Week 3 - Posterior Pituitary Flashcards
Which 2 hormones are secreted by the posterior pituitary?
- Oxytocin
2. Antidiuretic hormone (ADH)
What are 2 functions of ADH?
- Maintenance of plasma osmolality
2. Actions on the kidney
What are 2 disorders of the posterior pituitary?
- Syndrome of inappropriate antidiuretic hormone (SIADH)
2. Diabetes Insipidus
T/F: Posterior pituitary is not a gland but only the distal axon terminals of the hypothalamic magnocellular neurons
True
Hormones originate in the ____________ nucleus of the hypothalamus, travel down the axons of neurons to the posterior pituitary, where they enter general circulation
paraventricular
Oxytocin is primarily from the posterior pituitary, which 6 other glands also secrete oxytocin ?
- Corpus luteum (placenta)
- Leydig cells (male testes)
- Retina
- Adrenal Medulla
- Thymus
- Pancreas
What are the 2 major functions of oxytocin?
- Milk secretion during lactation (Letdown reflex) - stimulates contraction of smooth muscle in the breast
- Contraction of the uterine smooth muscle during labor - also involved in cervical dilation
What are 2 sexual functions of oxytocin?
- Stimulate pair-bonding/maternal behaviors
2. Released during orgasm: possibly associated with sexual arousal
Anti-stress effects of oxytocin produce which 5 responses?
- Lowers BP
- Lowers cortisol levels
- Increase tolerance to pain
- Reduces anxiety
- Anti-depressant
Low levels of oxytocin and oxytocin receptor genes (OXTR) have been found associated with which condition?
Autism
Oxytocin is available as an injection called ________
Pitocin
What is the other term for ADH?
Vasopressin (Arginine vasopressin - AVP)
Which 2 signals stimulate ADH release?
- Increase in plasma osmolality
2. Decrease in plasma volume
An increase in plasma osmolality is detected by _______ in the hypothalamus and triggers _______.
osmoreceptors; thirst (as does hypotension and hypovolemia)
T/F: Nausea triggers ADH release
True
A decrease in plasma volume is detected by ________ in the chest, carotid sinus, aortic arch, and pulmonary venous system.
Baroreceptors
T/F: ADH secretion is more greatly influenced by changes in plasma volume than by changes in osmolality
FALSE! ADH secretion is LESS influenced by changes in plasma volume than by changes in osmolality
What is the term for a measure of the body’s electrolyte-water balance?
Plasma osmolality
Which 6 nutrients mostly determine plasma osmolality?
- Na (most important osmole)
- Cl
- bicarbonate
- proteins
- glucose
- urea
When ADH secretion is increased it triggers which response to water, which does what to plasma osmolality? What happens to urine and thirst?
Water is retained; DECREASING plasma osmolality;
Urine is more concentrated
Thirst is stimulated
Pressure and volume of blood are mediated by changes in ___________ balance Determined mostly by which 3 things?
Sodium (Na+) 1. Renin 2. Angiotensin 3. Aldosterone (all secreted by the kidneys/adrenals)
What is the main action of ADH?
Decreases water excretion in the kidneys
ADH causes water resorption in _________ of the kidneys via _____________
Collecting ducts
via aquaporin-2
Ethanol and caffeine _______ ADH secretion - this results in what response to fluid
reduces; MORE fluid excreted
ADH does what to BP? How?
Raises BP; constricts peripheral capillaries
What are the 4 forms of diabetes insipidus?
- Central
- Nephrogenic
- Dipsogenic
- Gestational
Which form of DI is a true deficiency of ADH?
Central DI
Which form of DI is kidney or nephron dysfunction which causes an insensitivity of kidneys to ADH?
Nephrogenic DI
Which form of DI is from excessive intake of fluids and maybe due to damage of hypothalamic thirst mechanism or mental illness?
Dipsogenic DI
Which form of DI occurs during pregnancy and post partum periods? The placenta produces vasopressinase which breaks down ADH and is associated with acute fatty liver and pre-eclampsia.
Gestational DI
Excess ADH leads to which 4 things?
- Reduced urination
- Concentrated urine
- Edema & hypervolumia
- Dilutional hyponatremia
Lack of ADH activity leads to which 4 things?
- Excessive urination
- Dilute urine
- Excessive thirst
- Dehydration
What are 4 treatment options for SIADH?
- Water restriction
- Diuretic
- Salt Administration
- Various medications
What are 3 treatment options for DI?
