Title: TOPIC 3: OSMOREGULATION AND EXCRETION
1TOPIC 3 OSMOREGULATION AND EXCRETION
- Internal homeostasis
- 1. Osmotic regulation
- 2. Ionic regulation
- 3. Excretion
- 3 process are closely related
- Problem maintain
- internal environment
NaCl K Ca2
External Environment
2Freshwater versus Seawater
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4Functions of Major Solutes
- Na
- Major extracellular cation
- K
- Major cytoplasmic cation
- Ca2
- Mg2
- Pi, HCO3-
- NH4
5Intracellular versus extracellular regulation
- 1. Intracellular and extracellular
- 2. Extracellular and external
6Problems of Osmoregualtion
- Water
- entry routes
- exit routes
- entry exit regulation
- Salt entry routes
- exit routes
- entry exit regulation
- Regulation requires energy therefore some animals
conform
7- Osmotic and ionic exchanges
- 1. Obligatory exchanges
- 2. Regulated exchanges
- Factors affecting obligatory exchanges
- Trans-epithelial gradients
- Surface-to-volume ratios
- Permeability
- Feeding
- Temperature, exercise, convection
- Metabolism
8Osmoregulators versus Osmoconformers
9Osmoregulation in Aquatic Animals
- Definitions
- Euryhaline
- Stenohaline
- Hyperosmotic/hyperionic
- Hypoosomotic.hypoionic
- Isoosmotic/isoionic
- Isotonic
10Freshwater Animals
- Body fluids are hypertonic therfore two problems
- water influx
- salt loss
NaCl lt 1 mmol L-1
O2, CO2
NaCl 150 mmol L-1
H2O
Na, Cl-
H2O, ions
11Solutions
- Freshwater fishes
- 1. Teleosts
- blood osmolarity 300 mosm
- compromise between need for effective gas
transfer and obligatory exchanges - reduce gill surface area
- reduce permeability
- dilute urine (lt10 mmol l-1)
- do not drink (water)
- active NaCl uptake by the gill
12The Fish Gill
13The Fish Gill
14NaCl Uptake in Freshwater Teleosts
Na
H
Cl-
ATP
HCO3-
PVC
CC
15- 2. Elasmobranchs
- Permanent or temporary FW dwellers
- Low blood solute levels therefore less water
influx - Less renal salt loss
- 3. Amphibians
- Similar to teleosts
- Skin replaces gills
- Active ion uptake
- 4. Invertebrates
- FW crayfish versus FW clam
16- FW crayfish
- blood conc. 420 mM
- Urine conc. 124 mM
- low urine volume becuaew permeability is low
- active NaCl uptake
- FW clam
- blood conc. 42 mM
- urine conc. 24 mM
- urine volume is high because permeability is high
17Marine Animals
- Body fluids hypotonic therefore 2 problems
- Water loss
- Salt gain
- Marine invertebrates
- Many are isoionic therefore isoosmotic
- exceptions
- Artemia
- Isoosmotic vertebrates
- Hagfish
- Isoionic but divalents are regulated
18- Elasmobranchs
- Isoosmotic but NOT isoionic
- Urea and TMAO
- Rectal gland, renal excretion
- The coelocanth
- Similar to elasmobranchs
- Hypotonic vertebrates
- Marine teleosts
- Drink SW, absorb 70-80 of SW
- Divalents are eliminated in faeces and by kidney
- Monovalents excreted by the gill
- Very low volume of isotonic urine
19NaCl Excretion in SW Teleosts
-
Water
Blood
Na
K
Na
-
Cl-
Chloride cell
20Osmoregulation in Terrestrial Environments
- Problems
- 1. Continuous dehydration therefore water
conservation is primary concern - 2. Excretion of salts
- Solutions
- 1. Less permeable integuments
- e.g. terrestrial arthropods - epicuticle
- skin permeability related to temperature
regulation
21- 2. Drinking of water
- complex feedback system
- freshwater versus seawater
- 3. Extrarenal salt excretion
- salt glands of marine or land birds and reptiles
- Marine reptiles
- marine lizards
- marine turtles
- sea snakes
- marine birds
- size and fluid composition related to habitat and
diet - greater volumes than human kidney
- 4. Reduction of glomerular filtration
- Reduced capillary development in arid-dwelling
snakes and lizards
22- Extreme reduction in bird kidney
- Minimal filtration is unavoidable
- Why are glomeruli retained?
