9.3 & 9.4: The Excretory System

Functions of the excretory system

  • Excretion

    • concentration of nitrogenous wastes (urea) and removal from the body

  • Osmoregulation

    • maintain isosmotic conditions between ICF and ECF

  • pH regulation

    • maintains pH baby secreting/absorbing H+

Structures of the excretory system

  • Ureters

  • Urinary Bladder

  • Urethra

  • Kidneys

    • mammals have 2 kidneys: left & right
    • filters wastes from the blood
    • renal artery supplies blood (waste)
    • branches from abdominal aorta
    • renal vein removes blood (clean)
    • branches from the inferior vana cava
    • layers to kidneys:
    • renal cortex
    • renal medulla
    • renal pelvis
    • ureter removes urine to urinary bladder, and urethera removes urine from the body

  • Nephrons

    • functional unit of the kidney
    • system of %%blood vessels%% and %%tubes%% that filter waste from blood
    • blood enters via renal artery → afferent arterioles → %%glomerulus%% (bundle of capillaries)
    • %%Bowman’s capsule%% surrounds glomerulus and performs first filtration step
    • Blood moves from the glomerulus to %%peritubular capillaries%% via efferent arterioles
    • Peritubular capillaries surround p%%roximal convoluted tubule, Loop of Henle, distal convoluted tubule%% for further filtration and urine formation
    • Blood exists kidney via the renal vein
    • Urine drains through %%collecting ducts%% to %%urinary bladder%%

Urine Formation

  • Filtration

    • Location: Bowsman’s capsule
    • Process:
    • water, ions, small nutrients (glucose, amino acids), urea move from glomerulus into tubules forming filtrate
    • cells and large proteins remain in capillaries

  • Reabsorption

    • Location:
    • proximal convoluted tubule
    • loop of henle
    • distal convoluted tubule
    • collecting duct
    • Process:
    • ions are pumped from filtrate into interstitial space
    • filtrate becomes hypnotic, interstitial space become hypertonic
    • water diffuses into interstitial space (reabsorbed into blood)
    • nutrients (glucose, amino acids) are actively reabsorbed

  • Secretion

    • Location:
    • proximal convoluted tubule
    • distal convoluted tubule
    • collecting duct
    • Process:
    • H+ actively secreted from interstitial fluid tubules, regulates pH
    • urea and other wastes passively secreted into tubules