The Functions of the Liver 5 CEU S / PDA s in Biomedical Science

Transcription

1 The Functions of the Liver 5 CEU S / PDA s in Biomedical Science OPTIONS FOR WELLNESS, INC SW 53 LN MIAMI, FL fax CEU PROVIDER Florida Board of Acupuncture NCCAOM ACHB-038 CALIFORNIA CEP 722

2 The liver is the largest glandular organ in the body and performs many vital functions to keep the body pure of toxins and harmful substances. The liver is located in the upper right-hand portion of the abdominal cavity, just inferior to the diaphragm and on top of the stomach, right kidney, and intestines. The gall bladder is attached to the lower portion of the right side of the liver. The liver is considered a gland because it is an organ that makes and secretes bile, a substance that aids in digestion and transports fats and waste products to the intestines. Bile s salts break up fat into smaller pieces so it can be absorbed more easily in the small intestine. The liver, along with parts of the pancreas and intestines, work together to digest, absorb, and process food. An average adult liver is roughly 2% of body weight, or about 3 lbs for a 150 lb adult. It consists of very soft, pinkish-brown tissues and is encapsulated by a connective tissue capsule. This capsule is further covered and reinforced by the peritoneum of the abdominal cavity, which protects the liver and holds it in place within the abdomen. The peritoneum connects the liver in 4 locations: the coronary ligament, the left and right triangular ligaments, and the falciform ligament. These connections are not true ligaments in the anatomical sense. They are condensed regions of peritoneal membrane that support the liver. The wide coronary ligament connects the central superior portion of the liver to the diaphragm. Located on the lateral borders of the left and right lobes, respectively, the left and right triangular ligaments connect the superior ends of the liver to the diaphragm. The falciform ligament runs inferiorly from the diaphragm across the anterior edge of the liver to its inferior border. At the inferior end of the liver, the falciform ligament forms the round ligament (ligamentum teres) of the liver and connects the liver to the umbilicus. The round ligament is a remnant of the umbilical vein that carries blood into the body during fetal development.

3 The Liver can be divided into two parts or sections right and left lobes with 8 independent segments (each having its own blood supply and biliary drainage. The left and right lobes are the largest lobes and are separated by the falciform ligament. The right lobe is about 5 to 6 times larger than the tapered left lobe. The left lobe of the liver is the smaller and flatter of the two liver lobes.

4 Below is a diagram of the two lobes and 8 segments. Segments I- IV make up the left lobe and V-VIII make up the right lobe The liver's main job is to filter the blood coming from the digestive tract, before passing it to the rest of the body. It also detoxifies chemicals and metabolizes drugs ( and herbs). The liver also makes the proteins important for blood clotting and other functions. The blood supply of the liver is unique among all organs of the body due to the hepatic portal vein system. Blood traveling to the spleen, stomach, pancreas, gallbladder, and intestines passes through capillaries in these organs and is collected into the hepatic portal vein. The hepatic portal vein then delivers this blood to the tissues of the liver where the contents of the blood are divided up into smaller vessels and processed before being passed on to the rest of the body. Blood leaving the tissues of the liver collects into the hepatic veins that lead to the vena cava and return to the heart. The liver also has its own system of arteries and arterioles that provide oxygenated blood to its tissues just like any other organ. The hepatic portal vein has a number of branches. It carries blood from networks in the stomach, intestines, pancreas, and spleen to the liver. There, the vein branches out similar

5 to an artery and the blood enters capillary-like hepatic sinusoids. After passing through the portal veins of the liver, blood is carried through a series of merging vessels into the hepatic veins. These empty into the inferior vena cava, and return the blood into circulation. The branch of the hepatic artery supplies oxygen-rich blood to the liver, the duodenum, the pylorus, and the pancreas. The internal structure of the liver is made of around 100,000 small hexagonal functional units known as lobules. Each lobule consists of a central vein surrounded by 6 hepatic portal veins and 6 hepatic arteries. These blood vessels are connected by many capillary-like tubes called sinusoids, which extend from the portal veins and arteries to meet the central vein like spokes on a wheel. Each sinusoid passes through liver tissue containing 2 main cell types: Kupffer cells and hepatocytes. Kupffer cells are a type of macrophage that capture and break down old, worn out red blood cells passing through the sinusoids. Hepatocytes are cuboidal epithelial cells that line the sinusoids and make up the majority of cells in the liver. Hepatocytes perform most of the liver s functions metabolism, storage, digestion, and bile production. Tiny bile collection vessels known as bile canaliculi run parallel to the sinusoids on the other side of the hepatocytes and drain into the bile ducts of the liver. The liver receives about 1.5 quarts of blood every minute via the hepatic artery and portal vein.

