Topic 15 Flashcards
Kidney functions
- maintain plasma voltume (bp MAP)
- regulate ion and H2O
- acid base balance
- eliminate waste, drugs and hormones
- endocrine
Nephron
functional unit of kidney = renal corpuscle and tubule.
Processes in nephron leading to urine formation
- glomerular filtration
- tubular reabsorption
- tubular secretion
Glomerular filtration
20% of plasma in glomerulus is filtered into bowman capsule (bulk flow across filtration membrane)
Filtration membrane of glomerular
- fenestrated endothelium
- fused basement membranes
- podocytes with filtration slits between
Glomerular filtrate
- identical to plasma minus large protein
- H2O, glucose, aa, vitamins, ions, urea, some small proteins
- pH 7.45
Net filtration pressure (NFP) =
(55+0) - (30+15) = 10 mmHg
Glomerular filtration pressure (GFP)
at this NFP, 180L/day filtrate both kidneys = 125 mL/min (entire plasma vol. filtered 65x/day). however <1% of filtered volume remains at end of collecting duct (reabsorption)
Regulation of GFR
keeps GFR from changing when bp changes. if not increase MAP and increase GFR (vice versa)
Intrinsic regulation (auto regulation) of GFR
for bp in range of resting to moderate exercise.
Intrinsic regulation of GFR in the myogenic
⇑MAP ⇒ stretch ⇒ afferent arteriole smooth muscle contracts ⇒ prevents ⇑BP in glomerulus (+ vice versa)
Extrinsic regulation
primarily SNS (arteriolar vasocon.)
- afferent low flow into glom
- efferent blood backs up in glom
Moderate SNS activation
both balance and GFR dent change much. (extreme stress, heavy exercise, hemorrhage is high GFR)
NFP can change blood OP (proteins)
- dehydration causes high BOP and low GFR
- burns, nephrotic syndrome causes low BOP and high GFR
NFP can change capsular hydrostatic P
-urinary tract obstruction (kidney stone, inflammation, rotate enlargement) causes high CHP and low GFR
Tubular reabsorption
1-1.5 L/day urine but 180 L/day filtered so 99% filtrate reabsorbed from tubules into peritubular and vasa recta capillaries
Active tubular reabsorption
requires energy. (Na, ions, glucose, aa)
Passive tubular reabsorption
no energy required. (Cl, H2O, urea.
Proximal convoluted tubule (PCT) (unregulated)
- -glucose, aa – 100% - act. transport
- -NaCl - 66% - act. transport
- -small proteins (endocytosis ⇒ aa ⇒ blood)
- -vitamins
- -obligatory (unregulated) reabsorption of H2O (osmosis as solutes reabsorbed ⇒ water “obliged” to follow)
Result of proximal convoluted tubule
- large amount of solute removed + ⇓ filtrate volume
- filtrate is isotonic to plasma = 300 mOsmoles/L (mOsm/L = unit of OP)
Loose of henle
reabsorbs into vasa recta from:
- descending limb (DL): h2o only
- ascending limb (AL): NaCl only
Distal convoluted tubule (ACT)
initial part. reabsorbs Na, Cl, Ca. impermeable to h2o
Late DCT and collecting duct (CD)
reabsorb Na which increases aldosterone and decreases atrial natriuretic peptide ANP. facultative reabsorption of h2o. ADG increase (ANP inhibits ADH)
Nephrons normally reabsorb…
→ 99% of filtered H2O
→ 99.5% of filtered NaCl
→ 100% of filtered glucose
→ 50% of filtered urea
Filtrate may contain ..
trace aa and proteins (depends on diet) but no glucose or blood
Tubular secretion
from peritubular blood into filtrate.
Main substances secreted from tubular..
