Osmoregulation Flashcards
Definitions;
- Osmoregulator
- Osmoconformer
- Osmoregulator: Controls extraceullular solute profile
- is most vertebrates
- Ensure that internal ion and water composition
- Osmoconfomer: Exerts little control over their extracellular solute profile
- Stenohaline animal: can only deal with a narrow range of osmolarities
- Euryhaline animal: can tolerate a wide range of osmolarities
Metabolic water
- what is it, how much water produced
- e.g. of animal that relies on it
- Carbohydrates, fats and protein H2O content
- Metabolic water is water generated as a result of oxidative phosphorylation
- for every mol of glucose, 6 moles of water produced
- small desert animals mainly rely on this method for obtaining water
- Carbohydrates: 0.56g H2O/g food
- Fats: 1.07 g H2O/g food
- Proteins: 0.40 g H20/g food
Performed water
- what is it
- % water in different types of food
- Performed water: Water associated with food
- dry seeds = 5 - 10%; insects, meat = 60-70%; pasture = 80-90% and nectar = 80-95%
Classification of Solutes (3)
- what it does
- e.g.
- Perturbing: Disrupt macromolecule function
- Na, K, Cl, SO4, charged a.a.
- as conc increases, enzyme has to work harder
- Compatible: little effect; polyols (glycerol, glucose) and uncharged amino acids
- Counteracting: Disrupt function on own but counteract disruptive effects of another solute when in combo
- Urea disrupts and methylamines strengthen hydrophobic interactions -> together = little effect
Molarity (calculation)
- number of moles of solute present in 1 litre of solution (expressed in mol/L)
- mol = grams/MW
Osmolarity - definition
-Osmolarity: Total osmotic activity in a solution as the sum of the individual osmotic activities of all the solutes in the soln.
Nitrogenous Excretions
- how it comes about
- 3 types
- a.a. used in proteins and other nitrogen-containing molecules
- when a.a. oxidised or converted to other kinds of molecules, the amino group must be removed
- nitrogenous wastes are ammonia, urea or uric acid
Nitrogenous excretions; Ammonia
-basics - when produced and what transformed into
- Produced during a.a. and other nitrogen-containing molecule breakdown
- Is toxic and must be excreted
- Can be transformed into other forms (urea and uric acid)
Ammonia -> Advantages and disadvantages
Advantages: direct end-product of deanimation of a.a. therefore requires no extra energy
-highly soluble in water
Disadvantages: Very toxic (needs 400ml H2O to dilute each gram)
-must be excreted rapidly or converted to less toxic form
Urea -> Advantages and disadvantages
-where produced
Advantages: -Less toxic than ammonia (10 x less water for storage)
-Highly soluble (can be moderately conc to conserve water)
Disadvantages: -Requires more energy to produce than ammonia
-Fair amount of water needed for its storage and excretion
*produced in the liver
Uric acid (Urate) -> Advantages and disadvantages
Advantages: -Produced in concentrated crystal form (saves water)
-Low toxicity
-Can be stored
Disadvantages: synthesis requires more energy
*important in egg-laying terrestrial vertebrates
Nitrogen Excretion - General rules as to what organisms excrete what
- Teleost fish -> ammonia and urea
- Chondrichthyes -> urea
- Amphibians -> Ammonia, urea and uric acid
- Birds and reptiles -> uric acid
- Mammals -> urea
Varies with;
- Life stages (tadpoles - ammonia to frogs - urea)
- Diets (hummingbirds - high conc = uric acid; low conc nectar = ammonia)
- Species/breed: dalmation dogs = uric acid
- Habitat: turtles/tortoises
Marine Fish:
-When marine environment has higher osmolarity than fish
- Marine teleosts (bony fish)
- hypotonic to medium (higher osmolarity in external enviro)
- Drink lots of seawater
- Chloride cells in their gills excrete salts
- Kidneys - few or no glomeruli
- Urine volume very small (no bladder)
- most solutes move in to animal and H2O moves out (need to continually remove solutes and get H2O in
Marine fish;
-When fish has about the same osmolarity as external environment
- “primitive fish” and cartilaginous fish are iso-osmotic with sea water
- conc solutes in tissues of osmoconfomers is similar to ocean
- high solutes conc due to urea and TMAO
- well-developed kidneys
- specialised rectal gland excretes excess salts
Freshwater vertebrates;
-When osmolarity is higher in fish than environment
- Freshwater teleosts
- Do NOT drink water - gain water from environment by osmosis
- Produce large quantities of dilute urine
- Chloride cells in the gills use active transport to pump salts into their body
