Renal anatomy and physiology

• Renal stenosis is the most common cause of secondary hypertension:

  • Typically due to atherosclerotic disease
  • Presents with accelerated or difficult to control hypertension
  • Reduced perfusion to the kidney leads to activation of the RAAS pathway
  • Diagnosis is with duplex ultrasound, MRI or CT
  • Anti-hypertensive medication, angioplasty and stenting
• Ammonia is converted to urea in the liver by the urea cycle

  The kidney then excretes the urea

  Raised urea = dehydration, GI bleed, trauma, infection and malignancy

  Low urea = malnutrition, liver disease (high ammonia) and pregnancy
• Creatinine is a waste product of muscle metabolism excreted entirely by the kidney

  Serum creatinine level is naturally higher in individuals with greater skeletal muscle mass

  A raised creatinine level is an indicator of kidney dysfunction
• Function of the kidneys:

  • Regulation of the water and electrolyte content of the body
  • Excretion of waste product (e.g. urea), water soluble toxic substances and drugs
  • Retention of substances vital to the body such as protein and glucose
  • Maintenance of acid/base balance
• Endocrine functions:

  • Secrets renin - RAAS
  • Makes active form of vitamin D
• Kidneys and abdominal part of the ureters are retroperitoneal - pain often refers to the bank/flanks
• The right kidney is slightly lower than the left kidney
• Renal arteries enter the hilum at L1 - transpyloric plane
• Kidneys are protected by the 11th and 12th ribs
• Ureters run along the tips of the transverse spinal processes
• Muscles that protect the kidneys:

  ·       Lateral- transversus abdominis muscle

  ·       Quadratus lumborum muscle

  ·       Medial- psoas major muscle (main hip flexor muscle)
• Morrison’s pouch/hepatorenal space- space between the liver and right kidney due to fold of peritoneum- fluid can collect here (especially after pelvic injury)
• Posteriorly the kidneys span T12-L3
• Pleura of the lungs overlap the kidneys
• Gross anatomy of the kidney:

  • Cortex - around the edge
  • Medulla starts at the pyramids
  • Pyramids go into the minor calyx
  • Minor calyx join together to form the major calyx
  • Major calyx becomes the renal pelvis which drains into the ureter
• Nephrons are within the pyramid of the renal medulla
• Renal arteries arise as a pair from the abdominal aorta at L1 - branch to supply segments of the kidney
• Venous drainage of the kidneys is by the paired renal veins to the inferior vena cava
• ·       Left gonadal vein drains into the left renal vein before draining into the IVC

  ·       Right gonadal vein drains directly into the IVC
• Nephrons:

  • blood enters via the afferent arteriole
  • Leaves via he efferent arteriole
  • Microscopic functional units of the kidney - filtration, reabsorption, secretion and excretion
• Proximal convoluted tubule is where the majority of reabsorption occurs

  The driving force of reabsorption is sodium - e.g. SGLTs co-transport sodium with glucose
• The loop of henle in the nephrons is the urine concentrating mechanism
• The main role of the collecting duct is reabsorption of water through the action of ADH and aquaporins
• Kidney can help compensate for blood acidosis/alkalosis

  Will reabsorb bicarbonate when there is respiratory acidosis

  Will secrete bicarbonate when there is respiratory alkalosis
• Glucose acts as an osmotic diuretic

  • There is a balance in filtration and reabsorption until cannot reabsorb anymore so has to be excreted in the urine
  • The glucose in the urine acts as a diuretic - water moves with it
  • Causes polyurea in diabetes
• Kidney metabolism:

  ·       Kidney produces active form of vitamin D

  ·       Vitamin D maintains calcium balance in the body

  ·       Leads to increased calcium absorption in the small intestine, increased urinary calcium re-absorption in the kidneys and increased bone metabolism

  ·       Patients with renal failure can develop secondary hyperparathyroidism as a response to low plasma calcium levels

  ·       Kidneys produce erythropoietin- CKD patients are normally profoundly anaemic but don’t get transfused due to risk of fluid overload and sensitisation prior to transplant
• Duplex collecting system- two ureters – usually asymptomatic but susceptible to infection and reflux into the kidneys that can cause scarring
• Horseshoe kidney- fusion of lower poles of the kidney and not fixed to the abdominal wall- more risk of injury. Usually asymptomatic but more risk of traumatic injury, stones and transitional cell cancer
• Pelvic kidney- usually asymptomatic but more chance of kidney infection due to shorter ureter
• Vesico-ureteric reflex:

  • Most common in young girls around 3 years old
  • Failure of the valve mechanism at the opening of the ureter opening into the bladder
  • Reflux up to the kidneys
• Hydronephrosis = swelling of the collecting system in the kidneys - long term leads to scarring

  Hydroureter = dilation of the ureter normally due to a stone or blockage - can lead to hydronephrosis
• Posterior urethral valves:

  • Tissue blocks the urethral opening
  • Commonest bladder outflow obstruction in newborns- only affects boys
  • Can lead to UTI and CKD
  • Leads to hydronephrosis and hydroureter
• 80% of renal cancers are renal cell carcinomas

  When the cancer arises in the renal pelvis it is a urothelial transitional cancer
• Renal cell carcinoma often presents quite insidiously- haematuria, mass, weight loss, anaemia
• Renal tract calculi can get stuck in the minor and major calyxes and the ureter

  Stones normally calcium and oxalate = radiopaque
• Typical presentation of kidney stones = colicky loin to groin pain

  Can shoot to scrotum in males
• Management of kidney stones:

  ·       Ureteroscopy and laser ablation

  ·       Extra corporal shock wave lithotripsy
• The bladder is supplied by the superior and inferior branches of the internal iliac arteries

  Veins from the bladder drain into the internal iliac vein
• Bladder muscle = detrusor muscle
• Ureter enters the bladder posteriorly in the center of trigone (triangular area)