- wastes e.g. urea, uric acid, some hormones
- K+ (⇑ by aldosterone)
- H+ or NH4+ ⇒ maintains blood plasma pH
Counter current multiplier mechanism
tubular reabsoption. permits excretion of urine that is dilute (100 mOsm/L) to concentrated (1200 mOsm/L). produces/ maintances vertical osmotic gradient = increase solute in ISF as you move deeper into medulla.
Within loop of henle
- – fluid flows in parallel tubes (DL, AL) in opposite directions
- – DL - permeable to H2O, impermeable to NaCl
- – AL - impermeable to H2O, permeable to NaCl - NaCl
- – As filtrate moves down DL - H2O into ISF (osmosis)
- – Highly concentrated filtrate enters AL. NaCl pumped out against gradient (200mOsm/L gradient)
- – filtrate leaving AL ( = 150 mOsm/L) is lower osmolarity than plasma due to AL imperm to H2O and AL NaCl pump
Within early DCT
more salt removed from filtrate (reabsorbed), no H2O removed ∴ 100 mOsm/L when enters late DCT
Urine production
filtrate 100 mOsm/L enters late DCT, CD
Concentrated urine
dehydrated, low bp. in late DCT, CD aldosterone increase Na reabsorb and ADH increase facultative H2O reabsorb. urine can be up to 1200 mOsm/L
Dilute urine
excess plasma h2o, high bp. in late DCT CD ANP inhibits ADH, aldosterone. impermeable to h2o, NaCl
Average urine passed per day
1-1.5 L/day
Hormonal regulation of urine renin angiotension system
renin from juxtaglomerular cells (modified smooth muscle cells of aff. and eff. arterioles).
Renin angiotension system: high renin when..
- ⇓ stretch of juxtaglomerular cells (i.e. ⇓ bp or blood volume)
- ⇑ SNS activity
- ⇓ NaCl in filtrate (detected at macula densa)
Renin angiotension system: low renin when…
- ⇑ stretch of juxtaglomerular cells (i.e. ⇑ bp or blood volume)
- ⇑ ADH, angio II
- ⇑ NaCl in filtrate
- ⇓ SNS activity
Renin converts..
angiotensinogen to angiotensin I, which is then activated to angiotensin II by angiotensin-converting enzyme (ACE)
ADH
high facultative reabsorbs h2o (late DCT, CD)
ADH high if..
- – low blood vol or P
- – ⇑ plasma osmolarity (concentration)
- – ⇑ angio II
- – nicotine, nausea
ADH low if..
- – reverse of high ADH
- – high ANP
- – alcohol
Diabetes insipidus
no ADH or no receptors. large vol. of dilute urine, ⇑ thirst, normal blood + urine glucose
Aldosterone (steroid hormone)
- ⇑ ald when angio II, high plasma K+
- turns on genes that ⇑ # of Na+/K+ ATPase in late DCT, CD
- – ⇑ Na+ reabsorption in late DCT, CD ∴ H2O follows (osmosis, if ADH present), Cl- follows (charge)
- – ⇑ K+ secretion
Atrial Natriuretic Peptide (ANP)
⇑ by ⇑ bp. result = ⇓ renin (∴ angio II), ⇓ ADH, ⇓ aldost, ⇓ vasocon ⇒ ⇑ urine vol
High SNS impulses
aff. + eff. arterioles constrict
Low SNS impulses
aff. + eff. arterioles relax
Myogenic response (stretch causes constriction) is..
powerful in kidney..
If high MAP
⇑ flow to kidney causes vasocon. (myogenic), in spite of ⇓ SNS, renin, angio II + ⇑ ANP (result of these = ⇓ vasocon.) ⇒ GFR returns to resting
Lack of ADH, aldosterone means the urine will be dilute ..
- blood volume will ⇓ (urine volume high) ∴ MAP ⇓
- -extrinsic signals correct bp, intrinsic mechanism keeps GFR constant
If large drop in bp or volume ..
vascon. signals stronger than intrinsic mechanisms ⇒ get ⇓ in GFR
Normal urine constituents
- h2o
- nitrogenous wastes
- regulated substances
- pH 4.5 to 8.0 (average 6)
Nitrogenous wastes in urine
- urea: from aa metabolism (50% reabsorbed)
- uric acid: from nucleic acid breakdown. secreted. 10% reabsorbed. poorly water soluble and accumulation= gout or kidney stones.
