Lecture 7. Excretion and Osmoregulation

• maintenance of the volume and composition of extracellular fluid

• removes metabolic wastes from the bloodstream

Osmoregulation

• maintenance of proper internal salt and water concentrations in a cell or in the body of a living organism

• active regulation of internal osmotic pressure

Fig. 30.2

Fig. 30.3

• anhydrobiosis, dormant state when habitats dry up– tardigrades or water bears

Animal Nitrogenous

Wastes

Excretory Organelle

Contractile vacuole• Tiny, spherical, intracellular vacuole found in

protozoa• Expels excess water gained by osmosis

Excretory Organelle

Contractile vacuole

Protonephridia• branching network of

dead-end tubules• found in flatworms,

rotifers, some annelids, larval mollusks, and lancelets

• closed system

Excretory Organs

Metanephridia

Excretory Organs

• Found in annelids, molluscs, and other phyla• Made of tubules that are open at both ends• Surrounded by a network of blood vessels that

assists in reclamation of water and valuable materials such as salts, sugars and amino acids

Metanephridia

Excretory Organs

Excretory Organs

Antennal gland• Found in crustaceans

Malpighian tubules

Excretory Organs

• Found in insects

Kidneys

Excretory Organs

Fig. 30.9a

Fig. 30.9b

Nephron• Basic functional

unit of the excretory organ in vertebrates

Physiological Processes in the Formation of Urine

Regulation of Excretion

juxtaglomerular apparatus (JGA)

renin-angiotensin-aldosterone system (RAAS)

Low homeostatis

(blood protein) (from liver)

Antidiuretic hormone(promotes water conservation in liver)

• atrial natriuretic factor (ANF), hormone that opposes the RAAS– released by the walls of the atria in response to an

increase in blood volume and pressure– inhibits the release of renin from the JGA– inhibits NaCl reabsorption by the collecting ducts– reduces aldosterone release from the adrenal

glands– these actions lower blood pressure and volume