Biology 12

Chapter 4 Homeostatic Mechanisms • MHR 113

Another waste product found in the blood is
uric acid, which is usually produced by the
breakdown of nucleic acids such as DNA and RNA.
Creatinine is a waste product of muscle action. All
of these waste products are potentially harmful to
the body and therefore must be removed.
The kidneys are more than excretory organs;
they are one of the major homeostatic organs of the
body. In addition to filtering the blood to remove
wastes they also control the water balance, pH, and
levels of sodium, potassium, bicarbonate, and

calcium ions in the blood. They also secrete a

hormone (erythropoietin) that stimulates red blood

cell production, and they activate vitamin D

production in the skin. Since the kidneys are

involved with so many of the body’s functions, the

analysis of a urine sample can tell a physician a

great deal about a patient. For example, diabetes

and pregnancy can be determined using a urine test.

Each kidney is composed of three sections — the

outer cortex, the medulla, and the hollow inner

pelviswhere urine accumulates before it travels

Canadians in Biology

Cellophane and Imagination —

Dr. Gordon Murray

On December 6, 1946, Dr. Gordon Murray was called

into Toronto General Hospital. A female patient in a coma

was wheeled into the room on a stretcher. She was

“uremic,” which means her kidneys were not functioning

and the toxins in her blood were poisoning her body.

Staff from all over the hospital watched as Murray set up

an innovative apparatus. He inserted one end of 46 m of

tubing into a vein in one of the patient’s legs and the

other end into an artery in her other leg. He then turned

on a pump. The patient’s blood immediately began to

circulate through the tubing, which was strapped to a

cylinder, immersed in a bath, coiled around and around,

and then diverted back to the patient. Regular readings

were taken of both the patient’s blood and the bath

solution to see if the toxins were leaving the blood. As

time passed, the readings proved the device was working.

The patient regained consciousness in six hours.

The Steps to Success

Dr. Gordon Murray was born in 1894 in Stratford,

Ontario. He was awarded the Order of Canada in 1967

as the first North American to develop and use kidney

dialysis (also known as “hemodialysis”). Dr. Murray became

renowned as a hard-working and imaginative scientist.

An impediment to successful kidney dialysis was how to

get impure blood outside the body and keep it from

clotting. In 1935, Dr. Murray pioneered the use of the

drug heparin, an anticoagulant that keeps blood from

clotting and keeps sutures pliable after surgery. Heparin

brought Dr. Murray one step closer to successful dialysis.

The second problem to overcome was how to filter

impurities from the blood. Dr. Murray considered using

the principle of osmosis. He looked for a material that

was porous enough to let the smaller, toxic particles in

the blood pass through into another solution while

keeping in the larger particles (plasma).

In a series of experiments, Murray tried a variety of

materials, including leather and nylon, to form the tubing

for his machine. Finally, he tried cellophane designed for

use as sausage casing. It was the ideal filter; it retained the

important contents of blood while allowing the toxins to

escape into a solution in which the tubing was immersed.

In Dr. Murray’s first experiment on an animal, he attached

one end of his tubing to an artery and the other to a vein,

letting the heart pump the blood from the artery through

the tubes and back into the vein. The experiment was

successful — the toxins left the animal’s blood. However,

recalling that blood returning tothe heart fromthe body’s

extremities (venous blood) is the most impure blood,

Murray developed a pump that would simulate the heart’s

action and pump the blood the opposite way through

the tube.

A Partial Victory

Today, kidney dialysis (or the “artificial kidney”) enables

people with kidney disease to live relatively normal lives.

However, these patients must undergo regular dialysis

sessions — usually three six-hour sessions per week.

Researchers are striving to invent a machine to make

this labour-intensive process obsolete.

Dr. Gordon

Murray