IELTS Listening Practice 227
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Created Date: Sat 26 Jan 2013
Copyright: Introductory Medical-Surgical Nursing Tenth Edition, B. Timby and N. Smith
Lippincot Williams and Wilkins
The renal system consists of the kidneys, the connecting arteries and veins and the urinary tract.
The kidneys are paired, bean shaped organs lying outside the peritoneal cavity in the back of the upper abdomen, one on each side of the vertebral column.
The kidneys function as the body's main excretory organs eliminating the body's metabolic waste products by filtering the blood.
Substances that are un-needed or are present in excess are filtered out of the blood and form into urine moving via the ureter into the bladder before being expelled through the urethra.
The kidneys also selectively reabsorb those substances that are needed to maintain the normal composition of the blood.
By adjusting the blood composition, the kidneys are able to maintain blood volume and pressure, ensure the proper balance of sodium, chloride, potassium, calcium, hydrogen, phosphate and pH and eliminate products of metabolism such as urea, uric acid and creatinine.
The medial border of the kidney is indented by a deep fissure called the Hilus where the blood vessels, nerves and ureters connect to the kidney.
The kidney is composed of upto 18 lobes.
Each lobe is composed of nephrons.
Nephrons are the functional units of the kidney and each kidney contains more than 1 million nephrons.
Each nephron consists of a glomerulus and a system of tubules.
The glomerulus is a unique high pressure mass of capillaries that filter the blood.
The glomerulus is encased in a thin double walled capsule called Bowman's capsule.
The space inside the capsule and surrounding the glomerulus is called Bowman's space.
Plasma like fluid is filtered from the capillary blood into Bowman's space through the glomerular filteration membrane.
The glomerular filteration membrane consists of 3 layers of capillary wall.
The endothelium, the basement membrane and the epithelial membrane.
This membrane allows some particles from the blood to pass through but not all.
The fluid that is filtered from the capillary blood into the Bowman's space is called filtrate and forms the primary urine.
The filtrate then diffuses across Bowman's space and into the tubule system of the nephron.
In the tubules, some substances are added to the filtrate as a part of the urine formation and some substances are re-absorbed out of the filtrate and back into the blood.
The nephron tubule is divided into 4 segments.
The filtrate passes through each of these segments before reaching the ureter.
A highly coiled segment called the proximal convoluted tubule which drains Bowman's capsule and where almost complete absorption of nutritionally important substances take place.
A thin loop structure called the Loop of Henle which re-absorbs the water and ions from the urine and plays a role in controlling the concentration of urine.
A distal coiled portion called the Distal convoluted tubule which regulates potassium, sodium and pH and where further dilution of the urine takes place and the Collecting tubule which joins with several tubules to collect the filtrate and where final sodium regulation takes place.
Each kidney is supplied with blood by a single renal artery that arises on its respective side of aorta before diving into 5 segmantal arteries that enter the Hilus.
Within the kidney, each segmental artery branches into several Lobular arteries.
The lobular arteries further subdivide to form inter lobular arteries which branch off into afferent arterials. Blood flows into the glomerulus through the afferent arterials.
Blood flows out of the glomerulus through the efferent arteriole.
The afferent and efferent arterioles regulate glomerial capillary pressure by selectively dilating or constricting.
The kidney's vena blood now filtered flows from the glomerulus via the efferent arterioles into the peritubular capillary network.
A low pressure low absorbtive system surrounding all portions of the tubules.
This arrangement permits rapid movement of solutes and water between the fluid and tubular lumen and the blood and the capillaries.
The peritubular capillaries rejoin to form the vena channels by which blood leaves the kidneys and empties into the inferior vena cava.
Urine formation involves the filtration of the blood by the glomerulus to form an ultra filrate of urine.
The tubular reabsorption of electrolytes and nutrients needed to maintain the constancy of the internal environment and the secretion of waste materials.
Filtration occurs as blood flows into the glomerulus from its afferent arterial and plasma moves through the glomerial capillaries into Bowman's space.
From Bowman's space the glomerial filtrate moves into the tubular segments of the nephron.
Here, through tubular reabsorption, electrolytes and nutrients move from the filtrate back to the bloodstream.
Here also through tubular secretion, substances move from the peritubular capillaries into the urine filtrate.
The filtrate concentrates in the collecting tubules, then finds its way to the renal pelvis where it is directed to the ureter, bladder and the urethra for elimination.
The kidneys perform an excretory function by filtering the blood and selectively reabsorbing those materials that are needed to maintain a stable internal environment.
The nephron is the functional unit of the kidney and is composed of a glomerulus, which filters the blood and a tubular component, where necessary substances are reabsorbed into the blood stream and unneeded materials are secreted into the tubular filtrate for elimination in urine.
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