Download The Excretory System: Urine Formation

The Excretory System:
Urine Formation
… eww
The Excretory System
• Mammals must excrete many different wastes in
order to remove toxic substance from the body
• The wastes form as a result of the metabolic
processes of the body and degeneration of cells
(ie. urea, ammonia, CO2, lactic acid, etc.)
• Much of the excretory system flows through the
kidneys
Kidneys
• Part of excretory system, controlled by
nervous and endocrine system
• Weighing ~0.5 kg each, kidneys may hold as
much as 25% of the body’s total blood volume
at any given time
• Involved in the production of urine
Kidneys
Stabilize internal environment by:
• regulating water content (osmoregulation)
• eliminating poisonous by-products of biological
reactions
• regulating ion concentration
Mechanisms of Regulation:
• diffusion/osmosis
• forced filtration
• active transport
Nephron
• Each kidney contains over 1 million slender
tubules called nephrons
• The functional
units of the
kidney
Nephron Structure
Glomerulus:
• High-pressure capillary
bed
• The site of blood
filtration
Bowman’s Capsule:
• Funnel-like structure
• ‘Beginning’ of the
nephron
Each nephron has its own
independent blood
supply (renal arterioles
and veins)
Nephron Structure
Components not
entering capsule:
• Blood proteins
• Blood Cells
• Platelets
Nephron Structure
Proximal Tubule:
• Re-absorption of
molecules
important to the
blood
Loop of Henle:
• Concentration of
urine (solutes to
be excreted)
Nephron Structure
Distal Tubule:
• Final re-absorption
and secretion of
molecules
Collecting Duct
• Collection of urine
from multiple
nephrons
• Joins with the
ureters; ultimately
the bladder
Urine Formation
Accomplished by 3 functions of the nephron:
Forced filtration of blood from the afferent
arteriole into the glomerulus, and through
Bowman’s capsule under high pressure
• proteins, blood cells and platelets are too
large to pass through & stay in the blood
• sodium chloride, glucose, amino acids, ions
enter the nephron
Urine Formation
Re-absorption of most fluids and solutes from the filtrate
back into the blood
• for every 120 mL of fluids filtered, only 1 mL becomes
urine
• many solutes are removed from the nephron into the
capillary beds surrounding the convoluted tubules
• passive transport moves Na+, Cl- and HCO3
• active transport moves glucose and amino acids
• an osmotic gradient is created by the solutes in the
capillary bed, drawing water out of the nephron (in all
tubules but the ascending Loop of Henle)
Urine Formation
Secretion moves wastes from blood into the
distal tubule of the nephron
• Urea, uric acid, ammonia, excess ions,
minerals, drugs, etc. moved by active
transport
How it all works:
How it all works:
YouTube Link:
http://www.youtube.com/watch?v=vNvZaGcLzE
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Lab Exercise
Comparing Solutes in the Plasma, Nephron &
Urine
• Activity: 7.5.1 - p.363