URINARY TRACT – I
The kidney
Maria M. Picken MD, PhD
mpicken@lumc.edu
Renes = latin kidneys
nephros = greek kidney
Outline:
I – the kidney
development
gross structure
vasculature
glomerulus
II – the structure and function of the
tubules
renal pelvis
ureter
urinary bladder
urethra
Objectives:
General objectives:
- to identify the kidney’s structures, function and location
- to analyze the relationship between microscopic structure and function
Specific objectives:
1. To identify elements of the gross and microscopic structure of the kidney and analyze the relationship between them
2. To list the special features of renal vasculature and correlate these with function
3. To describe and analyze the structure and function of the glomerulus as a whole
4. To describe and analyze the structure and function of the glomerular filtration barrier
5. To identify elements of the nephron and the collecting system
7. To contrast and compare the structure and function of different segments of the nephron
8. To evaluate the relationship between the vasculature and the nephron
9. To identify the elements of the juxtaglomerular apparatus and define their relationship to each other
10. To identify the general structural features of the ureters, the urinary bladder and the urethra
11. To contrast and compare the male versus the female urethra
Retroperitoneum,
Thoracic vertebra12-Lumbar vertebra3
115-170 g (M>F)
11-12 x 5-7.5 x 2.5-3 cm
- Kidneys – paired, bean shaped
- Ureters – paired
- urinary bladder
- Urethra, male versus female
Renes = latin kidneys
Nephros = greek kidney (Nephrology)
Function:
1. Filter blood & reabsorb nutrients
2. Control water, ion, and salt balance of the body
3. Maintain acid-base balance of the blood
4. Excrete metabolic wastes (urea and uric acid), toxins, drug components
5. Secrete hormones (renin, erythropoietin)
6. Produce calcitriol (active form of vitamin D – absorption of dietary calcium into the blood)
Kidney development through a series of successive phases:
- the pronephros (most immature)
- mesonephros
- metanephros (most developed) which persists as the definitive adult kidney
The final stage of kidney development, metanephros, arises caudal to the mesonephros at 5 weeks of development.
As the kidney develops in the elongating fetus, it 'ascends' from its original location (adjacent to the developing bladder)
to its mature location in the retroperitoneum, just caudal to the diaphragm.
As the kidney moves cephalad (towards the head) relative to the bladder, it takes new arterial supply from the aorta and
new venous drainage into the vena cava.
Kidney development is complex and developmental abnormalities are relatively common. They constitute an
important consideration in pediatric nephrology.
http://www.meddean.luc.edu/lumen/MedEd/urology/nlrendev.htm
Kidney structure: bean shaped
- capsule
- cortex (outer)
- medulla (inner)
- hilum (pelvis, ureter, renal artery, vein)
Cortex, renal columns (septa) of Bertin
(cortical tissue on either side of the medullary pyramids)
Medulla divided into several (8-18) – conical pyramids
Papillae at apex of medullary pyramid
Papillae lead into minor calyces
Minor Calyces lead into 2-3 major calyces
Major Calyces lead to the expanded upper end of the ureter called the renal pelvis (latin: pelvis=basin)
Glossary:
capsule - a structure enclosing an organ, usually composed of dense connective tissue
cortex - the outer portion of an organ, distinguished from its inner, medullary portion
hilus or hilum - a depression or pit at that part of an organ where the vessels and nerves enter
medulla - the inner portion of an organ, usually in the center.
See also: http://www.bu.edu/histology/m/glossary.htm
on either side of medullary pyramid
Posterior division
of renal artery
Interlobular
arteries
Kidney blood supply:
0.5% of total body weight, 25% of the cardiac output
- renal artery, anterior & posterior divisions, segmental arteries (do not anastomose, “end arteries”)
- interlobar arteries on either side of medullary pyramid
- arcuate artery (Latin = curved) between cortex and medulla, parallel to kidney surface), interlobular arteries
Posterior segment
juxtamedullary
glomerulus
- interlobular arteries → afferent arteriole → glomerulus → efferent arterioles
- efferent arterioles in the cortex form peritubular capillary plexus
- efferent arterioles of juxtamedullary nephrons (juxta [Latin] close to)
go into medulla and loop back “vasa recta” (straight vessels [Latin])
Afferent, from afferre [Latin] = to bring toward
Efferent, from efferre [Latin] = to bring out
Correlation with pathology:
- cortex: 90% of blood supply
- medulla is relatively a-vascular (10%, low oxygenation)
- tubular capillary beds derived from the efferent arterioles
- acute tubular necrosis (injury), papillary necrosis
vascular pole
Bc
*
tubular pole
Afferent arterioles arise from interlobular vessels
and supply the glomeruli
Efferent arterioles arise from glomerular capillaries
Glomerulus in paraffin section:
Bowman’s capsule (Bc)
+
glomerular tuft*
Glomerulus
Paraffin section
network of capillaries:
- mesangium: cells & matrix
(mes angium = in the middle of vessels)
- contractile
- phagocytic
- proliferation
- endothelium
- basement membrane
- 2 layers of epithelium
visceral (aka “podocytes”) – anchored on glomerular basement membrane
parietal – line Bowman’s capsule
Urinary space
podocyte
foot process (pedicel)
slit diaphragm pedicellus [Latin] small foot)
lamina rara externa
glomerular basement membrane
lamina densa
lamina rara interna
blood
fenestrated endothelium
without diaphragms
Electron microscopy of the glomerular capillary wall (aka glomerular filtration barrier):
- fenestrated endothelium (fenestra [Latin] – window)
- glomerular basement membrane – lamina rara interna & externa, lamina densa
- visceral epithelial cells (podocytes) – foot processes, filtration slits with thin diaphragm
Note: other capillaries in the kidney are fenestrated with diaphragms
Foot process
Schematic drawing of the slit membrane
- disruption of the slit diaphragms or destruction of the podocytes can lead to “proteinuria” where
large amounts of protein are lost from the blood into urine
- effacement of slit diaphragms with “fusion” of the foot processes may be transient and treatable or permanent
Examples: minimal change disease, reversible
Congenital disorder Finnish-type nephrosis - neonatal proteinuria leading to end-stage kidney failure, caused by a mutation in the nephrin gene.
Glomerular filtration barrier – glomerular basement
membrane
• Glomerular basement membrane:
combined basal lamina of
glomerular endothelium & pedicels
• High permeability to water & small
solutes
• Impermeability to proteins
- size barrier (<70,000 MW and <10 nm in
diameter proteins pass easily)
- charge dependent restriction
Pathology:
-
Proteinuria, loss of charge, slit membrane…
Hematuria - loss of integrity, “structural”
damage
Lamina rara externa & interna = heparan sulphate (-)
Lamina densa: collagen type IV, laminin (size)
Glomerular filtrate – “primary urine”:
125 ml/min; 180 L/24 hr
124 ml/min reabsorbed…
Daily urinary output 1.5 L
End of the urinary tract – part I
Questions?
mpicken@lumc.edu