4.5.4 Dialysis: Mechanism

Dialysis is a procedure to filter toxins from the blood by artificial methods when the kidneys are unable to perform this function. It works on the principle of kidneys, although it is not as effective, efficient, or thorough as the natural processes performed by the kidneys. There are two general types of renal dialysis: haemodialysis and peritoneal dialysis.

Definition

Dialysis: A procedure to filter toxins from the blood by artificial methods when the kidneys are unable to perform this function is called renal dialysis.

Dialyzer: The dialyzer is an external filter that consists of tubes of semipermeable membrane, used in haemodialysis.

Dialysate: The dialysis fluid that pours into the machine and attracts certain substances (minerals, electrolytes, and waste by-products) to cross the membrane from the blood is called dialysate.

Main Idea

• Dialysis filters toxins from the blood by artificial methods.
• It works on the principle of kidneys.
• It is not as effective, efficient, or thorough as the natural processes performed by the kidneys.
• There are two general types of renal dialysis: haemodialysis and peritoneal dialysis.
• Haemodialysis uses an external filter called a dialyzer.
• Peritoneal dialysis uses the peritoneum, a natural membrane in the body.

Core Concept

• Dialysis = artificial filtering of blood
• Two types = haemodialysis, peritoneal dialysis
• Haemodialysis = uses dialyzer
• Dialyzer = tubes of semipermeable membrane
• Dialysate = dialysis fluid
• Peritoneal dialysis = uses peritoneum
• Peritoneum = natural membrane enclosing abdominal cavity
• Catheter = tube inserted into blood vessel or abdominal cavity
• Dialysis machine = pump and container

Detailed Explanation

Mechanism of Dialysis

• A procedure to filter toxins from the blood by artificial methods when the kidneys are unable to perform this function is called renal dialysis.
• Dialysis works on the principle of kidneys although it is not as effective, efficient or thorough as the natural processes performed by the kidneys.
• There are two general types of renal dialysis: haemodialysis and peritoneal dialysis.

Haemodialysis

• Haemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer, which consists of tubes of semipermeable membrane.
• In this process, a catheter is inserted into a blood vessel, usually in the arm.
• It routes the blood circulation externally through a machine that removes wastes.
• The cleansed blood then returns to the body through a second catheter.
• The haemodialysis machine consists of a pump and a container in which a network of synthetic tubes made up of cellophane membrane, called the dialyzer, is situated.
• The blood moves into the tubes of dialyzer from the top through blood pump.
• After circulating through the dialyzer, blood leaves the machine from the bottom and transfuses back to the body.
• On the other hand, dialysate (dialysis fluid) pours into the machine from bottom, which after circulating around the membranous tube, leaves the machine from the top.
• The dialysate attracts certain substances — minerals, electrolytes, and waste by-products — to cross the membrane from the blood.
• The dialysate absorbs these substances.

Peritoneal Dialysis

• Peritoneal dialysis involves the use of a natural membrane in the body, the peritoneum, which encloses the abdominal cavity.
• In this process, two catheters are surgically inserted into the abdominal cavity that serve as the portals through which dialysate enters and leaves the cavity.
• During circulation, when blood passes through the blood capillaries within the peritoneum, the dialysate attracts certain molecules to cross the membrane into the dialysate.

