8a. Endocrine System Disorders

Thyroid Glands

•Bi-lobed structure located lateral to the cranial tracheal rings

•Not normally palpable in a healthy animal

•Only organ that utilises iodine

•Controlled by TSH released by the pituitary gland

•Responsible for production of….

•Triiodothyronine (T₃) and thyroxine (T₄)

•Calcitonin – decreases Ca concentration of the blood

•Parathyroid gland produces parathyroid hormone

•Increases Ca concentration of the blood

Hyperthyroidism

An overreactive thyroid gland - causes over-production of T3 and T4, which increases metabolic rates - cells in the body start to work harder and faster due to the overload

• common in middle to old aged cats - both genders

clinical signs -

• palpable enlarged thyroid

• no matter how much they eat they don’t gain weight

• heart murmur and tachycardia

• polyuria and polydipsia - kidneys become overloaded - thirstier so urinate more

Diagnostics -

• blood tests - including total T4

• thyroid scintigraphy

Treatment - depends on severity, age, finance, facilities and patient behaviour

• monitor vital signs

• reduce stress

• fresh water available

• suitable diet

• medication under VS direction

Hypothyroidism

An underactive thyroid gland

most commonly caused by auto-immune destruction of thyroid gland - decreased production of T4 leading to a decreased metabolic rate

Clinical Signs -

• lethargy

• obesity

• bradycardia

Diagnostics -

• blood tests

• Total T4 and thyroid stimulating hormone assay

Treatment -

• monitor vital signs

• assist VS

• fresh water available

• feed a suitable diet - weight loss type diet (measure portions)

Adrenal Glands

located dorsally and cranially to the kidneys

Adrenal Medulla - adrenaline and nor-adrenaline - controlled by sympathetic nervous system

Adrenal Cortex - glucocorticoids

Hyperadrenocorticism - Cushing’s

Pituitary dependent hyperadrenocorticism -

• Over-secretion of ACTH by the anterior pituitary gland (most likely due to a tumour).

• ACTH is a hormone that stimulates the adrenal gland to produce glucocorticoids.

• compression of the base of the brain and the optic nerves (can cause neurological issues and blindness)

Adrenal-based hyperadrenocorticism -

• Adrenal tumour causes an over-secretion of cortisol.

• Adrenal tumours are responsible for around 20% of the cases of canine Cushing's disease.

clinical signs -

• Polyuria

• loss of muscle tone

• pot belly

• panting

• polyphagia - difficulty swallowing

Diagnosis -

• abdominal ultrasonography

• abdominal radiography

• MRI / CT

• general blood tests

Treatment -

• fresh water available

• oral medications

• careful handling due to easily bruising

• frequent toileting

Hypoadrenocorticism - Addison’s Disease

•Atrophy of adrenal cortex resulting in decreased production of glucocorticoids and mineralocorticoids

•Most commonly caused by auto-immune destruction of adrenal gland

•Lack of cortisol causes…

•Weakness, vomiting and anorexia (esp. when stressed)

•Lack of aldosterone causes electrolyte imbalances…

•Hyponatraemia (low sodium)

•Hyperkalaemia (high potassium)

Clinical signs -

• lethargy

• dehydration

• V + D

• coat changes

Diagnostics -

0 blood tests

ACTH stimulation test

ECG

Treatment -

• IVFT

• monitor vital signs

• meds under VS direction

• ECG

• fresh water available