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Urinary system


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Urinary system

  1. 1. State University of Medicine and Pharmacy “Nicolae Testemitanu” Urinary System Department of Histology, Cytology and Embryology Tatiana Globa
  2. 2. Urinary System Functions Clear the blood of nitrogenous and other waste metabolic products (urea, uric acid, toxic stuff, drugs) by filtration and excretion Regulation of – blood volume – concentration of blood solutes – pH of extracellular fluid Endocrine function: synthesis of erythropoietin, renin, prostaglandins Makes calcitrol (from Vit D3: stim Ca2+ absorption by intestinal epithelium) Recovers by reabsorbtion small molecules (amino acids, glucose, and peptides), ions (Na, Cl, Ca, PO), and water, in order to maintain blood homeostasis. Assists liver in detoxification of poisons
  3. 3. Urinary SystemConsists: Kidneys Ureters Urinary bladder (storage) Urethra
  4. 4. Kidneys Kidney are paired, bean-shaped organs, enveloped by a thin capsule of connective tissue Renal hilum is the concavity on the medial border of the kidney where there are: – Renal artery, vein; nerves, lymphatic vessels and ureter Sizes:10 cm X 5.5 cm X 3 cm Each kidney is divided into an outer cortex and an inner medulla Each kidney contains about 2 million nephrons – morpho-functional units
  5. 5. Kidney consists of Cortex, which is divided into inner and outer regions. – Renal corpuscles and convoluted tubules Medulla, which is formed by conical masses, the medullary pyramids, with their bases located at the cortico-medullary border. – 10-18 renal pyramids – Each renal pyramid opens into the renal papilla – A medullary pyramids, together with the associated covering cortical region, constitutes a renal lobe Minor calyx Major calyx Renal pelvis (connected to ureter)
  6. 6. Medulla Medulla divided into pyramids Tip of pyramid like top of salt shaker
  7. 7. Medullapyramid …. …. …. Minor calyx urine
  8. 8. Parts of the Kidney Within the kidney, utilize the diagram on the right to identify the capsule, cortex, renal corpuscles, and medulla, which has no renalcorpuscles. The slide on the left is a representative section from this part of the kidney.cortex medullaSlide B93 Monkey Kidney H&E X20
  9. 9. Parts of the KidneyOn the left, locate an area in the cortex where tubules run parallel to oneanother and are cut longitudinally. This is a pars radiata or medullaryray. On either side is a pars convoluta, which contains renal corpuscles and coiled tubules. cortex M ed ull ar yR ayPars Convoluta medulla B93 Monkey Kidney H&E X20
  10. 10. Kidney: Cortex versus Medulla With the same image, note the medullary rays are composed ofcollecting tubules. On either side is a pars convoluta, which contains renal corpuscles and coiled tubules. Pars Rad M cortex ed ul la Pars Convoluta ry ata i R ay Pars Convoluta medulla
  11. 11. Kidney Blood Supply The main function of the kidney is to filter the blood The kidneys receive 20-25% of the total cardiac output per minute and filter about 1.25 L of blood per minute. All the blood of the body passes through the kidneys every 5 minutes About 90% of the cardiac output goes to the renal cortex; 10% of the blood goes to the medulla Approximately 125 ml of filtrate are produced per minute, but 124 ml of this amount are reabsorbed About 180 L of fluid ultrafiltrate are produced in 24 hours and transported through the uriniferous tubules. Of this amount, 178.5 L are recovered by the tubular cells and returned to the blood circulation, whereas only 1.5 L are excreted as URINE
  12. 12. Kidney Blood Supply Renal artery – Branches until afferent arterioles to nephrons – GLOMERULI capillaries – Efferent arterioles – Secondary capillary network, surrounding the cortical segments of the superficial uriniferous tubules Venules    renal vein
  13. 13. Nephron- morphofunctional unitConsists of 2 components:1. Renal corpuscle – Bowman’s capsule and glomerulus1.Renal tubule Proximal thick segment Proximal straight tubule – Proximal convoluted tubule and proximal straight tubule Thin segment Distal straight tubule – descending and ascending limbs of loop of Henle Distal thick segment – Distal convoluted tubule and distal straight tubule
  14. 14. Glomerulus
  15. 15. Types of NephronsDepending on the distribution nephrons can be: Cortical (85%) – Is located in the outer region of the cortex – Its loop of Henle is short and does not enter the medulla – Most of reabsorption and secretion Juxtamedullary (15%) – Is located in the cortex region adjacent to the medulla – Its loop of Henle is longer and extends deep into the medulla – Create conditions for making concentrated urine
  16. 16. Terms Blood filtration and formation of the primary urine: Cause: high pressure in glomeruli, glomeruli caps more permeable than others in body Reabsorption Formation of the Secretion secondary urine Peritubular caps/vasa recta
