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Urine formation in Excretory
System
Chapter 10.1 & 10.2
McGraw-Hill Ryerson
Biology 12 (2011)
Simple Excretory Systems
• Unicellular organisms
get rid of wastes by the
use of a contractile
vacuole.
• It expels excess water
that enters the cell
through osmosis since
the organism is
hypertonic to the
surrounding solution.
http://dbs.umt.edu/courses/biol103/labs/Westphal/7a_osmoregulation_paramecium_files/image004.jpg
Complex Excretory Systems
• More complex
organisms
(multicellular, or
living on land) need
to store wastes and
use special cells that
are in the excretory
system to remove
wastes from the
body.
Organs of the Excretory system
• Lungs: gas waste, i.e. CO2
• Colon: solid wastes from the digestive system
• Kidneys: water-soluble waste, as well as
regulation of body pH and water levels.
Processing of Wastes
• The liver transforms ingested toxins such as
alcohol, heavy metals and waste from protein
metabolism into soluble compounds that can
be removed by the kidney:
Water soluble wastes
• Ammonia: produced by
protein metabolism. It is
very toxic so the liver
converts it to...
• Urea (100,000x less toxic
than ammonia)
• Uric acid comes from the
metabolism of nucleic
acids. Less soluble than
urea; a build of uric acid
can lead to kidney stones.
The Urinary System
• Wastes are filtered
from blood into
the kidneys and
sent to the
bladder.
• Renal arteries pass
blood to the
kidneys.
• Ureters pass urine
to the bladder.
Be sure you can label this diagram!
The Urinary System
• Urinary sphincter controls the
release of urine from bladder.
• Urethra is the tube used to
void the bladder.
• 200 mL of urine  bladder
expands  stretch receptors
send a signal to the brain. You
choose whether to void
(voluntary control over
sphincter)…to a point.
Kidney Structure
•
•
•
Cortex: outer layer of
connective tissue
Medulla: inner layer
under the cortex
renal pelvis: hollow
chamber which
connects the kidney
with the ureter
Take a minute to memorize this diagram.
NEPHRON
• Nephrons:
approximately one
million small functional
units of the kidney
spanning the cortex and
the medulla
• They are comprised of
specialized blood
vessels and tubes that
wrap around each other
for filtering wastes from
the blood and
producing urine.
http://www.sciencetechnologyaction.com/lessons/8/fig1.gif
Microscopic Anatomy of the Kidneys



Filtration
 Filtrate of blood
leaves kidney
capillaries
Reabsorption
 Most nutrients,
water, and essential
ions reclaimed
Secretion
 Active process of
removing
undesirable
molecules
The mammalian nephron
This nephron has been spread out.
BLUE= tubes RED = blood vessels
Blood flow in the Nephron
• Afferent arterioles supply blood to the kidney from
the renal artery. They end in a capillary network or
capillary bed called the glomerulus.
Blood flow in the Nephron
• Blood exits the glomerulus through efferent
arterioles that lead to a network of peritubular
capillaries which surround the tubules of the
nephron.
Blood flow in the Nephron
• They collect into the renal venules and blood exits
the kidney through the renal vein.
Fluid Flow in the nephron
• The glomerulus is surrounded by the Bowman's
capsule. It, along with the afferent and efferent
arterioles and the glomerulus are in the cortex of
the kidney.
Fluid Flow in the nephron
• Fluids that are to be processed as urine enter the
Bowman's capsule from the blood in the
glomerulus.
Fluid Flow in the Nephron
• The Bowman's capsule leads to a thin tubule
called the proximal tubule.
• Proximal tubule use active transport to bring Na, glucose, and
other solutes back into the blood
• Negative ions tag along back to blood due to attraction
• Water follows the ions by osmosis back into blood
Fluid Flow in the Nephron
• Urine goes from the proximal tubule around the
loop of Henle, which descends into the medulla
of the kidney then ascends to the cortex.
• Function is to reabsorb water and ions back to blood
• Medulla is very salty so water diffuses by osmosis in descending
loop
• Ascending loop is impermeable to water so solutes diffuse
• Thick segment of ascending limb actively transports Na in blood
Fluid Flow in the Nephron
• Urine then moves through the distal tubule
• K ions are actively secreted from blood
• H+ are actively secreted from blood to maintain blood pH
• Other substances not normally part of body are secreted
Fluid Flow in the Nephron
• Urine moves into collecting ducts, which collect
urine from many nephrons and lead into the renal
pelvis of the kidney.
• Filtrate still possesses lots of water
• Permeability to water being reabsorbed is increased depending on
concentration of blood plasma (i.e. dehydration leads to increased
permeability meaning more reabsorbtion)
Identify the structures:
D
C
I
K
Collecting ducts
Bowman’s Capsule
B
L
Proximal tubule
Distal tubule
A
Loop of Henle
Glomerulus
G
Peritubular Capillaries
Renal venule
H F
Renal vein
Renal artery
E
Afferent arteriole
J
Efferent arteriole
You can refer to page 447 of your textbook for help
Homework
• Pg 448 #4, 5, 6, 7, 8
• Pg 455 #2-5, 11, 12
• Be sure to look at Table 10.3 on pg 454!!