W9 PRE Thyroid gland

Thyroid gland location

Over trachea, caudal to/level of larynx (two lobes)

Made of follicles, within connective tissue capsule

Parafollicular cells (C cells)

Between follicles and produce calcitonin (regulate blood calcium)

Thyroid gland hormones

• Throxine T4

• Triiodothyroxine T3

• Calcitonin (Thyrocalcitonin)

T4 / T3

• Regulate metabolic rate

Release of T4 control

• Thyrotropin-releasing hormone (hypothalamus)

• Thyroid-stimulating hormone (pituitary gland)

T4 to T3

• Act on all cells; essential for normal growth

• Effect skin, skeleton, cardiovascular system, neurological and reproductive

Calcitonin (Thyrocalcitonin)

Decrease blood calcium by slowing resorption from bone

Decreases calcium reabsorption from GI tract, increases excretion through urine

Release of T4 into bloodstream

• Hypothalamus produces Thyrotropin releasing hormone (TRH)

• Pituitary gland - stimulates secretion of Thyroid stimulating hormone (TSH)

• Thyroid - stimulates Thyroxine T4 release into blood

• Feedback signal: Normal levels - body decreases hormone amount produced through negative feedback

Calcium

Functions in nerve transmission, blood clotting and muscle contraction.

High level Calcium

Calcium deposites within kidney

Heart rhythm abnormalities

Neurological disturbances

Calcitonin negative feedback mechanism

And parathyroid hormone ensures blood level remain appropriate

Blood Calcium:Phosphorus

1-1.5 Calcium : 1 Phosphorus

T4 to T3 Conversion

Thyroid-releasing hormone (TRH) released by hypothalamus to stimulate pituitary gland to release thyroid-stimulating hormone (TSH)

Thyroid gland releases T4, converted into T3 within tissues

T3 (active hormone form) sets metabolic rate

Hypothyroidism

Lack of thyroxine thf T3, due to atrophy/lymphocytic infiltration of thyroid gland

Primary - (excess TSH) destruction of thyroid gland, either lymphocytic thyroiditis (immune disease) or idiopathic

Secondary - (Lack TSH), Rarely pituitary tumour prevent TSH production

Hypothyroidism signs

(reduced metabolic rate, slow tissue regeneration, healing)

• Lethargy, exercise intolerance

• Obesity

• Bradycardia

• Hypothermia

• Dermatological condition e.g. alopecia, seborrhoea

• Hyperpigmentation, pyoderma

Hypothyroidism diagnosis

CE

Blood test Total T4, free T4 and TSH

Low T4

High TSH

Low fT4

Hypothyroidism treatment

Lifelong medication (supplement thyroxine with synthetic T4)

Levothyroxine - Soloxine, Thyforon

Thyroxine medications

Pregnant handle with caution

Wear gloves, washing hand after administering/handling

Thyforon

synthetic levothyroxine increase T4 levels

Per os

Overdosing hyperthyroidism, weight loss, hyperactivity, excitability, panting, tachycardia, polydipsia, pu/pp

Split tablets stored blister pack, Wash hands after administration. Pregnant care

Hyperthyroidism signs

• Accelerated metabolism - agression, overgroom, hyperactive

• Polyphagia, weight loss emaciatione

• Tachycardia, hypertension, heart murmur

• V/D

Primary - Overactive gland typically from benign hyperplasia, result overproduction of thyroxine

Secondary - TSH secreting pituitary adenoma

Hyperthyroidism similarity to CKD

Increased activity, restless, aggression, weight loss despite PP key differences

Hyperthyroidism diagnosis

T4 blood tests, additional scintigraphy

Ectopic thyroid tissue

Ectopic thyroid tissue in chest, highlighted in green. 

Identifying areas of extra-thyroid tissue useful when determining treatment option

Hyperthyroidism treatment

Anti-thyroid medication, thyroidectomy, radioactive iodine therapy (RIT), dietary

Anti-thyroid medication

Methimazole (coated tablet) active form

Carbimazole (prolonged release) metabolised into methimazole by liver

Thiamazole (solution)

Side effects: V/D, inappetence, iatrogenic hypothyroidism (consequent renal failure)

Facial pruritus, jaundice, cytopaenia, immune disorder

Transdermal methimazole gel

Ear pinnae application to inappetent/fractious cats

Not licensed, used under prescribing cascade, specially formulated by company

Thyroidectomy

Bilateral/unilateral surgical removal of thyroid gland

Thyroidectomy issues

• Medical treatment administered prior surgery to ensure patient euthyroid (normal function), lowering bp, hr and reduce anaesthetic risk

• Parathyroid tissue can be damaged/removed with diseased tissue, lead to hypoparathyroidism, hypocalaemia

Post surgery thyroidectomy

• Monitor low blood calcium levels, implement IV calcium gluconate

• May require life supplementation of calcium and vitamin D

• Remaining tissue produce thyroxine - persistent signs of hyperthyroidism

Radioactive iodine therapy (RIT)

SC/ oral administration of radioactive iodine isotope

Iodine and bound radioactive isotope collects in thyroid, killing thyroid tissue due to radioactive iodine build up in gland

RIT handling

Strict safety protocols, isolation following administration

Safe housing, disposal of radioactive waste

Dietary management

Prescription diet manage thyroxine production

Diet restrict iodine within food, starving thyroid gland of nutrient require to synthesise thyroxine

ONLY consume this food, several month full effect