water balancechapter 42

maintaining water balance• osmoregulation

• water and dissolved solutes• metabolic wastes (nitrogen)• excess water / homeostasis

• adjusting the composition of internal body fluids• in arthropods -- hemolymph• in vertebrates -- interstitial fluid / blood

maintaining water balance• transport epithelia

• extensive surface area• water balance and excretory• examples

• marine birds like albatross• drink seawater

Ducts

Nostrilwith salt

secretions

Nasal saltgland

nitrogenous wastes• ammonia

• many aquatic invertebrates • highly soluble, but very toxic -- requires lots of water

• ammonium -- NH4+

• common in freshwater fish... • exchanged for Na+ in freshwater fish

• urea• mammals, adult amphibians, many marine fishes, and turtles -- • low toxicity, can be concentrated• requires much less water than ammonia• requires energy to produce from ammonia

nitrogenous wastes• uric acid

• Land snails, insects, spiders, birds, and many reptiles

• relatively nontoxic.• largely insoluble in water • more expensive• related to mode of reproduction

• amniotic eggs

osmosis• central problem of osmoregulation --

• how to balance uptake and outflow of water?• osmosis• osmolarity • human blood is about 300 mosm/L• seawater is about 1,000 mosm/L.

• hypertonic = hyperosmotic; hypotonic = hypoosmotic

homeostasis• marine

• hypoosmotic regulators -- • problems • retaining water • getting rid of salt

• isoosmotic conformers.• fresh

• hyperosmotic regulators -- • problems • removing excess water • acquiring salt

• variability• anadromy/catadromy• stenohaline/euryhaline

Excretion of salt ions from

gills

Gain of water and salt ions from food

Osmotic water loss through gills and other parts of body

surface

Excretion of salt ions and small amounts of water in scanty urine from

kidneys

Gain of water and salt ions from

drinking seawater(a) Osmoregulation in a saltwater fish

Uptake of water and some ions in food Uptake of salt

ions by gills Osmotic water gain through gills and other parts of body

surface

Excretion of large amounts of water in dilute

urine from kidneys(b) Osmoregulation in a freshwater fish

terrestrial concerns• dessication?• adaptations to prevent water loss:

• anhydrobiosis• nocturnal activity• waxy cuticle in arthropods...• keratin • many desert animals can reabsorb water from bladder

excretory organs• specilized organs (comparative anatomy)

• general scheme for filtration• blood or hemolymph or coelomic fluid

collected• filtration

• composition of filtrate is changed

organs• protonephridia

• network of branching tubules• flame cell

• or solenocyte• nephridiopores• osmoregulation

Tubule

Tubules of protonephridia

Cilia

Interstitial fluid flow

Opening in body wall

Nucleus of cap cell

Flame bulb

Tubule cell

organs• metanephridia

• nephrostome• capillaries surrounding tubules• nephridiopore

nephrostomenephridiopore

bladder

organs• malpighian tubules

• connected to digestive tract• tips immersed in hemolymph• water, various solutes reabsorbed in

rectum

Rectum

Digestive tract

HindgutIntestine

Malpighiantubules

Rectum

Feces and urine

HEMOLYMPH

Reabsorption

Midgut(stomach)

Salt, water, and nitrogenous

wastes

organs• Vertebrate kidneys

• profused by renal artery and renal vein

• nephron• glomerulus

• afferent arteriole• efferent arteriole• bowman’s capsule

• proximal tubule• loop of henle• distal tubule

• two distinct regions• renal cortex and renal medulla

• cortical nephrons• juxtamedullary nephrons

Corticalnephron

Juxtamedullarynephron

Collectingduct

Torenalpelvis

Renalmedulla

Renalcortex

Posteriorvena cava

Renal arteryand vein

Urinarybladder

Ureter

Urethra

Kidney

Aorta

Renalcortex

Renalmedulla

Renalpelvis

• homeostatic control mechanisms • antidiuretic hormone - osmolarity• blood pressure

• renin - angiotensin II - aldosterone• atrial natriuretic factor -

• opposes RAAS• reduces blood pressure

Renin

Distal

tubule

Juxtaglomerular

apparatus (JGA)

STIMULUS:

Low blood volume

or blood pressure

Homeostasis:

Blood pressure,

volume

Liver

Angiotensinogen

Angiotensin I

ACEAngiotensin II

Adrenal gland

Aldosterone

Arteriole

constriction

Increased Na+

and H2O reab-

sorption in

distal tubules

PSA about next slide

Kidneys

• kidney disease -- • inflammation

• causes an increase in renin• can be genetic, viral or cancerous

or bacterial...• E. coli -- HUS -- kidneys

shut down... • Streptococcus -- strep

throat• hemodialysis • peritoneal dialysis