Chapter 7The Urinary SystemHow and Why urine

is secreted from the body

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The Human body is an integrated, intricate system.

As we eat food, nutrients are absorbed into the body and cellular process break down food to be used as energy to perform the body's necessary functions.

The Human Body

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Waste is a natural result of food consumption.

Human waste takes the form of FECES as food passes through the digestive system. CARBON DIOXIDE as we exhale through the respiratory process and URINATE as one expels urine through the act of VOIDING (expelling urine through the urethra).

Waste

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When food containing protein is used by cells in the body waste products containing nitrogen are released into the bloodstream. One of these nitrogenous waste products, Urea, is removed from the body through the urinary system.

Nitrogenous waste

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Urea = Nitrogenous waste

Where is urea formed?◦ In the liver

How does urea leave the body?◦ Urea travels from the

liver to the kidney’s where it passes out of the bloodstream with urine (which is composed of water, salts and acids).

Urea and Urine

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The kidneys are two bean shaped organs behind the abdominal cavity on either side of the spine in the lumbar region.

They are responsible for the complex filtration process that results in the formation of urine.

The Kidneys

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Blood is brought into the kidney through the renal artery

The renal artery leads to smaller arterioles, arterioles lead to a mass of very tiny, coiled and intertwined smaller blood vessels called capillaries.

A collection of capillaries is called a glomerulus.

The glomerulus is the kidneys filtration system.

There are about 1 million glomeruli in the cortex of a kidney.

The kidney’s filtration system (glomerulus)

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Each glomeruli is surrounded by a cup-like structure called a Bowman capsule.

As blood passes through the thin walls of the glomeruli, water, salts, sugar and urea leave the bloodstream and collect in the Bowman capsule.

The kidney’s filtration system continued (Bowman capsule)

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Attached to each Bowman capsule is along twisted tube called a renal tubule.

The combination of a glomerulus and a renal tubule is called a nephron.

There are more than 1 million nephron’s in a kidney.

All renal tubules lead to the renal pelvis, which eventually narrows into the ureter.

The kidney’s filtration continued (nephrons)

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Water, salts, sugar and urea are filtered from the bloodstream through the thin walls of the glomerulus, into the collecting cup-like structure that surrounds the glomerulus, the bowman capsule.

3 steps to the formation of urineStep 1: Glomerular filtration

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In the nephron (combination of the glomerulus and renal tubule) tubular reabsorption occurs. Water, all of the sugar and some of the salts are reabsorbed back into the body.

Step 2: Tubular Reabsorption

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The substances that are NOT REABSORBED BACK INTO THE BODY are secreted out of the body, (tubular secretion). These substances move from the renal tubules, into the renal pelvis, which narrows into the ureter.

Step 3: Tubular Secretion

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From the ureters urine travels to the trigone, this is the area where the ureters enter and the urethra exits the body. Urine is excreted through the urethra.

Urine is composed of 95% water, 5% wastes, (urea, creatinine), salts, acids and drugs

URINE