Chapter 44

1. Chapter 44 Osmoregulation and Excretion

2. Osmosis • Over time the rates of water uptake and loss must balance. • Osmosis- movement of water across a selectively permeable membrane • Osmolarity- total solute concentration expressed as molarity (unit of measurement- mosm/L) • -If 2 solutions separated by a selectively permeable membrane have the same osmolarity, they are isoosmotic. When 2 solutions have different osmolarities, they are hypoosmotic.

3. Osmotic challenges • Osmoconformer- an animal that does not actively adjust its internal osmolarity and often lives in water with a very stable composition • Osmoregulator- an animal that must control its internal osmolarity because its body fluids are not isoosmotic with the outside environment • Stenohaline- cannot tolerate substantial changes in external osmolarity • Euryhaline- can survive large fluctuations in external osmolarity

4. Marine Land • Most invertebrates are osmoconformers. The fishes that are hypoosmotic balance water loss by drinking large amounts of seawater. Their gills dispose of the salt • In sharks most of the salt is excreted by the rectal gland. • -Body coverings help prevent dehydration (skin and fur) • -Gain the water they need by drinking and eating moist foods

5. Freshwater Temporary Water • Animals that live in freshwater constantly gain water by osmosis and loose salt through diffusion • Anhydrobiosis- some aquatic invertebrates living in temporary ponds and films of water can lose almost all their body water • Can survive in a dormant state when their habitats dry up. • Contain large amounts of sugar (trehalose) which replace the missing water

6. Transport epithelia • The ultimate function of osmoregulation is to maintain the composition of cellular cytoplasm • Transport epithelia- layers of specialized epithelial cells that regulate solute movements • In most animals one or more layers of transport epitheliaare essential to osmotic regulation and metabolic waste disposal

7. Forms of nitrogenous wastes

8. Excretory processes 1. body fluid is collected- involves filtration through selectively permeable membranes 2. selective reabsorption- excretory systems use active transport to reabsorb valuable solutes from the filtrate 3. selective secretion- nonessential solutes and wastes are added to it 4. the processed filtrate is then excreted by the system and from the body as urine

9. Excretory systems • Protonehrodium-network of dead end tubes lacking internal openings- flatworms The smallest branches are capped by a flame bulb- tuft of cilia projecting into the tubule. It draws water and solutes from the interstitial fluid into the tubule and then moves urine outward through the nephridiopores • Metaphridia-has internal openings that collect body fluids-earthworms  The internal opening of a metaphridium is surrounded by the nephrostome. Fluid enters it and passes through a coiled collecting tubule • Malpighian tubules- remove nitrogenous wastes and also function in osmoregulation- insects

10. Continued • Tubules open into the digestive tract and end at tips that are immersed in hemolymph and secrete certain solutes from the hemolymph into the lumen of the tubule. • Vertebrate kidneys: kidneys are built of tubules

11. Kidneys • Each of the 2 kidneys is supplied by a renal artery and drained by a renal vein • urine exits each kidney through the ureter and they both drain into the urinary bladder • Urine is expelled through the urethra

12. Structure and function of the nephron and associated structures • Each kidney has an outer renal cortex and an inner medulla • Nephron-functional unit of the kidney- consists of one long tubule and a ball of capillaries called the glomerulus • The blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule, which surrounds the glomerulus

13. Pathway of the filtrate • Filtrate passes through the proximal tubule, the loop of Henle (a hairpin turn), and the distal tube. The distal tube empties into a collecting duct, which receives processed filtrate and flows into the renal pelvis, which is drained by the ureter. • 80% cortical nephrons (reduced loops) • 20% juxtamedullarynephrons(well-developed Henle loops)

14. Blood vessels associated with the nephrons • Each nephron is supplied with blood by an afferent arteriole- a branch of the renal artery that is subdivided into the capillaries of the glomerulus • The capillaries converge as they leave the glomerulus, forming an efferent arteriole and it subdivides again forming the peritubular capillaries which surround the proximal and distal tubules. • More capillaries extend downward and form the vasa recta, the capillaries that form the loop of the Henle.

15. From blood filtrate to urine • Proximal tubule- secretion and reabsorption in the proximal tubule substantially alter the volume and composition of the filtrate. One of the main functions is the reabsorption of NaCl and water from the huge initial filtrate volume • Descending limb of the loop of Henle- the transport epithelium is freely permeable to water but no to salt and other small solutes. The osmolarity of the interstitial fluid becomes greater • Ascending limb of the loop of Henle: the transport epithelium of the ascending limb is permeable to salt but not water. 2 regions- a thin segment near the loop tip and a thick segment adjacent to the distal tubule. Salt diffuses out

16. Continued • Distal tubule- regulates the K and NaCl concentration of body fluids. Contributes to pH regulation too. • Collecting duct- carries the filtrate from the medulla into the renal pelvis. Actively reabsorbs NaCl. Permeable to water but not to salt • The filtrate becomes more concentrated as it loses water.

17. Solute gradients and water conservation • As the filtrate flows from cortex to medulla in the descending limb of the loop of Henle, water leaves the tubule by osmosis. The osmolarity of the filtrate increases as solutes become more concentrated. • Countercurrent multiplier systems-expend energy to create concentration gradients. Maintains a high salt concentration in the interior of the kidney, enabling the kidney to form concentrated urine. Consumes considerable ATP • The kidney has one of the highest metabolic rates of any organ

18. Regulation of kidney function • Kidneys can adjust to the volume and osmolarity of urine • Antidiuretic hormone (ADH)- important in regulating water balance. Produced in the hypothalamus of the brain and is stored in the posterior pituitary gland • Juxtaglomerular apparatus (JGA)- located near the afferent arteriole that supplies blood to the glomerulus. When blood pressure drops, the enzyme renininitiates chemical reactions that convert a plasma protein called angiotensinogen to a peptide called angiotensin II (raises blood pressure and stimulates the adrenal gland to release aldosterone which makes nephrons reabsorb more sodium and water and increased blood pressure).

19. Continued • The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis. • Atrialnatriuretic factor (ANF)- opposes RAAS but still regulates blood pressure and blood volume • Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in their various habitats.

20. The end!