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How does an albatross drink saltwater without ill effect?
Figure 44.1
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Selectively permeable membrane
Solute concentration and osmosis Selectively permeable membrane Solutes Net water flow Water Figure 44.2 Hyperosmotic side Hypoosmotic side
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Sockeye salmon = euryhaline osmoregulators
Figure 44.3
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Osmoregulation in marine and freshwater bony fishes: a comparison: drinking, gills, urine …
Gain of water and salt ions from food Excretion of salt ions from gills Osmotic water loss through gills and other parts of body surface Uptake of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Gain of water and salt ions from drinking seawater Excretion of salt ions and small amounts of water in scanty urine from kidneys Excretion of large amounts of water in dilute urine from kidneys Figure 44.4 Osmoregulation in a saltwater fish Osmoregulation in a freshwater fish
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Anhydrobiosis - adaptation… Hydrated = active state dehydrated = dormant state.
Figure 44.5 (a) Hydrated tardigrade (b) Dehydrated tardigrade
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Water balance in two terrestrial mammals
balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Ingested in food (0.2) Ingested in food (750) Ingested in liquid (1,500) Water gain (mL) Derived from metabolism (1.8) Derived from metabolism (250) Figure 44.6 Feces (0.09) Feces (100) Water loss (mL) Urine (0.45) Urine (1,500) Evaporation (1.46) Evaporation (900)
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How do seabirds eliminate excess salt from their bodies?
EXPERIMENT Nasal salt gland Ducts Nostril with salt secretions Figure 44.7
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Countercurrent exchange in salt-excreting nasal glands
Vein Artery Secretory tubule Secretory cell Salt gland Countercurrent exchange in salt-excreting nasal glands Capillary Secretory tubule Transport epithelium NaCl NaCl Direction of salt movement Figure 44.8 Central duct Blood flow Salt secretion (a) (b)
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Nitrogenous wastes Proteins Nucleic acids Ammonia Urea - less toxic
Amino acids Nitrogenous bases Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Figure 44.9 Ammonia Very toxic Urea - less toxic Uric acid - not soluble
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Key functions of excretory systems: an overview
Filtration Blood --> tubule Capillary Filtrate Excretory tubule Reabsorption Tubule --> blood Figure 44.10 Secretion Urine Excretion
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Protonephridia: the flame bulb system of a planarian
Nucleus of cap cell Cilia Flame bulb Interstitial fluid flow Tubule Opening in body wall Figure 44.11 Tubules of protonephridia Tubule cell
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Metanephridia of an earthworm
Coelom Capillary network Components of a metanephridium: Internal opening Figure 44.12 Collecting tubule Bladder External opening
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Malpighian tubules of insects
Digestive tract Malpighian tubules of insects Rectum Hindgut Intestine Midgut (stomach) Malpighian tubules Salt, water, and nitrogenous wastes Feces and urine Figure 44.13 Rectum Reabsorption HEMOLYMPH
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Overview: mammalian Excretory System
Posterior vena cava Renal artery and vein Kidney Aorta Ureter Figure 44.14a The Urinary bladder Urethra Excretory organs and major associated blood vessels
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The mammalian kidney has two distinct regions: an outer renal cortex and an inner renal medulla
pelvis Figure 44.14b The mammalian excretory system Ureter Section of kidney from a rat Kidney structure 4 mm
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Nephron = the Functional Unit of the Kidney
Glomerulus Afferent arteriole from renal artery Juxtamedullary nephron Bowman’s capsule Cortical nephron 10 µm SEM Proximal tubule Peritubular capillaries Renal cortex Efferent arteriole from glomerulus Collecting duct Distal tubule Renal medulla Branch of renal vein Collecting duct Descending limb To renal pelvis Figure 44.14cd The mammalian excretory system Loop of Henle Ascending limb Vasa recta Nephron types Filtrate and blood flow
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Nephron Functional Unit of the Kidney
Juxtamedullary nephron Cortical nephron Renal cortex Collecting duct Figure 44.14c The mammalian excretory system Renal medulla To renal pelvis Nephron types
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Filtrate and blood flow
Nephron Afferent arteriole from renal artery Glomerulus 10 µm Bowman’s capsule SEM Proximal tubule Peritubular capillaries Efferent arteriole from glomerulus Distal tubule Branch of renal vein Collecting duct Descending limb Figure 44.14d The mammalian excretory system Loop of Henle Ascending limb Vasa recta Filtrate and blood flow
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The Nephron and Collecting Duct: regional functions of the transport epithelium
Proximal tubule Distal tubule NaCl Nutrients H2O HCO3– H2O K+ NaCl HCO3– H+ NH3 K+ H+ Filtrate CORTEX Loop of Henle NaCl H2O OUTER MEDULLA NaCl NaCl Collecting duct Figure 44.15 Key Urea Active transport NaCl H2O Passive transport INNER MEDULLA
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Two Solute Model: How the kidney concentrates urine
Osmolarity of interstitial fluid (mOsm/L) 300 300 300 100 100 300 300 H2O NaCl H2O CORTEX 400 200 400 400 H2O NaCl H2O NaCl H2O NaCl H2O NaCl H2O NaCl H2O OUTER MEDULLA 600 400 600 600 Figure How the human kidney concentrates urine: the two-solute model H2O NaCl H2O Urea H2O NaCl H2O 900 700 900 Key Urea H2O NaCl H2O Active transport INNER MEDULLA Urea 1,200 1,200 Passive transport 1,200
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Regulation of fluid retention by antidiuretic hormone = ADH
COLLECTING DUCT LUMEN Osmoreceptors in hypothalamus trigger release of ADH. INTERSTITIAL FLUID Thirst Hypothalamus COLLECTING DUCT CELL ADH ADH receptor Drinking reduces blood osmolarity to set point. cAMP ADH Second messenger signaling molecule Pituitary gland Increased permeability Storage vesicle Distal tubule Exocytosis Aquaporin water channels H2O H2O reab- sorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity H2O Figure 44.19 Collecting duct (b) Regulation of fluid retention by antidiuretic hormone = ADH Homeostasis: Blood osmolarity (300 mOsm/L) (a)
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Regulation of blood volume and pressure by RAAS The Renin-Angiotensin-Aldosterone System
Liver Distal tubule Angiotensinogen Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood volume or low blood pressure Adrenal gland Figure 44.21 Aldosterone Increased Na+ and H2O reab- sorption in distal tubules Arteriole constriction Homeostasis: Blood pressure, volume
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Summary Review Freshwater marine Terrestrial Large volume of urine
Animal Inflow/Outflow Urine Freshwater fish Does not drink water Large volume of urine Salt in active transport by gills Urine is less concentrated than body fluids H2O in Salt out Bony marine fish Drinks water Small volume of urine Salt in H2O out Urine is slightly less concentrated than body fluids Salt out - active transport by gills Terrestrial vertebrate Drinks water Moderate volume of urine Salt in (by mouth) Urine is more concentrated than body fluids H2O and salt out
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You should now be able to:
Distinguish between the following terms: isoosmotic, hyperosmotic, and hypoosmotic; osmoregulators and osmoconformers; stenohaline and euryhaline animals. Define osmoregulation, excretion, anhydrobiosis. Compare the osmoregulatory challenges of freshwater and marine animals. Describe some of the factors that affect the energetic cost of osmoregulation.
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Describe and compare the protonephridial, metanephridial, and Malpighian tubule excretory systems.
Using a diagram, identify and describe the function of each region of the nephron. Explain how the loop of Henle enhances water conservation. Describe the nervous and hormonal controls involved in the regulation of kidney function.
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