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NPB 101 > renal system > Flashcards

renal system Flashcards

1
Q

nephrons

A

renal corpuscle made of:

  • glomerulus = collection of capillaries hugged by bowman’s capsule that filters plasma into tubular component
  • bowman’s capsule (glomerulus capsule) = cup shape around glomerulus formed from tubule

renal tubule made of:

  • proximal tubule
  • loop of henle
  • distal tubule
  • collecting duct
  1. vascular component:
    • afferent arteriole (AA) brings blood to glomerulus
    • glomerulus
    • efferent arteriole (EA) carries blood from glomerulus (only place in body where arteriole comes from capillary)
    • peritubular capillaries from EA supply renal tissue & involved in exchanges w/ tubular lumen
  2. tubular component:
    • bowman’s capsule collects globular filtrate
    • proximal tubule extends between Bowman’s capsule & loop of Henle where unregulated reabsorption & secretion occurs
    • loop of henle establishes osmotic gradient important in concentrating urine
    • distal tubule & collecting duct: regulated reabsorption of Na+ & H2O and secretion of K+ & H+
  • 2 types:
    • juxtamedullary nephron found at border btwn cortex & medulla with a long loop of henle inside medulla & are specialized in concentration of urine
    • cortical nephron are the majority with a short loop of henle in medulla
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2
Q

renal corpuscle

A

glomerulus = collection of capillaries inside bowman’s capillaries that filters plasma into tubular component

bowman’s capsule = cup shape around glomerulus formed from tubule

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3
Q

renal tubule

A
  • proximal tubule
  • loop of henle
  • distal tubule
  • collecting duct
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4
Q

vascular component of a nephron

A
  • afferent arteriole (AA) brings blood to glomerulus
  • glomerulus filters plasma into tubular component
    • glomerular capillaries = specialized for filtration
      • no ATP used so filtration depends on capillary pressure
  • efferent arteriole (EA) carries blood from glomerulus
  • peritubular capillaries from EA supply renal tissue & involved in exchanges w/ tubular lumen ➔ where reabsorbed solute is returned to blood
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5
Q

tubular component of a nephron

A
  • bowman’s capsule collects globular filtrate
  • proximal tubule extends between Bowman’s capsule & loop of Henle where unregulated reabsorption & secretion occurs
  • loop of henle establishes osmotic gradient important in concentrating urine
  • distal tubule & collecting duct: regulated reabsorption of Na+ & H2O and K+ & H+ secretion
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6
Q

types of nephrons

A

juxtamedullary nephron

  • found at border btwn cortex & medulla
  • long loop of henle inside medulla
  • specialized in concentration of urine
  • ~15 %

cortical nephron

  • majority
  • short loop of henle in medulla
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7
Q

filtration through renal corpuscle

A
  1. blood flows through AA into glomerulus & leaves through efferent arterioles
  2. substances in blood < 8nm are filtered through pores & fenestrations btw/in glomerular capillary endothelial cells
    • mol too large to pass = RBC, plasma proteins, large anions, protein-bound minerals & hormones
  3. then across basement membrane = acellular gelatinous layer that surrounds endothelial cells
  4. then through filtration slits between podocytes in bowman’s capsule that line glomerulus & allow fluid to pass from capillaries to bowman’s capsule
  5. transported to lumen of proximal tubule that exits bowman’s capsule
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8
Q

juxtaglomerular apparatus

A

where the glomerulus meets the distal convoluted tubule

  • ascending limb passes through fork btwn AA/EA
  • distal convoluted tubule starts
  • juxtaglomerular/JG cells = enlarged SM cells in AA with secretory vesicles containing renin
    • mechanoreceptors that sense BP around AA
    • renin = hormone part of renin-angiotensin system (RAS) that ↑ BP
  • macula densa cells = chemoreceptors that respond to changes in NaCl of filtrate ➔ AP & osmotic balance
    • release endothelin as vasoconstrictor & bradykinin as vasodilator
  • mesangial cells engulf macromolecules stuck in filtration
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9
Q

