The Urinary SystemFunction of the Kidneys

KidneysUreters (urinary tract)Urinary BladderUrethraUrinary System

Kidneys- Major FunctionsExcretion (removal of organic waste products from body fluids)Elimination (discharge of waste products into the environment via urination or defecation )Homeostatic regulation (regulation of blood plasma volume and solute concentration of blood plasma)

Waste Products & Foreign SubstancesAmmonia/urea from amino acid deaminationBilirubin from Hb catabolismCreatinine from breakdown of creatine phosphate in muscle fibresUric acid from nucleic acid catabolismForeign Substances (drugs, environmental toxins)

Other FunctionsRegulation of blood volume & BPRegulation of Na+, K+, Cl-, Ca2+ & other ionsRegulation of blood pHRegulation of blood glucose levelConserve nutrientsProduce hormones (calcitriol, erythropoietin)Assist liver in detoxification process

Structure of the Kidney

Nephron functional unit of the kidney

Types of Nephron2 types:Cortical nephrons (80-85%)- within cortex of kidney- short loop of Henle- efferent arterioles delivers blood to peritubular capillaries which surrounds entire renal tubule

Types of NephronJuxtamedullary nephrons (15-20%)- long loops of Henle extending deep into the medulla- peritubular capillaries connected to vasa recta (long straight capillaries parallel to loop of Henle)

Types of nephron

Parts of Nephron

Renal Corpuscle Production of filtrate Proximal Convoluted Tubule (PCT) Reabsorption of H2O, ions & organic nutrients. Secretion of H+, NH4+, creatinine, drugs, toxins Loop of Henle Further reabsorption of H2O (descending limb) & Na+, Cl- ions (ascending limb)

Parts of Nephron

Distal Convoluted Tubule (DCT) Secretion of ions, acids, drugs & toxins. Variable reabsorption of H2O, Na+, Cl- ions. Collecting Duct Variable reabsorption of H2O & reabsorption/ secretion of Na+, K+ , H+ , HCO3- ions. Papillary duct Delivery of urine to minor calyx

Juxtaglomerular Apparatus nuclei of epithelial cells of DCT form region known as macula densa cells of macula densa closely associated/ in contact with wall of afferent arteriole known as juxtaglomerular cells hence forming juxtaglomerular apparatus (JGA) JGA is an endocrine structure secreting erythropoietin and the enzyme renin

The Collecting SystemDetermines final osmotic concentration & volume of urineLike DCT, also regulated by anti-diuretic hormone (ADH) which enhances reabsorption of waterUnder aldosterone stimulation (also like DCT) which will enhance H2O & Na+ conservation