6 The biliary tree is the common anatomic term for the path by which bile is secreted by the liver on its way to the duodenum, or small intestine. It is referred to as a tree because it begins with many small branches which end in the common bile duct, sometimes referred to as the trunk of the biliary tree. The Gall bladder stores the bile that is produced by the liver and it is drained by the biliary tree, regulating the delivery of bile into the intestines. The liver performs many essential functions related to digestion, metabolism, immunity, and the storage of nutrients within the body. These functions make the liver a vital organ without which the tissues of the body would quickly die from lack of energy and nutrients. Without a healthy liver, a person cannot survive. Fortunately, the liver has a remarkable capacity to regenerate very quickly, replacing damaged tissue and restoring normal size and function. The liver has well over 500 functions. Listed below are some of the important functions of the liver:

7 ! Provides immunity against infection. The liver s lymphocyte population is selectively enriched in natural killer T cells which play critical roles in the first line immune defense against invading pathogens.! Produces bile Bile describes the fluid produced in the liver that contains water, electrolytes and organic molecules including the bile acids, cholesterol, fats and bilirubin the waste product produced by the breakdown of old red blood cells. The liver uses cholesterol to produce two main bile acids: cholic acid and chenodeoxycholic acid. When the bile acids combine with the amino acids glycine or taurine, they form the bile salts. Because bile salts contain a fatsoluble portion and a water-soluble portion, they cause the fat globules to break down into tiny droplets that allow the lipase enzyme to access and break down the fat. Converts essential fatty acids such as GLA, EPA, and DHA into the lipoprotein forms necessary to allow transport via the bloodstream to the 50 trillion cells requiring fatty acids.! Detoxifies the blood to rid it of harmful substances such as alcohol, drugs, and chemicals The liver must try to cope with every toxic chemical in our environment, as well as damaged fats that are present in processed and fried foods. Substances like pesticides, growth hormones given to farm animals for slaughter, metabolic waste, drugs, alcohol and so many other chemicals, so that they can be excreted. These are sometimes referred to as xenobiotic chemicals. Under a microscope, rows of liver cells separated by spaces which act like a filter or sieve, through which the bloodstream flows can be seen. The liver filter is designed to remove toxic matter such as dead cells, microorganisms, chemicals, drugs and particulate debris from the bloodstream. The liver filter is called the sinusoidal system, and contains specialized cells known as Kupffer cells which ingest and break down toxic matter. Main poison-detoxifying organ in the body. The liver must break down every substance toxic to the body including metabolic wastes, insecticide and pesticide residues, drugs, alcohol, etc. Failure of this function will usually cause death in 12 to 24 hours.

8 ! Stores some vitamins and minerals Activates B vitamins into their biologically active coenzyme forms. Virtually every nutrient must be bio-transformed by the liver into its proper biochemical form before the nutrient can be stored, transported or used in cellular metabolism. Stores various nutrients, especially A, D, B-12 and copper, folate, and iron for release as needed.! Stores the simple sugar glucose Converts stored sugar to usable sugar when the body s glucose levels fall below normal. The liver is essential for monitoring and maintaining a relatively constant level of glucose in the bloodstream. Conditions leading to glucose concentrations being too high or too low are dangerous. The liver is involved in gluconeogenesis in the Cori cycle and is involved in glycogen breakdown and synthesis because these pathways allow the liver to remove glucose from the bloodstream for glycogen synthesis when blood glucose is high and to release glucose into the bloodstream from glycogen breakdown when blood glucose levels are too low. The enzyme glucose-6-phosphatase (G6Pase) catalyzes the last step of gluconeogenesis - conversion of G6P to glucose + phosphate. This enzyme is necessary also for release of glucose into

