Dialysis - Allied Guru

Table of contents

Introduction

Dialysis is one of the most remarkable applications of biochemical and physiological principles used in modern medicine.
It is a semipermeable membrane-based purification process that removes waste products, toxins, and excess fluid from the blood when the kidneys fail to function properly.
The process works on the principles of diffusion and osmosis, demonstrating how these fundamental biochemical mechanisms maintain internal chemical balance.
In simple terms, dialysis functions as an artificial kidney, performing the excretory role normally handled by the nephrons.
From a deeper biochemical perspective, dialysis is a controlled and selective exchange system that allows solute and solvent movement depending on molecular size, concentration gradient, and membrane permeability.

Principle of Dialysis

The principle of dialysis is based on the combined actions of diffusion and osmosis:

Diffusion: The passive movement of solute molecules (like urea, creatinine, and electrolytes) from a region of higher concentration (blood) to lower concentration (dialysate) through a semipermeable membrane.
Osmosis: The movement of solvent (water) through the same membrane to maintain osmotic equilibrium and regulate fluid balance.

In both medical and laboratory settings, this principle ensures that small molecules and ions can move freely across the membrane, while large molecules (proteins, polysaccharides, or blood cells) remain confined to their original compartment.

Structure and Function

The semipermeable membrane is the heart of any dialysis system.

It may be cellophane, synthetic polymer (e.g., cellulose acetate, polysulfone), or a biological membrane (peritoneum) in case of peritoneal dialysis.
The membrane is designed with micropores that allow molecules below a certain molecular weight (usually <10,000 Da) to pass through while restricting larger macromolecules.
The pore size, charge, and hydrophilicity determine the selectivity and rate of filtration.

In a biochemical context, this mimics the glomerular filtration barrier of the kidneys, which differentiates between waste metabolites and essential plasma proteins.

Types of Dialysis

Dialysis can be classified into two major types based on the membrane used and the site of filtration:

1. Hemodialysis

In hemodialysis, blood is withdrawn from the patient and pumped through an artificial dialyzer, commonly known as an artificial kidney.
The dialyzer contains thousands of hollow fibers or thin capillary tubes, each acting as a semipermeable membrane.
On one side flows the patient’s blood; on the other, a dialysate solution containing carefully controlled concentrations of electrolytes and glucose.
Diffusion and ultrafiltration remove urea, creatinine, uric acid, and excess salts while retaining essential molecules like proteins and blood cells.
The purified blood is then returned to the patient’s body.

Clinical Note: Hemodialysis is typically performed 3 times a week, each session lasting about 4 to 5 hours.

2. Peritoneal Dialysis

In this type, the patient’s own peritoneum (lining of the abdominal cavity) acts as the semipermeable membrane.
A dialysis fluid (dialysate) is introduced into the abdominal cavity through a catheter.
Waste products and excess water from the blood vessels in the peritoneal capillaries diffuse into this fluid by osmosis and diffusion.
After a few hours, the fluid is drained and replaced with fresh dialysate.

Advantages: Can be performed at home, offers more flexibility, and is continuous in nature.
Limitation: Risk of infection (peritonitis) and requirement for strict aseptic techniques.

Composition of the Dialysate

The dialysis solution (dialysate) is a crucial component designed to create the appropriate concentration gradients for waste removal while maintaining electrolyte and pH balance.
Typical components include:

Component	Function
Sodium (Na⁺)	Maintains osmotic balance
Potassium (K⁺)	Prevents hypokalemia
Calcium (Ca²⁺)	Regulates cardiac and neuromuscular activity
Bicarbonate (HCO₃⁻)	Corrects metabolic acidosis
Glucose	Provides osmotic pressure and energy source
Buffer system	Maintains physiological pH (7.4)

Steps Involved in Hemodialysis

Blood Access: Blood is withdrawn through a vascular access point (fistula or catheter).
Circulation: Blood flows into the dialyzer where the exchange occurs.
Filtration: Waste solutes diffuse across the membrane into the dialysate.
Fluid Removal: Excess water is removed via ultrafiltration, controlled by transmembrane pressure.
Return: Cleaned blood is pumped back into the patient’s circulation.

Clinical Applications and Importance

Treatment of Chronic Kidney Disease (CKD):
Dialysis compensates for the loss of glomerular filtration rate (GFR) in advanced CKD.
Acute Kidney Injury (AKI):
Temporarily removes toxins and stabilizes patients until kidney recovery.
Electrolyte and Fluid Balance:
Corrects hyperkalemia, acidosis, and fluid overload.
Toxin Removal:
Used in certain poisonings or drug overdoses (e.g., ethylene glycol, lithium).
Pre-Transplantation Support:
Maintains patients awaiting kidney transplantation.

Advantages of Dialysis

Maintains life in patients with kidney failure.
Efficiently removes waste and toxins from the body.
Balances pH, electrolytes, and fluid volume.
Non-invasive in peritoneal form and compatible with long-term use.
Applicable in both clinical and research biochemistry.