- Synthetic ADH (desmopressin)
- Remove cause
- Various medications
Hyponatremia is classified as ____ mEq/L
<135mEq/L
Hyponatremia may cause a shift of fluid from the vascular space to the intracellular space. What is the most important consequence?
cerebral edema
Which condition causes acute cerebral edema, nausea, vomiting, headache and if worsens can lead to seizure, coma, respiratory arrest and has a 50% mortality
Acute hyponatremia (develops <24 hours)
Which condition causes lethargy, confusion, muscle cramps, neurologic impairment and has a 10% mortality (associated with underlying condition)?
Chronic hyponatremia (develops > 48 hours)
Which part of the body is least tolerant of hyponatremia? What is a treatment for seizures related to this condition?
The skull
Tx with 100ml bolus of 3% solution of hypertonic saline IV
What are 3 types of hyponatremia?
- Hypertonic
- Isotonic
- Hypotonic
Which type of hyponatremia is caused by resorption of water caused by glucose or mannitol?
Hypertonic
Which type of hyponatremia is considered “pseudohyponatremia” and is caused by measurement error or high triglycerides or proteins?
Isotonic
Which type of hyponatremia is considered “true hyponatremia”, is the most common type, and is associated with low plasma osmolality?
Hypotonic
What are the 3 types of hypotonic hyponatremia?
- Hypervolemic
- Euvolemic
- Hypovolemic
Hypervolemic hyponatremia is ________TBW and ___________ total body Na
Increased; increased
What are 5 causes of hypervolemic hyponatremia?
- CHF
- Kidney Dz
- Conn syndrome
- Cirrhosis
- Intake of excessive salt water
What are 3 treatments for hypervolemic hyponatremia?
- Fluid restriction
- Sometimes a diuretic
- Correct underlying cause
Euvolemic hyponatremia is ________TBW with ___________ ECF and total body Na
Increased; near normal
What are 8 causes of euvolemic hyponatremia?
- Pharmaceuticals (diuretics, barbiturates, etc.)
- Addison disease
- Hypothyroidism
- SIADH
- Primary polydipsia
- Pain
- Post-op state
- “Beer potomania”
What are 3 treatment options for euvolemic hyponatremia?
- Fluid restriction (<1 liter/24 hours)
- Possibly vaptans
- Correct underlying cause
Hypovolemic hyponatremia is ________TBW/ECF and Na with ___________ total body Na
Decreased; relatively greater decrease
What are 5 causes of hypovolemic hyponatremia?
- Low intake of water and low sodium intake (m/c in elderly)
- GI losses (diarrhea/vomit)
- Skin losses (sweating, burns)
- Renal (glycosuria, kidney dz)
- “Appropriate” secretion of ADH (seen in severe GI illness, marathon runners, and heavy exercisers)
What is the treatment for hypovolemic hyponatremia? What is a risk of this treatment?
IV saline 0.9% (not to exceed 10mEq/24 hours)
Risk of osmotic demyelination syndrome
Correcting hyponatremia too rapidly may result in ______ ______ _______ with permanent neurological deficits
Central pontine myelinolysis (CPM)
What is first-line treatment of SIADH?
Restrict fluid intake (1-1.5 liters/day)
What are 2 second-line treatments of SIADH?
- Increase solute intake with 0.25g/kg per day of urea
- OR- - Combo of low-dose loop diuretics and oral sodium chloride
T/F: Use of lithium, demeclocycline, or vasopressin receptor antagonists are recommended treatment for SIADH
FALSE! They are NOT recommended
T/F: Symptoms of DI are similar to those of untreated DM, except that urine does not contain glucose
True
What are 3 major clinical features of DI?
- Polyuria
- Polydipsia
- Low urine osmolality
What are 4 ways to diagnose DI?
- Head MRI (r/o pituitary/hypothalamic lesion)
- Measure ADH levels
- Water deprivation testing
- Desmopression stimulation test
What are 5 etiologies of Central DI?
- Pituitary tumor
- Autoimmune
- Surgery
- Ischemic encephalopathy
- Idiopathic
What are 2 etiologies of Nephrogenic DI?
- Hereditary (ADH receptor mutation)
2. Secondary to hypercalcemia, lithium, demeclocycline (ADH antagonist)
What is the difference in ADH levels between Central and Nephrognic DI?
Central DI: Decreased ADH
Nephrogenic DI: Normal ADH levels
What is treatment for Central DI?
Intranasal desmopressin acetate
Carbamezepine
What is treatment for Nephrogenic DI?
HCTZ, Indomethacin, Amiloride
