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HLTH1030 > the renal system > Flashcards

the renal system Flashcards

1
Q

list the organs involved in the urinary system and the flow of urine

A
  • 2 kidneys (retro-peritenell)
  • 2 ureters (transport urine to bladder)
  • 1 bladder (storage reservoir)
  • 1 urethra (urine excretion)
  • renal pyramid - minor calyx - major calyx - renal pelvis - ureter - bladder - urethra
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2
Q

what are the functions of the kidney

A
  • excreting metabolic wastes (urea), toxins and drugs
  • activation of vitamin D
  • long term acid-base balance (pH)
  • regulation of water volume and total solute concentration (osmotic pressure)
  • gluconeogenesis to maintain equilibrium
  • regulation of ion concentration
  • produces erythropoietin (regulate RBC prod.) and renin (regulates BP)
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3
Q

describe the gross / macroscopic structure of the kidney

A
  • cortex: outer, light coloured, granular appearance
  • medulla: darker reddish-brown, cone shaped (medullary / renal pyramids)
  • nephron, structural / function unit, renal corpuscle / renal tubule
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4
Q

what are the 4 major renal processes of the kidney (overview)

A
  • glomerular filtration: produces cell / protein free filtrate
  • tubular reabsorption: selectively returns 99% of substances from filtrate to blood in tubules
  • tubular secretion: selectively moves substances from blood to filtrate in tubules
  • excretion: removal of urine from the body
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5
Q

what are the two types of nephrons

A
  • cortical: almost entirely in renal cortex, 85% of nephrons, only tip of LOH dips into medulla
  • juxtamedullary: renal corpuscle, near medulla, LOH dips deep into medulla, function in maintaining osmotic gradient
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6
Q

what blood vessels go to and from the kidney / overall pathway

A
  • arterial: aorta - renal artery - segmental - interlobar - arcuate - cortical radiate artery
  • capillaries: afferent - capillaries - efferent - peritubular capillaries (cortex, low BP, porous, absorption of water / solute) / vasa recta (medulla, formation of concentrated urine)
  • venous: cortical radiate vein - arcuate - interlobar - renal veins - inferior vena cava
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7
Q

describe the cells of the glomerulus

A
  • epithelial: surround lumen, make up BV (capillaries) of glomerulus
  • podocytes: make up filter, spider shaped, can’t self renew, support / structure, cover large areas, fluid moves in-between slits (regulate pore size)
  • mesangial: specialised, around BV, support capillary loops, engulf macromolecules that are ‘stuck’ in filtration membrane (free from debris), phagocytosis
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8
Q

how does glomerular filtration occur

A
  • barriers: filtrate crosses 3 barriers to enter glomerular capsular space
  • capillary epithelial cell layer: all blood components except BC to pass through
  • basement membrane: allows smallest proteins / most other solutes to pass through
  • epithelial layer of visceral: podocytes (filtration slits)
  • passive process: no metabolic energy (blood pressure increases the rate)
  • filtrate: fluid entering bowman’s capsule, no reabsorption into capillaries of glomerulus (amino acids, water, toxins, glucose / salt, proteins, ions)
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9
Q

what are starlings forces

A
  • hydrostatic pressure pushes water out while oncotic pressure pulls it in
  • difference between the two decides which direction water goes, opposing forces
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10
Q

what is hydrostatic pressure (HP)

A
  • glomerular blood pressure
  • pushes water and solutes out of the blood and across the filtration membrane
  • high to low hydrostatic pressure (movement from inside to outside capillary)
  • pathway: along capillary, through pores - interstitial space - semi-permeable membrane from high to low
  • pressure exerted by blood becomes lower along capillary (arterial to venous)
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11
Q

what is oncotic pressure (OP)

A
  • presence of non-permeating solutes exert an oncotic pressure, created predominantly by proteins
  • low to high (movement from outside to inside capillary)
  • pathway: draws water from areas of low solute to high solute
  • proteins cannot move across the membrane, but water can hence concentration gradient
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12
Q

provide and overview of HP and OP in the kidney

A
  • glomerular capillary HP: favours filtration from glomerulus, higher than normal BP, resistance in efferent (smaller) = pressure to build upstream - 60mm Hg
  • bowman’s capsular HP: net HP gradient favours filtration at glomerulus - 15 mm Hg
  • glomerular OP: opposes filtration, presence of proteins in plasma draws fluid back to glomerulus - 30 mm Hg
  • bowman’s capsule OP: little osmotic force, proteins are not normally present in filtrate, if present (leakage), favours filtration = 0 mm Hg
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13
Q

what is glomerular filtration rate (GFR), what effects it and how do you calculate net glomerular filtration pressure (GFP)

