Chpt 44 Excretory System osmoregulation. I. Osmoregulation – *management of the body’s water...
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Transcript of Chpt 44 Excretory System osmoregulation. I. Osmoregulation – *management of the body’s water...
I. Osmoregulation – *management of the body’s water content & solute concentration*absorption & excretion of H2O & solutes so that water balance & osmotic pressure are maintained -- homeostasis
A. Types• 1. Marine Fish
– a. fish body is hypotonic/hypoosmotic = less dissolved solutes in body than in water envr.
– b. SO, water is constantly lost through osmosis• 1) marine fish must constantly drink & RARELY urinate –
the urine is very concentrated
• 2) secrete excess salt out through gills
2. Fresh water fish
• a. body is hyperosmotic/hypertonic to envr. – more dissolved solutes IN body than in water envr.
• b. SO, water is constantly GAINED– 1) fresh water fish RARELY drink & constantly
urinate – urine very dilute– 2) absorb salt through gills
3. Urine – NH3 is the waste product from the breakdown of amino acids
• a. aquatic orgs – NH3 or NH4+ very concentrated
but dilutes quickly in the water envr.
• b. birds – convert urea to uric acid (highly toxic) that’s insoluble in water so it comes out mostly solid w/ the feces (but it’s energy expensive)– 1) this allows bird embryos in the egg to separate their
wastes into a separate sack (allantois) so they aren’t “swimming” in their wastes!
• c. mammals- convert NH3 to urea in liver – this requires less water to excrete since it’s less toxic than NH3
II. Excretory Mechanisms• A. Contractile Vacuoles
– 1. found in protists – paramecium
– 2. accumulates excess water then merges w/ cell membrane & releases the H2O to the envr.
• B. Flame Cells (protonephridia)– 1. found in
flatworms/platyhelminthes – planaria
– 2. branched system of tubes w/ cilia-containing cells at end of each tube
• a. cilia move waste fluids through tubes & out a series of pores along sides of body
C. Malpighian Tubules• 1. found in insects/arthropods
• 2. tubes in dig. tract collect body fluids – a. the materials to be kept are reabsorbed & the
wastes pass out through the anus
D. Nephridia (metanephridia)• 1. found in annelids/segmented worms
• 2. ciliated funnel system – as fluids travel through the funnel some liquid is reabsorbed so wastes become more concentrated then are excreted out pores along sides of body
E. Kidney
• 1. found in vertebrates
• 2. made of 1 million filtering tubes called nephrons– a. wastes pass from
kidney ureter bladder urethra then out of the body
Cell produces
metabolic
wastes
Wastes picked up by blood stream
Kidney filters blood & removes wastes
B. Physiology
• 1. Filtration– a. blood enters through renal artery which
branches into capillaries of the glomerulus almost immediately
– b. this greatly increases pressure – c. water & dissolved substances are forced out of
capillaries & in to Bowman’s capsule (leaving the rbc’s, wbc’s, platelets, large proteins & some plasma in the vessels)
• 2. Secretion– a. as the filtrate passes through the proximal (&
later distal) tube some more interstitial fluid enters in (it is secreted into the tube by both active & passive transport)
• 3. Reabsorption– a. as filtrate goes DOWN through loop of Henle
it becomes more concentrated due to the movement of water OUT of the tube
– b. as the filtrate goes UP through the loop of Henle is becomes more dilute due to salts moving OUT of the tube
– c. as it moves DOWN the collecting duct it again becomes more concentrated -----urine
IV. Excretory System Control
• A. Hormones– 1. ADH – antidiuretic hormone – controls urine
volume• a. ADH ↑ - increases the reabsorption of H2O by
causing the collecting duct to become MORE permeable to water --so more water is reabsorbed
– urine becomes more concentrated & less water is released from body
B. Aldosterone – increases both reabsorption of water & Na+ by increasing the permeability of the distal convol. tube & collecting duct to Na+ (so more Na+ is reabsorbed)
the water moves passively in with the Na+