Urinary System: Summary PDF

The urinary system 1 Brief introduction The urinary system, also known as the renal system, consists of the kidneys, ureters, bladder, and urethra. Its main function is to eliminate the waste products of metabolism from the body by forming and excreting urine. Typically, bet...

The urinary system 1 Brief introduction The urinary system, also known as the renal system, consists of the kidneys, ureters, bladder, and urethra. Its main function is to eliminate the waste products of metabolism from the body by forming and excreting urine. Typically, between one and two liters of urine are produced every day in a healthy individual. 2 Brief introduction It includes organs that form, transport, store, and excrete urine 3 General structure The kidneys are large, reddish brown, bean shaped organs. Located on either side of the spinal column in the retroperitoneal space of the posterior abdominal cavity. They extend from the 12th thoracic to the 3rd lumbar vertebrae, with the right kidney positioned slightly lower. 4 General structure Each kidney approximately 10 - 12 cm long 5 - 6.5 cm width 3 - 4 cm thick On the upper pole of each kidney, the adrenal gland is embedded within the renal fascia and a thick protective layer of perirenal adipose tissue 5 The kidney The nephron is the basic structural and functional unit Produce Urine (an unfiltrate of the blood) The urine via ureters to the urinary bladder discharged via the urethra 6  General kidney Functions Maintenance of Metabolites water balance Drugs Maintenance of Toxins electrolytes Maintenance of acid-base balance Excretory Homeostatic The kidney converts 25,OH vitD3 Renin by the active vit D3 1,25 Endocrine Endocrine juxtaglomerular cells dihydroxy (hormonal (hormonal Erythropoeitin cholecalciferol by metabolic) secretory) 1a hydroxylase hormone by enzyme in cells of endothelial cells of PCT under effect peritubular capillaries of PTH of renal cortex Gluconeogenesis prostaglandins in the cortex 7 The kidney structure 8 The kidneys Are highly vascular organs Receive approximately 25% of the cardiac output The parenchyma of the kidney is made up of myriad minute uriniferous tubules (nephrons) that are its functional unit The connective tissue of the kidney parenchyma called interstitial tissue: 7% of cortex volume 20% of medulla volume 9  Urinary system The Renal capsule Is a connective covering the kidney is a tough fibrous layer covered in a thick layer of perinephric adipose tissue. It provides some protection from trauma and damage. 2 layers: a. outer layer of fibroblast and collagen fibers b. inner layer with a cellular component of myofibroblast (resisting volume and pressure variations that accompany kidney functions) 10  Urinary system The capsule passes inward at the hilum, where it forms the connective tissue covering the sinus and continuous with the connective tissue forming the walls of the calyces and renal pelvis 11  Kidney lobes and lobules The number of lobes in a kidney equals the number of the medullary pyramids Lobar organization is typical in developing fetal kidney and usually disappear after birth Surface convexity may persist after birth and in some cases into adulthood. Human kidney (multilobar):8 to 18 lobes. 12  Urinary system Medullary rays are vertical striations originate from medulla and project to the cortex Each medullary ray contains straight tubules of the nephrons and collecting tubules and collecting ducts 13 14 15  Cortex and medulla In fresh hemisected kidney the cortex is the outer reddish brown part. The medulla is the much lighter colored inner part The color seen in the cut surface of the unfixed kidney reflects the distribution of blood in the organ 90 to 95% of the blood passing through the kidney is in the cortex 16  The urineferous tubules 2 functionally distinct portions: 1- the Nephron: collects a filtrate of the blood 2- the collecting tubule: absorb water from the filtrate to concentrate its solutes. 17  The urineferous tubules There are approximately 1.5million uriniferous tubules in a human kidney 18  Urinary system 4 segments of renal tubules were recognized 19  The renal tubules - Proximal tubule - Intermediate tubule - Distal tubules - Collecting system (ducts) 20  The Cortex is charterized by : Renal corpuscles and their associated tubules Renal corpuscles along with the convoluted tubules Straight tubules of the nephron The collecting tubules The collecting ducts Extensive vascular supply Interstitial cells (connective tissues) 21 is charterized by : The medulla Straight tubules of the nephron (continue from the cortex) The collecting ducts (continue from the cortex) Special capillary network running in parallel with various tubules, the vasa recta Connective tissue (interstitial