Removal of Metabolic Wastes: The kidneys filter and remove excess waste products from the blood.
Maintenance of Blood Fluid and Electrolyte Balance: Helps keep proper levels of electrolytes, crucial for heart and muscle function.
Maintenance of Blood pH: Regulates the acidity or alkalinity of the blood to maintain homeostasis.
Regulation of Blood Pressure: Through various mechanisms, including the renin-angiotensin-aldosterone system (RAAS).
Regulation of Erythropoiesis: Produces erythropoietin, which stimulates red blood cell production in bone marrow.
Metabolic Functions: Involves drug secretion and metabolism.
Anatomy of the Nephron
Structure:
Renal Corpuscle: Site of blood filtration, consisting of the glomerulus and Bowman's capsule.
Renal Tubule: A series of tubes consisting of proximal convoluted tubule, nephron loop, and distal convoluted tubule.
Collecting System: Further modifies filtrate as it moves towards the renal pelvis.
Filtration in the Nephron
Glomerular Filtration: Blood is filtered through the glomerulus, allowing small substances like water and solutes to pass while retaining blood cells and large proteins.
Filtration Process:
Glomerular Hydrostatic Pressure (GHP): Forces fluid into Bowman's capsule.
Opposing Pressures: Includes glomerular colloid osmotic pressure (GCOP) and capsular hydrostatic pressure (CHP), which resist filtration.
Net Filtration Pressure (NFP): Calculated as NFP = GHP - (GCOP + CHP).
Regulation of Glomerular Filtration Rate (GFR)
Regulated by both intrinsic and extrinsic mechanisms:
Intrinsic: Autoregulation via the myogenic response and tubuloglomerular feedback.
Extrinsic: Hormonal control via the RAAS.
Tubular Reabsorption and Secretion
Reabsorption:
Processes transferring substances from the filtrate back into the blood, primarily in the proximal tubule.
Includes Na+ and glucose via co-transport mechanisms.
Bicarbonate Reabsorption: Occurs through multiple steps involving carbonic anhydrase.
Secretion: Movement of substances from the blood into the filtrate, eliminating waste.
Hormonal Regulation of Electrolytes and Water
ADH (Antidiuretic Hormone): Promotes water reabsorption by increasing aquaporin channels in the collecting ducts.
Aldosterone: Stimulates Na+ transport in distal tubules and collecting ducts, aiding in Na+ and water reabsorption, thereby increasing blood volume and pressure.
Summary of Important Terminology
Glomerular Filtration Rate (GFR): Indicator of kidney function, calculated as the volume of fluid filtered per unit time.
Stages of Kidney Disease:
Stage 1: GFR 90 or higher (normal function).
Stage 2: GFR 60-89 (mild loss of function).
Stage 3: GFR 44-59 (moderate loss of function).
Stage 4: GFR 15-29 (severe loss of function).
Stage 5: GFR less than 15 (kidney failure).
Key Mechanisms in Nephron Function
Reabsorption Mechanisms:
Osmosis: Water reabsorption linked to solute reabsorption (obligatory water reabsorption).
Transporters: Involved in moving solutes against concentration gradients using energy.
Filtration Membrane: Composed of fenestrated capillary endothelium, a basal lamina, and podocytes that control filtration size.
Effector Mechanisms:
Renin-Angiotensin-Aldosterone System (RAAS): Synthesizes angiotensin II, which promotes arteriolar constriction and Na+ reabsorption, ultimately influencing blood pressure and fluid balance.