Internal Affairs (110.0K) Introduction to the Urinary
System - The urinary system consists
of two kidneys, two ureters, the urinary bladder, and the urethra.
- The urinary system maintains
the composition and properties of body fluid, which establishes the extracellular
environment. The end product of the urinary system is urine, which is voided
from the body during micturition.
Kidneys - The kidneys are retroperitoneal,
embedded in a renal adipose capsule.
- Each kidney is contained
by a renal capsule and divided into an outer renal cortex and an inner renal
medulla.
- The renal medulla
is composed of renal pyramids separated by renal columns.
- The renal papillae
empty urine into the minor calyces and then into the major calyces, which
drain into the renal pelvis. From there, urine flows through the ureter.
- Each kidney contains
more than a million microscopic functional units called nephrons.
- Filtration occurs
in the glomerulus, which receives blood from afferent glomerular arterioles.
- Glomerular blood
is drained by efferent glomerular arterioles that deliver blood to peritubular
capillaries surrounding the nephron tubules.
- The glomerular capsule
and distal convoluted tubules are located in the renal cortex.
- The nephron loop
is located in the renal medulla.
- Filtrate from the
distal convoluted tubule is drained into papillary ducts that extend through
the renal medulla to empty urine into the calyces.
Ureters, Urinary Bladder,
and Urethra - Urine is channeled from
the kidneys to the urinary bladder by the ureters and expelled from the urinary
bladder through the urethra. The detrusor muscle of the urinary bladder and
the sphincter muscles of the urethra are used in the control of micturition.
- Each ureter contains
three layers: the mucosa, muscularis, and adventitia.
- The lumen of the
urinary bladder is lined by transitional epithelium, which is folded into
rugae. These structures enhance the ability of the urinary bladder to
distend.
- The urethra has an
internal sphincter of smooth muscle and an external sphincter of skeletal
muscle.
- The male urethra
conducts urine during urination and seminal fluid during ejaculation.
The female urethra is much shorter than that of a male and conducts only
urine.
- The male urethra
is composed of prostatic, membranous, and spongy portions.
- Micturition is controlled
by reflex centers in the second, third, and fourth sacral segments of the
spinal cord.
|