What Is Dialysis? Understanding Its Role in Biology
In medicine, Dialysis is also known as renal dialysis, hemodialysis, or kidney dialysis. It is the method of extracting blood from a patient whose kidney function is impaired, purifying it with dialysis, and then adding it to the patient's bloodstream. Hemodialyzer or artificial kidney is a machine, which provides a means for removing certain undesirable substances from blood or adding required components to it. By these particular processes, the apparatus may control the acid-base balance of the blood, including its content of dissolved materials and water.
Dialysis Treatment - Introduction
In 1945, Dialysis was first used to treat human patients, such as replacing or supplementing the kidneys' action in a person suffering from chronic or acute renal failure or from poisoning by diffusible substances, such as bromides, barbiturates, or aspirin. Usually, the blood is diverted from an artery, one in the wrist, into the dialyzer, in which it flows either by its own respective impetus or with the mechanical pump's aid - along one membrane's surface.
Finally, the blood passes via a trap, which removes bubbles, clots, and returns to a vein in the forearm of the patient. In persons with chronic kidney failure, who need frequent dialysis, repeated surgical access to the blood vessels that are used in the treatments is obviated by a provision of an external plastic shunt between them.
Function of Dialysis
The secretion of hormones, which affect blood pressure and cannot be duplicated, is another known feature of the natural kidney. Many modern dialyzers rely on the two physicochemical principles, ultrafiltration, and dialysis.
In dialysis, two liquids separated by a porous membrane exchange those components, which exist as particles small enough to diffuse via pores. When the blood is brought to contact with a single side of such a membrane, the dissolved substances (including inorganic salts and urea) pass via a sterile solution placed on the membrane's other side. Since the particles are too huge, white and red cells, proteins, and platelets cannot pass through the membrane.
To limit or prevent the diffusible loss of substances required by the body, such as amino acids, sugars, and required amounts of salts, such compounds are added to the sterile solution; hence their diffusion from the blood is offset by an equal movement in the opposite direction. The shortage of diffusible materials in the blood can be remedied by including them in the solution, where they join the circulation.
Although water easily passes via the membrane, it is not removed by dialysis since its concentration in the blood is less than that in the solution; indeed, water tends to pass from the solution into the blood. The blood's dilution that would result from this particular process is prevented by ultrafiltration, where some of the water, along with few dissolved materials, is forced via membrane by maintaining the blood at higher pressure than the solution.
Symptoms for Dialysis Treatment?
The following symptoms associated with kidney failure may or may not point to being indications of needing a dialysis treatment:
A sudden and/or persistent change in urination
A metallic taste in the mouth, known as ammonia breath
Itching or pruritus
Fatigue
Nausea followed by throwing up
Aversion from protein
Loss of appetite
Swelling
Types of Dialysis
Let us look at the types of dialysis and the dialysis procedure.
There exist three primary and two secondary types of dialysis, which are
Hemodialysis dialysis (primary)
Peritoneal dialysis (primary)
Hemofiltration dialysis (primary)
Hemodiafiltration dialysis (secondary)
Intestinal dialysis (secondary)
Hemodialysis Procedure In hemodialysis, the patient's blood is pumped into the dialyzer's blood compartment (using a hemodialysis machine), where it is exposed to a partly permeable membrane. Then, the dialyzer is composed of thousands of tiny and hollow synthetic fibres, and the fibre wall acts as a semipermeable membrane. Blood circulates through fibres, dialysis solution circulates around the outside of the fibres, and wastes and water circulate between the two solutions. Then, the cleansed blood can be returned through the circuit back to the body. Ultrafiltration takes place by increasing the hydrostatic pressure across the dialyzer membrane usually; this can be done by applying negative pressure to the dialyzer's dialysate compartment.
Peritoneal Dialysis In the case of peritoneal dialysis, a sterile solution with glucose (known as dialysate) is run via a tube into the abdominal body cavity around the intestine, the peritoneal cavity, where the peritoneal membrane will act as a partially permeable membrane.
Hemofiltration Hemofiltration is the same treatment as hemodialysis, but it will make use of a varied principle. The blood is pumped via "hemofilter" or dialyzer as in dialysis, but no dialysate can be used. A pressure gradient will be applied, and as a result, water will quickly pass through the very permeable membrane, "dragging" many dissolved substances along with it, including those with extremely large molecular weights that are not cleared by hemodialysis.
Hemodiafiltration Hemodiafiltration is given as a combination between hemofiltration and hemodialysis, hence used to purify the blood from toxins when the kidney is not functioning normally and also used to treat the acute kidney injury (AKI).
Intestinal Dialysis In the case of intestinal dialysis, the diet can be supplemented with soluble fibres like acacia fibre that is digested by the colon's bacteria. This particular bacterial growth increases the amount of nitrogen, which is eliminated in the faecal waste. A secondary native approach utilises the ingestion from 1 to 1.5 litres of non-absorbable solutions of mannitol or polyethylene glycol every fourth hour.
