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Science Projects or Science Experiments: Grades 5 & 6

Kidney and the Urinary System

The Urinary System
The urinary system is concerned with the formation and elimination of urine. In an adult, more than 2,500 pints of blood passes through the kidneys each day. Blood enters via the renal arteries and is filtered to remove most of the waste products of metabolism. Seven pints of filtrate are produced every hour. Purified blood returns to the body circulation via the renal veins.
The filtering process is carried out by more than two million tiny kidney units, or nephrons, which produce a highly concentrated solution of chemicals known as urine, which is harmful to the body if allowed to remain. Urine flows from the nephrons, first into the funnel-shaped renal pelvis and then into the ureter. Waves of muscular contraction passing down the ureters push the urine into the bladder. With continuous filling, the bladder, a muscular bag, expands until it holds about one pint of fluid. A circular band of muscle around the neck of the bladder, the sphincter, controls the release of urine from the body.

The Urinary System
This program provides a description of the urinary system. It discusses the role of the kidneys, ureters, bladder, and urethra
Anatomy of a Kidney This cross section of a kidney, almost three times life-size, shows its blood supply and one of the filter tubules, a nephron, highly magnified. The nephron is a highly specialized coiled tubule measuring up to one inch in length. There are more than one million nephrons in each kidney. They function as the kidney's filter units. The kidneys filter unwanted materials from the blood and regulate the levels of water and chemicals in the body.
As blood flows through a glomerular tuft, a tight knot of blood capillaries from which water and chemicals filter into the nephrons, fluid is forced into the Bowman's capsule. The Bowman's capsule, the expanded beginning of the tubule, acts as the nephron's collecting cup for fluid filtering from the blood. The filtrate then flows along the coiled tubule. Further waste material is secreted directly into the nephron tubule. At the same time, reaabsorption of essential chemicals into the capillaries takes place. The loop of Henle, the central region of the nephron, acts as the primary reabsorption area.
Urine, the yellowish liquid remaining, passes from the nephron-collecting ducts into the renal pelvis, which lies at the core of the kidney and acts as a funnel to conduct the liquid into the ureter. Through the ureters, the urine is conducted away from the kidney and emptied into the bladder The cortex, or the outer region of the kidney, houses the glomreulus of each nephron. The medulla, or the inner region of the kidney, contains the loops of Henle and the collecting ducts.


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