URINARY SYSTEM
Your body takes in nutrients from food and uses them to maintain body functions. After your body
has taken what it needs, waste products are left in the blood. The urinary system works to filter the
blood to remove nitrogenous waste and keep certain chemicals and water in balance.
FUNCTIONS: KIDNEYS --1. Maintain purity and constancy of internal fluids by filtering
the blood – removing nitrogenous waste and excess ions
from the blood --returning needed substances back to the
blood
2. Regulate blood volume and chemical makeup so there is a
balance between water, salts, and acids/bases
3. Produce enzyme renin – regulate blood pressure
4. Produce hormone erythropoietin – stimulate erythropoiesis
5. Convert Vitamin D to active form
FUNCTIONS: URETERS, BLADDER, URETHRA
1. provide temporary storage for urine (bladder)
2. serves as transportation channels to carry urine (ureter,
urethra)
Anatomy of the Kidney
 The kidneys lie against the dorsal body wall in the retroperitoneal position (beneath the parietal
peritoneum) in the superior lumbar region. The right kidney is positioned lower than the left to
make room for the liver. The medial indention is called the renal hilus. Adrenal glands sit atop of
each kidney.
 Renal capsule is a fibrous layer
surrounding the kidneys that
contains adipose to hold the
kidneys in place.
 The kidneys are composed of 3
regions: cortex, medulla, pelvis
 Renal arteries branch from the
descending aorta to bring blood to
kidneys for filtration. Renal veins
return filtered blood to the inferior
vena cava.
One-quarter of the total blood
supply of the body passes through
the kidneys each minute.
Average adult produces 3 pints of
urine a day.
NEPHRONS –
Each kidney contains millions of nephrons. Nephrons are the
structural and functional units of the kidneys. Nephrons regulate
the concentration of water and soluble substances by filtering
the blood, reabsorbing what is needed and excreting the rest as
urine. Each nephron consists of 2 structures:


Glomerulus – knot of capillaries
Renal tubules – Bowman’s capsule, proximal convoluted
tubule, loop of Henle, distal convoluted tubule
Formation of URINE:
1. Renal artery brings blood to kidneys – afferent arteriole feeds blood to glomerulus in the cortex.
2. Filtration occurs – water, excess salts, glucose and waste (urea) are forced through the capillary
walls into the Bowman’s Capsule. This is FILTRATE! The efferent arterioles receive blood from
the glomerulus.
3. Tubular Reabsorption – movement of water,
glucose, other nutrients and ions out of the renal
tubules back into blood capillaries.
4. Tubular Secretion – ions (Na/K/NH3) and drugs
move out of the blood capillaries into the renal
tubules.
5. Collecting tubules receive urine and carry it to
the calyxes then the pelvis, which connects to
the ureter.
6. Ureter carries urine to bladder – micturition or
voiding occurs (emptying the bladder).
7. Urine enters urethra and is carried out the body.
Urine Composition –
95% water
5% other solutes – urea, uric acid, creatinine & ions
 Contains urochrome – a yellowish pigment
from the breakdown of hemoglobin
 Urine is sterile.
Regulating water & electrolyte BALANCE:
Reabsorption of water and electrolytes is regulated
primarily by hormones. When blood volume drops, arterial blood pressure drops which decrease the
amount of filtrate formed by the kidneys. Receptors in the hypothalamus trigger the posterior pituitary
to release antidiuretic hormone (ADH) that causes more reabsorption of water to increase blood
volume and pressure. Renin stimulates the adrenal cortex to secrete aldosterone which causes Na
and water reabsorption to increase blood volume which increases blood pressure.