pediatric renal system

1. RENAL SYSTEM

2. ANATOMY
• Kidney lies in the
retroperitoneal space slightly
above the level of umbilicus
• 6cm and 24g in a full term
newborn to > 12cm and 150g
• Outer layer is cortex, it
contains glomeruli, proximal
and distal convoluted tubules
and collecting ducts

3. • The inner layer, medulla contains st. portions of the
tubules, loops of Henle, vasa recta and terminal
collecting ducts
• Lies from T12 –L3 of vetrebral column, next to
psoas major muscle
• Superior parts are protected by rib 11-12
• Tilted superior poles are closer to midline than lower
poles

4. • The basic funtional unit of kidney is nephron.
There are about a million nephrons in each
kidney
• Each glomerulus is made up of tuft of
capillaries and a central region of mesangium

5. • The capillaries arise from the
afferent arteriole and join to
form the efferent arteriole,
the entry and exit being at
hilum
• The capillary wall consists of
a fenestrated endothelium,
GBM and foot processes of
visceral epithelial cells.
• The glomerulus is
surrounded by the Bowman’s
capsule lined by the parietal
epithelium which is
continuous with visceral
epithelium

6. • Juxtaglomerular apparatus: the
early part of the distal tubule on
its ascent from the medulla to the
cortex lies near the glomerulus
of the same nephron
• The cells of the tubule that come
in contact with the afferent
arteriole of the glomerulus are
more dense than the rest, and are
called macula densa which stores
renin
• JGA is involved in systemic
blood pressure regulation,
electrolyte homeostasis and
tubuloglomerular feedback

7. Blood supply to each kidney usually consists of main
renal artery
Renal artery- interlobar arteries- arcuate arteries-
interlobular arteries which gives rise to afferent
arterioles of the glomeruli – glomerular capillaries
which then recombines into effferent arterioles- form a
meshwork called vasa recta- it returns to the cortex and
empty into the interlobar veins.

8. PHYSIOLOGY
• Filters blood, removes waste products, conserves
salts, glucose, proteins, nutrients and water
• Produces urine
• Endocrine functions
• Regulates blood pressure, produces renin,
erythropoietin, prostaglandins, converts vitamin D to
active form

9. It depends on the higher pressure in
afferent arteriole
The filtration barrier is constituted by
the endothelium with slit pores, BM
and podocytes of visceral epithelium
cells.
Filtration of solutes depends on their
molucular size, shape and electrical
charge.
Electrostatic hindrance
GLOMERULAR FILTRATION

10. • The filtrate contains all difffusible and ultrafiltrable
substances present in plasma. Small quantities of
protein are usually present, but are reabsorbed in
proximal tubule.
• Normally, about 20% of plasma appears as
glomerular filtrate. Bulk of it is absorbed into the
peritubular capillaries and only about 0.5% of the
volume filtered is excreted as urine

11. TUBULAR REABSORPTION
• The proximal tubule
reabsorb about 80% of the
glomerular filtrate
• Sodium gets reabsorbed
through several active
transport systems
• It is dependent on parallel
transport of bicarb, chloride,
amino acids and glucose.

12. • Tubular reabsorption of sodium and other permeable
solutes is promoted by the phenomenon of “solvent
drag” during the transport of water across the tubular
epithelium
• Sudden changes in the glomerular filtration rate are
accompanied by simultaneous and parallel changes in
tubular reabsorption

13. • The filtration rate of individual nephron is regulated
by tubuloglomerular feedback that depends upon the
functional integrity of the JGA
• Increased filtration and thus increased delivery of
sodium and chloride to the macula densa results in
local activation of renin-angiotensin mechanism. The
constrictive action of angiotensin causes reduction in
glomerular filtration
• The RAAS, prostaglandins, catecholamines, kinins
and natriuretic peptides are involved in sodium
handling

14. FUNCTION OF DISTAL TUBULES AND
COLLECTING DUCTS
• They are responsible for
urinary acidification,
urinary concentration ad
regulation of sodium
balance
• Exchange of potassium or
hydrogen ions for sodium
takes place in the distal
tububles under the
regulation of aldosterone

15. • Antidiuretic hormone mediates absorption of water
through insertion of “water channels” on the luminal
surface of cells in the collecting tubules. With low levels
of this hormone,as in central diabetes insipidus, large
amounts of dilute urine are excreted. The converse occurs
during dehydration
• The kidney helps in regulation of acid-base balance by
maintaining the plasma bicarbonate conc at 24-26mEq/L

16. MECHANISM OF URINARY CONC AND
DILUTION
• Renal medullary
interstitial
hyperosmolarity
• This is also called
corticoc-papillary
osmolarity gradient

17. • Medullary interstitial
hyperosmolarity is
produced mainly via
two mechaisms
1. Countercurrent
multipliers : occurs
along the way of loop
of Henle
2. Urea recycling in renal
medullary area

19. RAAS

20. DEVELOPMENT OF STRUCTURE AND
FUNCTION
• Differentiation of the primitive kidney is stimulated
by penetration of the metanephrons by the ureteric
bud
• Ureteric bud gives rise to the intrarenal collecting
system, renal calyces, pelvis and ureter
• Dysgenesis at various stages of development may
result in congental anomalies of kidney and urinary
tract

21. GLOMERULAR FILTRATION
• It begins between 9-12 weeks of gestation, initiating
urine formation
• Fetal urine is a major component of amniotic fluid
after 15-16wks
• The fetal kidney recieves about 2-4% of cardiac
output, whereas in the neonate, renal blood flow
amounts to 15-18% of cardiac output
• Transition from fetal to newborn thus causes a sudden
rise in GFR

22. • Serum creatinine level is high at birth reflecting the
maternal value but falls rapidly to about 0.4mg/dl by
the end of the first week
• 92% neonates pass urine within the first 48hrs
• Depending upon the solute intake, a healthy infant
excretes 15-30ml/kg/day of urine on first two days
and 25-120ml/kg/d during the next 4 weeks.

23. • The GFR is low at birth (15-20ml/min/1.73m2 in
term and 10-15ml/min/1.73m2 in preterms). These
values increase rapidly to 35-45ml/min/1.73m2 at 2
wks and 75-80ml/min/1.73m2 by 2 months of life
• Tubular function also follows a pattern largely similar
to GFR during the first few weeks of life. Compared
to adults there is reduced sodium and bicarbonate
reabsorption and limited hydrogen ion excretion. The
pH of urine in newborn is inappropriately high for
the degree of acidemia

24. PLASMA OSMOLALITY
• Kidney helps regulate plasma osmolality very
intricately
• Neonate has limited ability to concentrate urine
• An infant can concentrate his urine to a max of 700-
800 mOsm/kg whereas the older child can achieve
1,200-1,400 mOsm/kg.

25. • Growing babies utilize most of the protein available
for growth rather than catabolize it to urea. Decreased
production and excretion of urea result in a relatively
hyposmolar interstitium resulting in reduced urinary
concentration compared to older children
• The newborn can dilute his urine to a minimum of
50mOsm/kg much like older child. However, time
taken to excrete a water load is much longer in the
neonate. Therefore, delayed feeding, overdiluted or
conc. feeds are potentially harmful

26. MATURATION OF FUNCTION
• Kidney function continues to improve during the first
two years of life, at the end of which, various
parameters of renal function approach adult values, if
corrected to standard surface area.
• Structural growth parallels the functional maturation