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- regulation in 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