Summary Table of Dialysis Types

Intermediate Level

Haemodialysis vs Peritoneal Dialysis

Haemodialysis: Key Steps

Peritoneal Dialysis: Key Steps

Principles of Dialysis

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Dialysis filters toxins from the blood by artificial methods.
• 2. Dialysis works on the principle of kidneys.
• 3. Dialysis is not as effective as natural kidneys.
• 4. Two types: haemodialysis and peritoneal dialysis.
• 5. Haemodialysis uses an external filter called a dialyzer.
• 6. Dialyzer consists of tubes of semipermeable membrane.
• 7. Catheter is inserted into a blood vessel in haemodialysis.
• 8. Blood moves into dialyzer from top.
• 9. Dialysate pours into machine from bottom.
• 10. Waste diffuses from blood to dialysate.
• 11. Cleansed blood returns to body.
• 12. Used dialysate leaves from top.
• 13. Peritoneal dialysis uses the peritoneum.
• 14. Peritoneum encloses the abdominal cavity.
• 15. Two catheters are inserted into abdominal cavity.
• 16. Dialysate attracts waste molecules.
• 17. Dialysate enters and leaves cavity.
• 18. Dialysis keeps patients alive until transplant.
• 19. Dialysis is not a cure.
• 20. Dialysis is a life-saving treatment.

Remember

• - Dialysis = artificial filtering of blood
• - Two types = haemodialysis, peritoneal dialysis
• - Haemodialysis = uses dialyzer
• - Dialyzer = tubes of semipermeable membrane
• - Dialysate = dialysis fluid
• - Peritoneal dialysis = uses peritoneum
• - Peritoneum = natural membrane enclosing abdominal cavity
• - Catheter = tube inserted into blood vessel or abdominal cavity
• - Dialysis machine = pump and container
• - Blood flow = top to bottom
• - Dialysate flow = bottom to top

Common Mistakes

• 1. Confusing haemodialysis and peritoneal dialysis — Haemodialysis = external filter; peritoneal = peritoneum.
• 2. Mixing up blood and dialysate flow — Blood: top to bottom; dialysate: bottom to top.
• 3. Thinking dialysis is a cure — Dialysis is a treatment, not a cure.
• 4. Forgetting the role of the dialyzer — Dialyzer is the filter.
• 5. Confusing dialyzer and dialysate — Dialyzer = filter; dialysate = fluid.
• 6. Thinking peritoneal dialysis uses an external filter — It uses the peritoneum.
• 7. Mixing up the catheters — Haemodialysis: one catheter in blood vessel; peritoneal: two catheters in abdominal cavity.
• 8. Believing dialysis is as effective as kidneys — Dialysis is not as effective, efficient, or thorough.
• 9. Forgetting the countercurrent flow — Blood and dialysate flow in opposite directions.
• 10. Thinking dialysis is only for kidney failure — Dialysis is also used for other conditions like poisoning.

Quick Revision

Dialysis is a procedure to filter toxins from the blood by artificial methods when the kidneys are unable to perform this function. It works on the principle of kidneys, although it is not as effective, efficient, or thorough as the natural processes performed by the kidneys. There are two general types of renal dialysis: haemodialysis and peritoneal dialysis. Haemodialysis removes wastes and water by circulating blood outside the body through an external filter called a dialyzer, which consists of tubes of semipermeable membrane. A catheter is inserted into a blood vessel, usually in the arm, and blood is routed externally through a machine that removes wastes. The cleansed blood then returns to the body through a second catheter. Peritoneal dialysis involves the use of a natural membrane in the body, the peritoneum, which encloses the abdominal cavity. Two catheters are surgically inserted into the abdominal cavity that serve as the portals through which dialysate enters and leaves the cavity. During circulation, when blood passes through the blood capillaries within the peritoneum, the dialysate attracts certain molecules to cross the membrane into the dialysate.

60-Second Revision

• Dialysis = artificial filtering of blood
• Two types = haemodialysis, peritoneal dialysis
• Haemodialysis = uses dialyzer
• Dialyzer = tubes of semipermeable membrane
• Dialysate = dialysis fluid
• Peritoneal dialysis = uses peritoneum
• Peritoneum = natural membrane enclosing abdominal cavity
• Catheter = tube inserted into blood vessel or abdominal cavity
• Blood flow = top to bottom
• Dialysate flow = bottom to top
• Warning: Dialysis is not as effective as natural kidneys

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• Chapter:
• 4. Urinary System of Man

• Topic:
• 4.5.5 KIDNEY TRANSPLANT: PROCESS AND PROBLEMS

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