basic renal procceses

A
  1. gomular filtration
  2. tubular secretion
  3. tubular absorption

amount extcreted = filtered + secreted - reabsorbed

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10
Q

glomerular filtration

A
  • pressure from large V of AA being squished into smaller arterioles forces plasma into bowman’s capsule
    • filtrate = plasma in bowman’s capsule
  • will filter anything < 8nm
  • only ~20% of plasma that enters is filtered
    • important to keep plasma proteins in plasma to maintain oncotic pressure (proteins in blood cause backwards pressure)
    • RBC or protein in urine (protinuria) = problem with filtration membrane (common for diabetes & hypertension)
  • ↑ venous return
  • majorty of of plasma reabsorbed ➔ prevents dehydration
  • passive: hydrostatic force pushes fluids & solutes
  • entire plasma volumes is filtered to kidneys ~65x/d
  • more efficient than body capillaries b/c
    1. filtration membrane = ↑ SA & very permeable
    2. glomerular pressure is much higher
  • forces involved:
    1. glomerular capillary BP (PGC) proportional to GFR ➔ favors filtration
    2. fluid pressure in bowman’s space (PBS) ➔ opposes filtration
    3. osmotic force from plasma proteins (πGC) ➔ opposes filtration

net glomerular filtration rate (GFR) = glomerular capillary BP − bowman’s space fluid pressure − plasma protein osmotic force

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11
Q

oncotic pressure

A

backwards pressure created by plasma proteins

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12
Q

GFR

A

glomerular filtration rate = V of filtrate/min

  • affected by:
    1. V of SA
    2. membrane permeability
    3. net filtration pressure (NFP) (proportional to GFR)
  • ↑ BP = ↑ NFP = ↑ GFR
  • controlled by vascular changes (BP)
  • regulated by
    • sympathetic control
      • baroreceptor reflex: arterial carotid sinus & aortic arch baroreceptors detect ↑ & ↓ in arterial BP & send signals to cardiovascular control center in brainstem that adjusts levels of sympathetic activity
      • ↑ CO & total peripheral resistance & ↓ GFR to maintain plasma V by constricting AA (conserving blood for FOF)
    • autoregulation
      • myogenic mechanism contracts in response to ↑ stretch & relaxes in response to ↓ stretch
      • tubuloglomerular feedback: macula densa cells in juxtaglomerular apparatus detect changes in fluid rate through [NaCl] & release hormones
        • endothelin = vasoconstrictor that ↓ GFR
        • bradykinin = vasodilator that ↑ GFR
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13
Q

sympathetic regulation of GFR

A
  • ↑ CO & total peripheral resistance ↓ GFR to maintain plasma V by constricting AA (conserving blood for FOF)
  • baroreceptor reflex: arterial carotid sinus & aortic arch baroreceptors detect ↑ & ↓ in arterial BP ➔ CVCC in brainstem adjusts levels of symp
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14
Q

regulation of GFR

A

sympathetic

  • ↑ CO & total peripheral resistance & ↓ GFR to maintain plasma V by constricting AA (conserving blood for FOF)
  • baroreceptor reflex: arterial carotid sinus & aortic arch baroreceptors detect ↑ & ↓ in arterial BP ➔ CVCC in brainstem adjusts levels of symp
  • can override autoregulation

autoregulation changes caliber of AA to maintain constant blood flow into glomerular capillaries

  • AA vasoconstriction ↓ blood flow = ↓ glomerular capillary BP = ↓ NFP = ↓ GFR
  • AA vasodilation = ↑ glomerular capillary BP = ↑ NFR = ↑ GFR
  • myogenic mechanism:
    • contracts in response to ↑ stretch
    • relaxes in response to ↓ stretch
  • tubuloglomerular feedback in juxtaglomerular apparatus
    • macula densa cells detect changes in fluid rate through [NaCl] & release hormones
    • endothelin = vasoconstrictor
    • bradykinin = vasodilator
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15
Q

control of GFR

A

vascular changes (BP)

  • constrict AA = ↓ blood flowing through glomerular capillary = ↓ pressure = ↓ GFR
  • dilate EA = more blood can flow easily out = ↓ glomerular capillary pressure = ↓ GFR
  • constrict EA = less blood can exit ➔ backflow ↑ glomerular capillary pressure = ↑ GFR
  • dilate AA = more blood enters & must squeeze into smaller glomerular capillary = ↑ GCP = ↑ GFR
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16
Q

tubular secretion

A
  • from peritubular capillaries to tubular lumen
  • important for:
    1. disposing of drugs & drug metabolites
    2. eliminating undesired substances/end products that have been reabsorbed by passive processes (urea & uric acid)
    3. removing excess K
    4. controlling blood pH
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17
Q

