Pituitary

Question 1

Where is the adenohypophysis located?

Answer 1

Front of pituitary

Question 2

How is blood supplied to the adenohypophysis?

Answer 2

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

Question 3

What are the 6 adenohypophysical hormones?

Answer 3

Somatotrophins
Prolactins
Thyroid Stimulating Hormone
LH
FSH
ACTH

Question 4

Where do neurones terminate in the adenohypophysis?

Answer 4

@ the Median Eminence

Question 5

Where is the neurohypophysis located?

Answer 5

Back of pituitary

Question 6

How is blood supplied to the neurohypophysis?

Answer 6

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

Question 7

What hormones are produced by the neurohypophysis?

Answer 7

none

Question 8

What hormones are secreted by the neurohypophysis?

Answer 8

Oxytocin and vasopressin (ADH)

Produced in the hypothalamic neurones

Question 9

Where do neurones terminate in the neurohypophysis?

Answer 9

Posterior pituitary gland

Question 10

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

Answer 10

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

Question 11

What is the hypothalamo-adenohypophysial axis regarding growth?

Answer 11

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

Question 12

What is the hypothalamo-adenohypophysial axis regarding lactation?

Answer 12

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

Question 13

What is the hypothalamo-adenohypophysial axis regarding thyroid stimulation?

Answer 13

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

Question 14

What is the hypothalamo-adenohypophysial axis regarding gonad stimulation?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

What stimulates somatotrophin production?

Answer 17

Sleep
Stress
Oestrogen
Exercise
Fasting
Amino acids
Ghrelin

Question 18

What supresses hypothalamic dopaminergic neurones in the prolactin pathway?

Answer 18

Suckling

Question 19

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

Answer 19

Supraoptic neurones - above optic chiasm

Paraventricular neurones - next to 3rd ventricle

Question 20

What are features of supraoptic neurones?

Answer 20

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

Question 21

What are features of paraventricular neurones?

Answer 21

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

Question 22

What differentiates vasopressin from oxytocin?

Answer 22

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

Question 23

What are the similarities between vasopressin and oxytocin?

Answer 23

Nonapeptides

Initially prohormones that are cleaved to form hormone

Question 24

What is the principle action of vasopressin?

Answer 24

ADH anti diuretic hormone

acts on kidney to promote water retention

Question 25

Where are vasopressin receptors found?

Answer 25

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)

Question 26

What is the vasopressin dependent aquaporin?

Answer 26

Aquaporin 2

Question 27

How is vasopressin synthesised?

Answer 27

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

Question 28

How is oxytocin synthesised?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

What is the purpose of Herring bodies?

Answer 30

Allow movement and storage of hormones

Question 31

How does vasopressin promote water retention?

Answer 31

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

Question 32

What are the major therapeutic advantages of oxytocin?

Answer 32

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

Question 33

What are the minor unwanted effects of oxytocin?

Answer 33

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

Question 34

What are the effects of oxytocin on the CNS?

Answer 34

'tend and befriend' behaviour maternal behaviour social recognition

Question 35

How is vasopressin controlled by osmoreceptors?

Answer 35

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

Question 36

How is vasopressin controlled by baroreceptors?

Answer 36

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

Question 37

How is oxytocin controlled?

Answer 37

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

Question 38

How may vasopressin dysregulation present?

Answer 38

Diabetes insipidus if vasopressin absent - polydipsia and polyurea