TOB Urinary (15)

  1. Major Functions of the Kidney
    • removal of metabolic waste products from blood (heme -> bilirubin -> urobilin)
    • regulation of ion concentration (Na+, K+, etc.)
    • regulation of blood acid-base balance
    • regulation of blood pressure (renin, secretion)
    • regulation of erythrocyte production (erythropoietin)
    • vitamin D activation (parathyroid hormone controls 2nd hydroylation in the kidney --> active vitamin D)
  2. vitamin D
    • a 'hormone' synthesized in skin but turned into its active form in the kidney
    • it increases Ca2+ absorption in small intestine
    • increases Ca2+ absorption in renal tubules
    • increases osteoclast (bone breakdown) activity to increase Ca2+ levels
  3. What two hormones are synthesized & released by the kidney?
    • renin: increases blood pressure
    • erythropoietin: regulates RBC production in bone marrow
  4. medullary rays
    • straight tubules in the medulla that extend up into the cortex; signify the middle of each one of the kidney lobules
    • what gives medulla striated appearance
    • all urine drains through these tubules
    • Image Upload 1
  5. Image Upload 2
    • interlobular vessels define the border of lobules
    • medullary rays define the middle of lobules
    • renal corpuscles are ONLY located in the kidney cortex, NOT the medulla
    • the arcuate vessels define the border between the cortex & medulla
  6. renal corpuscles
    • round dark areas that contain a tuft of capillaries called the glomerulus
    • the combination of glomerulus & Bowman's capsule
  7. Image Upload 3
    • stained for the peritubular capillary network
    • the afferent & efferent capillaries feeding into & out of glomeruli located in the OUTER cortex
    • glomeruli in the inner cortex closer to the medulla have efferent capillaries that form vasa recta, straight capillaries that go deep into the medulla
  8. erythropoetin (EPO)
    synthesized and secreted by peritubular capillaries & tubule cells which regulates red blood cell production
  9. Path of Blood Flow Through the Kidney:
    aorta -> renal artery -> segmental artery -> lobar artery -> interlobar artery -> arcuate artery -> interlobar artery -> afferent arteriole -> GLOMERULUS -> efferent arteriole -> peritubular capillaries + vasa recta -> interlobar vein -> arcuate vein -> interlobar vein -> renal vein -> inferior vena cava
  10. Bowman's Capsule
    • cup shaped-structure made up of 2 layers that holds the glomerulus (tuft of capillaries)
    • squamous outer (parietal) layer is continuous with the proximal convoluted tubule
    • inner (visceral) layer differentiates to form podocytes
  11. Image Upload 4
    • podocytes
    • specialized cells that make up the visceral (inner) layer of the Bowman's capsule
    • they completely invest the glomerular capillaries & their multiple foot processes form filtration slits through which blood plasma must pass to get into the bowman's space
  12. filtration barrier through which blood plasma must pass:
    • Image Upload 51. from inside capillaries of the glomerulus
    • 2. through the fenestrated epithelium of capillaries
    • 3. through the thick basement membrane (a double basement membrane synthesized by both the blood endothelial cells and podocytes)
    • 4. through the podocyte filtration silts INTO the Bowman's space
    • only molecules smaller than approximately 70 kD are able to pass through these filters (proteins, ions, etc.)
    • plasma is now free to enter proximal conv. tubule
    • Image Upload 6
  13. plasma enters the _________ & is urine by the time it reaches the __________
    • PLASMA enters the glomerulus
    • URINE is what ends up in the collecting duct
  14. nephron
    • renal corpuscle (glomerulus & Bowman's capsule) + tubule (proximal convoluted tubule, loop of Henle, & the distal convoluted tubule)
    • there are about 2 million per kidney
  15. uriniferous tubule
    nephron + collecting duct
  16. cortical labyrinth
    network of tubes in the kidney cortex; see MOSTLY proximal & some distal convoluted tubules
  17. What purpose does the afferent arteriole being larger than the efferent arteriole serve?
    creates pressure that forces plasma OUT of glomerulus/capillary loops into the Bowman's space