Limitations

Time-consuming and requires repeated sessions.
Risk of infection, especially in peritoneal dialysis.
May lead to fatigue, hypotension, or cramps.
Does not replace all kidney functions such as erythropoietin production.
Expensive in long-term management.

MCQs

Dialysis is mainly based on which principle?
a) Active transport
b) Diffusion and osmosis
c) Filtration and absorption
d) Endocytosis
The main purpose of dialysis is to:
a) Destroy toxins
b) Remove waste products and excess fluid from blood
c) Increase blood glucose level
d) Produce hormones
In dialysis, which type of membrane is used?
a) Permeable membrane
b) Semipermeable membrane
c) Impermeable membrane
d) None of the above
Dialysis replaces the function of which organ?
a) Liver
b) Heart
c) Kidney
d) Lungs
The movement of solutes in dialysis occurs due to:
a) Osmosis
b) Active transport
c) Diffusion
d) Filtration
In dialysis, larger molecules such as proteins:
a) Pass through the membrane
b) Remain retained
c) Convert into smaller molecules
d) Are filtered completely
Which of the following is NOT removed during dialysis?
a) Urea
b) Creatinine
c) Glucose
d) Excess salts
The solution used on the other side of the dialysis membrane is called:
a) Serum
b) Dialysate
c) Plasma
d) Filtrate
In hemodialysis, the artificial kidney is also known as:
a) Hemofilter
b) Dialyzer
c) Purifier
d) Osmometer
Dialysis is an example of which type of process?
a) Chemical reaction
b) Physical separation
c) Biological transformation
d) Enzymatic degradation
The primary waste removed by dialysis is:
a) Carbon dioxide
b) Urea
c) Lipids
d) Amino acids
The semipermeable membrane used in dialysis allows passage of:
a) Proteins
b) Large cells
c) Small solutes and water
d) Lipoproteins
The key process responsible for water removal in dialysis is:
a) Osmosis
b) Diffusion
c) Ultrafiltration
d) Evaporation
Hemodialysis is performed:
a) In the lungs
b) In the brain
c) Outside the body using a machine
d) Inside the peritoneal cavity
The membrane used in peritoneal dialysis is:
a) Cellulose
b) Peritoneum
c) Paper
d) Protein sheet
Which of the following is a component of dialysate?
a) Urea
b) Glucose
c) Creatinine
d) Proteins
Which of the following best describes osmosis?
a) Movement of solutes
b) Movement of solvent across semipermeable membrane
c) Active pumping of ions
d) Movement of gases
What is the role of bicarbonate in dialysate?
a) Provides energy
b) Corrects metabolic acidosis
c) Removes proteins
d) Acts as anticoagulant
Which of the following is true about peritoneal dialysis?
a) It uses the patient’s peritoneum as a membrane
b) It requires a large dialysis machine
c) It filters blood directly without fluid exchange
d) It cannot be done at home
The movement of solutes across the dialysis membrane stops when:
a) Temperature rises
b) Equal concentration is achieved on both sides
c) ATP is exhausted
d) Pressure difference is lost
Dialysis in biochemistry laboratories is mainly used for:
a) DNA replication
b) Protein purification
c) Enzyme inhibition
d) Cell lysis
The unit operation similar to dialysis in chemistry is:
a) Chromatography
b) Filtration
c) Distillation
d) Evaporation
The membrane used in laboratory dialysis is usually made of:
a) Rubber
b) Cellophane or cellulose acetate
c) Plastic
d) Protein film
The pore size of dialysis membrane determines:
a) Diffusion speed only
b) Selectivity of molecule passage
c) Protein shape
d) Color of dialysate
Which molecule remains retained during dialysis of blood?
a) Albumin
b) Urea
c) Sodium
d) Potassium
The process of dialysis can correct which condition?
a) Hyperglycemia
b) Uremia
c) Hypoxia
d) Hypertension only
Which of the following is an advantage of peritoneal dialysis?
a) Portable and can be done at home
b) No infection risk
c) Faster than hemodialysis
d) Does not require dialysate
Which complication can occur during dialysis?
a) Hypotension
b) Hyperglycemia
c) Fever only
d) Dehydration of membrane
The process of dialysis requires:
a) Energy from ATP
b) Only passive diffusion and pressure difference
c) Enzymatic catalysis
d) Redox reactions
Dialysis removes substances mainly based on:
a) Charge
b) Size and concentration gradient
c) Color
d) Temperature
In clinical dialysis, blood access is achieved by:
a) Arteriovenous fistula or catheter
b) Nerve connection
c) Muscle channel
d) Simple needle
What is the function of glucose in dialysate?
a) Acts as an osmotic agent
b) Increases diffusion of proteins
c) Prevents infection
d) Stabilizes hemoglobin
The process of dialysis is:
a) Exothermic
b) Endothermic
c) Neither, it’s a physical process
d) Catalytic
Dialysis can also be used to:
a) Separate large proteins from small molecules in lab research
b) Destroy bacteria
c) Add enzymes to blood
d) Perform PCR
In patients with complete kidney failure, dialysis is:
a) Temporary relief until transplantation
b) Permanent cure
c) Useless
d) Painful but unnecessary

✅ Answer Key