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Key Concepts Osmoregulation balances the uptake and loss of
water and solutes An animal’s 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 kidney’s ability to conserve
water is a key terrestrial adaptation Diverse adaptations of the vertebrate kidney
have evolved in different environments
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 osmoregulatio
n urea
Types of metabolic waste produced by living systems
1. Digestive waste (elimination)
2. Respiratory waste
3. Excess water and salts (osmoregulation)
4. Nitrogenous waste (excretion)
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)
Types of nitrogenous wastes
Deamination – protein and nucleic acid metabolism
Three main types differing in terms of:1. Toxicity2. Amount of water
needed for excretion
3. Energy needed for synthesis
300 – 500 mL/gN
1 step rxn
50 mL/gN4 step
rxn
10 mL/gN15 step
rxn
Type of Organism
Structure Product of
excretion
Other features
Plants
Stomata, lenticels for gas exchange Insoluble
crystals Crystals are kept inside plant cells
Cnidarians and
echinoderms
No excretory organ-
Osmoconformers, isoosmotic with environment
Freshwater protists, sponges
Contractile vacuole Porocytes and flagella
Excretory Systems Dispose of metabolic wastes Regulate solute concentrations in
the body Transport epithelia arranged in
tubes 4 major processes
1. Filtration, pressure-filtering of body fluids producing a filtrate (water, salts, sugars, amino acids, N-wastes)
2. Reabsorption, reclaiming valuable solutes (glucose, salts, amino acids) from the filtrate
3. Secretion, addition of larger molecules like toxins and other excess solutes from the body fluids to the filtrate
4. Excretion, the filtrate leaves the system
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
Type of Organism
Structure Product of
excretion
Other features
MolluscsMetanephridia
Crustaceans
Antennal/green gland
Insects
Malpighian tubules and digestive tract
Uric acid
Type of Organism
Structure Product of
excretion
Other features
Marine fishes Gills for
osmoregulation, kidneys
Ammonia
Elasmobranchs (sharks,
skates, rays)
Kidneys Urea
Rectal glands – excrete excess NaCl
Freshwater fishesGills for
osmoregulation, kidneys
Ammonia or urea
Amphibians and mammals
Kidneys UreaLiver converts ammonia to urea
Reptiles and birds
Kidneys Uric acid Salt glands
Type of Organism
Structure Product of
excretion
Other features
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
Nervous system and hormones regulate kidney functions
Antidiuretic hormone (ADH)
Stimulated by a rise in the blood’s osmolarity (>300 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
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
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