Chapter 46

Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 46

Osmoregulation and Osmoregulation and Disposal of Metabolic Disposal of Metabolic

WastesWastes


Biology, Seventh Edition CHAPTER 46 Osmoregulation and Disposal of Metabolic Wastes

• Osmoregulation• The active regulation of osmotic

pressure of body fluids so that homeostasis is maintained

• Excretory systems• Help maintain homeostasis by

regulating the concentration of body fluids



• Principal waste products of animal metabolism• Water• Carbon dioxide• Nitrogenous wastes

–Ammonia (excreted mainly by aquatic animals)

–Urea–Uric acid



• Osmoconformers• Includes most marine invertebrates• Salt concentration of their body

fluids varies with changes in the seawater



• Osmoregulators• Marine invertebrates that inhabit

coastal habitats• Maintain an optimal salt

concentration despite changes in the salinity of their surroundings



• Nephridial organs• Include protonephridia and

metanephridia• Function in osmoregulation and

waste disposal



• Protonephridia• Found in flatworms and

nemerteans• Tubules with no internal openings• Interstitial fluid enters their blind

ends, which consist of flame cells• Beating of the cilia propels fluid

through the cilia



Protonephridia of a flatworm



• Metanephridia• Found in annelids and mollusks• Tubules open at both ends• As fluid from the coelom moves

through the tubule, materials are reabsorbed by capillaries

• Urine exits the body through nephridiopores



Metanephridia of an earthworm



• Malpighian tubules• Extensions of the insect gut wall• Have blind ends that lie in the

hemocoel• Cells of the tubule actively

transport uric acid, etc., into the tubule

• Water follows by diffusion



• Malpighian tubules, cont.• Contents of the tubule pass into the

gut and water and some other solutes are reabsorbed in the rectum

• Malpighian tubules effectively conserve water



Malpighian tubules of an insect



• Freshwater fishes• Take in water osmotically• Excrete a large volume of dilute urine

• Marine bony fishes• Lose water osmotically• Compensate by drinking seawater

and excreting salt through gills• Produce a small volume of urine



• Sharks and other marine cartilaginous fishes• Retain large amounts of urea• Take in water osmotically through

the gills• Excrete a large volume of urine



Osmo-regulationin fishes



• Marine mammals• Ingest seawater with their food• Produce a concentrated urine



• Terrestrial vertebrates• Must conserve water• Endotherms have high metabolic

rate• Produce a large volume of

nitrogenous wastes• Conserve water through efficient

kidneys and other adaptations



Excretory organs in terrestrial vertebrates



• Vertebrate kidney• Functions in excretion and

osmoregulation• Is vital in maintaining homeostasis• Its structure and function are

adapted to the lifestyle of the animal



• Organs of the mammalian urinary system• Kidney

–Key organ of the urinary system, the principal excretory system in humans and other vertebrates

–In mammals, the kidney produces urine



• Organs of the mammalian urinary system, cont.• Urine passes through the ureters to

the urinary bladder• During urination, the urine is

released through the urethra



The human urinary system



• Structure of the kidney• Outer portion is the renal cortex

• Inner portion is the renal medulla–Contains eight to ten renal pyramids–Tip of each pyramid is a renal papilla–Urine flows into collecting ducts, which

empty through a renal papilla into the renal pelvis

• Functioning unit is a nephron



Structure of the kidney



Structure of the nephron



Detailed view of Bowman’s capsule



• Urine formation is accomplished by the• Filtration of plasma• Reabsorption of needed materials• Secretion of substances such as

potassium and hydrogen ions into the renal tubule



General regions of filtration, reabsorption, and secretion



Filtration membrane of the kidney



Movement of water, ions, and urea through the renal tubule and collecting duct



Concentration of the filtrate as it moves through the nephron



• Urine volume is regulated by ADH• Released by the pituitary gland in

response to an increase in osmotic concentration of the blood

• ADH increases the permeability of the collecting ducts to water

• As a result, more water is reabsorbed



Regulation of urine volume by ADH



• Aldosterone andatrial natriuretic peptide work antagonistically• When blood pressure decreases,

cells of the juxtaglomerular apparatus secrete renin, which leads to production of angiotensin II

• Angiotensin II stimulates aldosterone release, which raises blood pressure



• When blood pressure increases• Atrial natriuretic peptide (ANP)

increases sodium excretion• Inhibits aldosterone secretion• These actions increase urine

output and lower blood pressure



Hormonal control of kidney function

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Chapter 46