Lecture 5 : Clearance and Measures of Kidney Function Flashcards
___ is specialized to transport urine to bladder
Ureter
Ureter has 3 layered wall:
Mucosa - Transitional epithelium and lamina propria
Muscularis - inner longitudinal, outer circular smooth muscle
Adventitia – outer CT layer holding ureter in place
Urine stretches muscularis layer – stimulates ____ of contraction which propels urine toward bladder
peristaltic waves
_____ is specialized for urine storage
Urinary bladder
Mucosa:
Transitional epithelium – stratified (barrier)
Lamina propria
Muscularis:
Detrusor Muscle – extensive smooth muscle layers; contract to void urine
Adventitia or serosa:
outer CT layer
Transitional epithelium creates barrier –
epithelium has ability to stretch or flatten, depending on “fullness” of bladder
The urinary bladder is very distensible
When empty, wall is thrown into folds called rugae; disappear when bladder is stretched full with urine
Detrusor Muscle
smooth muscle in wall stretches and thins allowing for increased storage without increasing internal pressure; under control of autonomic nervous system
urinary bladder capacity
500 – 1000 ml capacity
Trigone –
triangular region formed by openings of ureters and urethra; may be site of persistent infections
_____ carries urine out of the body
Urethra
The urethra is different in males and females:
Female: ~3-4 cm long
Male: ~20 cm long, 3 regions
Both males and females have urinary sphincters:
Internal urethral sphincter: smooth muscle controlled by ANS
External urethral sphincter:
skeletal muscle, voluntary - controlled by somatic NS
Micturition:
the act of emptying the urinary bladder
Micturition (urination, voiding) is a spinal reflex with CNS influence
______contracts detrusor muscle, relaxes internal urethral sphincter.
Parasympathetic nervous system
_______ is active during bladder filling : relaxes detrusor, and contracts internal urethral sphincter to prevent voiding.
Sympathetic nervous system
_____ Determine urine storage or emptying
CNS Centers
Urinary incontinence –
inability to control urination
weak pelvic floor muscles, pressure in pregnancy, stress, nervous system problems
Urinary retention -
bladder unable to expel urine
general anaesthesia, hypertrophy of prostate in men
may require catheterization
____ is the result of all the processes that take place in the kidney.
Urine output
____ the process of eliminating waste
Excretion:
Excretion = Filtration - Reabsorption + Secretion
Looking at the excretion rate of a substance tells us:
nothing about how the kidney handled the substance.
Excretion rate of a substance depends on:
The filtration rate of the substance
Whether the substance is reabsorbed, secreted, or both
If it is filtered at glomerulus:
it ends up in tubule and if we leave it there (don’t reabsorb it), it will be excreted.
If we leave it in the tubule, and secrete more of it into the tubule:
even more of it will be excreted.
Proximal Convoluted Tubule (PCT)
Reabsorption of all nutrients, many electrolytes, most Na+ and water (obligatory water reabsorption)
Descending limb of nephron loop
Reabsorption of water only through aquaporins
Ascending limb of nephron loop
ion of solutes (Na+, K+, Cl-)
Distal Convoluted Tubule (DCT) and/or Collecting Duct :
Regulated Reabsorption/Secretion
___________ stimulates aquaporin synthesis increasing water reabsorption (regulated water reabsorption)
Antidiuretic hormone
__________ stimulates synthesis of Na+ channels (apical) and Na+/K+ ATPase (basolateral) increasing Na+ reabsorption
Aldosterone
___________ inhibits Na+ reabsorption (so opposes effect of aldosterone)
Atrial natriuretic peptide (ANP)
_________ increases Ca2+ reabsorption
Parathyroid hormone
Tubular secretion moves substances that we don’t want from the _________ through the tubule cells into the filtrate
peritubular capillaries
Things that are secreted during tubular secretion:
Drugs and drug metabolites
Urea, uric acid, nitrogenous wastes
Creatinine (muscle metabolism)
Excess K+ (driven by aldosterone)
Excess H+ is secreted when blood is too acidic
Most secretion happens in ______, but aldosterone driven K+ secretion and some secretion for acid-base balance occurs in _______ and ________.