cells 22 The Cortex 23  The medulla The tubules in the medulla because of their arrangement and differences in length, and the convergence of straight portions of the tubules to the papilla form conical structures (Pyramids) 24 The Nephron 25  The Nephron The nephron consist of the renal corpuscle and a tubule system Each human kidney contains approximately 1.5 million nephrons Responsible of urine prodution and correspond to secretory part of a gland 26 Renal corpuscle The renal corpuscle is spherical and contains the filtration apparatus of the kidney Average diameter of 200 microm It consists of the glomerular capillary tuft and the surrounding visceral and parietal epithelial layers of bowman’s capsule. 27 Renal corpuscle 28 29 The Filtration apparatus of the kidney In the renal corpuscle Enclosed by the parietal layer of Bowman’s capsule Consists of 3 components: 1- Endothelium of the glomerular capillaries 2- Glomerular Basement membrane 3- Viscersl layer of Bowman’s capsule (podocyte) 30  The parietal and visceral layers of Bowman’s capsule The parietal layer forms layer of simple squamous epithelium. At the urinary pole it is continuous with the cuboidal cells of the proximal convoluted tubule (PCT) The visceral layer of Bowman’s capsule contains specialized cells called podocytes or visceral epithelial cells. These cells extend processes around the capillaries and develop numerous secondary processes called pedicels or foot processes that interdigitate forming between them filtration slits 31 32  The parietal and visceral layers of Bowman’s capsule The space between parietal and visceral layer is called urinary or Bowman’s space The space is the receptable for the ultrafiltrate The space is continuous with lumen of PCT 33 34 The 3 components of the filtration apparatus: 1- Endothelium of the glomerular capillaries 2- Glomerular Basement membrane 3- Viscersl layer of Bowman’s capsule (podocytes and pedicels...) 35 36  Filtration membranes A- Endothelium of the glomerular capillaries B- Glomerular Basement membrane C- Visceral layer of Bowman’s capsule (podocytes and pedicels...) 37 38 1- Endothelium of the glomerular capillaries Large fenestration 70 to 90 nm Possess a large number of aquaporin-1 (AQP-1) water channels that allow the fast movement of water through the epithelium. Unlike those of the other fenestrated capillaries , the pores of the glomerulus capillaries do not have a pore diaphragm 39 1- Endothelium of the glomerular capillaries Large fenestration 70 to 90 nm 40  Juxtaglomerular apparatus Includes: - The macula densa - The juxtaglomerular cells - The extraglomerular mesangial cells  Function of Juxtaglomerular apparatus The juxtaglomerular apparatus regulates blood pressure by activating the renin-angiotensin- aldosterone system Plays an important role in maintaining sodium hemeostasis and renal hemodynamics Not only as an endocrine organs secreting renin, but also as sensor of blood volume and tubular fluid composition This system is activated in certain physiological conditions: - Low sodium intake - Hemorrhage (decrease in circulating blood) - Reduction in renal perfusion Renal corpuscle 44  Function of Juxtaglomerular apparatus 1- Macula densa cells monitor the Na+ concentration in the tubular fluid and regulate both: - the glomerular filtration rate and - the release of renin from the juxtaglomerular cells. 2- Juxtaglomerular cells: The wall of the afferent arteriole contains large, vascular smooth muscle cells called juxtaglomerular cells. These cells are responsible for activating the renin-angiotensin- aldosterone system 3- Mesangium (mesangial cells) - Phagocytosis: keeping the glomerular filter free of debris - Structural support for podocytes - Secretion: synthesize and secrete IL-1 and platelet derived growth factor(PDGF) which play a central role in the response to glomerular injury  From the zona Aldosterone act on glomerulosa of the collecting tubules adrenal gland Water reabsorption raising blood volume and pressure  Kidney tubule function As the glomerular filtrate passes through the uriniferous and collecting tubules of the kidney, it undergoes changes that involve both active and passive absorption as well as secretion  Certain substances within the ultrafiltrate (primary urine) are reabsorbed : - Partially (H2O, Na+, bicarbonate) - Completely (glucose) Other substances (creatinine, organic acid and bases) are added The volume of the ultrafiltrate is reduced and the urine is made hyperosmotic (concentrating it)  Mechanisms of Urine Formation Each minute the glomerulus filtrates 120- 125ml of fluids (GFR: Glomerular filtration rate) The majority of this filtrate is reabsorbed back into blood in the renal tubules The kidneys filtrates ~ 180 L daily. – Of this,