S2 Development of the urinary system and Measurement of Kidney function Flashcards
how does the urinary system develop in summary
embryonic kidney and gonad both originate from the urogenital ridge, a region of intermediate mesoderm
the organisation of intermediate mesoderm leads to 3 system developing sequentially , the disappearance of one system marks the start of the next
where does the kidney system first appear
cervical region- the pronephros
describe the pronephros
the first kidney system - never functions in humans
produces the pronephric duct which extends to the cloaca and drives the development of the next stage (becoming the mesonephric duct)
appears - start of week 4
regresses- end of week 4
functional - no
describe the mesonephros
the mesonephros sprouts tubules
uses duct by pronephros to connect to the cloaca
these tubules plus the mesonephric duct make up the embyronic kidney
the mesonephric duct sprouts the ureteric bud, which induces development of the definitive kidney
the mesonephric duct also has role in the development of the male reproductive tract
describe the metanephros
induces the development of the definitive kidney within the intermediate of the caudal region of the embryo
it expands and branches into the metanephric blastema forming the definitive kidneys structure - minor calyx and major calyx
the collective system is derived from the ureteric bud itself
the excretory component is derived from the intermediate mesoderm under the influence of the ureteric bud
describe the ascent of the kidney
the metanephric kidney first appears in the pelvic region
undergoes apparent caudal to cranial shift crossing the arterial fork formed by vessels returning blood from the foetus to the placenta. gonad in turn descends
do the kidneys move during development
no, development is cranial to caudal and the trunk just extends downwards making it appear as though the kidneys move
does the blood supply change as the kidneys ascend
as the kidneys ascend, they receive their blood supply from new branches and the original disappear.
H/e if the original remain they form accessory renal arteries which are end arteries so have no collateral blood supply
what is renal agenesis
ureteric bud fails to interact with the intermediate mesoderm so cant form kidney. can affect one (unilateral) or both (bilateral, can’t survive ) kidneys
describe migration defects of the kidney
if a kidney fails to cross the arterial fork, it ends up much lower than it should be
during ascent of the kidneys, the kidneys lie extremely close to one another, their inferior poles can fuse and can form a horseshoe kidney (B)
describe duplication defects of the kidney
splitting of the ureteric bud, results in an ectopic ureteral opening, for e.g. into the vagina or urethra, bypassing the bladder and causing incontinence
what is cystic kidney disease
multicystic kidney disease - atresia of ureter
polycystic kidney disease - recessive, presents early and poor prognosis
what is the urogenital sinus
the bladder is a hindgut derivative, it is derived from the caudal portion of the primitive gut tube formed during embryonic folding in the fourth week of development
the cloaca is divided by the urorectal septum into the urogenital sinus( future bladder and urethra) and anorectal canal ( future rectum and anal canal)
the lumen on the allantois becomes obliterated to become the urachus - the median umbilical ligament in adults
what is the structure to the urogenital sinus
superior part connects to umbilicus
majority differentiates to form the urinary bladder
inferior part develops into the urethra
how does the male bladder form
mesonephric duct reaches urogenital sinus
ureteric bud sprouts from MD - ureteric bud will become ureter opening into the bladder
smooth musculature appears
UBs and MDs make independent openings in UGS
prostate and prostatic urethra formed. MD is maintained in males forming the prostate and ducts of the male reproductive system
how does the female bladder form
develops in the same way as men but without male hormones, the mesonephric duct regresses, therefore females do not form the prostates or the tubes of the male reproductive system
how is the urethra formed
the female urethra is formed by the pelvic part of the urogenital sinus
the male urethra is divided into four parts
1. pre - prostatic
2. prostatic
3. membranous
4.spongy
what is hypospadias ?
a defect in fusion of urethral folds. the urethra opens onto the ventral surface, rather than at the end of the glans
how is kidney function measured
measured in terms of GFR ; the amount of filtrate produced from blood flow per unit time
normal GFR is 90-120 ml/min/1.73m2
the normal total glomerular filtrate per day is 140-180 L/day
depends on factors such as gender size age pregnancy
when does nephron development finish
by 35-36th week of foetal development
premature and LBW infants have lower nephron numbers
foetal excretion predominantly via placenta
why does GFR decline after ~ 30 yrs
loss of functioning nephrons
kidney volume reduces with age
describe compensatory hypertrophy of the kidneys
reduced nephron number so exisiting nephrons get bigger
healthy kidney also gets bigger
nephrons end up working harder so can wear out
occurs mainly in childhood
what happens to GFR in pregnancy ?
in pregnancy, GFR increases by 50% kidney size also increases but nephron number remains constant
what happens to GFR in disease
GFR varies between people but in one person it remains constant. if it declines this may be due to decline in nephron number or decline in GFR within the individual nephrons
what does a fall in GFR indicate
a fall in GFR means that kidney function has worsened a rise means that kidney function has recovered. when kidney function declines slowly , individual nephrons may hypertrophy so actual GFR may not fall until significant damage has occured
how do we measure kidney function
cannot measure GFR so we measure clearance - the volume of a substance of plasma cleared of a substance per unit of time
renal clearance = excretion rate / plasma concentration
excretion rate = U * V u = amount in urine v= urine flow rate
what criteria should a substance meet to measure kidney clearance
be produced at a constant rate
be freely filtered across glomerulus
not be reabsorbed or secreted into the nephron
if all these are true then excretion rate = GFR
describe inulin clearance
inulin used to measure renal clearance - therefore a surrogate for GFR
most accurate
h/e measurement is impractical due to continuous IV or a catheter
what is 51 Cr-EDTA ?
radio-active labelled marker. Approx 10% lower clearance than inulin. used clinically in children or where indication of renal function required e.g kidney transplant
what is creatinine and can it be used a measure of kidney function
end product of muscle metabolism
measured by collecting urine over 24 hours and measurement of serum creatinine(via blood sample)
gives an estimate of GFR (10-15%) as creatinine is secreted into the tubule. used in pregnancy
how are creatinine levels affected
intake
metabolism
renal excretion
furthermore, muscular black men who eat meat shall have higher serum creatinine than old vegetarian asian females (wth?!)
Serum creatinine remains stable in individuals so most common way to measure but can reflect different GFRS in different individuals
SC levels are inversely proportional to GFR but the relationship is non-linear - downwards curve
what is estimated GFR
SC varies between individuals and does not accurately predict GFR. MDRD eGFR is used in some hospitals but it is inaccurate in those without kidney disease, kids, elderly and pregnancies
less accurate with mild kidney disease due to reduction in GFR, reduced nephrons leading to nephron hypertrophy, reduced filtration of creatinine
eGFR taken from serum creatinine and not all changes in serum creatinine are due to change in GFR
