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Flashcards in ME04 - Posterior Pituitary Deck (49):
1

Also called the Neurohypophysis

Posterior Pituitary Gland

2

Glial-like cells in Post Pituitary Gland; Do not secrete hormones

Pituicytes | Neurons secretes hormones

3

Function of Pituicytes

Act to support large numbers of terminal
nerve fibers and terminal nerve endings from nerve tracts that originate in the supraoptic and paraventricular nuclei of the hypothalamus

4

What are Neurohypophysial Hormones?

Anti-diuretic hormone (ADH) or vasopressin (Supraoptic Nuclei) and Oxytocin (Paraventricular Nuclei)

5

Carrier proteins that transports neurohypophysial hormones down to the nerve endings in the neurohypophysis
(requires several days)

Neurophysins

6

Formed primarily in the supraoptic nuclei

ADH

7

Formed primarily in the paraventricular nuclei

Oxytocin

8

Flow of Neurohypophysial Hormones

Nerve impulses transmitted in nuclei >> Hormone + neurophysin immediately released from the secretory granules in the nerve endings by exocytosis >> Hormone absorbed in nearby capillaries >> Hormone separates from neurophysin (no function after leaving nerve terminal)

9

Differentiate ADH and Oxytocin in terms of molecular formula

Both are polypeptides, each containing nine amino acids
Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-ArgGlyNH2
Oxytocin: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH2
DIFFERENCE: Phe, Arg for Vasopressin; Ile,Leu for Oxytocin

10

Causes decreased excretion of water by the kidneys

Injection of ADH (as small as 2 nanograms)

11

What happens to the collecting tubules and ducts without ADH?

Collecting tubules and ducts become almost impermeable to water and allows extreme loss of water into the urine

12

ADH causes insertion of aquaporins which causes absorption of water from the collecting tubules and ducts by osmosis. True or False?

True.

13

Effect of Low concentrations of ADH

Water Reabsorption

14

Effect of Higher concentrations of ADH

A potent effect of constricting the arterioles throughout the body

15

Stimulus on the Vasoconstrictor Effect of ADH

Decreasedbloodvolume
Decreased stretch signal from atrial stretch receptors,
baroreceptors of the carotid, aortic, and pulmonary regions

16

Primarily regulates secretion of ADH

Osmotic & volume stimuli

17

Most important physiologic stimulus/ MOST POTENT for ADH secretion

_ INC plasma osmolarity

18

Also potent stimulus for ADH secretion

Hypovolemia or volume contraction

19

Flow of Regulation of ADH

H2O is conserved in the body while Na & other solute continue to be excreted in the urine >> causes dilution of the solutes in the ECF >> correcting the initial excessively concentrated ECF

20

Factors for Inhibiting/Supressing ADH

DEC serum osmolarity, ECF volume, Temp; ANP, GABA, CORTISOL, Thyroid Hormone, ETHANOL (30-90ML whiskey sufficient)

21

Factors for Stimulating ADH

INC serum osmolarity, ECF volume, CSF sodium, Temp, STRESS, EXERCISE, SENESCENCE, Drugs: Nicotine, Opiates, Barbiturates, Nausea Vomiting Pain Hypoglycemia

22

Diseases involving ADH

Diabetes insipidus (DI) ( Central & Nephrogenic)
Syndrome of Inappropriate Anti-diuretic Hormone
(SIADH)

23

State of excess free water excretion

Diabetes Insipidus (DI)

24

Manifestations of Diabetes Insipidus (DI)

Excretion of excessive amounts of dilute urine
Excessive thirst
Reduction of fluid intake will not affect the
concentration of the urine

25

Total or partial loss of the ability to synthesize or release AVP

Central Diabetes Insipidus

26

Causes of Central Diabetes Insipidus

Causes:
brain tumor
head trauma
brain surgery that damages the posterior
pituitary or hypothalamus

27

Loss of free water leads to ? In Central Diabetes Insipidus

_INC in plasma osmolality

28

Hyperosmolality in Central Diabetes Insipidus cannot increase AVP sufficiently but usually results in a large increase in thirst. True or False?

True.

29

In many patients with central DI, the patient has:

a. high water intake and output
b. normal plasma osmolality

30

In patients with Central DI, severe
hyperosmolality becomes apparent only when?