- Formation of hypertonic urine
- Related to loop of Henle
- Greatest in desert rodents (9000 mOsm)
- Minimize faecal water loss
- Absorption of faecal water
- insects
- desert rodents
- Uricotelism
- Requires least water of 3 nitrogenous wastes
23- Water absorption across body surfaces
- Amphibians - pelvic patch
- Terrestrial arthropods - absorption of water
vapour - Storage of water
- Urinary bladder of amphibians and reptiles
- Correlation between available water storage and
storage capacity - Behavioural responses
- Avoidance of desiccating environments
- Minimizing respiratory water losses
- Internalization of respiratory surfaces
- Temporal counter-current system
24- Hygroscopic materials
- Tolerance to dehydration
- Man versus spadefoot toad
- Essential to maintain blood pressure
- Production of metabolic water
- Consequence of substrate oxidation
- Glucose 0.69 g H2O
- Protein 0.40 g H2O
- Fat 1.07 g H2O
- Starch 0.56 g H2O
- Starch is most favourable substrate
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26Water Balance in the Kangaroo Rat
27THE VERTEBRATE KIDNEY
- Paired, 1 of body weight YET 20-25 of cardiac
output - Inner layer medulla
- Outer layer cortex
- Micturition not continuous due to sphincter
- Stretch receptors
28- Paired, 1 of body weight YET 20-25 of cardiac
output - Inner layer medulla
- Outer layer cortex
- Micturition not continuous due to sphincter
- Stretch receptors
29The Nephron
- Functional unit of the kidney
- Five regions
- 1. Renal corpuscle
- glomerulus
- Bowmanss capsule
- 2. Proximal tubule
- proximal convoluted tubule
- proximal straight tubule
- 3. Loop of Henle
30- Descending limb
- Ascending thin limb
- Ascending thick limb
- 4. Distal convoluted tubule
- 5. Collecting duct system
- Connecting tubule
- Cortical collecting duct
- Medullary collecting duct
- Renal pelvis
31Overview of Urine Formation
- 3 processes involved
- 1. Filtration
- depends on molecular size
- filtrate blood plasma
- 15-25 of H2O solutes are filtered
- rate of filtration GFR 125 ml/min 200 L/day
- Most of the water and salts are reabsorbed
- 2. Reabsorption
- 99 of of H2O salts are reabsorbed
32- NaCl reabsorption involves active transport
- H2O reabsorption is passive
- 3. Secretion
- some substances are secreted and thus more
concentrated than initial filtrate - secretion is selctive and relies on active
transport
1. Filtration 2. Secretion 3. Reabsorption
33Quantification of Renal Function
- The Renal Clearance Ratio
- 1. Determine GFR
- inject animal with inulin
- inulin in filtrate inulin in urine
- inulin in filtrate inulinf X Vf
- inulin in urine inulin X Vu
- If X Vf Iu X Vu
- Vf Iu X Vu/If GFR
34- for inulin
- the ratio Iu X UFR/Iplasma X GFR 1 renal
clearance ratio - 2. Measure UFR, Xurine, Xplasma
- RCR gt 1 net secretion
- RCR lt1 net reabsorption
35Details
- 1.Glomerular filtration
- 3 factors involved
- 1. hydrostatic pressure differences
- 2. colloid osmotic pressure differences
- 3. permeability of the three-layered tissue
- Net filtration pressure 5 - 25 mmHg
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38- 2. Tubular reabsorption
- Original filtrate is quickly modified
- 99 of water reabsorbed
- 99 of NaCl reabsorbed
- All glucose is reabsorbed
- Proximal convoluted tubule
- 75 of NaCl and H2O are reabsorbed
