10. The liver and the kidneys
Contents of the chapter
10.1 The liver
The liver is our largest internal organ and our largest gland. It weighs 1.5 kilograms. It is located under the ribs in the upper abdominal cavity, below the diaphragm.
The liver is a chemical processing factory. It produces bile, which contributes towards the digestion of lipids (fats and oil) and gets rid of toxins. Liver also converts sugars, stores and releases them when needed, thereby regulating the blood sugar level.
The liver converts nitrogenous breakdown products of proteins into urea, which is carried by the blood to the kidneys.
The liver produces blood during fetal development and acts as a blood recycler during adulthood.
10.2 The kidneys
The bean-shaped kidneys are located at the bottom of your ribcage and towards the back of your body on both sides of the spine. They weigh a total of 300 grams.
The kidneys are protected by the ribs and the back muscles. The main function of the kidneys is to filter your blood in order to remove excess water and waste products, which are secreted from your kidneys in the form of urea. The kidney also functions to keep the composition of blood constant.
The urea is filtered through minute filtration units known as nephrons.
Nephrons filter water, salts and other substances out of your blood and then reabsorb some of them back into your blood. This keeps your blood composition constant. Excess water and waste products are secreted in the form of urine.
Liver and kidney interactions keep our vital signs stable.
The kidneys can be seriously damaged by drugs, alcohol, fungicides, and the hepatitis A virus. A person can survive with one kidney, but not without a liver.
The woman holds the kidney model in its correct place.
10.3. The liver and substance production
The liver produces a variety of substances: these include bile fluid, blood coagulation factors, and proteins such as fibrinogen and albumin. Cholesterol is synthesised by the liver in addition to ketones, which the body can use as an energy source, for example, during prolonged fasting.
The bile produced by the liver is particularly important for digestion. Bile is stored in the gall bladder, from which it is transported, if necessary, to the first section of the small intestine called duodenum. The bile breaks down and absorbs fats to facilitate the digestion of the enzymes secreted by the pancreas.
| Function | Examples |
|---|---|
| Preparation of bile fluid | Bile contributes to the breakdown of lipids (fats) in small intestine. |
| Detoxification | The modified substances pass through the gallbladder into the intestine. |
| Removing damaged red blood cells | Bilirubin pigment is made. |
| Storage | The liver stores glucose, blood, iron, as well as vitamins A and B12. |
| Energy release | Releases glucose when necessary. |
| Producing other substances | Albumin is a protein in the blood which binds water. Fibrinogen is needed for blood clotting. Cholesterol is needed for e.g. cell membranes. |
| Pathogen destruction | Destroying microbes and cell debris. |
10.4 The liver's role as the regulator of substances
The liver is the central laboratory of the body. It stores, produces, breaks down and releases several substances into the bloodstream. These substances are vital to the functions of the body.
Up to 1,5 litres of blood flow through the liver each minute. Much of this blood comes from the digestive system, as all the nutrients absorbed there have to pass through the liver.
The liver also stores various substances, such as excess sugar. If your blood sugar falls, your liver releases glucose into the bloodstream. This is especially important for brain function, because the brain is rich in nerve cells that depend on glucose as their main source of energy.
The liver also absorbs glucose from the blood and transforms it into fatty acids. These fatty acids are stored in the form of body fat. The liver is also able to store some vitamins and iron.
The liver also regulates the amount of amino acids in the blood. It breaks down the amino acid parts of unnecessary proteins, and converts the toxic ammonia produced during this process into urea. The urea then passes through the bloodstream to the kidneys and is eliminated from the body in the urine.
10.5 The liver and harmful substances
The liver breaks down, deactivates and removes toxic substances that we may have ingested. These substances include things such as food additives, harmful minerals, toxic pharmaceuticals, alcohol and excess hormones.
However, fat can accumulate in the liver, which is detrimental to its function. A fatty liver occurs when too much fat builds up in liver cells. Lifestyle changes can help reverse fatty liver disease, but the liver cells can also sometimes be destroyed permanently.
The liver is also able to remove germs and break down harmful substances from blood. Hazardous substances in the liver are eliminated from the body with the help of bile. Other substances can be converted into a water-soluble form, which makes it possible for them to be removed from the body alongside urine.
However, not all toxic substances can be broken down by the liver. To prevent them from being absorbed elsewhere, the liver stores them in itself. These kinds of substances stored in the liver include many PCBs and heavy metals.
10.6 The function of the kidneys
The function of the kidneys is to maintain the water and salt balance of the body, to regulate the excretion of many substances in the urine and to remove waste products such as urea.
Each kidney has a million microscopic small filtration units called nephrons.
Every day, 1500 litres of blood flow through the kidneys. About 160 litres of primary urine is formed through filtration. Note that the kidneys filter much more fluid than the amount of urine that is excreted (about 1,5 liters per day).
Glomerular filtration is the first step in making urine. It is the process that your kidneys use to filter excess fluid and waste products from blood plasma to the kdiney's renal tubule, so they may be eliminated from your body.
The artery that enters the kidney branches into a cluster of tiny capillaries, which form a structure known as a glomerulus. Within the glomerulus, the blood pressure is so high that some of the blood plasma is pushed through the walls of the capillaries. This primary urine contains water, salts, sugar and urea.
Blood cells and blood proteins are so large in molecular size that they do not pass the "filter" in a healthy kidney but remain in the bloodstream.
Reabsorption is the process where water and solutes, such as glucose and bicarbonate, are transferred from the renal tubule back into blood plasma. The reabsorption of water and specific solutes occurs to varying degrees over the entire length of the renal tubule.
Even after filtration has occurred, the tubules continue to secrete additional substances into the tubular fluid.
Excretion is the term used for the substances that are removed from the body with urine. Excretion is therefore the end result of the above three processes. The urine is made up of water, salts and urea. It continues its journey from the kidneys to the renal pelvis. From the renal pelvis, the urine travels down a narrow tube called the ureter into the bladder. The bladder slowly fills up with urine, which empties from the body through another small tube called the urethra.
10.7 Kidney damage
The kidneys can be damaged by inflammation or toxic substances. When this occurs, harmful substances will start to accumulate in the blood. The blood can be cleaned in a process known as dialysis, which has to be repeated a couple of times a week. The patient's blood needs to flow through the dialyzer for several hours in order for the blood to become adequately clean and for excess fluid to be removed from the body. Another possibility is to transfer a kidney to the patient, for example from a relative.
An urine sample can be used to detect diseases or foreign substances in the body. If a person has excess sugar in their urine, it is often a sign of diabetes. Diabetes occurs when healthy blood sugar levels are not maintained. In diabetes, a person has so much glucose in their blood that the kidneys cannot return all of it back to the bloodstream. Diabetes is usually caused by a lack of insulin in the pancreas.
Blood cells or proteins in the urine may be a symptom of kidney inflammation. Bacteria in the urine, in turn, refer to urinary tract infection, which is a common and painful illness.
Doping substances that may have been used to improve competitive performance are often detected in urine tests.