24. Osmoregulation and the kidney

Question 1

What are the main functions of the excretory organs?

Answer 1

1. Maintain osmotic concentrations
2. Maintain proper concentrations of ions
3. Remove metabolic end products

Question 2

What is the definition of osmolarity?

Answer 2

The concentration of moles of active solutes per litre of solvent

Question 3

What is osmotic pressure?

Answer 3

Force associated with the movement of water

Question 4

What is the relationship between osmolarity and osmotic potential?

Answer 4

Low osmolarity = equals high osmotic potential

Question 5

What is osmolality?

Answer 5

The concentration of solutes per kilogram of solvent

Question 6

What is tonicity?

Answer 6

The concentration of non permeable solutes per litre of solvent

Question 7

How do excretory organs control osmolarity and volume of extracellular fluids?

Answer 7

• By excreting water and solutes that are in excess

- By conserving water and solutes that are valuable or in short supply (eg glucose)

Question 8

What are the three examples of nitrogenous waste?

Answer 8

• Ammonia (most water needed)
• Urea
• Uric acid (least toxic)

Question 9

Where is urea synthesised?

Answer 9

in the liver

Question 10

What are the challenges of marine animals?

Answer 10

They have to conserve water and excrete excess salts

Question 11

What are the challenges of freshwater animals?

Answer 11

They have to excrete excess water and conserve salts

Question 12

What are the challenges of terrestrial animals?

Answer 12

They have to conserve water and salts

Question 13

What are osmoregulators?

Answer 13

Osmoconformers match their body osmolarity to their environment actively or passively

Question 14

What are osmoconformers?

Answer 14

Osmoconformers are marine organisms that maintain an internal environment which is osmotic to their external environment

Question 15

What are 3 measures marine teleost fish take to maintain the osmolarity of their body fluids (osmoregulator)?

Answer 15

• 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

Question 16

What are chloride cells?

Answer 16

Cells in gills which actively transport salts from the blood into the environment

Question 17

What is the main nitrogenous waste in aquatic invertebrates and bony fish?

Answer 17

Ammonia

Question 18

How is ammonia excreted from aquatic invertebrates and bony fish?

Answer 18

Excreted by diffusion across the gill membranes directly into water
- Easily removed because it is very soluble in water

Question 19

What is the behavioural stresses of desert animals to prevent water loss?

Answer 19

Avoid the daytime heat and emerge at night

Question 20

What is aestivation?

Answer 20

Similar to hibernation, desert animals have low metabolic activity and low H2O turnover

Question 21

What are physical and physiological strategies desert animals have to prevent water loss?

Answer 21

• They have a thick keratinised cuticle with a high lipid content
• Have efficient kidneys and excrete highly concentrated urine (long loops of Henle)

Question 22

Who excretes uric acid?

Answer 22

Land animals, reptiles, birds and insects (uricotelic animals)

Question 23

Who excretes urea?

Answer 23

Mammals, amphibians and cartilaginous fish (ureotelic animals)

Question 24

Why is uric acid and urea preferred for terrestrial animals rather than ammonia?

Answer 24

They need less water to remove and thus conserve water in terrestrial animals

Question 25

What is the nephron?

Answer 25

the functional unit of the vertebrate kidney

Question 26

What is the glomerulus?

Answer 26

Dense ball of capillaries which filter the blood plasma to produce a fluid (renal filtrate) lacking cells, proteins and other large molecules

Question 27

What is the renal tubule?

Answer 27

It processes filtrate into urine

Question 28

What is the bowman’s capsule?

Answer 28

Receives renal filtrate from glomerulus, mainly water and small molecules, amino acids and ions (salts)

Question 29

Why is there a high rate of filtration in the glomerulus?

Answer 29

• High capillary blood pressure
• High permeability of glomerular capillaries and their podocytes (which wrap around capillaries and leave slits between them)

Question 30

How does vasoconstriction affect the glomerulus?

Answer 30

It gives little flow to the glomerulus so there is little urine production

Question 31

Where goes glomerular filtrate flows to?

Answer 31

Flows into the renal tubule, where it is modified by reabsorption of water and ions

Question 32

Why do you only produce a small amount of urine?

Answer 32

98% of water and solutes are filtered out of the glomerulus are reabsorbed and do not appear in urine

Question 33

Where does this absorption occur?

Answer 33

• 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

Question 34

What is the shape of the cells in the proximal convoluted tubule?

Answer 34

PCT cells are cuboidal with increased surface area due to microvilli

Question 35

PCT have large numbers of which organelle?

Answer 35

Large numbers of mitochondria near the apical surface - PCT cells are highly metabolically active

Question 36

What do PCT cells actively transport?

Answer 36

• 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)

Question 37

What do aquaporins do?

Answer 37

They assisting in osmosis

- AQP1 regulates movement of water molecules in the proximal convoluted tubule

Question 38

What happens to mice that do not have aquaporins?

Answer 38

They cannot concentrate their urine because there is no movement of water from the renal filtrate in the PCT