96% water, 2.0% urea, 1.8% mineral salts (NaCl), other nitrogenous waste
urine is made by ultrafiltration and reabsorption
bowman's capsule (ultrafiltration)
each nephron begins in the cortex as the bowman's capsule
blood enters the kidneys via the renalartery which branches into afferent arterioles which further branch into capillaries (collectively called the glomerulus) in the bowman's capsule
a partially permeable membrane wraps around the glomerular blood capillaries
only small substances can pass through the pores of the basement membrane into the bowman's capsule, forming the filtrate.large molecules are retained in the capillaries
the capillaries then merge to form the efferent arteriole
the diameter of the efferent arteriole is much smaller than that of the afferent arteriole, creating high hydrostatic pressure in the glomerulus which is the main driving force for ultrafiltration