Unit 26

For this week, your readings are taken from two chapters of Hole's Human Anatomy and Physiology: chapters 20 & 21. Some of chapter 20 simply describes the anatomy of the kidney, nephron, and urinary system; since we did that material in lab, we will not continue much with it here. Instead, I will mainly focus on the physiology of the nephron (and control of urine release) for this lecture unit. We are also covering the remainder of chapter 21-- the sections on water and electrolyte balance (pages 816 - 823). These sections of chapter 21 fit nicely into this unit, since the kidney is involved in the maintenance of proper body fluid composition.

We talked in lab about how the kidneys filter our blood. Now you will see what is really meant by that. If you think about the composition of blood, you will realize that blood plasma receives materials from the interstitial fluid and from lymph... these fluids are all really one large extracellular fluid system anyway (as we saw back in Unit 23 when we read the other portions of Chapter 21). So, when the kidney filters out the blood, it is really filtering out all the extracellular fluids; but it only works directly on blood fluid. It has to remove the wastes, but leave the nutrients in the blood. It has to also be able to maintain most of the water in our bodies, yet maintain osmotic balance when it removes the wastes. These are very challenging tasks.

Despite the complexity and difficulty of the tasks of the kidneys, a person can function just fine with only one working kidney. A friend of my family suddenly became ill last year... he went to the doctor, and his tests revealed that his whole life he had been walking around with only one functional kidney! He never knew that one of his kidneys had never formed properly. His illness came because his one working kidney began to have difficulty functioning. Once a person's kidneys are damaged, if that person is not a kidney transplant candidate, they can continue to live by using a dialysis machine to filter their blood. This is not a wonderful substitute for a kidney, since a person typically has to spend many hours each week hooked up to a machine, with their blood flowing out of their body, into the machine, and back into their body through tubes and needles. However, it is better than the alternative of not using the machine at all! The person I was telling you about at the beginning of this paragraph has been lucky that his kidney problems were temporary... he does not have to go in for dialysis.

Here is the way that I have organized this Unit's web pages:

Additional Nephron features (not discussed in lab)

What wastes are we trying to get rid of?

Urine Formation involves: glomerular filtration, tubular reabsorption, and tubular secretion

Using A.D.A.M.

Glomerular filtration

What happens in the proximal convoluted tubule?

What happens in the loop of Henle?

	Ascending and descending the loop
	Osmosis and Concentration Gradients

What happens in the distal convoluted tubule and collecting duct?

When is enough enough? What is the goal for all the exchange of fluid that occurs in the tubules? Homeostasis!

	Water Balance: losing and gaining water
	Electrolyte Balance: maintaining the right amount of electrolytes

Elimination of Urine

Here is the diagrammatic outline of this week's web pages:

outline26.jpg (12308 bytes)

Some useful kidney links:

	How the kidney works
	PowerPoint presentation on the kidney (it is like an entire chapter)