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-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

1. Perturbing: Disrupt macromolecule function
-Na, K, Cl, SO4, charged a.a.
-as conc increases, enzyme has to work harder
2. Compatible: little effect; polyols (glycerol, glucose) and uncharged amino acids
3. 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)


-Are highly dependent on water
-skin is permeable to water (waxy secretion can decrease permeability)
-No loops of Henle - means can't concentrate urine

-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


-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)
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

1. Ion Balance
2. Osmotic Balance
3. Blood pressure
4. pH balance
5. Excretion
6. 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;

-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



-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)



-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
-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