1. 11.3 The kidney and osmoregulation
Essential idea: All animals excrete nitrogenous waste products and some animals also balance water and solute concentrations.
The form in which nitrogenous waste is excreted reflects evolution and ecological niche occupied, by the animal.
By Chris Paine

2. Understandings Statement Guidance 11.3.U1
Animals are either osmoregulators or osmoconformers.
11.3.U2
The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes.
11.3.U3
The composition of blood in the renal artery is different from that in the renal vein.
11.3.U4
The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.
11.3.U5
The proximal convoluted tubule selectively reabsorbs useful substances by active transport.
11.3.U6
The loop of Henle maintains hypertonic conditions in the medulla.
11.3.U7
ADH controls reabsorption of water in the collecting duct.
ADH will be used in preference to vasopressin.
11.3.U8
The length of the loop of Henle is positively correlated with the need for water conservation in animals.
11.3.U9
The type of nitrogenous waste in animals is correlated with evolutionary history and habitat.

3. Applications and Skills
Statement
Guidance
11.3.A1
Consequences of dehydration and overhydration.
11.3.A2
Treatment of kidney failure by hemodialysis or kidney transplant.
11.3.A3
Blood cells, glucose, proteins and drugs are detected in urinary tests.
11.3.S1
Drawing and labelling a diagram of the human kidney.
11.3.S2
Skill: Annotation of diagrams of the nephron.
The diagram of the nephron should include glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule; the relationship between the nephron and the collecting duct should be included.

5. Much of metabolic waste is in the form of Nitrogen
11.3.U9 The type of nitrogenous waste in animals is correlated with evolutionary history and habitat.
Much of metabolic waste is in the form of Nitrogen
Animals such as fish and amphibians, which have constant access to water flush their nitrogenous
waste primarily as ammonia.
Terrestrial animals, however, because they have less access to water, have been under selective pressure to "repackage" their toxic ammonia as less toxic molecules which can be flushed with less water
Reptiles and birds go one step further, packaging their nitrogenous waste as uric acid. It requires more metabolic energy to make than urea, but is less toxic, and requires very little water to flush from the body.
Mammals metabolize ammonia into a molecule called urea.

6. 11.3.U1 Animals are either osmoregulators or osmoconformers.
Osmoconformers maintain an internal conditions that are equal to osmolarity of their environment.
Minimizing the osmotic gradient minimizes the water movement in and out of cells. A disadvantage is that internal conditions may be sub- optimal.
Most Osmoconformers are marine invertebrates, e.g. starfish.
Osmoregulators tightly regulate their body osmolarity, which always stays constant, irrespective of their environment.
Kidneys play a large role in osmoregulation by regulating the amount of water reabsorbed. A disadvantage is that osmoregulation costs the animal ATP.
Osmoregulators are much more common in the animal kingdom, e.g. bony fish.
Osmoregulation in saltwater fish
Osmoregulation in freshwater fish

7. 11.3.U2 The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes.
The removal of nitrogenous waste and osmoregulation in insects by the Malpighian tubule #
*Hemolymph is a fluid (analogous to the blood) that circulates in the interior of the insect’s body remaining in contact with the tissues. *
#Malpighian tubules are longer and more convoluted than shown in this simplified illustration, they extend into the body cavity, where they are surrounded by hemolymph.

9. 11.3.S1 Drawing and labelling a diagram of the human kidney.

10. The kidney causes changes in the composition of blood
11.3.U3 The composition of blood in the renal artery is different from that in the renal vein.
The kidney causes changes in the composition of blood
renal vein
(filtered blood)
blood in the renal vein compared and contrasted with the renal artery has …
no change in proteins – not filtered
less urea and toxins#
less oxygen*
more carbon dioxide*
less salts and ions$ (if in excess)
less water$ (if in excess)
less glucose*
renal artery
(unfiltered blood)
ureter
(urine)
urea
toxins
water
salts
ions
# Undesired waste is removed from the blood.
$ The blood water and salt concentration needs to be balanced (osmoregulation). The kidney helps by removing these molecules if in excess.
*Oxygen and glucose are used for cell respiration in the kidney and carbon dioxide is produced.

12. 11.3.S2 Skill: Annotation of diagrams of the nephron.

