Hypothalamus and Pituitary Flashcards
The hypothalamus and pituitary gland form a unit that exerts control over the function of:
Thyroid
Adrenals
Gonads
The pituitary is the:
“master gland”
The hypothalamic-pituitary axis (HPA) is responsible for:
Brain-endocrine interactions
The hypothalamus is the:
coordinating center of the endocrine system
They hypothalamus consolidates signals from:
-Upper cortical inputs
-autonomic function
-environmental cues
-Peripheral endocrine feedback
The hypothalamus delivers precise signals to the _____ gland which releases hormones that influence other endocrine systems
Pituitary gland
The pituitary gland rests in the _____ bone in the area called the _____ ____
Sphenoid bone
Sella tursica
4 divisions of the pituitary gland:
1.) Anterior pituitary/ adenohypophysis
-largest
2.) Pars Intermedius
-gone after fetal development
3.) Pars tubularis
-highly vascular, no known hormones secreted
4.) Posterior pituitary/ neurohypophysis
The anterior and posterior portions of he pituitary are ____ from one another
Distinct
The anterior and posterior pituitary have different:
Connections to the hypothalamus
cell types
Secrete different hormones
The anterior pituitary is highly vascularized and connected to the hypothalamus via a:
Portal venous network
The anterior pituitary is responsible for the regulation of the _____, ____, and _____ glands
Thyroid
Adrenal
Mammary
The anterior pituitary also regulates ____ ___, _____, and ____
Growth hormone
Gonads
Melanocytes
Somatotropes
30-40%
-Most abundant
-Growth hormone (GH)
Corticotropes
20%
Adrenocorticotropic hormone (ACTH)
Thyrotropes
3-5%
Thyroid-stimulating hormone (TSH)
Gonadotropes
3-5%
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
goes right to site of action
Lactotropes
3-5%
Prolactin (PRL)
goes right to site of action
The posterior pituitary is largely a collection of ____ ___ from the hypothalamus
axonal projections
The posterior pituitary produces what 2 hormones
Oxytocin
Vasopressin (ADH)
What does Oxytocin do?
Regulates uterine contractions
What does Vasopressin (ADH) do?
Regulates water balance
Where are the hormones synthesized before being transported intracellularly for secretion from the pituitary?
Hypothalamus
The posterior pituitary is fed by which artery?
inferior hypophyseal artery
The hypothalamus is supplied by which artery?
superior hypophyseal artery
How is the anterior pituitary supplied blood?
Venous by way of long portal vessels
Which nerve fiber supplies oxytocin?
Paraventricular nucleus
Which nerve fiber supplies antidiuretic hormone (vasopressin)?
Supraoptic nucleus
What is the mechanism of action of vasopressin?
Increases permeability of the collecting ducts, increasing free water absorption.
-increased urine osmolality
-decreased plasma osmolality
-Increased ECF volume
How does Vasopressin (ADH) produce vasoconstrictive/pressor effects?
Causes contraction of vascular smooth muscle
-more prevalent in large doses
V1 receptor:
Pressor effect
-vasoconstriction = increased arterial pressure
-prevalent w extreme increases in circulating levels (hemorrhage)
V2 receptor:
ADH effect
- renal fluid reabsorption= increased blood volume = increased arterial pressure
Vasopressin is released from the posterior pituitary d/t :
Angiotensin 2
Sympathetic stimulation
Hyperosmolarity
Hypovolemia
HoTN
Stimulus for release of vasopressin (ADH):
Osmoreceptor in the hypothalamus is activated by plasma osmolarity > 290 mosm/L
-other receptors in the hypothalamus send sensation of thirst
Decreased ECF volume activates ____ receptors in the ____ ____, _____, and _____ ____ for ADH release
stretch receptors
-great veins
-atria
-pulmonary vessels
Other stimulators of ADH release:
-High sodium
-Low BP
-angiotensin 2
-nicotine
-nausea
-pain
-stress
-PPV
Release of ADH is depressed by:
-Decreased plasma osmolality
-Increased ECF volume
-Alcohol
Large volume changes activate:
baroreceptor in the carotid sinus and aortic arch
Diabestes insipidus (DI)
excessive thirst= dilute urine
What is Diabetes insipidus caused by?
ADH deficiency caused by an inability to release (neurogenic/central- most common) or inability of kidney to respond (nephrogenic)
What are the results of Diabetes Insipidus?
Excretion of large amounts of hypoosmotic urine w hyperosmotic plasma
polydipsia, polyuria w/o hyperglycemia
What keeps DI pts from severe dehydration?
Water intake
Treatment for DI:
Limit sodium intake
Give ADH (1-Deamino-8-D-arginine vasopressin/ DDAVP for central
What is Hypernatremia a result of?
Loss of H2O, an excess of Na or retention of large quantities of sodium.
When is transient central DI commonly seen?
Post-head injury or surgery
What can cause Nephrogenic DI?
Chronic renal disease
Lithium toxicity
Hypercalcemia
Hypokalemia
Tubulointerstitial disease (drugs)
Above what sodium level should elective surgery be cancelled?
> 150
What are symptoms of hypernatremia?
Restlessness
Lethargy
Hyperreflexia
Seizure
Coma
Death
Is MAC increased or decreased w hypernatremia?
Increased
Is MAC increased or decreased w hypernatremia?
Increased (decreased potency)
Is the uptake of inhalation agents increased or decreased with hypernatremia?
