Renal Anatomy & Disease

Question 1

Total Body Water

Answer 1

• Varies between 50-70% of body weight
• Average person (70kg) this is 42kg/42L
• Disparity between males and females is due to fat distribution
  
  • Proportionally more of males weight is due to water than females

Question 2

Body Fluid Compartments

ICF vs ECF

Answer 2

• Intracellular fluid (ICF)
  
  • 62% intracellular ~25-30L
• Extracellular fluid (ECF)
  
  • 3% transcellular ~1.5-2L (eg cerebrospinal, gastrointestinal (urine))
  • 7% plasma ~3-4L
  • 28% interstitial ~11-12L (surrounds cells - outside cells)
• Physiology is underpinned by the differences between ECF & ICF

Question 3

ICF & ECF Ion Conc.s

Answer 3

• ICF Compartment
  
  • Cations: high K⁺, low Na⁺
  • Anions: (most) low Cl^-, high proteins, bicarbonate
  • -ve membrane potential
• ECF Compartment
  
  • Cations: low K+, high Na+

Anions: high Cl^-

• ​K⁺ transport pathway: K⁺ channels in membrane allow it to leave setting up -ve membrane potential
• Cl^- moves into cell down electrochemical grdt

Question 4

ECF: Plasma

Answer 4

• Higher protein conc. in plasma than interstitial fluid
• Starling’s forces: fluid movement due to filtration across wall of capillary is dependent on the balance between hydrostatic pressure grdt & oncotic pressure grdt (osmotic pressure exerted by proteins in blood vessels) across the capillary.
• Proteins can’t cross
• Amount of Na⁺ sets up “effective circulating vol” : vol of arterial blood (vascular ECF) effectively perfusing tissue
  
  • decrease circulating vol = decrease BP

Question 5

Body Fluid Homeostasis: Daily balances of H20 & Na

Answer 5

• Inputs
  
  • Na+ 150mmoles/day (dietary)
  • H2O 2.6L/day
    
    • drink 1.2L
    • Food 1L
    • Metabolism 0.35L
• Outputs
  
  • H2O 2.6L/day
    
    • Urine 1.5L
    • Respiration, stool, sweat 1.1L
  • Na+ 150mmoles/day
    
    • Urine 140mmoles
    • Stool, sweat 10mmoles
• Conclusion: Kidneys are major site of excretion of excess fluid & Na

Question 6

Kidney: General Morphology

Answer 6

• 10cmx5.5cm, 150g
• Renal artery and vein
• Adrenal gland
• Between 12th thoracic and 3rd lumbar vertebrae, toward back
• Kidney transplant, often in pelvis

Question 7

Congenital Abnormalities

Renal Agenesis

Answer 7

• one or both kidneys fail to develop
• 1 in 2500 foetuses
• Incompatible with life
• Most: spontaneous miscarrige in 1st 3 months
• If born live, baby will die

Question 8

Congenital Abnormalities

Ectopic Kidney

Answer 8

• Pelvic kidney
• Increase risk of damage and kidney stones
• 1 in 800

Question 9

Congenital Abnormalities

Horseshoe Kidney

Answer 9

• Kidney’s fused across midline
• 1 in 1000
• Increased risk of damage and renal stones

Question 10

Kidney: Longitudinal Section

Answer 10

• Outer region - cortex (light)
• Inner region - medulla (capillaries- more dense blood supply - dark)
• Capsule - tough, fibrous layer, surrounds kidney, structure and protection (some force absorbed)
• Medullary rays - striped region (blood vessels)
• Papilla - area for drainage (blood and urine)
• Hilus - area where ureter leaves kidney
• Urine: calyx-pelvis-ureter

Question 11

The Nephron

Functional unit

Answer 11

• Several nephrons leading into 1 collecting duct
• ~6 nephrons for 1 collecting duct

Question 12

Glomerula Function

Answer 12

• Plasma filtered in glomerulus - moves into Bowman’s capsule
• After collecting duct no further regulation of compostion of urine
• Glomerulus surrounds Bowman’s capsule
  
  • Full of glomerular capillaries
  • ~20% of plasma removed
  • Plasma remaining leaves via efferent arteriole
  • Individual glomerulus per nephron
• Glomerular Filtration Rate (GFR)=125ml/min (autoregulated)

Question 13

What are the two types of nephron?

