Endocrine

• Why is a normal endocrine system essential?

  A normal endocrine system is essential to maintain homeostasis.

  
• What are the mechanisms of dysfunction in the endocrine system?

  1. Primary hypofunction – loss of secretory cells
  2. Secondary hypofunction – loss of trophic hormone
  3. Primary hyperfunction – proliferation of secretory cells
  4. Secondary hyperfunction – excessive trophic hormone
  5. Hormone production by non-endocrine tissue
  6. Hormone receptor failure
  7. Hyperfunction due to disease in other organs
  8. Iatrogenic hyperfunction

  
• What is primary hypofunction in the endocrine system?

  Primary hypofunction is the loss of secretory cells.
• What is secondary hypofunction in the endocrine system?


  Secondary hypofunction is the loss of trophic hormone.
• What is primary hyperfunction in the endocrine system?

  Primary hyperfunction is the proliferation of secretory cells.
• What is secondary hyperfunction in the endocrine system?

  Secondary hyperfunction is excessive trophic hormone.
• What does hormone production by non-endocrine tissue refer to?

  It refers to hormones being produced by tissues that are not part of the endocrine system.
• What is hormone receptor failure?

  Hormone receptor failure is when the receptors for hormones do not function properly.
• What can cause hyperfunction due to disease in other organs?

  Disease in other organs can lead to excessive hormone production or activity.
• What is iatrogenic hyperfunction?

  Iatrogenic hyperfunction is hyperfunction caused by medical treatment or intervention.
• Where is the pituitary gland located?

  The pituitary gland is on the ventral aspect of the brain caudal to the optic chiasma.

  
• What are the two main parts of the pituitary gland?


  The two main parts are the adenohypophysis (anterior pituitary) and the neurohypophysis (posterior pituitary).

  
• What does the adenohypophysis produce?

  The adenohypophysis produces and releases many different hormones.

  
• What is the role of the neurohypophysis?

  The neurohypophysis is a releasing center for ADH and oxytocin produced in the hypothalamus.

  
• What is a pituitary cyst and its effects?

  • Most common in German Shepherds
  • Failure of ectoderm in Rathke’s pouch to fully differentiate into adenohypophysis
  • Cyst forms and slowly enlarges
  • Cyst compresses remainder of adenohypophysis preventing hormone production
  • Reduced GH production most obvious

  
• What are the clinical signs of pituitary dwarfism in dogs?

  Clinical signs include failure to grow and retention of puppy hair coat.
• What can severely affected pups with pituitary cysts develop?

  Severely affected pups can develop hypothyroidism and hypoadrenocorticism.
• How does acromegaly occur in dogs?

  Acromegaly occurs due to excessive GH after growth plate closure.
• What are the characteristics of hyperpituitarism in dogs?

  • Wide spacing of teeth due to excessive maxillary development
  • Enlarged skull
  • Excessive folds of skin
• What is the most common type of neoplasia in dogs related to the pituitary gland?

  Chromophobe adenomas are the most common and most are functional.
• What do chromophobe adenomas produce in dogs?

  Chromophobe adenomas produce ACTH resulting in secondary hyperfunction of the adrenal cortex (Cushing’s disease).
• What are the effects of non-functional tumors in the pituitary gland?

  Non-functional tumors compress surrounding tissue, leading to issues like tunnel vision.
• What is the most common type of neoplasia in horses related to the pituitary gland?

  Chromophobe adenomas of the pars intermedia are the most common.
• What do chromophobe adenomas in horses secrete?

  Most secrete proopiomelanocortin (POMC), not ACTH.
• What clinical signs are caused by hypothalamic compression in horses?

  Clinical signs include PU/PD, polyphagia, hyperthermia, sweating, muscle weakness, and hirsutism.
• What is the common neoplasia in rats related to the pituitary gland?

  Common in some rat strains, usually producing prolactin.
• Where are the thyroid glands located?

  The thyroid glands are paired glands close to the trachea.

  
• What hormones do the thyroid glands produce?

  The thyroid glands produce T3 and T4, which control the basal metabolic rate.
• How are thyroid cells arranged?

  Thyroid cells are arranged in follicles, and T3 and T4 are made in the lumen referred to as colloid.
• What determines the release of colloid from the thyroid glands?

  The release of colloid is determined by TSH.
• What additional hormone do thyroid glands contain cells that produce?

  Thyroid glands also contain cells that produce calcitonin (C cells).
• What are the two main types of hypothyroidism in dogs?

  1. Idiopathic loss of thyroid cells
  2. Autoimmune destruction of thyroid cells
• What are the clinical signs of hypothyroidism in dogs?

  Reduced metabolic rate causes clinical signs such as weight gain and lethargy.
• What is myxedema in dogs?

  Myxedema is a non-specific clinical sign in dogs with long-term hypothyroidism.
• What causes atherosclerosis in canine hypothyroidism?

  Atherosclerosis is due to persistently elevated serum cholesterol concentration.
• What is goitre and its major mechanisms?


  • Non-neoplastic increased thyroid gland size
  • Major mechanisms:

  1. Iodine deficiency goitre
  2. Excess dietary iodide
  3. Defects in the enzymes or thyroglobulin
  4. Idiopathic hyperplasia
• What are the two mechanisms that result in iodine deficiency goitre?


  1. Primary lack of iodine in diet 2. Goitrogenic substances in diet inhibit iodine uptake.
• What are the consequences of iodine deficiency goitre?

  Consequences include stillborn or dying shortly after birth, and if they survive, hyperplastic goitre develops into colloid goitre.
• What happens in foals of mares fed dry seaweed?

  Foals develop thyroid hyperplasia due to increased iodide interfering with hormone synthesis.
• What are the clinical signs of hyperthyroid cats?

  • Weight loss despite polyphagia
  • PU/PD
  • Vomiting and loss of house training
  • Hypertrophic cardiomyopathy