Renal Flashcards
How is glomerular filtration rate measured?
creatinine
* if elevated = kidney disease
Significance of proteinuria?
> 150 mg/day = significant glomerular damage
Normal kidney?
Microalbuminuria?
Clinical proteinuria?
Nephrotic?
Normal
- dipstick = negative
- PCR <15
- total protein <0.150g
- ACR <2.5 (M), <3.5 (F)
Microalbuminuria
* ACR = 2.5 - 30 (M), 3.5 - 30 (F)
Clinical proteinuria
- 1+ or 2+ on dipstick
- PCR = 45 - 449
- Total protein = 0.45 - 1.49
- ACR = >30
Nephrotic
- 3+ on dipstick
- PCR > 450
- total protein > 4.5 g
- ACR >30
Microalmbuminaemia?
Significance?
excretion of almbumin in abnormal quantities but still below limit of protein detection by dipstick
* earliest expression of diabetic nephropathy!!
Tubular function in oliguric patient?
Pre-renal failure i.e. tubules working
- urine Na = <20
- Urea = >10 (urine): 1 (serum)
- osmolality = >1.5 (urine): 1 (serum)
Renal damage (tubules not working)
- Na = >40
- Urea = 3 (urine): 1 (serum)
- osmolality = <1 (urine): 1 (serum)
what hormones does kidney release? (3)
- Renin
- 1, 25 dihydroxycholecalciferol (gut)
- erythroprotein (bone marrow)
Function of kidney? (3)
- maintain water and electrolyte balance
- excrete toxic metabolic waste (urea + creatinine)
- produces renin and erythroprotein
lobe of kidney?
each medullary pyramid
basic functional unit of kidney?
nephron
what is kidney nephron made up of?
renal corpuscle and renal tubules
function of renal corpuscle?
production and collection of glomerular filtrate
Order of nephron structures?
- renal corpuscle: production and collection of glomerular filtrate
- proximal convoluted tubule: reabsorption of water, proteins, amino acids, carbohydrates + glucose
- loop of henle: creates hyperosmotic environment in medulla
- distal convoluted tubule: acid-base and water balance
Bowman’s capsule?
simple squamous epithelium at blind end of nephron that capillaries invaginate into
podocytes?
specialised epithelium which seperates blood from glomerular filtrate (sit on top of glomerular capillaries)
mesangial cells?
produce connective tissue core called mesangium
Blood supply and drainage to renal corpuscle?
How do they enter/leave?
supply = afferent arteriole drain = efferent arteriole
(enter and leave thru bowman’s capsule)
Poles of renal corpuscle?
- Vascular pole (bowman’s capsule)
* Urinary pole (opposite end - proximal convoluted tubule)
components of glomerular filter?
1) fenestrated endothelium of capillary wall
2) thick basement membrane (endothelium + podocyte)
3) filtration slits between pedicels
Function proximal convoluted tubule?
reabsorption of water, proteins, amino acids, carbs + glucose
significance of proximal tubule?
- 70% of sodium + water reabsorbed
Function of loop of Henle?
creation of hyperosmotic environment in medulla
Blood supply to medulla?
Vasa recta
structure of loop of Henle?
1) thick descedning limb
2) thin descending limb which makes ahairpin turn and becomes thin ascending limb
3) transitions to thick ascending limb
What are thick limbs of loop of Henle lined with?
Thin limbs?
Thick = simple cuboidal epithelium Thin = simple squamous
Vasa recta?
loops of thin walled blood vessels that dip down into the medulla and then climb back up to the cortex
function of distal convoluted tubule?
acid-base and water balance
What is reabsorption of Na+ in distal convoluted tubule controlled by?
Aldosterone (results in greater Na+ and water reabsorption therefore increases blood pressure)
Function of collecting tubules and collecting ducts?
Reabsorption of water under the control of ADH
what are medullary rays?
proximal + distal tubules + collecting ducts running in parallel bundles
What hormone is active in collecting ducts?
ADH (vassopresin)
* results in concentrated urine as water is reabsorbed
what are conducting areas of the urinary tract lined with?
What is special about the luminal (i.e. facing the lumen) cells?
transitional epithelium/urothelium (renal papilla, minor calyx, major calyx, bladder, urethra)
* luminal cells are called umbrella cells because they are domed = highly impermeable barrier
what exists below urothelium?
lamina propria + 2-3 layers of smooth muscle
Explain structure of urethra?
Females
- 3-5 cm
- lined by transitional epithelium then transitions to stratified squamous
Males
- 20 cm
- prostatic urethra
- membranous urethra (from prostate to bulb of penis) - it is at this point transitional epithelium changes to stratified columnar
- penile urethra = stratified columnar becomes stratified squamous
What is osmolarity?
Concentration of osmotically active particles present in a solution
Units for osmolarity?
osmol/l or mosmol/l
mosmol/l for body fluids
How is osmolarity calculated?
1) molar concentration of solution
2) number of osmotically active particles present
e. g. 150 mM NaCl
* molar concentration = 150
* no. of osmotically active particles = 2 (Na+ and Cl-)
* osmolarity = 2(150) = 300 mosmol/l
Osmolarity of body fluids?
