• 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

Osmo-regulationin fishes

• 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

The human urinary system

Structure of the kidney

Structure of the nephron

Detailed view of Bowman’s capsule

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