24. Osmoregulation and the kidney Flashcards
What are the main functions of the excretory organs?
- Maintain osmotic concentrations
- Maintain proper concentrations of ions
- Remove metabolic end products
What is the definition of osmolarity?
The concentration of moles of active solutes per litre of solvent
What is osmotic pressure?
Force associated with the movement of water
What is the relationship between osmolarity and osmotic potential?
Low osmolarity = equals high osmotic potential
What is osmolality?
The concentration of solutes per kilogram of solvent
What is tonicity?
The concentration of non permeable solutes per litre of solvent
How do excretory organs control osmolarity and volume of extracellular fluids?
- By excreting water and solutes that are in excess
- By conserving water and solutes that are valuable or in short supply (eg glucose)
What are the three examples of nitrogenous waste?
- Ammonia (most water needed)
- Urea
- Uric acid (least toxic)
Where is urea synthesised?
in the liver
What are the challenges of marine animals?
They have to conserve water and excrete excess salts
What are the challenges of freshwater animals?
They have to excrete excess water and conserve salts
What are the challenges of terrestrial animals?
They have to conserve water and salts
What are osmoregulators?
Osmoconformers match their body osmolarity to their environment actively or passively
What are osmoconformers?
Osmoconformers are marine organisms that maintain an internal environment which is osmotic to their external environment
What are 3 measures marine teleost fish take to maintain the osmolarity of their body fluids (osmoregulator)?
- Drink seawater to replace the water lost to the environment
- Produce little urine (kidney has reduced role in ion and H2O excretion)
- Eliminate the salts ingested from salt water
What are chloride cells?
Cells in gills which actively transport salts from the blood into the environment
What is the main nitrogenous waste in aquatic invertebrates and bony fish?
Ammonia
How is ammonia excreted from aquatic invertebrates and bony fish?
Excreted by diffusion across the gill membranes directly into water
- Easily removed because it is very soluble in water
What is the behavioural stresses of desert animals to prevent water loss?
Avoid the daytime heat and emerge at night
What is aestivation?
Similar to hibernation, desert animals have low metabolic activity and low H2O turnover
What are physical and physiological strategies desert animals have to prevent water loss?
- They have a thick keratinised cuticle with a high lipid content
- Have efficient kidneys and excrete highly concentrated urine (long loops of Henle)
Who excretes uric acid?
Land animals, reptiles, birds and insects (uricotelic animals)
Who excretes urea?
Mammals, amphibians and cartilaginous fish (ureotelic animals)
Why is uric acid and urea preferred for terrestrial animals rather than ammonia?
They need less water to remove and thus conserve water in terrestrial animals
What is the nephron?
the functional unit of the vertebrate kidney
What is the glomerulus?
Dense ball of capillaries which filter the blood plasma to produce a fluid (renal filtrate) lacking cells, proteins and other large molecules
What is the renal tubule?
It processes filtrate into urine
What is the bowman’s capsule?
Receives renal filtrate from glomerulus, mainly water and small molecules, amino acids and ions (salts)
Why is there a high rate of filtration in the glomerulus?
- High capillary blood pressure
- High permeability of glomerular capillaries and their podocytes (which wrap around capillaries and leave slits between them)
How does vasoconstriction affect the glomerulus?
It gives little flow to the glomerulus so there is little urine production
Where goes glomerular filtrate flows to?
Flows into the renal tubule, where it is modified by reabsorption of water and ions
Why do you only produce a small amount of urine?
98% of water and solutes are filtered out of the glomerulus are reabsorbed and do not appear in urine
Where does this absorption occur?
- 75% of the reabsorption is achieved int he proximal convoluted tubule, resulting in filtrate that is isosmotic to blood
- Remainder occurs in the rest of the renal tubule resulting in filtrate that is more concentrated than blood
What is the shape of the cells in the proximal convoluted tubule?
PCT cells are cuboidal with increased surface area due to microvilli
PCT have large numbers of which organelle?
Large numbers of mitochondria near the apical surface - PCT cells are highly metabolically active
What do PCT cells actively transport?
- Na+, glucose and amino acids out of filtrate back into tissue fluid
- This causes water to follow by osmosis. Water and solutes in tissue fluid are taken up by peri-tubular capillaries (vasa recta)
What do aquaporins do?
They assisting in osmosis
- AQP1 regulates movement of water molecules in the proximal convoluted tubule
What happens to mice that do not have aquaporins?
They cannot concentrate their urine because there is no movement of water from the renal filtrate in the PCT
