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G2 2017-2018 > Physiology - Posterior Pituitary > Flashcards

Physiology - Posterior Pituitary Flashcards

1
Q

What is the main type of neurons in the post pit? Describe them.

A

Magnocellular neurons: large and contain sulfur (through cysteine)

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2
Q

From what 2 hypo nuclei do the magnocellular neurons of the post pit originate from?

A
  1. Paraventricular2. Supraoptic
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3
Q

Describe the characteristics of the magnocellular neurons of the post pit.

A

Slow and high affinity: meaning they release hormones slowly but a very slight stimulus will cause them to release hormones because these are released in small quantities in the whole blood stream so concentrations are very small

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4
Q

What are the 2 neurohormones released by the magnocellular neurons of the post pit?

A
  1. Oxytocin2. Vasopressin (ADH)
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5
Q

What is the role of oxytocin?

A

Uterus and mammary glands contraction of smooth muscle

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6
Q

What is the role of ADH?

A

Reabsorption of water in kidney tubules to decrease plasma osmolality and concentrate urine

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7
Q

What kind of hormones are oxytocin and vasopressin? Therefore, where are they secreted?

A

Nonapeptides (9 AAs): hydrophilic so secreted directly into blood

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8
Q

How closely related are oxytocin and vasopressin? 3 arguments.

A
  1. Share 7 out of 9 AAs (differ at 3rd and 8th positions)2. Arise from same progenitor: vasotocin3. Located on same chromosome and inverted (probably evolved through gene duplication)
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9
Q

What protects oxytocin and vasopressin from degradation by enzymes? Why is this important?

A
  • Carboxy end protected by AMIDATION: amide group left over from peptide bond cleavage to glycine that is not recognized as the carboxy-end by enzymes- Amino end protected by DISULFIDE BOND: forms a cyclic structure Important because we have very low concentrations in the blood
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10
Q

What are 5 kinds of enzymes that degrade peptides?

A
  1. Proteases2. Exonucleases3. Amino-peptidases4. Carboxy-peptidases5. Endopeptidases
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11
Q

What are both oxytocin and vasopressin synthesized as? Why?

A

Inactive precursors that are later cleaved Purpose: to have the carboxy-end protected from enzyme degradation

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12
Q

What are the 3 vasopressin receptors?

A
  1. Vasopressin V22. Vasopressin V1a3. Vasopressin V1b
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13
Q

Where is Vasopressin V2 located? How does it work?

A

Location: kidney (distal and collecting tubules)Allows for vasopressin to function as ADH to reabsorb water

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14
Q

What does ADH stand for?

A

Anti-diuretic hormone

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15
Q

Where is Vasopressin V1a located? How does it work?

A

Location: vasculature of CNS, smooth muscle, and liverActs as a vasoconstrictor: 1. PLC-beta degrades membrane phospholipids into DAG and IP32a. DAG stimulates PKC to stimulate contraction2b. IP3 travels to ER to release calcium to stimulate contraction

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16
Q

Where is vasopressin V1b located? How does it work?

A

Location: corticotrophs of ant pit Works with CRH to release ACTH

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17
Q

Which neurohormone is the dominant regulator of ACTH?

A

CRH

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18
Q

Where are oxytocin receptors located? 2 locations

A
  1. Uterus: myometrium 2. Mammary glands: myoepithelium (smooth muscle)
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19
Q

What is the role of osmoreceptor afferent magnocellular neurons?

A

Regulate vasopressin secretion by post pit when plasma osmolality increases

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20
Q

What are the 2 types of magnocellular neurons?

A
  1. Osmoreceptor afferent2. Non-osmoreceptor afferent
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21
Q

What is the role of non-osmoreceptor afferent magnocellular neurons?

A

Baroreceptors/volume receptors in carotid and aortic circulation to inhibit vasopressin secretion when BP or BV is too high

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22
Q

How do the osmoreceptor afferent magnocellular neurons detect high blood osmolality? How sensitive are they?

A

When body is hyperosmolar the fenestrations of hypo let solute go through, this shrinks the cells that have fenestrations and activates the magnocellular neurons VERY sensitive: respond to changes in osmolality of less than 1%

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23
Q

How would you characterize the osmotic regulation of vasopressin secretion?

A

Linear: increases as osmolality increases AT ANY BP!

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24
Q

How is urine osmolality affected by an increase in vasopressin secretion?

A

Increase in urine osmolality

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25
Q

What is the osmotic threshold?

A

The plasma osmolality threshold before vasopressin secretion = 280 mosm/kg

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26
Q

Equation to calculate vasopressin plasma concentration?

