Other Animals
The thyroid gland is found in all vertebrates. In fish, it is usually located below the gills and is not always divided into distinct lobes. However, in some teleosts, patches of thyroid tissue are found elsewhere in the body, associated with the kidneys, spleen, heart, or eyes.
In tetrapods, the thyroid is always found somewhere in the neck region. In most tetrapod species, there are two paired thyroid glands - that is, the right and left lobes are not joined together. However, there is only ever a single thyroid gland in most mammals, and the shape found in humans is common to many other species.
In larval lampreys, the thyroid originates as an exocrine gland, secreting its hormones into the gut, and associated with the larva's filter-feeding apparatus. In the adult lamprey, the gland separates from the gut, and becomes endocrine, but this path of development may reflect the evolutionary origin of the thyroid. For instance, the closest living relatives of vertebrates, the tunicates and Amphioxus, have a structure very similar to that of larval lampreys, and this also secretes iodine-containing compounds (albeit not thyroxine).
Read more about this topic: Thyroid
Famous quotes containing the word animals:
“Chinese civilisation is so systematic that wild animals have been abolished on principle.”
—Aleister Crowley (1875–1947)
“He will deliver you from six troubles; in seven no harm shall touch you. In famine he will redeem you from death, and in war from the power of the sword. You shall be hidden from the scourge of the tongue, and shall not fear destruction when it comes. At destruction and famine you shall laugh, and shall not fear the wild animals of the earth. For you shall be in league with the stones of the field, and the wild animals shall be at peace with you.”
—Bible: Hebrew, Job 5:19-23.