4/4 Adrenal Glands - PPID in Horses COMPLETE *** Flashcards
Where is the Pituitary gland located in the brain? 3
- How is it separated from the brain?
on the ventral aspect of the brain
within the sella turcica
caudal to the optic chasm
by the diaphragm sella
Pituitary gland: What 2 sections can it be divided into?
- What is the anterior one further divided into? 2
adenohypophysis
neurohypophysis
pars distalis
pars intermedia
Pituitary gland: What hormones does the Adenohypophysis secrete (with examples) ? 5
gonadotrophin including FSH and lH
corticotrophs including POMC and ACTH
lactotrophs including prolactin
somatotrophs including growth hormones
thyrotrophs including thyroid stimulating hormone
Pituitary gland: What does the Pars intermedia do?
- Hence, where is most POMC produced?
- What is different about the ACTH produced by the pars intermedia?
- What happens to most ACTH produced by the pars intermedia?
it secretes POMC which is cleaved to ACTH
in the pars distalis
it is not biologically active so will not affect cortisol concentrations
it is further cleaved into other hormones
PPID: Why is PPID not thought of as the horse equivalent of Hyperadrenocorticism?
because you do not get elevated cortisol concentrations
PPID: Describe how PPID occurs 2
hypertrophy of melanotropes in the pars intermedia
these cells are responsible for secreting POMC
Pituitary gland: Why in PPID do you get this overgrowth of melanotropes? 2
neuro-degeneration of the periventricular neurones impairs hypothalamic dopamines ability to have negative feedback on the pituitary
this permits the development of adenomas
PPID: What after causes the disease process of PPID?
a pars intermedia adenoma which is a benign tumour in the pars intermedia
PPID: As PPID progresses, why do you get other neurological signs and symptom progression?
because the tumour is pushing on other parts of the pituitary gland causing dysfunction
PPID: Give the signalment 2
older horses over 7
ponies are predisposed
PPID: State the clinical signs from most common to least common 8
generalised hypertrichosis
weight loss
muscle wastage
polyuria and polydipsia
laminitis
recurrent infections
potbellied
neurological signs
PPID: What causes the generalised hypertrichosis, even in warmer seasons?
the elevated MSH and pituitary compression of the hypothalamus thermoregulatory centre
PPID: What causes Laminits?
due to persisten hyperinsulinaemia resulting from CLIP release
PPID: What causes PU/PD?
due to pituitary compression causing reduced secretion of ADH
PPID: What causes neurological signs?
blindness may be due to compression of the optic chiasm
PPID: Describe the generic steps you would take to help diagnose 3
- State the names of 2 specialised tests that can be done
review history
review clinical examination
blood biochemistry
resting ACTH
TRH stimulation test
PPID: What causes recurrent infections?
alpha MSH is an immunosuppressive hormone
PPID: What could you expect to see on blood biochemistry? 4
hyperglycaemia
hyperinsulinaemia
neutrophilia
lymphopaenia
PPID: Describe the process to carry out the resting ACTH test 3
collect blood in EDTA tubes
separate plasma within 4 hours of collection
chill in fridge and submit to lab
PPID: Resting ACTH
- Describe the sensitivity and specificity of this test
- Why might you get false positives?
- Why might you get false negatives? 2
moderate sensitivity and high specificity
due to stress and pain from laminitis
if the sample was stored incorrectly
early PPID
PPID: TRH Stimulation test
- What does TRH normally do?
- What is different in a PPID horse?
- Hence, what happens when injected with exogenous TRH?
- When would you perform this test?
it stimulates the pars intermedia to produce ACTH and MSH
the hyper plastic melotropes have a higher affinity for the TRH
the pars intermedia will secrete excessive ACTH in response
when you get a normal resting ACTH but have a high clinical suspicion
What diagnostic imaging could be used to identify pituitary enlargement?
CT and MRI
