1. The Kidney and osmoregulation
Topic 11.3
The Kidney and osmoregulation
Bellwork:
On your own whiteboard and without looking at a drawing, draw the human excretory system. Label kidney, bladder, ureter, and urethra.

3. Understanding: Animals are either osmoregulators or osmoconformers
Osmolarity = solute concentration of a solution
Osmoregulator = an animal who maintains constant internal solute concentration (even when living in salt water!)
e.g. all terrestrial & freshwater animals and some marine (bony fish)
Maintain body solute concentration of ~1/3 seawater & 10x freshwater
Osmoconformer = an animal whose internal solute conc. is SAME as environment
e.g. marine invertebrates (starfish, scallops, mussels, lobster, jellyfish) & sharks

4. Osmoregulator or osmoconformer?

5. Understanding: The Malpighian tubule system in insects & the kidney carry out osmoregulation & removal of nitrogenous wastes.

6. Osmoregulation
Osmoregulation = form of homeostasis where concentration of blood or hemolymph is kept within narrow range
Hemolymph = combo of blood & lymph (tissue fluid); in arthopods, including insects
Malpighian tubules = tubes that branch off intestinal tract
Cells actively transport ions & uric acid from hemolymph into tubule lumen
Water passively transported from hemolymph into tubule lumen
Tubules empty contents into gut
Water & ions reabsorbed
Uric acid excreted with feces

7. In mammals…

8. Insects have Malpighian tubules!

9. Birds have a cloaca!

10. What’s in a bird dropping?

11. Skill: Drawing & labelling a diagram of human kidney

15. Skill: Annotation of diagrams of the nephron
Nephron = functional unit of kidney
Tube whose walls are made of one layer of cells
Structure & function:
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Blood vessels
Afferent arteriole
Glomerulus
Efferent arteriole
Peritubular capillaries
Vasa recta
venules

17. Understanding: The composition of blood in the renal artery is different from that in the renal vein.
Renal Artery
Renal Vein
blood enters kidney
blood leaves kidney
before osmoregulation
after osmoregulation
variable water (from cell resp or food/drink) or salt content (from food)
more constant water or salt content
higher amount of toxins & other substances not metabolized by body (pigments, drugs)
lower amount of toxins & other unwanted substances
more urea
less urea
more O2
less O2
less CO2
more CO2
more glucose
less glucose
same concentration of plasma proteins

18. Understanding: Ultrastructure of the glomerulus & Bowman’s capsule facilitate ultrafiltration.
Glomerulus = ball of capillaries in nephron where ultrafiltration takes place
Very high pressure & permeable (volume of fluid forced out is ~100x greater than in other capillaries)
Ultrafiltration = separation of particles differing in size by only a few nm’s
Permeability to larger molecules depends on their shape & charge.
Too large: most proteins, and blood cells

20. Structure of glomerulus

21. 3 parts to ultrafiltration system
Fenestrations = pores (100nm diameter) between cells of capillaries allowing fluid to escape, but not blood cells
Basement membrane = the filter that covers & supports wall of capillaries
3. Podocytes = strangely shaped cells with finger-like extensions which wrap around capillaries & provide support; on inner wall of Bowman’s capsule
If molecules pass through all 3 parts, they become part of the glomerular filtrate!

22. Understanding: The proximal convoluted tubule selectively reabsorbs useful substances by active transport.
Almost all glomerular filtrate gets reabsorbed back into blood!
Most reabsorption happens in the PCT.
Substances reabsorbed:
All glucose (co-transport)
All amino acids
80% water (osmosis)
80% sodium ions (active transport)
Chloride ions

24. Sample Exam Question: Explain how the structure of the PCT is adapted to carry out selective reabsorption:

25. Reabsorption vs secretion

26. Understanding: The loop of Henle maintains hypertonic conditions in the medulla.

27. Countercurrent mechanism in kidney
Expends energy to create a concentration gradient
Flow of fluid in descending & ascending limb is in opposite directions
Causes steeper gradient of solute concentration
Loop of Henle = countercurrent multiplication system
Vasa recta = countercurrent exchange system – allows vasa recta to supply kidney with nutrients without messing up the conc. gradient

28. Understanding: Length of the loop of Henle is positively correlated with the need for water conservation in animals.
Loops of Henle found within medulla of kidney (short ones are just in cortex)
The longer the loop of Henle, the more water volume will be reclaimed
Dryer environment = longer loops of Henle = thicker medulla

29. Understanding: ADH controls reabsorption of water in the collecting duct.
The kidney functions in osmoregulation = keeps the relative amounts of water and solutes in balance
If solute concentration in blood too high, hypothalamus detects and causes pituitary gland to secrete hormone ADH
ADH = antidiuretic hormone
ADH causes walls of DCT & collecting duct to become
more permeable to water (aquaporins allow H2O out)
In the presence of ADH, 99% of H2O is reabsorbed!
Adult beverages inhibit ADH! (close aquaporins)

30. Understanding: The type of N waste in animals is correlated with evolutionary history & habitat.

31. Application: Consequences of dehydration & overhydration!
from exercise, insufficient drinking of water, diarrhea
Sign: dark yellow urine due to increased solute concentration
Water needed for removal of wastes, so dehydration can cause:
Tiredness & lethargy due to decreased efficiency of muscle function & increased tissue exposure to waste
Decreased BP due to low blood volume
Increased heart rate due to low BP
Lower ability to sweat, therefore difficult body temp regulation

32. Overhydration Less common
Over-consumption of water, such as after exercise, without replacing electrolytes lost at same time
Causes dilution of blood solutes
Swelling of cells due to osmosis
Headache
nerve function disruption

33. Application: Treatment of kidney failure by hemodialysis or kidney transplant.
Most commonly occurs as complication of diabetes or hypertension
Dialysis machine = artificial kidney

34. Application: Blood cells, glucose, proteins and drugs are detected in urinary tests.
Urinalysis = analysis of urine composition
Tests for pH, glucose and protein
High levels of glucose & protein may indicate diabetes
High protein may indicate kidney damage
Drug test = monoclonal antibody test: looks for presence of drugs
Microscopic examination:
presence of wbc’s may indicate UTI
Presence of rbc’s may indicate kidney stone or tumor