A

[AVP]p = 0.3 x (Posm - 280)

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27
Q

What is the plasma osmolality of a normally hydrated person?

A

287 mosm/kg

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28
Q

What is the plasma concentration of vasopressin of a normally hydrated person?

A

2.0 pg/mL

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29
Q

What is the urine osmolality of a normally hydrated person?

A

500 mosm/kg

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30
Q

Does duration of urination change with body size?

A

NOPE

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31
Q

What % increase in TBW causes maximal dilution of plasma vasopressin concentration and urine osmolality?

A

2%

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32
Q

What % decrease in TBW causes maximal concentration of urine osmolality? What is max concentration of urine?

A

2% Max Uos > 1000 mosm/kg

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33
Q

What is the plasma concentration of vasopressin at maximal antidiuresis? Can it increase beyond that?

A

5 pg/mL Yes, but this will have no effect on reabsorption of water in kidney

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34
Q

What happens to increase TBW once maximal antidiuresis has been reached?

A

THIRST!

35
Q

How does drinking water affect vasopressin secretion? How? When? Purpose?

A

It inhibits it BEFORE CHANGES IN FLUID VOLUME OR OSMOLALITY by cold-sensitive oropharyngeal receptors being activated Purpose: to ensure we are not overhydrated

36
Q

How does increasing BP influence the linear curve of vasopressin concentration vs plasma osmolality? Explain what this means.

A

The slope decreases making the osmotic threshold greater => this makes it more difficult for vasopressin to regulate plasma osmolality at high BP

37
Q

What is the relationship between vasopressin concentration and mean arterial pressure (MAP)?

A

Exponential

38
Q

What is the most powerful regulator of vasopressin concentration?

A

Hemorrhage aka BP

39
Q

What is the most important regulator of vasopressin concentration?

A

Osmotic regulation

40
Q

Describe the 8 steps that happens when vasopressin binds the V2 receptors?

A
  1. Vasopressin binds V2 on basolateral membrane2. Gas activation3. Adenylyl cyclase activation4. cAMP synthesis 5. Protein kinase A activation6. Phosphorylation of vesicles in cytoplasm that contain aquaporins (AQP-2)7. Insertion of aquaporins into apical membrane to reabsorb water 8. Water pumped back into the cell and then interstitial space via the AQP3 and 4 aquaporins of the basolateral membrane
41
Q

What kind of transport happens through aquaporins?

A

Facilitated diffusion

42
Q

What are the 8 ways in which the body regulates fluid electrolytes and BV?

A
  1. RAA system2. Adrenergic NS3. Vasopressin4. Atrial netriuretic hormone (ANP)5. Kinins6. Endothelins7. Prostaglandins8. Nitric oxide system
43
Q

What is diabetes insipidus characterized by?

A

Low BV and large dilute urine volume

44
Q

What are the 4 types of diabetes insipidus? What is the treatment for all of them?

A
  1. Central = neurogenic = hypothalamis2. Nephrogenic3. Dipsogenic4. GestationalTreatment: long-lasting vasopressin agonist (snorted)
45
Q

What is central/neurogenic diabetes insipidus due to? Overall and 6 causes?

A

Inability to synthesize or secrete active vasopressin: 1. Metastatic tumor2. Idiopathic3. Histiocytosis (immune related)4. Severe whiplash that severes the pituitary stalk 5. Genetic6. Anatomical defect

46
Q

What is nephrogenic diabetes insipidus due to?

A

Inability of kidney to detect vasopressin: usually V2 or aquaporin receptor (AQP2) mutation

47
Q

What is dipsogenic diabetes insipidus associated with?

A

Excessive water drinking linked to psychiatric disorders: schizophrenia with over consumption of water

48
Q

What is gestational diabetes insipidus due to?

A

Placenta secretes vasopressinase that degrades vasopressin

49
Q

What is the effect of oxytocin on men?

A

Pair-bonding, fidelity and trust

50
Q

What is the suckling pathway of oxytocin production?

A

Infant sucks on boob stimulates reflex loop that synapses at spinal cord with hypo neurons which stimulates oxytocin secretion causing milk ejection

51
Q

What is the visual stimulus pathway of oxytocin production?

A

Woman sees, hears, or smells a crying baby it will stimulates oxytocin secretion causing milk ejection

52
Q

Where is milk ejected after oxytocin secretion?

A

Lumen of mammary gland

53
Q

How is uterine contraction stimulated during labor?

A

Increase in expression of oxytocin receptors in the myometrium

54
Q

How is uterus stretching stimulated during labor? 4 steps

A
  1. PLA2 and PLC are activated (PLC normal pathway)2. PLA2 produces arachidonic acid 3. Arachidonic acid stimulates prostaglandin production: PGE2 and PGF2alpha4. Prostaglandins soften uterus
55
Q

What is atosiban? What has been figured out about it?

