Case Study:

In a government hospital in Delhi, a patient named Ramesh was diagnosed with severe kidney failure. The kidneys normally filter blood to remove waste products like urea, excess salts, and water. When kidneys stop functioning properly, these harmful substances accumulate in the bloodstream, which can be life-threatening.

To manage this condition, doctors recommended hemodialysis, a medical procedure that uses a dialysis machine (often called an artificial kidney). During dialysis, blood from the patient’s body is pumped through a device called a dialyzer. Inside this device, the blood flows through thousands of tiny tubes made of a semi-permeable membrane.

On the other side of the membrane flows a special fluid called dialysate. Waste substances such as urea and excess salts move from the blood into the dialysate by diffusion, because molecules naturally move from regions of higher concentration to lower concentration. 

Large components of blood such as red blood cells and proteins cannot pass through the membrane pores, so they remain in the blood. After filtration, the cleaned blood is returned to the patient’s body. 

A typical dialysis session lasts 4-5 hours and may be required several times a week depending on the patient’s condition. 

This technology acts as a temporary replacement for kidney function and helps maintain the balance of water, salts, and waste products in the body. The example shows how understanding biological processes like excretion, diffusion, and filtration can help scientists design life-saving medical technologies.

Questions

Section A - MCQs

1. The main purpose of dialysis in a patient with kidney failure is to:

A. Increase blood pressure
B. Remove waste substances from blood
C. Produce hormones in the body
D. Increase the number of red blood cells

2. In a dialysis machine, waste substances move from blood to dialysate mainly by:

A. Photosynthesis
B. Diffusion
C. Active transport
D. Digestion

3. Why do red blood cells remain in the blood during dialysis?

A. They are destroyed during dialysis
B. They are too large to pass through the membrane
C. They dissolve in dialysate
D. They move into the dialysate and return later

4. Which structure in the dialysis machine performs the filtering function similar to the kidney?

A. Dialyzer
B. Heart pump
C. Stomach
D. Nerve cell

Section B - Short Answer Questions

1. Why is a semi-permeable membrane essential in a dialysis machine?

2. Explain why dialysis is required when kidneys fail.

3. How does diffusion help remove urea from blood during dialysis?

Section C - Long Answer Question

1.A patient suffering from kidney failure undergoes dialysis regularly.

a) Explain how the dialysis machine acts as an artificial kidney.
b) Why are large molecules like proteins not removed during dialysis?
c) What could happen if dialysis is not performed for a patient with kidney failure?

Answer Key

MCQ Answers

1. B - Dialysis removes waste products such as urea from blood.
2. B - Diffusion allows waste molecules to move from higher concentration in blood to lower concentration in dialysate.
3. B - Red blood cells are too large to pass through the membrane pores.
4. A - The dialyzer acts as the filtering unit of the dialysis machine.

Short Answer Solutions

1.A semi-permeable membrane allows small waste molecules and water to pass through while preventing large molecules like proteins and blood cells from crossing.

2.When kidneys fail, waste products such as urea and excess salts accumulate in the blood. Dialysis removes these substances and maintains chemical balance in the body.

3.Urea concentration is higher in blood than in dialysate. Due to diffusion, urea molecules move across the semi-permeable membrane into the dialysate until concentrations balance.

Long Answer Solution

a) Artificial kidney function

The dialysis machine filters blood using a dialyzer containing a semi-permeable membrane. Waste products diffuse into dialysis fluid while clean blood is returned to the body.

b) Large molecules remain

Proteins and blood cells are larger than the membrane pores, so they cannot pass through and remain in the bloodstream.

c) Without dialysis

• Waste products accumulate in blood
• Body fluid balance becomes disturbed
• Toxic substances may damage organs and can become life-threatening.