Conclusion
Did you know? Earlier, the membranes that were used for dialysis were procured from animals. It was in the late 1960s, that other materials like hollow filaments made out of synthetic and/or cellulosic materials were used for dialysis. To get more information, study materials, questions on dialysis you can register at Vedantu.com.
FAQs on Dialysis: Functions, Types, Procedures & FAQs
1. What is dialysis and why is it necessary for a person with kidney failure?
Dialysis is a medical procedure that artificially filters waste products and excess fluid from the blood when the kidneys can no longer perform this function adequately. It is necessary in cases of end-stage renal disease (ESRD) or acute kidney failure to prevent the toxic build-up of nitrogenous wastes like urea and to maintain the body's essential fluid and electrolyte balance, a process vital for survival.
2. What are the two main types of dialysis used in medical treatments?
The two principal types of dialysis are:
- Haemodialysis: This is the most common method, where blood is drawn from the body, circulated through an external artificial kidney machine (dialyser) for filtration, and then returned to the patient's bloodstream.
- Peritoneal Dialysis: In this method, the patient's own abdominal lining, the peritoneum, is used as a natural filter. A cleansing fluid called dialysate is introduced into the abdominal cavity to absorb waste products from the blood vessels within the peritoneum.
3. Explain the fundamental principle on which haemodialysis works.
Haemodialysis operates on the principles of diffusion and ultrafiltration across a semipermeable membrane. Blood flows on one side of the membrane, while a special fluid called dialysate flows on the other. As blood has a high concentration of waste products like urea, these substances diffuse across the membrane into the dialysate, where their concentration is zero. Excess water is removed by creating a pressure gradient, a process known as ultrafiltration.
4. What are the key components of an artificial kidney, or dialyser?
An artificial kidney, or dialyser, is the core of a haemodialysis machine. It is composed of a bundle of thousands of hollow fibres made from a semipermeable membrane, such as cellophane. During the process, blood flows through these hollow fibres while the dialysing fluid circulates around the outside of the fibres in the opposite direction. This counter-current flow maximises the concentration gradient, making the removal of waste highly efficient.
5. What are the main advantages and potential risks associated with dialysis treatments?
The primary advantage of dialysis is that it is a life-sustaining treatment that performs the vital excretory and homeostatic functions of a failed kidney. However, it also carries potential risks, including:
- Hypotension (a sudden drop in blood pressure)
- Muscle cramps
- Risk of infection at the access site
- Anaemia, due to reduced erythropoietin production
- Fatigue and weakness post-treatment
6. How does an artificial kidney (dialyser) functionally differ from a natural human kidney?
While both filter blood, their functions differ significantly. A natural kidney is a complex organ that performs crucial metabolic and endocrine roles, such as producing hormones like erythropoietin to stimulate red blood cell production and regulating blood pressure. In contrast, an artificial kidney is primarily a filtration device. It effectively mimics the excretory function but cannot replicate the hormonal and metabolic activities of a healthy kidney.
7. Why is the dialysing fluid used in haemodialysis free of nitrogenous wastes but contains normal levels of essential salts and glucose?
This specific composition is crucial for selective filtration based on concentration gradients. The complete absence of wastes like urea in the dialysate ensures a steep gradient, causing these toxins to diffuse rapidly out of the blood. Conversely, the dialysate contains essential substances like glucose and electrolytes at the same concentration as healthy blood. This equilibrium prevents these vital nutrients from being accidentally removed from the patient's body during dialysis.
8. What is the specific role of the semipermeable cellophane membrane in a dialyser?
The semipermeable cellophane membrane acts as a precise filter, mimicking the function of the glomeruli in a natural kidney. Its pores are large enough to allow small waste molecules like urea, creatinine, and excess salts to pass from the blood into the dialysate. However, the pores are too small for larger, essential components such as proteins and blood cells (RBCs, WBCs) to pass through, ensuring they are retained in the bloodstream.
9. How does peritoneal dialysis use the body's own membrane for filtration, and how does this compare to haemodialysis?
In peritoneal dialysis, the peritoneum—the membrane lining the abdominal cavity—serves as the internal filter. Dialysate is infused into the abdomen via a catheter, and waste products from the blood vessels in the peritoneum diffuse into this fluid, which is then drained. Compared to haemodialysis, it is less mechanically invasive as it doesn't require external blood circulation and can often be performed at home, offering more flexibility. However, it may carry a higher risk of abdominal infection (peritonitis).
10. Beyond removing urea, what other homeostatic functions of the kidney does dialysis help regulate?
While removing nitrogenous waste is its primary purpose, dialysis is also critical for maintaining overall homeostasis. It helps regulate:
- Fluid Balance: By removing excess water from the blood through ultrafiltration, it prevents fluid overload and helps control blood pressure.
- Electrolyte Balance: It corrects and maintains safe levels of crucial electrolytes like potassium, sodium, and chloride.
- Acid-Base Balance: It addresses metabolic acidosis, a common issue in kidney failure, by removing excess acids and managing bicarbonate levels in the blood.