A
  • sum of starling forces favouring filtration minus forces opposing filtration
  • GFR outcome: V (plasma) filtered through both kidneys per unit time (125mL/min)
  • determined by: net GFP, permeability of barrier, SA available for filtration
  • key: π (oncotic pressure) and P (hydrostatic pressure)
  • favour: Pgc and πbc
  • oppose: Pbc and πgc
    GFP = (PGC + πBC ) - (PBC + πGC)
    GFP = (60 + 0) – (15 + 30)
    GFP = 60-45 = 15 mmHg (net +ve GFP)
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14
Q

what is unregulated / regulated reabsorption

A
  • UNR: different portions of the nephron differ in their capacity to reabsorb, mass reabsorption in PCT (99% recycled)
  • R: fine tuning reabsorption in DCT / CT
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15
Q

what is the solute reabsorption pathway (PCT)

A
  1. solute in filtrate within PCT
  2. through apical membrane, basolateral membrane and basement membrane of epithelial cell
  3. out of PCT through peritubular space between PCT and capillary
  4. through capillary endothelial cells and into the peritubular capillary blood vessel
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16
Q

what are the two different ways solute passes through the epithelial cells

A
  • transcellular: through tubule cells, solute enters apical membrane of tubule cells, through cytosol and exists basolateral membrane of tubule cells (active / passive)
  • paracellular: between two tubule cells, movement through leaky tight junctions particularly in PCT (water, Ca2+, Mg2+, K+, some Na+)
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17
Q

what passive tubular reabsorption occurs (PCT)

A
  • passive: through phospholipid bilayer (water)
  • facilitated: using a channel in bilayer
  • water: always passive, diffuses to area of greater osmolarity (high solute), follows salt as it increases osmolarity of peritubular fluid
  • urea: water reabsorption creates urea gradient, passive movement from tubule to capillaries dependent on water movement (~50%)
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18
Q

what active tubular reabsorption occurs (PCT)

A
  • simple A: against conc. gradient., apical / basolateral
  • NaK pump: basolateral, ATP consuming ion pump, produces gradient = Na across luminal section and K moves in opposite direction
  • secondary A: 2 molecules at same time (1 against gradient and 1 with gradient), energy released simultaneously from passive facilitates active transport (symport - same side of membrane) (anti port - opposite sides of membrane)
  • glucose: freely filtered, 100% reabsorbed at PCT, active co-transport with Na at apical membrane, simple diffusion at basolateral, ATP used in NaK pump = low intracellular Na
19
Q

what is the tubular transport maximum

A
  • maximum rate at which a solute can be transported (reabsorbed), hence all channels occupied
  • solute conc. increase = more pumps used = full capacity/ saturation of pumps = excess solute cannot be transported
  • more solute than Tm = excretion of solutes in urine
  • renal threshold: plasma conc. at which Tm is reached
20
Q

how does renal handling of glucose occur

A
  • reabsorption of glucose = proportional to plasma conc. until saturation
  • normal filtered load: 100% glucose reabsorbed
  • renal threshold: Tm reached, glucose in urine
21
Q

what is clinical correlation of diabetes mellitus

A
  • normally insulin lowers blood glucose levels
  • type 1: no insulin
  • type 2: cells don’t respond to insulin
  • glycosuria: glucose exceeds renal threshold / Tm
  • polyuria: excessive urination
  • polydipsia: excessive drinking
22
Q

what is tubular secretion (PCT)

A
  • transport of molecules from plasma of capillaries to lumen of renal tubules
  • secretion of ions (K and H), waste products (urea) and some drugs
23
Q

what is excretion

A
  • elimination of a solute and water from the body in the form of urine
  • excretion rate (E) = means of assessing renal function
  • depends on: filtered load (F), secretion rate (S) and reabsorption rate (R)
  • E = (F + S) - R
  • excretion more than filtered blood = net secretion
  • excretion less than filtered load = net reabsorption
24
Q

what occurs at the loop of henle (LOH)