9 the bloodstream from glycogen metabolism (glycogen -> G1P -> G6P -> Glucose). It is interesting to note that G6Pase is ABSENT FROM MUSCLE. This is because muscle does NOT export glucose. The liver has abundant supplies of this enzyme. It converts and stores extra sugar (glucose) in the form of starch (glycogen) which can be used in times of starvation.! Breaks down insulin and other hormones Breaks down hormones after they have served their function. i.e., if the liver does not break down insulin fast enough, hypoglycemia results because the circulating insulin continues to lower blood sugar. Creates GTF (Glucose Tolerance Factor) from chromium, niacin and possibly glutathione. GTF is needed for the hormone insulin to properly regulate blood-sugar levels. Manufactures bile salts which emulsify fats and the fat-soluble vitamins A, D, E, and K for proper absorption. The liver also removes some fat-soluble toxins from the body. Converts the thyroid hormone thyroxine (T4) into it more active form triiodothyronine (T3). Breaks down and eliminates excess hormones. The liver is also responsible fore producing cholesterol. It produces about 80% of the cholesterol in your body.! Converts ammonia to urea, vital to metabolism Removes ammonia, a toxic by-product of protein metabolism, from the body. The ammonia is absorbed into the portal circulation, taken up by the liver and converted in the liver, via the urea cycle, into urea. Urea is then excreted into the gastrointestinal system (producing a futile cycle) and into the urine. Ammonia is toxic to the CNS (Central Nervous System) and is one of the causes of hepatic encephalopathy! Destroys old red blood cells The destruction of old red blood cells produces waste that gives fecal matter its brown color. When red cells reach the end of their life due to aging or defects, they are broken down by the liver, the hemoglobin molecule is broken up and the iron gets recycled. The red blood cell are first broken up into components by the spleen. It's released from the spleen as "unconjugated" bilirubin into the blood, where it circulates in the blood bound to albumin. The liver efficiently takes up bilirubin and chemically modifies it to "conjugated," or water-soluble, bilirubin that can be excreted into bile.

10 The liver regulates clotting of blood by manufacturing vital proteins Because the liver performs so many vital functions, it is prone to disease. Common liver diseases include hepatitis infection, fatty liver disease, cancer, damage from alcohol abuse, acetaminophen, and drugs. Cirrhosis of the liver occurs when the organ becomes scarred and hardened so that it cannot function properly. This is most often caused by chronic liver disease brought on by long-term alcohol abuse or hepatitis C infection. Many people with liver damage have NO symptoms. Sudden damage can come from an acute (recent or sudden) infection or exposure to toxins. The damage can also build up slowly over time from continued exposure to viruses, parasites, alcohol, or toxins. When symptoms of liver disease appear, they are signs that the liver is not performing one or more of its functions. Early symptoms may include: Nausea, vomiting, fatigue (tiredness), and weight loss. Later symptoms may include: Jaundice, Slow blood clotting, confusion (encephalopathy), sking changes (itching, red palms and face), decreased red blood cells, bleeding in the stomach or throat, Ascites, High blood sugar and hormone imbalances.

11 With a healthy liver, all functions will remain normal even if 70% is removed. The liver is the only organ in the body that can regenerate itself after large portions of it are removed. Small remnants of liver grow back to normal size within a few weeks. These are the many tests that may be used to check the condition of the liver. Blood Tests: Liver function panel: checks how well the liver is functioning This Liver Function Panel (Hepatic Function) includes the following tests: 1. Total Protein 2. Albumin 3. Total Bilirubin 4. Direct Bilirubin 5. Alkaline Phosphatase 6. AST 7. ALT

12 Hepatitis A,B,C tests: If hepatitis is suspected Prothrombin Time (PT): commonly done to see if someone is taking the correct dose of the blood thinner warfarin (Coumadin). It also checks for blood clotting problems. Partial Thromboplastin Time (PTT): check for blood clotting problems. Imaging Tests: Ultrasound: An abdominal ultrasound can test for many liver conditions, including cancer, cirrhosis, or problems from gallstones. CT scan (computed tomography): detailed pictures of the liver and other abdominal organs. Liver biopsy: commonly done after another test, such as a blood test or ultrasound, indicates a possible liver problem. Liver and spleen scan: This nuclear scan uses radioactive material to help diagnose a number of conditions, including abscesses, tumors, and other liver function problems.