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4) Metabolic Endocrinology > 5) Posterior Pituitary > Flashcards

5) Posterior Pituitary Flashcards

1
Q

What hormone does the supraoptic nuclei produce?

A

ADH

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2
Q

What hormone does the paraventricular nuclei produce?

A

Oxytocin

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3
Q

Where are nuclei located?

A

Within a specific region of the hypothalamus

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4
Q

How many amino acids compose the posterior pituitary hormones?

A

9 amino acids (nonapeptide)

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5
Q

What does the disulfide bridge form in posterior pituitary hormones?

A

Ring structure

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6
Q

Which amino acids differentiate ADH and oxytocin?

A
  • Amino acid 3 and amino acid 8

- They are structurally similar

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7
Q

How is oxytocin and ADH structure similar? How is it different?

A
  • The linear structure of amino acids is similar

- The three-dimensional structure is different

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8
Q

Oxytocin causes the contraction of two types of muscle cells. What are they?

A
  • Myoepithelial cells of the alveoli of the breast

- Smooth muscle cells of the uterus during labour

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9
Q

What are the two primary functions of ADH?

A
  • H2O retention by the kidney

- Contraction of blood vessels (arterioles)

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10
Q

What are the two physiological systems regulated by ADH?

A
  • Osmotic

- Pressure/volume

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11
Q

Are the two receptors utilized for operating different physiological systems by ADH the same, or different?

A

They are different

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12
Q

Where is the V1a receptor located?

A
  • Vascular smooth muscle
  • Platelets
  • Hepatocytes
  • Myometrium
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13
Q

Where is the V1b receptor located?

A

Anterior pituitary

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14
Q

Where is the V2 receptor located?

A
  • Basolateral membrane collecting tubule
  • Vascular endothelium
  • Vascular smooth muscle
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15
Q

What is the function of the V1a receptor in vascular smooth muscle?

A
  • Vasoconstriction

- Myocardial hypertrophy

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16
Q

What is the function of the V1a receptor in platelets?

A

Platelet aggregation

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17
Q

What is the function of the V1a receptor in hepatocytes?

A

Glycogenolysis

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18
Q

What is the function of the V1a receptor in the myometrium?

A

Uterine contractions

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19
Q

What is the function of the V1b receptor in the anterior pituitary?

A

ACTH release

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20
Q

What is the function of the V2 receptor in the basolateral membrane of the collecting tubule?

A

Insertion of AQP2 water channels into apical membrane

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21
Q

What is the function of the V2 receptor in the vascular smooth muscle?

A

Vasodilation

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22
Q

What is the water-retaining hormone in mammals?

A

Vasopressin

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23
Q

What are the primary regulators of osmolarity?

A
  • Thirst

- Vasopressin

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24
Q

What does the osmostat control?

A
  • Conservation of water

- Regulation of sodium concentrations in plasma

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25
Q

What physiological system is modulated by the regulation of sodium concentration in plasma? What does that involve?

A
  • Pressure-volume

- Involves baroreceptors, the renin-angiotensin system, and aldosterone

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26
Q

How does the relationship for the conservation of water differ from the mechanism for the regulation of sodium?

A
  • Water is simple

- Sodium is complicated

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27
Q

What receptors detect changes in blood plasma? Where are they located?

A

Osmoreceptors located in the hypothalamus

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28
Q

How do osmoreceptor-containing cells vary when the blood is too dilute?

A

Cell expands

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29
Q

How do osmoreceptor-containing cells vary when the blood is too concentrated? What signal is sent?

A
  • Cell contracts

- Contraction sends neural signal to supraoptic nuclei to release vasopressin

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30
Q

What are the homeostatic effects in response to hypotonicity?

A
  • Decrease in natriuresis (Na+ retention)
  • Increase in salt appetite
  • Decrease in thirst
  • Decrease in vasopressin
  • Dilute urine produced
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31
Q

What are the homeostatic effects in response to hypertonicity?

A
  • Increase in natriuresis (Na+ excretion)
  • Decrease in salt appetite
  • Increase in thirst
  • Increase in vasopressin (water retention)
  • Concentrated urine produced
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32
Q

What characterizes a hypotonic cell?

A
  • Cell expands

- Net flow of water into the cell

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33
Q

What characterizes a hypertonic cell?

A
  • Cell shrinks

- Net flow of water out of the cell

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34
Q

How does VR-OAC receptor sense a change in osmolarity?

A
  • Receptor is membrane-bound, and the intracellular domain is linked to the cytoskeleton
  • As the cell expands or contracts, it pulls against the cytoskeleton, changing the conformation of the receptor
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35
Q

What factors stimulate the posterior pituitary to synthesize vasopressin?

