Posted on: Mar 18, '08
Dialysis by Kidney and dilalysing machine
This artcle is posted in deference to the wishes of Olive intl, who asked for a write-up on the mechanism of dialysis. I got to see his post only 13 the evening of March. Compiling material took me one full day. One day for assimilation. Three days of holidays and a net outage I have managed it this day the 18 th March , 2008. I was not aware of the International Kidney coming up. Further sharing the grief of Olive intl whose wife passed away due to kidney failure, I felt compelled to do some digging into the subject, though science-writing and science-fiction are my gleeful domain
Let me begin with the kidneys, The subject came to be discussed due to it's failure to do it's assigned duty.
Kidneys are our dialysis machines. Each one of us has two kidneys one each at each side of the back bone between the think muscle of the back and the abodomen. It is the size of our clenched fist weighing around 150 gms.
Our blood carries nutrients and oxygen to the body cells and take away waste materials arising from the metabolism, from the cell.. The essential function of the kidney is to remove toxins and impurities from the blood. Kidneys, apart from removing impurities from the blood also make harmones to control the rate of formation of red blood cells in the bone marrow. Kidneys also control and regulate blood pressure.
Even when kidneys are severely damaged, they continue to filter toxins, excess water and wastes and maintain body chemistry effectively. As long as atleast ten percent of the kidneys are functional, these activities are carried out. Nonetheless, the damage in the kidneys may become a drag on it's capacity and cause complete failure. when the kidneys fail completely, artificial means to carry out the work of kidneys has to be resorted to.
A look at the functioning of the kindneys will make our understanding of the artificial dialysis better. The kidneys employ a three stage mechanism namely filtration, readsorption and secretion. The basic functional unit of the kindney which does the three stage operation is called nephron. Each kidney has around a million such nephrons. A nephron contains a cluster of blood vessels known as glomerulus, surrounded by bowman's capsule. The Bowman's capsule leads into a U-shaped tubule that empties into a collecting duct. The collecting duct from various nephrons merge together and ultimately empty into the bladder and lead to the Urethra outside.
The blood from the body cell enters the kidney through the renal artery. First, the blood goes to the tiny blood vessels of the glomerulus which filters proteinds and cells from the blood. As the membrane channels of the glomerulus do allow passage of large sized proteins and cells, they go back to the blood. The smaller particles - the ions, sugars and ammonia pass through the glomerulus membranes into the bowman's capsule. The smaller components of blood then enters the membrane-enclosed tubules. Therefore the fluid entering tubules is blood minus the proteins and cells.
The tubule is the real dialysis unit of the kidney. The tubule is enclosed by a semi-permeable membrane which allows passage of toxins and the naturfal by-products of the body's metabolism- Urea, Uric acid.
The other substances vital to the body- glucose is reabsorbed into the blood. The material that is filtered and secreted in the tubules less the material reabsorbed into the blood is ultimately excreted from the body. The secreted material fluid in the tubules enters the collecting duct and feeds into the ureter. The ureters( one each from each kidney) enter the bladder and lead to Urethra for ultimate discharge as Urine.
When the kidneys fail, the toxic materials urea and uric acid accumulate in the blood resulting in "Uremia". The blood pressure also rises. The body loses the ability to make enough red blood cells. Patient develops fatigue, nausea and loss of appetite.
The failure of kidneys necessitates artificial means of dialysis. There are mainly two types of dialysis. Hemodialysis and Peritoneal dialysis.
In Hemodialysis the blood from the patient's body is pumped into a dialysing machine called dialyser, purified and returned to the body. Dialysis works on the principle of diffusion and osmosis across a semi-permeable membrane. In the dialysing machine, the blood from the patient's body flows in one direction and dialysing called flows opoosite direction. A semi-permeable membrane is between the blood flowing in and the dialysate flowing in the other direction. A negative pressure is applied on the dialysate compartment of the dialyser. The pressure difference causes water and dissolved particles in the blood to move from the blood to the dialysate, filtered and drained out and the purified blood goes back to the body. This allows removal of several litres of excess fluid in a 3 to 5 hour treatment. Hemodialysis treatment is given in a dialysis center three times a
week. In Hemodialysis, dialysing fluid may be altered contain more lesser quantity of potassium, and depending on the level of these in the blood. For instance, if there is high amount of potassium in the blood, then the level of potassium is lowered in the dialysate to facilitate the removal of excess potassium from the blood.
In peritoneal dialysis, a sterile solution containing minerals and glucose is run through a tube inserted into the peritoneal cavity of the patient, i.e., abdominal cavity. The abdominal membrane acts as a semi-permeable membrane and excess fluid wastes are drawn into the sterile solution let into the body and drained out.
Peritoneal dialysis has to be done daily.
Complications do arise in the artificial dialysis- hypertension, light headedness, nausea or vomiting, muscle cramps and fatigue develop as result of dialysis. Suitable remedial steps are taken to offset these complications.
In peritoneal dialysis, there is a chance of bacterial infection Using clean sterile solution will fix this.
For patients undergoing dialysis a strict diet regimen is enforced. from adequate protein the intake of lesser amounts of phosphate and calcium are restricted in the diet.
I am coming to a question that should have been asked at beginning. Why at all the kidneys should fail. Kidneys may fail due to a host of reasons- diabetes, high blood pressure, excessive intake of pain killers, injuries, tuberculosis, bright'sdiseases(nephritis), stone formation and tumours.
Adopting suitable life-style and diet is the only way out.
Thanks for reading. The elaboration may easily run into pages. I have manged to give the gist. Your valuable comments are welcome.
Bharath selvan
Tags: dedicated to kidney patients
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