Endocrine - Pituitary Flashcards
What is the “master gland”?
pituitary gland
What is responsible for brain-endocrine interactions?
Hypothalamic pituitary axis (HPA)
Coordinating center of the endocrine system
hypothalamus
The hypothalamus consolidates signals from what 4 sources?
- Upper cortical inputs
- Autonomic fx
- Environmental cues
- Peripheral endocrine feedback
T/F: The hypothalamus delivers vague signals to the pituitary gland which will release hormones that influence other endocrine systems.
False. the hypothalamus delivers PRECISE signals
Where is the pituitary gland located?
Sella tursica (area of the the sphenoid bone)
4 divisions of the pituitary gland
- anterior pituitary / adenohypophysis (largest)
- Pars intermedius (gone after baby develops)
- Pars tubular (highly vascular, no known hormones secreted)
- Neurohypophysis
Name three ways in which the anterior and posterior portions of the pituitary are distinct from one another
- different connections to the hypothalamus
- different cell types
- secrete different hormones
What is another name for the anterior pituitary?
adenohypophysis
How is the anterior pituitary connected to the hypothalamus?
portal venous network (the anterior pituitary is highly vascularized)
The adenohypophysis is responsible for the regulation of which 6 things?
- thyroid gland
- adrenal glands
- mammary glands
- growth hormone
- gonads
- melanocytes
Type of anterior pituitary cell that is the most abundant and secretes growth hormone
Somatotropes
Type of anterior pituitary cell that secretes adrenocorticotropic hormone (ACTH)
Corticotropes
Type of anterior pituitary cell that secretes thyroid stimulating hormone (TSH)
Thyrotropes
Type of anterior pituitary cell that secretes lutenizing and follicle stimulating hormones (FSH and LH)
Gonadotropes
Type of anterior pituitary cell that secretes prolactin (PRL)
Lactotropes
What is another name for the posterior pituitary gland?
Neurophypophysis
T/F: The posterior pituitary is largely a collection of axonal projections from the hypothalamus.
True
What 2 hormones are produced by the posterior pituitary? What do they regulate?
- Oxytocin and vasopressin
- Uterine contractions and water balance
After hormones are synthesized in the hypothalamus, how are they transported to the posterior pituitary for secretion?
intracellularly
Where is vasopressin primarily synthesized?
supraoptic nucleus
What are the actions of vasopressin, and what are the results of those actions?
- Increases permeability of collecting ducts –> increased free water reabsorption
1. increased urine osmolality
2. decreased plasma osmolality
3. increased ECF volume - Causes contraction of vast smooth muscle
1. vasoconstriction
2. more prevalent in larger doses
What do effects do the V1 and V2 receptors have?
V1 - pressor effect; prevalent w extreme increases in circulating levels, i.e. hemorrhage
V2 - ADH effect
What is the stimulus for vasopressin release?
Osmoreceptor in hypothalamus (HT) activated by plasma osmolality >290 mOsm/kg
(other receptors in HT send sensation of thirst)
_____________ activates stretch receptors in the great veins, atria, and pulm veins for ADH release
Decreased ECF volume
Name 5 things (other than osmolality >290) that stimulate ADH release
angiotensin II nicotine nausea pain stress
How is release of ADH depressed?
- decreased plasma osmolality
- increased ECF volume
- ETOH
How are baroreceptors in the carotid sinus and aortic arch activated?
large volume changes
Describe SIADH
Autonomous release from pituitary (or tumor) cause water retention, low Na with concentrated urine, and hypoosmolar (dilute) plasma
Causes of SIADH
- CNS disorders
- Cold stress
- Trauma
- Drug induced
- Squamous cell lung CA
How to treat SIADH
- Find cause
2. Limit fluid intake
T/F: Symptoms of hyponatriema relate to rapidity of onset
True
A hyponatremic pt is usually asymptomatic until Na is ____ mEq/L, with serious symptoms below ____ mEq/L
125
120
Mild, mod, and severe s/s of hypoNa
Mild: anorexia, nausea, weakness
Moderate: lethargy, confusion
Severe: sz, coma, death
Na >____ is safe for elective procedures
130
Na < ____ may lead to cerebral edema, and elective procedures should be held.
130
If doing an emergent procedure on a pt with Na <130, what would you expect to see intra-op and post-op related to the hypoNa?
Intra-op: decrease MAC
Post-op: agitation, confusion, somnolence
Why must hypoNa be corrected slowly?
