Steroids Lecture 3

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SteroidsLecture 3

• Bile acids
• D Vitamins

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Bile acids

• Consist of
• Steroidal acid
• Amine containing compound

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Bile acids
Cholic acid R OH Chenodeoxycholic acid R
H
R
COOH
OH
HO
H
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Amino compounds

• Glycine
• H
• NH2 C COOH
• H
• Taurine
• NH2 CH2 CH2 SO3H

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Naming
Based on two constituents e.g. Taurine Cholic
acid Taurocholic acid
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Taurocholic acid
OH
C NH CH2 CH2 SO3H
O
Polar (Sulphonic acid)
HO
OH
H
Non-polar (especially ? face)
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Bile acids as surfactants
Typical surfactant structure (Polar and non-polar
parts to the molecule.) Physiological function
is to break up fat in the diet into finely
dispersed particles that are more accessible for
digestive enzymes.
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Entero-hepatic circulation
Bile salts in bile
Liver
Reabsorbed
Small intestine
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Colestyramine etc.
Anion exchange resins Bind to all acidic
molecules (inc. bile acids) Prevent re-absorption
re-use New bile acids have to be synthesised
from cholesterol Uses up the bodys cholesterol
reserves Lowers blood cholesterol levels e.g.
Colestyramine Colestipol
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Conversion of primary to secondary bile acids

• Gut bacteria
• 7?-Dehydroxylation
• Deconjugation

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OH
Deconjugated
C NH CH2 CH2 SO3H
O
7?-Dehydroxylated
HO
OH
OH
H
Taurocholic acid
C
OH
O
HO
H
Deoxycholic acid
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D Vitamins
Involved in the retention of Calcium in the body.
Lack causes calcium loss - weak, deformed bones
(Ricketts) Can be synthesised within the body or
obtained from the diet. Dietary sources may be
natural (e.g. Cod liver oil) or synthetic.
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Synthesis within the body(In vivo)
7-Dehydrocholesterol Cholecalciferol (Vit D3)
Ultraviolet
In skin. 7-Dehydrocholesterol is an intermediate
on the minor route to cholesterol Lack of sun
Lack of Vit D Vitamin supplementation
required
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Synthesis outside the body(In vitro)
Ergosterol (Plant sterol) Ergocalciferol
(Vitamin D2)
Ultraviolet
Industrial process.
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Ergocalciferol (Vitamin D2)
CH2
Bond broken by high energy of ultraviolet
HO
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Metabolism of D vitamins
Cholecalciferol (D3) 25-Hydroxy
D3 1?,25-Dihydroxy D3
Low activity
Liver
Main storage form Low activity
Kidneys
Highly active
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Control of blood calcium(Negative feedback loop)

Blood calcium
Calcium absorption and retention
Parathyroid hormone

1?-hydroxylation of Vitamin D

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Terms with which you should be familiar

• Bile acids
• Entero-Hepatic Circulation (EHC)
• Colestyramine
• Primary and Secondary bile acids
• D Vitamins

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What you should be able to do

• Describe the general structure of bile acids
• Name bile acid based on their structure
• Relate the function of bile acids to their
  structure
• Describe the EHC of bile acids
• Describe how drugs may be used to lower
  cholesterol levels by inhibiting the EHC of bile
  acids
• Describe the conversion of primary to secondary
  bile acids
• Describe the distinctive structural feature of D
  vitamins
• Distinguish between the in vivo and in vitro
  synthesis of D vitamins
• Describe the metabolism and biological role of D
  vitamins