The Kidney & Dialysis

Diffusion, osmosis, & active transport in the body

Gross Anatomy

Posterior in the abdominal cavity Bean shaped Just below the rib cage Size of a fist

What do they do?

Kidneys filter waste products and make urine1. Waste products from cells end up in the blood 2. Blood circulates around the body including the

kidneys – Artery = away from the heart, into the kidney– Capillaries = thin walls allow waste to leave– Vein = leaves the kidney, back to the heart

Kidney Facts

The rate of filtration is approximately 125 ml/min or 45 gallons (180 liters) each day. Considering that you have 7 to 8 liters of blood in your body, this means that your entire blood volume gets filtered approximately 20 to 25 times each day!

www.how.stuffworks.com

A closer look

Nephron

The repeating functional unit of the kidney A semi-permeable tube whose job is:

1. Filtration

2. Reabsorption

3. Secretion

Filtration

Plasma (containing water, salts, food, waste, and other solutes) pass from the blood into the nephron.

Blood cells cannot fit through the membrane filter and remain in the capillary.

Reabsorption

Both active and passive transport move good molecules from the nephron tube back into the blood stream

Solutes are pumped (actively transported) back into the capillaries

Water follows osmosis Bad stuff like waste is left in the

tube headed to the bladder

Anything that doesn’t get reabsorbed into the blood gets “peed” out (becomes urine)

Secretion

Opposite of reabsorption Waste (H+ ions, drugs) are pumped from

capillaries directly into the tube

What if it doesn’t work?

Kidney usage is usually measured in percent If you lose a kidney you can still filter 100%

(you really only need one) When total kidney function drops below 20%

it can be lethal Treatment- dialysis

The dialysis

A dialysis tube acts as the nephron

Blood is pumped through the dialysis tube into a machine

The dialysis tube passes through a solution allowing diffusion and osmosis to remove waste and excess water

Why does it work?

A waste product like urea is more concentrated in the blood than in the fluid (dialysate) so the urea passes through and is washed away

What’s happening in the nephron?

How does structure meet function?

Cells that make up the tube are different depending on their jobs!

Hemodialysis

hemo = blood Internal filters don’t

work, use an external filter

Blood is filtered through an external machine

Life on dialysis

Kidneys work 24/7 to get the job done

Dialysis is periodic, not continuous

Dialysis takes 4-5 hours Why can’t all the blood be

filtered at once? Patients go to a clinic 3 times

a week (MWF or THS)

Is hemodialysis just as good as a kidney?

What do you think?

Hemodialysis Effectiveness

About 10% as effective as normal kidneys

Became available in the early 60s

Some of the first patients are still alive

Not a full life expectancy Without dialysis- certain death 20 million Americans

Be the doctor! Manipulating the dialysate

In end-stage renal (kidney) failure potassium concentrations get really high

This can cause big problems (Na+/K+ pump)

What should you do to the concentration of potassium ions in the dialysate to fix this problem?