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HN220 > Chapter 18 + 19: Renal > Flashcards

Chapter 18 + 19: Renal Flashcards

1
Q

what is the renal system?

A
  • also known as the urinary system
  • filters blood and create urine as a waste by-product
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2
Q

5 functions of the kidneys

A

1) regulates plasma ion concentrations
2) regulates blood volume and blood pressure
3) regulation of blood osmolarity
4) helps stabilize blood pH
5) removal of waste and foreign substances from body

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3
Q

structures of the urinary system

A
  • two kidneys
  • two ureters
  • urinary bladder
  • urethra
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4
Q

characteristics of kidneys

A
  • located on either side of the vertebral column
  • left kidney is a bit superior to the right kidney
  • typical adult kidney is 4inches long, 2.2 inches wide, 1.2inches thick and weighs 150g
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5
Q

3 regions of the kidney

A

1) renal cortex
2) renal medulla
3) renal pelvis

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6
Q

what is the renal cortex?

A
  • the outer layer of the kidney
  • is a reddish-brown colour
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7
Q

what is the renal medulla?

A
  • inner region, deep to the cortex
  • is darker in colour and has a stripled appearance
  • composed of cone-shaped renal pyramids
  • each kidney has about 8 lobes, which composed a renal pyramid and its surrounding cortical tissue
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8
Q

characteristics of renal pyramids

A
  • the broad base of the pyramid faces the cortex
  • each pyramid has a tip, called a papillia, faces inwards
  • renal pyramids are separated by renal colums which are inward extensions of the cortical tissue
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9
Q

what is the renal pelvis and its components?

A
  • a funnel shaped tube that is continuous with the ureter
    1) minor calyces = cup-shaped areas that collect urine draining from pyramidal papillae
    2) major calyces = area that collect urine from minor calyces and empty into renal pelvis
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10
Q

steps to urine flow in renal pelvis

A

renal pyramid –> minor calyx –> major calyx –> renal pelvis –> ureter

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11
Q

what are nephrons?

A
  • the structural and functional units that filter blood and form urine
  • composed of 2 main parts:
    1) renal corpuscle
    2) renal tubule
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12
Q

components of renal corpuscle

A

1) bowmans capsule
- hollow structure containing the glomerulus
2) glomerulus
- “ball” of specialized capillaries (fenestrated)

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13
Q

anatomy of the nephron

A

1) proximal convoluted tubule
- most reabsorption occurs here
- cuboidal cells with dense microvilli that form a border to increase surface
2) loop of Henle
- composed of the descending limb, thin ascending limb, thick ascending limb
- creates a concentration gradient that allows for the production of concentrated urine
3) distal convoluted tubule
- shorter version of proximal tubule
- responsible for regulation of salt (sodium, potassium) and water balance in the urine.
4) collecting ducts
- collects filtrate from numerous nephrons

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14
Q

2 classes of nephrons

A

1) cortical nephrons
- located in the renal cortex (85%)

2) juxtamedullary nephrons
- originate close to the junction between the cortex and the medulla
- have very long nephron loops
- important for the production of concentrated urine

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15
Q

4 basic steps involved in renal system

A

1) filtration: blood to lumen
2) reabsorption: lumen to blood
3) secretion: blood to lumen
4) excretion: lumen to external environment

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16
Q

path of blood flow into and out of the kidneys

A

renal artery –> segmental artery –> interlobar arteries —> arcuate arteries –> interlobular arteries –> afferent arterioles –> glomerulus capillaries –> efferent arterioles –> capillary beds: peritubular cappilaries OR vasa recta –> interlobular veins –> arcuate veins –> interlobar veins –> segmental vein –> renal vein

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17
Q

3 nephron capillary beds

A

associated with renal tubule:
- glomerulus
- peritubular capillaries

associated with juxtamedullary nephrons:
- vasa recta

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18
Q

characteristics of glomerulus capillary bed

A
  • capillaries within the glomerulus are specialized for the filtration of blood and remove waste products
  • unlike typical capillary beds, the glomerulus is both fed and drained by arterioles.
    –> afferent arteriole = enters the glomerulus, supplying blood for filtration.
    –> efferent arteriole = leaves the glomerulus, regulating blood flow and pressure.
  • blood pressure is high in the glomerulus
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19
Q

why is blood pressure high in glomerulus?

