Osmoregulation and Excretion

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Osmoregulation and Excretion
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Key Concepts

• Osmoregulation balances the uptake and loss of
  water and solutes
• An animals nitrogenous wastes reflect its
  phylogeny and habitat
• Diverse excretory systems are variations on a
  tubular theme
• Nephrons and associated blood vessels are the
  functional units of the mammalian kidney
• The mammalian kidneys ability to conserve water
  is a key terrestrial adaptation
• Diverse adaptations of the vertebrate kidney have
  evolved in different environments

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Key Words

• homeostasis
• excretion
• uric acid
• filtration
• renal vein
• urethra
• nephron
• proximal tubule
• collecting duct
• efferent arteriole
• antidiuretic hormone (ADH)

• secretion (selective reabsorption)
• renal artery
• urinary bladder
• renal medulla
• Bowman's capsule
• distal tubule
• afferent arteriole
• vasa recta

• ammonia
• filtrate
• ureter
• renal cortex
• glomerulus
• loop of Henle
• cortical nephrons
• peritubular capillaries
• aldosterone
• osmoregulation
• urea

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Types of metabolic waste produced by living
systems

1. Digestive waste
2. Respiratory waste
3. Excess water and salts (through osmoregulation)
4. Nitrogenous waste (through excretion)

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Osmoregulation

• Balance of uptake and loss of water and solutes
• Controlled movement of solutes between internal
  fluids and environment
• Osmoconformer
• (marine animals isoosmotic with environment)
• Osmoregulator (freshwater, marine, and
  terrestrial animals that adjust internal
  osmolarity)

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Types of nitrogenous wastes

• Deamination protein and nucleic acid metabolism
• Three main types differing in terms of
• Toxicity
• Amount of water needed for excretion
• Energy needed for synthesis

300 500 mL/gN 1 step rxn
50 mL/gN 4 step rxn
10 mL/gN 15 step rxn
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Type of Organism Structure Product of excretion Other features
Plants Stomata, lenticels Insoluble crystals Crystals are kept inside plant cells
Cnidarians and echinoderms No excretory organ - Osmoconformers, isoosmotic with environment
Freshwater protists and sponges Contractile vacuole
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Excretory Systems

• Dispose of metabolic wastes
• Regulate solute concentrations in the body
• Transport epithelia arranged in tubes
• 4 major processes
• Filtration, pressure-filtering of body fluids
  producing a filtrate (water, salts, sugars, amino
  acids, N-wastes)
• Reabsorption, reclaiming valuable solutes
  (glucose, salts, amino acids) from the filtrate
• Secretion, addition of larger molecules like
  toxins and other excess solutes from the body
  fluids to the filtrate
• Excretion, the filtrate leaves the system

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Type of Organism Structure Product of excretion Other features
Flatworms Flame cells
Unsegmented roundworms Protonephridia, closed network of dead-end tubes lacking openings
Annelids Metanephridia, open-ended network of tubes with internal openings that collect body fluids
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Type of Organism Structure Product of excretion Other features
Molluscs Nephridia or metaphridia
Crustaceans Antennal/green gland
Insects Malpighian tubules and digestive tract Uric acid
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Type of Organism Structure Product of excretion Other features
Marine fishes Gills Ammonia
Elasmobranchs (sharks, skates, rays) Kidneys Urea Rectal glands excrete excess NaCl
Freshwater fishes Gills Ammonia or urea
Amphibians and mammals Kidneys Urea Liver converts ammonia to urea
Reptiles and birds Kidneys Uric acid Salt glands
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From Blood Filtrate to Urine A Closer Look
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• Two solutes NaCl and urea, contribute to the
  osmolarity of the interstitial fluid
• Cause the reabsorption of water in the kidney and
  concentrates the urine

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Nervous system and hormones regulate kidney
functions

• Antidiuretic hormone (ADH)
• Stimulated by a rise in the bloods osmolarity
  (gt300 mosm/L)
• Enhances fluid retention by making the kidneys
  reclaim more water
• Increases water reabsorption in the distal
  tubules and collecting ducts of the kidney

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• The renin-angiotensin-aldosterone system (RAAS)
• Responds to a loss of salt and water in the blood
• Stimulated by low blood volume or pressure
• Increases water and sodium ion reabsorption in
  the proximal and distal tubules
• Leads to an increase in blood volume and pressure
• Opposed by the hormone atrial natriuretic factor
  (ANF)
• Released by atria
• Inhibits release of renin

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Some medical aspects concerning the excretory
system

• Urinary tract infection (UTI)
• bacterial infection
• cystitis/pyelonephritis
• treated by antibiotics and prevented through
  proper hygiene
• Kidney stones
• solidified crystals in kidneys or ureters
• Calcium oxalate
• Uric acid
• nephrolithiasis/urolithiasis
• prevention
• Drinking adequate water
• Proper diet low in protein, N, and Na
• Avoid excess Vitamin C intake
• Dialysis
• Hemodialysis
• Peritoneal dialysis