Post on 07-Mar-2018
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The Excretory System
Gets rid of wastes and other substances that the body doesn�t
need.
Definitions
Excretion - release of metabolic wastes and
excess water - eg. Urinate (aka #1)
Metabolic Wastes • produced by chemical reactions like respiration,
hydrolysis, synthesis and neutralization. • Water • Carbon Dioxide • Salts • Urea
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Definitions Elimination - release of unabsorbed wastes from
the digestive tract - eg. Feces via defecation (aka #2)
Removal of Wastes - Examples
• Liver - excretes bile • Skin - sweat, excretes salt and urea • Lung - excretes CO2 and H2O
• KIDNEYS • Excrete UREA,water, salts and various other
wastes as part of the urine
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Organs of Excretion
" Skin – Allows water, salt and urea to
diffuse from the blood (capillaries) into the sweat glands.
– Releases sweat from the sweat glands through the sweat ducts out to the skin pores.
Organs of Excretion " Liver
– Part of the digestive, circulatory and excretory systems.
– Removes excess amino acids from the body.
– Breaks down the amino acids through deamination to form the urea which is excreted in the urine.
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Organs of Excretion
" Lungs – Excretes the waste product of respiration during exhalation.
– Carbon Dioxide and Water Vapor.
Organs of Excretion " Kidneys
– Major excretory organs of the body which removes most of the body wastes.
– Purify blood by filtering out water, salts, digested food particles and urea in the form of urine.
– Urine passes out through the urinary tract.
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Urinary System
Excretion of Urine
" Kidney " Ureter – a tube that transports urine to the
urinary bladder. " Urinary Bladder – a sac of tissue that has
the ability to expand as it fills with urine. " Urethra – a tube at the bottom of the
bladder where urine passes out of the body.
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Kidney
Nephron
Nephron
- the functional unit of the kidney
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Human Biology
Urinary System - Formation of Urine
Nephron Structure
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Urine Formation
3 Steps:
1. Glomerular Filtration
2. Selective Reabsorption
3. Tubular Secretion
• Blood flows into nephron via afferent arteriole & then into glomerulus • Site of Glomerular Filtration
Afferent arteriole
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• The filtrate is pushed out into the Bowman’s capsule • These are small particles (water, urea, ions (H+,
HCO3-, Na+), glucose, amino acids, vitamins… etc.
• Larger molecules (RBC, WBC, proteins) carry thru the efferent arteriole
• Leads to peritubular capillaries eventually to the renal vein
efferent arteriole
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• Filtrate enters the proximal convoluted tubule (PCT) • Site of Selective reabsorption
Reabsorption of:
- most glucose
- most A.A.
- ~65% of Na+
- ~65% water
- small proteins
- HCO3-
- vitamins
- Other ions
Glucose, A.A., water
• Concentrated filtrate moves into the loop of Henle • Descending loop - 10-20% water reabsorbed • Ascending loop - 20% Na+
Na+
H2O
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• Concentrated filtrate moves into the distal convoluted tubule (DCT)… from efferent arteriole… • Site of Tubular Secretion (some in the PCT too!)
H+ NH3
This is a mechanism for
removing unwanted
substances from the plasma via active transport
H+ NH3 NH4
Excess K+
Penicillin Etc…
• Concentrated filtrate moves into the Collecting Duct • and now the URINE passes into the:
renal pelvis → ureter → urinary bladder → urethra → out of body
H2O
Urine
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Composition: • Dissolved salts (NaCl) • Metabolic waste (ammonia, urea)
• Note: ammonia is toxic so it is quickly converted to urea in the liver
• Small molecules from the breakdown of hormones • Sometimes there is protein, glucose, blood
• These are NOT normal and usually signal something is nor functioning properly
Urine
n Crash Course – Excretory System