Functions of Urinary System
• Kidneys carry out four functions
– Filter nitrogenous wastes, toxins, ions, etc. from blood
to be excreted as urine.
– Regulate volume and chemical composition of blood
(water, salts, acids, bases).
– Produce regulatory enzymes.
• Renin – regulates BP/ kidney function
• Erthropoeitin – stimulates RBC production from marrow.
– Metabolism of Vitamin D to active form.
• Two Kidneys
– Perform all functions except actual excretion.
• Two Ureters
– Convey urine from Kidneys to Urinary Bladder
• Urinary Bladder
– Holds Urine until excretion
– Conveys urine from bladder to outside of body
Kidney general info
• Lie against posterior abdominal wall at level of
• Right kidney is lower than left kidney due to the
shape of the liver.
• Lateral surface of kidney is convex while medial
– Concave side has a cleft – Renal Hilus
– Inside hilus is Renal sinus
• Where kidneys receive renal vessels and nerves.
Kidney External Anatomy
• Average size – 12cm x 6cm x 3 cm
• Weights 150 grams or 5 oz
• Surrounded by three membranes (deep to
– Renal capsule – fibrous barrier for kidneys.
– Adipose capsule – fatty tissue designed for protection /
– Renal fascia – dense fibrous CTP anchors kidneys/
adrenals/ membrane 1 and 2 to surroundings.
Urine Formation I
• Glomerular filtration
• Water, ions, amino
acids, and glucose get
into capsular space
• Proteins stay in blood
– too big to leave
Urine Formation II
• Proximal convoluted
tubule and Peritubular
• Na+ goes down
gradient and brings
glucose, amino acids,
etc. back into blood
• Reabsorbs about 65%
Urine Formation III
in the Nephron Loop
• Descending limb
• Ascending limb
• Goes into medulla
- increasing salt
• Water leaves
• Fluid concentrates
• Goes up toward cortex
- decreasing salt
• Na+ pumped out
• Fluid relatively diluted
– 25 cm long
– Enters on the floor of bladder
• Urinary Bladder
Muscular sac on floor of pelvic cavity
Muscle layer formed by detrusor muscle
Average bladder volume is 500 ml
Max capacity is 700-800 ml
Conveys urine out of body
Female urethra – 3 - 4 cm
Opens into external urethral oriface
Lies between vaginal oriface and clitoris
Male urethra – 18 cm
• Prostatic urethra – 2.5 cm
• Membranous urethra – 0.5 cm
• Penile urethra – 15 cm
Bladder with >= 200 ml of urine
Sensory input to parasympathetic system
Contraction of detrusor muscle and
relaxation of internal urethral sphincter
Relaxation of external urethral sphincter
• A hard granule of calcium, phosphate, uric acid
• Form in renal pelvis and get lodged in pelvis or
• Caused by urinary tract infections, dehydration,
pH imbalances, or an enlarged prostate gland.
• Treated with stone dissolving drugs, surgical
removal, or lithotripsy (ultrasonic vibrations)
Visualizing the Urinary System
• Be able to identify layers of the kidney on
• Be able to locate kidneys, ureters, urinary
bladder, and urethra on cat.