1. Lecture 15 Outline (Ch. 44) I. Homeostasis II. Water Balance
III. Animal Excretory Systems
Human Urinary System
Bladder
Kidneys
Water Control
VI. Summary
An albatross can drink salt water – how can they do this without getting sick?!

2. If you eat a lot of salt, what happens to your urine?
Thought Questions:
If you eat a lot of salt, what happens to your urine?
If you do not drink enough water, what happens to your urine?
If you drink excess water, what happens to your urine?

3. Urinary System aka ‘Excretory System’
Maintains homeostasis of body fluids via water balance
Osmolarity, (solute concentration of solution), determines movement of water across selectively permeable membranes
Hypoosmotic: lower solute conc, higher water
Hyperosmotic: higher solute conc, lower water

4. Water Balance Osmoconformer: isoosmotic with surrounding
Osmoregulator: control internal osmoslarity
Uptake water, ions in food
Uptake
salt ions
by gills
Osmotic water
gain from gills, body surface
Excretion of large
amounts of dilute urine
(b) Osmoregulation in a freshwater fish
Excrete
salt ions
from gills
Gain water, salt ions from food
Osmotic water
loss from gills,
body surface
Gain water, salt ions from
seawater
Excrete salt ions &
little water in scanty urine from kidneys
(a) Osmoregulation in a saltwater fish

5. Water Balance Water gain (mL) loss Urine (0.45) (1,500)
Evaporation (1.46)
Evaporation (900)
Feces (0.09)
Feces (100)
Derived from
metabolism (1.8)
metabolism (250)
Ingested
in food (750)
in food (0.2)
in liquid (1,500)
balance in a
kangaroo rat
(2 mL/day)
balance in
a human
(2,500 mL/day)

6. Animal Excretory Systems
Simplest system
Tubule
Tubules of
protonephridia
Cilia
Interstitial
fluid flow
Opening in
body wall
Nucleus
of cap cell
Flame
bulb
Tubule cell
Flatworms use protonephridia
Wastes stored in excretory pore, drawn out by water
environment

7. Animal Excretory Systems
Capillary
network
Components of
a metanephridium:
External opening
Coelom
Collecting tubule
Internal opening
Bladder
Worms use metanephridia
Collect body waste
Remaining waste excreted

8. Animal Excretory Systems
Rectum
Digestive tract
Hindgut
Intestine
Malpighian
tubules
Feces and urine
HEMOLYMPH
Reabsorption
Midgut
(stomach)
Salt, water, and
nitrogenous
wastes
Insects use malpighian tubules
Actively pump waste across a transport epithelium, extra salt and water into tubules

9. Vertebrate Urinary System
Most urinary waste nitrogenous – from digesting protein
Blood filtered by a transport epithelium in kidneys
Desert kangaroo rat – excretes very concentrated urine
Fish excrete ammonia (toxic at high levels)
Land vertebrates convert to urea – add to urine
A well-adapted desert dweller
The desert kangaroo rat of the southwestern United States seldom drinks, partly because its long loops of Henle allow it to produce very concentrated urine.
To reduce water-loss, desert animals (reptiles, snakes, birds) excrete uric acid (non-toxic, hydrophobic)

10. Which animal excretory system produces the most concentrated excretion product?
Flatworms
Earthworms
Saltwater fish
Freshwater fish
Humans
Birds

11. Human Urinary System 1) Kidneys 2) Ureters 3) Bladder 4) Urethra
Blood w wastes brought by renal artery to kidney
Filtered blood carried away by renal vein
2) Ureters
urethra
left renal
artery
left kidney
vein
left ureter
urinary
bladder
Transport urine away
from kidney
3) Bladder
Stores urine
Max capacity ~ 1 L
4) Urethra
Transport urine from
bladder to outside body

12. Human Urinary System - Bladder
Micturition
(urination)
Ureter
Gotta pee?
Stretch stimulates contractions
Bladder
Sphincters control release
Internal urethral
sphincter (involuntary)
Urogenital diaphragm
External urethral
sphincter (voluntary)

13. Human Urinary System - Bladder
Brain
(-)
Sensory Input
(spinal cord)
(-)
Stretch
(~200 ml)

14. Urinary Disasters Tycho Brahe: When you SHOULD go
Tycho suddenly contracted a bladder ailment after attending a banquet in Prague, and died eleven days later, on 24 October According to Kepler's first hand account, Tycho had refused to leave the banquet to relieve himself because it would have been a breach of etiquette.[18] After he had returned home he was no longer able to urinate, except, eventually, in very small quantities and with excruciating pain.
Although lurid anecdotes of attacks on humans abound, there is only one documented case of a candiru entering a human orifice.[7] In this instance, the victim claimed that the candiru "jumped" into his urethra as he urinated while thigh-deep in a river.[8] It was also once thought that the fish was attracted to urine (as the candiru's primary prey emits ammonia from its gills, a chemical found in urine), but this was later discredited in formal experimentation.
Tycho Brahe: When you SHOULD go
The infamous candiru: When NOT TO go