- creatinine: breakdown of creatine in skel. muscle. production/excretion contact. no reabsorption. used to estimate GFR (indicate kidney disease before symptoms)
Micturition (bladder) reflex
kidney to ureters to urinary bladder then contraction of sm. muscle (detrusor) produces P gradient to the urethra
Renal plasma clearance (PC)
volume of plasma cleared of a substance each mind (rate a substance is removed blood by kidney) used to estimate time a substance remains in blood
PC of substance “A”
[A] in arterial plasma
Inulin (CHO from daffodils can be used…
to estimate GFR. its filtered by not reabsorbed, secreted, metabolized so amount of urine = amount filtered
If PC
substance is reabsorbed from filtrate
If PC>GFR
substance is serviette into filtrate
Acid base balance
regulation of free H in ECF. H normally produced by metabolism
H buffered to prevent change in pH then eliminated by..
- respiratory system
- renal system
Buffer systems =
pairs of chemicals..
- bases take up H
- acids give up H
- balance of 2 minimizes pH change
Major buffer in blood
Bicarbonate system
Other buffers are..
- Hb + H HbH in rbc
- proteins –> cells, plasma
Respiratory system in control of acid base balance
eliminates CO2, short term solution. if high H get hyperventilation. is low H get hypoventilation
Renal system in control off acid base balance
eliminates H form metabolically produced acids. secretes H into tubule lumen. converse and increases blood HCO3
For each H secreted, 1 HCO3 enters blood to remove H and maintain/increase HCO3..
- – H+ (as H+) lost in urine, 1 HCO3- gained in blood
- –secreted H+ combines with filtered HCO3- ⇒ CO2 + H2O in lumen
- -no H+ is lost, but HCO3- is “reabsorbed” indirectly to maintain buffer
- – secreted H+ combines with filtered Pi ⇒ lost in urine
- result: 1 H+ (as HPi) lost, 1 HCO3- gained to blood
- – 2 ammonia (NH3) formed from 1 glutamine (aa) in tubule cell and combine with H+ to form 2 ammonium ions (NH4+)
- -result: 2H+ (as NH4+) lost and 2 HCO3- gained to blood
Acidosis
plasma pH < 7.35 (excess H) CNS depressed will result in coma, irregular heart beat. urine will contain H, HP, NH4, little HCO3
Respiratory acidosis
arterial PCO2 increase, H increase, pH decrease. due to hypoventilation (lung disease). lungs cannot compensate.kidneys increase H secretion and HCO3 into blood
Metabolic acidosis
high H from any source other than CO2. lungs increase ventilation (due o high H at peripheral chemoreceptors) and low H (but central chemoreceptors will eventually decrease ventilation due to low CO2), kidneys (if not damaged) will increase H secretion and HCO3 into blood
Example of metabolic acidosis
- diarrhea: loss of HCO3
- uncontrolled diabetes mellitus: high fat metabolism to keto acids
- strenuous exercise: lactic acid
- renal failure
Alkalosis
pH> 7.45 (fewer H). over excitation of the CNS, spasms in skel. muscle. urine will contain HCO3, no HP, no NH4 and little H
Respiratory alkalosis
arterial Pco2. due to hyperventilating. (anxiety) lungs cannot compensate. kidneys decrease secretion of H so low HCO3 to blood (lost in urine)
Metabolic alkalosis
caused by any reason but respiratory. (ex: excess vomiting, ingestion of alkaline drugs). lungs decreased H causes vent to decrease and high arterial CO2 and high H (eventually high CO2 will increase ventilation) kidneys decrease secretion of H and lower HCO3 to blood (lost in urine)
