Final answer:
Peptide hormones and catecholamines are water-soluble and circulate freely in blood plasma, while steroid and thyroid hormones are lipid-soluble and require carrier proteins such as albumin or binding globulins like TBG to be transported in the bloodstream.
Step-by-step explanation:
When being transported in the blood, peptide hormones and catecholamines are dissolved in plasma. In contrast, steroid hormones and thyroid hormones are bound to carrier proteins to remain soluble in the bloodstream. Peptide hormones and catecholamines are water-soluble, which means they can circulate freely in the blood without needing a carrier. On the other hand, steroid and thyroid hormones, which are hydrophobic and lipid-soluble, require special carrier proteins like albumin or specific binding globulins to be transported through the bloodstream.
These transport proteins, such as Thyroxine binding globulin (TBG) for thyroid hormones and various serum proteins for steroid hormones, play a critical role in the circulation and regulation of these hormones, ensuring that they reach their target cells effectively.