~300 mosmol/l
Tonicity?
Effect a solution has on cell volume
e.g. hypo, hyper, iso
Isotonic?
doesn’t mean water isn’t moving across membrane – just means no net movement of water
Hypotonic?
Hypertonic?
Hypo = increase in cell volume (more water, less salt) Hyper = decrease in cell volume
Osmolarity of cell <300?
>300?
<300 = hypotonic >300 = hypertonic
Difference between 300 mM urea and 300 mM sucrose on red blood cells?
- Sucrose = isotonic (RBC impermeable)
* Urea = hypotonic
TBW males and females?
- Male = ~60% of body weight
* Female = ~50%
Total body water compartments?
What is ECF composed of?
- ICF = 67%
- ECF = 33%
ECF
- plasma (20%)
- interstitial fluid (80%)
- Lymph + transcellular fluid (negligible)
How are body fluid compartments measured?
Examples?
using “tracers”
- TBW = 3H20
- ECF = inulin
- plasma = labelled albumin
TWB = ECF + ICF (so can calculate ICF if we know TBW and ECF)
Greatest loss of water from body?
Input and output?
Urine
Homeostasis
Input = output
i.e. 2500 = 2500
How is water balance increased?
Water balance is maintained by increased water ingestion. Decreased excretion of water by the kidneys alone is insufficient to maintain water balance
Ionic composition of ICF and ECF?
ICF = more K+, less Na, less Cl, less HCO3
ECF = less K+, more Na, more Cl, more HCO3 (think sea water!)
Main ions in ICF?
K+ and Mg2+
Osmotic concentrations of ICF and ECF?
Identical ~300 mosmol/l
Fluid shift?
Movement of water between the ICF and ECF in response to an osmotic gradient
What would happen to ECF and ICF volumes for the following situations:
1) if osmotic concentration of ECF increases
2) if osmotic concentration of ECF decreases
Increases
- Would become hypertonic compared to ICF
- Cell volume decreases
Decreases
- ECF were to gain additional water but not salt
- Would become hypotonic compared to ICF
- Cell volume increases
ECF NaCL gain?
ECF NaCl loss?
- Gain = increase ECF volume, decrease ICF volume
* Loss = decrease ECF, increase ICF
Effect of gain or loss of isotonic fluid on fluid osmolarity?
Example?
No change in fluid osmolarity
(change in ECF volume only!)
* e.g. 0.9% NaCL solution
What alters composition + volume of ECF?
Kidney
Why is it vital to regulate Na?
Major determinant of ECF volume
for ICF it is potassium
What can increase/decrease of K+ lead to? (2)
1) muscle weakness (paralysis)
2) cardiac arrest
(because it plays a major role in establishing membrane potential)
What is the key role of K+?
Establishing membrane potential
Function of kidney nephrons?
- filtration
- reabsorption
- secretion
Blood supply to nephron?
- Afferent arteriole drains into glomerular capillary (called glomerulus)
- Then drains into efferent arteriole
- Efferent arteriole drains into peritubular capillaries which eventually drain into renal vein
What is the fluid that flows through nephron?
End product?
Tubular fluid
* end product is urine
difference between juxtamedullary and cortical nephrons? (3)
- Juxta = has much longer loop of henle
- Cortical = have peritubular capillaries (juxtamedullary have vasa recta, single capillary), follows loop of henle
- Juxta = able to produce much more concentrated urine
What are most nephrons?
80% = cortical 20% = juxtamedullary
Function of macula densa?
salt sensitive cells, monitor level of salt in tubular fluid
Function of granular cells?
Production + secretion of renin
What percentage of plasma that enters glomerulus is filtered?
20%
Relationship between filtration, secretion, reabsorption and excretion?
- Filtration + secretion = reabsorption + excretion
* Rate of excretion = rate of filtration + rate of secretion - rate of reabsorption
Rate of filtration =?
Rate of filtration = [X] in plasma x GFR
What is normally the value of GFR?
~125 ml/min
(plug in to equations)
so would be 0.125 l/min
Rate of excretion =?
Rate of excretion = [X] in urine x Vu
Vu = rate of urine production
Rate of reabsorption =?
rate of reabsorption = rate of filtration - rate of excretion
What if rate of filtration > rate of excretion?
Net reabsorption of that substance has occured
* rate of reabsorption = rate of filtration - rate of excretion
Rate of secretion =?
Rate of secretion of = rate of excretion – rate of filtration
What if rate of filtration < rate of excretion?
Net secretion of the substance has occured
Filtration barriers in glomerular filtration?
(1) Glomerular Capillary Endothelium (barrier to RBC)
(2) Basement Membrane (basal lamina) = plasma protein barrier)
(3) Slit processes of podocytes (plasma protein barrier)
Podocytes?
Make up inner membrane of bowman’s capsule
Which arteriole has larger diameter?