A
  • afferent arterioles have a larger diameter compared to efferent arterioles so there is an increased blood flow
  • arterioles are high-resistance vessels which causes increased pressure within the glomerular capillaries
    –> large blood volume + high resistance = higher blood pressure
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20
Q

characteristics of peritubular capillary bed

A
  • low pressure, porous capillaries
  • they cling and surround to adjacent renal tubules in the cortex
  • arise from efferent arterioles and recieve blood that has already passed through the glomerulus and empty into venules to return filtered blood
  • adapted for the absorption of water and solutes back into the blood stream
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21
Q

vasa recta capillary bed

A
  • long, thin-walled blood vessels that run parallel to the loop of Henle of juxtamedullary nephrons
  • arise from the efferent arterioles that serve the juxtamedullary nephrons (replace the peritubular capillaries)
  • it maintains the concentration gradient which is important for the reabsorption of water and solutes (concentrated urine)
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22
Q

what is the juxtaglomerular apparatus?

A
  • each nephron has one juxtamerular complex (JGC)
  • is located at the inital portion of the distal convoluted tubules that comes into contact wth the nephrons afferent and efferent arterioles
  • plays a role in regulating rate of filtrate formation (blood volume) and blood pressure
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23
Q

3 cell types in the juxtaglomerular complex

A

1) macula densa
2) granular cells
3) extraglomerular mesangial cells

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24
Q

what are macula densa?

A
  • tall, closely packed cells located in the ascending limb of the nephron.
  • contain chemoreceptors that sense the NaCl content of the filtrate.
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25
Q

what are granular cells?

A
  • aka juxtaglomerular or JG cells
  • are enlarged smooth muscle cells found in the wall of the afferent arteriole.
  • they act as mechanoreceptors to sense blood pressure in the afferent arteriole.
  • contain secretory granules containing the enzyme renin (is involved in the regulation of blood pressure)
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26
Q

what are extraglomerular mesangial cells?

A
  • interconnected cells via gap junctions that allow for signal communication between the macula dense and granular cells
  • are located between the arteriole and tubule cells
27
Q

3 processes involved with urine formation

A

1) glomerular filtration
- bulk flow of protein-free filtrate from the glomerular capillaries into Bowman’s capsule.
2) tubular reabsorption
- selective return of filtered substances from the renal tubules and collecting ducts back into the bloodstream
3) tubular secretion
- selective movement of substances from the bloodstream into the renal tubules and collecting ducts to be excreted in the urine.

28
Q

characteristics of glomerulus filtration (step 1)

A
  • glomerular filtration is passive process
  • no metabolic energy is required to carry it out
  • hydrostatic and osmotic pressures (starlings forces) force fluids and solutes from the bloodstream in the glomerular capillaries through a filtration membrane and into the bowman’s capsule via a pressure gradeint
  • there is no reabsorption into glomerulus capillaries
29
Q

what is the filtration membrane?

A
  • a porous membrane between the blood an the interior of glomerular capsule
  • it allows water and solutes smaller than plasma proteins to pass
  • the glomerular filtrate must pass 3 players to enter bowman capsule
30
Q

3 layers of the filtration membrane

A

1) glomerular capillary endothelial layer (with fenestrations/ pores)
2) a basement membrane (formed by fused basal laminae)
3) epithelial cell (podocytes with filtration slits)

31
Q

how does glomerulus filtration occur?

A
  • hydrostatic pressure pushes water and solutes through the gaps between podocytes (slits) of the filtration membrane and into the glomerular (bowmans) capsule
  • small molecules such as water, glucose, amino acids and nitrogenous wastes pass
  • large macromolecules get stuck in the filtration membrane are engulfed via glomerular mesangial cells
  • plasma proteins remain in the blood to maintain colloid osmotic pressure (prevents the loss of all water to capsular space)
32
Q

what is glomerular filtration rate (GFR)

A
  • the volume of plasma filtered from the glomerulus into Bowman’s space per unit of time
  • approximately 125mL/min = 180 L/day
  • glomerular filtration pressure is the result of four Starling forces (hydrostatic and oncotic pressure)
33
Q

what factors influence glomerular filtration rate?

A

1) net filtration pressure (NFP)
- primary pressure is glomerular hydrostatic pressure
2) total surface area available for filtration
- the larger the surface area of the glomerular capillaries available for filtration, the higher the GFR.
- glomerular mesangial cells control this by contracting (less SA) or relaxing (more SA)
3) filtration membrane permeability
- filtration membrane in the glomerulus is much more permeable than other capillaries

34
Q

characteristics of tubular reabsorption (step 2)

A
  • refers to movement of filtered solutes and water from the lumen of the tubules back into the plasma
  • reabsorption is a highly selective transepithelial process
  • tubular reabsorption involves both active and passive transport mechanisms
  • nearly all organic nutrients (glucose, amino acids) are reabsorbed to prevent their loss in urine.
  • the reabsorption of water and ions is hormonally regulated
35
Q

where does tubular reabsorption occur?

