slowed, as in between meals, the duodenal orifice of the duct is closed, causing the bile to Òback ups and eventually enter the gall- bladder where it is stored.Bile is formed by the liver cells (the liver cells are epithelial cells), and excreted into tiny bile canaliculi located between the cells. Bile does not enter the sinusoids. Instead, the canaliculi come together at the portal triad where the portal ductule is formed. These bile ductules coalesce as they approach the surface of the liver (near where the hepatic portal vein and the hepatic artery enter) to form the hepatic duct which emerges from the inferior surface of the liver.When food enters the duodenum, cholecystokinin is released from the intestinal mucosa which will cause gallbladder contraction, leading to the secretion of bile into the small intestine. Bile is an active emulsifying (suspension of fats) agent and thus plays a part in the digestion and absorp- tion of fat from the intestine.The second item to be considered is the production of plasma proteins. The liver playsan intricate role in the synthesis of these plasma proteins and is able to provide for an interconversion (i.e. converting one type of amino acid to another by the process of transamination) of amino acids which, you will recall, are the Òbuilding blocksÓ of protein structures. The source of the amino acids necessary for this plasma protein production are:1.metabolic turnover of proteins2.dietary proteins
3.glucose (glucogenic amino acids)Because proteins are stored for only limited periods of time, any imbalance between the amino acids required and those which are available is handled quite readily by the liverÕs amino acid interconversion capability.Two major categories of proteins produced by the liver are the albumins and the globulins. The albumins are large colloidal protein molecules which have an influenceon osmotic pressure, plasma volume and tissue fluid balance. The globulins are involved in many functions such as: the transport of several key substances (iron, copper, lipids); serving as a precursor to fibrin (fibrino- gen); serving as antibodies or immunoglobins (Gamma globulin, IgG, IgE, IgA, IgD, IgM).Furthermore, several proteins concerned with blood coagulation are produced by the liver, such as:1. Fibrinogen2. Prothrombin3.Factor VII4.Factor IX5.Factor XAnother function of the liver is detoxification. You will recall from an earlier pharmacology mini- course that in this process, which can manifest itself as either conjugation, oxidation, or reduction, the liver metabolizes the by-products of cellular metabolism and exogenous materials such as drugs. Of particular importance is the removal of ammonia which is toxic to the human organism. This ammonia is removedfrom amino acids via deamination and converted to a normally non- toxic material called urea. Urea, which has the following structure: is formed during a series of reactions called the urea cycle (Krebs-Henseleit cycle) and is excreted in the urine.
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- Fall '19
- hepatic portal vein