Production & Regulation Of Bile
PRODUCTION & REGULATION OF BILE
Introduction:
Major constituents:
- Bile salts – Mainly, taurcocholates & glycocholates)
- Bile pigments – bilirubin & biliverdin
- Lipids (cholesterol, lecithin, fatty acid, & triglycerides)
- Electrolytes – Na+, K+, Cl–, HCO3– and Ca++.
- “Golden yellow color” of bile –
- Glucuronides of bile pigments, bilirubin & biliverdin..
PRODUCTION:
- Small amount continuously synthesized in liver.
- Transferred to gallbladder through cystic duct.
- About 500 ml of bile is secreted/day (20.8 mL/hr) by liver.
Transport:
- Gallbladder stores & concentrates bile.
- After a meal contraction of gallbladder transfers large bile volume into duodenum.
- Most of bile reabsorbed in terminal ileum & undergoes enterohepatic circulation.
- Excreted back by liver.
Components:
1. Bile acids:
- Primary bile acids are synthesized from cholesterol in liver.
- About half of body cholesterol ultimately metabolized to bile acids.
- Important acids – Cholic acid & chenodeoxycholic acids.
- Rate limiting enzyme in primary bile acids synthesis –
- 7α – hydroxylase (cholesterol 7α – hydroxylase).
- Enzyme inhibited by bile acids & induced by cholesterol.
- Thyroid hormones induce transcription of 7a-hydroxylase.
- Hence, hypothyroidic patients, plasma cholesterol rises.
- Due to 7α-hydroxylase inhibition inturn inhibiting cholesterol conversion to bile acids.
2. Bile salts:
- Most important bile constituent.
- Are sodium & potassium salts of bile acids, conjugated to amino acids, glycine or taurine.
REGULATION OF BILIARY SECRETION:
Stimulating factors:
- Bile production increased by vagus nerve stimulation & by hormone secretin.
Secretion regulation:
- Food entering mouth decreases Sphincter of Oddi resistance under hormonal & neural influences.
- Fatty acids & amino acids in duodenum release CCK
- Inturn causes gallbaldder contraction.
- Bile entry into duodenum increases when,
- Liver cells increases bile secretion.
- Also when gallbladder pours out stored bile.
Cholerectics:
- Substances increasing hepatic bile secretion.
- Most important cholerectics are bile salts themselves.
- Also Secretin.
Cholagogues:
- Substances causing gallbladder contraction secreting bile.
- Most important cholagogue – Cholecystokinin (CCK).
- Fatty acids & amino acids in duodenum stimulate CCK release.
- Inturn causing gallbladder contraction.
Exam Question
PRODUCTION OF BILE:
Introduction:
- Bile salts – Mainly, taurcocholates & glycocholates)
- Bile pigments – bilirubin & biliverdin
- Glucuronides of bile pigments, bilirubin & biliverdin – “Golden yellow color”.
Synthesis:
- Small amount of bile is continuously synthesized in the liver.
- About 500 ml of bile is secreted per day (20.8 mL/hr) by liver.
Components:
1. Bile acids:
- Primary bile acids synthesized from cholesterol in liver.
- Important acids – Cholic acid & chenodeoxycholic acids.
- Rate limiting enzyme- 7α – hydroxylase (cholesterol 7α – hydroxylase).
2. Bile salts:
- Are sodium & potassium salts of bile acids, conjugated to amino acids, glycine or taurine.
REGULATION:
Stimulating factors:
- Bile production increased by vagus nerve stimulation & by hormone secretin.
Cholerectics:
- Substances increasing hepatic bile secretion.
- Most important cholerectics – Bile salts themselves.
- Others – Secretin
Cholagogues:
- Substances causing gallbladder contraction secreting bile.
- Most important cholagogue – Cholecystokinin (CCK).
- Fatty acids & amino acids in duodenum stimulates CCK release.
Don’t Forget to Solve all the previous Year Question asked on Production & Regulation Of Bile