Thyroid Hormone Transportation

00:00 Thyroid Hormones Transportation.

00:03 It is important to be able to transport T4 and T3.

00:08 The reason is because these are hydrophobic hormones.

00:15 They would come out of solution if it was only then in the blood.

00:19 Therefore, you bind them to thyroid binding globulin, or transthyretin or albumin.

00:28 They help carry them around in the blood.

00:32 You have a little less than 1% in it's free non-bound form.

00:39 This is also handy because it provides a longer lasting thyroid hormone.

00:46 So what happens here is you can have T3 or T4 around for somewhere between 1 day and 1 week.

00:55 It increases it's 1/2 life.

00:58 It also allows for more of a larger storage pool of T3 and T4.

01:05 Because it will be in a bound state for a longer period of time.

01:09 T3 and T4 will get delivered to peripheral tissues.

01:15 It's important to think about how they get into those cells.

01:20 They would be able to cross the plasma membrane because they are lipophilic in nature.

01:26 There are sometimes however, that they will travel through larger pores as well.

01:31 T4 will be converted to T3.

01:36 This peripheral conversion is done by a specific enzyme 5'/3' monodeiodinase.

01:47 This enzyme facilitates that conversion by taking off one of the iodine.

01:54 T3 is important because it is so much more biologically active.

02:01 In fact it has a binding affinity for the hormone receptor 10 times that of T4.

02:09 The thyroid hormone receptor will then complex together and go into the nucleus binding to a thyroid nucleus response element, undergoing both than transcription and translation to make new proteins.

02:27 These new proteins are myriad of different functions.

02:32 Anything from the sodium-potassium-ATPase to enzymes involved with metabolism, to other things like myosin heavy chain that are involved in muscle, beta adrenergic receptors and many many others.

02:47 This up regulation of all of these processes you can think about, are driving the responses that we see with thyroid hormone physiological function.