DIALYSIS AND ARTIFICIAL KIDNEY

 

DIALYSIS AND ARTIFICIAL KIDNEY

INTRODUCTION

The kidneys continuously remove:

• Urea
• Uric acid
• Creatinine
• Excess salts
• Excess water
• Toxic metabolites

When kidneys fail to perform these functions adequately, toxic wastes accumulate in the blood. This condition is called uremia and may eventually lead to renal (kidney) failure. In such situations, an artificial method of blood purification called dialysis is used.

KIDNEY FAILURE (RENAL FAILURE)

Definition

Renal failure is the inability of the kidneys to filter blood and maintain normal body fluid composition.

Causes of Renal Failure

Acute Causes

• Severe blood loss
• Shock
• Poisoning
• Drug toxicity
• Severe infections

Chronic Causes

• Diabetes mellitus
• Hypertension
• Chronic kidney diseases
• Glomerulonephritis
• Polycystic kidney disease

Consequences

• Accumulation of urea in blood (uremia)
• Fluid retention
• Electrolyte imbalance
• Acidosis
• High blood pressure
• Toxic effects on brain and heart

Without treatment, severe renal failure can be fatal.

UREMIA

Definition

Accumulation of urea and other nitrogenous wastes in the blood due to kidney malfunction is called uremia.

Symptoms

• Nausea
• Vomiting
• Fatigue
• Loss of appetite
• Breathlessness
• Mental confusion
• Swelling (edema)

DIALYSIS

Definition

Dialysis is an artificial process used to remove waste products and excess water from the blood when kidneys are unable to function properly. It acts as a temporary substitute for kidney function.

WHY IS DIALYSIS NEEDED?

Dialysis becomes necessary when:

• GFR falls drastically
• Urea accumulates in blood
• Excess potassium accumulates
• Excess water accumulates
• Kidneys lose filtration ability

It prevents life-threatening complications of kidney failure. (GeeksforGeeks)

ARTIFICIAL KIDNEY

Definition

An artificial kidney (hemodialyzer) is a machine that performs the filtration function of the kidneys by removing waste products and excess fluid from blood.

What Functions Does an Artificial Kidney Perform?

Performs

✓ Removal of urea

✓ Removal of uric acid

✓ Removal of creatinine

✓ Removal of excess salts

✓ Removal of excess water

Does NOT Perform Completely

✗ Erythropoietin production

✗ Vitamin D activation

✗ Full endocrine functions of kidney

✗ Continuous filtration like natural kidneys

Therefore dialysis is not a complete replacement for a healthy kidney.

PRINCIPLE OF DIALYSIS

The artificial kidney works on the principle of:

Diffusion

Movement of substances from higher concentration to lower concentration.

and

Selective Permeability

A semipermeable membrane allows passage of small molecules but prevents passage of large molecules.

Examples:

Can Pass

• Urea
• Uric acid
• Creatinine
• Water
• Salts

Cannot Pass

• RBCs
• WBCs
• Platelets
• Plasma proteins

HEMODIALYSIS

Definition

The process of purification of blood using an artificial kidney is called hemodialysis.

"Hemo" = blood, "Dialysis" = separation through a semipermeable membrane

COMPONENTS OF AN ARTIFICIAL KIDNEY

The hemodialysis apparatus contains:

1. Blood Pump

Moves blood through the machine.

2. Dialyzer

Main filtering unit.

Contains:

• Long coiled cellophane tubes
• Semipermeable membrane

3. Dialysing Fluid (Dialysate)

Special fluid surrounding the tubing.

4. Heparin System

Prevents clotting of blood.

5. Return System

Returns purified blood to patient.

DIALYSING FLUID (DIALYSATE)

Composition

Dialysing fluid has composition similar to normal blood plasma except:

Nitrogenous wastes are absent

Specifically:

• No urea
• No excess uric acid
• No creatinine

This creates a concentration gradient that allows wastes to diffuse out of blood.

STEPS OF HEMODIALYSIS

Step 1

Blood is withdrawn from a patient's artery.

Step 2

An anticoagulant called heparin is added.

Purpose:

Prevents blood clotting inside the machine.

Step 3

Blood is pumped into the dialyzer containing coiled semipermeable tubes.

Step 4

The tubes are surrounded by dialysing fluid.

Step 5

Due to concentration gradients:

The following diffuse out:

• Urea
• Uric acid
• Creatinine
• Excess salts
• Excess H⁺ ions

into dialysing fluid.

Step 6

Blood cells and plasma proteins remain inside the tubing because they are too large to cross the membrane.

Step 7

Purified blood leaves the dialyzer.

