Processes in Nephron

  1. Glomerular filtration

    takes place in Malpighian body (Bowman’s capsule & Glumerulus) of nephron

    Blood enters glumerulus from renal artery through afferent arteriole and exits through the efferent arteriole

    Adaptations of Malphignian body to ensure filtration :

    • Afferent arteriole is wider than efferent arteriole, resulting in blood being put under high pressure forcing plasma with dissolved substances into capsular space of Bowman’s capsule

    • Walls of glumerulus capillaries are thin and consist of a single layers of squamos epithelial cells + podocytes on inner wall of Bowman’s capsule allow for ultrafiltration

    • Only smaller dissolved substances travel through filtration slits between podocytes; larger proteins remain in blood

    • Bowman’s capsule is cup shaped to enlarge contact area with glumerulus

    Formation of glumerulur filtrate is a non-selective process, meaning both useful substances (glucose, amino acids, vitamins, minerals and water) AND waste substances are filtered through into the capsule

  1. Tubular re-absorption

    Takes place in proximal convoluted tubule

    Process where useful substances are transferred from nephron tubules back into bloodstream

    Involves active re-absorption of useful substances listed above that ended up in glomerulur filtrate

    65% of water moves back into blood of peritubular capillaries via osmosis to prevent dehydration and unnecessary loss of substances

    What makes it efficient?

    • Energy is required for active transport, so there are cuboidal epithelial cells that line the tubules that are packed with mitochondria for cellular respiration

    • There are also microvilli on these same cells to maximise reabsorption

    • Movement of water is done through osmosis

    Fluid in renal tubule is now called tubular filtrate

    Loop of Henle then ensures water is conserved and recovered from filtrate and returned to blood

    Cells lining loop of Henle are impermeable to water, and also have a sodium pump, which means that they actively pump out sodium(Na+) into the medulla tissue of the kidney and chloride ions(Cl-) follows to make salt (NaCl), making the medulla hypertonic

    A steep water gradient is made between the tubular filtrate and the medulla tissue

    The distal convoluted tubule and collecting ducts are very permeable to water, so when the filtrate enters these areas water will passively flow in via osmosis into the medulla tissue and back into the peritubular capillaries

    The amount of water that flows out is dependent on the level of hydration of body fluids and is regulated by the antidiuretic hormone(ADH)

  2. Tubular secretion

    Involves active removal of unnecessary substances from blood in peritubular capillaries into tubular filtrate in distal convoluted tubule

    Substances removed include :

    • creatinine

    • ammonia

    • potassium ions (K+)

    • hydrogen ions (H+)

    • Sodium ions (Na+)

    • Bicarbonate ions (HCO3-)

    • drugs

  3. Excretion of urine

    Filtrate that enters collecting duct is called urine and consists of urea, excess water and salts

    useful substances should NOT be excreted in urine

    Urine collects in collecting ducts in the medulla region and empties into pelvic region of kidney

    Urine then goes down the ureter into the bladder, which has muscles which control the release of urine into the urethra and urination occurs