  17. 17. Renal Corpuscle - site of filtrationConsists of :1) Glomerulus2) Bowman’s capsule Glomerulus – tufts of fenestrated capillaries; fed by afferent arteriole and drains to efferent arteriole Mesangial cells – Support capillaries – Phagosytose – Contraction and regulation of blood flow – Secretion of amorphous extracellular matrix Bowman’s capsule – double-walled (visceral and parietal) epithelial capsule – Visceral layer: is attached to the capillary glomerulus, is lined by podocytes – modified simple squamous epithelium; – Parietal layer: is lined by simple squamous epithelium – Bowman space (containing primary urine) – Vascular pole: site of afferent (incoming) and efferent (outgoing) arterioles supplying glomerulus – Urinary pole: leads to proximal convoluted tubule; route of filtrate
  18. 18. Renal Corpuscle Bowman’s Capsule
  19. 19. Kidney: Renal CorpuscleNote the schematic of the renal corpuscle (glomerulus) on theright and how it is suspended in the urinary (Bowman’s) space.The afferent and efferent arterioles enter and leave theglomerulus at the vascular pole. DCTSlide B92 Human Kidney PAS X200
  20. 20. Renal filtration barrier Capillaryfenestrated endothelium Basement Membrane – Much thicker than typical basement membrane  Lamina rara externa – an electron-lucent zone  Lamina densa – an electron dense intermediate zone  Lamina rara interna – an electron-lucent zone Bowman’s Capsule Visceral Epithelium – Podocytes – have long and branching cell processes that completely encicle the surface of the glomerular capillary. The endings of the cell processes, the pedicels, from the same podocyte or adjacent podocytes, interdigitate to cover the basal lamina and are separated by gaps, the filtration slits (are bridged by a membranous material, the filtration slit diaphragm).
  21. 21. Capillary Endothelium Basement MembranePodocytes Podocyte
  22. 22. Composition of the primary urine Water Ions (K, Ca, Mg, bicarbonate, phosphate, sulfate ions) Glucose Small-weight proteins (less than 69,000 Daltons Amino acids Urea
  23. 23. Renal tubule – site of selective re-absorption / secretion of solutes Proximal convoluted tubule Functions:  receives filtrate from urinary space  site of selective re-absorption of most solutes – all glucose and amino acids  60 - 80% of NaCl (active) and water (passive)  proteins absorbed by pinocytosis followed by lysosomal degradation and release of amino acids  re-absorbed materials released to peritubular capillary network  site of pH balance  site of creatinine secretion
  24. 24. Proximal Convoluted TubuleSTRUCTURE tubules formed by simple cuboidal / columnar epithelia apical surface covered with microvilli creating LM brush border – increase surface area for ion absorption cells tightly bound to one another to seal off intercellular space from lumen – tight junctions and zonula adherens apically; interdigitating plicae (folds) laterally interdigitating basal processes contain numerous mitochondria; creates LM basal striations; associated with ion transportHistological appearance most abundant tubule in cortex eosinophilic cytoplasm with basal nucleus (polarized) – brush border rarely preserved producing occluded lumen – Indistinct cell margins due to basal and lateral border interdigitations
  25. 25. Proximal Straight Tubule locatedwithin or near medulla, depending upon type of nephron lower cuboidal epithelium – microvilli and basal and lateral interdigitations simplified
  26. 26. Loop of Henle: Thin SegmentDescending thin tubule located within medulla low cuboidal to squamous epithelium microvilli and basal and lateral interdigitations poorly developed creating leaky cell site of passive transport of ions (inward) and water (outward) between lumen and interstitiumAscending thin tubules located within medulla similar in appearance to descending thin tubules water impermeable; passive transport of NaCl into interstitium
  27. 27. Distal Convoluted & Straight TubulesDistal straight tubule located within medulla and cortex simple cuboidal epithelium with sparse microvilli and lacking lateral interdigitations – apical nucleus – basal interdigitations present with abundant mitochondria function: water impermeable; site of ion transport from lumen to interstitum which establishes ion gradient of medullaDistal convoluted tubule located within cortex approximately 1/3 as long as proximal contacts renal corpuscle at macula densa to form juxtaglomerular apparatus (below) morphology similar to straight portion function: ion exchange
  28. 28. Kidney: Convoluted Tubules Within the pars convoluta, identify proximal convoluted tubules (PCT) and distal convoluted tubules (DCT). The PCT is more than twice as long as the DCT, so the majority of tubules are PCT. DISTINGUISHING CHARACTERISTICS PCT DCT DCT PCT star-shaped lumen DCT glycocalyx debris DCT in lumen highly PCT DCT eosinophilic tall PCT cuboidal cell DCT DCT PCT more cells per lumen PCTclear lumen (no debris) PCT no or minimal PCT PCTbrush border less eosinophilic cells normal cuboidal PCT Slide B92 Human epithelium Kidney PAS X200