K secretion & absorption

A

K reabsorption:

  • active reabsorption in in proximal tubule
  • constant & unregulated
  • ~all filtered K is reabsorbed
    • [K] between proximal & distal tubule: ≈ 0

K secretion:

  • active secretion is regulated in distal & collecting tubules
    • ~all K in urine was secreted
    • ↓ [K] ➔ ↓ secretion in distal portion of nephron
    • ↑ [K] ➔ ↑ secretion in distal portion of nephron
  • basolateral pump simultaneously transports Na into lateral space & K into tubular cell then K passively diffuses into tubular lumen
  • aldosterone triggered by:
    • ↑ [K] in plasma ➔ activates adrenal cortex to secrete aldosterone ➔ cortical collecting ducts ↑ rate of K secretion & Na & H2O reabsorption ➔ ↑ K excretion in urine ∴ less K in plasma
    • renin-angiotensin pathway
  • maintaining proper ECF levels of K = extremely important: ↑ [K] ➔ depolarization & ↓ [K] ➔ hyperpolarization
  • could lead to over or under excitability of neurons & muscle cells
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18
Q

tubular reabsorption general

A
  • filtrate moves from tubular lumen back into peritubular capillaries
  • 80% reabsorbed so no dehydration
  • active Na reabsorption responsible for passive reabsorption of Cl, H2O, & urea
  • begins once filtrate enters tubular lumen (of nephron)
  • tubular endothelial cells:
    • luminal (apical) & basolateral membranes
    • tight junctions btwn cells
    • interstitial fluid in lateral spaces
  • most materials besides water have to pass through cells to enter blood
  • transcellular transport requires substances cross 5 barriers
    1. luminal membrane of tubular cell
    2. cytosol of tubular cell
    3. basolateral membrane of tubular cell
    4. intersitial fluid
    5. capillary wall
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19
Q

active transport for reabsorption

A

in Na/K pump in basolateral membrane of intertubular lumen

Na = 99.5% reabsorbed through

  • proximal tubule (main): role = reabsorbing glucose, AA, H2O, Cl & urea
  • loop of henle: role = varying concentrations & volumes produced by kidneys
  • distal & collecting tubule: absorption influenced by hormones ➔ important in regulation of ECF volume
20
Q

Na transport during reabsorption

A
  • extracellular [Na] < intracellular: Na diffuses into tubular cell
  • intracellular [Na] < interstitial: Na/K ATPase required to transport into interstitial fluid
  • interstitial [Na] > peritubular capillary: Na diffuses into blood
21
Q

reabsorption in proximal tubule

A
  • Na important for reabsorbing glucose, AA, H2O, Cl-, & urea
  • glucose & AA are reabsorbed against [gradient] from lumen in proximal tubule into tubule cells via Na cotransporter
  • Na/K ATPase generates electrochemical gradient that powers the transport of glucose & AA via secondary active transport
    • G-coupled protein receptor that activates adenylate cyclase which activates cAMP which activates protein kinase A which phosphorylates proteins for aquaporins in the tubular & basolateral membranes
    • responsible for passive reabsorption of Cl, H2O, & urea
    • Cl- pass between tubular cells
  • aquaporins in proximal tubule always open
22
Q

reabsorption in loop of henle

A
  • Na invoved in producing urine of varying concentrations & volumes
  • water passively reabsorbed via osmosis
  • key to ECF tonicity control ➔ kidneys can excrete urine at diff concentrations
23
Q

reabsorption in distal tubules

A
  • subject to hormonal control
  • Na important in the regulation of ECF volume
  • ~20% water reabsorbed
  • vasopressin regulates aquaporins
  • aldosterone ↑ Na reabsorption by inserting Na channels in luminal membrane & Na/K ATPases carriers in basolateral membranes
  • atrial natriuretic peptide (ANP) inhibits Na reabsorption
24
Q

