Function of the Urinary System • Rid the body of metabolic waste, particularly those from proteins, ie urea and uric acid which contain nitrogen. • Maintain osmotic balance within the body.
Basic Terminology • Osmosis • the process in which water migrates through a semipermeable membrane from an area containing a lesser concentration of dissolved particles to an area containing a greater concentration of dissolved particles.
Basic Terminology • Hyperosmotic • Refers to a solution whose osmotic pressure is greater than that ofanother solution with which it is compared. Contains a greater concentration of dissolved particles, and gains water through a semipermeable membrane from a solution containing fewer particles.
Basic Terminology • Hyposmotic • (hypotonic) refers to a solution whose osmotic pressure is less than that of another solution with which it is compared. • Isosmotic • (isotonic) having an osmotic concentration equal to that of a solution with which it is compared.
Basic Terminology • Nephron: The basic functional and structural unit of the kidney. • Renal corpuscle. • Glomerulus • Bowman’s capsule • Proximal and Distal convoluted tubules.
Evolution of the internal glomerulus • In the hypothetical ancestral protochordate stage there is one pair of uriniferous tubules per body segment (metameric organization again). These uriniferous tubules are connected by a holonephric duct (archinephric duct) which runs the entire length of the body on both sides. These uriniferous tubules simple drain the ceolomic cavity of filtrates produced by capillary beds in the mesoderm.
Evolution of the Internal Glomerulus • Aglomerular stage • Each uriniferous tubule drains a special pocket in the ceolom, the nephrocele. • The opening of the nephrocele into the splanchnocele is the peritoneal funnel. • Extraction of metabolic wastes is again simply via drainage of the ceolomic fluids.
Evolution of the Internal Glomerulus • External glomerular stage • Found in hypothetical holonephric animals. It is found in no extant adults, only in embryos. • The circulatory system now empties filtrate via a glomerulus, directly into the nephrocele.
Evolution of the Internal Glomerulus • Primitive internal glomerular stage. • Found in some anamniotes. • Very little excretory material is picked up from the ceolom, virtually all the material is from the glomerulus. • The peritoneal funnel becomes constricted.
Evolution of the Internal Glomerulus • Advanced internal glomerular stage • Found in amniotes. • Complete separation of the renal corpuscle from the ceolom.
Evolution of Kidney Types • Unlike most other organs, kidneys must function at a very early stage in life. • For this reason, embryonic kidneys often differ from those found in adults. • The sex glands lie close to the urinary system, and tend to invade the system.
Evolution of Kidney Types • Holonephros • The idealized embryonic kidney. • Found in the larvae of hagfishes • Each metamere is drained by one pair of nephrons. • Opisthonephros • Found in adult hagfishes. • Pronephric portin of the holonephros is lost, it is functional only in the embryo, results in the opisthonephros.
Evolution of Kidney Types • Mesonephros • found in adult fishes and amphibians. • Metanephros • Found in adult amniotes • Amniote embryo still utilizes a mesonephric kidney. • Testis have invaded the holonephric duct (now called the wolfian duct). The kidney is not drained by a new duct, the ureter.
Evolution of the Tubular Capillary Network • Cyclostome condition • No capillary network surrounds the uriniferous tubule • The glomerulus is fed via a renal artery from the dorsal aorta and drained via a renal vein leading to some systemic vein. Each individual glomerulus is not fed and drained by a renal artery and vein, rather, all of them together are fed and drained by a renal artery and vein leading to and from each kidney.
Evolution of the Tubular Capillary Network • Gnathostome fishes, amphibians, and reptiles • A tubular capillary network now surrounds the convoluted tubule. • The capillary network (vasa recta) is supplied with blood from the venous renal protal vein. • An efferent renal vein drains the vasa recta. • The posterior cardinal vein drains both the glomeruli and the vasa recta of each urinifeous tubule.
Evolution of the Tubular Capillary Network • Changes in endotherms • Anastomosis of the tubular capillary network with the base of the efferent renal vein. • Transformation of the anastomosis and part of the efferent renal vein between the glomerulus and the anastomosis into a single efferent glomerular artery. • Loss of the part of the efferent renal vein between the anastomosis and the branch draining the tubular capillary network.
Evolution of the Tubular Capillary Network • Los of the afferent renal vein. • Loss of the renal protal vein (mammals only)