1. Osmoregulation and Excretion
Chapter 44

2. Osmoregulation
Osmoregulation: management of the body’s water content and solute composition
Excretion: removal of nitrogenous wastes from the body
Nitrogenous wastes: produced by the breakdown of proteins and nucleic acids; very toxic
Ammonia: most aquatic animals, many fish
Urea: mammals, most amphibians, sharks, bony fish (in liver; combo of NH3 and CO2)
Uric acid: birds, insects, many reptiles, land snails

3. Evolution of Excretory Systems
Protonephridia/ Flame-bulb system: Platyhelminthes (planaria)
Metanephridia: Annelida (earthworm)
Malpighian Tubules: Insects and terrestrial arthropods
Kidneys: Vertebrates

4. Vertebrate Excretory Systems
Mammalian excretory system involves
Urinary bladder: urine storage
Urethra: urine elimination tube
2 kidneys and each has:
Renal artery/vein: kidney blood flow
Ureter: urine excretory duct
Renal cortex (outer region)
Renal medulla (inner region)
Nephrons: functional unit of kidney
Cortical nephrons (cortex; 80%)
Juxtamedullary nephrons (medulla; 20%)

5. Nephron Structure Glomerulus: ball of capillaries
Bowman’s capsule: surrounds glomerulus
Proximal tubule: secretion & reabsorption
Loop of Henle: water & salt balance
Distal tubule: secretion & reabsorption
Collecting duct: carries filtrate to renal pelvis

6. Nephron Function
Proximal tubule: secretion and reabsorption change the volume and concentration of the filtrate
bicarbonate, NaCl, H2O, glucose, & amino acids reabsorbed out; H+ and toxins secreted in; ammonia passively diffuses into filtrate
Descending loop of Henle: reabsorption of water only
Ascending loop of Henle: filtrate loses salt without giving up water and becomes more dilute
Distal tubule: potassium and salt levels are regulated as well as pH
Collecting ducts: carries the filtrate through the medulla to the renal pelvis, and the filtrate becomes more concentrated by the movement of water out

7. Hormone Involved in Water Regulation
Antidiuretic Hormone (ADH): produced in the brain (hypothalamus) and stored and released from the pituitary gland in the brain; makes the collecting ducts more permeable to water so more water is reabsorbed producing concentrated urine