The Mammalian Excretory System

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The Mammalian Excretory System
Principles of Modern Biology II At Wilkes
University Kenneth M. Klemow, Ph.D.
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One problem

• Mammalian blood contains metabolic waste products
  that must be removed - without removing useful
  materials.

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Another problem

• Terrestrial mammals must maintain a relatively
  constant osmotic level.
• Living on land promotes desiccation thus must
  retain water.
• Occasionally we have excess water and must
  excrete it.

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The solution

• Mammals have an excretory system that removes
  waste products and maintains osmotic balance.

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Mammalian excretory system

• Kidneys
• Ureters
• Urinary bladder
• Urethra

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b/1/18/Illu_urinary_system.jpg/300px-Illu_urinary_
system.jpg
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The mammalian kidney

• Cortex
• Medulla
• Renal pelvis
• Renal pyramids
• Blood vessels
• Renal artery
• Renal vein
• Ureter

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idney.gif
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The mammalian kidney

• Have gradient of increasing salinity from cortex
  to medulla

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idney.gif
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Nephron basic urine-producing unit of kidney

• Each kidney contains about one million nephrons
• Spans cortex and medulla
• Sac with long tube leading to ureter

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Nephron consists of five parts
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Nephron consists of five parts

• Bowmans capsule

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Nephron consists of five parts

• Bowmans capsule
• Proximal tubule

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Nephron consists of five parts

• Bowmans capsule
• Proximal tubule
• Loop of Henle

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Nephron consists of five parts

• Bowmans capsule
• Proximal tubule
• Loop of Henle
• Descending branch

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Nephron consists of five parts

• Bowmans capsule
• Proximal tubule
• Loop of Henle
• Descending branch
• Ascending branch

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Nephron consists of five parts

• Bowmans capsule
• Proximal tubule
• Loop of Henle
• Descending branch
• Ascending branch
• Distal tubule

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Also have collecting duct

• Collects urine from distal tubule
• Passes through medulla
• Discharges to renal pelvis

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And blood vessels
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And blood vessels

• Afferent arteriole

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And blood vessels

• Afferent arteriole
• Glomerulus

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And blood vessels

• Afferent arteriole
• Glomerulus
• Efferent arteriole

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And blood vessels

• Afferent arteriole
• Glomerulus
• Efferent arteriole
• Peritubular capillaries

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Major processes of nephron

• Filtration
• Secretion
• Reabsorption
• Excretion

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At the glomerulus

• Blood is filtered
• 2000 L/day
• Raw urine passes into capsule space
• 180 L/day
• Remaining blood flows into efferent arteriole

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.jpg
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At the proximal tubule

• Useful molecules (sugars, amino acids,
  bicarbonate, potassium) are resorbed from
  filtrate into blood
• Na is resorbed by active transport
• Cl- and water follow passively
• Urine is iso-osmotic to blood

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ronS.gif
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Making hyperosmotic urine
Concentrated
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Making hyperosmotic urineStep 1

• In ascending branch, Na is resorbed by active
  transport
• Cl- follows passively
• Water stays behind
• Urine becomes more dilute
• Medulla tissue becomes more salty - giving
  gradient

Cl-
Na
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Making hyperosmotic urineStep 2

• In descending branch, urine enters salty medulla
• Water diffuses from tubule
• Urine becomes more concentrated

H2O
H2O
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Making hyperosmotic urineStep 2

• In descending branch, urine enters salty medulla
• Water diffuses from tubule
• Urine becomes more concentrated

H2O
H2O
Opposite flow in loop of Henle magnifies
saltiness in tissue, giving Countercurrent
Multiplier effect.
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Making hyperosmotic urineStep 3
H
K

• In distal tubule, urine is hypo-osmotic to blood
• H and K are secreted into tubule
• Urine becomes more acidic

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Making hyperosmotic urineStep 4

• In collecting duct, watery urine passes through
  salty medulla.
• H2O leaves, assuming antidiuretic hormone (ADH)
  is present
• Urine becomes more concentrated

H2O
H2O
http//renux.dmed.ed.ac.uk/EdREN/makingimages/Neph
ronS.gif
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Making hyperosmotic urineStep 4

• In collecting duct, watery urine passes through
  salty medulla.
• H2O leaves, assuming antidiuretic hormone (ADH)
  is present
• Urine becomes more concentrated

H2O
H2O
Note ADH allows us to retain water under normal
circumstances
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ADH may not be present

• Excessively dilute urine or alcohol in blood cuts
  off flow of ADH from posterior pituitary
• Collecting ducts do not resorb water
• Watery urine leaves collecting duct

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Finally

• Sodium concentrations and blood pressure are
  regulated by hormones aldosterone and atrial
  natriuretic hormones
• See P. 1035-1036 of your text!

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