Osmoregulation Flashcards
1
Q
Osmoregulation
A
The control of water and solute balance.
2
Q
Main osmoregulatory organs
A
Gills, kidneys and intestines.
3
Q
What do water and ion exchanges occur between?
A
External and internal fluids.
4
Q
Internal fluids that exchanges occur in?
A
Interstitial fluid, extracellular fluid, plasma and intracellular fluid.
5
Q
Osmosis
A
Diffusion of water through a semi-permeable membrane.
6
Q
Osmotic pressure
A
Pressure that must be applied to prevent osmotic movement across a semi-permeable membrane.
7
Q
Hypotonic blood
A
Less than 275mOs.
8
Q
Isotonic blood
A
300mOs.
9
Q
Hypertonic blood
A
Greater than 300mOs.
10
Q
What happens to hypotonic blood?
A
RBCs bloat and explode, leaving RBC ghosts.
11
Q
What happens to hypertonic blood?
A
RBCs shrivel.
12
Q
Seawater osmotic pressure
A
1000mOs.
13
Q
Freshwater osmotic pressure
A
<5mOs.
14
Q
Osmoconformer
A
An organism that allows its internal concentration of salts to change in order to match the external concentration of salts in the surrounding water.
15
Q
Osmoregulators
A
An organism that controls its internal salt concentration.
16
Q
Zone of stability
A
Where homeostasis is maintained in osmoregulators.
17
Q
Euryhaline
A
An organism that can tolerate a wide range of salinities.
18
Q
Stenohaline
A
Cannot tolerate substantial changes in external osmolarity.
19
Q
Stenohaline fish
A
Most marine and freshwater fish.
20
Q
Euryhaline fish
A
Estuary, tidal zone, salt march and diadromous fish.
21
Q
2 types of diadromous fish
A
Anadromous (salmon) and catadromous (eel).
22
Q
Anadromous life cycle
A
Hatch in freshwater, live in seawater and then lay eggs in freshwater.
23
Q
Catadromous life cycle
A
Hatch in seawater, live in freshwater and then lay eggs in seawater.
24
Q
What determines mechanism of maintaining water balance?
A
The external environment.
25
Obligatory osmotic exchanges
Transepithelial diffusion (respiratory and other moist epithelia), ingestion, urination and defecation.
26
Excretory organs
Respiratory organs (lungs and gills), digestive system, skin and glands and renal system.
27
What do the respiratory organs excrete?
CO2, NH4+, HCO3-, Na+ and Cl-.
28
What does the digestive system excrete?
Undigested food, metabolic by-products like bilirubin, Na+ and water.
29
What do the skin and glands excrete?
Water and salts.
30
What does the renal system excrete?
Metabolites like urea/uric acid, hormones and drug by-products.
31
Primary urine formation
By filtration or active solute secretion.
32
What does primary urine flow through and what happens?
Flows through kidney tubules with its volume and composition modified by active/passive transport of solutes and water osmosis across epithelial cells.
33
4 processes of urine production
Glomerular filtration, tubular reabsorption, tubular secretion and excretion.
34
Glomerular filtration
The passage of water, urea, glucose and salts from the plasma into the renal tubule, it excludes RBCs and large plasma proteins.
35
Tubular reabsorption
Selectively returns 99% of water and salts from filtrate to blood in renal tubules and collecting ducts, with glucose reabsorbed in proximal tubule.
36
How is water reabsorbed?
Passively through osmosis.
37
How is NaCl reabsorbed?
Active transport.
38
Tubular secretion
Selectively moves K+, H+, HCO3- and foreign substances from blood to filtrate in renal tubules and collecting ducts by active transport, it also includes tubular synthesis.
39
Tubular synthesis
NH4+ synthesised in tubular lumen from NH3 by protein deamination and H+.
40
Molecules that leave in the proximal tubule
HCO3-, H2O and K+ passively and NaCl and nutrients actively.
41
Molecules that enter in the proximal tubule
Protons actively and NH3 passively.
42
Molecules that leave in the loop of Henle
H2O and NaCl (inner medulla) passively and NaCl (outer medulla) actively.
43
Molecules that leave in the distal tubule
NaCl and HCO3- actively and H2O passively.
44
Molecules that enter in the distal tubule
K+ and H+ actively.
45
Molecules that leave in the collective duct
Urea and H2O.
46
Driving force of proximal tubule reabsorption
3Na/2K ATPase.
