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The Excretory System
Honors Biology
Facilitator: Mr. Lee
Room 320
Objectives
• Describe the function of the kidneys
• Identify the functional unit of the kidney
• Describe the role of the liver in the
excretory system
Functions of the Excretory
System
• Every cell in our bodies produce metabolic
wastes, such as:
– Excess salts
– Carbon dioxide
– Urea
• The excretory system removes the
metabolic wastes
Organs of the Excretory System
• Skin:
– Excretes excess water, salts, and
some urea in our sweat
• Lungs:
– Excretes carbon dioxide
• Liver:
– Converts excess amino acids into
useful compounds
– Converts nitrogen waste into urea
Organs of the Excretory System…
• Kidneys (main organ):
– Filter blood
• Nitrogenous wastes are
eliminated by the kidneys
• Waste laden blood enters
from the renal artery
• Clean blood leaves through
the renal vein
– Maintain blood pH
– Regulates water content of
blood
Organs of the Excretory System…
• Kidney Structure- There are
three main parts of the:
– Cortex:
• Outermost portion
– Medulla:
• Inner portion
– Renal pelvis:
• Funnel-shaped structure
in the center
Organs of the Excretory System…
• Ureter:
– Carries urine to
the urinary
bladder
• Bladder:
– Stores urine
• Urethra:
– Where urine is
excreted
Kidney Structure
• Nephrons are the functional units
of the kidney
– Stretched out, they would
extend for 50 miles
– They remove toxins, urea,
water, and salts from the blood
to form urine
– Blood enters the nephrons
through the arteriole,
impurities are filtered out and
emptied into the collecting
duct
Kidney Structure …
• The filtered blood (filtrate) exits the nephrons
through the venule
• Blood purification involves:
– Filtration
– Reabsorption
Anatomy of a Kidney.mp4
Filtration
• Filtration of the blood takes place in the
glomerulus
• The glomerulus is a network of capillaries that
at the top of the nephrons that is enclosed by
the Bowman’s capsule
• Blood pressure forces smaller molecules out of
the blood
Reabsorption & Secretion
• The kidneys filter all our blood in about 45
minutes
• Most reabsorption takes place in the proximal
convoluted tubule
• About 75% of the water is reabsorbed through
osmosis
• Glucose and minerals are returned to the
blood by active transport
Urine Formation
• Materials that is left is called urine
• Urine is primarily concentrated at the Loop of
Henle
• Urine is stored in the urinary bladder until it
is released through a tube called the urethra
Control of Kidney Function
• Activity of the kidneys are mainly controlled
by the composition of blood
• Regulatory hormones are also released
Review
• Describe the function of the kidneys:
– Filter blood
– Maintain blood pH
– Regulates water content of blood
• Identify the functional unit of the
kidney:
– Nephrons are the functional units of the
kidney
Review…
• Describe the role of the liver in the
excretory system:
– Converts excess amino acids into useful
compounds
– Converts nitrogen waste into urea