أسئلة الأولى نفرو حورس

Anatomy of the Kidney

• Kidneys have a bean-shaped structure.
• Kidneys measure 11 cm x 6 cm x 3 cm.
• Adult kidneys weigh between 120-170 grams.
• The kidneys are enclosed in a fibrous capsule.
• The hilum, located medially, contains the components:
  • Renal artery
  • Renal vein
  • Lymphatics
  • Pelvis of the ureter
• The kidney is surrounded by peri-renal fat.
• Kidneys are located in the paravertebral gutter on the posterior abdominal wall, retroperitoneally, and opposite the 12th thoracic to the 3rd lumbar vertebra.
• The right kidney sits lower than the left due to the liver, with its lower pole reaching one finger breadth above the iliac crest.

Pelvis of Ureter and C/S

• The pelvis of the ureter branches inside the kidney into 2-4 major calyces, each branching into several minor calyces.
• Outer cortex:
  • Is 1 cm thick.
  • Has a granular appearance.
  • Contains extensions of pyramids forming columns of Bertini.
• Parenchyma contains 8-18 striated pyramids.
• Inner medulla:
  • Has a conical shape.
  • Its base is at the cortico-medullary junction.
  • Apex projects into minor calyces as papillae.

Surface Anatomy

• Upper pole is at the 11th rib (2.5 cm from the midline).
• Lower pole is at the disc between L3 and L4 vertebrae, 7.5 cm from the midline.
• Hilum lies at the transpyloric plane (opposite the 1st lumbar spine, 5 cm from the midline).
• The kidneys are situated within Morris's rectangle, defined by 2 horizontal and 2 vertical lines:
  • Horizontal lines are opposite the spine of T11, L3 vertebrae.
  • Vertical lines are drawn 2.5 cm and 7.5 cm from the median plane.
• The kidney is vertical, with the upper pole medial and the lower pole lateral.

Blood Supply of the Kidney

• Renal arteries originate from the aorta opposite the intervertebral disc L1-2.
• In the hilum, the renal artery branches into anterior and posterior arteries, which form interlobar arteries that run between renal pyramids.
• At the corticomedullary junction, they form arcuate arteries that run along the base of the pyramids and branch into interlobular arteries at a 90° angle.
• Interlobular arteries penetrate the cortex and form afferent arterioles, which invaginate Bowman's capsule to form the glomerular tuft.

Nephrons

• A nephron consists of a renal corpuscle (glomerulus) connected to a complicated and twisted tubule that finally drains into a collecting duct.
• The tubular part of the nephron is made of a proximal tubule and a distal tubule connected by the loop of Henle.
• Nephrons are classified based on the location of renal corpuscles within the cortex:
  • Superficial nephrons
  • Midcortical nephrons
  • Juxtamedullary nephrons
• Superficial and mid-cortical nephrons have a short loop of Henle that turns back in the outer medulla or even in the cortex.
• Juxtamedullary nephrons have long loops of Henle that turn back at successive levels of the inner medulla.

Glomerulus (Renal Corpuscle)

• The glomerulus is a modified capillary structure where glomerular filtrate exits into Bowman's capsule.
• The renal corpuscle consists of two modified structures of different embryonic origins: Bowman's capsule and tuft of capillaries.

Bowman's Capsule

• Space lined by basement membrane and flat epithelial cells.
• There are two layers:
  • Outer parietal layer: Lined by flat epithelial cells.
  • Inner visceral layer: In contact with capillary tuft lined with visceral epithelial cells (podocytes).
• There is a space called the urinary space between the two layers.

