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The Urinary System
FYI: The Kidneys…
• Each kidney has a mass of 150 g and are
the size of your fist.
• They hold 25% of the body’s blood.
• They filter 200 L of fluid each day!
The Kidneys
• Key role in removing waste, maintaining
water balance and balancing blood pH.
Metabolic Wastes
Waste
Origin of Waste
Organ of
Excretion
Ammonia Deamination of a.a. by liver
Urea
Uric Acid
Two ammonia combine
with CO2
Byproduct of nucleic acid
breakdown (e.g., DNA)
Carbon
dioxide
Cellular respiration
Lactic
acid
Anaerorbic respiration
Kidneys
Lungs
Liver
FYI:
Bladder Capacity
• 200 mL: stretch receptors send impulses to
the brain; urge to urinate.
• 400 mL: more receptors activated & higher
frequency of impulses; feeling of urination
more urgent.
• 600 mL: voluntary control
is lost; micturition reflex
occurs.
Nephron Functions
• Other functions:
–
–
–
–
eliminate wastes
regulate blood volume
regulate blood pressure
control levels of
electrolytes &
metabolites
– regulate blood pH
Formation of Urine
Question One
(discuss in small groups)
Does everything contained within the
glomerulus filter into the Bowman’s capsule?
No – plasma proteins, blood cells & platelets
are too large.
Stage 1: Filtration
• Solutes and water move from the blood
into the Bowman’s capsule.
• Dissolved solutes move from areas of high
pressure to areas of low pressure.
– 2.5 times greater pressure than in a normal
capillary bed.
• Plasma proteins, blood cells, glucose
platelets are too large
• Glomerular filtrate, fluid formed
in Bowman’s capsule
Question Two
(discuss in small groups)
Does everything that was filtered into the
Bowman’s capsule become urine?
No – without reabsorption, 120 mL of urine
would be formed each minute…1 L of
water must be consumed every 10
minutes.
Stage 2: Reabsorption
• Solutes and water move from the nephron
back into the blood.
• 600 mL of fluid flows through the kidneys
each minute.
• 120 mL (20%) is filtered into the nephrons.
– 1 mL of urine is formed.
– 119 mL is reabsorbed.
Stage 2: Reabsorption
• Reabsorption of water and
solutes are regulated and
adjusted in response to
hormonal signals.
• Can be active or passive.
• Occurs until the threshold
level of a substance is
reached.
Stage 2: Reabsorption
• Na+ is actively
reabsorbed; negative ions
(Cl- & HCO3-) follow.
• Glucose and amino acids
are actively transported
out of the proximal tubule.
• An osmotic gradient forms
and pulls water into the
interstitial fluid (ISF).
Stage 2: Reabsorption
• Plasma proteins create another osmotic
gradient that draws water from the ISF and
into the blood.
• Remaining solutes in filtrate become more
concentrated.
Test It
Out!
Question Three
(discuss in small groups)
The last stage involves the movement of wastes
from the blood back into the nephron.
This primarily occurs via active transport. Which
organelle is likely found in high concentration
within the cells that line the tubules involved with
secretion?
Mitochondria
Stage 3: Secretion
• Movement of wastes
from the blood into the
nephron via active
transport.
– Primarily in the distal
tubule.
• Includes nitrogenous
wastes, medication,
excess H+ and K+
ions.
Why / how is urine used to
determine if individuals have
various disorders?
Is my
colour
normal?