A

Oxytocin antagonist that is ineffective at delaying labor because oxytocin only plays a minor role

56
Q

What is adoptive breastfeeding?

A

The stimulation of breast enlargement and milk ejection without labor

57
Q

What is tocolysis?

A

The delaying or inhibition of labor during the birth process

58
Q

Why has pair-bonding become evolutionarily adaptive?

A

Because with pair-bonding you have a longer life-span, more intimacy (inversely correlated with negative psychological states, such as depressed mood, and positively correlated with immune function and cardiovascular health), and more paternal involvement leading to improved well-being of children

59
Q

What is the effect of vasopressin and oxytocin when secreted centrally in the brain?

A

Important for pair-bonding

60
Q

How do prairie and montane voles differ? Why?

A

Prairie voles share nests, take care of children, have monogamous relationships and montane voles do not, this is because prairie voles have more V1a receptors

61
Q

What part of the human V1a receptor is associated with fidelity and pair-bonding? What does a specific allele lead to?

A

The RS3 regionAllele: decreased likelyhood of marriage, happy relationships, and happy partner

62
Q

How does [AVP]p increase when there is a 2% TBW decrease?

A

Increases: x2

63
Q

Describe the sensitivity of the ADH and oxytocin receptors?

A

VERY sensitive because concentration in the blood is so low

64
Q

What enzyme cleaves the amide group protecting the carboxy end of oxytocin and vasopressin?

A

A signal peptidase in the ER

65
Q

What type is the V2 vasopressin receptor?

A

G alpha S protein coupled receptor: adenylyl cyclase activation

66
Q

What does stimulation of the V1a receptors cause? Inhibition?

A

Gq stimulation: Activation of phospholipase CGi inhibition: Activation of adenylyl cyclase

67
Q

What does stimulation of the oxytocin receptors cause?

A

Gq receptors: 1. Activation of phospholipase C2. PLC degrades membrane phospholipids into DAG and IP33a. DAG stimulates PKC to stimulate contraction3b. IP3 travels to ER to release calcium to stimulate contraction

68
Q

What are the 2 most important fenestrations for the osmoreceptor afferent magnocellular neurons of the hypothalamus?

A
  1. OVLT2. SFO
69
Q

What is the plasma concentration of vasopressin prior to osmotic threshold being reached?

A

~0.5 pg/mL

70
Q

What does a 0.3 difference in Pavp cause? What does this mean?

A

A 3 L difference in urine volume over 24 hours with half the osmolality! Very small changes in Pavp have huge consequences

71
Q

What is the osmotic threshold of thirst osmoreceptors? How does this compare to the osmotic threshold of vasopressin secretion? Why?

A

285-290 mosm/kg (higher than the vasopressin osmotic threshold)Because our body can handle small changes in osmolarity, we have a whole system for that, might as well use it.

72
Q

What is a volitional control or incentive behavior? What is an example?

A

Cognitive process by which an individual decides on a particular course of actionDrinking or putting on a sweater when I’m cold

73
Q

What types of people do not feel thirst as much?

A

Old people

74
Q

Why do we prefer to drink cold water?

A

Because our oropharyngeal receptor will be better satisfied and thirst will be better satisfied

75
Q

What does volemia mean?

A

Tension

76
Q

What are the 2 parts of the kidney collecting duct that contain V2 receptors?

A
  1. Cortical collecting duct2. Inner medullary collecting duct
77
Q

What regulates oxytocin secretion? 3 factors

A
  1. Osmotic regulation 2. Suckling at nipple3. Sex4. Hearing/seeing/smelling a crying baby
78
Q

Which is the strongest oxytocin secretion regulator?

A

The first cry of a baby

79
Q

Why don’t increases in oxytocin induce labor?

A

Because it’s the increase in the number of receptors that really causes labor

80
Q

What is the only difference between the mammary and uterine oxytocin receptors?

A

In uterus PLA2 is also activated, in mammary glands only PLC beta is

81
Q

What drugs can be used to help adoptive breastfeeding? How does each work?

A
  1. Domperidone/Metoclopramide/Sulpiride/Chloropromazne: blocks pituitary dopamine receptors2. TRH: directly stimulates lactotrophs (PRL)
82
Q

What 3 things is pair-bonding characterized by?

A
  1. Partner preference2. Mate-guarding3. Bi-parental care of young
83
Q

What does parturition mean?

A

Labor

G2 2017-2018 (45 decks)

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