Kidneys Kidney Function Purpose of Kidney Kidney Description Urine Production Urine

Understanding Kidneys

Mammals are made up of millions of cells, each containing cytoplasm and a nucleus surrounded by a membrane. Together these cells make up all of our being including blood, bone, and organs. Each organ has a purpose, and one of the main purposes of our kidneys is to filter waste products out of the body. This complex organ helps regulate our systems by filtering and producing blood cells, maintaining proper blood pressure, and balancing chemicals and minerals that flow through them, monitoring the acidic development of such substances.

Description of a kidney

So what do kidneys look like and how do they do all of this? Mammal kidneys occur in pairs, and they look an awful lot like beans. There is one on each side of the body, usually toward the back, just below the ribcage. Kidneys have 2 main parts to them: the outer layer called the cortex, the inner layer called the medulla. Within these layers is the actual functioning part of the kidney, nephron cells which look a bit like a tangled up hose, and are the part of the kidney that does most of the work with the help of some capillaries.

Nephrons can be found only in the cortex of the kidneys, or they can extend into the medulla as well. Blood vessels lead into and out of the nephrons, which have 4 main regions they utilize to create urine. Blood enters into the nephrons, and as it filters out toxins and impurities, urine is created along the way. The urine then makes its way to the ureter, so it can be deposited into the bladder.

Urine Production and Elimination

In order to filter toxins, nephrons in the kidney have a renal corpuscle which is the point of entry for blood. As soon as the blood enters the renal corpuscle it has to go through a maze of tubular nephrons called the glomerulus, where it filters out toxins in a pre-urine stage. Within the glomerulus is Bowmans’s capsule where there are large pores that filter the blood, splashing it in and out of slits and ridges located in their membrane. Tiny bits of water and other minute cells are flushed from the blood, leaving only the larger cells to remain with the blood flowing throughout the rest of the body. Only the cells small enough to be filtered remain in the nephron system, and become diluted and develop into urine.

After the pre-urine stage, the fluid consisting of salts, sugars, amino acids, and vitamins leaves Bowman’s capsule it enters the proximal tubule, flows down around the loop of Henle, and up to the distal tube where it excretes itself into the collecting duct. It is in the lining of the collecting duct that the fluid actually turns into urine through the process of reabsorption, where almost all of the sugar, vitamins, and organic nutrients are returned to the blood, leaving only water and waste behind in the form of urine.

Blood flows in, out, around, and through the kidneys as they filter it, collecting nutrients and gathering waste. They then filter these essential elements and redistribute them accordingly, allowing goods to reenter the bloodstream, while discarding toxins through the process of creating and eliminating urine. Kidney cells look and function according to necessity and purpose, theirs being to create an intricate filtration system for the bodies they inhabit.


Biological Science: Freeman, Scott; Pearson Education Inc., San Francisco, CA Copyright 2008

Biology: Campbell & Reece, Pearson Education Inc., San Francisco, CA Copyright 2005