The Urinary System

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