13. 11.3.S2 Skill: Annotation of diagrams of the nephron.

14. Ultrafiltration occurs in the Bowman’s capsule
11.3.U4 The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.
Ultrafiltration occurs in the Bowman’s capsule
The capillary wall is fenestrated (it contains pores) allowing fluid to move through it
The basement membrane only allows smaller molecules to be filtered
filtration slits between foot projections of podocyte cells
act as a filter allowing only smaller molecules to be filtered.
Edited from:

15. 11.3.U4 The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.
Edited from:

16. Occurs in the Bowman’s/renal capsule; In the kidney cortex;
11.3.U4 The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration.
Occurs in the Bowman’s/renal capsule;
In the kidney cortex;
The (entering) afferent arteriole has a larger diameter than the (leaving) efferent arteriole;
This creates high pressure in the capsule;
Some smaller molecules are forced out of the glomerulus/blood into the capsule;
Through basement membrane and the fenestrations/pores in the capillary wall;
filtration slits between foot projections of podocyte cells also act as a filter;
Molecules in the filtrate include water, urea, glucose, amino acids, salts;
Plasma proteins, platelets, and cells are too large so remain in the blood;
Glomerular filtrate is then transported through the nephron;
Edited from:

17. 11.3.U5 The proximal convoluted tubule selectively reabsorbs useful substances by active transport.
Selective reabsorption of useful substances from the proximal convoluted tubule (PCT)
The PCT extends from the Bowman’s capsule to the loop of Henle
This where most selective reabsorption occurs: All glucose, amino acids, vitamins and hormones are reabsorbed here, along with approx 80% of the mineral ions and water
plasma
capillary
a large number of mitochondria provide ATP for active transport
PCT cell
microvilli cell lining to increase the surface area for the absorption
Carrier proteins and pumps are present to actively transport substances.
filtrate
lumen of the nephron

18. 11.3.U5 The proximal convoluted tubule selectively reabsorbs useful substances by active transport.
Selective reabsorption of useful substances from the proximal convoluted tubule (PCT)
The PCT extends from the Bowman’s capsule to the loop of Henle
This where most selective reabsorption occurs: All glucose, amino acids, vitamins and hormones are reabsorbed here, along with approx 80% of the mineral ions and water
plasma
capillary
a large number of mitochondria provide ATP for active transport
Due to high concentrations of recovered substances in PCT cells the substances can passively diffuse into the bloodstream (along the concentration gradient)
PCT cell
Amino acids, hormones mineral ions & vitamins are actively transported into the PCT cells
Glucose is actively transported across the membrane in symport* with sodium
Water follows the movement of the ions passively (by osmosis)
microvilli cell lining to increase the surface area for the absorption
filtrate
lumen of the nephron
*symport is a type of cotransport here a molecule of glucose and sodium are moved together in the same direction.

19. 11.3.U6 The loop of Henle maintains hypertonic conditions in the medulla. AND 11.3.U7 ADH controls reabsorption of water in the collecting duct.
Osmoregulation is the control of water and solute concentrations in the body fluids (e.g. the blood plasma).
The job of the loop of Henlé is to generate a high concentration of solutes (low concentration of water) in the tissue fluid of the medulla compared to the filtrate in the nephron. This aids the reabsorption of water in the collecting duct.
The hormone ADH balances the water concentration of the blood by changing the permeability of the collecting duct.

20. 11.3.U6 The loop of Henle maintains hypertonic conditions in the medulla.

21. 11.3.U6 The loop of Henle maintains hypertonic conditions in the medulla.

22. 11.3.U6 The loop of Henle maintains hypertonic conditions in the medulla.

23. 11.3.U7 ADH controls reabsorption of water in the collecting duct.

24. 11.3.U7 ADH controls reabsorption of water in the collecting duct.

25. 11.3.U7 ADH controls reabsorption of water in the collecting duct.

