Hormone Delivery and Effectiveness at the Target

How do most amine hormones circulate in the bloodstream?

They circulate freely in the blood plasma.

Why do steroid and thyroid hormones have low concentrations in plasma?

They do not dissolve well in plasma.

What is the fate of small peptide hormones in the bloodstream?

They dissolve easily in plasma but have short half-lives due to rapid clearance by proteolytic enzymes and renal filtration.

What is the role of carrier proteins in hormone transport?

They increase total hormone concentration in blood plasma and prolong the half-life of hormones.

What is the significance of free hormones in the bloodstream?

Only free hormones can exit the bloodstream and reach target cells; bound hormones cannot.

What are the two types of binding proteins for hormones?

Nonspecific binding proteins (like albumins) and specific binding proteins (like SHBG and TBG).

What is the function of sex hormone binding globulin (SHBG)?

It binds male and female sex steroids.

How do thyroid hormone binding globulin (TBG) and androgen binding protein (ABP) function?

TBG binds thyroid hormones, while ABP concentrates testosterone for sperm production in the testes.

What factors can alter hormone effectiveness at target cells?

Up-regulation, down-regulation, and the presence of other hormones (agonists and antagonists).

What are agonist hormones?

Hormones that enhance the effects of another hormone on a target cell.

What are the two types of antagonists?

Competitive antagonists and noncompetitive antagonists.

What is desensitization in the context of hormone action?

It is when target cells become unresponsive to excessive or prolonged hormone stimulation.

What determines the effectiveness of a hormone?

The amount of hormone secreted, delivery rate, potency at target cells, and rate of clearance.

How are protein and peptide hormones degraded?

They are degraded by proteases into amino acids or smaller peptide fragments.

What happens to amine hormones in the body?

They are degraded by enzymes primarily located in target cells and then excreted by the kidneys.

How are thyroid hormones metabolized?

They are degraded by deiodinase enzymes that remove iodine before excretion.

What modifications can steroid hormones undergo?

They can be modified or conjugated to glucuronides or sulfates to increase water solubility for excretion.

What is the effect of altering hormone structure on potency?

Chemical modifications can either increase or decrease a hormone's affinity for its receptors.

What is up-regulation in hormone action?

An increase in receptor number, making the cell more sensitive to the hormone.

What is down-regulation in hormone action?

A decrease in receptor number, making the cell less sensitive to the hormone.

What are competitive agonists?

Agonists that bind to the same receptor site as the hormone, enhancing its effects.

What are permissive effects in hormone action?

When one hormone prepares the cell to respond more strongly to a second hormone.

What is the fate of hormones in the body?

They must be removed or degraded to terminate their action, often metabolized in the liver or kidneys.

What enzymes are involved in the degradation of peptides and proteins?

Proteases and peptidases.

What enzymes degrade amine hormones?

Monoamine oxidase (MAO) enzymes.

What enzymes are involved in the degradation of steroids?

Hydroxysteroid dehydrogenase (HSDH), reductases, sulfotransferases, and glucuronidases.

What is the role of deiodinases in thyroid hormone metabolism?

They remove iodine from thyroid hormones, leading to inactive forms.