Malabsorption of FAT

Malabsorption of FAT

1. Nutritional importance of dietary lipids

   • Vitamin A D E K
     • Fat soluble vitamins are absorbed by fat globules (chylomicrons) and travel in the lymphatic system into the SI and blood
       • Difficult to excrete as they are stored in fat
         • This can lead to a dangerous condition called hypervitaminosis (toxic symptoms)
     • Vitamin A - Deficiency will cause corneal degeneration and blindness
     • Vitamin D: Deficiency will cause osteomalacia/ rickets
       • Vitamin D2/D3 is taken to the liver where is is converted to 25-hydroxyvitamin-D. Then in the kidneys it is converted to 1,25 dihyroxyvitamin D. This is involved in the regulation of calcium and phosphorus levels. It does this by switching on gene transcription factors
       • Vitamin D2: Acquired from foods Vitamin D3: Produced from 7-dehydrocholesterol in the skin under UV
         • However both can still be produced synthetically and put in supplements
       • Vitamin D2/D3 is taken to the liver where is is converted to 25-hydroxyvitamin-D. Then in the kidneys it is converted to 1,25 dihyroxyvitamin D. This is involved in the regulation of calcium and phosphorus levels. It does this by switching on gene transcription factors
     • Vitamin E: Deficiency can cause infertility
       • An antioxidant
     • Vitamin K: Deficiency will cause reduced blood clotting and can lead to acquired haemophilia
       • Vitamin K forms Gla residues by carboxylation which are needed for blood coagulation and bone
       • Bacteria in the colon make it and also in some foods
   • Essential fatty acids that our body doesn't make
     • Omega 3 & 6

2. Liver Disease

   • Causes
     • Cirrhosis
       • Alcohol abuse
       • Hepatitis C
       • Non-alcoholic steatohepatitis (NASH) that causes excess fat to build up in the liver, this is due to obesity
     • Haemochromatosis causes increased iron absroption in body (toxic)
   • Bile acids synthesized in liver
     • Bile consists of bile acids (for breaking down fat) and bilirubin (waste product for excretion)
     • Allows emuslification of fat due to its detergant properties, it also allow transportation of fat by making it water soluble by forming micelles
     • Bile secreted by hepatocytes into canaliculi which drain into bile ducts
     • The hepatic artery provides oxygentated blood for the liver and the hepatic portal vein provides most of the blood - it contaions all the absorbed products from the GI tract
       • The venous blood drains into sinusoids which contain Kupffer cells, these are macrophages that break down any pathogens that entered in the GI
         • The area between synusoid and hepatocytes in called the space of Disse, here the plasma is filtered by the microvilli of hepatocytes which contain enzymes
         • Stellate cells are also found in the spaces of Disse, these are responsible for producing scar tissue which leads to fibrosis due to liver damage

3. Pancreatic disease

   • Produces pancreatic lipase which is the main digester of fat
     • Needs colipase for optimal activity
       • Secreted by pancreas as the zymogen procolipase
         • The zymogen is activated by tripsin
           • The zymogen tripsinogen is activated to tripsin by the enzyme enteropeptidase which is produced by the duodenum and secreted from the crypts of Lieberkühn
         • CCK stimulates acinar cells to produce zymogens
     • Pancreas secretes lipase as a functioning enzyme not a zymogen
     • Needs correct pH (7.5 – 8)
     • Orlistat given to bind to lipase to prevent triglyceride breakdown to induce weight loss
   • Causes
     • Pancreatitis
       • Cystic Fibrosis
         • Mucus secreted blocks pancreas ducts so enzyme cannot be released leading to pancreatic insufficiency
           • Also produces thick mucus in the lungs
       • Alcohol Induced
       • Gall stones
         • ERCP

4. Intestinal Disease

   • Crohn's Disease
     • Strictures and Fistulas
     • Inflammation of ileum and colon
   • Coeliac disease
     • Autoimmune condition where body treats gluten as a foreign body
       • Microvilli are damaged which reduces absorption
         • Villi shortened and flattened
   • Zollinger-Ellison syndrome
     • Tumour at the head of the pancreas causing excess secretion of gastrin causing stomach and duodenum ulcers
   • TB
   • Terminal ileal disease so less bile acids to create emulsifcation

5. Patient complains of weight loss and diarrhoea. He presents with pale bulky stools and analysis indicates faecal fatty acid exceeding 7g indicating clinical steotorrhoea

6. Obstruction in lymph

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