Urinary System
Cleaning up the system
Parts
 Kidney - filters the blood
 Ureter – transports the waste material to the bladder
 Urinary Bladder – stores the waste products
 Urethra – releases waste products out of the body
Kidney
 Located next to the vertebral column.
◦ Top about even with the 12th thoracic vertebra and the bottom about even with the 3rd
lumbar vertebra
 Reddish brown, bean shaped
◦ Adults about 13 cm long, 6 cm wide, and 3cm thick
 Located in a fibrous capsule
Function
 Maintain homeostasis by regulating the blood pH, volume, and composition
◦ Removes metabolic wastes from blood
▪ Are diluted with water and electrolytes to make urine
 Secretes erythropoietin – controls rate of red blood cell production
 Helps activate vitamin D
 Secretes renin, an enzyme that maintains blood volume and pressure
Structures
 Renal sinus – hollow chamber where blood vessels, nerves, lymphatic vessels and the ureter
enter and leave
 Renal pelvis – superior end of the ureter expanded into a sac inside the renal sinus
 Renal medulla – inner region of the kidney composed of the renal pyramids
 Renal cortex – outer shell around medulla that dips into the medulla to create the renal columns
 Nephrons – the functional unit of the kidney about 1 million/kidney
To clean blood, you need blood
 Renal Artery
◦ Branches from the abdominal Aorta
◦ 15-30% of total cardiac out put is sent to the kidneys when you are at rest
◦ The renal artery branches into smaller and smaller vessels until it becomes the afferent
arterioles that lead to the nephrons
 Renal Vein
◦ “Clean” blood travels through ever larger vessels to the renal vein
◦ Empties into the Inferior Vena Cava that leads to the heart
Okay, we got blood, now it is the nephron's turn
 Blood vessels become tangled into a glomerulus which is located in a glomerular capsule (AKA
Bowman's capsule)
◦ Fluid in the blood is filtered into the capsule ( the proximal end of the renal tubule)
 Renal tubule becomes highly coiled then dips down into the Loop of Henle
◦ This is interlaced with capillaries
◦ Fluid is returned to the blood and electrolyte balances are fine tuned here

The renal tubule climbs back up and empties into the collecting duct – we now have urine
We got urine... now what?
 The collecting ducts merge together and empty into a minor renal calyx which in return empties
into a major calyx, which them empties into the renal pelvis, which empties into the ureter
 The ureter is a tube that leads to the urinary bladder
◦ Uses peristaltic waves to move the urine down its length
We made it to the bladder
 A hollow, distensible, muscular organ
◦ Stores urine and then forces out the urethra
◦ In the pelvic cavity, behind the symphysis pubis and under the parietal peritoneum
◦ A sphincter at the neck of the bladder hold urine in until the pressure inside is to a certain
level Involuntary control
◦ External urethral sphincter – skeletal muscles – voluntary control
Micturition AKA urination
 How do we know to go? By the amount there
◦ 150 ml typically = urge to go
◦ 300 ml sensation of fullness, bladder contraction intensify
◦ 600 ml typically = pain
 Bladder signals spinal cord, which releases involuntary sphincter, you feel like you must go
 External urethral sphincter is released when you go to the restroom.