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Urinary System
Urinary System Function
• The function of the urinary system is to
help maintain the appropriate balance of
water and solutes in the bodies fluids
Urinary System:
General Anatomy
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The urinary system is
composed of the
Kidneys involved in
chemical balance
Ureters that channels
urine to the bladder
Urinary Bladder that
stores urine
Urethra that channels
urine to the body
surface
Kidney Anatomy
• Each kidney has a
generous blood supply
distributed to both the
external cortex and
internal medulla where
its concentrations are
manipulated in
nephrons, the resulting
urine filling the renal
pelvis
Nephron Anatomy
• The kidney is composed of over 1 million
separate nephrons
• The nephron is composed of a Bowman’s
capsule, proximal tubule, loop of Henle, distal
tubule, and collecting duct
• A blood capillary forms a bulbous glomerulus
just inside Bowman’s capsule and then
descends into the peritubular capillaries that
surround the nephron tubules
The Nephron
Nephron Physiology: General
• The nephron is the site of
1. Filtration in Bowman’s capsule
2. Secretion and re-absorption in the proximal
tubule
3. Changes in NaCl and Water permeability in
the Loop of Henle
4. Secretion in the distal tubule
5. Variable re-absorption of water in the
collecting duct
Filtration
• Each minute 120 ml of water
and solutes are filtered from
the glomerular capillaries
into the Bowman’s capsules
• The filtrate does not contain
large molecules like proteins
but can contain amino acids
and glucose.
• Salt and Water are filtered
(important in osmolarity)
• Urea and H+ are also filtered
(important to Nitrogen waste
and pH balance)
Proximal Tubule
• Important organic
molecules are
reabsorbed.
• Na+ are actively
transported and Cl- and
water follow by diffusion
and osmosis.
• Bicarbonate is reabsorbed to aid in pH
buffering.
• Continues with a
concentrated filtrate of
H+, urea, and ammonia.
Proximal Tubule - Descending
• As the filtrate descends
it re-absorption of water
continues.
• The nephron is
impermeable to NaCl
though.
• So, the filtrate becomes
more concentrated with
solutes (increase in
osmolarity)
Loop of Henle and Ascending
Tubule
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In the Loop of Henle the
nephron becomes impermeable
to water but permeable to NaCl.
This helps in developing the
hyperosmolar concentration of
the interstitial fluid of the
medulla.
In the Distal Tubule the NaCl is
actively transported in the
interstitial fluid.
The filtrates osmolarity
decreases as salt is removed
and it become relatively dilute
because water can’t leave.
Distal Tubule & Collecting Duct
• In the distal tubule, K+
ions are variably
secreted while NaCl
variably re-absorbed.
• The secretion of H+ and
re-absorption of
bicarbonate occurs here
too.
• In the collecting duct
the NaCl is reabsorbed, while water’s
permeability is
controlled by hormones.
Antidiuretic Hormone
•
When extracellular
volume decreases
(osmolarity increases)
1. The hypothalamus
triggers the secretion
of ADH from the post.
pituitary
2. ADH increases the
permeability of the
distal tubules to water
(so re-absorbs more)
3. Urine becomes more
concentrated.
Aldosterone
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1.
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3.
4.
When extracellular volume decreases
resulting in a lowering in blood
pressure.
Sensors in the heart and blood
vessels of the kidney signal cells in
the glomerulus which secretes renin.
Renin activates the plasma protein
Angiotensin II which triggers the
adrenal cortex to secrete Aldosterone.
Aldosterone acts on distal tubule so
that they reabsorb Na+ and promote
the reabsorption of water.
This cause the blood pressure to
increase.