Examine how health is impacted by disordered physiological and mental ill-health.
Analyse the findings of nursing assessments, explaining the underlining disordered physiology.
Apply the principles of pharmacodynamics, pharmacokinetics, and pharmacology to disordered physiology, and the safe and accurate administration of medication.
Accurately process information gathered during assessment and observations to identify the abilities and needs of people and families and use this to develop evidence-informed person-centred plans of care.
Lecture Learning Outcomes
Review the structure and function of the renal system.
Consider normal and abnormal parameters associated with the renal system.
Critically review the pathophysiology of the renal system.
Apply this knowledge to the nursing considerations needed to safely care for a person with altered renal function.
Components of the Renal System
Kidneys: Left and Right
Ureters: Left and Right
Bladder: Medial
Urethra: Medial
Anatomical Location of the Kidneys
Shape: Bilateral bean-shaped, reddish-brown in appearance.
Location: Retroperitoneal (behind the peritoneum), in the abdominal cavity, either side of the vertebral column, usually extends from T12 to L3 (the right kidney is usually slightly lower due to the presence of the liver).
Size: Approximately 3 vertebrae in length.
Adrenal Glands: Sit immediately superior (on top) of the kidneys.
Renal Structure
Renal Capsule: Tough fibrous capsule surrounding the kidney.
Perirenal Fat: Collection of extraperitoneal fat surrounding the kidneys.
Renal Fascia: Encloses the kidneys and the suprarenal glands.
Pararenal Fat: Mainly located at the posterolateral aspect of the kidney.
External Structure of the Kidney
Shape & Size: Bean-like shape, approximately 12 cm x 7 cm x 4 cm, and weighing around 150g.
Hilum: Medial concave border that includes the entry and exit points for the renal artery, renal vein, ureter, and nerves. It serves as the gateway to the internal structures of the kidney.
Internal Anatomy of the Kidney
Renal Cortex: Reddish-brown due to the presence of glomeruli, blood vessels, and parts of the nephrons; extends into the inner kidney via renal columns; separates renal pyramids.
Medulla: Contains cone-shaped structures called renal pyramids, usually 8-18 per kidney, characterized by a striated appearance due to nephron loops and collecting ducts.
Renal Pyramids: The base faces the cortex, and the apex (renal papilla) points inwards; pyramids drain urine into minor calyces.
Internal Structure of the Kidneys
Minor and Major Calyces: Urine is initially collected in minor calyces; several minor calyces converge to form major calyces (usually 2-3 per kidney).
Renal Pelvis: Major calyces merge to create a funnel-shaped structure that collects urine and drains it into the ureter; located at the hilum.
Functional Unit of the Kidney
Nephron: Approximately one million nephrons per kidney.
Bowman's Capsule: Surrounds a network of capillaries called the glomerulus (the renal corpuscle, where blood filtration occurs).
Filtered fluid enters the Proximal Convoluted Tubule (PCT), which is a twisted segment of nephron located in the cortex.
The Loop of Henle dips into the medulla, consisting of descending and ascending limbs, essential for urine concentration.
The Distal Convoluted Tubule (DCT) is in the cortex and drains into the collecting ducts.
The Collecting Ducts run through the renal pyramids and merge with others to deliver urine to the renal papillae.
Vascular Supply to the Kidney
Renal Artery: Blood is supplied to the kidney via the renal artery, which branches directly off the aorta at approximately L1-L2; about 20-25% of the cardiac output flows to the kidneys.
Some Filtration Facts
The kidneys filter approximately 180-190 liters of blood per day, with only 1-2 liters becoming urine.
The normal glomerular filtration (GFR) rate is 125 ml/min.
Blood passes through the kidneys 180-300 times per day.
Functions of the Kidney: A WET BED
A = Acid-base balance: Maintains the body’s pH balance.
W = Water balance: Regulates the body’s water levels.
E = Electrolyte balance: Maintains electrolyte levels.
T = Toxin removal: Filters waste products and toxins from the blood.
B = Blood pressure regulation: Helps regulate blood pressure through the renin-angiotensin system.
E = Erythropoiesis: Stimulates production of red blood cells.
D = Vitamin D activation: Converts vitamin D into its active form for calcium absorption.
Detailed Kidney Functions
Acid-Base Balance:
Blood pH must be maintained between 7.35 – 7.45.
