This chapter will talk about human excretion. Excretory systems of other animals will be discussed in the Diversity of Life chapter. The excretory system is necessary for humans to filter out metabolic wastes from the body’s fluids and eliminate them as urine, all while making sure the body retains the water and solutes it needs to survive.
Although there are several major players in the excretory system, the most significant and prominent one is the kidney. Humans have two kidneys. The top, outer portion of the kidney is called the cortex (this is where the blood enters the kidneys). The middle portion is called the medulla. The very inner portion is called the pelvis (this is where the filtrate exits the kidneys).
A nephron is the single, functional unit of a kidney. Kidneys are made up of thousands and thousands of individual nephrons. The following picture shows a single nephron.