A
  • most solute reabsorption occurs in the proximal convoluted tubules
  • some occurs in the distal convoluted tubules
  • the substance must move across two barriers:
    (1) the tubule epithelium
    (2) the capillary endothelium (only for macromolecules)
36
Q

2 routes to tubular reabsorption

A

(1) transcellular route
(2) paracellular route

37
Q

what is the transcellular route?

A
  • solute enters the tubule cells through the apical membrane
  • the solute travels through the cytosol of the tubule cells
  • the solute exits the tubule through the basolateral membrane and travels through interstitial fluid
  • the solute then enters the bloodstream through the endothelium of peritubular capillaries
38
Q

what is the paracellular route?

A
  • the solute goes between tubule cells via leaky tight junctions
  • the solute moves through the interstitial fluid and into the capillary
  • water, Ca2+, Mg2+, K+ and some Na+ use this route
39
Q

importance of regulating GFR

A
  • constant GFR allows kidneys to make filtrate and maintain extracellular homeostasis
  • GFR affects systemic blood pressure
40
Q

characteristics of tubular secretion (step 3)

A
  • tubular secretion is essentially reabsorption in reverse
  • selected substances are moved from the peritubular capillaries through the tubule cells and into the filtrate.
  • tubular secretion occurs predominantly in the proximal convoluted tubules
  • various substances are secreted, including K+, H+, NH4+, creatinine, organic acids, and bases
  • substances synthesized in tubule cells, such as bicarbonate ions (HCO3-), can also be secreted
41
Q

what is renal threshold?

A
  • the plasma concentration of solute at which the transport maximum is exceeded and excess solute appears in the urine
    –> when carriers for a solute are saturated, excess is secreted in urine
42
Q

what is tubular secretion important for?

A
  • disposing of substances, such as drugs or metabolites, that are bound to plasma proteins
  • eliminating undesirable substances that were passively reabsorbed (example: urea and
    uric acid)
  • ridding body of excess K+ (aldosterone effect)
  • controlling blood pH by altering amounts of H+ or HCO3- in urine
43
Q

goal of intrinsic regulation in renal system

A
  • renal autoregulation
  • to maintain GFR in the kidneys because it affects blood pressure
    –> increased GFR = more urine output = reduce blood pressure
44
Q

goal of extrinsic regulation in renal system

A
  • to maintain systemic blood pressure
    –> if blood pressure is too high = reduced filtration at the glomerulus = less urine output
45
Q

intrinsic controls of renal system

A

1) myogenic mechanism
2) tubuloglomerular feedback mechanism

46
Q

how does the myogenic mechanism intrinsically regulate GFR?

A
  • local smooth muscle in the afferent arteriole with contract when stretched
    –> increased BP causes the muscle to stretch = constriction of afferent arterioles = restricts blood flow into the glomerulus to regulate the rate of filtration
  • this mechanism protects the glomeruli from damage caused by excessively high blood pressure
    –> decreased BP = dilation of afferent arterioles = adequate blood flow
  • both help maintain normal GFR despite normal fluctuations in blood pressure
47
Q

how does the tubuloglomerular feedback mechanism intrinsically regulate GFR?

A
  • macula densa cells can trigger constriction or dilation of an afferent arteriole in response to the NaCl concentration in the filtrate
    –> if GFR increases = higher filtrate flow rate = reduced reabsorption time = leading to elevated NaCl levels in the filtrate = constriction of the afferent arteriole to low NFP and GFR to create more time for NaCl reabsorption
    –> Conversely, when GFR decreases, the feedback mechanism relaxes the afferent arteriole, increasing NFP and GFR to ensure sufficient filtration and reabsorption.
48
Q

extrinsic controls of renal system

A
  • sympathetic nervous system
  • renin-angiotensin-aldosterone
    mechanism
49
Q

how does the sympathetic nervous system extrinsically regulate GFR?

A

at normal conditions:
- renal blood vessels are dilated
- renal autoregulation mechanisms maintain appropriate blood flow and GFR

at abnormal conditions (low BP):
- norepinephrine from sympathetic nerves and epinephrine from the adrenal medulla are released
- systemic vasoconstriction occurs to increase blood pressure
- afferent arterioles constrict = reducing blood flow into the glomerulus and decreasing GFR
- this increases blood volume and blood pressure

50
Q

how does the renin-angiotensin-aldosterone
mechanism extrinsically regulate GFR?

