The Excretory System

To maintain life processes, the body must eliminate waste products. The main function

of the urinary system is to excrete waste.

The kidneys play a crucial role in removing waste, balancing blood pH, and maintaining water balance.

Urinary System Anatomy

- Wastes are filtered from the blood by the kidneys and conducted to the urinary bladder by ureters.

- The urinary sphincter muscle located at the base of the bladder acts as a valve, permitting the storage of urine.

- When approximately 200 mL of urine has been collected, the bladder stretches slightly and nerves send a signal to the brain.

- at 400 mL, more stretch receptors are activated and the message becomes more urgent.

- at 600 mL, voluntary control is lost. The sphincter relaxes and urine enters the urethra and it is released.

The Kidney The kidneys filter out

wastes and excess ions, which leave the body in the urine, and return any needed substances back to the blood.

In one day, the kidneys filter over 140 L of blood.

The body's entire volume of blood is filtered every 40 minutes!

The human kidney weighs about 0.5 kg, but may hold up to as much as 25% of the body's blood supply at any given time.

Cross section of the kidney:

The Nephron: the function unit of the kidney

There are approximately one million nephrons in each kidney.

Nephron location in kidney...

Efferent arteriolessmall branches that carry blood away from the glomerulus to a capillary bed

Peritubular capillaries network of small blood vessels that surround the nephron

Bowman's capsule cup-like structure that surrounds the glomerulus

Proximal Tubulesection of the nephron joining the Bowman's capsule with the loop of Henle

Loop of Henle carries filtrate from the proximal tubule to the distal tubule

Distal tubule conducts urine from the loop of Henle to the collecting duct

Collecting ducttube that carries urine from nephrons to the pelvis of a kidney