Only when water intake is restricted

31

Levels of ADH is normal or elevated but the renal tubules cannot respond appropriately to ADH

Nephrogenic Diabetes Insipidus

32

Causes of Nephrogenic Diabetes Insipidus:

Failure of the countercurrent mechanism to form a hyperosmotic medullary interstitium
ADH receptors in distal tubules & collecting ducts maybe non-functional or kidneys damaged
Drugs : lithium (drug for bipolar disorder) & tetracyclines

33

In water deprivation test, differentiate Central DI, Nephrogenic DI and Psychogenic Polydipsia

In CENTRAL DI, DEC ADH in 6-8H (510,520,55)
In Nephrogenic DI, DEC ADH in 6-8H (170,173,175)
In Psychogenic Polydipsia (Increase water intake) DEC ADH in 6-8H (520,520,525) _

34

Treatment of Diabetes Insipidus - Central DI:

SyntheticanalogofADHlikedesmopressin (subcutaneous or nasal spray)

35

Treatment of Diabetes Insipidus - Nephrogenic DI:

Correct the underlying renal disorder for
hypernatremia: low Na diet
Diuretic that enhances sodium excretion: Thiazides

36

Overproduction of ADH not accounted for by hyperosmolality or non-osmotic stimuli to ADH

Syndrome of Inappropriate Anti-diuretic Hormone (SIADH)

37

Flow of SIADH

Excessive secretion of ADH _ reduces urine output _ retention of water and increase in volume of ECF _ secondary increase in urine output
_ urine formed is concentrated
_ Na+ and other ions excreted in urine _lowNa+inECF
_ brain swelling _ seizures, coma , death

38

Treatment of SIADH (Aimed towards correcting hyponatremia and its symptoms)

Loop diuretic (furosemide): promotes free water excretion
Isotonic and sometimes, hypertonic saline
Fluid intake restriction to 0.5 to 1.0 L/day
Aquaretics/vaptans: agents that competitively
block ADH action and increase water excretion
Demelocycline (an older tetracycline)

39

Powerfully stimulates contraction of the pregnant uterus
Causes milk to be expressed from the alveoli into the ducts of the breast _
Facilitates bonding or attachment between mother & infant

OXYTOCIN

40

Functions of Oxytocin

At least partially responsible for causing birth of the baby:
In a hypophysectomized animal, the duration of labor is prolonged
Amount of oxytocin in the plasma increases during labor, especially during the last stage
Stimulation of the cervix in a pregnant animal elicits nervous signals that pass to the hypothalamus and cause increased secretion of oxytocin

41

Inhibit OTC secretion and depress milk ejection

Psychogenic factors(STRESS) and sympathetic activation

42

OXYTOCIN IN LACTATION: Milk Letdown

Baby suckles mothers nipple >> Signals transmit through sensory nerves to the oxytocin neurons in the paraventricular (and supraoptic nucle) in the hypothalamus >> Released oxytocin from neurohypophysis carried by blood to the breasts >> Contraction of myoepithelial cells that lie outside of and form a latticework surrounding the alveoli of the mammary glands

43

OXYTOCIN as a Drug

Brand names: Syntocinon, Pitocin
Used therapeutically to decrease immediate postpartum
bleeding
Used to induce labor
OTC assists in ovulation & in the termination of the
corpus luteum

44

More Reasons to Breastfeed

_ Oxytocin is not only extensively interconnected to the cortisol, noradrenaline and several neurotransmitter systems to produce long-term effects
_ It is also highly correlated to resilience to stress, growth, healing and well-being.

45

How does Oxytocin influence Glucocorticoid receptor activity

Reduces excess cortisol in stress HPA-axis

46

How does Oxytocin influence Alpha2 receptor function

Blocks or modulates noradrenaline stress effects, eliciting calm behavior, decrease in arterial pressure and heart rate improved pattern of secretion of gastric hormones

47

How does Oxytocin influence Opiodergic activity

Reward and Pain-free

48

How does Oxytocin influence 5HT Synthesis

Happiness

49

How does Oxytocin influence Cholinergic Activity

Consumption, Coitus, Calm and Sleep