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Endocrinology > Hypothalamo-adenohypophysical axis > Flashcards

Hypothalamo-adenohypophysical axis Flashcards

1
Q

Where is the pituitary gland

A

Attached to the base of the brain in a bony dip (sella turcica)

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2
Q

Draw a diagram of the brain showing the hypothalamus and pituitary glands

A

diagram

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3
Q

What grows into the posterior and anterior pituitary glands

A

anterior: upwards growth from the buccal cavity
Posterior: downwards growth from neural tissue

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4
Q

what structure is close to the anterior pituitary gland

A

Optic chiasm

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5
Q

What are the hypothalamic nuclei

A

Clusters of neural cell bodies

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6
Q

Describe the how the axons reach the pituitary glands

A

posterior- axon extends all the way down to the gland

Anterior - axon extends to the median eminence where hormones may enter the primary capillary plexus

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7
Q

What feature of the plexus make them important for secretion

A

Leaky walls (large SA?|)

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8
Q

Give the route of blood flow through the hypothalamus

A 
Superior hypophysial artery
primary capillary plexus
long portal veins
secondary capillary plexus
Cavernous sinus
Jugular veins
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9
Q

Which 5 hormones are secreted by the adenohypophysis

A 
Somatotrophs
Lactotrophs
Thyrotrophs
Gonadotrophs
Corticotrophs
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10
Q

What are somatotrophs and what is the target

A

Growth hormones, proteins and general body tissue

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11
Q

What are Lactotrophs and what is the target

A

Prolactins, proteins, breasts in lactating women

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12
Q

What are thyrotrophs and what is the target

A

Thyroid stimulating hormone (TSH), glycoproteins and thyroid

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13
Q

What are gonadotrophs and what is the target

A

Luteinising hormone and follicle stimulating hormone, glycoprotein and testes/ovaries

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14
Q

What are corticotrophs and what is the target

A

adrenocorticotrophic hormone (ACTH), polypeptide and adrenal cortex

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15
Q

How are somatotrophs controlled

A

Growth hormone releasing hormone to increase or somatostatin to decrease

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16
Q

How are lactotrophs controlled

A

Negatively by dopamine and a bit by TRH

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17
Q

How are thyrotrophs controlled

A

thyrotrophin releasing hormone

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18
Q

How are gonadotrophs controlled

A

gonadotrophin releasing hormone

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19
Q

How are corticotrophs controlled

A

corticotrophin releasing hormone or vasopressin

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20
Q

Where can somatotrophs bind

A

Liver or other body tissues

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21
Q

What happens when somatotrophs bind to the liver

A

release of somatomedin - IGF I and IGF II

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22
Q

What can somatotrophs do

A

stimulate amino acid transport to cells and increase protein synthesis
Increase gluconeogenesis
Increase lipolysis and fatty acid synthesis
increase cartilaginous growth and somatic cell growth
IGF I can give direct feedback to the adenohypophysis or indirect feedback to the hypothalamus

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23
Q

What factors effect release of growth hormone releasing hormone

A 
Stress
Sleep
Certain amino acids
Ghrelin
Oestrogens
Fasting
Hypoglycaemia
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24
Q

How does dopamine normally affect hormone release

A

Dopamine is released from the hypothalamic nuclei. It inhibits lactotrophs so that prolactin is not released

25
Q

How does milk form when a baby suckles on the mother

A
  1. When the baby suckles, tactile receptors on the nipple feedbacks to the hypothalamus.
  2. hypothalamic dopaminergic neurones are suppressed
  3. Less dopamine released
  4. Prolactin released into the circulation
  5. milk formation in the breast
26
Q

Where do the neurones that lead to the neurohypophysis originate from

A

Supraoptic and paraventricular nuclei

27
Q

What is the name of the neurone that extends to the gland

A

Magnocellular neuron

28
Q

Describe the route from the supraoptic nuclei

A

Supraoptic nuclei
Pass the median eminence
Terminate in the neurohypophysis
Oxytocinergic or vasopressinergic

29
Q

Describe the route from the paraventricular nuclei

A

Paraventricular nuclei
Some terminate at the median eminence
Some travel to other parts of the brain
Some terminate at the neurohypophysis: vasopressinergic or oxytocinergic

30
Q

Which amino acids differ between vasopressin and oxytocin

A

Phe vs Ile

Arg vs Leu

31
Q

How is vasopressin synthesised

A
  1. pre-provasopressin transcribed
  2. signal peptide directs it to the golgi
  3. cleavage produces provasopressin
  4. As vesicles move along the axon, enzymes split provasopressin to produce vasopressin, glycopeptide and neurophysin
  5. vesicles may be stored in herring bodies along the way
32
Q