  18. What cells are present in the glomerulus?
    • endothelial cells
    • mesangial cells
    • podocytes
  19. intraglomerular mesangial cells
    • specialized smooth muscle cells around the capillaries in the glomerulus
    • they regulate blood flow through the capillaries
    • they physically support the capillary loops
    • they anchor the capillary loops to the vascular pole
    • are found in the basal lamina
    • are also involved w/ both phagocytosis & repair, & are contractile (influence on bp)
  20. extraglomerular mesangial (lacis) cells
    • light-staining cells in the kidney found OUTSIDE the glomerulus, near the vascular pole (where afferent arterioles enter the glomerulus) & macula densa
    • they are mostly involved with blood pressure monitoring (direct contraction or expansion of capillary vessels)
    • part of the juxtaglomerular apparatus
  21. Image Upload 7
    • glomeruli + surroundings
    • red splotches = blood in capillaries
    • thin green nuclei (sort of around red splotches) = endothelial cell nuclei
    • more round/floating green nuclei = mesangial cells
    • surrounding = PROXIMAL conv. tubules (PCT)
  22. Proximal convoluted tubule (PCT)
    • region just distal to Bowman’s capsule receives the glomerular filtrate and functions in a manner analogous to the small intestine in the GI tract: it is the primary site for resorption of useful sugars, small proteins and salts
    • cuboidal cells of the PCT have a rich brush border (apical microvilli) and mitochondria-rich basal infoldings that are essential for rapid resorption
  23. Image Upload 8
    • fuzzy stuff facing inside/lumen: brush border (not seen in DCT)
    • area surrounding PCT lumen = very red b/c it's FILLED with mitochondria
    • in between tubules = blood vessels where useful materials are resorbed
    • Image Upload 9
    • basal laminal infoldings, lots of mitochondria, apical glycocalyx
  24. Resorption in the Proximal convoluted tubule
    • is a two-step process:
    • 1. active movement of NON-waste products into the interstitium at the cells’ basal surface
    • 2. subsequent passive movement into nearby peritubular capillaries (eg. by pinocytosis)
    • Image Upload 10
  25. Distal convoluted tubule (DCT)
    contains low cuboidal cells that have a much diminished brush border, a more clear cytoplasm than PCT cells (owing to the reduced number of mitochondria), & serve mainly as the site for sodium (+ water, by osmosis) resorption --> less resorption
  26. Which region of the uriniferous tubule is sensitive to the hormone aldosterone?
    • the Distal convoluted tubule (DCT)
    • aldosterone = a steroid hormone (mineralocorticoid) produced by the zona glomerulosa of the adrenal cortex that increases reabsorption of ions & water in the kidney, increasing blood pressure
  27. Loop of Henle
    • region that lies between the PCT & DCT necessary for establishing & maintaining an osmotic gradient in the interstitium of the medulla
    • this is necessary for the resorption of water
    • the loops are surrounded by interstitial tissue, blood vessels (vasa recta), & numerous collecting ducts
  28. ascending limb of the loop of Henle
    • also called the thick limb
    • pumps sodium ions into the interstitium
    • is NOT permeable to water
  29. descending limb of the loop of Henle
    IS permeable to water
  30. What do the different attributes of the descending & ascending limbs of the loop of Henle lead to?
    • the formation of a sodium concentration gradient
    • the MOST concentrated region is located within the interstitium at the tip of the loop (bottom)
    • this salt distribution is essential to create the osmotic gradient needed for the removal of water from the urine as it passes through the collecting ducts in the deep medulla
  31. main function of the medulla:
    • to concentrate the urine aka retrieve water FROM the collecting ducts
    • the cells of the medulla generate a salt gradient, resorb water, & manage the pH of the blood (control acid-base balance)
  32. Image Upload 11
    • cross-section of the medulla
    • largest structure: collecting ducts
    • 2nd largest: thick (ascending) loop of Henle limb
    • thin limbs of loop of Henle: very thin circle filled with CLEAR lumen
    • vasa recta: very thin circle filled with BLOOD (colored, not clear)
    • Image Upload 12
  33. Collecting Duct (CD)
    • receives the partially concentrated urine from the distal end of the DCT
    • are clumped within the center of the cortical renal lobules to form the medullary rays
    • as these “descend” into the medulla, individual rays blend with neighboring rays and cannot be distinguished
  34. Image Upload 13
    • longitudinal section of the collecting duct
    • intercalated cells (DARKER): monitor the pH of the blood
    • light cells (light, the majority): respond to ADH; have cilia that serve as mechanosensors
    • next to it (with less defined cells) = the thick (ascending) loop of Henle
  35. intercalated cells
    • darker, less abundant cells in the collecting duct walls which monitor the pH of the blood outside the collecting duct; are 2 types
    • α intercalated cells: secrete H+ if the blood pH is too high
    • β intercalated cells: secreted HCO3 (bicarbonate) if the blood pH is too low
  36. polycystic kidney disease
    • can be caused by mutations in polycystin-1 & -2 genes which code for cilia on light cells of the collecting ducts
    • if the genes --> cilia are mutated they are unable to serve as mechanosensors & intracellular calcium transport is compromised
    • characterized by bilaterally enlarged kidneys w/ multiple cysts
  37. What is required for the cells of the collecting duct to be permeable to water (aka release it into the interstitium?