Risk for Central Pontine Myelinolysis
What is Central Pontine Myelinolysis?
- demyelinating lesions in the pons R/T rapid correction of hypoNa
Central Pontine Myelinolysis is seen with a change in Na > ____ mEq/L/hr
0.5
What are some of the possible outcomes of central pontine myelinolysis?
- Serious permanent neurologic sequelae
- Death
- Spastic quadriplegia
- pseudo bulbar palsy (inability to control facial movements)
- varying degrees of encephalopathy or coma from acute, noninflammatory demyelination that centered within the basis pontis
Conditions that predispose its to CPM
- alcoholism
- liver disease
- malnutrition
- hypoNA
Risk factors for CPM in the hyponatremic pt
- serum Na <120 mEq/L for >48hrs
- aggressive IVF therapy with hypertonic saline solutions
- development of hyperNa during tx
Symptoms of CPM usually occur within _____ hours post therapy
48-72
2 causes of diabetes insipidus (DI)
ADH deficiency caused by:
- inability to release ADH (central/most common)
- inability of kidney to respond to ADH (renal)
Results of DI
Excretion of lg acts of hypoosmotic urine withhyperosmotic plasma and polydipsia
polyuria w/o hyperglycemia
What keeps DI its from severe dehydration?
Water intake
Tx for DI
- central
- renal
central: exogenous ADH (desmopressin nasal spray)
renal: demeclocycline (decreases responsiveness of collecting tubules to ADH)
When is transient central DI common?
- post head injury or surgery
Causes of nephrgenic DI
- CKD
- lithium toxicity
- hypercalcemia
- hypokalemia
- tubulointerstitial disease (Drugs)
- hereditary (rare)
Anesthetic considerations for DI/hypernatremia
- increased MAC
- decreased uptake of IAs from decreased CO
- decreased doses of IV agents (b/c of hypovolemia)
Elective surgery should be postponed for Na >____
150
S/S of hyperNa
- restlessness
- lethargy
- hyperreflexia
- sz
- coma
- death
T/F symptoms of hyperNa correlate w rapidity of development
true
Rapid correction of hyperNa results in:
- sz
- brain edema
- permanent neurologic damage
- death
Oxytocin is secreted from the _______
supraoptic nucleus of the posterior pituitary
What are the actions of oxytocin
- contraction of the uterus during labor
- contraction of myopeithelial cells of the lactating breast and sm muscle of the uterus
Labor effects and breast feeding effects of oxytocin are an example of _________ feedback.
positive
How is oxytocin used in OB?
to increase contraction of the uterus to organize labor
to contract the uterus and decrease blood loss after birth
Complications of oxytocin (pitocin)
- fetal distress r/t hyperstimulation
- uterine tetany
- maternal water intoxication (ADH effects, rare)
Rapid IV infusion of pitocin can cause:
- HTN
- Tachycardia
- N/V
- Sz (rare)
How to reconstitute Pitocin
Add 20 units (no more than 40 units) of Pitocin to 1 L crystalloid and titrate to uterine contraction
How are pituitary tumors often found?
as a result compression on adjacent structures, such as visual changes with impingement of optic chiasm
Compression of the optic chiasm can result in ________
bitemoral hemianopsia (seeing only the medial half of both visual fields)
T/F: Pituitary tumors can manifest with systemic effects due to hormonal changes.
True
Patients undergoing pituitary resection should undergo evaluation of their hormonal function to detect either:
hypersecretion or panhypopituitarism
Anesthetic implications of pre-existing hormonal disorders:
- GH
- TSH
- ACTH
- Panhypopituitarism
- GH - acromegaly, difficult airway
- TSH - hyperthyroid, tachycardia, wt loss
- ACTH - Cushing’s disease, difficult airway and access
- Panhypopituitarism - need HRT with cortisol, synthroid, or DDAVP (vasopressin)
T/F: Most pituitary resections are done with trasnsphenoidal approach, tho some may require craniotomy
True
Patients undergoing pituitary surgery may develop _____ but to loss of ADH
DI - may be temporary or permanent; may be evident intra-op or post op
Intraoperatively, what would cause an anesthetist to suspect DI in a pt undergoing pituitary surgery?
high UOP; confirm w specific gravity <1.005
Intraoperative tx of DI during pituitary surgery
DDAVP 0.5-1 mcg IV or SQ with volume replacement