Homeostasis and the kidney Flashcards
What are the different types of nitrogenous waste?
Ammonia, uric acid and urea
Which animals excrete ammonia?
Aquatic animals
What are the properties of ammonia molecules?
Small, very toxic and soluble
Where does urea come from?
Terrestrial animals convert ammonia to urea
Why do terrestrial animals convert ammonia to urea?
Lots of urine would have to be produced to get rid of ammonia as it’s so toxic it has to be diluted
What are the benefits of excreting urea instead of ammonia?
Less water used to discard nitrogenous waste, as urea 100,000x less toxic than ammonia so can be excreted in a very concentrated form
What animals excrete uric acid?
Land snails, insects, birds and some reptiles
How many times less soluble is uric acid compared to urea or ammonia?
1000x
What advantage does uric acid have over urea and ammonia?
1000x less soluble
Less water used
Reduced mass to allow flight (birds)
Why is blood pressure in the capillaries so high?
Smaller lumen diameter of efferent arteriole compared to large lumen of afferent arteriole
What is ultrafiltration?
Small molecules being filtered out of capillaries
What materials pass from the blood into bowman’s capsule?
Water
Amino acids
Urea
Glucose
Vitamins
NA+ ions (salts)
What is the fluid called that continues down the nephron?
Glomerular filtrate
Which materials do not pass out of the blood into the nephron?
Large plasma proteins
Blood cells
Platelets
What is the order of selective reabsorption?
Na+ pumped out of cell and K+ in by selective reabsorption
2. High conc of Na+ in filtrate so moves into cell via facilitated diffusion. Only allowed to enter if coupled with glucose
3. Once in cell, glucose passes down a conc gradient into blood through a channel protein via facilitated diffusion
4. Flow of blood in vessels maintains conc gradient
How much water is absorbed in the nephron via selective reabsorption?
90%
The remaining 10% is regulated in the loop of Henle and collecting duct
Where does selective reabsorption take place?
In the proximal convoluted tubule (PCT)
What does ‘renal threshold’ for glucose mean?
The level above which glucose conc is too high and cannot all be transported (with NA+) out of the filtrate. Some exit through urine
What else apart from glucose and water is reabsorbed in the PCT?
Urea
Ions
Amino acids
Vitamins
What happens in the loop of Henle?
- Na+ and Cl- are actively pumped out of ascending limb, causing water potential in medulla tissue fluid to decrease
- Water moves out of descending limb by osmosis. Reabsorbed into blood by vasa recta capillaries
- Fluid in descending limb becomes more concentrated as it moves down (less water)
- Most concentrated at the tip of the loop of Henle
What is the function of the loop of Henle?
Reabsorb water and sodium ions
What does ADH stand for?
Anti-diuretic hormone
What are the detectors in osmoregulation?
Osmoreceptors in hypothalamus
What is the coordinator in osmoregulation?
Posterior lobe of pituary secreting ADH
What is the effector in osmoregulation?
DCT and collecting ducts of kidney
What are the stages of osmoregulation?
- ADH detected by cell surface receptors
- Enzymes controlled reactions occur causing
- Vesicles containing water permeable channels (aquaporins) to fuse with DCT membrane
- More water reabsorbed into blood (out of filtrate down the water potential gradient)
What would happen if there was a decrease in the water potential of the blood plasma?
Osmoreceptors detect decrease
Posterior pituary gland releases ADH
Causes more aquaporins to fuse with cell membrane of DCT
More water reabsorbed
Small volume of concentrated urine produced
What would happen if there was an increase in the water potential of the blood plasma?
Osmoreceptors detect increase
Posterior pituary gland stops release of ADH
Causes less aquaporins to fuse with cell membrane of DCT
Less water reabsorbed
Large volume of dilute urine produced
Which enzymes are produced in the pancreas?
Trypsin (endopeptidase), exopeptidases, lipase, amylase
