The human kidney is shaped much like a kidney bean. Lined with tight gap junctions, the kidney cannot leak for it interacts with toxins, keeping them from the rest of the body. Simple cuboidal epithelium lines the many tubules within the kidneys.
Such tissue is known for allowing the exchange of water and small nutritional molecules. It must be thin to allow secretion and reabsorption as directed by the kidneys. The organs are supported by connective tissue called renal fascia further surrounded by adipose tissues. They are also encased by connective tissue capsule.
Kidneys Functions Are Many
As part of the urinary system, the function of the kidney is important. The kidneys help balance and purify body fluid and also filter waste creating what most call urine. People usually start with two of these organs but can exist with one. However, as the driving element of an efficient and silent process, the kidneys should not be taken for granted.
Kidneys and the Circulatory System
One may not expect the kidneys to be associated with the circulatory system. Yet the blood passes through the kidneys several times throughout a day. Driven through the renal artery, the blood is processed by capillaries. A fraction of the plasma containing water and nutrients is flushed into a tubule for further production. The held portion is called filtrate.
How the Kidneys Work
The kidneys are lined with tiny tubules but the filtrate travels through what is called the nephron. There are several of these within a single kidney. As filtrate is pushed along the nephron tubule, the components are separated and dealt with necessarily.
For instance, usable nutrients and water removed from the filtrate are reabsorbed into the consistent blood flow and exit the urinary system through the renal vein. Broken down and used substances secreted into filtrate (or remaining depending on the point of entry) remain in the tubule to be excreted as waste.
Because the kidneys manage bodily fluids, they are associated with homeostasis. Part of filtration involves cleansing but also balancing blood and fluid consistency. The human body, each cell actually, relies on a consistent amount of water to function.
Hormones and the Kidneys
Antidiuretic hormone (ADH) dispersed into the blood directs the nephrons to absorb more water from filtrate when water is low. In this case, the water is reabsorbed and hopefully the body rehydrates. If the body is too hydrated, then ADH drops and the nephrons leave water in the filtrate to become urine. Such communication is constant and a vital part of homeostasis and health.
References
Campbell, N.A., Reece, J.B., Taylor, M.R. & Simon, E.J. (2006). Biology: Concepts and Connections. San Francisco, CA: Pearson Education, Inc.
Carpi, A. (2010). Basic Anatomy – Tissue and Organs. The National Science Pages. Retrieved May 8, 2010 from National Science Pages website.
National Kidney Foundation. (2010). The Facts About Chronic Kidney Disease. Retrieved May 8, 2010 from the Nationals Kidney Foundation website.
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