The Functions of the Liver
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H.4.1 Outline the circulation of blood through the liver tissue including hepatic artery, hepatic portal vein, sinusoids and hepatic vein.

            Blood full of just digested nutrients from the intestine and the stomach enter the liver via the hepatic portal vein.  This is located in the cartilage in the liver, between the lobules.  Also in this area is the hepatic artery, where a branch of the aorta is with oxygenated blood.  The hepatic artery serves as the source of oxygen and nutrients for the liver tissue.  These two, the hepatic portal vein and the hepatic artery, sources of blood then go through the liver lobules through spaces called sinusoids.  This allows for very close contact of blood with the surrounding tissue.  The cells then are capable of removing substances, such as oxygen or excess nutrients from hepatic portal vein, or toxins, before the blood leaves via the hepatic vein.  The hepatic vein then circulates back towards the heart.  The liver in this way is capable of acting as a ‘filter’ of the blood.

H.4.2 Explain the need for the liver to regulate levels of nutrients in the blood.

            In mammals, whatever is eaten and digested is capable of entering the blood.  This could have very harmful effects because some of the substances could be toxic.  Also, for nutrients like glucose, there is a need for an organ to maintain a certain level of it in the blood, so that homeostasis is maintained. 

H.4.3 Outline the role of the liver in the storage of nutrients including carbohydrate, iron, the vitamins retinol and calciferol.

            The liver cells because of their constant exposure to a high concentration of nutrients are capable of storing nutrients more than other cells.  They store carbohydrates (conversion of glucose to glycogen), iron, and vitamins A and D (retinol and calciferol).  They do this because when these nutrients are digested, they are very useful to the body and so cannot be wasted through excretion.  Thus, the liver cells store them as accessible substances when the body lacks them.

H.4.4 Describe the process of bile secretion.

            Bile is produced and secreted by the liver.  It is an alkaline, mucous fluid containing bile pigments (which are excretory products formed from the breakdown of haemoglobin from worn-out red blood cells) biliverdine and bilirubin.  Bile also contains bile salts which are sodium glycocholate and sodium taurocholate which are reclaimed by the liver from the blood.  These salts are reused in lipid absorption.  Bile pigments and salts are produced by the liver cells and then secreted into bile canaliculus (small spaces in the membranes of the hepatocytes), and it make s its way to the bile duct.  The bile duct then transports the bile to the gall bladder, where it is released by muscular contractions into the duodenum, under the control of hormones involved in digestion. 

H.4.5 Describe the process of erythrocyte and haemoglobin breakdown in the liver including phagocytosis, digestion of globin, and bile pigment formation.

            Red blood cells that have reached the end of their lives are engulfed by Phagocytic cells called Kupffer cells which line the sinusoids.  These cells break down the haemoglobin part of the blood cell.  The protein part (the globin) is converted back into the amino acids which make it up, and these amino acids are then released into the bloodstream.  The non-protein part (the haem residue) has the iron removed and stored.  The rest of it is known as a system of pyrrole rings, is converted into bile pigments.  (Note:  an erythrocyte is a red blood cell).

H.4.6 Outline the synthesis of plasma proteins by the liver. 

            The liver is the site of the de-amination of excess amino acids, and also the site of the synthesis of proteins of the blood plasma.  These proteins are blood-clotting agents prothrombin and fibrin, and plasma albumin and globulin, which includes the antibodies.  The liver cells break down amino acids and other nutrients which then constitute the blood proteins. 

Other Notes in this Category

1. Gas Exchange
2. Homeostasis Basics
3. The Functions of the Liver
4. Transport

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