Glomerular Capillaries

• Modification of the end of the afferent arteriole, which divides into several primary branches, which in turn give rise to several lobules of capillaries.
• The other end of this capillary tuft gives rise to the efferent arteriole.
• Component:
  • Line glomerular capillaries.
• Basement membrane:
  • Covered from inside with endothelial cells and from outside by epithelial cells (podocytes).
  • Formed of type IV collagen and negatively charged glycosaminoglycans.
• Cytoplasm: The thin cytoplasm of the endothelial cells shows multiple open fenestrae.
• Outer epithelial cells:
  • Show elongated foot processes which rest on the outer surface of GBM.
  • The foot processes interdigitate with those of nearby epithelial cells to form slit pores.

Mesangium

• Located at the hilum of the glomerulus and extends between capillary loops.
• Composed of special cells and matrix.
• Function is to support the capillary tuft, phagocytic, and contractile functions.

Efferent Arterioles

• From the outer and middle cortical glomeruli: efferent arterioles get down between tubules where they divide into capillary networks called peritubular capillaries.
• From the inner cortical glomeruli: efferent arterioles penetrate deeply into medullary pyramids forming vasa recta, which share in the medullary countercurrent exchange system.

Juxta-glomerular Apparatus

• A specialized structure present at the hilum (vascular pole) of glomerulus.
• Includes:
  • Macula densa cells: Modified cells in the distal convoluted tubule (DCT) that detect changes in luminal NaCl concentration.
  • Epithelioid cells: Modified cells in the wall of afferent arterioles that contains renin granules.
  • Lacis cells: Interstitial cells in continuity with mesangial cells.

Functions of the Kidney

• Excretory:
  • Production of urine
  • Elimination of waste products and toxins.
• Metabolic:
  • Control of water and electrolyte balance.
• Regulation of Acid Base balance:
  • Secretion of H+ ions and bicarbonate reabsorption
  • Formation of ammonia and titratable acidity
• CVS:
  • Control of blood pressure.
• Hemopoietic:
  • Erythropoiesis in BM through secretion of erythropoietin.
• Endocrine:
  • The kidney forms, activates, or degrades many hormones:
    • Renin
    • Prostaglandins
    • Active vitamin D
    • Bradykinin
    • Erythropoietin

Functions of Different Segments of Nephron

• Proximal Convoluted Tubule (PCT): - Reabsorption of 65-80% of its H2O, Na+, K+ and Cl-. - Selective reabsorption of glucose, amino acid, & bicarbonate.
  • Secretion of weak acids & weak bases at the distal part of PCT.
• Loop of Henle:
  • Acts as a countercurrent multiplier system.
  • Reabsorption of 25% of filtered Na+ in the ascending thick limb.
  • This segment is impermeable to H2O.
  • The fluid leaving this segment is hypotonic to plasma
  • The Vasa Recta is permeable to water and solutes accumulating in the renal medulla.
    • Its loop structure minimizes the loss of sodium chloride and urea from the renal medulla maintaining its hypertonicity.
• Distal convoluted tubule (DCT): - Reabsorption of some sodium chloride and calcium. - It is impermeable to water and is relatively insensitive to aldosterone or ADH.
• The collecting duct: - Reabsorption of Na+ actively (under control of aldosterone). - Excretion of K+ and H+ (related to Na+ reabsorption and aldosterone). - Reabsorption of water (under the control of ADH).

Concentration and Dilution of Urine

• This process is facilitated through:
  • The countercurrent multiplier system in the Loop of Henle.
  • The effect of ADH on the collecting tubules.

Investigations of Renal Disease

• Lab (Biochemical) studies:
  • Urine tests: Routine / Culture (Microbiology).
  • Renal Function Tests (RFT): Assessment of glomerular and tubular functions.
• Immunological tests: - Autoantibodies - Complement - Immunoglobulins
• Pathology (Biopsy/Tissue): - Light Microscopy (LM) - Immunofluorescence Microscopy (IFM) - Electron Microscopy (EM)
• Radiology:
  • KUB
  • IVU
  • US
  • CT/MRI
  • Doppler US
  • Cystography
  • Voiding cystourethrography
  • Angiography
  • Digital subtraction angiography
  • Radionuclide imaging
    • Static imaging (DMSA)
    • Dynamic (DTPA)

