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Excretory System: 1. Cell Surface or Cell Membrane

There are three main types of nitrogenous waste excreted by animals: ammonia, urea, and uric acid. Ammonia is excreted by invertebrates and fish, urea by mammals and some other vertebrates, and uric acid by birds, insects, and reptiles. Invertebrates use various excretory structures like cell membranes, contractile vacuoles, protonephridia, metanephridia, and Malpighian tubules to remove nitrogenous wastes from their bodies. These tubule systems filter wastes from body fluids and secrete or release them to the exterior through pores or into the digestive tract.

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186 views2 pages

Excretory System: 1. Cell Surface or Cell Membrane

There are three main types of nitrogenous waste excreted by animals: ammonia, urea, and uric acid. Ammonia is excreted by invertebrates and fish, urea by mammals and some other vertebrates, and uric acid by birds, insects, and reptiles. Invertebrates use various excretory structures like cell membranes, contractile vacuoles, protonephridia, metanephridia, and Malpighian tubules to remove nitrogenous wastes from their bodies. These tubule systems filter wastes from body fluids and secrete or release them to the exterior through pores or into the digestive tract.

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Joanna AC
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Excretory System

Three types of nitrogenous wastes excreted by animals:


 Ammo - the primary nitrogenous waste for invertebrates, teleost
nia and larval
amphibians.
- readily soluble in water but highly toxic.
- excreted from the body only in dilute solutions.
 Urea - produced by mammals, most by amphibians, some
reptiles, some marine
fishes, and some terrestrial invertebrates.
- formed by combining ammonia with bicarbonate ion.
- about 100,000x less toxic than ammonia.
- its excretion requires only about 10% as much water
compared to ammonia.
 Uric - excreted by birds, insects, and terrestrial reptiles.
acid - relatively non-toxic.
- more energetically expensive to produce than urea.
- largely soluble in water.
- excreted by semisolid paste or precipitate with very little
water loss.

Excretory System in Invertebrates


1. Cell surface or Cell membrane
 Allows passage of wastes in unicellular organisms

2. Contractile vacuole
 A specialized cytoplasmic organelle in many freshwater protists (e.g.
Paramecium) that expels excess water out of the cell to prevent lysis.

3. Protonephridia or Flame Bulb system


 Network of tubules that are lack internal openings but have external
openings at the body surface called nephridiopores.
 Smallest branches of the tubule network end with a large cell called a
flame bulb or cell.
 Water and solutes in body fluids the flame cell and get filtered.
 Specific molecules and ions are removed by reabsorption.
 Other ions and nitrogenous wastes are released into the tubules
network and excreted via the nephridiopore.
4. Metanerphidia
 The excretory tubule of most annelids and adult mollusks
 Nephrostome collects body fluid
 Some ions and molecules are reabsorbed while other ions nitrogenous
wastes are secreted into the tubules.
 The bladder stores in the nitrogenous wastes as urine and later on
excreted from the body surface via nephridiopore.
5. Malpighian tubules
 The excretory tubules of the insect and other terrestrial arthropods
attached to the right digestive tract (midgut)
 The tubules have ends that are immersed in the hemolymph
(circulatory fluid) while the distal ends empty into the gut.
 Malpighian tubules employ secretion to generate the fluid for
released from the body
 Help actively secrete uric acid and ions into the tubules.
 The fluid then passes into the hindgut (intestine and rectum) of the
insect as dilute urine.
 Reabsorption of ions and water occurs in the hindgut wall causing
the formation of uric acid crystals that are released with the feces.

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