Angela Herrick - Pen and Ink
The Urinary System
The urinary system produces and excretes urine from the body. This system is comprised of the kidneys, ureters, and the urinary bladder.
The primary function of the kidneys is to remove waste products from the blood. Normally about 20% of the total blood pumped from the heart each minute enters the kidneys. This rate of blood flow from the kidneys is among the highest in the body. Maintaining high blood flow rate and normal blood pressure in the kidneys is essential for the formation of urine. The kidneys balance the amount of many substances entering and leaving the blood over time so that normal concentrations can be maintained. In this way, the kidneys help maintain homeostasis in the body.
Millions of microscopic units called nephrons make up the kidneys interior. The nephrons form urine by a series of three processes: (1) filtration of water and dissolved substances out of the blood, (2) reabsorption of substances needed by the body, and (3) secretion of unneeded substances through urine. Urine then drains from the kidneys, down the ureters, to the urinary bladder. Elastic fibers and involuntary muscle fibers in the wall of the urinary bladder make it well suited for expanding to hold variable amounts of urine and then for contracting to empty itself.
Urine passes from the bladder, down the urethra, and out its external opening, called the urinary meatus. The urethra is a narrow tube, only about 1 ½ inches long in women and about 8 inches long in men.
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The Skeletal System The Muscular System The Nervous System The Digestive System The Respiratory System |
The Endocrine System The Lymphatic System The Urinary System The Reproductive System |
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