Steroids and hormones

What is a hormone?

A signalling molecule that regulates physiology and behaviour in organisms.

What is a steroid?

A class of compounds defined by a structure of 17 carbon atoms arranged in four rings.

What is a steroid hormone?

A hormone that has the characteristic 17-carbon, four ring steroid structure.

What is negative feedback?

A control mechanism where the output of a process reduces or inhibits its own production.

What is positive feedback?

A mechanism where the output enhances or amplifies the process (e.g uterine contractions)

Name the main classes of hormones

Steroids, proteins/peptides, amino acid derivatives, eicosanoids.

Give examples of peptide hormones.

Insulin, glucagon, oxytocin

Give examples of amino acid-derived hormones.

norepinephrine, melatonin, thyroxine

What is endocrine signalling?

Hormones travel through the bloodstream to act on distant cells

What is paracrine signalling?

Hormones act on nearby cells

What is autocrine signalling?

Hormones act on the cell that secreted them

What is intracrine signalling?

Hormones act within the cell that produced them.

How many rings do steroids have and what are they called?

Four rings: A,B,C, and D

What is the gonane skeleton?

The core steroid structure that forms the basis of all steroids.

Why do small changes to steroid structure matter?

Minor modifications can cause large changes in biological activity.

What is a sterol?

A subgroup of steroids that includes. Cholesterol.

What percentage of the cel membrane is cholestrol?

30%

What re the key functions of cholesterol?

• modulates membrane fluidity

• Precursor for steroid hormones

• Precursor for vitamin D and bile acids

Why can steroid hormones cross cell membranes?

They are lipophilic and membrane-permeable

Why can’t peptide hormones cross cell membranes?

They are hydrophilic and membrane-impermeable

What do glucocorticoid receptors do?

They act as transcription factors when activated by hormone binding

What is transcription?

The process of making an mRNA copy of gene’s DNA sequence

What are corticosteroids?

Tetris hormones produced in the adrenal gland

What do glucocorticoids regulate?

metabolism of carbohydrates, fats, and proteins(e.g cortisol)

What do mineralocorticoids regulate?

Electrolyte balance via io transport in the kidneys (e.g. aldosterone)

Main natural sex hormones

Androgens-testosterone

Estrogens-estradiol

Progestogens-progesterone

Examples of synthetic progestogens

Levonorgestrel, norethisteroe, desogestrel