Osmoregulation and Excretion

1. Osmoregulation and Excretion Darian Hands Lisa Fan Victoria Donelan TJ Kellogg

2. Osmoregulation Osmoregulation is how animals regulate solute concentrations and balance the gain and loss of water Excretion is how animals get rid of the nitrogen-containing waste products of metabolism • The dilemma: Rates of water uptake and loss must balance Or else cells… • Burst • shrivel

3. Two Basic Solutions • Osmoconformer • An animal that does not actively adjust its internal osmolarity because its internal osmolarity is the same as that of its environment • Only for marine animals • Osmoregulator • An animal that must control its internal osmolarity because its body fluids are not isoosmotic with the outside environment • Must discharge excess water

4. Osmotic Challenges • Stenohaline • Can’t tolerate substantial change in external osmolarity • Euryhaline • Can survive large fluctuations in external osmolarity

5. Marine Animals (Saltwater) the ocean is much saltier than internal fluids, and water tends to be lost from their body by osmosis Bony fishes are hypoosmotic to seawater and constantly lose water by osmosis and gain salt both by diffusion and from food They balance the water loss by drinking large amounts of seawater Their gills and skin dispose of sodium chloride passively and the kidneys dispose of excess calcium, magnesium, and sulfate ions

6. Sharks Are different. Instead of losing a lot of water, they maintain high concentrations of nitrogenous waste urea and have trimethylamine oxide (TMAO) to protect proteins from damage

7. Marine Animals (Freshwater) They have the opposite problem They constantly gain water by osmosis because the osmolarity of their internal fluids is much higher than that of the surrounding water They excrete large amounts of very dilute urine

8. Anhydroboisis The ability to survive in a dormant state when an organism′s habitat dries up Animals that live in temporary waters

9. Land Animals • Adaptations to reduce water loss: • Waxy cuticles • Layers of dead skin • Lose water from moist surface of gas exchange organs, in urine and feces, and across the skin • Can withstand a certain level of dehydration

10. Transport Epithelia Layer(s) of specialized epithelial cells that regulate solute movement Are essential in osmotic regulation and metabolic waste disposal Move specific solutes in controlled amounts in specific directions Arranged in complex tubular networks with extensive surface area

11. An animal’s nitrogenous waste reflects its phylogeny and habitat When macromolecules are broken apart for energy, enzymes remove nitrogen in the form of ammonia (NH3) Ammonia is very toxic and very soluble Many species first convert it to another compound

12. Urea A soluble nitrogenous waste excreted by mammals, most adult amphibians, sharks, and some marine bony fishes and turtles produced in the liver by a metabolic cycle that combines ammonia with carbon dioxide Low toxcitiy Permits animals to transport and store safely Animals must expend energy to produce it from ammonia

13. Uric Acid An insoluble precipitate of nitrogenous waste excreted by land snails, insects, and many reptiles, including birds Relatively nontoxic Insoluble in water Little water loss More energetically (ATP) expensive than urea

14. Influence of Evolution and Environment on Nitrogenous Wastes • Type of nitrogenous waste depends on animal’s evolutionary history and habitat-availability of water • Aquatic, urea • Shelled eggs, uric acid The amount of nitrogenous waste produced is coupled to the animal’s energy budget and amount of dietary protein Endotherms eat more food, produce more nitrogenous waste

15. Excretory Processes • Although the problems of water balance on land or in salt water are very different, the solutions all depend on the regulation of solute movements between internal fluids and the external environment. • Much of this is handled by excretory systems.

16. Protonephridum • Flatworms have an excretory system called protonephridia, consisting of a branching network of dead-end tubules. • They are capped by a flame bulb which draws water and solutes from the interstitial fluid, through the flame bulb, and into the tubule system. • The urine in the tubules exits through openings called nephridiopores. • In these freshwater flatworms, the major function of the flame-bulb system is osmoregulation, while most metabolic wastes diffuse across the body surface or are excreted into the gastrovascular cavity. • However, in some parasitic flatworms, protonephridia do dispose of nitrogenous wastes.