Na reabsorption

A
  • Na is most cation in tubular lumen filtrate
  • via active transport
  • 67% in proximal tubule
  • 25% in loop of henle
  • 8% in distal tubule ➔ regulates balance
  • proximal tubule & loop of henle: always absorbed (body [Na] does not matter)
  • in distal & collecting tubules: under hormonal control
    • aldosterone stimulates Na reabsorption
    • atrial natriuretic peptide (ANP) inhibits Na reabsorption
25
Q

renin-angiotensin-aldosterone system

A
  1. ↑ Na reabsorption (Cl follows passively)
  2. conserve H2O
  3. ↑ thirst & fluid consumption
  4. ↑ arteriolar vasoconstriction
  • net result: ↑ ECV & BP
  • angiotensinogen = synthesized in liver & present in plasma
  • renin = released into plasma from JG cells in kidneys ➔ activates/converts angiotensinogen ➔ angiotensin I
  • angiotensin-converting enzyme (ACE) in lungs converts angiotensin I ➔ angiotensin II
  • angiotensin II stimulates
    • vasopressin
    • thirst
    • arteriolar vasoconstriction
    • adrenal cortex to release aldosterone
    • ↑ resistance
    • kidney holds on to more water ➔ ↑ SV
  • aldosterone increases Na reabsorption in distal & collecting tubules by inserting Na channels in luminal membranes & Na/K ATPase carriers in basolateral membranes
26
Q

hypertension

A

↑ BP

  • sometimes due to abnormal ↑ in renin-angiotensin-aldosterone activity
    • tx: diuretics &/or ACE inhibitors
  • inactivity
27
Q

atrial natriuretic peptide (ANP)

A
  • hormone that ↑ Na urine output
  • specialized cardiac atrial cells produce & store ANP
  • released when cells are mechanically stretched from↑ ECF volume
    • ↑ ECF = ↑ SV
  • inhibits Na reabsorption in distal & collecting tubules
  • inhibits
    • renin secretion by kidneys
    • aldosterone secretion from adrenal cortex
    • SM of AA ➔ leads to dilation of AA & ↑ GFR
    • SNS ➔ ↓ CO & total peripheral resistance
  • net effect: ↓ in ECF volume & BP
28
Q

countercurrent exchange

A
  • maintenance of osmolarity
  • fluids in adjacent tubiles flow in opposite directions which ↑ exchange by ↑ SA
  • involved in urine concentration
  • powered by differences in permeability in the different parts of the loop of henle
    1. produces: hypotonic urine that can be excreted if body’s ECF has too much water
    2. establishes vertical osmotic gradient that collecting ducts can use to concentrate urine w/in body if not enough water
29
Q

ECF tonicity during urine concentration

A
  • H2O > solute = hypotonic (ECF osmolarity < normal)
  • H2O < solute = hypertonic (ECF osmolarity > normal)
  • vertical osmotic gradient in interstitial fluid of medulla balances ECF osmolarity
    • osmolarity in cortex stays constant
    • gradient ↑ inward through medulla
    • junction between inner medulla & renal pelvis = highest osmolarity
    • juxtamedullary nephrons = specialized in concentrating urine
    • any osmolarity > 300 is in medullary
30
Q

filtrate osmolarity throughout the loop of henle

A
  • filtrate = isotonic as it approaches loop of henle
  • unregulated osmotic reabsorption of filtered H2O happens immediately after filtrate formation in proximal tubule (secondary to active Na reabsorption)
  • descending limb
    • highly permeable to water
    • does not secrete Na
    • water leaves ➔ ↑ osmolarity (↑ amount of solutes per V of water & hypertonic)
  • ascending limb
    • actively transports Na out of tubular lumen into surrounding interstitial fluid
    • is impermeable to water ➔ salt leaves without water following
    • hypotonic going into collecting duct
31
Q

renin

A

enzyme secreted by juxtaglomerular cells that ↑ BP

  • part of renin-angiotensin-aldosterone system (RAS)
32
Q

JG cells

A

juxtaglomerular cells = mechanoreceptors that sense ↓ BP in AA & secrete renin in response

  • surround AA
33
Q

macula densa cells

A
  • tall & closely-packed
  • adjacent to JG cells
  • chemoreceptors in the lining of the distal tubule of the juxtaglomerular apparatus
  • respond to changes in NaCl of filtrate ➔ regulate AP & osmotic balance
  • release renin in response to ↓ NaCl in tubular lumen
  • secrete nitric oxide = vasodilator that stops ATP & adenosine at the AA
34
Q

mesangial cells

A

btwn macula densa & AA/EE

  • engulf macromolecules stuck in filtration
  • structure
35
Q

renin triggered by:

