ME04 - Posterior Pituitary Flashcards
Also called the Neurohypophysis
Posterior Pituitary Gland
Glial-like cells in Post Pituitary Gland; Do not secrete hormones
Pituicytes | Neurons secretes hormones
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
What are Neurohypophysial Hormones?
Anti-diuretic hormone (ADH) or vasopressin (Supraoptic Nuclei) and Oxytocin (Paraventricular Nuclei)
Carrier proteins that transports neurohypophysial hormones down to the nerve endings in the neurohypophysis
(requires several days)
Neurophysins
Formed primarily in the supraoptic nuclei
ADH
Formed primarily in the paraventricular nuclei
Oxytocin
Flow of Neurohypophysial Hormones
Nerve impulses transmitted in nuclei»_space; Hormone + neurophysin immediately released from the secretory granules in the nerve endings by exocytosis»_space; Hormone absorbed in nearby capillaries»_space; Hormone separates from neurophysin (no function after leaving nerve terminal)
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
Causes decreased excretion of water by the kidneys
Injection of ADH (as small as 2 nanograms)
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
ADH causes insertion of aquaporins which causes absorption of water from the collecting tubules and ducts by osmosis. True or False?
True.
Effect of Low concentrations of ADH
Water Reabsorption
Effect of Higher concentrations of ADH
A potent effect of constricting the arterioles throughout the body
Stimulus on the Vasoconstrictor Effect of ADH
Decreasedbloodvolume
Decreased stretch signal from atrial stretch receptors,
baroreceptors of the carotid, aortic, and pulmonary regions
Primarily regulates secretion of ADH
Osmotic & volume stimuli
Most important physiologic stimulus/ MOST POTENT for ADH secretion
_ INC plasma osmolarity
Also potent stimulus for ADH secretion
Hypovolemia or volume contraction
Flow of Regulation of ADH
H2O is conserved in the body while Na & other solute continue to be excreted in the urine»_space; causes dilution of the solutes in the ECF»_space; correcting the initial excessively concentrated ECF
Factors for Inhibiting/Supressing ADH
DEC serum osmolarity, ECF volume, Temp; ANP, GABA, CORTISOL, Thyroid Hormone, ETHANOL (30-90ML whiskey sufficient)
Factors for Stimulating ADH
INC serum osmolarity, ECF volume, CSF sodium, Temp, STRESS, EXERCISE, SENESCENCE, Drugs: Nicotine, Opiates, Barbiturates, Nausea Vomiting Pain Hypoglycemia
Diseases involving ADH
Diabetes insipidus (DI) ( Central & Nephrogenic)
Syndrome of Inappropriate Anti-diuretic Hormone
(SIADH)
State of excess free water excretion
Diabetes Insipidus (DI)
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
Total or partial loss of the ability to synthesize or release AVP
Central Diabetes Insipidus
Causes of Central Diabetes Insipidus
Causes:
brain tumor
head trauma
brain surgery that damages the posterior
pituitary or hypothalamus
Loss of free water leads to ? In Central Diabetes Insipidus
_INC in plasma osmolality
Hyperosmolality in Central Diabetes Insipidus cannot increase AVP sufficiently but usually results in a large increase in thirst. True or False?
True.
In many patients with central DI, the patient has:
a. high water intake and output
b. normal plasma osmolality
In patients with Central DI, severe
hyperosmolality becomes apparent only when?
Only when water intake is restricted
Levels of ADH is normal or elevated but the renal tubules cannot respond appropriately to ADH
Nephrogenic Diabetes Insipidus
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
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) _
Treatment of Diabetes Insipidus - Central DI:
SyntheticanalogofADHlikedesmopressin (subcutaneous or nasal spray)
Treatment of Diabetes Insipidus - Nephrogenic DI:
Correct the underlying renal disorder for
hypernatremia: low Na diet
Diuretic that enhances sodium excretion: Thiazides
Overproduction of ADH not accounted for by hyperosmolality or non-osmotic stimuli to ADH
Syndrome of Inappropriate Anti-diuretic Hormone (SIADH)
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
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)
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
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
Inhibit OTC secretion and depress milk ejection
Psychogenic factors(STRESS) and sympathetic activation
OXYTOCIN IN LACTATION: Milk Letdown
Baby suckles mothers nipple»_space; Signals transmit through sensory nerves to the oxytocin neurons in the paraventricular (and supraoptic nucle) in the hypothalamus»_space; Released oxytocin from neurohypophysis carried by blood to the breasts»_space; Contraction of myoepithelial cells that lie outside of and form a latticework surrounding the alveoli of the mammary glands
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
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.
How does Oxytocin influence Glucocorticoid receptor activity
Reduces excess cortisol in stress HPA-axis
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
How does Oxytocin influence Opiodergic activity
Reward and Pain-free
How does Oxytocin influence 5HT Synthesis
Happiness
How does Oxytocin influence Cholinergic Activity
Consumption, Coitus, Calm and Sleep