- 70 of filtrate is reabsorbed - isoosmotic
- Descending limb
- No active salt transport, low NaCl permeability
- High water permeability water leaves
- Thin ascending limb
- No active salt transport
39- High NaCl permeability,
- NaCl exits
- Thick ascending limb
- Low water permeability
- Active NaCl transport
- The filtrate becomes hypoosmotic
- Distal convoluted tubule
- Active NaCl transport
- Water follows passively
- Collecting duct
- Variable permeability to water
- Final step in formation of hyperosmotic urine
40- 3. Tubular secretion
- K, H, NH3, acids and bases
- Number of secretory pathways is small
41Concentrating mechanism of the nephron
- Osmotic removal of water from the collecting duct
- due to formation of standing osmotic gradient
- Corticomedullary conc. gradient
- differential permeabilities
- functional asymmetry
- counter-current principle
42Figure 14-33
43Figure 14-34
44Control of Kidney Function
- Body fluid disturbances are minimised
- Neural and/or endocrine
- 3 methods of regulation
- 1. Control of GFR
- 2. Control of salt reabsorption
- 3. Control of water reabsorption
45Control of GFR
- Important that GFR be maintained
- Renal blood flow is fairly constant
- Lower vertebrates
- GFR can be adjusted
46Control of Renal Na Reabsorption
- The juxtaglomerular apparatus
- Macula densa
- juxtaglomerular cells
- Stimulated by
- sympathetic stimulation
- reduced Na
47- Circulating catecholamines
- Decreased blood pressure
- Decreased plasma volume
- Response
- renin release into afferent arteriole
- formation of angiotensin I
- Angiotensin II
- increased blood pressure
- release of aldosterone
- Aldosterone promotes Na reabsorption
48 49- Summary of renin release
- Angiotensin II and aldosterone
- Increased NaCl reabsorption
- Increased water reabsorption
- Increased plasma volume
- Peripheral vasoconstriction
- INCREASED BLOOD PRESSURE
50Control of osmotic water retention
- Depends on collecting duct permeability
- Regulated by ADH
- ADH increases water permeability
- ADH secretion controlled by
- plasma osmolality
- blood pressure
- ethanol
51Nitrogen Excretion
- Toxicity
- Fish - 0.05-1.0 mmol L-1
- Mammals - lt0.05 mmol L-1
52Uric acid
Ammonia
Urea
0.001 L g-1
0.4 L g-1
0.04 L g-1
much less toxic
highly toxic
less toxic
synthesis requires ATP
synthesis requires ATP
Aquatic invertebrates,bony fish, larval
amphibians
Birds, reptilesterrestrial insects
Mammals,adult amphibians
53- Ammonia-excreting animals
- Aquatic invertebrates, bony fish, larval
amphibians - NH3 synthesis
- Excreted by diffusion across gills or body
surface. - Cuttlefish
- NH3 H2O NH4 OH-
NH4
cation (e.g. K)
NH3
54- Urea-excreting animals
- Advantages and disadvantages
- Some molluscs and annelids, mammals, adult
amphibians, elasmobranch fish - Urea synthesis
- Excreted by kidneys or gills.
- Elasmobranchs??
- Osmoregulatory strategy - urea plus
trimethylamine oxide (TMAO)
urea 400 mM TMAO 70-100mM
55- Urea-excreting bony fish??
Toadfish
Lungfish drought
pulsatile
Urea excretion (µmol kg-1)
Time (h)
56Xenopus
57- Uric acid-excreting animals
- Advantages and disadvantages
- Birds, reptiles, terrestrial insects, land
snails - Crocodiles
- Uric acid synthesis
- Excretion by kidneys or Malpighian tubules
- Cleidoic eggs
58Linkage between NH3 and CO2 excretion