URINARY TRACT – IURINARY TRACT – IThe kidneyThe kidney

Maria M. Picken MD, PhDMaria M. Picken MD, PhDmpicken@lumc.edumpicken@lumc.edu

Renes = latin kidneysnephros = greeknephros = greek kidney kidney

Outline:

I – the kidneydevelopmentgross structurevasculatureglomerulus

II – the structure and function of the tubulesrenal pelvisureterurinary bladderurethra

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 function3. To describe and analyze the structure and function of the glomerulus as a whole4. To describe and analyze the structure and function of the glomerular filtration barrier5. To identify elements of the nephron and the collecting system7. To contrast and compare the structure and function of different segments of the nephron8. To evaluate the relationship between the vasculature and the nephron9. To identify the elements of the juxtaglomerular apparatus and define their relationship to each other10. To identify the general structural features of the ureters, the urinary bladder and the urethra11. To contrast and compare the male versus the female urethra

Retroperitoneum, Thoracic vertebra12-Lumbar vertebra3115-170 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 kidneysNephros = greek kidney (Nephrology) Function:1. Filter blood & reabsorb nutrients2. Control water, ion, and salt balance of the body3. Maintain acid-base balance of the blood4. Excrete metabolic wastes (urea and uric acid), toxins, drug components5. 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 animportant 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 pyramidsPapillae at apex of medullary pyramidPapillae lead into minor calycesMinor Calyces lead into 2-3 major calycesMajor 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 tissuecortex - the outer portion of an organ, distinguished from its inner, medullary portionhilus or hilum - a depression or pit at that part of an organ where the vessels and nerves entermedulla - the inner portion of an organ, usually in the center.

See also: http://www.bu.edu/histology/m/glossary.htm

Kidney blood supply: Kidney blood supply: 0.5% of total body weight, 25% of the cardiac output0.5% of total body weight, 25% of the cardiac output- renal artery, anterior & posterior divisions, segmental arteries (do not anastomose, “end arteries”)renal artery, anterior & posterior divisions, segmental arteries (do not anastomose, “end arteries”)- interlobar arteries on either side of medullary pyramid interlobar arteries on either side of medullary pyramid - arcuate artery (- arcuate artery (Latin = curvedLatin = curved) between cortex and medulla, parallel to kidney surface), interlobular arteries) between cortex and medulla, parallel to kidney surface), interlobular arteries

on either side of medullary pyramid

Interlobulararteries

Posterior division

of renal artery

- 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 towardEfferent, 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

juxtamedullary glomerulusPosterior segment

Glomerulus in paraffin section: Glomerulus in paraffin section: Bowman’s capsule (Bowman’s capsule (BcBc))

++ glomerular tuftglomerular tuft**

*BcBc

Afferent arterioles arise from interlobular vesselsand supply the glomeruliEfferent arterioles arise from glomerular capillaries

tubular pole

vascular pole

network of capillaries:network of capillaries:- mesangium: cells & matrix- mesangium: cells & matrix(mes angium = in the middle of vessels)(mes angium = in the middle of vessels)

- contractilecontractile- phagocyticphagocytic- proliferationproliferation

- endothelium- endothelium - basement membrane- basement membrane-- 2 layers of epithelium2 layers of epithelium

visceral (aka “podocytes”) – anchored on glomerular basement membranevisceral (aka “podocytes”) – anchored on glomerular basement membrane parietal – line Bowman’s capsuleparietal – line Bowman’s capsule

GlomerulusGlomerulus

Paraffin section

Electron microscopy of the glomerular capillary wall (aka glomerular filtration barrier):Electron microscopy of the glomerular capillary wall (aka glomerular filtration barrier):- fenestrated endothelium - fenestrated endothelium (fenestra [Latin] – window)(fenestra [Latin] – window)

- glomerular basement membrane – lamina rara interna & externa, lamina densa- glomerular basement membrane – lamina rara interna & externa, lamina densa- visceral epithelial cells (podocytes) – foot processes, filtration slits with thin diaphragmvisceral epithelial cells (podocytes) – foot processes, filtration slits with thin diaphragm

Note: other capillaries in the kidney are fenestrated Note: other capillaries in the kidney are fenestrated withwith diaphragms diaphragms

blood

Urinary space

fenestrated endotheliumfenestrated endotheliumwithout diaphragms

glomerular basement membraneglomerular basement membranelamina densalamina densa

lamina rara externalamina rara externa

lamina rara internalamina rara interna

podocytepodocytefoot process (pedicel) foot process (pedicel) slit diaphragmslit diaphragm pedicellus [Latin] small foot)pedicellus [Latin] small foot)

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 permanentExamples: minimal change disease, reversibleCongenital disorder Finnish-type nephrosis - neonatal proteinuria leading to end-stage kidney failure, caused by a mutation in the nephrin gene.

Foot process

Glomerular filtration barrier – glomerular basement Glomerular filtration barrier – glomerular basement membranemembrane

• Glomerular basement membrane: Glomerular basement membrane: combined basal lamina of combined basal lamina of glomerular endothelium & pedicelsglomerular endothelium & pedicels

• High permeability to water & small High permeability to water & small solutessolutes

• Impermeability to proteinsImpermeability to proteins - size barrier - size barrier ((<70,000 MW and <10 nm in

diameter proteins pass easily)

- charge dependent restriction- charge dependent restriction

Pathology:- Proteinuria, loss of charge, slit membrane…- Hematuria - loss of integrity, “structural”

damage Lamina rara externa & interna = heparan sulphate (-)Lamina rara externa & interna = heparan sulphate (-)Lamina densa: collagen type IV, laminin (size)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