Physiology
Gastrointestinal
About what percentage of bile acids undergo enterohepatic circulation:
Answer:
Of the bile acids excreted into the intestine, about 95% are reabsorbed into the portal circulation by active transport mechanisms in the distal ileum and recycled by the liver.Bile Acids
Physiology / Gastrointestinal / Liver and Gallbladder
Last Updated: 6th December 2020
Bile acids are detergents which emulsify lipids. They have a hydrophobic and a hydrophilic end and in aqueous solution, bile salts orient themselves around droplets of lipid forming micelles to keep the lipid droplets dispersed.
Production
Bile acids are synthesised from cholesterol by hepatocyte and excreted into bile. Synthesis of new bile acids occurs as needed to replace bile acids that are excreted in the faeces.
The principal primary bile acids are cholic acid and chenodeoxycholic acid. They are made more soluble by conjugation with taurine or glycine in the liver.
Enterohepatic Circulation
Of the bile acids excreted into the intestine, about 95% are reabsorbed into the portal circulation by active transport mechanisms in the distal ileum and recycled by the liver.
Many of the bile salts are reabsorbed unaltered, some are converted by intestinal bacteria into secondary bile acids (deoxycholic acid and lithocholic acid) and then reabsorbed and a small proportion escapes reabsorption and is excreted in the faeces.
Function
The main functions of bile acids are:
- Emulsification of lipids to increase the surface area available for digestion by pancreatic lipase
- Micelle formation to facilitate lipid transport and absorption
- Stimulation of bile production by osmotically attracting water and electrolytes into the bile canaliculi
- Regulation of bile acid synthesis via negative feedback
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