17. Earthworm As urine moves along the tubule, the transport epithelium bordering the lumen reabsorbs most solutes and returns them to the blood in the capillaries. Nitrogenous wastes remain in the tubule and are dumped outside. Metanephridia

18. Excretory Processes • Most excretory systems produce urine by refining a filtrate derived from body fluids • Key functions of most excretory systems: • Filtration: pressure-filtering of body fluids • Reabsorption: reclaiming valuable solutes • Secretion: adding toxins and other solutes from the body fluids to the filtrate • Excretion: removing the filtrate from the system

19. Filtration • The Excretory tubule collects a filtrate from the blood. • Large molecules are left in the filtrate • Water and solutes are then forced by blood pressure into the excretory system .

20. Selective Reabsorption • Essential Small molecules are recovered from the filtrate and returned to the body fluids. • Active Transport is used to reabsorb valuable solutes (glucose, salts, amino acids) • Nonessential solutes and wastes are left in the filtrate or added by secretion.

21. Kidneys • The Excretory System of mammals, is centered around the kidneys. • Each kidney has a renal artery and a renal vein. About 20% of the blood pumped by each heartbeat passes through the kidneys. • Urine exits each kidney through a ureter and both ureters drain into a common urinary bladder. • During urination, urine is expelled through from the urinary bladder. • Sphincter muscles near the junction of the urethra and bladder control urination

22. Kidney’s Continued • The two distinct regions of the kidney are the outer renal cortex and inner renal medulla. • Nephron, the functional unit of the kidney, consist of a single long tubule and its associated capillaries called gomerulus. • The blind end of the renal tubule that receives filtrate from the blood forms a cup shaped called the Bowman's capsule, which surrounds a the glomerulus's.

23. Filtration of the Blood • Blood pressure forces fluid from the glomerulus into the lumen of the Bowman's capsule. • Filtration of small molecules is nonselective • The filtrate in Bowman’s capsule mirrors the concentration of solutes in blood plasma

24. Pathway of the Filtrate • Filtrate then passes through the three regions of the nephron: the proximal tubule, the loop of Henle (a long hairpin turn with a descending limb and an ascending limb) and the distal tubule, which empties into a collecting duct. The collecting duct receives filtrate from many nephrons • Filtrate flows from the collecting ducts into the renal pelvis. The filtrate then drains from renal pelvis into the ureter. • The nephron and collecting duct are lined by transport epithelium that processes the filtrate into urine.

26. Blood Vessels Associated with the Nephrons • Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that divides into the capillaries • The capillaries converge as they leave the glomerulus, forming an efferent arteriole • The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules

27. From Blood Filtrate to Urine: A Closer Look • Filtrate becomes urine as it flows through the mammalian nephron and collecting duct • Secretion and reabsorption in the proximal tubule greatly alter the filtrate’s volume and composition • Reabsorption of water continues as filtrate moves into the descending limb of the loop of Henle

28. In the ascending limb of the loop of Henle, salt diffuses from the permeable tubule into the interstitial fluid • The distal tubule regulates the K+ and NaCl concentrations of body fluids • The collecting duct carries filtrate through the medulla to the renal pelvis and reabsorbs NaCl

33. Solute Gradients and Water Conservation • Osmotic gradient - Concentrates urine - Formed by the arrangement of the loops of the Henle and its collecting ducts and maintained by active transport - Primary solutes: NaCl and urea -Enables kidney to produce urine hyperosmotic to the blood • Countercurrent Multiplier System -Maintains high salt concentration in kidney

34. Regulation of Kidney Function Osmolarity of the urine is regulated by nervous system and hormonal control of water and salt reabsorption. • Antidiuretic hormone (ADH) -Produced in hypothalamus, stored in pituitary gland -Main targets: distal tubes and collecting ducts -If above set point: ADH released→increases permeability of epithelium to water→increases water absorption→lowers urine volume→helps prevent further increase of blood osmolarity

35. Regulation of Kidney Function • Renin-angiotensin-aldosterone system (RAAS) - Functions in homeostasis - Drop in blood pressure and blood volume triggers renin release from the justaglomerular appartus (JGA) -Rise in blood pressure and volume resulting from stimulation of NaCl and water absorption by angiotensin II and aldosterone - Responds to situations of reduced blood volume without increase of osmolarity (injury, severe diarrhea) - Opposed by the atrial natiutretic factor

36. Diversity and Adaptation Form and function of nephrons in different vertebrates have adapted for osmoregulation in different environments. Variations: • Length of Henle loops (long vs. short) • Concentration of urine (isoosmotic vs. hyperosmotic) • Removal of nitrogen as uric acid • Amount of urine • Slower filtration rates