1 / 85

The Urinary System

25. The Urinary System. Kidney Functions. Regulate chemical composition of body fluids Eliminates waste Controls composition of bloods – ion levels and concentration Help maintain PCO2 & acid/base balance [pH] Help regulate blood pressure by secreting renin [ renin-angiotensin system].

yoshe
Download Presentation

The Urinary System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. 25 The Urinary System

  2. Kidney Functions • Regulate chemical composition of body fluids • Eliminates waste • Controls composition of bloods – ion levels and concentration • Help maintain PCO2 & acid/base balance [pH] • Help regulate blood pressure by secreting renin [renin-angiotensin system]

  3. Kidney Functions • Contribute to metabolism • detoxify free radicals and drugs [with peroxisomes] • gluconeogenesis [during fasting] • produce erythropoietin – stimulates red blood cell production • activation of vitamin D [as calcitrol]

  4. NITROGENOUS WASTES • Metabolic waste – waste substance produced by the body [often lethal] • 50% of N containing waste is urea [from protein – aa  NH2 ammonia  urea [by liver] • Uric acid – from nucleic acids • Creatinine – from creatine phosphate

  5. NITROGENOUS WASTES • BUN – typical = 10-20 mg/dL Too high = azotemia [renal insufficiency] • Plasma creatinine increase above 1.5 mg/dL with decreased filtration normal = 0.6-1.2 mg/dL

  6. Kidney Location and External Anatomy • Retroperitoneal in the superior lumbar region. • Extend from twelfth thoracic to third lumbar vertebra. • Right kidney is lower than left because it is crowded by the liver.

  7. Urinary System Organs

  8. Layers of Tissue Supporting the Kidney • Renal fascia – outer layer of dense fibrous connective tissue that anchors the kidney to abdominal wall. • Adipose capsule – shock absorbing. • Renal capsule – fibrous cover that prevents kidney infection.

  9. Kidney Location and External Anatomy

  10. Internal Anatomy • Cortex –outer - cortical zone and juxtamedullary zone • Medulla – renal pyramids [8-18] • Renal papillae – narrow ends of pyramids • Renal columns – between pyramids

  11. Internal Anatomy • Urine Flow – formed in nephrons  papillary ducts  minor calyx  major calyx  renal pelvis

  12. Internal Anatomy

  13. Blood and Nerve Supply • ~ one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute. • Arterial flow into venous flow out of the kidneys follow similar paths. Figure 25.3c

  14. Blood and Nerve Supply • Renal Arteries  segmental arteries  interlobar arteries  arcuate arteries  cortical radial arteries  afferent arterioles • Efferent arterioles also form vasa recta with deep juxtamedulary nephrons • Venules  cortical radial veins  arcuate veins  interlobar veins  segmental veins  renal veins  inferior vena cava Figure 25.3c

  15. Blood and Nerve Supply NERVE SUPPLY - • Renal plexus of sympathetic division of ANS – to afferent & efferent arterioles [vasomotor nerves] - regulate flow and pressure Figure 25.3c

  16. The Nephron • Nephrons are the structural & functional units that form urine, consisting of: • Renal Corpuscle – glomerulus + Bowman’s capsule • Renal Tubule - PCT, loop of Henle, DCT

  17. Histology of Nephron – Corpuscle BOWMAN”S CAPSULE • Parietal layer – simple squamous epithelium. • Capsular space. • Visceral layer consists of modified, branching epithelial podocytes.

  18. Histology of Nephron – Corpuscle • Functions – pressure filtration of blood – water and small solutes leave blood • vascular pole - blood in • urinary pole -urine out

  19. VP UP

  20. Histology of Renal Tubule • Proximal convoluted tubule (PCT) – cuboidal epithelium with microvilli & mitochondria

  21. Histology of Renal Tubule Loop of Henle [nephron loop]: • Descending limb [thin] simple squamous epithelium – permeable to water [out], urea [in]; thick walls • Ascending limb [thick] – cuboidal to low columnar epithelium; thick at top, then thin

  22. Connecting Tubules Distal convoluted tubule (DCT): • Principal cells: • Cuboidal cells without microvilli. • Help maintain water & salt balance.

  23. Collecting Ducts • Collecting Ducts - drains several DCT's • Combine to form papillary ducts  calyces • Cuboidal epithelium, then columnar

  24. Nephrons All nephrons begin in the cortex. Where the loop of Henle reaches to determines type • Juxtamedullary nephrons: • Have loops of Henle that deeply penetrate medulla. • Cortical nephrons – 85% of nephrons: • Have loops of Henle that only slightly penetrate medulla.

