THE URINARY SYSTEM
FORM AND FUNCTION
COMPONENTS
 2 Kidneys
 2 ureters
 1 urinary bladder
 1 urethra
FUNCTIONS:
 Excretion and filtration
 Regulation of blood volume and pressure
 Regulation of blood solutes
 Regulation of pH
 Regulation of Red Blood Cell synthesis
 Vitamin D synthesis
Regulation of blood cell synthesis
 Production of Erythropoietin (a glycoprotein
hormone) by the kidneys controls manufacture of
new RBC’s
EPO is banned from use
by professional athletes
The kidneys and Vitamin D
The skin synthesizes inactive Vitamin
D and the kidneys convert it to the
active form.
KIDNEY STRUCTURE
 Kidneys are fist sized organs
 They are located on the posterior abdominal wall
on either side of the vertebral column
THE NEPHRON
 Each kidney is composed of millions of
microscopic filtering units known as nephrons
 The nephron is the functional unit of the kidney,
doing all of the actual work
INTERNAL STRUCTURE
NEPHRON STRUCTURE
FILTRATION
 21% of blood pumped by the heart each minute
flows through the kidneys
 19% of the blood plasma that flows through the
capillary bed of the glomerulus passes through
the filtration membrane into Bowman’s
Capsule, the first part of the nephron.
 The liquid is called the filtrate.
What is in the filtrate?
The filtrate should
contain water, salts,
glucose, amino acids,
wastes such as urea,
vitamins, minerals,
drug metabolites, and
ions (H+, Na+, and
K+)
Bowman’s Capsule
FILTRATION
Glomerulus
The filtrate should not contain blood cells, proteins,
or glucose (after initial rebsorbtion).
REABSORPTION
 180 liters of filtrate are produced daily!
 Plasma volume is only 3 liters so how many times
daily is the entire plasma volume filtered?
 60 times!
 Only 1-2 L of urine are produced daily
 Almost all of the water and useful solutes are
reabsorbed
THE PROXIMAL CONVOLUTED TUBULE
 Absorbs 65% of water and NaCl that passes through
 The Na+/K+ pump transports ions from the filtrate
into the tubule cells (simple cuboidal epithelium)
Important substances
such as amino acids,
glucose, vitamins, and
minerals are
reabsorbed into the
peritubular capillaries
MORE REABSORPTION
 The descending Loop of Henle concentrates the filtrate
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by removing water through osmosis
This reduces the filtrate volume by another 15%
Urea is removed by facilitated diffusion
In the acsending loop, the Na+/K+ pump moves Na+
to the interstitial fluid surrounding the loop.
Cl- and K+ are moved by symport
This part of the loop is impermeable to water, so it
cannot follow the ions passively
LOOP OF HENLE
THE DISTAL CONVOLUTED TUBULE
 About 80% of water and 90% of solutes have been
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removed from the filtrate so far
Helps regulate pH by controlling H+ elimination and
retention.
Works with PTH to reabsorb Ca2+ ions
Further water reabsorption is under hormonal control
ADH- Anti-diuretic Hormone causes water to leave the
filtrate and enter the tubule cells
When do you need ADH?
Not a vampire
Vampire
Sleeping
Dehydration
Sudden blood loss (aka,
hypovolemic shock
NITROGENOUS WASTE
 The metabolism of proteins produces nitrogen-based
waste products such as ammonia and urea
 These two substances can be toxic if they remain in the
body.
 The kidneys remove them in the distal convoluted tubule
THE COLLECTING DUCT SYSTEM
 It is controlled by hormones like ADH and Aldosterone
 The cells are impermeable to water, so any water in the
filtrate remains and is excreted with other wastes as
urine
The Collecting
Duct
What if your kidneys are not working?
DIALYSIS TREATMENT
The Kidneys at Work
http://www.youtube.com/watch?v=aQZaNXNroV
Y&feature=related
http://www.youtube.com/watch?v=glu0dzK4dbU