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! 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 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 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 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 Key Points Define countercurrent. Look at the following picture and explain how countercurrent is advantageous. Kidney - Nephron Peritubular capillaries pick up substances being reabsorbed from renal tubules Common collecting tubule collects urine from all renal tubules Kidney Longitudinal kidney duct – Carries urine to cloaca in all but placental mammals – Various names for this duct depending on group 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 Pronephros is the functional embyronic kidney in anamniotes 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 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 Mammalian Vasa Efferentia & Persistent Mesonephric Duct Kidney Types Metanephros Caudal-most intermediate mesoderm Becomes the adult amniote kidney Kidney Types Metanephros – adult amniote kidney Cortex –outer region Medulla – inner region – Pyramids – Papillae Pelvis – slit-like funnel collecting urine from medulla Kidney Types Metanephros – adult amniote kidney Ureter = Metanephric duct Carries urine caudally 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 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 Urinary Bladder The urinary bladder is formed from the embryonic membrane called the allantois The remnant of the allantois is called the urachus which becomes an umbilical ligament Urinary Bladder In mammals, the urinary bladder is drained by the URETHRA Urinary Bladder Functions: – Water reservoir except placental mammals – Under ADH control – Holding tank in placental mammales – Pheromones – Marking territory 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?
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