Afferent arteriole larger than efferent
what must fluid filtered from glomerulus into bowman’s capsule pass through?
three layers that make up glomerular membrane
why does basement membrane have a net negative charge?
fluid passes from capillary through endothelial cell -> basement membrane -> podocyte -> bowman’s capsule
Net negative charge – plasma proteins should be contained within the capillary (none should enter lumen of bowman’s capsule)
Forces that increase net filtration pressure? forces that compromise net filtration pressure?
so what is total net filtration pressure?
Increase
- glomerular capillary blood pressure
- bowman’s capsule oncotic pressure
Decrease
- bowman’s capsule hydrostatic pressure
- Capillary oncotic pressure
Net filtration pressure = 10 mm Hg
Starling forces?
balance of hydrostatic pressure and osmotic forces
does glomerular filtration require energy?
Biggest driver of process
No, passive
* glomerular capillary blood pressure
glomerular filtration rate (GFR)?
Biggest determinant of GFR?
rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule
* glomerular capillary blood pressure
Equation GFR?
GFR = Kf x net filtration pressure
kf = filtration coefficient
Normal GFR?
125 ml/min
Regulation of GFR and renal blood flow?
Extrinsic
* baroreceptor reflex
Intrinsic
- myogenic
- tubuloglomerular feedback mechanism
Effect of increased arterial blood pressure on GFR?
GFR increases
if BP falls, then decrease
Vasoconstriction of afferent arteriole?
Vasodilation?
Vasoconstriction = decreases blood flow to glomerulus (decrease GFR) Vasodilation = increases (thus increase in GFR)
Baroreceptor reflex GFR?
- fall in blood volume e.g. haemorrhage
- decrease BP
- baroreceptors increase sympathetic activity
- cause vasoconstriction (incl. afferent arterioles)
- decreased BPgc
- decreased GFR
- decreased urine production
Do slight changes in arterial BP cause changes in GFR?
No, renal blood blow and GFR protected over a wide range of MABP
Autoregulation (intrinsic) of GFR? (2)
Myogenic
* vascular smooth muscle constricts in response to stretching (i.e. increased BP)
Tubuloglomerular feedback
* if GFR rises, more NaCl flows into tubule causing constriction of afferent arteriole
what can cause increase in bowman’s capsule pressure?
What does this result in?
kidney stone
* decreased GFR
what can cause increase in capillary oncotic pressure?
What does this result in?
Diarrhoea
* decreased GFR
What causes decreased capillary oncotic pressure?
Resulting in?
Severe burns
* increased GFR
Plasma clearance?
A measure of how effectively the kidneys can ‘clean’ the blood of a substance (each substance will have a different plasma clearance value)
Plasma clearance equation?
Units?
clearance of X = rate of excretion of X/plasma concentration of X
otherwise written as
clearance = [X]urine x V(urine)/[X] plasma
Units = ml/min
Example of substance that clearance = GFR?
Why is this?
Inulin (creatinine can also be used)
* inulin is filtered but is NOT secreted or reabsorbed!
Example of substance for which clearance = 0?
Why?
Glucose
* it is filtered, COMPLETELY reabsorbed, and NOT secreted
Example of substance for which clearance < GFR?
Why?
Urea
* filtered, PARTLY reabsorbed, and NOT secreted
(
Example of substance for which clearance> GFR?
Why?
H+
* filtered, secreted but NOT reabsorbed
If clearance < GFR?
If clearance = GFR?
If clearance > GFR?
- clearance < GFR = reabsorbed
- clearance = GFR = substance is neither reabsorbed nor secreted
- clearance > GFR = secreted
What is para-amino hippuric acid (PAH)?
Why?
Used to measure renal plasma flow
* it is fully secreted (not reabsorbed)
Normal value of renal plasma flow?
650 ml/min
Requirements of a GFR marker?
A RPF marker?
- GFR marker = should be filtered but NOT secreted nor reabsorbed!!
- RPF marker = should be filtered AND completely secreted!
Filtration fraction?
Value?
Remaining %?
fraction of plasma flowing that is filtered into the tubules
- value = 20% filtered
- remaining 80% enters efferent arteriole then peritubular capillaries
Renal blood flow value?
What % of CO do kidneys receive?
~1200 ml.min
* kidneys receive ~24% of CO
GFR?
125 ml/min
* 180 litres/day
How much fluid is reabsorbed in the proximal tubule?
So how much, therefore, flows into loop of Henle?
80 ml/min of filtered fluid
- so 125 ml/min (GFR) - 80 ml/min = 45 ml/min
- 45 ml/min flows into loop of Henle
Substances reabsorbed in proximal tubule? (5)
Secreted in proximal tubule? (7)
Reabsorbed
* sugars, amino acids, phosphate, sulphate, lactate
Secreted
* H+, hippurates, neurotransmitters, bile pigments, uric acid, drugs, toxins
Types of reabsorption? (2)
- Transcellular (tubular)
* paracellular
How is glucose transported into cells? (2)
Either by
- Facilitated diffusion
- secondary active transport with Na+
What is essential for Na+ reabsorption?
NaKATPase carrier
active transport
How is Na reabsorbed in proximal tubule?
Due to:
- osmotic gradient
- oncotic pressure gradient
Glucose reabsorption in proximal tubule?
100% of glucose reabsorbed in proximal tubule