A
  1. ↓BP
  2. sympathetics nerves
  3. macula densa cells sense ↓Na = filtration pressure in glomerulus is too low
36
Q

vasopressin aka anti-diuretic hormone

A
  • released from posterior pituitary in response to hypertonic ECF (dehydration)
  • inserts aquaporins via G coupled protein receptors that ↑ water permeability in distal & collecting tubules ➔ body is reabsorbing water
    • vasopressin binds to G coupled protein receptor in basolateral membrane & activates adenylate cyclase ➔ converts ATP to cAMP ➔ activates protein kinase A ➔ protein phosphorylation ➔ aquaporin vesicle fuses with tubular (apical) membrane to create aquaporin channels
  • promotes arteriolar vasoconstriction
37
Q

water absorption in distal convoluted tubule & collecting duct

A
  • impermeable to water under stable conditions
  • permeable to water when stimulated by vasopressin/anti-diuretic hormone (ADH) in response to dehydration ➔ body can reabsorb more water
38
Q

aldosterone

A
  • ↑ Na reabsorption in distal & collecting tubules by inserting Na channels in luminal membranes & Na/K ATPase carriers in basolateral membranes
  • ↑ K excretion
  • triggered by ↑ [K] in plasma ➔ activates adrenal cortex to secrete aldosterone ➔ cortical collecting ducts ↑ rate of K secretion & Na & H2O reabsorption ➔ ↑ K excretion in urine ∴ less K in plasma
39
Q

aquaporins

A
  • always open in proximal tubule
  • regulated by vasopressin (ADH) in distal & collecting tubules
  • ↑ permeability to water in distal & collecting tubules when activated by G-proteun coupled receptors
40
Q

Baroreceptor Control of Vasopressin Secretion

A

↓ plasma V = ↓ in BP aortic arch & carotid sinus baroreceptors stimulate secretion of vasopressin ➔ ↑ water permeability in collecting ducts so more water can be absorbed & less is excreted

  • vasopressin ↑ BP & ECF
41
Q

Osmoreceptor Control of Vasopressin Secretion

A

too much water ↓ ECF osmolarity (hypotonic) ➔ ↓ hypothalamic osmoreceptors that inhibit vasopressin secretion & makes collecting ducts less permeable to water so less water is reabsorbed & more is excreted

42
Q

micturition

A

urination

  • peristaltic contractions move urine
  • as bladder fills pressure against ureters prevents backflow, but urine can still enter
  • bladder SM inhibited by sympathetic stimulation & stimulated by paraym to contract
  • can occur by reflex action or voluntary control
  • 2 sphincters prevent continuous emptying
    1. internal urethral sphincter made of SM ≠ voluntary: when bladder relaxes sphincter closes, contracts sphincter opens
    2. external urethral sphincter made of skeletal muscle = voluntary: motor neurons continuously firing (keeping closed) until they are inhibited
  • micturition reflex (spinal cord reflex) initiated when stretch receptors in bladder wall stimulate parasympathetic pathway
    • parasympathetic stimulation = contraction
    • deliberately tightening external sphincter can prevent contraction & emptying
43
Q

internal urethral sphincter

A

prevents continuous emptying

  • made of SM ≠ voluntary
  • when bladder relaxes sphincter closes
  • when bladded contracts sphincter opens
44
Q

external urethral sphincter

A

prevents continuous emptying

  • made of skeletal muscle = voluntary
  • motor neurons continuously firing (keeping closed) until they are inhibited
45
Q

micturition reflex

A

spinal cord reflex initiated when stretch receptors in bladder wall stimulate parasympathetic pathway

  • parasympathetic stimulation = contraction
  • deliberately tightening external sphincter can prevent contraction & emptying
46
Q

cardio & renal hormones

A
  • Alsosterone ↑ Na reabsorption, BP & K+ secretion,
  • ANP inhibits aldosterone & renin secretion, ↓ BP & Na+ reabsorption ➞ ↓ECF & BP
  • vasopressin (ADH) ↑ BP through a G coupled receptor cascade that adds aquaporins to the luminal membrane of the collecting tubule cells

NPB 101 (13 decks)

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