What is the Hypothalamic Pituitary Axis?
Unit formed by hypothalamus & pituitary responsible for brain-endocrine interactions and control Gonads, Thyroid, and Adrenal glands
Which endocrine gland is considered the Master Gland?
Pituitary
How does the Hypothalamus work?
Coordinating Center
Gets signals from cortical inputs, autonomic function, environment, and endocrine feedback then delivers precise signals to the pituitary to release hormones influencing other endocrine systems
Where can the Pituitary Gland be found?
In the Sella tursica of the Sphenoid Bone
How is the Pituitary Gland divided?
- Anterior Pituitary (Adenohypophysis)
- Pars Intermedius
- Pars tubularis
- Neurohypophysis - Posterior Pituitary
Which part of the Pituitary Gland is highly vascular and does not secrete any hormones?
Pars Tuburalis
Which is the largest part of the Pituitary Gland?
Anterior Pituitary / Adenohypophysis
Which part of Pituitary Gland is present only up until Fetal Development?
Pars Intermedius
What makes the Anterior and Posterior Pituitary distinct?
Different connections to hypothalamus
Contain different cell types
Secrete different hormones
What are the main functions of the Hypothalmus?
- Produce Releasing and Inhibiting hormones that influence Anterior Pituitary
- Produces Oxytocin & ADH and stored in Posterior Pituitary
- Oversees ANS and helps stimulate Adrenal Medulla
How does the Anterior Pituitary connect to the Hypothalamus?
Portal Venous Network
Which hormones and glands does the Anterior Pituitary regulate?
FLATPIG
- *F** ollicle Stimulating Hormone - gonads
- *L** uteinizing Hormone - Ovaries
- *A** Adrenocorticotropic Hormone (ACTH)
- *T** hyroid Stimulating Hormone
- *P** rolactin (PRL) - mammary
- *I** gnored - Melanocyte Stimulating Hormone
- *G** rowth Hormone - Somatotropic
What are the different cell types of the Anterior Pituitary
Somatotropes - most abundant (30-40%)
Corticoctropes (20%)
Thyrotropes (3-5%)
Gonadotropes (3-5%)
Lactotropes (3-5%)
What is the Posterior Pituitary made of?
Collection of Axonal Projections from the Hypothalamus
What are the functions of the Posterior Pituitary?
Receives Oyxtocin & ADH made in the Hypothalamus and secretes these hormones
Regulates Uterine Contraction & Water Balance
What supplies blood to the Hypothalamus?
Superior Hypophyseal Artery
What supplies blood to the Posterior Pituitary?
Inferior Hypophyseal Artery
How is ADH & Oxytocin transported from the Hypothalamus to the Posterior Pituitary?
Via nerve fibers in the Supraoptic Nucleus & Paraventricular Nucleus
What does Vasopressin do?
↑Collecting Duct Permeability
↑Water Reabsorption
↑ECF Volume
↑Urine Osmolality
↓Plasma Osmolality
Vasoconstriction
What does the V1 & V2 Vasopressin receptors do?
V1: Pressor Effect
V2: ADH effect
What stimulates Vasopressin/ADH release?
- Plasma Osmolality > 290
- Decreased ECF Volume
- Increased Sodium
- Low BP
- Angiotensin II
- Nicotine
- Stress & Pain
- Positive Pressure Ventilation
Alcohol, Increased ECF, and Decreased Plasma Osmolality causes what?
Depressed release of Vasopressin/ADH
What conditions are due to ADH disturbances?
Diabetes Insipidus & SIADH
How does Diabetes Insipidus happen?
Inability to release ADH causing ADH Deficiency
Can be Neurogenic (most common) or Nephrogenic
What are the symptoms of Diabetes Insipidus?
Pee Alot
Extreme Thirst
Hyperosmotic Plasma
HypoOsmotic Urine
How should patients w/ Diabetes Insipidus be managed?
Water Intake
Limit Sodium
Give DDAVP
What can cause Nephrogenic Diabetes Insipidus?
Chronic Renal Disease
Lithium Toxicity
Hypercalcemia
Hypokalemia
Tubulointerstitial Disease
What are some Anesthetic considerations for a pt w/ Hypernatremia r/t DI?
Increased MAC
Decreased CO = decreased uptake
Hypovolemia = decreased IV dose
What are symptoms of Hypernatremia?
Restlessness
Lethargy
Hyperreflexia
Seizures
Coma
Death
CORRECT SLOWLY
An overload of Vasopressin/ADH causes this type of ADH Disturbance?
Syndrome of Inappropriate ADH
What can cause SIADH?
CNS Disorders
Head Trauma
Lung Squamous Cell Carcinoma
Pulmonary Infection
Pituitary Surgery
What are the signs and symptoms of SIADH?
Water Intoxication
Hyponatremia
Concentrated Urine
Dilute Plasma
Brain Edema
Lethargy, Seizure, Coma
How should a patient w/ SIADH be managed?
Treat underlying cause
Fluid Restriction
Demeclocycline
3% Hypertonic Saline
Lasix
CORRECT SLOWLY & Monitor Na q1-2 hrs
At what levels of sodium should postponing elective surgeries be considered?
Sodium < 130 or > 150
What can happen if Hyponatremia is treated too aggressively?
Central Pontine Myelinolysis
Spastic Quadriplegia
Pseudobulbar Palsy
Encephalopathy
Coma
Where is Oxytocin secreted from?
Paraventricular Nucleus
How does Oxytocin increase Lactation?
Positive Feedback
Oxytocin –> Lactation –> Baby Eats –> Activates Afferent Fibers –> Signals Paraventricular Nuclei to release more Oxytocin
Beside lactation, what else is Oxytocin/Pitocin used for?
Organize Labor by increasing Uterine Contraction & Decreasing Blood loss after birth
What are some complications associated w/ Pitocin?
Fetal Distress d/t hyperstimulation
Uterine Tetany
Maternal Water Intoxication
Hypertension
Tachycardia
N/V
Seizures
What can happen if the Pituitary grows too big or if there are tumors on it?
Compression of Optic Chiasm causing vision problems
What should you expect for a patient having Pituitary surgery and has too much Growth Hormone?
Acromegaly making it difficult to mask & intubate
(Use smaller ETT)
Glucose Intolerance
HTN
Cardiomyopathy
LVH
What is to be expected w/ a patient who has too much ACTH?
Cushing’s Disease & Difficult Airway
What should be given to a patient w/ Panhypopituitarism?
Hormone replacement:
DDAVP
Cortisol
Levothyroxine
During Pituitary surgery, when would you suspect IntraOp Diabetes Insipidus and how would you treat?
High uring output w/ < 1.005 specific gravity
DDAVP 0.5 - 1 mcg
Fluids