A
  • establish medullary osmotic gradient (mainly juxtamedullary nephrons)
  • gradient = necessary for reabsorption
  • adjacent to vasa recta
  • outer medulla (near cortex) = lowest osmolarity (300)
  • inner medulla = highest osmolarity (1200-1400)
  • countercurrent multiplier
25
Q

what is the counter current multiplier

A
  • fluid flow in ascending / descending limbs = opposite flow of fluid
  • descending LOH: permeable to water, impermeable to solutes, water leaves = filtrate osmolarity increases
  • ascending LOH: impermeable to water, active transport of solutes
  • constant diff. of 200 osmoles between two limbs and between ascending / interstitial fluid
  • countercurrent exchanger: vasa recta, counter current, reabsorbs water / solutes without undoing gradient (highly permeable), blood = isosmotic to surrounding fluid
26
Q

what reabsorption occurs in the DCT and CT

A
  • hypoosmotic: tendency for water to move from lumen to interstitial fluid along gradient
  • reabsorption depends on gradient and water permeability of epithelium
27
Q

how does urea recycling / medullary osmotic gradient relate

A
  • urea helps form medullary gradient
    1. urea enters filtrate of LOH by facilitated diffusion
    2. cortical CT reabsorbs water, urea left behind
    3. medullary CT = urea enters interstitial fluid
    4. urea moves back to ascending limb and contributes to high osmolarity in the medulla
  • water reabsorption = increased urea conc. in fluid
  • recirculation = high conc. of urea in blood
  • excretion of necessary amounts urea in a small volume of water
28
Q

describe a summary of the overall functions and structure of the nephron

A
  • PCT: reabsorption (microvilli / highly in-folded basolateral, all nutrients (glucose and AA), most water reabsorbed, many ions (Na+), almost all uric acid, half of urea (later secreted back into filtrate)
    LOH: establishes osmotic gradient, descending limb (water can leave solutes can’t), ascending limb (water cant leave and solutes can), thin segment cells
    DCT / CT: main area of secretion (K / H), reabsorption is hormonally regulated (water, NaCl, Ca), CT (intercalated / principal cells)
29
Q

how is the kidney intrinsically controlled (renal auto regulation)

A
  • kidney focused
  • maintains nearly constant GFR when mean arterial BP is in range of 80-180mmHg
  • renal auto regulation: myogenic and tubulo-glomerular mechanisms
  • myogenic: maintain GFR, high BP = afferent constrict, restrict BF to glomerulus = less GFR (high BP = damage to filter), low BP = afferent dilates = raises glomerular hydrostatic pressure
30
Q

what is the tubulo-glomerular mechanism

A
  • high BP = high BF into glomerulus = faster filtrate flow = not enough time to reabsorb / secrete (high NaCl in filtrate)
  • juxtaglomerular complex: DCT loops and comes into contact with afferent / efferent
  • macula densa: DCT, responsive to NaCl in filtrate, directs flow / slows movement, sends signal to release renin
  • granular cells: smooth muscle of afferent, produce renin (intense vasoconstriction of afferent, reduction in BF)
  • mesangial cells: keep filter clean
31
Q

how is the kidney extrinsically controlled

A
  • entire body focused (excessive bleeding etc)
  • regulation of GFR
  • low BP = <80mmHg, essential blood to vital organs, less to kidneys
  • norepinephrine / epinephrine: SNS / adrenal medula, vascular smooth muscle to constrict (afferent) = decrease GFR
  • renin: constrict afferent
  • low ECF volume - low MAP - increase sympathetic tone - arteriole constrict - renin - low GFR / renal BF
32
Q

what is renin-angiotensin aldosterone system (RAAS)

A
  • F: constriction, stimulates thirst, ADH, aldosterone hence stabilisation of arterial BP / ECF
    1. enzyme secreted by macula densa
    2. binds with angio-tensinogen (plasma protein made by liver)
    3. forms angiotensin 1 and reacts with angiotensin converting enzyme (ACE)
    4. forms angiotensin 2 (powerful constrictor, effective on efferent (maintains GFR without decreasing RBF)
  • ACE inhibitors: prevent conversion from 1 to 2, vasodilation, diuresis, decrease MAP (treat high BP)
33
Q

what is ADH

A
  • posterior pituitary in response to angiotensin 2
  • osmorec. = change in ECF osmolarity, increased ECF = ADH secretion
  • barorec. = changes in BV / BP / MAP, decreased BP / BV = ADH (or stress, nausea etc)
  • increase water reabsorption / permeability (DCT / CT)
  • acts on: intercalated cells (simple cuboidal microvilli), type a (acid secretion / HCO3 reabsorption) and type b (HCO3 secretion / acid reabsorption), principal cells (reabsorb H2O / Na, secrete K)
  • decreased ECF osmolarity, increase MAP / BV = inhibits
  • minimum volume of water must be excreted to eliminate solutes (~440mL/day)
34
Q

what is aldosterone

A
  • adrenal cortex in response to angiotensin 2
  • increase reabsorption of Na in DCT, maintains MAP indirectly through subsequent water reabsorption
  • high aldosterone = little Na / water leaves body (lots of K leaves) = increase BP
  • principal cells (reabsorb Na / water, secrete K)
  • synthesis of new Na K channels on apical, promotes basolateral Na K ATPase’s for Na reabsorption
35
Q

what is atrial natriuretic peptide (ANP)