Biochemical - Urine Analysis

• This is a valuable method for screening if renal diseases.
• Look at the following:
  • Physical characteristics: colour, odour, transparency, and presence of froth.
  • Dip-stick test: To determine certain urine chemicals e.g. glucose, albumin, Hb, result in change in colour.
  • Cells (RBC's, leukocytes,)
  • Casts (hyaline, RBCs, leucocyte, granular casts)
  • Crystals (uric acid, oxalate)
  • Bacterial count of ≥100,000 is diagnostic of a urinary tract infection.
  • Sterile Pyuria: Repeated negative urine culture in the presence of pyuria.
• Causes:
  • TB, Anaerobes
  • Stones
  • Chlamydia
  • Viral infection
  • Malignancy
  • SLE
• Urine Protein quantification:
  • Protein in 24 hours urine collection (normally < 150 mg/24 hours)
  • Albumin/Creatinine Ratio in random urine sample (normally < 0.1)

Renal Function Tests

• Glomerular: -SCr (normally is 0.6-1.2 mg/dl) -GFR (> 90) -Plasma urea (15-40 mg/dl) -BUN (8-13 mg/dl)
• Tubular:
  • Urine Acidification Test:
    • Ammonium chloride test
    • Tests the ability of the kidney to acidify urine (excrete H+).
  • Urine Concentration Test:
    • Water deprivation / Vasopressin test
    • Examine early morning urine specimen for osmolality.
    • If it is > 700 mosmol/L, concentrating capacity is considered normal.
  • Urinary B2-macroglobulin:
    • Marker for tubular diseases
    • Analgesic and toxic nephropathies
    • Fanconi's syndrome

Immunological Investigations

• Hypocomplementemia (C3, C4):
  • Post streptococcal glomerulonephritis
  • Shunt nephritis
  • Lupus nephritis
  • Membrano-proliferative glomerulonephritis
• Autoantibodies:
  • Antinuclear Antibodies (ANA)
  • Anti-DNA
  • Antineutrophil Cytoplasm Autoantibodies (ANCA)
• Immunoglobulins: - Serum IgA: high in IgA nephropathy and HSP. - Serum IgE: high in minimal change nephritis & allergic nephropathies.

Kidney Biopsy

• Indications:
  • Nephrotic syndrome
    • Adults with nephrotic syndrome
    • Children with steroid resistant or dependent nephrotic syndrome
  • Renal impairment of unknown etiology
  • Systemic lupus erythematosus (SLE) with renal disease
• Complications: - Hematoma - Hematuria - Pain - Intrarenal AVF
• Requirements before biopsy: - Blood picture - Platelet count - Coagulation profile

Radiological - Renal Function Tests

• Assessment of Renal Size: Look for Obstruction
• Assessment of Contour: Look for a Renal mass
• Assessment of Echotexture: Look for a Renal cyst
• Assessment if there is a Stone: Look for Perirenal collection

Renal US

• Longitudinal and Transverse View

Pelvic US

• Bladder mass
• Residual urine
• Prostate lesions

Doppler US

   - Renal artery stenosis
   - Renal vein thrombosis

Voiding Cystourethrography

• Diagnosis of Vesico-Ureteric Reflux.

Computerized Tomography

• Helps in the diagnosis of:
  • Peri-renal lesions
  • Retroperitoneal space lesions (lymphadenopathy, tumors)
  • Solid renal masses
  • Stones & obstructive uropathy

RadioNuclide Scan

• DMSA Scan:
  • Tracer retained
  • Helps in diagnosis of:
    • Renal scarring
    • Renal tumors
    • Anatomic abnormalities
• Dynamic renal imaging (DTPA):
  • Tracer not retained
  • Helps in diagnosis of:
    • Renal vascular occlusion (embolism or thrombosis or stenosis)
    • Ureteric obstruction
    • Measurement of GFR and renal blood flow