NBIC57 osmoregulation

Osmotic U/P ratio.

The ratio urine composition over the plasma’s composition => relativ osmoticity of urine which affects the water and solute excretion. Measurment of iso/hypo/hyperosmocity.

Sources of water for the body.

• You cannot consume drinks with higher [salt] than you kidney can process or you’ll become dehydrated.

• Some airdried foods contain moisture

• Protein-rich foods can be dehydrationg since it’s nitrogenous and doesn’t produce metabolic water.

• Lipids produce most metabolic water

Obligatory water losses.

When water is needed for catabolism.

• Through respiration when obtaining O₂ inhale and exhale.

• water loss through catabolism

• Urinary for excretion

• Fecally to store organic material

Types of osmolytes and how do they contribute to osmotic pressure.

Osmolytes are solutes that has effekt on the osmotic pressure. they can be inorganic ions or organic solutes (which are mostly used as osmotic effector)

• Inorganic ions in high conc disturb propertios of molecules 

• Compatible solutes, often organic, contribute to the osmotic pressure of body fluid without effecting the properties of the macromolecules. Ex: free aa, betaines, taurine, glycerol.

• Counteracting solutes can have strong effect on macromolecules and act in teams of two to not effect, such as urea & methylamines.

Hyperosmotic (freshwater) vs. hypoosmotic (saltwater) regulators.

Hyperosmotic regulators have higher osmotic pressure in blood than ambient water & has to gain water via osmosis and lose ions via diffusion, can concentrate excretion. Active gill trp of ions by gills.

Hyposmotic has lower osmotic pressure in blood than ambient water with more dialute ions. These are less permeable to water and dialuted water exit the body. Ions diffuse via electrical gradient & gill permeability.

Ion regulation organ in freshwater and saltwater fish.

The gills. Excrete Cl^- actively with the help of chloride cells or mt-rich-cells (MRC) and Na⁺ can be active or passive.

Function of the salt glands in reptiles, including birds.

Excretion in saltglands have higher [salt] than in seawater and water via osmosis moves to lower concentrations, they are hyperosmotic to the blood. The parasympatic nervesystem is responsible for secretion when blood osmotic pressure is high.

Salt gland of elasmobranchs.

Elasmobranch fish have low [inorganic solutes] but high organic (urea & TMAO) => hyperosmotic to seawater. They use kidney and rectal salt glands consisting of secretory tubules that secrete NaCl and other osmolytes.

Coping with the transition from fresh- to saltwater and viceversa.

Hyper-hypoosmotic regulation. Reverse direction of transport of NaCl (NaCl pumps) in gills. From freshwater to saltwater NaCl transports out, they increase drinking rate, decrease [urine] & produces isosmotic urine to the plasma. Morphological changes but also endocrine regulation.

Unavoidable evaporative water loss in land animals.

Skin is permeable to water, humidity and temperature of air.

In respiratory tract to be able to exchange gases.

How is excretory water loss and urine-concentrating ability related?

Excretory water loss depends on urine concentration ability and amounts of solutes that needs to be excreted. Nitrogen can excrete solutes that are poorly soluble. If you excrete more water than you take in → dehydration

How do amphibians avoid dehydration?

Could go into dormacy or live in sheltered area.

They could also regulate (upregulate) ADH levels which can reduce rate of urine production and regulate [urine]. An increased amount of NaCl reabsorbes and bladder could be more permeable to water. It can increase water influx through skin by increasing bloodflow and increase aquaporin insertion.

Hormonal control of water and salt balance.

Hormonal control could be diuretic (dialute urine) or antidiuretic (low volumes of urin and osmolytes)

Vertebrates are antidiuretic: AHD-excretion of water. Aldosterone holds Na⁺ and excrete K⁺ to maintain stable extracellular fluid osmotic pressure. Natriuretic are types of peptides that adds Na⁺ to urine (excrete Na⁺)

Urine formation in amphibians.

They have nephrons in kidney consisting of:

• Proximal convolted tubule: reabsorbs solutes, ex NaCl to blood without changing osmotic pressure. Also reabsorbes glucos and aa.

• Distal convoluted tubule: reabsorbs water and body fluids, regulating volume and osmotic concentration of urine (changes osmotic pressure). ADH here regulates permeability.

• Bladder stores urine and can adjust volume & composition of urine bc it’s regulated by ADH.

Why does larger relative medullary thickness allow higher urine concentration?

Larger RMT allows longer loops of Henle which results in higher osmotic pressure deeper into the medulla. As the tubular fluid passes the collecting duct more water can get reabsorbed to reach equilibrium with the osmotic pressure in the interstitial medullary fluid. But permeability in the collecting duct is regulated by vasopressin that creates cell response to add aquaporins on the membrane walls of the collecting ducts. 

Why is there diversity in relative medullary thickness in mammals.

Diversity of RMT depends on the different needs to concentrate urine because of the diverse environmental habitat that the animals live in. When living in dry and hot environments the abiliry to reabsorbe and preserve water from urine is crutial. Mammals living in sea needs to be able to drink water without becoming dehydrated.

Malpighian tubules and urine formation in insects.

Malpigian tubules creates primary urine where solutes as KCl transports actively into the tubular fluid. Some solutes reabsorbes or secretes as it empties into mid- and hindgut where water reabsorbs to the blood. Hindgut with rectum modifies secretion to uric acid.

Means of nitrogen disposal.

There is no endproduct of nitrogen so it has to be excreted as urine, ammonia or uric acid depending on nitrogenous endproduct.

• Ammonotelism: ammonia is primitive endproduct. This is toxic when accumulated and has to ecrete with a lot of water. Cheapest endproduct since it requires no endproduct. Oceanic invertebrates and some aquatic animals.

• Urea: less toxic and more soluble but costs ATP to produce. Mostly terrestrial vertebrates.

• Uric acid are purines, low toxicity and low solubility. Cations (+) can be incorporated in uric acid to use less water.

Osmoregulators and osmoconformers.

Regulators keeps a constant osmotic pressure, independent of evironment.

Conformers are isosmotic to environment. They could be regulators depending on environment.

Kidney function

Function is to excrete waste products from blood and reabsorb water for optimal osmotic pressure.

Urine formation in mammals and countercurrent multiplication.

In neohrons. Firstly creating primary urine then reabsorbs nutrients and water to lastly secrete urin through collecting duct.