A
  • cardiac atrial cells if BV / BP is elevated
  • ANP increases excretion of Na = dilates afferent / constricts efferent = increase GFR = increase filtered load = increase Na secretion
  • inhibition of RAAS = decrease renin / aldosterone secretion
36
Q

how does fine tuning of osmolarity occur

A
  • regulation of water, urea and salts
  • CT uses osmotic gradient (normal = 300) to adjust urine osmolarity by varying water / Na reabsorption in DCT
  • dilute urine = eliminate excess water (50)
  • concentrate urine = conserve water (1400)
37
Q

how do we control water reabsorption (ADH)

A
  1. pituitary releases ADH, travels via blood to epithelial cells of DCT
  2. increases number of aquaporin 2 channels in apical membrane of principal
  3. aquaporins = diffusion of water across membrane
  4. CT = permeable to water, water reabsorption and concentrated of urine
38
Q

how does renal handling of K occur

A
  • ratio of extracellular : intracellular K = critical to function of excitable cells
  • K = freely filtered at glomerulus
  • unregulated: reabsorption from PCT (60%) and ascending LOH (30%)
  • regulated: secretion in late DCT / CT (diet dependent / aldosterone)
  • hyperkalaemia: K > normal
  • hypokalaemia: K < normal
39
Q

describe how K is reabsorbed at PCT and secreted at DCT

A

PCT
- from peritubular fluid into cell via Na+/K+ pump and then moves down gradient via channels in basolateral membrane to peritubular fluid
- from tubular fluid across apical membrane
- between epithelial cells to peritubular fluid
DCT
1. K+ from peritubular fluid into cell via Na+/K+ pump on basolateral membrane (secretion coupled with Na reabsorption)
2. K+ moves through principal cells towards apical membrane
3. synthesis of new K+ channels on apical membrane and movement into tubular fluid

40
Q

describe how Na is reabsorbed at PCT and DCT

A

PCT (water follows salt)
1. across apical membrane into epithelial cells via Na anti-ports / symports
2. across basolateral membrane Na/K pump
3. diffusion across capillary endothelial cell
DCT (aldosterone / ANP)
1. co transport with Cl or facilitated diffusion via channels across apical membrane
2. across basolateral membrane Na/K pump (reabsorption coupled with K secretion)
3. diffusion across capillary endothelial cell

41
Q

how is calcium conc. regulated

A
  • 70% (PCT), 20% (aLOH), remainder = DCT / CT
  • critical to function of all cells (esp. heart, muscle, bones)
  • plasma conc. = regulated
  • Ca added to plasma from bone and absorption at digestive tract
  • Ca removed from plasma by bone / kidneys
  • hypercalcaemia: high Ca, calcitonin (thyroid, increases Ca uptake by bone, decreases renal Ca reabsorption)
  • hypocalcaemia: low plasma Ca, PTH (Ca reabsorption in aLOH and DCT, resorption from bone and activation of calcitrol (Ca absorption at gut / reabsorption at kidney)
42
Q

what are examples of kidney diseases

A
  • chronic renal disease: GFR < 60 ml/min for 3 months
  • renal calculi (kidney stones): crystallised Ca, Mg, or uric acid salts in renal pelvis = block ureter (pressure / pain)
  • anuria: low urinary output (<50 ml/day)
  • UTI: dysuria (painful urination), short urethra / faecal bacteria
  • renal failure: GFR < 15ml/min = need hemodialysis or transplant
43
Q

describe the structure of the nephron

A
  • corpuscle: bowman capsule and glomerulus
  • BC: cup, hollow, surrounds glomerulus, outer parietal layer (simple squamous) and inner visceral layer (clings to capillaries, epithelial podocytes)
  • G: afferent / efferent arterioles, capillaries (porous / filtration), filters small molecules (AA, water, glucose, nitrogenous waste)
  • tubule: long coiled tube, collects filtrate, 4 parts, PCT (reabsorption), LOH (conc. gradient), DCT (secretion) and CT (secretion / excretion)
44
Q

compare ADH, ANP and aldosterone

A
  • ADH: by hyp / PP, due to high osmolarity, decreased MAP / BV, causes increased water reabsorption
  • ANP: by cardiac cells due to increased BV, causes decreased renin and increased GFR (Na excretion)
  • aldosterone: by adrenal cortex due to decreased MAP via RAAS, causes increased Na reabsorption and K secretion

HLTH1030 (9 decks)

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