Functions of the Kidneys

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The kidney is a very important organ in the mammalian body which serves to perform several functions. The kidneys are characteristically bean shaped and dark red in color. They are located in the lumbar region of the abdominal cavity with each located on either sides of the body, one on the right and the other on the left side. The dorsal part of the abdomen of a mammal is also referred to as the lumbar region.

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The outer layer of the kidney gives it the red coloration and is called the cortex and is a part of the inner convex part of the kidney. The concave part is the hilum through which a renal artery enters to supply blood and a renal vein is available to take out blood from the kidney. Each of the two kidneys also contains approximately five million nephrons which help mostly in blood cleaning and purification for re-use in the body. The nephrons are the basic functional units of the kidneys as they are the main locations in the kidneys from where waste products are eliminated from the body


Removing waste from the blood

Filtering the blood to remove toxic wastes that would otherwise be deathly to other tissues and organ cells in the body is the primary function of the kidney. Filtration of the blood and removal of nitrogenous waste is mainly done by the kidney nephrons. Blood that is supplied to the kidneys goes through a filtration process to remove toxic waste from the blood. The major waste product is the urea and the uric acid.

Accumulation of these waste products in the body could result into threatening illnesses. Through the process of excretion the kidneys are able to get rid of the waste products. For good filtration, the dirty blood passes through a long loop of henle for more filtration and reabsorption of water and some mineral ions into the body. The longer the loop of henle, the easier and more efficient the process of blood cleaning becomes.

How the kidney nephron functions

Nephrons are the basic functional units of the kidneys and it is here that most of the wastes are eliminated from the body. Inside the nephrons, are tiny tubes which carry urine and are intertwined with capillaries which are tiny blood vessels running inside the kidneys. A very complex chemical exchange is performed with some excess water and waste materials being forced out of the system through the urinary tract.

The kidneys are designed to measure the ionic balance in the body allowing it to re-absorb any minerals it needs to use like potassium, sodium and phosphorous. By doing so, the kidneys are able to keep the body at a suitable ionic balance. The excess are removed from the body because in as much as they are helpful, they could also be very toxic to the body.

The diagram below shows a cross section of the kidney with a kidney nephron projected.

The glomerulus

This is a tiny capillary tubing which resembles a ball of yarn and it is the location where the actual filtering of the blood takes place. It functions just like a sieve where only waste materials are allowed to pass through leaving behind any of the proteins and other components which make up the blood like plasma and blood cells.

The tubule

This is commonly known as the tubule of the kidney and is where all the substances that the body can re absorb pass through. Here, substances like excess sodium and potassium can be found in significant quantities.

Bowmans corpuscle

This is a single layer of epithelium which surrounds the glomerulus. It is usually s cup like sack located just at the mouth of the tubular part of the kidney of a mammalian kidney.

The renal corpuscle

This is the combination of the glomerulus and the Bowmans capsule. This structure is located in the renal cortex in the human kidney. The renal corpuscle is the first most significant structure in the kidney which aids in the formation of urine. The renal tubule then completes the cycle and the urine then exits to the ureter. The main process here is called ultrafiltration and is the most complex function of the kidney.

The Afferent and Efferent arteriole

These are the two main units which aid in the ultrafiltration of blood. The afferent arteriole is a small blood vessel which supplies blood to the glomerulus. The efferent arteriole, another tiny artery carries blood away from the glomerulus. The process of ultrafiltration here is made possible by the structural construction of the arterioles with the efferent arteriole having a smaller diameter to create a back flow pressure build up which in return then allows ultrafiltration to take place.

Formation of urine

According to Rose et al, (2015), Urine is a liquid waste product that is excreted by mammals in the process of urination. Metabolism of body cells makes it necessary to eliminate waste products from the body as the wastes can be highly toxic if left to accumulate in the body. This makes it necessary for the body to form urine, which aids in the removal of any waste products that are water soluble. On average, the human kidneys have the capacity of producing about 1.4 litters of urine per day. However, 0.6 liters to 2.6 liters per day is possible based on the water intake of that particular individual as well as other external factor such as the outside temperatures and humidity. The higher the outside body temperatures, the more the body loses a lot of water through sweating and the lower the amount of urine produced in the kidneys. The vice versa is also true for cold weather since the body does not lose a lot of water through sweating.