47
How does sodium passively cross apical membrane in the proximal tubule?
Na+/2Cl-/K+ and glucose/Na+ cotransporters.
48
What actively removes Na+ from cells in blood?
Na+/K+ pump in the basolateral membrane.
49
What does movement of Na+ down concentration gradient in the proximal tubule cause?
Energises outward movement of protons via an electrically neutral Na+/H+ antiporter
50
Basolateral sodium pump in proximal tubule
Transports Na+ from cell into the blood.
51
Distal tubule epithelial cells
Secrete K+ into tubular filtrate.
52
K+ in distal tubule
Transported into cell by basolateral Na+/K+ pump, with it then moving down the concentration gradient via apical K+ into the lumen.
53
Elasmobranch nephron
Retains most urea and TMAO.
54
What nephrons can produce concentrated urine?
Avian, amphibian, reptile and mammal.
55
Formula for Osmolarity
Particles/L and 1Osm= 1 mole particles/L.
56
Formula for Osmolality
Dissolved particles/kg solvent.
57
What is osmolality used for?
Dilute aqueous solutions.
58
Examples of osmolarity
1M glucose= 1 Osm, 1M NaCl= 2 Osm, 1M CaCl2= 3 Osm.
59
Salt content of sea water
3% Salt.
60
Composition of extracellular fluid in marine invertebrates and hagfish
Very similar to sea water, with same osmotic pressure.
61
What are marine invertebrates and hagfish?
Osmoconformers and ionoconformers.
62
What are marine chondrichthyes (e.g. sharks and rays)?
Osmoconformer (regulates urea) and ionoregulators.
63
What are marine osteichthyes (bony fishes)?
Osmoregulator and ionoregulator.
64
What are freshwater vertebrates?
Osmoregulator and ionoregulator.
65
What are terrestrial vertebrates?
Osmoregulator and ionoregulator.
66
Marine elasmobranch comparative osmoregulation
Slightly hyperosmotic blood compared to environment, with urine iso-osmotic to blood.
67
Marine elasmobranch osmoregulatory mechanisms
Does not drink seawater, it passively attracts water via diffusion and it releases Na+ content from rectal gland.
68
Marine teleost comparative osmoregulation
Hypo-osmotic blood to environment, iso-osmotic urine to blood.
69
Marine teleost osmoregulatory mechanisms
Drinks seawater with excess salt excreted from gills.
70
Freshwater teleost osmoregulation and mechanisms
Hyperosmotic blood to the environment, with hypo-osmotic urine to the blood, they drink no water and absorbs salt and water through gills.
71
Amphibian osmoregulation and mechanisms
Hyperosmotic blood to environment and hypo-osmotic urine to blood, they absorb salt through skin.
72
Marine reptile osmoregulation and mechanisms
Hypo-osmotic blood relative to environment, iso-osmotic urine to blood, drinks seawater and has hyperosmotic salt gland secretion.
73
Desert mammal osmoregulation and mechanisms
Hyperosmotic urine compared to blood, they drink no water and rely on metabolic water.
74
Marine mammal osmoregulation and mechanisms
Hypo-osmotic blood to environment, hyperosmotic urine to blood, they drink some seawater.
75
Marine and freshwater birds osmoregulation and mechanisms
Hyperosmotic urine, drink sea/freshwater with marine birds having hyperosmotic salt gland secretion.
76
Osmoregulation in saltwater elasmobranches
Water absorbed by gills and skin, gills block loss of urea and TMAO which are also retained in kidneys, ingests salt with food which is lost in faeces or excreted by rectal gland.
77
What makes saltwater elasmobranches hyperosmotic?
They retain urea and TMAO.
78
Body fluids excreted by saltwater elasmobranches
~1100 mOSm.
79
Cartilagenous fish
Lower osmolarity for salt than seawater with salt diffusing through gill, animal fluids slightly hyperosmotic to seawater due to TMAO accumulation, water enters body via osmosis.
80
Saltwater teleost osmoregulation
Gills actively secrete NaCl and water loss, stomach sees passive reabsorption of NaCl and water, intestinal waste voided as MgSO4 which is actively secreted by kidney along with urea and little water.
81
What are marine teleost gills and salt glands in sharks, birds and reptiles comparable to?
Kidney proximal tubule with the key difference being chlorine orientation in transport.
82
Salt secreting cell mechanism
Na+/K+ ATPase and Na+/2Cl-/K+ cotransporter in basolateral membrane move Cl- from blood into cell and then leave cells into environment via Cl- channel in apical membrane, this drags Na+ with it via paracellular channels.
