Body Fluid Regulation
and Excretory System
Body Fluid regulation
 Retaining or eliminating certain ions (such as
Na+, Cl-, K+, HCO3-) and water (in and out
must be equal)
 Osmosis – movement of water from greater
concentration to less concentration (toward
higher solutes!!)
Aquatic animals
 Marine invertebrates (mollusks and
arthropods) and cartilaginous fish (sharks)
have body fluids isotonic to sea water
 Bony fish – have some salt, prone to water
loss

Salt water bony fish


Drink water constantly
Freshwater bony fish – hypertonic

Never drink water, constantly eliminate excess
Terrestrial animals
 Lose water by evaporation, respiration, sweat
and feces
 Drink water occasionally to replace what is
lost
 Birds and reptiles can drink salt water
because they have a salt gland near the eyes
 Humans conserve water by producing a
hypertonic urine
Nitrogenous waste products
 Amino acid metabolism – broken down for
energy or converted to fats, carbs for storage

amino groups are removed and excreted as
ammonia, urea, or uric acid, depending on
species
 Ammonia – little or no energy needed in
conversion by adding H (NH3)


Toxic and needs a lot of water to wash away
Excreted by bone fish, aquatic invertebrates,
amphibians
Nitrogenous waste continued
 Urea – excreted by terrestrial amphibians and
mammals



Less toxic than ammonia and needs less water to
remove from body
Requires energy
Produced in liver
 Uric acid – insects, reptiles and birds
 Not very toxic, poorly soluble in water
 Requires most energy, but conserves most water
 White stuff in bird droppings
Excretory organs
 Planarians
 Excretory tubules
 Flame cells – contain beating cilia, propels fluid
through tubules and out of body
 Earthworms
 Nephridia – tubule with ciliated opening and excretory
pore
 Urine contains metabolic wastes, salts and water
 Insects
 Malpighian tubules – attached to gut
 Uric acid flows from hemolymph into tubules
 water flows from salt gradient but is usually reabsorbed
Urinary system in humans
 Kidneys – size of fist, lower back, right slightly lower
than left.


Urine – product
Kidney  ureter  urinary bladder  urethra
 In males, urethra also carries sperm
 3 parts
 Renal cortex – outer region, nephrons
 Renal medulla – renal pyramids
 Renal pelvis – inner hollow changer, urine collects
here and carried to bladder via ureter
 Kidney stones (renal calculus), can block renal pelvis
or ureter
Nephron
 Over 1 million in each kidney
 Produce urine
 Primarily found in renal cortex
 Structure: Glomerular capsule  proximal
convoluted tubule loop of the nephron
 distal convoluted tubule collecting
duct (delivers urine to renal pelvis)
 Glomerulus – capillary bed
Urine formation – 3 processes
 Glomerular filtration at the glomerular
capsule
 Tubular reabsorption at the convoluted
tubules
 Tubular secretion at the convoluted tubules
 Figure 38.9
Urine formation and homeostasis
 Hypertonic urine – more concentrated than blood
 occurs as result of reabsorption of water
 ADA – antidiruetic hormone – post. Pituitary
 Water reabsorption at collecting duct
 Aldosterone – adrenal glands
 Excretion of K+, reabsorption of sodium
 Renin – enzyme, stimulates adrenal gland to
relsease aldosterone due to low blood volume
 ANH – atrial natriuretic hormone – atria of heart due
to increase in blood volume, blocks uptake of renin
Acid- base balance
 Kidneys reabsorb bicarbonate ions and
excrete hydrogen ions as need to maintain
the normal pH of the blood.
 Urine pH = 6


Excess of H+ excreted
Ammonia provides a buffer for H+