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kris Endocrinology > 7 > Flashcards

7 Flashcards

1
Q

Hormones of posterior pituitary

A

oxytocin and vasopressin (ADH)

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2
Q

Describe the make up of Posterior pituitary

A

Posterior pituitary is a collection of axons terminals arising from 2 main nuclei of hypothalamus
these 2 nuclei are secretory in nature
these secretions from neurones do not end up in synaptic gap (which normally happens)- their secretions end up in the circulation instead
the axon terminals are called in neural endophysis/posterior pituitary as it’s nothing but neurones

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3
Q

What are the hypothalamic nuclei who’s neural axons make up the posterior pituitary?

A

PVN- makes OCT

SON- maked ADH

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4
Q

Describe the structure of Posterior pituitary hormones

A
  • Are structurally similair, but have very different functions
  • Both are nonapeptides- made of 9 AA
  • Formation of ring via disulfide bridge-> between 1st and 6 AA-> creates ring structure
    ring structure is present in both hormones
  • Highly conserved amino acid sequences among varied species. Exception: Pigs have lysine-vasopressin at 8th position, whereas humans have arginine
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5
Q

Oxytocin function

A

Contraction of smooth muscle cells:

  • Myoepithelial cells of the alveoli
  • Smooth muscle cells of the uterus during labour
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6
Q 
Arginine Vasopressin
(antidiuretic hormone) function
A
  • H2O retention by the kidney
  • Contraction of blood vessels (arterioles)
  • regulation of blood volume and pressure
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7
Q

Vasopressin/antidiuretic hormone (ADH) receptor

A

Two different receptors used named V1 and V2

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8
Q

Describe V1 ADH receptor

A

V1a and V1b

V1a is found in vascular smooth muscle, platelets, hepatocytes and myometrium
Function: vasoconstriction, myocardial hypertrophy, platelet aggregation, glycogenolysis, uterine contraction
Acts via GPCR-> IP3

V1b is found in anterior pituitary
Function: ACTH release

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9
Q

Describe V2 ADH receptor

A

Found: endothelium, smooth muscle, collecting kidney tubule

Function: involved in water reabsorption and epithelium cells where it is involved in blood clotting

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10
Q

Vasopressin function

A

Regulation of water retention and thirst – primary regulator of blood osmolality

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11
Q

Osmolarity vs osmolality

A

osmolarity= concentration of solute in a volume of solvent (per L)
vs
osmolality-concentration of solute in a mass of solvent (per kg)

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12
Q

Where is osmolality control centre found? How does it analyze it? what are the functions?

A

osmostat in hypothalamus expresses osmoreceptors- resulting in an osmostat- > reads the osmotic pressure of the blood
functions:
- Control/conservation of water
- Regulation of Na concentrations in plasma
- Pressure-volume (involves baroreceptors)

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13
Q

What does the regulation of thirst involve?

A

Involves renin-angiotensin system and aldosterone

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14
Q

What are the 2 systems used by the vasopressin?

A

osmoreceptors in the hypothalamus and baroreceptors in blood vessels

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15
Q

Is the osmostat receptor very sensitive

A

Yes, Osmostat responds to a little as 1 % change in osmolality

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16
Q

What is the receptor of the osmostat system? Describe its function and location

A

Vanilloid Receptor-related Osmotically Activated Channel (VR-OAC are the candidate osmoreceptor)
ligand activated channel that is connected to the cytoskeleton of the cells
allows water to go in and out; as it is connected to the cytoskeleton, it allows cells to change in size-> increase or decrease
they seem to be spread around in different nucleus of the hypothalamus

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17
Q

Isotonic vs hypotonic vs hypertonic

A

Hypotonic- increased volume, decreased ionic strength
Isotonic- have a certain shape
Hypertonic- decreased volume, increased ionic strength

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18
Q

Homeostatic response to hypertonicity

A 
Increased Natriuresis, (Na excretion). 
Decreased Na intake (behaviour), 
increased thirst (behaviour),
increased vasopressin (water retention)
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19
Q

Homeostatic response to hyportonicity

A 
Decreased Natriuresis, (Na retention). 
Increased Na intake (behaviour), 
Decreased thirst (behaviour), 
Decreased vasopressin (water excretion)
20
Q

What 2 things involved homeostatic response to changes in tonicity

A

behavioural changes, vasopressin

21
Q

What are the factors that affect vasopressin release?