This is made possible because of the high pressure created in the glomerulus pushing the fluid from the capillaries into the capsule of the glomerulus which has a layer of highly specialized cells. As soon as blood is filtered and all impurities removed, the waste product is supposed to be discarded because of its toxic nature. The urine formation is a process where kidneys prepare waste products which are filtered from the blood for elimination from the body. During the filtration process, the kidneys determine the correct volume of water and the correct amount of sodium, phosphorus or potassium that should remain in the blood. Collectively urine is made of excess water, chemicals (sodium, phosphorus, potassium) and nitrogenous waste.

Some filtrate is absorbed in the glomerulus and it flows through the renal tubule from where further re-absorption of important substances takes place. The waste substances are mainly mineral ions, hydrogen ions and some of the water that is not needed by the body. These waste products are then passed on to the renal tubule in a process known as excretion, ready to be taken out of the body. The now already formed urine flows from the nephron tubule and into the collecting duct which then passes on the urine into the renal pelvis and finally into the ureter which then empties its contents into the urinary bladder which is simply a balloon like bag which holds the urine temporarily before it is excreted out of the body. Visible body, (2016)

Regulation of water volume / osmoregulation

According to Rodger, (2006) water is very essential for most bodys biological functions. Water should be in the right amount because too much or too little could cause different serious health complications. Too much water could dilute the blood, affecting the environment in which the cells operate in a negative way while little water could cause neurological dysfunction and circulatory shock. The nephron is able to correctly adjust the volume and concentration of water through the filtering and reabsorption process.

In as much as water is not nutritious, it is very essential in the normal functioning of the body and is therefore a mandatory requirement for the body otherwise the body would just come into a crush. When the body is deprived of the precious liquid, it creates highly concentrated urine which can be even six times the concentration of blood in the body. This is made possible as the body struggles to keep the blood and the internal organs at the best working conditions.

It is however important to notice that when you drink a lot of fluids or water, your body will definitely have a fluid overload and this calls for a corrective mechanism from the kidneys leading to diuresis. Diuresis is the highly increased production of urine in the kidneys in an effort to reduce the water content in the blood.

This is made possible because of the presence of a long loop of henle whose primary purpose is the re-absorption of water and sodium salts into the body. This makes it possible for the kidneys to produce little urine which is highly concentrated with waste products. Under normal circumstances, the liquid part that enters the loop of henle is usually composed of urea, salt and other waste substances which are supposed to be excreted. This is normally from the proximal convoluted tubule which re absorbs water, glucose, sodium bi-carbonate and amino acids which are needed by the body.

Regulating bodys salt content

According to Sandy Caloun, (2015) the relative amount of water and salt in the blood give the blood a particular concentration, which is necessary for good health. By regulating the amount of salt and water in the blood, the kidneys ensure that the concentration and volume of the blood stay at the correct level at all times. Salt and water are regulated through a similar process. The kidneys are able to determine the correct concentration based on the bodys overall concentration.

This is made possible by a very important hormone in the body called the ADH. ADH is the antidiuretic hormone which helps the kidney manages the amount of water and salt in the body. This hormone is manufactured in the hypothalamus in the human brain and then sends to the pituitary glands for storage. Water metabolism is maintained in the body by the use of highly specialized baroreceptors and osmotic sensors which then send signals to the brain and it sends the necessary corrective instructions to the kidneys which then work on the impending situation. Higher water volumes are known to increase the overall volume of the blood and consequently the total blood pressure of blood.

The osmotic sensors are located in the hypothalamus and they measure the concentration of potassium, sodium, carbon dioxide as well as chloride ions. When the blood pressure is low or the concentration of these ions is low, the kidneys get a message to store or release more water in order to maintain a balanced working environment in the body.

In the event of excess ADH in the blood stream one may experience continuous headaches, vomiting, nausea and even coma or convulsions. In most cases, people suffering from high ADH normally have underlying medical conditions which may include but not limited to Leukemia, lymphoma, pancreatic cancer, brain cancer, lung cancer, systematic cancers which produce ADH on their own, Guillain-Barre syndrome, multiple sclerosis, epilepsy, cystic fibrosis, emphysema, tuberculosis, HIV/AIDS. It is also common for brain trauma and some surgical procedures to cause excess production of ADH.

Regulating blood pressure

This is done by hormonal reactions and regulating the volume of water in the body. Renin is an enzyme secreted by the kidney which helps to control blood pressure. It also regulates the electrolyte balance. When blood pressure begins to fall the kidneys release enzyme renin. The enzyme converts blood protein into a hormone called angiotensin. Angiotensin then induces adrenal gland to release aldosterone which causes reabsorption of water and sodium into the blood.

Regulation of pH balance

Acidity of the blood is also a necessary checkup. High blood acidity means there is an excess of hydrogen ions. The excess hydrogen ions are remo...

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