Osmoregulation and Excretion

1. Osmoregulationand Excretion

2. Key Concepts • Osmoregulation balances the uptake and loss of water and solutes • An animal’s nitrogenous wastes reflect its phylogeny and habitat • Diverse excretory systems are variations on a tubular theme • Nephrons and associated blood vessels are the functional units of the mammalian kidney • The mammalian kidney’s ability to conserve water is a key terrestrial adaptation • Diverse adaptations of the vertebrate kidney have evolved in different environments

3. Key Words • ammonia • filtrate • ureter • renal cortex • glomerulus • loop of Henle • cortical nephrons • peritubular capillaries • aldosterone • osmoregulation • urea • secretion (selective reabsorption) • renal artery • urinary bladder • renal medulla • Bowman's capsule • distal tubule • afferent arteriole • vasa recta • homeostasis • excretion • uric acid • filtration • renal vein • urethra • nephron • proximal tubule • collecting duct • efferent arteriole • antidiuretic hormone (ADH)

4. Types of metabolic waste produced by living systems • Digestive waste (elimination) • Respiratory waste • Excess water and salts (osmoregulation) • Nitrogenous waste (excretion)

5. Osmoregulation • Balance of uptake and loss of water and solutes • Controlled movement of solutes between internal fluids and environment • Osmoconformer (marine animals isoosmotic with environment) • Osmoregulator(freshwater, marine, and terrestrial animals that adjust internal osmolarity)

6. Types of nitrogenous wastes • Deamination– protein and nucleic acid metabolism • Three main types differing in terms of: • Toxicity • Amount of water needed for excretion • Energy needed for synthesis 300 – 500 mL/gN 1 step rxn 50 mL/gN 4 step rxn 10 mL/gN 15 step rxn

8. Dispose of metabolic wastes Regulate solute concentrations in the body Transport epithelia arranged in tubes 4 major processes Filtration, pressure-filtering of body fluids producing a filtrate (water, salts, sugars, amino acids, N-wastes) Reabsorption, reclaiming valuable solutes (glucose, salts, amino acids) from the filtrate Secretion, addition of larger molecules like toxins and other excess solutes from the body fluids to the filtrate Excretion, the filtrate leaves the system Excretory Systems

15. From Blood Filtrate to Urine: A Closer Look

16. Two solutes: NaCl and urea, contribute to the osmolarity of the interstitial fluid • Cause the reabsorption of water in the kidney and concentrates the urine

17. Nervous system and hormones regulate kidney functions • Antidiuretic hormone (ADH) • Stimulated by a rise in the blood’s osmolarity (>300 mosm/L) • Enhances fluid retention by making the kidneys reclaim more water • Increases water reabsorption in the distal tubules and collecting ducts of the kidney

18. The renin-angiotensin-aldosterone system (RAAS) • Responds to a loss of salt and water in the blood • Stimulated by low blood volume or pressure • Increases water and sodium ion reabsorption in the proximal and distal tubules • Leads to an increase in blood volume and pressure • Opposed by the hormone atrialnatriuretic factor (ANF) • Released by atria • Inhibits release of renin

19. Some medical aspects concerning the excretory system • Urinary tract infection (UTI) • bacterial infection • cystitis/pyelonephritis • treated by antibiotics and prevented through proper hygiene • Kidney stones • solidified crystals in kidneys or ureters • Calcium oxalate • Uric acid • nephrolithiasis/urolithiasis • prevention: • Drinking adequate water • Proper diet low in protein, N, and Na • Avoid excess Vitamin C intake • Dialysis • Hemodialysis • Peritoneal dialysis