What function does the thyroid have in the dog’s body?
A while back we talked about sick euthyroid syndrome – a condition that complicates the diagnosis of hypothyroidism in dogs.
Say your veterinarian determines that your dog truly has hypothyroidism. What the thyroid gland does and how does its dysfunction affects the body?.
What does the thyroid gland do?
The thyroid gland sits on the front of the dog’s neck–one segment on either side of the trachea (windpipe). It makes hormones – primarily thyroxine (T4), but also 3,5,3’-triiodothyronine (T3), reverse T3, and other metabolites.
T3 is the more potent hormone. The thyroid gland produces it directly as well as it can be derived from T4.
These hormones consist of amino acid tyrosine bound to iodine.
This is the only place the body utilizes iodine.
Thyroid hormone secretion is regulated by a negative feedback mechanism of the hypothalamic-pituitary-thyroid axis (from the brain to the thyroid).
In other words, a decrease in T4, triggers T4 production. Likewise, when there is an excess amount, the thyroid produces less. This ensures the correct levels of the hormone at any given time.
What do the thyroid hormones do?
On a molecular level, thyroid hormones
- bind cellular receptors (intracellular DNA-binding proteins)
- enter into cells via membrane transporter proteins
- and interact with specific sequences of DNA to modulate gene expression.
In other words, thyroid hormones turn some genes on and other genes off.
On a physiological level, thyroid hormones affect many, if not, all areas of the body.
Their absence or excess may not be immediately life-threatening. However, maintaining appropriate levels is essential for a good quality of life.
Some known functions of thyroid hormones include:
The thyroid hormones help to regulate body temperature and can stimulate fat and carbohydrate metabolism.
In other words, it controls the levels of fatty acids and glucose–in the blood. Therefore, when the hormone is deficient, the blood cholesterol and triglyceride levels become elevated.
2. Growth and brain development
Normal growth and brain development in young animals depend on thyroid hormones. As a result, thyroid deficiency leads to growth-retardation and neurologic impairment.
3. Cardiovascular effects
The thyroid hormones cause an increased heart rate, cardiac output, and blood flow to many organs.
4. Central nervous system
Excess thyroid hormones cause agitation and anxiety, and sluggishness and dullness if deficient.
5. Reproductive system
Sufficient levels of thyroid hormone are necessary for fertility.
6. Many other effects
Further, the thyroid hormones play a role in other processes such as maintaining healthy skin and good muscle tone.
You can see why having appropriate amounts of thyroid hormones is critical to the well being of dogs.
Thankfully, treating hypothyroidism in dogs is about as easy as it gets.
- give synthetic thyroid hormone as prescribed by your veterinarian
- follow the monitoring schedule that he or she recommends
It can take some time to find the right dose and a dog’s needs may change.
What if, despite this, your dog’s condition does not improve? Your veterinarian needs to revisit their initial diagnosis. Your dog might have an euthyroid sick syndrome.