Pathophysiology of the Pituitary Gland Flashcards
what secretes growth hormone releasing hormone?
hypothalamus
what stimulates the hypothalamus to produce growth hormone releasing hormone?
ghrelin
what is growth hormone important for?
glucose homeostasis
lipolysis
insulin secretion
what is primary hypopituitarism?
deficiency of one or more pituitary hormones
what are the two forms of primary hypopituitarism?
congenital: pituitary dwarfism
acquired: adult-onset
who is primary hypopituitarism (pituitary dwarfism) most common in?
German Shepherds
can primary hypopituitarism (pituitary dwarfism) be seen with other pituitary hormone deficiencies, including ACTH?
yes, but not with ACTH
what are the causes of primary hypopituitarism (pituitary dwarfism)?
cystic dilation of rathke’s pouch
developmental failure of trophic cells
pituitary tumor
what is the presentation of primary hypopituitarism?
failures of normal growth
clinically can mimic congenital hypothyroidism
what are the clinical signs of primary hypopituitarism (pituitary dwarfism)?
dwarfing/short stature
abnormal haircoat
infantile genitalia
delayed closure of growth plates
delayed dentition
mental dullness
what are some useful diagnostic aids for pituitary dwarfism?
comparison of height with littermates
radiographs of open epiphyseal lines
thyroid function tests
skin biopsy (mostly to rule out other causes of alopecia)
serum determination of: growth hormone, insulin-like growth factor-1 (a lot of labs do not measure)
what are the laboratory findings of pituitary dwarfism?
usually pretty normal: things associated with being a tiny puppy
what can cause primary hypopituitarism (adult-onset hypopituitarism)?
non-functional pituitary or other brain tumors
inflammation, thrombosis, trauma
what are the clinical signs of primary hypopituitarism (adult-onset hypopituitarism)?
neurologic abnormalities
those of ADH, TSH, or ACTH deficiency
pituitary dwarfism is familial in which dog breed?
german shepherds
what can cause adult-onset hyperpituitarism?
functional micro or macroadenoma
pituitary-dependent hyperadrenocorticism
what are the causes of hyperpituitarism in dogs?
other growth hormone-producing tumors: mammary, progesterone therapy, primary hypothyroidism
functional pituitary tumor (rare)
what is the etiology of hyperpituitarism in cats?
growth hormone-secreting pituitary tumor
who is most likely to get hyperpituitarism?
middle-aged to older animals
dogs: primarily females
cats: primarily males
what is the pathophysiology of hyperpituitarism due to?
excessive growth hormone production
what are the clinical signs of hyperpituitarism?
prominent skin folds of face and neck
blunt, broad head
enlarged chin, forehead, limbs, feet
enlarged interdental spaces
abdominal enlargement
what organ enlargement does hyperpituitarism cause?
hepatomegaly
renomegaly
cardiomegaly
respiratory stridor: increase in upper airway soft tissue, macroglossia
what is a complication of hyperpituitarism?
diabetes mellitus
how can you diagnose acromegaly?
no singe diagnostic test: clinical signs associated with poorly-controlled type 2 diabetes mellitus
laboratory measurement of IGF-1
CT/MRI imaging of the pituitary gland
what are the two types of central diabetes insipidus?
absolute
partial
what happens with complete central diabetes insipidus?
persistent hyposthenuria and severe diuresis despite dehydration
what are the etiologies of central diabetes insipidus?
congenital
infection
trauma
neoplasia
idiopathic: most common
what is the etiology of nephrogenic diabetes insipidus?
impaired responsiveness of the nephron to ADH: primary and secondary
what are the clinical signs of diabetes insipidus?
severe polyuria/polydipsia
dehydration
neurologic signs
what are the laboratory findings of diabetes insipidus?
increased serum osmolality
decreased urine osmolality
hyposthenuria
inadequate water intake
water deprivation test
ADH-response test
what are some laboratory abnormalities associated with inadequate water intake?
azotemia
hypernatremia
hyperproteinemia
erythrocytosis
how is an ADH-response test performed?