Answer 13

• Superficial nephron 85%
• Juxtamedullary nephron 15%

• Name based on where they lie
• Juxtamedullary nephron
  
  • ability to concentrate urine
  • deep within cortex
  • LoH almost exclusively in medulla

Question 14

Renal Failure

Answer 14

• Defined as a fall in GFR
• Leads to increased serum urea and creatine

Question 15

Acute vs Chronic Renal Failure

Answer 15

• Acute
  
  • reversible
  • quick onset
  • normal Hb levels
  • normal size
• Chronic
  
  • irreversible damge
  • speed of progression dependent on underlying cause (but will progress)
  • decreased Hb levels (anaemia)
  • decreased size
  • dialysis/ transplant needed
  • peripheral neuropathy present

Question 16

What is peripheral neuropathy?

Answer 16

• Nerve damage
• Present in chronic but not acute renal failure
• Leads to problems with sensation and movement

Question 17

What is the progression of renal failure?

Answer 17

• Walls of glomerular capillaries thicken ( thickening of glomerular membrane) = reduced filtration
• Damged glomeruli
• Progressive scarring of glomeri (glomerulosclerosis) - deposition of material
• Tubular atrophy - less nephrons
• Interstial inflammation - damage nephrons
• Fibrosis
• Reduction in renal size
• Acceleration of progression: damage leads to more damage
• Normal ultrasound: dark

RF ultrasound: small and bright (scarring and fibrosis)

Question 18

What are the symptoms of renal failure (uraemia)?

Answer 18

• Failure to excrete salt and water
• Poor excretion of urea/ creatine
• Leak of protein into urine
• Failure to produce erythropoetin (stimulates rbc production)
• Failure to excrete PO₄^2- - lowers serum Ca²⁺

Question 19

What are the symptoms of renal failure (uraemia)?

• Failure to produce erythropoetin (stimulates rbc production)

Answer 19

• Anaemia
• Lethargy

Question 20

What are the symptoms of renal failure (uraemia)?

• Failure to excrete salt and water

Answer 20

• Hypertension
• Mild acidosis (kidneys excrete acid)
• Hyperkalaemia - high K⁺
  
  • innapropriate firing of neurons, muscle contraction, arrhythmias
• Impacts ability for normal excitabilty

Question 21

What are the symptoms of renal failure (uraemia)?

• Poor excretion of urea/ creatine

Answer 21

• Anorexia
• Nausea
• Vomiting
• Neuropathy
• Pericarditis - inflammation of pericardium - structural support of the heart

Question 22

What are the symptoms of renal failure (uraemia)?

• Leak of protein into urine

Answer 22

• Glomerula membrane breaks down
• Anorexia
• Nausea
• Vomiting
• Neuropathy
• Pericarditis - inflammation of pericardium - structural support of the heart

Question 23

What are the symptoms of renal failure (uraemia)?

• Failure to excrete PO₄^2- -lowers serum Ca²⁺

Answer 23

• Decreased Ca impacts bones
• Metastatic calcification - Ca deposited into soft tissue - pruritus (itch)
• Bone disease
  
  • Osteomalacia - soft bones
  • Osteoporosis - less dense - weak and fragile bones

Question 24

What are the stages of renal failure?

Answer 24

• Mild renal - not progressive
  
  • GFR >75ml/min
  • No uraemic syndrome
  • Normal serum
• Mild - early bone disease
  
  • GFR 50-70
  • No uraemic syndrome
  • Subtle serum
• Moderate - anaemia
  
  • GFR 25-50
  • Mild uraemic syndrome
  • Mild serum
• Severe - salt and water retention
  
  • GFR 10-25
  • Moderate uraemic syndrome
  • Moderate serum
• End-stage - 3 days to survive - need dialysis/transplant
  
  • GFR <5-10
  • Severe uraemic syndrome
  • Severe serum

Question 25

What are the causes of chronic renal failure?

Answer 25

• Glomoerulonephritis - inflammation of glomerula membrane (30%)
• Diabetes mellitus (25%)
• Hypertension (10%)
• Polycystic kidney disease (5%)
  
  • cysts replace normal
  • enlarged kidneys - decreased function

Question 26

What are the stages to decide how to treat renal failure?

Answer 26

1. Chronic vs acute
2. Aetiology and severity
   
   • Treat cause
3. Treat reversible factors and complications
   
   • Diet: restrict protein, salt, water
   • Phosphate binders: in plasma - ‘mop up’ phosphate - treat hyperphosphorylation
   • Na bicarbonate: binds H⁺ - treat acidosis
4. Reduces symptoms and slows progression
   
   • Diuretics: for Na retention
5. Plan dialysis and transplantation