1. The Urinary System
Part 1: Overview

2. Function of…
The urinary system gets rid of nitrogen containing waste in the body, regulates the amount of water, salts, and maintains the proper pH of the blood

3. Function (Con’t)
The kidneys filter gallons of fluid from your blood stream each day
This eliminates waste but also keeps your blood volume in check
The kidneys produce an enzyme that regulates your BP and a hormone that stimulates RBC production
And they produce urine

4. The Kidneys
Located against the dorsal body wall just under your 11th to 12th rib - protection
They are about the size of a large bar of soap
The medial side has the renal hilum or spot where the ureters, blood vessels, and nerves enter and exit

5. Kidney Anatomy The kidney has 3 main regions
The outer region is the renal cortex
The middle layer is the renal medulla, which contain the renal pyramids (the tip of the pyramids point deeper into the kidney)
The inner layer is the renal pelvis, which is a cavity or basin that collects urine and passes it to the calyces – both are extensions of the ureter

6. Blood Supply
25% of our blood is passing through our kidneys each minute!
This blood passes into the kidney via the renal artery
So “dirty blood” enters the kidney via the renal a. and “clean blood” leaves the kidney via the renal vein

7. Where the Magic Happens!
Nephrons are the functional unit of the kidney – they make urine
The players to learn here are the glomerulus, renal tubule, Bowman’s capsule, proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), afferent & efferent arterioles, and collecting ducts.

8. Nephron Anatomy

9. The Urinary System
Part 2: Making Urine

10. The Big Picture
Urine formation is complicated but can be broken down into 3 basic steps
Glomerular filtration – filter your blood
Tubular reabsorption – bring back “good” stuff that got filtered into the urine
Tubular secretion – getting the last of the “bad” stuff out of the blood

11. Complicated???

12. Step 1: Glomerular Filtration
The glomerulus is a filter
Fluid leaves the blood and enters Bowman’s capsule
This fluid is just blood plasma without the cells and other large proteins (too big to leave the blood)
It’s this fluid that will eventually become pee (urine)
This step is all driven by blood pressure

13. Blood in the Urine Not a good thing!
Blood cells should be too big to get through the capillary cells
So if blood is in the urine, something is wrong with the glomerulus – boxers often have blood in their urine from blows taken by their kidneys

14. Step 2: Tubular Reabsorption
The filtrate has a lot of good stuff in it and we don’t want to pee it out. Like what?
Stuff like water, glucose, amino acids, and useful ions – this gets reabsorbed by the blood stream
Bad stuff like nitrogenous waste (urea), uric acid, and creatinine stay behind
Note – most of this step takes place in the PCT – proximal convoluted tubule

15. Step 3: Tubular Secretion
This step makes sure we get rid of all the bad stuff
Certain drugs and ions are passed into the urine here
This occurs in both the PDT and the DCT or distal convoluted tubule

16. Loop of Henle & the K-Rat
This part of the nephron recovers water and salt before it leaves the body as urine
It is also the area that makes urine more concentrated then the blood in our blood stream – so we don’t need to drink too much water to survive
The Kangaroo rat loop of Henle is so long, and efficient that the K-rat of the desert never needs to drink a single drop of water in their entire life!

17. Urine
Despite up to 180 liters of blood plasma passing into the glomerulus, only 1 to 2 liters of urine are produced per day
Urine contains nitrogen waste and other substances not needed by the body
Color: clear to dark yellow (caused by the pigment urochrome, a breakdown product of hemoglobin
It is sterile, and picks up an ammonia odor over time
The pH is slightly acidic (pH of 6)
Its specific gravity is greater than 1.0 (1.001 – 1,035)
You should not find blood cells, blood proteins, sugar, glucose, hemoglobin, and white blood cells

18. The Urinary System
Part 3: The Three U’s

19. Ureters
The passageway for urine to leave the kidney and enter the bladder
Smooth muscle drives the urine down toward the bladder using peristalsis
Valves prevent the urine from going back up the ureter

20. Urinary Bladder A collapsible bag that stores urine
Your bladder holds about 500 ml or pee but can actually hold up to 1 liter
The bladder has three openings – 2 ureters and 1 urethra

21. Urethra The urethra carries your pee to the outside of your body
You have two valves or sphincter muscles – one is involuntary (smooth muscle) the other is voluntary (skeletal muscle)
In females it is short (1.5” long) but much longer in males (8” long)

22. Micturition The fancy name for peeing – micturition
After you get past 200 ml of pee, contractions of the bladder send pee past the first valve and up against the 2nd valve – you control that one
If you “hold it in” you can collect another 200 ml before the contractions start again

23. Incontinence/Retention
If you can’t control the 2nd valve, you are incontinent – common among younger children
If you can’t pee you have urinary retention and may need a catheter or drainage tube inserted