Urinary System- Kidney

1. Urinary System- Kidney • Overall function • Osmoregulation (water, salt) • Nitrogenous waste in tetrapods • Ammonia in amphibians • Urea in mammals • Uric acid in birds and reptiles • Note: uric acid in birds is 3000x more concentrated than blood!

2. Kidney - Nephron • The functional unit of the kidney • Filters blood to make urine • Glomerulus is a network of permeable blood capillaries • Afferent glomerular arteriole • Efferent glomerular arteriole

5. Kidney - Nephron • Bowman’s capsule is a cup-shaped capsule around the glomerulus to catch filtrate • Renal corpuscle – Glomerulus plus the Bowman’s capsule since they function as a unit

6. Kidney - Nephron • Renal Tubules • Increase in complexity with higher vertebrates • Function to secrete substances directly from blood to tubule • Function for reabsorption from tubules back to bloodstream based on need

8. Kidney - Nephron • ADH = Antidiuretic hormone promotes water reabsorption from renal tubules • Aldosterone – hormone that promotes sodium reabsorption from renal tubules and water passively follows • Renal tubules are countercurrent for maximum efficiency

9. Key Points • Define countercurrent. • Look at the following picture and explain how countercurrent is advantageous.

11. Kidney - Nephron • Peritubular capillaries pick up substances being reabsorbed from renal tubules • Common collecting tubule collects urine from all renal tubules

13. Kidney • Longitudinal kidney duct • Carries urine to cloaca in all but placental mammals • Various names for this duct depending on group

14. Kidney Types based on Embryology • Pronephros • Forms from intermediate mesoderm (mesomere) very far cranially • Renal tubules are temporary pronephric tubules • Pronephric duct carries urine to cloaca • Pronephric duct persists in anamniotes but changes its name to Mesonephric duct

16. Pronephros is the functional embyronic kidney in anamniotes

19. Kidney Types • Mesonephros • Middle region of intermediate mesoderm • Longitudinal duct is Mesonephric duct (we called it archinephric duct in lab) • Functional embryonic kidney in amniotes • Adult kidney of anamniotes

22. Kidney Types • Mesonephros • Mesonephric tubules invade testes and form the Vasa efferentia which carry sperm from testicle to mesonephric duct • Mesonephric duct carries sperm & urine in anamniotes • Mesonephric duct in amniotes will only carry sperm & is called the Spermatic Duct or Vas Deferens

24. Mammalian Vasa Efferentia & Persistent Mesonephric Duct

25. Kidney Types • Metanephros • Caudal-most intermediate mesoderm • Becomes the adult amniote kidney

28. Kidney Types • Metanephros – adult amniote kidney • Cortex –outer region • Medulla – inner region • Pyramids • Papillae • Pelvis – slit-like funnel collecting urine from medulla

31. Kidney Types • Metanephros – adult amniote kidney • Ureter = Metanephric duct • Carries urine caudally

33. Urinary bladder • Cyclostomes & Elasmobranchs have none • Most fish have a widening of the mesonephric ducts that form the urinary bladder • Dipnoans have a bladder that is an outpocketing of the cloaca

35. Urinary Bladder • Tetrapods have a urinary bladder that is an outpocketing of the cloaca • The urinary bladder then empties into the cloaca in all except placental mammals

37. Urinary Bladder • The urinary bladder is formed from the embryonic membrane called the allantois (cloacal derivative) in placental mammals • The remnant of the allantois is called the urachus which becomes an umbilical ligament

39. Urinary Bladder • In mammals, the urinary bladder is drained by the URETHRA

42. Urinary Bladder • Functions: • Water reservoir except placental mammals • Under ADH control • Holding tank in placental mammals • Pheromones • Marking territory

43. Key Points • What are two roots that both mean kidney? • Can you live without one kidney? Can you live without two? Why or why not?