15. Human Urinary System - Kidneys
Kidney Structure
Renal cortex
Renal medulla
Renal artery
Renal vein
Ureter
Renal pelvis
Urine forms in the nephron, ~1 million/kidney
nephron
Renal cortex
Renal medulla
FIGURE 35-4 Cross section of a kidney
A nephron is drawn considerably larger than normal (and further enlarged in the inset) to show its location in the kidney. Collecting ducts empty the urine into channels that lead to the renal pelvis, a chamber that funnels urine into the ureter and out of the kidney.

16. Human Urinary System - Kidneys
Afferent arteriole from renal artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Distal tubule
Efferent arteriole from glomerulus
Collecting duct
Branch of renal vein
Descending limb
Ascending limb
Loop of Henle
Each nephron is a filter:
Glomerulus- network of capillaries
Bowman’s capsule- cup around glomerulus
Loop of Henle-
Tubule network for adjusting water, salt, and waste levels
Collecting duct- carries fluid from nephron

17. Human Urinary System - Kidneys
Filtration
Water, nutrients, and wastes - filtered from
glomerulus into Bowman’s capsule

18. Human Urinary System - Kidneys
Proximal tubule
Distal tubule
Filtrate
CORTEX
Loop of Henle
OUTER MEDULLA
INNER MEDULLA
Key
Active transport
Passive transport
Collecting duct
Nutrients
NaCl
NH3
HCO3
H2O K H
Urea
Reabsorption
In proximal tubule, most water along with bicarbonate, K+, and NaCl are reabsorbed into blood.

19. Human Urinary System - Kidneys
Proximal tubule
Distal tubule
Filtrate
CORTEX
Loop of Henle
OUTER MEDULLA
INNER MEDULLA
Key
Active transport
Passive transport
Collecting duct
Nutrients
NaCl
NH3
HCO3
H2O K H
Urea
Loop of Henle
increasing osmolarity cortex to medulla
active transport of Na+ & Cl– at ascending loop

20. Human Urinary System - Kidneys
Proximal tubule
Distal tubule
Filtrate
CORTEX
Loop of Henle
OUTER MEDULLA
INNER MEDULLA
Key
Active transport
Passive transport
Collecting duct
Nutrients
NaCl
NH3
HCO3
H2O K H
Urea
Secretion
In distal tubule, additional wastes (like H+ and K+) are actively secreted into the tubule from the blood

21. Human Urinary System - Kidneys
Proximal tubule
Distal tubule
Filtrate
CORTEX
Loop of Henle
OUTER MEDULLA
INNER MEDULLA
Key
Active transport
Passive transport
Collecting duct
Nutrients
NaCl
NH3
HCO3
H2O K H
Urea
Concentration
At collecting duct, additional water (and NaCl) leaves; urine more concentrated than blood.

22. Osmolarity of interstitial fluid (mOsm/L)
Human Urinary System - Kidneys
Two-solute model:
NaCl and Urea are moved into the kidney medulla
The filtrate in the nephron passes into this area three times
Osmolarity of interstitial fluid (mOsm/L)
300
300
300
100
NaCl
200
400
700
NaCl
H2O
Urea
1,200
300
400
600
300
H2O
CORTEX
400
400
H2O
H2O
OUTER MEDULLA
H2O
600
600
H2O
H2O
900
900
Key
H2O
INNER MEDULLA
Active transport
1,200
1,200
Passive transport

23. Water Balance
Thirst
Hypothalamus
ADH
Pituitary gland
Osmoreceptors in hypothalamus trigger release of ADH.
STIMULUS: Increase in blood osmolarity (for instance, after sweating profusely)
Homeostasis: Blood osmolarity (300 mOsm/L)
Drinking reduces blood osmolarity to set point.
H2O reab- sorption helps prevent further osmolarity increase.
Increased permeability
Distal tubule
Collecting duct
Body detects dehydration. Signal from hypothalamus to posterior pituitary.
Posterior pituitary releases ADH into the bloodstream.
ADH (antidiuretic hormone) allows more water reabsorbed into the blood.
Concentrated urine produced

24. What effect would blocking ADH have?
Urine: Waste and remaining water from nephron
95% water / 5% solutes (ions, urea)
Alcohol interferes with ADH
Production of dilute urine – Dehydration
Headache
Fatigue
Nausea