proximal convoluted tubule
distal tubule
collecting duct
Urinalysis
analysis of urine, can be used to diagnose disease or detect illegal substances
Characteristics of Urine:
Color -
pH -
smell -
turbidity -
Constituents -
Color: indicator of hydration, blood in urine
pH: affected by diet (high protein – acidic urine; vegetarian – alkaline)
Smell: diabetics may have sweet smelling urine
Turbidity: normal is clear; increased turbidity due to suspended particles – due to cells, urinary tract infections
Constituents: water, urea, salts, pigments
Normal Urine composition:
95% water, 5% solutes
Nitrogenous wastes:
(in urine)
Urea – derived from normal breakdown of amino acids
Uric acid – end product of nucleic acid metabolism
Creatinine – breakdown product of creatine phosphate
Normal solutes in urine (in order of decreasing concentration):
Urea, Na+, K+, PO43-, SO42-, creatinine, uric acid
less: Ca2+, Mg2+, HCO3-
Abnormal Urine composition:
Plasma proteins, RBCs, WBCs, bile pigments may indicate pathology
______ is the main mechanism for eliminating drugs from your body
Renal Clearance
Renal Clearance (C)
is the volume of plasma from which the kidneys clear (completely remove) a particular substance in one minute
Renal Clearance tells us how quickly a substance is removed from plasma, but is also an indicator of kidney function
Any compound that is completely cleared by the kidneys can be used to estimate _____
GFR
To measure Renal Clearance of a substance (ml/min):
compare the amount of substance in the plasma (mg/ml)
to the amount of that same substance that ends up in the urine (mg/min)
clearance =
excretion rate in substance / concentration rate of substance in plasma
____ is plant compound that is freely filtered, and is not secreted or reabsorbed
Inulin
Inulin
the rate at which inulin shows up in urine is the same as glomerular filtration rate (GFR)
clearance of inulin can be used to accurately determine GFR (the “gold standard”).
It is ____ and ____ to test everyone with inulin to determine GFR.
expensive
impractical
_____ is a natural body substance (breakdown product of muscle creatine phosphate)
Creatinine
Creatinine
Produced at constant rate, little is reabsorbed, a small amount is secreted
Creatinine clearance is used clinically as an estimate of GFR -
but not as accurate as using inulin
The renal clearance of a substance tells us how that substance is handled by the kidneys:
whether it is reabsorbed from the filtrate, or whether it is secreted into the filtrate, and therefore excreted in the urine
The renal clearance of specific substances can be used as an indicator of glomerular filtration rate or GFR –
monitoring GFR over time allows us to detect glomerular damage or follow the progress of kidney disease
Understanding renal clearance of drugs can help determine :
dosage levels and dosing frequencies for medications
The clearance value of a substance tells us about the net handling of a substance by the kidneys :
If inulin clearance is used to measure GFR, it can be used to compare handling of other substances
If clearance value is equal to that of inulin:
the substance is filtered but neither reabsorbed or secreted
(the amount that is filtered at glomerulus is excreted in the urine)
A clearance value less than inulin:
(meaning there is less in the urine)
suggests that the substance is filtered but at least some is reabsorbed by tubule cells
eg. Glucose: Cglucose = 0, as it is completely reabsorbed in the PCT
A clearance value greater than inulin:
(meaning there is more in the urine) suggests that the substance is filtered but also being secreted by the tubule cells and added to the filtrate
eg. Creatinine, drugs and metabolites
Renal function can be assessed by:
Monitoring urine output (volume)
Measuring levels of nitrogenous wastes in blood (to make sure they aren’t accumulating)
Monitoring appearance of nitrogenous wastes in urine
Measure glomerular filtration rate
Glomerular Filtration Rate (GFR) –
volume of filtrate formed each minute by all glomeruli
Can be used to indicate how well kidneys are functioning
Normal GFR:
~ 125 ml/min (range 90 – 125 ml/min)
(result ~180 liters filtrate per day)
GFR ___ with advancing kidney disease
decreases
Chronic renal disease:
GFR<60 ml/min
Filtrate formation decreases gradually, nitrogenous wastes accumulate in blood, blood pH becomes more acidic
Causes: diabetes mellitus, hypertension, kidney infections, trauma, heavy metal poisoning
Renal Failure:
GFR < 15 ml/min
Filtrate formation decreases or stops completely
Patients require hemodialysis or kidney transplant
Nephrons ___ with increasing age
die
The threshold for chronic kidney disease is reached sooner with ____
more disease conditions
____ performs the role of failing kidneys
Dialysis
Hemodialysis –
patient’s blood passed through membrane tubing that removes wastes, excess ions and replaces beneficial substances such as pH buffers or glucose
Using Imaging to Assess the Urinary System
Dye is injected and x-ray is taken
kidney, bladder, ureter
Pyleogram
kidney, renal pelvis, ureter
Kidney stones
(renal calculi)
very common
Solutes in urine precipitate during concentration process