    • antidiuretic hormone (ADH)
    • the cells of the collecting duct are impermeable to water in the absence of ADH
    • with ADH, aquaporins open, allowing water to exit, concentrating the provisional urine
    • (alcohol inhibits ADH --> aquaporins stay closed, water isn't reabsorbed, have a lot more water in pee)
  38. diabetes insipidus
    • results from an inability to make, or respond to, ADH
    • as a result the collecting ducts remain impermeable to water despite the strong medullary osmotic gradient through which they pass
    • a much more copius volume flows through the kidneys and into the bladder
  39. diabetes mellitus
    • the insulin deficiency leads to excess glucose in the urinary filtrate (the large volumes of glucose exceed the glucose transporter capacity so not all can be resorbed)
    • glucose is osmotically active and thus cancels much of the sodium-generated osmotic gradient in the interstitium of the renal medulla; water doesn't leave collecting ducts thus leading to osmotic diuresis
  40. Kidney stones (renal calculi)
    • crystals may form from calcium, oxalate, or uric acid precipitates
    • precipitation may be caused by low fluid intake, high protein diets, & refined sugars
    • large precipitates clog up minor calyces, preventing urine from exiting the kidney
    • pelvic rim is a place they could get stuck; there's a sharp bend
  41. regulation of blood pressure
    • the kidneys are critical organs for regulating blood pressure
    • sensory cells exist for monitoring both blood pressure (juxtaglomerular, or JG, cells) & blood chemistry (macula densa cells) and these are collectively called the juxtaglomerular apparatus
  42. Juxtaglomerular apparatus
    • found where the vascular pole of the renal corpuscle & the distal convoluted tubule CONTACT each other; contains 3 cell types
    • 1. JG cells
    • 2. macula densa cells
    • 3. lacis cells
  43. juxtaglomerular cells (JG cells)
    • specialized smooth muscle cells that are baroreceptors: they physically monitor the BP
    • release renin, a protease that cleaves angiotensinogen in the blood producing angiotensin I, in response to low BP,
    • located in the wall of the afferent arteriole
  44. Angiotensin II
    • a vasoconstrictor made from cleavage of angiotensin I by angiotensin converting enzyme (ACE) in the LUNG
    • causes an immediate increase in blood pressure & stimulates release of aldosterone from the adrenal gland (further increases BP)
  45. What stimulates the release of renin?
    • 1. decreased blood pressure in the afferent arteriole
    • 2. decreased sodium content in the distal tubule
  46. What cells detect depressed sodium levels that stimulate the release of renin?
    macula densa cells - chemoreceptors monitor the salt concentration pressure
  47. Image Upload 14
    • macula densa cells
    • an area of closely packed specialized cells lining the wall of the distal convoluted tubule at the point where it returns to the vascular pole of its parent glomerulus (close to the afferent arteriole)
    • are chemoreceptors that monitor the salt concentration of the blood: when there's low ion concentration = low pressure, these cells signal nearby JG cells to release renin, initiating a BP increasing cascade
    • Image Upload 15
  48. calyces
    • funnel-shaped structures where concentrated urine from the medulla goes to
    • multiple calyces converge onto the renal pelvis, a dilated proximal portion of the ureter
    • nothing more can be done to change the urine at this point
    • Image Upload 16collecting ducts (in the renal papilla) drain into minor calyces
  49. Image Upload 17
    • top: epithelium of renal 'papilla (like that lining the collecting ducts)
    • bottom: epithelium of the calyces (& ureter and urinary bladder)
    • a change is made
  50. What type of epithelium lines the calyces, ureter, & the urinary bladder?
    • transitional epithelium (urothelium)
    • this epithelium is pseudostratified & usually has large, dome-shaped, often binuclate cells at the luminal surface
    • Image Upload 18stretched when you really have to pee (lots of urine)
    • relaxed when you don't
  51. Image Upload 19
    • Ureter
    • long muscular tubes containing two (or three, distally) layers of smooth muscle but NO muscularis mucosa
    • the innermost layer = longitudinal while the outer layer is circular
    • when present distally, the outermost third layer is longitudinal
    • transitional surface epithelium -> lamina propria -> goes straight to muscularis externa
    • the mucosa is usually folded upon itself but expands during peristalsis
    • works via peristalsis: gravity is not needed to move urine through/out
  52. Bladder
    • has a mucosal wall with rich layers of smooth muscle but poorly organized
    • it has NO distinct muscularis mucosa deep to the lamina propria
    • it's epithelial lining = transitional
  53. What are the arrows pointing to?
    Image Upload 20
    interlobular vessels
  54. What is the region with the * called?
    Image Upload 21
    • Urinary Pole: very beginning of the PCT system
    • on the opposite end is the vascular pole
Card Set
TOB Urinary (15)
Exam 4