Kidneys excrete hydrogen ions (acid) into urine and reabsorb bicarbonate (base) into the blood as needed to prevent acidosis or alkalosis.
Water Balance:
The kidneys adjust urine concentration and volume, conserving water during dehydration and excreting excess during overhydration, thus maintaining blood pressure and volume.
Electrolyte Balance:
Regulates key electrolytes such as sodium, potassium, calcium, and phosphate through filtration, excretion, and reabsorption.
Toxin Removal:
Filters blood to remove nitrogenous wastes (urea and creatinine) to prevent toxic buildup in urine.
Blood Pressure Regulation:
Through the renin-angiotensin-aldosterone (RAAS) system, kidneys adjust vascular resistance and sodium/water retention. Renin release triggers the production of angiotensin II, leading to vasoconstriction and fluid retention.
Erythropoiesis:
The kidneys detect low oxygen levels and release erythropoietin (EPO), stimulating bone marrow to produce red blood cells.
Vitamin D Activation:
Inactive vitamin D is converted into calcitriol (active form), enhancing calcium and phosphate absorption in the gut.
Frequent Tests for Renal Function
Blood Tests:
Urea and electrolytes (U&E), full blood count (FBC), albumin level.
Urine Tests:
Output monitoring and urinalysis.
Imaging:
Renal ultrasound or kidney/ureter/bladder imaging.
Biopsy:
Used for assessing kidney dysfunction.
Tests Needed – Normal Ranges
Urea and Creatinine (U&E):
Serum Creatinine:
Men: 60 – 120 μmol/l.
Women: 48 – 84 μmol/l.
Estimated glomerular filtration rate (eGFR): >90 ml/min/1.73 m² (with >60 being acceptable).
Urea: 2.5 – 7.8 mmol/l.
Sodium: 135 – 146 mmol/l.
Potassium: 3.5 – 5.3 mmol/l.
Interpretation of Key Metrics
Creatinine:
Waste product of muscle metabolism, excreted entirely by the kidneys. Higher levels often indicate renal dysfunction and can vary with muscle mass.
eGFR:
Mathematically derived estimate based on creatinine, age, sex, and race; indicates filtration rates; declines as creatinine rises, useful in staging kidney disease.
Urea:
Waste product of protein breakdown in the liver, mostly excreted via the kidneys; can indicate renal function but can be elevated due to dehydration or GI bleeding, even when renal function is normal.
Urine Output
Normal Urine Output: 0.5 ml/kg/hr, approximately 800 – 2000 ml in 24 hours depending on weight.
Urinalysis: Varies based on diagnosis.
Ultrasound in Renal Diagnostics
Used to detect:
Kidney/bladder stones, cysts, tumours, hydronephrosis (swelling of the kidney), congenital abnormalities, and monitor ongoing diseases.
Biopsy Significance
Used to determine the cause of kidney dysfunction, assess severity or progression, guide treatment decisions, and monitor health of transplanted kidneys.
Types of Renal Disease
Pre-Renal: Caused by factors before the kidneys, such as hypovolemia (low circulating fluid volume).
Intrinsic: Disease affecting the kidney itself, such as glomerulonephritis.
Post-Renal: Issues occurring after the kidneys, such as prostatic hyperplasia.
Kidney Disease Improving Global Outcomes (KDIGO) Criteria
Acute Kidney Injury (AKI)
Serum Creatinine Criteria:
Increase by ≥0.3 mg/dL (≥26.5 µmol/L) within 48 hours.
Increase to ≥1.5 times baseline, with a known or presumed occurrence in the last 7 days.
Urine Output Criteria:
<0.5 mL/kg/h for 6–12 hours indicates Stage AKI.
<0.5 mL/kg/h for ≥12 hours or <0.3 mL/kg/h for ≥24 hours, or anuria for 12 hours.
Chronic Kidney Disease (CKD) GFR Categories (G1–G5)
G1: ≥90 mL/min/1.73 m² (normal or high).
G2: 60–89 mL/min/1.73 m² (mildly decreased).
G3a: 45–59 mL/min/1.73 m² (mild-moderately decreased).
G3b: 30–44 mL/min/1.73 m² (moderately-severely decreased).
G4: 15–29 mL/min/1.73 m² (severely decreased).
G5: <15 mL/min/1.73 m² or dialysis (kidney failure).
Albuminuria Categories (A1–A3):
A1: <30 mg/g creatinine (normal to mildly increased).