Step 8

Anti-heparin is added.

Purpose: Restores normal clotting ability.

Step 9

Purified blood is returned to a vein of the patient.

FLOW CHART OF HEMODIALYSIS

Patient's Artery
↓
Heparin Added
↓
Artificial Kidney (Dialyzer)
↓
Removal of Urea & Wastes
↓
Anti-Heparin Added
↓
Patient's Vein

ROLE OF HEPARIN

Heparin

• Anticoagulant
• Prevents blood clotting during dialysis

Anti-Heparin

• Added before blood returns to body
• Restores normal clotting

ADVANTAGES OF DIALYSIS

1. Life-Saving Procedure

Allows survival despite severe kidney failure.

2. Removes Toxic Wastes

Efficiently removes:

• Urea
• Creatinine
• Uric acid

3. Corrects Fluid Overload

Removes excess water.

4. Maintains Electrolyte Balance

Helps regulate:

• Sodium
• Potassium
• Chloride

5. Useful Until Transplantation

Serves as a bridge to kidney transplantation.

LIMITATIONS OF DIALYSIS

Expensive

Requires specialized equipment.

Time Consuming

Needs repeated sessions.

Temporary Solution

Does not cure kidney disease.

Incomplete Replacement

Cannot perform endocrine functions of kidneys.

Risk of Complications

• Infection
• Hypotension
• Clot formation
• Electrolyte imbalance

SIDE EFFECTS OF HEMODIALYSIS

Possible complications include:

• Fatigue
• Low blood pressure
• Muscle cramps
• Infection
• Blood clotting problems
• Bleeding
• Fever

DIALYSIS VS NORMAL KIDNEY

Feature	Normal Kidney	Artificial Kidney
Filtration	Continuous	Intermittent
Waste removal	Yes	Yes
Water balance	Yes	Yes
Electrolyte balance	Yes	Partial
Erythropoietin production	Yes	No
Vitamin D activation	Yes	No
Hormonal functions	Yes	No

KIDNEY TRANSPLANTATION

Definition

Replacement of a diseased kidney by a healthy donor kidney.

Importance

• Most effective long-term treatment for end-stage renal failure.
• Provides near-normal kidney function.

Donor Sources

• Living donor
• Deceased donor

Limitation

Possibility of graft rejection. Immunosuppressive drugs are required.

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DIALYSIS VS KIDNEY TRANSPLANT

Feature	Dialysis	Kidney Transplant
Nature	Temporary support	Permanent replacement
Cost over time	High	Initially high
Repeated procedures	Required	Not required
Quality of life	Reduced	Better
Cure of renal failure	No	Yes (functional correction)

HIGH-YIELD NEET FACTS

✓ Dialysis is used in renal failure.

✓ Artificial kidney is called a hemodialyzer.

✓ Dialysis works on diffusion through a semipermeable membrane.

✓ Dialysing fluid has composition similar to plasma except nitrogenous wastes are absent.

✓ Heparin prevents clotting during dialysis.

✓ Anti-heparin is added before purified blood is returned.

✓ Plasma proteins and blood cells cannot pass through dialysis membrane.

✓ Urea, uric acid and creatinine diffuse into dialysing fluid.

✓ Dialysis removes wastes but cannot replace endocrine functions of kidney.

✓ Kidney transplantation is the ultimate treatment for end-stage renal failure.

NCERT-BASED NEET ONE-LINERS

1. Dialysis is the artificial purification of blood in renal failure.
2. The artificial kidney works on the principle of diffusion across a semipermeable membrane.
3. The dialysing fluid contains no nitrogenous wastes.
4. Heparin is added before blood enters the artificial kidney.
5. Anti-heparin is added before purified blood returns to the patient.
6. Plasma proteins cannot pass through the dialysis membrane.
7. Hemodialysis removes urea, uric acid and creatinine from blood.
8. Accumulation of urea in blood is called uremia.
9. An artificial kidney cannot produce erythropoietin.
10. Kidney transplantation is the most effective treatment for permanent renal failure.

NEET QUICK REVISION BOX

RENAL FAILURE → UREMIA → HEMODIALYSIS → ARTIFICIAL KIDNEY

Principle: Diffusion through semipermeable membrane

Dialysate: Plasma-like fluid without nitrogenous wastes

Anticoagulant: Heparin

Functional Unit: Dialyzer (Artificial Kidney)

Ultimate Treatment: Kidney Transplantation

Must Remember

Dialysis removes wastes from blood, but only a healthy kidney can perform all excretory, regulatory, and endocrine functions continuously. (Medicneet)