Osmoregulation - water balance
- Input + production = utilization + output
- What comes in body must eventually be used for excreted to maintain homeostasis
- done either by diet, environment, behaviour and thermoregulation
Main electrolytes in ECF and in ICF
- K and HCO3 are high in the intracellular fluid
- Na and Cl are high in the extracellular fluid
The integument in osmositic balance
- The Integument: Can mediate the permeability by changing amount of aquaporin proteins
- can add mucous to decrease H2O loss (frogs)
- thick integument also makes skin impermeable
Amphibian generalisations (H2O control) (3)
-Exceptions
- Are highly dependent on water
- skin is permeable to water (waxy secretion can decrease permeability)
- No loops of Henle - means can’t concentrate urine
EXCEPTIONS;
- several arid-adapted spp. can store urates in bladder (usu. adults secrete urea)
- also sheds skin to act as a cocoon)
- Water-holding frog burrows and aestivates and stores watter
Reptiles -> H2O control
- thinks they can do to decrease water loss
- waste they produce
- Have a relatively resistant integument (virtually waterproof)
- Cutaneous Evaporative Water loss (EWL) is still major water loss
- Can decrease respiratory EWL as can decrease metabolic rate and therefore low respiratory rate
- Simple kidneys (w/ no loop of Henle)
- obligatory drinking uncommon
- Produce urates
- reabsorb water at cloaca (via salt transport)
- Nasal salt glands
- very dry poo
Birds -> H2O Control
- types of nephrons
- waste
- other features
- birds near ocean
- Have 2 types of nephrons -> ‘reptile-like’ and ‘mammal-like’
- i.e. one with no loop of henle, one with
- nephron v. lobular
- Most birds only form modestly hyperosmotic urine (can get up to 3 x plasma concentration -tho mammals can get up to 27 x)
- waste = urate (crystals therefore no osmotic pressure)
- most lack urinary bladder
- cloaca and lower intestine can recover water
- nasal salt glands remove excess salt (excrete hyperosmotic solutions of Na and Cl via countercurrent system)
- only those that live near sea (allows them to consume seawater)
- Birds pant to try and cool down -> decrease foraging when temp hot
- EWL increases as temp increases
Mammal behaviour to control H2O loss
- Limit activity in the heat of day
e. g. being nocturnal, reducing metabolic rate and breathing (alter volume, NOT rate) - Diet (alter feeding times or plant sp.)
- Retreat (burrow, shade or orientation)
- Thermoregulation
- Drinking
e. g. Bedoin goat can drink every 2-4 days (stomach lining acts as an osmotic barrier)
Mammals -> EWL
-adaptations to minimise EWL
- Lose more water through EWL than other groups
- selective brain cooling (carotid rete) plays a role in reducing EWL
- some have specialised nasal adaptations (e.g. camels and dik-diks)
- warmer air holds more H2O - if not fully saturated, have to do so when breathed in
- when breathe out through mouth, can lose a lot of water
- longer nose = better at retrieving more H2O; is a countercurrent multiplier (is an evaporative cooling)
Faecal water loss in mammals
-urine too
- desert rodents have approximately 21-37%
- dik-dik, goat = 40-50%; horses/cow = 70-80%
- Produced concentrated urine -> thru well developed loops of henle
- it’s all about how they use structure
Countercurrent Multiplier Definition
- A structure in which two fluids flow in opposite directions on either side of an exchange surface, allowing high-efficiency exchange of materials by active means
e. g. ion concentration in the loop of Henle
6 Roles of the Kidney
- Ion Balance
- Osmotic Balance
- Blood pressure
- pH balance
- Excretion
- Hormone Production
*are less than 1% of body mass, but take 20 % of cardiac output
The Nephron
-2 general parts
- Glomerulus + Bowman’s capsule
- fluid relationship
- The functional unit of the kidney
- Made of renal tubule and associated vascular
- Renal Tubule = tube from single layer of epithelial cells
- Gomerulus = twisted ball of capillaries that delivers fluids to the tubule
- Bowman’s capsule = mouth of tubule (cuplike expansion that surrounds the gomerulus
- fluids that leave glomerulus enter Bowman’s capsule and move down PC tubule
- blood cells and large macromolecules are not filtered
Blood Supply to Nephron
- Blood enters Kidney via renal artery
- Afferent arteriole enters glomerulus, efferent leaves
- efferent flow into peritubular capillary beds that wrap around tubules (in cortical)
- also found around PCT and DCT
- in juxtamedullary, efferent diverges into vasa recta (run along loop of Henle)