26. Length of the loop of Henle and water conservation
11.3.U8 The length of the loop of Henle is positively correlated with the need for water conservation in animals.
Length of the loop of Henle and water conservation
The kangaroo rat’s (Dipodomys nitratoides) loop of Henle is much longer than that of other rodents. This in part explains the kangaroo rat’s amazing ability to survive in deserts.
The kangaroo rat's kidneys are especially efficient and produce only small quantities of highly concentrated urine. They have very long loops of Henle which builds a higher ion concentration in the medulla. Therefore allowing more water to be reabsorbed in the collecting duct.
Kangaroo rats can concentrate urea to 3,500 mmol/l, whereas humans can only concentrate urea to 400 mmol/l.

27. Length of the loop of Henle and water conservation
11.3.U8 The length of the loop of Henle is positively correlated with the need for water conservation in animals.
Length of the loop of Henle and water conservation
The ion concentration in the medulla builds as the loop of Henle descends. A longer loop of Henle in implies a larger medulla (compared to the kidney size) than in animals with a shorter loop of Henle. The shows the relationship between relatively medullary area in the mammalian kidney and the maximal urine concentration* that can be produced.
small medulla large medulla
*The higher the ion concentration the more water can be reabsorbed in the collecting duct making the urine more concentrated.

30. Consequences of dehydration and overhydration
11.3.A1 Consequences of dehydration and overhydration.
Consequences of dehydration and overhydration
Dehydration is due to loss of water from the body so body fluids become hypertonic.
Overhydration is less common and occurs when there is an over-consumption of water.
thirst, small quantities of dark coloured urine
lethargy, (exposure to higher levels of metabolic waste, reduced muscle effeciency)
low blood pressure (reduced blood volume)
raised heart rate (low blood pressure)
Inability to lower body temperature (lack of sweat)
in severe cases seizures, brain damage and death
clear urine
swelling of cells due to osmosis (from hypotonic body fluid)
Headache, disruption of nerve function (Swelled cells)
In more serious cases delirium, blurred vision, seizures, coma and death

31. Treatment of kidney failure
11.3.A2 Treatment of kidney failure by hemodialysis or kidney transplant.
Treatment of kidney failure
Kidney failure is a condition in which the kidneys fail to adequately filter waste products from the blood. It can be caused by injury or disease symptoms vary depending on the seriousness and progression of the disease. If not treated kidney failure leads to death.g
Treatment of kidney failure focuses on two main approaches:
Hemodialysis
Kidney transplants

32. Treatment of kidney failure
11.3.A2 Treatment of kidney failure by hemodialysis or kidney transplant.
Treatment of kidney failure
Hemodialysis treatment lasts about four hours and is done three times per week. A person can be treated this way for years.
Hemodialysis (commonly called kidney dialysis) is a process of purifying the blood of a person whose kidneys are not working normally.
Fresh dialysate contains*:
No urea – to encourage diffusion from the blood
Glucose and other useful molecules at optimal concentrations – to minimize loss from the blood.
High solute concentration removes excess water.
The Dialyser contains a semi-permeable membrane that allows small particles (e.g. urea) to diffuse through, but larger molecules and cells remain in the blood
Used dialysate collects filtered out small molecules such urea
Saline solution prevents excessive water loss which could lead to dehydration.
*Other molecules and ions are present and therefore filtered/balanced, but these are the key components of the dialysate.

33. Treatment of kidney failure
11.3.A2 Treatment of kidney failure by hemodialysis or kidney transplant.
Treatment of kidney failure
A transplant is the best long-term treatment.
Donors can be either:
Someone who has recently died
A person who has chosen to give up one of their two kidneys
Donors and the recipient have to be a close match in both blood and tissues to minimize the chance of rejection*.
The transplanted kidney is grafted in to the lower abdomen with the renal artery, renal vein and ureter connected to the recipient’s blood vessels and bladder.
*If the match is not close enough the receipient’s immune system will react to the new kidney as it would to a pathogen.

34. 11.3.A3 Blood cells, glucose, proteins and drugs are detected in urinary tests.
Urinalysis
Diagnostic tests of urine samples provide an easy effective way to detect illness and drug abuse.
Processes that affect the metabolism affect the metabolic waste that is produced and then excreted in urine.
Presence of blood cells infections, disease and some cancers.
Glucose is a strong indication of diabetes.
Trace amounts of protein are normal (some proteins are very small), but larger amounts indicate kidney disease.
Drugs (or their breakdown products) can often be detected in urine samples

35. Bibliography / Acknowledgments
Bob Smullen