  29. 29. Kidney: PCT versus DCT The diameter of the distal convoluted tubules (DCT) is much smaller than the proximal convoluted tubules (PCT), although the luminal diameter of the two tubules are approximately the same. DISTINGUISHINGCHARACTERISTICS PCT renal renalstar-shaped lumen is corpuscle corpuscle PCT due to the autolysisof the brush border.Fewer nuclei appearin cross-section and cell boundaries are indistinct.Basal infoldings due DCT PCT to mitochondriaDCTno precipitate in lumen more nuclei withdistinct cell boundaries Slide B90 Human paler cytoplasm DCT Kidney H&E X400
  30. 30. Collecting Tubules & Ducts Start in cortex and descend through medulla Is lined by a cuboidal epithelium composed of two cell types: – Principal cells – resorb Na and water and secrete K in a Na, K ATPase pump- depending manner – Intercalated cells – have abundant mitochondria and secrete either H and HCO3. they are important regulators of acid-base balance
  31. 31. Kidney: Collecting Ducts Photo of renal papilla projecting into renal calyx. The apex of the papilla contains openings, the collecting ducts (of Bellini). These ducts deliver urine from the renal pyramid to the minor calyx.Collecting tubules, renal calyx widen to form collecting ducts Collecting collecting ducts (columnar tubules (of Bellini). epithelium). Theouter portion of the renal papillaminor calyx is lined with transitional epithelium. renal (minor) calyx
  32. 32. Kidney: Renal PapillaHigher magnification photo of renal papilla projecting into renal calyx. The openings seen within the papilla are the collecting ducts (of Bellini). Note the renal transitional calyx epithelium lining the outer surface *of the minor calyx. * The renal papilla has a simple columnar * * epithelium renal papilla renal (minor) * calyx
  33. 33. Juxtaglomerular Apparatus - site of blood pressure regulation via renin-angiotensin-aldosterone system Macula densa: specialized cells in distal convoluted tubule adjacent to renal corpuscle – these cells have receptors for Na. If it is necessary they stimulate production of aldosterone Juxtaglomerular cells: modified smooth muscle cells of afferent and efferent arterioles – produce renin. Renin provides the transformation of angiotensinogen into angiotensin I, which transforms into angiotensin II (in lungs) that elevates the blood pressure Juxtavascular cells: extraglomerular mesangial cells – their function is not well known. Probably they are involved in the renin and erythropoietin secretion and blood pressure regulation
  34. 34. Juxtaglomerular ApparatusMechanism macula densa cells monitor NaCl levels in afferent arteriole renin secretion juxtaglomerular cells is stimulated by paracrine activity from the macula densa renin is a protease that cleaves plasma angiotensinogen into angiotensin I angiotensin I converted to angiotensin II in the lung (by enzyme in capillaries) angiotensin II promotes vascular smooth muscle contraction and release of aldosterone from the adrenal cortex aldosterone stimulates absorption of NaCl and water in the distal convoluted tubule thus increasing blood volume net result is to increase blood pressure
  35. 35. Kidney: Vascular PoleSearch for an area within the renal corpuscle where a distalconvoluted tubule makes contact with the vascular pole of therenal corpuscle. Note the macula densa and juxtaglomerular cells DCT DCTSlide B94 Rabbit Kidney PAS X200 Wheater’s Fig.16.18b
  36. 36. Kidney: Vascular PoleThe macula densa of the distal convoluted tubule and thejuxtaglomerular (JG) cells constitute a juxtaglomerular apparatus(JGA). The JG cells secrete renin and erythropoietin. PCT PCT
  37. 37. Ureters and Urinary Bladder
  38. 38. Ureter Drains urine from kidney to urinary bladderStructure mucosa – lined by transitional epithelium over connect tissue lamina propria – transitional epithelium – impermeable to water and salts; distendable – lamina propria - loose connective tissue muscularis externa – smooth muscle layer – bi-laminar: inner longitudinal and outer circular; produce peristalsis adventitia / serosa – connective tissue coat with or without mesothelial covering
  39. 39. Ureter
  40. 40. Urinary Bladder Hollow muscular organ: distensible reservoir Full: ~1 liter receives bilateral ureters and empties via midline urethra smooth muscle forms detrussor muscle; specialized distally as internal urethral sphincter
  41. 41. Urinary BladderThe gross regions of the urinary bladder are  Fundus  Body  NeckThe histology of the urinary bladder is as follows: Mucosa - transitional epithelium and lamina propria Submucosa - connective tissue with blood supply Muscularis externa - 3 layers of smooth muscle  termed the detrusor muscle Serosa/Adventitia
  43. 43. Urethra urethra urethra
  44. 44. Urethra Neck of bladder to exterior Female: – Short: 1-1.5 in  UTI (bacteria or fungus) – External urethral orifice: very close to vaginal orifice Male: – Long: 7-8 in – terminal duct for both urinary and genital systems – Prosthatic, membranous, penile Urogenital diaphragm: external urethral sphincter (skeletal muscle) – resting to urinate
  45. 45. Urinary SystemMale Sphincters Female Sphincters Internal urethral External Urethral sphincter Sphincter