Which of the following hormones travel readily in the bloodstream unbound to a carrier protein?

Question

 

Which of the following hormones travel readily in the bloodstream unbound to a carrier protein?

A.  Aldosterone

B.  Cortisol

C.  Estrogen

D.  Oxytocin

Answer 1

Correct Answer: D

Explanation :

Oxytocin is a peptide hormone that is soluble in water and therefore does not require a carrier protein while traveling in the bloodstream.

 

Hormones travel through the blood’s water-based plasma either as free unbound chemicals or bound chemicals attached to plasma protein carriers. Steroid hormones are non-polar molecules that exhibit hydrophobic properties and are therefore insoluble in the blood’s water-based plasma. Lipid derived steroid hormones must travel through the blood’s water-based plasma bound to plasma carrier proteins.

 

Nonsteroid hormones are polar and therefore hydrophilic, water soluble molecules that travel readily in the bloodstream’s water-based plasma free and unbound to transport proteins. The hydrophilic nature of nonsteroid hormones allows them to travel freely through the blood’s water-based plasma.

LIST OF NONSTEROID GLYCOPROTEIN HORMONES THAT TRAVEL READILY IN THE BLOODSTREAM →UNBOUND TO TRANSPORT PROTEINS

SITE OF RELEASE

1. Follicle-stimulating hormone (FSH)

Anterior pituitary (adenohypophysis)

1. Luteinizing hormone (LH)

Anterior pituitary (adenohypophysis)

1. Thyroid stimulating hormone (TSH)

Anterior pituitary (adenohypophysis)

LIST OF NONSTEROID PEPTIDE HORMONES THAT TRAVEL READILY IN THE BLOODSTREAM UNBOUND TO TRANSPORT PROTEINS

SITE OF RELEASE

1. Glucagon

Alpha cells of pancreas

1. Insulin

Beta cells of pancreas

1. Human growth hormone (HGH or GH)

Anterior pituitary (adenohypophysis)

1. Calcitonin

Parafollicular C-cells of the thyroid gland

1. Parathyroid hormone

Chief cells of the parathyroid gland

1. Adrenocorticotropic hormone (ACTH)

Anterior pituitary (adenohypophysis)

1. Melanocyte stimulating hormone (MSH)

Anterior pituitary (adenohypophysis)

1. Prolactin

Anterior pituitary (adenohypophysis)

1. Antidiuretic hormone (ADH or vasopressin)

Posterior pituitary (neurohypophysis)

LIST OF LIPID-DERIVED STEROID HORMONES THAT TRAVEL THE BLOODSTREAM BOUND TO TRANSPORT PROTEINS

SITE OF RELEASE

1. Aldosterone

Zona glomerulosa of adrenal cortex

1. Cortisol

Zona fasciculata of the adrenal cortex

1. Testosterone

Leydig cells of testes

1. Estrogen

Ovaries

Illustration demonstrating hormone transport in the blood. 

 

(Choice A) Lipid derived steroid hormones like aldosterone must travel to their target cell bound to a transport protein.

(Choice B) Cortisol is a steroid hormone that must travel in the bloodstream bound to a transport protein. 

(Choice C) Like all lipid-derived, steroid hormones, estrogen must travel in the bloodstream bound to a carrier protein.

Educational objective:



Hormones travel through the blood’s water-based plasma either as free unbound chemicals or bound chemicals attached to plasma protein carriers. Hydrophilic hormones travel as free unbound chemicals, while hydrophobic hormones travel as bound chemicals attached to plasma protein carriers.