- vasa recta prevents dissipation of osmotic gradient while supplying nutrients and removing wastes
Tubule Regions
definitions of;
- Filtration
- Reabsorption
- Secretion
- Excretion
- Proximal Tubules: Mass reabsorption
- Loop of Henle: Generates the interstitial concentration gradient
- Distal tubule: reabsorption completed for most soluts
- Collecting duct: drains multiple nephrons
Filtration” basis of size - fluid from blood to tubules
Reabsorption: Take out of filtrate that we want in blood
Secretion: blood to tubule
Excretion tubule to external environment
Filtration, Reabsorption, Secretion and Excretion in Nephron
- Filtration: Gomerulus
- Reabsorption: PCT, Ascending and Descending limbs of loop of henle, DCT and Collecting duct
- PCT is most important in reabsorption of H2O
- Secretion: PCT, DCT, Collecting Duct
- Excretion: Collecting Duct
Anti-diareutic hormones on aquaporins in collecting duct
- ADH absent: No reaborption of water = dilute urine
- ADH present = reabsorption of water = concentrated urine
*ADH present increases aquaporins, enables water to be uptaken in collecting duct
Filtration -> Glomerulus
- Glomerular capillaries
- Mesangial cells
- Glomerular capillaries are very leaky -> have foot processes that make filtration structure
- Mesangial cells control blood pressure and filtration within glomerulus
- Hydrostatic pressure w/in glomerulus determines how much fluid is pushed into renal corpsule
Primary Urine
- What it is it
- What happens to it later on
- Primary Urine: initial flitrate filtered in Bowman’s Capsule that is isosmotic to blood
- most water and salt in primary urine is reabsorbed using transport proteins and energy
Secretion
- Secretory products include K, NH4, H, pharmaceuticals and water-soluble vitamins
- requires transport proteins and energy
Features of Reabsorption and Secretion
- Are highly selective
- Some materials are actively reabsorbed (glucose and Na) others follow by passive diffusion (water)
Excretion
- parts
- micturition reflex
- After urine produced, leaves kidney and enters the urinary bladder
- urine lives the bladder via the urethra
- opening and closing of sphincters is controlled by a spinal cord reflex arc that can be influenced by voluntary controls
Basic Renal processes
-Fate of Urea, uric acid and glucose in filtrate
- Glucose: reabsorbed back into bloodstream via active transport
- Urea: Most left in filtrate - a little bit reabsorbed
- Uric acid: too big to be filtered in glomerulus, but secreted into filtrate later
Conserving water via filtrate
- High plasma osmolality
- low blood pressure
*due to decreasing Glomerular filtration rate
Producing copious dilute urine via filtrate
- low plasma osmolality
- high blood pressure
*Due to increasing Glomerular filtration rate
Hummingbirds and Aestivating frogs - adaptation
-Both shut down glomerular filtration to save energy (kindeys use up to 16% body’s ATP)
Cortical and Juxtamedullary nephrons
-relationship between loop of henle length and osmolality of urine
- Cortical: Nephrons that primarily sit in the cortex -> have a short loop of Henle that doesn’t contribute much to osmotic gradient
- Juxtamedullary: Sit closer to the corticomedullary junction -> have a longer loop of henle
- create strong concentration gradient inside kidney
- Animals that produce more concentrated urine have a longer loop of henle and a thicker medulla
- maximum urine osmolality and medullary area proportional (directly)
Loop of Henley and Collecting Ducts
- what are they classified as?
- What osmotic conc of final urine depends on
- Both act as countercurrent multipliers: create osmotic gradients that facilitate tranpsort processes
- gradients maintained by vasa recta capillaries
- Osmotic con. of final urine depends on permeability of the distal tubule and collecting duct
- impermeable = dilute; permeable = concentrated
Antidiuretic Hormone
- Controls urine volume
- secreted from pituitary gland (under control of hypothalamus)
- binds to receptors on DCT and collecting ducts and stimulate production of aquaporins
- Called arginie vasopressin in most mammals
*inhibited by alcohol and caffeine
Case example of H2O retention by Kangaroo Rat
- Never have to drink: rely on metabolic water and some preformed water
- Nocturnal
- Avoid movement while in burrow to decrease heat production
- dry food stored in burrow absorbs moisture lost in breathing
- Noses cool oxygen leaving nose - decreases EWL
- Large intestine absorbs alsmost all water in digestive tract (hard, dry faeces)
- Concentrated urine produced
