EXCRETORY SYSTEM by Nick Pekas and Gabe Sexton

1. Structures of the Renal (Excretory) System:
Kidneys (Main Organs of the Excretory System)

-Shaped like a kidney bean, with renal blood vessels entering & exiting the concave side.

Structures of the Kidney:

-Renal Pyramids are fan shaped structures made up of thousands of nephrons.

-Nephron (Main Component of the Kidney)

-Glomerulus (AKA renal corpuscle) – portion of a nephron that begins the process of filtration
· Blood enters the glomerulus by the renal artery

Function(s)of the Kidney:

  • Collects and excretes nitrogen waste
  • · Regulates blood pressure
  • · Activates Vitamin D (regulates calcium absorption)
  • · Controls erythropoiesis (blood cell creation) using the hormone erythropoietin (which activates when the kidney recognizes low Oxygen conditions)
  • · Osmoregulation (control of ions and water balance in the body)
a. After a nephron filtrates the blood, it empties the waste into a collecting duct

b. Collecting Ducts –Small tubes in a nephron that carry nitrogen waste

c. Minor Calyx - Many collecting ducts empty into the Minor Calyx (a larger duct)
d. Major Calyx – Many Minor Calyces empty into a Major Calyx

e. Renal Pelvis – All Major Calyces empty into the renal Pelvis where the nitrogen waste enters the ureters.


1. Renal pyramid • 2. Interlobular artery • 3. Renal artery • 4. Renal vein 5. Renal hilum • 6. Renal pelvis • 7. Ureter • 8. Minor calyx • 9. Renal capsule • 10. Inferior renal capsule • 11. Superior renal capsule • 12. Interlobular vein • 13. Nephron • 14. Minor calyx • 15. Major calyx • 16. Renal papilla • 17. Renal column


-Long tubes that carry urine from the kidneys to the urinary bladder

Urinary Bladder:

  • -Storage sack for urine. Has nerves within that create the urge to urinate when it is filled to 25% capacity.
  • Two muscles that control urination are the internal and external sphincter. The internal sphincter is involuntary, and the external one is voluntary.
  • If the Urinary Bladder ever reaches 100% capacity, the external sphincter is opened automatically, and urination takes place.

-Carries urine out of the body

2. Enzymes/Hormones

Antidiuretic Hormone (ADH)
  • Controls the reabsorption of water into the blood
  • Released by the pituitary gland in the brain
  • Low fluid levels in blood - Increased production of ADH, more water is reabsorbed
  • High fluid levels in blood - Decreased production of ADH, less water is reabsorbed

  • Controls passage of sodium ions from nephron to blood
  • Also affects water transfer, since "solute sucks"
  • The sodium ion has a positive charge, so negatively charged ions will also follow it into the blood

Renin (the only enzyme in this list)
  • Stimulates production of Angiotensin I, which is converted to Angiotensin II
  • Released by afferent arteriole cells (inside nephron)

Angiotensin II
  • Stimulates release of Aldosterone
  • Increases blood pressure by causing blood vessels to constrict
The co-operation of Renin, Angiotensin and Aldosterone is known as the Renin-Angiotensin-Aldosterone System (RAAS). Its overall effect is to regulate blood pressure and fluid balance.

3. Regulation of the Urinary System
  • · Adrenal Gland
    • sits on top of kidneys produces hormones that help control osmoregulation by determining how many sodium and chloride ions are reabsorbed into the bloodstream.

o This controls water balance because water follows the greatest concentration of solute i.e. “solute sucks”

  • · Antidiuretic Hormone (ADH), which is also known as Vasopressin
    • Is secreted by the pituitary gland and controls the amount of water absorption by nephron tubules (controls the amount of urine produced)

4. Communication

With Excretory cells/organs: Explained in section 2

With rest of body/other body systems:
The Nervous System is constantly communicating with all systems via nervous impulses.

The Circulatory System can communicate with the Excretory system through Atrial Natriuretic Hormones
  • Inhibits release of Aldosterone and ADH
  • Produced by the heart when there is excess blood in the body
  • Inhibition of Aldosterone and ADH means more ions and water are excreted in urine, decreasing blood volume

Anatomy Class Notes