The glomerulus is the first part of the nephron, which then continues as a highly specialized tubular structure responsible for creating the final urine composition. The urinary system’s ability to filter the blood resides in about 2 to 3 million tufts of specialized capillaries—the glomeruli—distributed more or less equally between the two kidneys.

Because the glomeruli filter the blood based mostly on particle size, large elements like blood cells, platelets, antibodies, and albumen are excluded. All other solutes, such as ions, amino acids, vitamins, and wastes, are filtered to create a filtrate composition very similar to plasma.

glomerulus — tuft of capillaries surrounded by Bowman’s capsule; filters the blood based on size. aquaporin — protein-forming water channels through the lipid bilayer of the cell; allows water to cross; activation in the collecting ducts is under the control of ADH. brush border — formed by microvilli on the surface of certain cuboidal cells; in the kidney it is found in the PCT; increases surface area for absorption in the kidney. inulin — plant polysaccharide injected to determine GFR; is neither secreted nor absorbed by the kidney, so its appearance in the urine is directly proportional to its filtration rate.

Be able to compare and contrast blood plasma, glomerular filtrate, and urine characteristics; describe the characteristics of a normal urine sample, including normal range of pH, osmolarity, and volume; identify the ureters, urinary bladder, and urethra, as well as their location, structure, histology, and function.