A
  • Angiotensin II
  • Hyperosmolarity
  • Decreased atrial receptor firing
  • Sympathetic stimulation
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36
Q

What regions of the nephron does vasopressin influence?

A
  • Distal tubule

- Collecting duct

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37
Q

How does vasopressin cause the insertion of new water channels?

A
  • Vasopressin binding from its receptor activates a GPCR (Gas), which increases cyclic AMP
  • Results in the insertion of aquaporins on the luminal side of the tubule
38
Q

Differentiate the functions of aquaporin 2 and aquaporin 3.

A
  • Aquaporin 2 (lumen of the collecting duct): water flows into the cell
  • Aquaporin 3 (blood): water flows out of the cell into the blood
39
Q

Which aquaporin subtype is constitutive?

A

3

40
Q

What are the effects of an increased quantity of aquaporins in the kidney tubules?

A
  • Production of concentrated urine

- Decreased urine output (antidiuresis)

41
Q

What is the function of the thirst reflex?

A
  • Replacement of water in the body (loss of water through urine, breathing, sweat)
  • Defense mechanism
42
Q

What changes trigger the thirst mechanism?

A

Changes in osmolarity or volume

43
Q

What is the thirst mechanism strongly triggered by, specifically?

A
  • Hypovolemia

- Decrease in blood pressure

44
Q

Generally, people ingest (not enough/too much) fluid.

A

too much

45
Q

Does osmolarity trigger the thirst reflex often?

A
  • No, changes are usually too small to trigger thirst

- Must be 1 to 2% below basal level to trigger thirst

46
Q

How is water balance regulated under normal conditions?

A

Water excretion

47
Q

What occurs to plasma osmolarity and blood volume during dehydration? What occurs as a result?

A
  • Osmolarity increases
  • Blood volume decreases
  • Vasopressin release to retain water produces concentrated urine
48
Q

What occurs to plasma osmolarity when water is in excess? What occurs as a result?

A
  • Small decrease in osmolarity

- Less vasopressin release, resulting in dilute urine

49
Q

What occurs to the osmostat during pregnancy? What occurs to volume and pressure?

A
  • Osmostat is reset (less sensitive)
  • Volume and pressure is reset
  • Total body water increases 7 to 8 L as a result of vasodilation
50
Q

How is the expanded volume during pregnancy sensed? What occurs to vasopressin?

A
  • Expanded volume is sensed as “normal”

- Vasopressin responds to the reset point

51
Q

What enzyme does the placenta produce that is related to vasopressin?

A
  • Vasopressinase

- Catabolizes vasopressin that is released, allowing for the control of the quantity of vasopressin

52
Q

How does total body water vary with age? What are the elderly more susceptible to?

A
  • Total body water declines to as low as 50%

- Susceptible to both hypo- and hypernatremia

53
Q

How does vasopressin and kidney function change in the elderly?

A
  • Decrease in kidney filtration rate

- Collecting duct is less responsive to vasopressin

54
Q

How does the thirst mechanism vary with plasma osmolarity?

A
  • Within a physiological range, thirst is NOT stimulated, until a certain set-point is reached
  • Afterwards, thirst increases linearly with plasma osmolarity
55
Q

How does the urine osmolarity vary with vasopressin release?

A
  • As osmolarity increases in the body, there is greater vasopressin release, and increased concentrated body urine (linear relationship)
  • At a certain point, we cannot make urine more concentrated
56
Q

How does urine volume vary with urine osmolarity?

A

As osmolarity increases, urine volume decreases (to its minimal level)

57
Q

How does alcohol affect urine output? Why?

A
  • Ethanol depresses the hypothalamic osmoreceptor
  • Results in less vasopressin
  • Increased urine output leading to dehydration
58
Q

Define diabetes insipidus.

A

The excretion of a large volume of urine (diabetes) that is hypotonic, dilute, and tasteless (insipid)

59
Q

What are the four causes of diabetes insipidus?

A

1) Lack of vasopressin
2) Lack of response to vasopressin in the kidney
3) Rapid metabolism of vasopressin
4) Polydipsia

60
Q

What may cause a lack of vasopressin?

A
  • Trauma

- Tumour

61
Q

What may cause a lack of response to vasopressin in the kidney?

A
  • Receptor defect

- Aquaporin defect

62
Q

What life stage is particularly associated with the rapid metabolism of vasopressin?

A
  • Vasopressin is less available during pregnancy

- Transient diabetes insipidus

63
Q

What is polydipsia?

A

Individual drinks too much, and excess urine is normal

64
Q

How is polydipsia differentiated from other diabetes insipidus?

A
  • Water deprivation test
  • Polydipsic patients produce concentrated urine
  • Patients with diabetes insipidus do not
65
Q

How is a lack of response to vasopressin differentiated from a lack of vasopressin?