  25. Nephrons Figure 25.5b

  26. Glomerular Filtration General • Glomerular filtrate - from plasma but with no protein • Tubular fluid - from PCT through DCT

  27. Filtration Membrane • Endothelium of glomerulus – open pores [fenestrations] – 70-90 nm diameter everything but cells and platelets pass through • Basal lamina [basement membrane] of glomerulus – serves as dialysis membrane –blocks large plasma proteins

  28. Filtration Membrane • Filtration slits - Endothelium of visceral layer of glomerular capsule – podocytes form filtration slits [spaces between pedicels] – negatively charged - repel anions - 30 nm slit width

  29. Net Filtration Pressure (NFP) • Glomerulus blood filtering depends on 3 main pressures –1 promotes, 2 oppose • Blood Hydrostatic Pressure [HPG] – about 60 torr – forces fluid out of capillaries • Capsular Hydrostatic Pressure [HPC] – about -18 torr – opposes –from fluid already in capsular space

  30. Net Filtration Pressure (NFP) • Colloidal Osmotic Pressure of blood [OPC] about -32 torr – opposes • NFP = HPG – [HPC +OPC] = 55 – [15- 30]] = about 10 torr outward • The positive pressure moves fluid out of the glomerulus into Bowman’s capsule.

  31. Net Filtration Pressure (NFP) • Pressure remains high throughout length so filtration continues. Especially sensitive to hypertension

  32. Glomerular Filtration Rate (GFR) • Amount of filtrate formed in all areas of the renal corpuscles of both kidneys every minute • Directly related to pressures that determine NFP • Adult rate is about 125 mL/min – 180L/day [males]

  33. GFR

  34. Regulation of Glomerular Filtration • If the GFR is too high: • Needed substances cannot be reabsorbed quickly enough and are lost in the urine. • If the GFR is too low: • Everything is reabsorbed, including wastes that are normally disposed of.

  35. Regulation of Glomerular Filtration • Three mechanisms control GFR: • Renal autoregulation (intrinsic system); • Neural controls; • Hormonal mechanisms (renin-angiotensin system).

  36. Regulation of Glomerular Filtration • Renal Autoregulation of GFR - blood flow autoadjustment • Myogenic Mechanism – Smooth muscle contracts when stretched  reduces blood flow which reduces pressure downstream.

  37. Regulation of Glomerular Filtration • Tubuloglomerular feedback – negative feedback mechanism using the • Juxtaglomerular apparatus [respond to NaCl concentration] • juxtaglomerular cells - smooth muscle fibers of afferent arterioles – mechanoreceptors - dilate or constrict with pressure change & secrete renin.

  38. Regulation of Glomerular Filtration • macula densa- chemoreceptors – at end of ascending limb tall crowded cells that monitor Na+ and Cl- concentration

  39. Juxtaglomerular Apparatus (JGA) DC Muller, Johns Hopkins School of Medicine

  40. Regulation of Glomerular Filtration • Neural Regulation – sympathetic • Norepinephrine causes vasoconstriction • Affects smooth muscles of vessels – low input  dilation, high constriction

  41. Regulation of Glomerular Filtration • Renin-angiotensin II pathway- JG cells release renin in response to • 1 – decreased delivery of fluid and NaCl to macula densa • 2 – decreased stretching of JG cells • 3 – increased rate of stimulation by renal sympathetic nerves

  42. Regulation of Glomerular Filtration Angiotensin II is the active hormone that • produces constriction of arterioles to increase GBHP and raise GFR • stimulates secretion of aldosterone, which enhances reabsorption of Na+ [and water] by principal cells in collecting ducts

  43. Regulation of Glomerular Filtration • stimulates the thirst center of the hypothalamus • stimulates release of ADH which increases water reabsorption  increase in blood volume  higher BP

  44. Capillary Beds of the Nephron • Every nephron has 2 capillary beds: Glomerulus & Peritubular • Each glomerulus is: • Fed by an afferent arteriole • Drained by an efferent arteriole

  45. Capillary Beds • Peritubular beds are low-pressure, porous capillaries. • Vasa recta – long, straight efferent arterioles of juxtamedullary nephrons.

  46. Capillary Beds

  47. Tubular Reabsorption • 99% of materials move from filtrate back into peritubular capillaries or vasa recta • Solutes are reabsorbed by active or passive transport • Water is reabsorbed by osmosis = facultative water reabsorption • Small peptides and proteins are reabsorbed by pinocytosis

More Related