urine specific gravity is determined at the start of the test
desmopressin acetate administered
bladder emptied after 2 hours
urine specific gravity measured at set intervals
expect increased USG if responsive to ADH
what can cause inappropriate release of ADH in absence of normal stimuli?
cerebral diseases
pulmonary diseases
idiopathic
drug idiosyncrasies
what happens in syndrome of inappropriate ADH secretion with decreased free water excretion?
volume expansion
hyponatremia
hypoosmolality
what hormones are secreted by the anterior pituitary?
growth hormone
prolactin
ACTH
thyrotropin stimulating hormone
follicle stimulating hormone
luteinizing hormone
melanocyte stimulating hormone
POMC
what hormones are secreted by the posterior pituitary?
antidiuretic hormone
oxytocin
what does growth hormone do?
adipose: increases lipolysis and decreases glucose uptake
liver (increases IGF-1): increases gluconeogenesis, glycogenolysis, gluconeogenesis (kidneys), decreases glucose uptake
muscle: increases glycogenolysis, decreases glucose uptake
pancreas: increases insulin secretion
primary hypopituitarism can clinically mimic _________________________
congenital hypothyroidism
what are some laboratory abnormalities associated with primary hypothyroidism/pituitary dwarfism?
mild anemia, hypophosphatemia, hypoalbuminemia
azotemia due to decreased GFR
hypercholesterolemia due to secondary hypothyroidism
what is acromegaly from?
from hyperpituitarism
which breed of cat is most likely to have hyperpituitarism?
domestic shorthairs
what mediates growth hormone’s effects on tissues?
insulin-like growth factor-1
what are the anabolic effects of excessive growth hormone on tissues?
overgrowth of connective tissue, bone, viscera
what are the metabolic effects of excessive growth hormone on tissues?
effects on glucose and insulin regulation
how does hyperpituitarism lead to diabetes mellitus?
excess growth hormones results in downregulation of insulin receptors and resistance to the action of insulin at the target cell level
what are the chemistry abnormalities associated with hyperpituitarism?
hyperglycemia
hypercholesterolemia
hyperproteinemia
hyperphosphatemia
what are the CBC abnormalities associated with hyperpituitarism?
erythrocytosis
what are the urinalysis abnormalities associated with hyperpituitarism?
glucosuria
how can we diagnose hyperpituitarism?
complicated: no single diagnostic test, looks similar to type 2 diabetes
laboratory measurement of IGF-1: usually elevated, repeat in 3-6 months
CT/MRI of the pituitary gland
what happens with partial central diabetes insipidus?
persistent hyposthenuria and severe diuresis as long as the animal has access to water
what is the most common cause of central diabetes insipidus?
idiopathic
what causes primary impaired responsiveness of the nephron to ADH?
congenital
what causes secondary impaired responsiveness of the nephron to ADH?
hyperadrenocorticism
hypercalcemia
therapy with outdated tetracyclines
endotoxemia
pyelonephritis
why do animals with diabetes insipidus have neurologic signs?
pituitary tumor
electrolyte abnormalities
what are the laboratory findings associated with inadequate water intake with diabetes insipidus?
azotemia
hypernatremia
hyperproteinemia
erythrocytosis
what are the differential diagnoses for polyuria/polydipsia?
diabetes insipidus
diabetes mellitus
drugs
hyperadrenocorticism
hypoadrenocorticism
hypercalcemia
hypertension
hyperthyroidism
hyperviscosity
hypokalemia
liver disease
pyelonephritis
pyometra
renal failure
psychogenic
what is syndrome of inappropriate ADH secretion?
inappropriate release of ADH in absence of normal stimuli: too much ADH
what can cause syndrome of inappropriate ADH secretion?
cerebral diseases
pulmonary diseases
idiopathic
drug idiosyncrasies
what are the neurologic clinical signs of syndrome of inappropriate ADH secretion from?
neuronal sensitivity for electrolyte abnormalities: swelling
brain tumor