A
  • Inject individuals with vasopressin
  • If they produce concentrated urine, they have a deficiency in vasopressin
  • If they do not, they have a downstream problem (rapid metabolism or cells don’t respond)
66
Q

What kind of receptors signal vasopressin release based on volume and pressure changes?

A
  • Aortic arch baroreceptor

- Carotid sinus baroreceptor

67
Q

Is vasopressin released when there is an increase or decrease in volume and pressure?

A
  • 8% decrease in volume

- 5% decrease in pressure

68
Q

What other systems respond to a decrease in volume and pressure?

A
  • Sympathetic stimulation

- Angiotensin II

69
Q

Where does extrapituitary synthesis of oxytocin occur?

A
  • Ovaries (corpus luteum), which is involved in luteolysis

- Uterus in some species

70
Q

What regulates oxytocin?

A

Suckling stimuli

71
Q

What are the critical function of oxytocin?

A
  • Lactation (milk let-down)

- Contraction of smooth muscle around the uterus during parturition

72
Q

Where are oxytocin receptors located?

A
  • Glandular cells in the mammary alveoli

- Myoepithelial layers in the mammary ducts

73
Q

How is the tactile response of the nipple for the secretion of milk regulated by the CNS and oxytocin?

A
  • Stimulation of the nipple results in a neuroreflex arc, which feedsback to the paraventricular nuclei in the hypothalamus
  • Oxytocin contents are released from the posterior pituitary, and bind to receptors on the myoepithelial cells, which contract
74
Q

How is the uterine myometrium during pregnancy? Which hormones regulate this state?

A
  • Relaxed during pregnancy
  • Progesterone from the placenta/corpus luteum
  • Relaxin from the cervix
75
Q

What do the smooth muscles of the uterus become responsive to as parturition approaches?

A
  • Oxytocin
  • Increased numbers of receptors
  • Formation of gap junctions (synchronous contraction)
76
Q

What does oxytocin work in conjunction with during parturition?

A

Prostaglandin F2a

77
Q

How does oxytocin secretion increase during labour?

A
  • Burst of oxytocin secretion by the posterior pituitary

- Released in a pulsatile manner

78
Q

Oxytocin release during parturition is triggered by the ________ reflex.

A

Fergusson reflex

79
Q

What is the Fergusson reflex?

A
  • Self-sustaining cycle of uterine contractions initiated by pressure at the cervix or vaginal walls
  • Positive feedback loop
80
Q

What primes postpartum secretion of oxytocin?

A

Changes in steroid hormone concentrations during parturition

81
Q

How do steroid hormone concentrations change during parturition?

A
  • Increase in estradiol

- Decrease in progesterone

82
Q

How does oxytocin function at the CNS level?

A
  • Maternal behaviour

- Sexual arousal

83
Q

How does oxytocin function in the regulation of the reproductive cycle?

A

Luteolysis

84
Q

What is luteolysis? When does it occur?

A
  • If fertilization does not occur

- The corpus luteum undergoes luteolysis and a new reproductive cycle is initiated

85
Q

How does oxytocin regulate luteolysis?

A
  • Oxytocin produced locally in the ovary binds to oxytocin receptors
  • Endometrial synthesis of PGF2a
  • Vasoconstriction of endometrial arterioles
  • Endometrial necrosis and sloughing off
86
Q

What are the two functions of the PGF2 receptor-complex?

A
  • Increases intracellular calcium concentrations, causing apoptotic effects
  • Activates PKC, which inhibits progesterone synthesis
87
Q

How is oxytocin implicated in social behaviour?

A
  • In females, bonding with new born or mate

- “The hormone of love and bonding”

88
Q

What animal study reinforced the idea that oxytocin is implicated in social behaviour?

A
  • Animal with high concentration of oxytocin receptors: mate for life
  • Animal with low concentration of oxytocins receptors: bang then bye-bye
89
Q

How is oxytocin related to anxiety and stress?

A
  • Oxytocin decreases anxiety and stress

- By inhibiting anxiety and stress, many maladaptive behaviours are inhibited as well, but this is not a magic solution

90
Q

What is thought to occur to oxytocin release when there is healthy social behaviour? What about during a deficit of social behaviour? Is this thought to be true?

A
  • Healthy social behaviour results in high oxytocin release
  • Deficit in social behaviour results in low oxytocin release
  • This is NOT likely to be true
91
Q

What life cycles is oxytocin thought to be implicated in?

A
  • Parturition: uterine contractions
  • Lactation: milk let-down
  • Childhood: maternal behaviour
  • Adulthood: bonding, sexual behaviour, aggressiveness

4) Metabolic Endocrinology (15 decks)

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