Ultrafiltration

Key components of urine

• water

  • drinks

  • food

  • metabolic reactions

  • reabsorption controlled by hydration

• urea

  • formed in the liver from deamination of amino acids

  • key nitrogenous waste product

• glucose

  • from digested carbs

  • urine presence indicates diabetes

• creatine

  • from breakdown of creatine in phosphate in muscles

  • used to clinically assess kidney function

Ultrafiltration

• blood enters the glomerulus through the afferent arteriole

• blood leaves the glomerulus via the smaller efferent arteriole 

  • maintaining a high hydrostatic pressure (smaller lumen)

• this high pressure forces molecules out of the blood through pores in the capillary endothelium

  • water and small solutes

• the molecules move through the basement membrane

  • has collagen fibres that act as a selective filter 

  • prevents large molecules an blood cells from passing into the Bowman’s capsule

• the molecules moved through the Bowman’s capsule epithelium

  • has specialised cells called podocytes with extensions called pedicels that wrap around capillaries to help filter blood

• filter fluid collects in Bowman’s capsule

Factors affecting filtration rate

• blood pressure

  • higher pressure increases glomerular filtration rate (GFR)

  • hypertension damages filtration structures

• arteriole diameter

  • constriction of afferent arteriole reduces GFR

  • efferent constriction can increase GFR

• water potential

  • filtration depends on effective filtration pressure

  • the balance of hydrostatic and osmotic forces

Glomerular filtrate formation