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EXCRETION (EXCRETORY SYSTEM (Malpighian tubules: Insects and terrestrial…

- - - - Land snails
      - Reptiles (including birds)
      - Insects
  - - - Aquatic animals (most bony fishes)
  - - - Some bony fish
      - Sharks
      - Amphibians
      - Mammals
- - - - Epithelial excretory surfaces
        
        Chloride cells of fish &
        Salt pumps of brine shrimp
      - Tubular excretory organs
        
        Nephrons in kidneys of vertebrates &
        Malpighian tubules in insect
- - - - Cuticle
      - Main excretory product is uric acid
        Other forms include ammonia and urea
        
        Reabsorption of salts in the hindgut
        
        Primary urine production in Malpighian tubules
        
        Synthesis of uric acid occurs in the fat body.
  - - - Live in salt water
        High urea in their blood - achieve osmotic equilibrium with surrounding sea water
        Retaining relatively low salt concentration in their tissues
  - - - Tubular reabsorption
        
        occurs at the proximal tubule, Loop of Henle & distal tubule
        
        Energy for reabsorption is supplied by Na-K ATPase pump
        
        Na, glucose and amino acids are 100% reabsorbed
        
        65% of the Na+ is absorbed (proximal tubule)
        
        25% of Na+ is reabsorbed (ascending loop of Henle)
        
        Remaining 10% of Na+ is reabsorbed (co-transport of Cl-)
      - Tubular secretion
        
        occurs at distal tubule
        
        Toxic substances (urea, uric acid) are eliminated.
        
        Some urea & water are reabsorbed at the collecting duct
      - Filtration
        
        occurs at the glomerular capsule
        
        Filtration Rate
        
        Volume of plasma filtered: 180 L /day
        
        Urine output is about 1- 2 L /day
        
        99% of filtrate is reabsorbed
        
        Non-selective filtration
        
        Filtration pressure forces
        
        heart’s pumping action
        
        differences in diameter of afferent
        and efferent arterioles