A

this mechanism is the primary pathway for raising blood pressure

there are 3 pathways to renin release via granular cells:

1) Direct stimulation of granular cells by the sympathetic nervous system.
2) stimulation occurs when macula densa cells detect low NaCl concentration in the filtrate.
3) there is reduced stretch of granular cells, signaling low blood pressure.

51
Q

what is the transport maximum?

A
  • rate of transport when carriers are saturated
  • when solute concentration is high enough and all carrier proteins and pumps are occupied, the system is working at transport maximum
52
Q

what is osmosis?

A
  • water diffuses down the concentration gradient
  • water moves from area of low solute
    concentration to area of high solute
    concentration
  • water reabsorption follows solute reabsorption
53
Q

where does water absorption occur?

A

1) proximal tubules
- 70% of water is reabsorbed here
- is not regulated
2) distal tubules and collecting ducts
- most remaining water is reabsorbed here
- regulated by antidiuretic hormones (vasopressin)

54
Q

how does water reabsorption occur?

A
  • water reabsorption occurs through osmosis
  • sodium is the primary solute responsible for creating the osmotic gradient that drives water reabsorption in the renal tubules.
  • active reabsorption of sodium in the renal tubules creates an osmotic gradient because it is actively transported across the basolateral membrane of tubule cells into the peritubular fluid.
  • this establishes an osmotic gradient where solute concentration is higher in the peritubular fluid compared to the tubular fluid.
  • this causes water to passively move from the tubular fluid into the peritubular fluid and eventually the plasma (water reabsorption).
  • the proximal tubule fluid becomes iso-osmotic (same solute concentation) with the interstitial fluid of the renal cortex.
  • the reabsorption of water creates a new concentration gradient for permeating solutes to move into the plasma of peritubular capillaries.
55
Q

how is urine concentration and volume regulated?

A
  • the use of the countercurrent mechanism
  • regulation occurs within the distal tubule and collecting ducts
    –> if the body is dehydrated, the kidney produce a small amount of urine
    –> if the body is overhydrated, the kidney will dilute the urine
56
Q

what is the countercurrent mechanism?

A
  • the mechanism that the kidneys use to concentrate urine
  • fluid flows in opposite directions in two adjacent segments of same tube with hairpin turn
57
Q

2 countercurrent mechanisms

A

(1) countercurrent multiplier
- interaction of filtrate flow in ascending/descending limbs in loops of juxtamedullary nephrons
(2) countercurrent exchanger
- blood flow in ascending/descending limbs of vasa recta

58
Q

what is the medullary osmotic gradient?

A
  • the gradient necessary for water reabsorption from the collecting duct
  • occurs due countercurrent multiplier mechanism
  • depends on the loop of Henle (descending/ascending limb)
    –> the outer regions of the medulla have a lower osmolarity than the inner regions
    –> the osmolarity varies from 300 mOsm at the cortical edge of the medulla to approximately 1200–1400 mOsm at the innermost portion of the medulla near the renal pelvis.
59
Q

perameability of Loop of Henle

A

descending limb
- permeable to water
- no transport of Na+, Cl- or K+

ascending limb:
- impermeable to water
- active transport of Na+, Cl- and K+ can occur

60
Q

how does the countercurrent multiplier establishes the medullary osmotic gradient?

A

1) fluid enters the tubule
2) the active transport of Ca2+, Cl-, K+ ions into medullary interstitial fluid increases osmolarity
3) water moves out of the descending limb via osmosis
4) the descending limb is in iso-osmotic state = an osmotic difference between descending and ascending limbs
5) more fluid enters the tubule and pushes fluid through via bulk flow
6) the active transport of Ca2+, Cl-, K+ ions into medullary interstitial fluid increases osmolarity
7) water moves out of the descending limb via osmosis
8) the descending limb is in iso-osmotic state = an osmotic difference between descending and ascending limbs
9) more water enters tubule and process continues until the system is in a steady state

61
Q

where is water reabsorbed?

A
  • 70% of water reabsorbed in proximal tubule
  • 20% reabsorbed in distal tubule
  • 10% reabsorbed in collecting ducts
62
Q

factors affecting water permeability

A
  • maximum amount of water reabsorbe depends on length of loop of Henle
  • dependent on water channels (aquaporin) and the presence of ADH (antidiuetic hormone)
63
Q

what water channels are found in renal system?

A
  • aquaporin-3 = present in basolateral membrane always
  • aquaporin-2 = present in apical membrane only when ADH
    present in blood
    –> secretion of ADH stimulates the insertion of water channels into the apical membrane

HN220 (12 decks)

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