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The aim of this essay is to explore and discuss the functions of kidneys and the main causes of chronic kidney disease. The mammalian kidneys are pair of organs located at the back of the abdominal cavity and are supplied with blood from the renal artery (Brenner and Rector, 1981) Functions of the kidney that will be discussed in this essay are the removal of waste products and excess fluids from the body through the urine, osmoregulation, blood pressure regulation and hormone secretion. (National Kidney Foundation, 2010)
Chronic kidney disease (CKD) defined by the (National Kidney Foundation, 2010) as kidney damage or decreased level of kidney function for a minimum of 3 months, is a worldwide health problem with a rising occurrence. The main causes of chronic kidney disease that will be discussed are diabetes, high blood pressure, glomerulonephritis and polycystic kidney disease.
The function of kidneys
(Patient UK, 2010)
The two kidneys weighing around 150g each are vital organs that have several renal functions, and without these functions death will usually occur within days. Urine is produced in the kidneys, passed down from the kidneys through the ureters to the bladder and it eventually leaves the bladder through the urethra. Internally the kidney consists of an outer cortex and an inner medulla and is composed of nephrons. These nephrons consists of the glomeruli, Bowman's capsule and convoluted tubules that lie in the cortex, loop of henlé, collecting ducts and blood vessels lie in the medulla. (Axford and O'Callaghan, 2004)
Removal of nitrogenous waste from the blood
We all depend on the process of urination for the removal of certain waste products in the body. The control of secretion of salt, water, amino acids and glucose in the urine is important for maintaining the homeostasis of the body. The kidneys nephrons form urine by three regulated processes: ultrafiltration, re-absorption, and secretion. (Roberts and Ingram, 2001)
Ultrafiltration is the separation of large molecules from small that occurs in glomerulus. The blood pressure is high on the walls of glomerulus due to wider afferent and narrower efferent arteriole that forces water and solutes from the glomerulus into Bowman's capsule. These substances must pass across walls of the capillaries, basement membrane and cells of Bowman's capsule. The fluid entering the Bowman's capsule is called glomerular filtrate. (Roberts and Ingram, 2001)
A study by Axford and O'Callaghan (2004) has shown that reabsorption takes place in the proximal convoluted tubules and the substances reabsorbed are water, glucose and other nutrients, and sodium (Na+) and other ions. Glucose is reabsorbed from the proximal convoluted tubule by active transport and also moves along with Na+ ions by the glucose-sodium cotransport mechanism. Chlorides and other negatively charged ions are reabsorbed into the blood stream following an electrochemical gradient. Amino acids are also reabsorbed 100% by active transport. Water is reabsorbed by osmosis and urea is reabsorbed by diffusion. (Brenner and Rector, 1981)
Secretion is the process where substances move out of the blood and into the distal convoluted tubule and collecting duct from the capillaries around these tubules. The loop of Henlé is a countercurrent mechanism and is responsible for producing concentrated urine. In the distil convoluted tubule Na+ are reabsorbed, but in much smaller amounts than the proximal convoluted tubule. Cells in the distil convoluted tubule secrete substances such as K+, H+ and ammonia into the lumen of the tubule. NH3 combines with H+ to form NH4+ where they are eventually eliminated in the urine. (Brenner and Rector, 1981)
Osmoreceptors are found in the hypothalamus of the brain and they monitor the water potential of blood. If water potential of the blood is higher that normal, less ADH is released from the posterior pituitary gland, which makes the collecting duct, and distal convoluted tubule to becomes less permeable to water therefore less water is reabsorbed from the filtrate and as a result the urine is more dilute and more in volume. The water potential of blood is kept constant by negative feedback. (Axford and O'Callaghan, 2004)
Blood pressure regulation
Kidneys produce a hormone called renin, which is synthesized and stored in the granules of the juxtaglomerular cells and another hormone called angiotensin. These hormones regulate how much sodium and fluid the body keeps, and how well the blood vessels that usually involve arteries can expand and contract, which helps control blood pressure. Checking the amount of water in the body is a way to regulate, if there is fluid overflow then blood pressure will increase, if the body is dehydrating then blood pressure will decrease. Blood pressure is also regulated by the width of the arteries, the narrower the arteries, the higher the blood pressure, this is where renin helps the control of narrowing of the arteries so if the kidneys are failing then they often make too much renin, which raises blood pressure. (Suzuki and Saruta, 2004)
Secretion of certain hormones from the kidney help in the production of red blood cells and the growth and maintenance of bones. A hormone known as erythropoietin stimulates the production of red blood cells in the bone marrow, which releases red blood cells into the bloodstream. Kidneys also regulate levels of calcium by using an activated form of vitamin D that promotes intestinal absorption of calcium and the renal reabsorption of phosphate. (Brenner and Rector, 1981)
Chronic kidney disease
What is chronic kidney disease?
According to Bomback and Bakris (1952) Chronic kidney disease is a slow progressive decline in the kidneys' ability to filter metabolic waste from the blood, which happens when there is a permanent loss of kidney function that gradually happens, usually months to years. In the table below you can see that chronic kidney disease is divided into 5 stages each stage increasing with severity.
(JNC 7, 2003)
Diabetes is a disease where your body does not make enough insulin, which is a hormone that regulates the amount of sugar in your blood, or cannot use normal amounts of insulin properly. This results in a high blood sugar level, which can cause problems in many parts of your body especially the kidney. There are two types of diabetes, type 1 and type 2 that cause a condition called diabetic nephropathy, which is the leading cause of kidney disease. (Bomback and Bakris, 1952)
High blood pressure
High blood pressure, also known as hypertension can damage the kidneys over time but also cause heart attacks and strokes. Blood pressure depends on how forcefully the heart pumps blood around the body and how narrow or relaxed your arteries are. Hypertension occurs when blood is forced against the artery walls at an increased enough pressure to cause damage, this in return puts strain on the arteries and on the heart itself causing an artery to rupture. When high blood pressure is controlled, the risk of complications such as chronic kidney disease is decreased. (National Kidney Foundation, 2010)
Glomerulonephritis is a condition that causes the inflammation of the kidneys glomeruli, which in return causes the kidneys to become swollen. When the kidneys become inflamed they are unable to work properly and as a result salt and excess fluid can build up leading to hypertension and possibly kidney failure. There are two types of Glomerulonephritis, acute which develops suddenly and often follows an infection and chronic which may develop silently without symptoms over several years. (NHS, 2010)
Polycystic kidney disease
Polycystic kidney disease is genetic or inherited disease that causes cysts or fluid filled pouches to develop on the kidneys. The symptoms which can include high blood pressure, abdominal pain and blood in the urine tend not to begin until the ages of 30 - 60, which is considered adulthood. Polycystic kidney disease is caused through genetic mutation that occurs when there is a change in structure or amount of DNA. (NHS, 2010)
The kidneys perform several important tasks including the removal of toxins and mineral impurities from the blood, controlling body fluids, help to control your body's production of red blood cells and regulate blood pressure. The kidney is able to do this as it is made up of millions of nephrons and these nephrons contain tiny blood vessels called glomerulus that filter and clean the blood as it flows through the kidney.
The most frequent causes of kidney disease are diabetes and high blood pressure but other common kidney diseases are glomerulonephritis, which causes inflammation and damage to the glomerulus, and polycystic kidney disease that is inherited and causes large cysts to form in the kidney.
There are things you can do to reduce the risk of getting kidney. For people with diabetes, it is vital to keep good control of blood sugar levels. Staying physically fit is also an important factor for kidney functions as exercise can help kidney disease by improving muscle function, lowering blood pressure, lowering cholesterol and keeping a healthy body weight.