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Invertebrates Excretory Systems. Protonephridia Metanephridia Malpighian Tubules. Protonephridia. freshwater flatworms network of blind-ended tubes opening only to the exterior tubes branch through the body, ending in flame bulbs tuft of cilia that beat, forcing fluids through tubes

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invertebrates excretory systems
Invertebrates Excretory Systems
  • Protonephridia
  • Metanephridia
  • Malpighian Tubules
protonephridia
Protonephridia
  • freshwater flatworms
  • network of blind-ended tubes opening only to the exterior
  • tubes branch through the body, ending in flame bulbs
      • tuft of cilia that beat, forcing fluids through tubes
  • urine empties via a nephridiopore
metanephridia
Metanephridia
  • most annelids
  • each segment contains a pair of metanephridia
    • tubules bathed in coelomic fluid and encircled by capillaries
    • nephrostome collects fluid from coelom ( ultra filtration) in the first filterate is isosomotic
    • transport epithelia in lumen of tubules resorb and secrete molecules
    • urine exits nephridiopore
osmoregulation in insects
Osmoregulation in insects
  • Osmoregulatory system of insects
    • The main organs involved in solute and water balance are:
      • Malpighian tubules (MTs)
        • Form primary urine
      • Lower MTs and hindgut (ileum, colon, rectum)
        • Reabsorption of water and ions
malpighian tubules
Malpighian Tubules
  • insects and other terrestrial arthropods
  • remove wastes from hemolymph and osmoregulate
  • open in digestive tract, tips immersed in hemolymph
  • transport epithelia line tubules
    • solutes are secreted into tubules and some are reabsorbed by the rectum
    • causes the precipitation of uric acid
osmoregulation in insects8
Osmoregulation in insects
  • Malpighian tubules
    • MTs empty into the alimentary canal between the midgut and hindgut
    • The number of MTs varies from 4-200 depending on the species
    • 2-100 mm in length and 30-100 μm in diameter
    • Walls of the MTs consist of a single layer of epithelial cells
    • Process ECF at high rates to regulate composition and volume of ECF
    • MTs are not innervated and fluid secretion is controlled by the action of hormones
osmoregulation in insects11
Osmoregulation in insects
  • Malpighian tubules
    • MTs lie free in hemocoel and are not supplied with blood vessels
    • Insect circulatory system is at relatively low pressure, therefore urine is formed entirely by secretion
    • NaCl and KCl are transported from the hemolymph into the lumen of the MT
    • MTs secrete K+ in herbivorous insects and Na+ in blood-feeders
    • NaCl and KCl are returned to the hemolymph across the rectal wall
slide12

Osmoregulatory system of an insect

Na+, K+, Cl-

-reabsorption of

water and ions

Hyperosmotic

or isosmotic

urine/excreta

K+, Cl-

Na+, K+, Cl-

& water

-formation of

primary urine

(Eckert, Fig. 14-42)

osmoregulation in insects13
Osmoregulation in insects
  • Hormonal control of fluid secretion
    • Diuretic hormones (DHs)
      • Substances that increase tubule secretion and/or inhibits fluid reabsorption in the hindgut
    • Antidiuretic hormones (ADHs)
      • Substances that inhibit tubule secretion and/or promotes reabsorption of ions and water in the hindgut
slide14

(or synthetic peptides,

neurotransmitters)

Liquid paraffin

Ramsay Assay for Measuring Fluid Secretion

osmoregulation in insects15
Osmoregulation in insects
  • Hormonal control of fluid secretion in Rhodnius prolixus
    • Types of DHs in Rhodnius :
      • Serotonin (5-hydroxytryptamine, 5-HT)
        • Also a cuticular plasticizing factor
        • Signals through cAMP pathway
        • Widely distributed in the nervous system and released from abdominal nerves into the hemolymph after feeding
      • Corticotropin-releasing factor (CRF)-like peptides
        • At least 15 different CRF-like peptides identified
        • 30-47 aa residues
        • Signal through a cAMP pathway
        • Present in the brain and mesothoracic ganglionic mass (MTGM) and released from abdominal nerves into the hemolymph after feeding
slide16

Central nervous system of Rhodnius

-contain CRF-like

peptides

subesophageal ganglion

prothoracic ganglion

Abdominal nerves

mesothoracic

ganglionic mass

-source of CRF&

other unidentified

diuretic peptides

Posterior lateral

neurosecretory cells

osmoregulation in insects17
Osmoregulation in insects
  • Hormonal control of fluid secretion in Rhodnius prolixus
    • Rhodnius consumes >10 times its body weight during a single blood meal
    • The excess fluid gained after feeding severely restricts mobility, therefore excess fluid load (salt and water) must be voided rapidly
    • Minutes after a blood meal, the MTs increase fluid secretion 1000-fold
    • Rapid elimination of Na+ and water requires coordinated synergistic action of diuretic hormones
slide18

Unfed Rhodnius prolixus

Blood-fed Rhodnius prolixus

osmoregulation in insects19
Osmoregulation in insects
  • Hormonal control of fluid secretion in Rhodnius prolixus
    • H+-ATPase on the apical membrane creates EC gradient
    • H+ is returned to the cytoplasm in exchange for either Na+ or K+
    • Na+-K+-2Cl- cotransporter on basolateral side
    • Cl- diffuses out on the apical side, some K+ recycled on the basolateral side
    • Extracts of MTGM (CRF +other peptide DHs) and 5-HT act synergistically to promote diuresis
osmoregulation in insects20
Osmoregulation in insects
  • Hormonal control of fluid secretion in Rhodnius prolixus
    • Cessation of urine production must also be tightly controlled to avoid dehydration and excessive loss of NaCl
    • Cardioaccelatory peptide 2b (CAP2b) functions as an antidiuretic hormone
    • CAP2b activates a cGMP second messenger pathway to increase a cAMP phosphodiesterase thereby inhibiting cAMP-mediated diuresis
ii osmoregulation in aquatic environments
II. Osmoregulation in aquatic environments
  • Marine mammals
    • Do not have salt glands and do not drink seawater
    • Obtain water from food and metabolism
    • Highly efficient kidneys produce a hypertonic urine
    • Nursing females produce milk with high fat but low water content
    • Some juvenile animals can use water derived from the oxidation of body fat
    • Modifications in nasal passages to reduce water loss
    • Ability to lower metabolic rate
slide27

Water-salt relations in a marine mammal

-obtain water from food and metabolism

-conserves water by producing a hypertonic urine