83
Marine fish body fluids
Hypo-osmotic, so loses water to surroundings by osmosis while attracting salt from diffusion and food, compensated by drinking lots of seawater and pumping out salt.
84
Freshwater teleost organ osmoregulation
Gills perform active NaCl absorption and osmosis of water, active tubular reabsorption of NaCl and the kidney excretes dilute urine, high urine volume loses ions unavoidably.
85
What are freshwater fish gills and frog skin similar to?
Kidney proximal tubule with key difference being the driving function by H+ V-ATPase, supported by carbonic anhydrase and anion antiporter.
86
What happens in freshwater fish gills and frog skin?
Epithelia take up Na+ from freshwater by proton pump in apical membrane, generating a gradient to move it into cell, but levels kept low by Na+/K+ pump in basolateral membrane.
87
Carbonic anhydrase and bicarbonate in freshwater fish gills and frog skin
Catalyses CO2 hydration which provides protons for proton pump, bicarbonate concentration gradient drives anion antiporter in apical membrane, takes Cl- into cell.
88
Freshwater fish fluids
Constantly hyperosmotic, take in water constantly via osmosis and lose salt by diffusion so excrete lots of dilute urine and regain lost salts.
89
Acclimatisation in freshwater to seawater fish
Proton pump powering NaCl uptake is downregulated, rise in Na+ flux raises plasma Na+ stimulating growth hormone and plasma cortisol increase triggering Cl cell production and basolateral membrane infolding, causing increase in Na/K pump activity.
90
Acclimatisation in seawater to freshwater fish
Paracellular gaps between Cl and accessory cells close due to low external Na so NaCl efflux drops rapidly, plasma prolactin increases causing number of Cl cells to decrease and loss of apical pits so Na/K pump drops and then proton pump is upregulated.
91
What helps acclimatisation?
Stem cell differentiation.
92
What do stem cells become in seawater?
Chloride cells.
93
What generally happens in seawater?
Ion secretion.
94
What generally happens in freshwater?
Ion uptake.
95
Osmoregulation on land
Vital to prevent dehydration.
96
Inspiration
Transfers heat and water vapour from nose to air, cooling the nose.
97
Expiration
Heat and water vapour transferred back to body, wetting the nose.
98
Water conservation in desert animals
Remain in burrows in the day, respiratory moisture condensed in nasal passages, free water in seeds and metabolic water used, faeces is dehydrated and urine is concentrated by countercurrent exchange.
99
Water gain in kangaroo rat
90% from metabolic water, 10% from free water in food.
100
Water loss in kangaroo rat
70% from evaporation and perspiration, 25% from urine and 5% from faeces.
101
Osmoregulation in marine reptiles and birds
Lack of freshwater, they drink seawater that is hyperosmotic to blood which would dehydrate if kidneys could not concentrate urine above saltwater concentration but also has osmoregulatory organs.
102
Avian salt glands
Highly vascularised, uses same molecular osmoregulation as chloride cells where Cl- concentrates to excrete salt with passive Na+ movement.
103
Marine reptile salt glands
May eat high salt concentration food, which kidney cannot handle so uses salt glands.
104
Nasal fluid concentration of marine birds
5% salt.
105
What does protein metabolism produce?
Nitrogenous wastes.
106
Most to least toxic nitrogenous waste
Ammonia, urea and then uric acid.
107
Ammonia
Used in most aquatic animals as it is very soluble in water, easily permeates membranes, diffuses out of entire body surface into surrounding water and excreted out of gills and some from kidneys.
108
Ammonia effects
Alters protein structure, substitutes for K+ in some pumps, interferes with blood flow to brain and synaptic transmission so can cause convulsions, coma and then death.
109
How much water is required to excrete 1g of ammonia?
500ml.
110
How much water is required to excrete 1g of urea?
50ml.
111
How much water is required to excrete 1g of uric acid?
1ml.
112
Urea
Excreted by most water-conserving animals, produced in liver by combining ammonia and CO2, travels to kidney to be excreted in urine, where it can be tolerated in a more concentrated form.
113
Uric acid
Excreted by land snails, insects, birds and many reptiles, more energy required than for urea but non-toxic, can be stored as a precipitate or for later use.
114
What do land vertebrates who use uric acid do?
Produce shelled eggs where it can be stored as a solid.
