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Human Form & Function
The urinary system
Urinary system
The major structural components of
the urinary system are:
 Kidneys
 Urinary
 Ureters
 Urethra
bladder
Urinary system
Function
 To
rid the body of wastes, especially
nitrogenous wastes such as urea.
 To regulate the balance of fluid, salt &
pH.
 The blood is filtered as it passes through
the kidneys.
 Waste substances are removed by the
processes of filtration and tubular
secretion.
 Useful substances are returned to the body
by the process of selective re-absorption.
The kidneys
The functional unit of
the kidney is the
nephron
 A nephron consists of
a Bowman’s capsule,
a renal tubule and the
associated blood
supply.
 It filters waste products
out of the blood
 Each kidney contains
about 1.2 million
nephrons

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Proximal
The kidney convoluting
tubule Glomerulus
Capsule
Cortex
Distal
convoluting
tubule
Medulla
Renal
artery
Renal
vein
Renal pelvis
Collecting
duct
Loop of
Henle
Capillaries
Ureter
KIDNEY
A NEPHRON
The kidneys
Renal medulla –
loops of Henle
Renal artery
Renal vein
Renal cortex –
Bowman’s capsules
Ureter –
to the bladder
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The nephron
Bowman’s capsule
Common
collecting duct
Renal
corpuscle
Proximal
convolute
tubule
Distal convolute
tubule
Loop of Henle
The renal corpuscle
Filtration
takes place in the
renal corpuscle.
The
renal corpuscle consists
of the Bowman’s capsule
and a mass of blood
capillaries – the glomerulus.
The renal corpuscle
Afferent
arteriole
Bowman’s
capsule
Efferent
arteriole
Glomerulus
Proximal
convolute
tubule
Filtration
• Filtering the blood is a passive
process and occurs under high
pressure.
• The filtrate includes:
Water
Urea
Glucose
Amino acids
Vitamins
Salts (sodium & chlorine)
Microscopic section through a kidney
Glomerulus
Tubule
Photograph of a glomerulus taken with a
scanning electron microscope
Capillaries of
the glomerulus
Wellcome Images – David Gregory & Debbie Marshall
Re-absorption
• Not all substances in the
filtrate are waste products
• The nephron re-absorbes
needed nutrients
• These include:
• water
water
• glucose
glucose,
amino acids • amino
acids
vitamins
• vitamins
salts
water
salts
urine
- water
- urea
- salts
Section through a renal tubule taken
with a scanning electron microscope
Wellcome Images – David Gregory & Debbie Marshall
The proximal tubule


Microvilli line
the proximal
convolute tubule
and create a
brush border
This greatly
increases the
surface area for
re-absorption.
Microvilli
L Slomianka ANHB - UWA
Re-absorption
Structure
Substance
Active/passive
Proximal
Water (60-70%)
convolute tubule
Salts (60-70%)
Glucose (100%)
Amino acids (100%)
Vitamins (100%)
Passive (osmosis)
Loop of Henle
Water (25%)
Passive (osmosis)
Na+/Cl- (25%)
Active transport
Distal convolute
tubule
Water (5%)
Passive (osmosis)
Na+/Cl- (5%)
Active transport
Collecting duct
Water (5%)
Passive (osmosis)
Active transport
Tubular secretion
• Wastes are transfered
from the blood into the
tubules for excretion
• This is an active process
H+
NH4+ (ammonium)
Creatinine
Toxins
Drugs
Neurotransmitters
Tubular secretion
Process
Tubular
secretion
Structure
Proximal
collection
tubule
(PCT)
Distal
collection
tubule
(DCT)
Substance
Mode
H+
Active
NH4+ (ammonium) transport
Creatinine
Toxins
Drugs
Neurotransmitters
Creatinine is a chemical waste molecule that is generated from
muscle metabolism.
Filtration – a summary
enters the glomerulus (Bowman’s
capsule) under high pressure.
2. Water and other small molecules are forced
out of the blood vessels
3. This filtrate is collected and passes through
several tubules
4. Some water and useful substances are
reabsorbed
5. The rest passes through to the ureters and
is stored in the bladder for excretion
1. Blood
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Filtration – a summary
Filtration
Re-absorption
+
Tubular secretion
Excretion
Renal
cortex
Renal
medulla
Deamination
Definition:
The stripping of nitrogen from
amino acid & nitrogen bases (RNA)
Deamination occurs in the liver
Nitrogen occurs in the
amino (NH2) part of an
amino acid.
 Nitrogen is toxic to the
human body and must The amino
group
be removed.

Alanine
Deamination – chemical reaction
acid → ammonia +
organic compounds (used
for respiration)
 Amino
 Ammonia
(very toxic) + CO2
→ urea (H2NCONH2)
Nitrogen wastes
Nitrogen
Source
compound
Amount
Relative
toxicity
Urea
Amino Acids 21 g/day
Moderate
Creatinine
Muscle
metabolism
1.8 g/day
High
Uric acid
RNA
480mg/day Weak
Urine
 Urine
is a clear, transparent fluid.
It normally has an amber colour.
 It is collected in the bladder and
eliminated through the urethra.
 The average amount of urine
voided in 24 hours is about
1,200 cm3.
Composition of urine
The composition of urine varies but typically
contains:
95% water
5% other
 solutes (organic molecules)
urea
creatinine
uric acid
 ions
sodium & chloride ions
 other metabolic wastes.
Elimination vs. excretion

Elimination is the
removal of
undigested food
and waste from the
body.

Excretion is the
removal of
metabolic waste
produced by cells
from the body
Kidney Failure
Most kidney diseases affect the glomeruli which
reduces their ability to filter the blood (proteins
and RBCs will be present in urine)
 Some lifestyle measures to reduce the risk of
kidney damage include:

1.
2.
3.
4.
Maintain a healthy weight
Don’t smoke
Drink plenty of water
Alcohol only in moderation
Kidney failure is when kidneys lose their ability to
excrete waste and control the level of fluid in the
body.
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Dialysis

Dialysis is a method of removing
wastes from the blood when kidney
failure occurs. There are two types of
dialysis
peritoneal dialysis
haemodialysis
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Peritoneal dialysis



Peritoneal dialysis occurs inside the body
using the peritoneum (a membrane that lines
the inside of the abdominal cavity and covers
organs such as stomach, liver and intestines)
A fluid containing glucose and other
substances at concentrations similar blood
(and no wastes) is pumped via catheter into
the abdominal cavity.
Because of the concentration gradient
wastes diffuse from the blood into the fluid in
the abdominal cavity, useful products stay in
the blood as there is not concentration
gradient.
Peritoneal dialysis
Peritoneal
dialysis is
usually done
each day
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Haemodialysis
Haemodialysis involves passing blood
through an artificial kidney or dialysis
machine
 The blood is passed through many tubes
made of differentially permeable membrane
and immersed in a bath of fluid.
 The concentration of substances in the fluid
bath are similar to those in the blood (fluid
has no waste)
 Due to concentration gradient wastes are
passed from the blood into the fluid, useful
substances remain in blood (no concentration
gradient)

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Haemodialysis
Haemodialysis
is done for 4
to 5 hours per
week.
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