Decreased from decreased CO
What can rapid correction of hypernatremia result in?
-Seizures
-Brain edema
-Permanent neurologic damage
-Death
What is Syndrome if inappropriate ADH (SIADH)?
ADH overload
What causes SIADH?
Autonomous release from the pituitary (or tumor)
CNS disorders
Head trauma
Squamous cell lung cancer
(SCC of lung)
Pulmonary infection
Pituitary signs and symptoms
What are the symptoms of SIADH?
Water retention
dilutional hyponatremia
Concentrated urine
Hypoosmolar (dilute plasma)
Water intoxication
Brain edema= CNS effects –> lethargy, seizure, coma
Treatment for SIADH
Tx underlying cause
restrict fluid
Demeclocycline
What causes hyponatremia?
Low Na+ reflects water retention either from an absolute increase in total body water (TBW) or Na+ loss in excess of H2O
Until what level is hyponatremia asymptomatic?
125 mEq/L
When can you see serious symptoms with hyponatremia
Below 120 mEq/L
Mild hyponatremia:
anorexia, nausea, weakness
Moderate hyponatremia:
lethargy, confusion
Severe hyponatremia:
seizures, coma, death
Above what sodium level is safe for elective procedures?
> 130
Anesthetic implications for a sodium level less than 130:
May lead to cerebral edema
Decreased MAC
Post-op agitation, confusion, somnolence
Tx: Hypertonic 3% saline, furosemide
What can happen is hyponatremia is corrected too quickly?
Central pontine myelinolysis
-demyelinating lesions in the pons
What are the recommended correction guidelines for hyponatremia?
1-2 mEq /hr
<12 mEq /24 hrs
What are symptoms associated w Central Pontine Myelinolysis?
Spastic quadriplegia
pseudobulbar palsy (inability to control facial movements)
varying degrees of encephalopathy or coma from acute, noninflammatory demyelination that is centered within the basis pontis
Conditions predisposing pts to CPM:
Alcoholism
Liver disease
Malnutrition
Hyponatremia
Risk factors for CPM in the hyponatremic pt include:
Serum sodium less than 120 mEq for more than 48 hrs
Aggressive IV fluid therapy w hypertonic saline solutions
Development of hypernatremia during tx
How often should serum Na+ be monitored?
Every 1-2 hrs.
Where is Oxytocin (Pitocin) secreted from?
paraventricular nucleus of posterior pituitary
What does oxytocin do?
Causes contraction of myoepithelial cells of the lactating breast and smooth muscle of the uterus
decreases blood loss after birth d/t uterine contractions
When does the secretion and sensitivity of oxytocin increase
late pregnancy
What causes the milk ejection reflex?
stimulation of touch receptors in the breast by infant suckling
activation of afferent fibers sends signals to the supraoptic and paraventricular nuclei to release oxytocin , contraction of myoepithelial cells and ejection of milk
Labor effects and breastfeeding are examples of what?
Positive feedback
Is the blood-brain barrier intact to the hypothalamus?
NO
Complications of oxytocin?
Fetal distress d/t hyperstimulation
Uterine tetany
Maternal water intoxication (ADH effects, rare)
Rapid IV infusion of oxytocin can cause:
HTN
Tachycardia
N/V
Seizures (rarely)
How are intracranial neoplasms found most often?
d/t hypersecretion of pituitary hormones
Galactorrhea
High prolactin secretion
Cushing disease
High ACTH
High cortisol
Acromegaly
High growth hormone secretion
How are pituitary tumors often found?
As a result of compression on adjacent structures
- visual changes w impingement of the optic chiasm
What can the compression of the optic chiasm result in?
Bitemporal hemianopsia
(Impaired peripheral vision in the outer temporal halves of the visual field of each eye.)
Anesthetic implications for Acromegaly (increased GH)
-difficult mask
-difficult intubation
-Large tongue and epiglottis
-enlarged mandible
-distorted facial features
-subglottic narrowing and vocal cord enlargement.
-May consider downsizing ETT.
-OSA is common.
-High risk of HTN, cardiomyopathy, LVH, arrhythmias.
-Enlarged spleen, heart, liver, kidneys
-Skeletal overgrowth
-Glucose intolerance
-Preferred surgery is pituitary tumor removal
Anesthetic implications for Hyperthyroid (TSH)
Tachycardia
Wt. loss
Anesthetic implications for Cushing’s (ACTH)
Difficult airway and access
Panhypopituitarism
Need hormone replacement w cortisol, levothyroxine (synthetic T4), DDAVP (vasopressin)
What kind of tube would you use for pituitary surgery?
ETT oral Rae
Implications for pituitary surgery:
Head pins
Deep extubate
Procedure 2-4 hrs
Dura is opened to expose tumor and repaired w fat or bone graft
EBL 20-200 ml
Keep pt normotensive and normocapneic
Why should you avoid hypocapnia in pituitary surgery?
Hypocapnia lowers ICP and pulls pituitary tumor further into brain
Which hormones are released by the anterior pituitary gland?
Prolactin
Luteinizing hormone
Antidiuretic hormone
Oxytocin
Corticotropin-releasing hormone
Growth Hormone
Prolactin
Luteinizing hormone
Growth Hormone
(anterior pituitary releases 6 hormones: “FLAT PiG)
-Follicle-stimulating hormone
-Luteinizing hormone
-Adrenocorticotropin
-Thyroid-stimulating hormone
-Prolactin
-Ignore
-Growth hormone
