Download Excretory System

Excretory System
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Help maintain homeostasis by regulating water
balance and removing harmful substances.
Osmoregulation
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The absorption and excretion of water and dissolved
substances so that proper water balance is maintained
between the organism and its surroundings.
Example:
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Marine fish
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Constantly drink, rarely urinate, & secrete accumulated salts.
Freshwater fish
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Rarely drink, constantly urinate, & absorb salts through their gills.
Various excretory mechanisms
1.
Contractile vacuoles
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2.
2.
Found in various protists, such as paramecia and amoebas.
Vacuoles accumulate water, merge with the plasma
membrane, and release the water to the environment.
Flame cells
1.
2.
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4.
Found in Platyhelminthes, such as planaria.
Flames cells are distributed along a branched tube system
that permeates the flatworm.
Body fluids are filtered across the flame cells.
Wastes (water and salts) are excreted from the tube system
through pores that exit the body.
Various excretory mechanisms
3. Nephridia
1. Occurs in pairs within each segment of most annelids, such as
earthworm.
2. Interstitial fluids enter a nephridium through a ciliated opening
called a nephrostome.
3. Fluids are concentrated as they pass through the collecting
tubule due to selective secretion of materials into the surrounding
coelomic fluid.
4. Blood capillaries that surround the tubule reabsorb the secreted
material.
5. At the end of the collecting tubule, the concentrated waste
materials are excreted through an excretory pore.
Various excretory mechanisms
4. Malpighian tubules
1. Found in many arthropods, such as terrestrial insect
2. Tubes attached to the midsection of the digestive
tract collect body fluids from the hemolymph.
3. The fluids, include both nitrogen waste and materials
to be retained (water and salts), are deposited into the
digestive tract.
4. As the fluids pass the digestive tract, materials to be
retained pass back out through the walls of the
digestive tract.
5. Wastes continue in the tract and are excreted
through the anus.
Various excretory mechanisms
5. Kidney
1. Produce waste fluids called urine.
2. Cortex; Medulla; Renal pelvis
3. Nephrons
a. Bowman’s capsule
b. Glomerulus
c. Convoluted tubule
1. Proximal tubule
2. Loop of Henle
3. Distal tubule
d. Collecting duct
Operation of human nephron
consists of three processes.
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Filtration
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Bowman’s capsule
Glucose; salts; vitamins; nitrogen wastes
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Secretion
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filtrate
Movement of material from the interstitial fluids joins the
filtrate.
Reabsorption
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Water moves out of descending portion of the loop of Henle and
filtrate becomes more concentrated.
Filtrate becomes more diluted due to passive and active transport of
salts out of the ascending portion of the loop of Henle.
Water moves out of the filtrate as it flows down the collecting tubule
through salts concentrated interstitial fluids of the medulla.
Hormonal Influence of Osmoregulation
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Antidiuretic hormone (ADH)
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Increases the reabsorption of water in the collecting
tubule.
Increases the concentration of salts in the urine
Aldosterone
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Increases both the reabsorption of water and the
reabsorption of Na+.
Increases the permeability of the distal tubule to
Na+.
Nitrogen waste
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Aquatic animals excrete NH3 directly into the
surrounding water.
Mammals convert NH3 to urea in their livers.
Birds, insects, and many reptiles convert urea
to uric acid.
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Uric acid is mostly insoluble in water, it precipitates
and forms a solid.
Allows considerable water conservation by
permitting the excretion of nitrogen waste as a solid.