorption, reducing plasma osmolarity
4) Reduced plasma osmolarity reduces vasopressin secretion

36
Q

How is vasopressin controlled by baroreceptors?

A

1) Decreased BP detected by baroreceptors causing a reduced rate in firing
2) Firing of baroreceptors normally inhibits vasopressin release, but reduced firing rate decreases inhibition and vasopressin release increases
3) This causes vasoconstriction to increase BP
4) Increased BP increases baroreceptor firing and inhibits vasopressin release again

37
Q

How is oxytocin controlled?

A

Neuroendocrine reflex arc
Suckling causes receptors linked to afferent nerves to fire towards brain
Hypothalamus stimulated to cause neurohypophysis to release oxytocin in efferent limb of reflex arc to cause milk ejection

38
Q

How may vasopressin dysregulation present?

A

Diabetes insipidus if vasopressin absent - polydipsia and polyurea

Y1 LCRS Endo (7 decks)

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