How does the oxytocin pathway differ from vasopressin

A

It is the same but no glycopeptides are produced and the neurophysin is different

33
Q

What are the two types of vasopressin receptor

A

V1 and V2

34
Q

Compare V1 to V2

A

Linked to G proteins via phospholipase C vs adenyl cyclase
Production of IP3 and DAG vs cAMP, PKA, aquaporins (AQP2)
Increase in calcium vs cAMP

35
Q

What are the two types of V1

A

V1a - arterial smooth muscle, hepatocytes, CNS neurones

V1b - corticotrophs

36
Q

Where is V2 found

A

collecting duct cells

endothelial cells

37
Q

What is the other name for vasopressin

A

Anti-diuretic hormone (ADH)

38
Q

What its the main effect of vasopressin

A

Stimulation of water reabsorption in the renal collecting ducts

39
Q

What is the vasopressin mechanism

A
  1. vasopressin binds to V2
  2. G-protein action activates adenyl cyclase
  3. ATP turns into cyclic AMP
    4 protein kinase A activated
  4. synthesis of aquaporin molecules (AQP2)
  5. aggraphores move to the apical membrane
  6. insertion of aquaporins onto the membrane
  7. Water moves through down its concentration gradient
  8. AQP 3 and 4 are less sensitive to vasopressin but attach to the basolateral (serosal) membrane
40
Q

What are aggraphores

A

They store AQP2

41
Q

Which structures does oxytocin have an effect on

A

uterus and mammary gland

42
Q

What are the minor (unwanted) effects of oxytocin

A

cardiovascular and kidney

43
Q

What are the additional effectsnof oxytocin

A

CNS

44
Q

What are the effects of oxytocin on the uterus

A

Rhythmic contraction (funds to urine)
Increase in prostanoid production
dilation of the cervix
At baby delivery the uterus becomes very sensitive to oestrogen
suppression of progesterone, enhancing of oestrogen

45
Q

What is the mechanism for baby delivery on release of oxytocin

A
  1. release of oxytocin
  2. Acts on the uterus at the parturition
  3. Travels to the myometrial cells
  4. Contraction
  5. Baby delivery
46
Q

What is the effect of oxytocin on the mammary gland

A

Contraction of myoepithelial cells, leading to milk ejection

47
Q

What is the mechanism for milk ejection on release of oxytocin

A
  1. oxytocin release
  2. Acts on the breasts during lactation
  3. Travels to myoepithelial cells
  4. Contraction
  5. Milk ejection
48
Q

What are the clinical uses of oxytocin

A

induction of labour at term (controlled IV)
Prevention treatment of postpartum haemorrhage
Facilitation of milk let-down (nasal spray)
Autism

49
Q

Describe the reaction to an increase in osmolality

A
  1. osmoreceptors shrink as they lose fluid to the blood
  2. stimulation neurones
  3. stimulation of vasopressin secretion
  4. vasopressin travels to the kidney
  5. increase in aquaporins
  6. increase in water absorption
  7. osmolality brought back to normal levels
50
Q

Describe the reaction to a decrease in blood pressure

A
  1. baroreceptors firing rate drops
  2. baroreceptor neurone causes less inhibition of vasopressin secretion
  3. more vasopressin released
  4. increase in vasoconstriction
  5. blood pressure returns to normal levels
51
Q

How is oxytocin release regulated

A
  1. stimulus = baby suckling on the nipple
  2. Nipple receptors linked to neural afferent limb
  3. oxytocin release from neurohypophysis
  4. activation of the endocrine efferent limb
  5. milk ejection
52
Q

What is the consequence of lack of oxytocin

A

Parturition and milk ejection can be induced or replaced by other means

53
Q

What is the consequence of lack of vasopressin

A

Diabetes insipidus

54
Q

What is syndrome of inappropriate ADH

A

Too much vasopressin.g. tumours absorb water

55
Q

What are the two type of diabetes insipidus

A

Central/ cranial and nephrogenic

56
Q

What causes central/cranial DI

A

Lack of vasopressin

57
Q

What causes nephrogenic DI

A

Kidneys are resistant to vasopressin

58
Q

What are the symptoms of DI

A

polydipsia (increased thirst)
polyuria (large urine volume)
Dilute urine (hypo-osmolar)

Endocrinology (9 decks)

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