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What are the three types of intercellular signalling?
Autocrine, paracrine and endocrine signalling
What is an endocrine gland?
A group of specialised epithelial cells that synthesise, store and release their secretions directly into the bloodstream for them to have physiological effects on distant target cells
What are the 5 mechanisms of endocrine disease?
- 1. Hypofunction
- 2. Hyperfunction
- 3. Endocrine dysfunction due to neoplasia
- 4. Failure of target cell response
- 5. Abnormal hormone degredation
What type of clinical signs can commonly be seen in the following body systems due to endocrine disease? a) skin b) nervous system c) urinary system d) skeletal system
- a) alopecia, hirsutism
- b) seizures
- c) PU, PD
- d) fractures
List some of the main endocrine organs
Pituitary, parathyroid, adrenal, thyroid, gonads, pancreatic islets,
Which hormones are secreted from the a) anterior pituitary b) posterior pituitary?
- a) GH, ACTH, TSH, FSH, LS, MSH, PRL
- b) ADH and oxytocin
Give possible causes of a) primary b) secondary anterior pituitary hypo function?
- a) Aplasia/hyperplasia or destruction secondary to a space occupying lesion e.g. cyclic Rathke's pouch
- b) hypothalamic malfunction
What is a clinical condition caused by pituitary hypo function?
What are the clinical signs of pituitary dwarfism?
- Decreased growth rate
- Abnormal hair coat - retention of puppy coat > alopecia, bilaterally symmetrical alopecia, hyper pigmentation
- Hypoplasia of gonads and genitalia
- Delayed permanent dentition and epiphyseal closure
Give an example of a breed that suffers from congenital cysts of Rathke's pouch leading to pituitary dwarfism?
GSD, Spitz, Toy pinscher, carellian bear dogs
What is the clinical syndrome of posterior pituitary hypo function?
Diabetes insipidus (watery urine)
Give examples of causes of a) primary b) secondary posterior pituitary hypo function?
- a) destruction of the neurohypophysis or central diabetes insipid us
- b) nephrogenic diabetes insipidus - renal tubules no longer respond to ADH
How does posterior pituitary hypo function result in diabetes insipidus?
- Primary - defect in hypothalamus, lack of secretion of ADH, diabetes insipidus i.e. PU, PD, low urine specific gravity
- Secondary - renal tubules insensitive to ADH, adequate ADH, diabetes insipidus i.e. PU, PD, low urine specific gravity
Give possible causes of pituitary hyperfunction
Functional neoplasms within the pituitary (adenoma, adenocarcinoma). Can also be due to pituitary hyperplasia.
What clinical condition can pituitary hyper function cause in dogs?
What are the clinical signs of Cushing's syndrome?
- Bilaterally symmetrical non-pruritic alopecia
- Comedones with dystrophic calcification
- Flaccid abdominal wall due to muscle wasting
What clinical condition can pituitary hyperplasia cause in horses?
Equine pituitary pars intermedia dysfunction (Equine PPID)
List some clinical signs seen with equine PPID
- Polyphagia, polyuria, polydipsia
- Generalised sweating
- Striking hypertrichosis
What clinical condition should you be careful not to confuse equine PPID with? How would you tell them apart?
- Equine metabolic syndrome
- EMS occurs at a younger age than equine PPID. A positive diagnostic test for PPID is increased plasma ACTH without pain or stress.
Give some examples of causes of hypoadrenocorticism?
- Damage - infectious, vascular, drug induced, etc
- Secondary to pituitary hypofunction
What is the clinical syndrome of hypoadrenocorticism?
When might horses experience sudden severe adrenocortical hypo function?
When there is massive, diffuse, often bilateral haemorrhage in overwhelming sepsis
What is the most common cause of adrenal cortical hyper function or hyperadrenocorticism?
Functional neoplasms within the adrenal cortex
What clinical syndrome is caused by hyperadrenocorticism?
If the adrenal cortex is hyper functional concentrations of what hormones are likely to be affected?
Cortisol, aldosterone and sex steroids
Which hormones is likely to have the most immediate and profound effects clinically?
What are the three forms of Cushing's Syndrome?
- Pituitary dependent
- Adrenal dependent
Describe what happens in pituitary dependent Cushing's syndrome
The pituitary produces excessive ACTH eg pituitary tumour. This stimulates the adrenal glands to produce more cortisol and results in bilateral adrenal enlargement.
Describe what happens in adrenal dependent Cushing's syndrome
The adrenal tumour produces increased cortisol which has negative feedback on the pituitary gland so less ACTH is produced by the pituitary
How common is pituitary dependent vs adrenal dependent Cushings syndrome?
85% vs 15% of cases
What can cause iatrogenic Cushing's syndrome?
Administration of exogenous steroids which act in lieu of the adrenal cortex
True or false: adrenal medulla hypo function is common?
False - it is rare
What is the cause of adrenal medulla hyper function?
Funcional neoplasia - phaeochromocytoma
If the adrenal medulla is hyper functional concentrations of which hormones are likely to be affected?
Catecholamines, adrenaline and noradrenaline
Describe normal thyroid function
The hypothalamus releases TRH which stimulates the pituitary to release TSH which acts on the thyroid gland and causes production of T4 and T3
Is hypothyroidism common in cats or dogs?
What are the possible a) primary b) secondary causes of hypothyroidism?
- a) idiopathic follicular atrophy, lymphocytic thyroiditis (immune mediated)
- b) decreased TSH from pituitary disease, Goitre
What are the clinical signs of hypothyroidism?
Lethargy, weight gain, exercise intolerance, hair thinning, poor quality coat, hyper pigmentation, pyoderma
What is Goitre?
A special type of thyroid dysfunction that results in inadequate T3/T4 synthesis and bilateral enlargement of the thyroid glands
What causes Goitre?
Iodine deficiency, iodine toxicity or goitrogenic plants
Why is there bilateral enlargement of the thyroid glands during goitre?
TSH production leads to thyroid enlargement but as there is no available iodine there is decreased T4 and T3 production. This feeds back to the pituitary and leads to increased TSH production, and the cycle continues.
What family of plants is goitrogen found in?
Brassica eg kale, rape
Give an example of when excess iodine is fed in the diet
Seaweed fed to mares
Is hyperthyroidism common in cats or dogs?
What is the most common cause of hyperthyroidism?
Parathyroid hypo function is rare but when might this occur?
When the thyroid is surgically removed
What are the three causes of secondary hyperparathyroidism?
- Renal - decreased GFR, increased phosphate retention and relative hypocalcaemia, continued stimulation of the parathyroid gland
- Nutritional - diet high in phosphate/low in calcium/low in vitamin D
- Psuedohyperparathyroidism - tumours of non endocrine origin secreted PTHrP
What can cause primary hyperparathyroidism?
What are the four causes of pancreatic islet hypo function?
Vacuolar degeneration, amyloidosis, immune mediated destruction, secondary to pancreatitis
What clinical syndrome is caused by pancreatic islet hypo function?
What causes pancreatic islet hyper function?
- Non functional neoplasms and hyperplasia less common
What type of tumour is more common: a cell or b cell pancreatic tumours? And what hormone do they secrete?
B cell - insulin