2. • Steroidal compounds are widely found in
animal and plant tissues and play an
important role in life activities of animals
and plants.
3. 1 The basic structure of steroids
• Steroid molecules contain a four-ring carbon skeleton called steroidal
nucleus. The ring generally has three side chains and its structure as below:
• R1, R2 are typically referred to as methylol, and R3 is other substituents
containing different numbers of carbon atoms. Apart from these three side
chains, many steroid nucleus also have double bonds, hydroxyl and other
substituents.
4. 2 Important steroids
• 2.1 Cholesterol
• Cholesterol is one of the earliest
discovered steroid compounds in human,
animal blood, fat, brain and nerve tissues.
Cholesteryl benzoate as below:
5. • Cholesterol is colorless or slightly yellow crystals. m.p 148.5 °C. It can be
sublimated at high vacuum. slightly soluble in water, soluble in ethanol, ethyl
ether, chloroform, organic solvents. Gallstones found in human body is
almost composed of cholesterol, that’s where the name derived from.
• Cholesterol can be enzymatically catalyzed to 7-dehydrocholesterol. 7-
Dehydrocholesterol present in the skin tissue and undergoes chemical
reaction and convert to vitamin D3 under sunlight. Vitamin D3 is a key
compound in the absorption of Ca2 + from the small intestine. If the
concentration of vitamin D3 is too low, which will lead to Ca2 + ion
deficiency, and can not to maintain the normal bone formation and result in
rickets.
6. 2.2 Ergosterol
• Ergosterol is a phytosterol, which originally obtained from ergot and more
readily available in yeast. In sunlight exposure, the B ring of ergosterol
stucture open loop to form re-calcified alcohol, and re-calcified alcohol
revert to vitamin D2 (ie calcified alcohol) after heating.
• Like vitamin D3, Vitamin D2 is also resistant to rickets. so ergosterol can be
added to milk and other foods when irradiated with UV light to ensure that
children obtain enough vitamin D.
7. 2.3 Bile acid
• Bile acids exist in bile of animals, and the
bile acids isolated from human bovine and
cattle bovine mainly are bile acids. Cholic
acid is an oil emulsifier, whose
physiological function is to emulsify the fat
and promote its hydrolysis and absorption
in the intestine. So bile acid is called
"animal soap."
8. 3 Steroid hormones
• Steroid hormone is a class of physiologically active compounds secreted by
various endocrine glands in animal body, which can directly enter the blood
or lymph and circulate to different tissues and organs in the body and play
an important role in various physiological and coordinating functions in
metabolic processes. Hormones can be divided into two broad categories
based on their different chemical structures: one is an N-containing
hormone, which includes amines, amino acids, peptides, and proteins; and
the other is steroids. And steroid hormones also can be classified into
adrenal hormones and sex hormones according to their origin. Their
structural feature is the absence of long carbon chains on C17 (R3).
9. 2.4.1 Sex hormones
• Sex hormones are secretions of gonads of higher animals that can control
sexual physiology, promote animal development, and maintain the
secondary sexual characteristics (such as sound, body shape, etc.). Their
physiological effect is very strong, even very small amount of them can
have a tremendous impact.
• Estradiol is secretions of ovary, which plays a major role in the development
of secondary sexual characteristics of females. The amount of testosterone
and estradiol secreted by animals is extremely low. For the purpose of
scientific research, only 0.012 g of estradiol is extracted from 4 tons of
porcine ovary.
• Norethindrone is a synthetic oral contraceptive for women, which plays an
important role in family planning.
10. 2.4.2 Cortina
• The Cortina is hormone secreted by the
mammalian adrenal cortex. The important
functions of corticosteroids is to maintain
the electrolyte balance of body fluids and
to control carbohydrate metabolism.
Cortina deficiency in animals body can
cause malfunction even death. Cortisol,
cortisone, corticosterone are all such
important hormones.