A

Angiotensin II
Hyperosmolarity
Decreased atrial receptor firing
Sympathetic stimulation

Allow for the secretion of vasopressin

22
Q

What are the 2 main effects of vasopressin and what do they lead to overall

A

1) Vasoconstriction-> Increased atrial pressure

2) Renal Fluid reabsorption-> increased blood volume-> Increased atrial pressure

23
Q

Where is the vasopressin receptor found in the kidney? What is the type of this receptor?
How does it function

A

Vasopressin receptor is found in the basal cells of distal tubules
GPCR receptor -> cyclic AMP-> result in opening of aquaporin channels-> allow for water movement form the filtrate in the lumen of the tubule into the blood

24
Q

specific aquporins for __ site, others for __ side

A

specific aquporins for luminal site, others for basal side

25
Q

Can urine production be terminated

A

no, can only be minimized

26
Q

What is Insensible water loss

A

basal level of urine formation

27
Q

Describe thirst response and how its triggered

A

It’s a behaviour -> allows fr water intake and stops water loss

  • Defense mechanism
  • Triggered by changes in osmolality or volume of blood
  • Strongly triggered by hypovolemia (reduced blood volume) and decrease in blood pressure
28
Q

Do we drink enough fluid

A

generally people ingest excess fluid

29
Q

How are changes in blood pressure and osmotic pressure sensed?

A

hypothalamic neurones can recognize osmotic pressure through osmoreceptors
blood pressure is recognized through baroreceptros

30
Q

What happens in blood pressure and osmotic pressure decreases?

A

Hypothalamic neurones are stimulated to release vasopressin and to send thirst signals
- Vasopressin results in arteriolar vasoconstriction-> Increased atrial pressure
- Vasopressin also results in increased permeability of distal basal cells-> reabsorption of water-> increased blood volume and decreased osmolarity-> Increased ECF volume and decreased osmolarity
These changes are detected by the hypothalamus-> vasopressin release ceases

31
Q

Pregnancy and vasopressin release

A
  • Increased blood volume, increased size of organs
  • Osmostat is reset (less sensitive) and vol/pressure reset
  • As a result of vasodilation (expanded vol. is sensed as “normal”)
    – Vasopressin responds to reset point, increased blood volume doesn’t dramatically effect vasopressin
  • Placenta produces enzyme to degrade vasopressin - wk 20-40 —> increased urination and water intake
  • Can lead to diabetes insipidus of pregnancy if over-expressed
32
Q

elderly and vasopressin release

A
  • By age 80 total body water declines to as low as 50 % of adult
  • decrease in kidney filtration rate
  • collecting duct less responsive to Vasopressin
  • decreased response to dehydration
  • reduced ability to excrete water load
  • elderly susceptible to both hypo and hypernatremia—> decreased or increased urine output
33
Q

What is Diabetes Insipidus

A

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

34
Q

What are the causes of Diabetes insipidus

A
  • lack of vasopressin (trauma, tumour etc)–> no water reabsorption
  • lack of response to vasopressin in kidney
    reduced CAMP and PKA-> reduced aquaporin
    also can be due to aquaporin defects
  • receptor defect or aquaporin defect
  • Rapid metabolism of vasopressin
  • Pregnancy i.e. transient diabetes insipidus
35
Q

What is polydipsia and what does it lead to?

A

individual drinks too much-> Polyurea

36
Q

Where are baroreceptors found?

A

they are present in aortic arch where aorta comes out of the heart (blood to the body), carotid sinus in the neck (blood to the brain)

37
Q

What are the changes that trigger AVP release?

A

8 % decrease (volume)
5 % decrease (pressure)
Very sensitive!!

38
Q

What is vasoconstriction caused by?

A 
Increased myogenic activity
Increased oxygen
Decreased CO2 and other metabolites
Increased sympathetic stimulation
Vasopressin, angiotensin II
Cold
39
Q

What is vasodilation caused by?

A 
Decreased myogenic activity
Decreased oxygen
Increased CO2 and other metabolites
Decreased sympathetic stimulation
Histamine
Heat
40
Q

Describe Physiological regulation of oxytocin secretion

A

Complicated

Differences among species

41
Q

What are the cites of oxytocin production apart from posterior pituitary?

A

Ovaries (corpus luteum) – involved in luteolysis

Uterus in some species

42
Q

What is the classical regulatory mechanism of oxytocin production?

A

Regulated by suckling stimuli

43
Q

How is milk let down triggered by oxytocin?

A

Oxytocin binding to Oxytocin receptors

-> Contraction of myoepithelial layer; surround each of alveoli-> alveoli contracts

44
Q

How does oxytocin participate in Contraction of smooth muscle around uterus during parturition

A
  • Acts upon uterine myometrium
  • Relaxed during pregnancy to allow for fetal development
  • This relaxed state is maintained due Progesterone (placenta/corpus luteum) and relaxin (hormone from cervix) which gets produced as pregnancy advances
  • also remains relaxed due to less oxytocin receptors being expressed
45
Q

How does oxytocin signalling change to give birth?

A

Become responsive to oxytocin as parturition approaches

  • > Increased number of receptors
  • > Formation of gap junctions (synchronous contraction) between smooth muscles cells in myometrium-> synchronized contraction of muscle cells
  • Works in concert with prostaglandin F2a; helps in contraction-> increased pressure that allows parturition to occur
46
Q

How does oxytocin affected by social behaviour

A

lot’s of oxytocin-> monogamous

few-> polygamous

47
Q

Which receptors are used by oxytocin when determining social behaviour?

A

Action via receptors in the brain

kris Endocrinology (17 decks)

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