Download Chapter 11 Notes – Excretion

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Chapter 11 – The Excretory System
Section 11.3 – The Human Excretory System
Objectives:
 I can explain the role of the excretory system to maintain a constant environment in the human body.
 I can identify and describe the main structures and functions of the urinary system, and the nephron.
 I can describe disorders of the excretory system.
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
Excretory systems help organisms maintain homeostasis by removing wastes such as salt, water, and metabolic
concentrations (CO2 and nitrogenous compounds).
Although most think of the kidney when speaking of the excretory system, there are actually several organs
involved, including:
o Lungs
o Liver
o Skin
o Kidneys
The Lungs
 Rid the body of carbon dioxide and water vapor
The Liver
 Removes metabolic wastes through detoxification, and creates urea.
o During detoxification harmful substances (bacteria, and certain drugs) are removed from the blood and
changed into a less poisonous form (inactive). These inactive substances are returned back to the
bloodstream and excreted by the kidneys.
o Urea is created as proteins are broken down into amino acids. This process creates poisonous ammonia
(NH3). The liver changes NH3 into urea which diffuses into the bloodstream and is transported to the
kidneys for excretion in urine.
The Skin
The skins main jobs include:
 Protects body from infection
- Keeps microorganisms and other foreign materials from entering the body
 It is a sense organ
- The skin contains nerve endings that receive messages from the environment that are interpreted by
the brain.
 Excretes a small amount of urea and salts in sweat
- Your skin has between 2 and 5 million sweat glands. When you sweat, you excrete salts and water.
When the sweat and water dry on the surface of your skin it helps to cool your body.
 Skin can keeps heat in when you are cool; producing heat as you shiver.
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The Structure of Skin
- Epidermis: the outer layer which is composed of
epithelial cells.
- Dermis: the inner which is made of elastic
connective tissue.
 Dermis contains blood vessels, lymph vessels,
nerves, sensory receptors, sebaceous glands,
sweat glands and hair follicles
- Sebaceous glands/(Oil glands): secrete oils to
provide a protective coating to skin and hair.
- Sweat glands: coiled tubes that open to the surface
of the skin through pores to release sweat.
- Fatty Tissue: layer of adipose tissue (fat) beneath the
dermis.
The Kidney
 Remove cellular waste products from the body.
The Human Urinary System

Humans have two kidneys, each the size of an adult
human fist, located on the lower back on either side
of the spine.

Kidneys release urine into tubes called ureters to the
bladder where it is stored.

Emptying the bladder is controlled by two sphincters
and urine leaves the bladder through a tube called
the urethra

The kidney’s main function is to filter the blood to
remove cellular waste.

The main metabolic wastes include urea, uric acid
and creatinine.

They also control water balance, pH, and levels of
sodium, potassium, bicarbonate and calcium ions.

Because the kidneys are involved in so many of the
body’s functions, a urine analysis can tell a physician
a lot about their patients.
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Structure of the Kidney
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
The kidney has three layers:
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the outer cortex: filters blood
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the middle medulla: collects filtrate
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the inner pelvis: accumulates urine leading to ureters
Also includes:
- Renal arteries: take blood from the heart to the kidney
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Renal veins: take filtered blood back to the heart.
Nephrons
 Where filtration of the blood and urine formation
occurs
 About 1 million of them are found in the cortex and
the medulla of each kidney
Parts of the Nephron include:
- Glomerulus: a tight ball of capillaries
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Bowman’s capsule: is a double-walled structure that
surrounds the glomerulus
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Proximal tubule: where the filtrate exits the
Bowman’s capsule
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Loop of Henle (U shaped loop): removes water from
filtrate through osmosis.
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Distal tubule – pulls toxins from blood.
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Collecting Tubule (duct) – transports filtrate to renal
pelvis for excretion.
Urine Formation
 Happens in two stages, filtration and absorption.
Filtration
 Takes place in the glomeruli and the Bowman’s capsule.
 Blood enter the glomerulus under pressure which forces the filtrate (water, urea, salts, and amino acids)
through the thin walls of capillaries into the Bowman’s capsule.
 Blood cells and blood proteins are too large to enter the capsule and remain in the blood.
 Kidneys form about 180 litres of filtrate per day but only 1 to 1.5 litres of urine results. If all of the filtrate that is
formed was excreted, too much water, minerals and salts would be lost (approx. 99% of the water reabsorbed).
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Reabsorption (Urine Formation)
 After the filtrate leaves the Bowman’s capsule, it enters the renal tubule (proximal tubule, loop of Henle, and
distal tubule).
 Reabsorption reduces the volume of filtrate and returns important substances to the blood.
 Water is reabsorbed by osmosis in to the capillaries surrounding the renal tubules.
 Glucose, amino acids and salts require active transport, fueled by the many mitochondria.
 After reabsorption, the fluid remaining in the renal tubule is urine
 Urine is made of water, urea and various salts.
 Urine flows into the collecting ducts, out of the kidneys and is carried to the bladder via the ureters.
Disorders of the Excretory System
Urinary Tract Infections (UTIs)
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More common in women than men
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Causes: bacterial infection from poor hygiene, and lack of water
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Symptoms: painful, burning urination, frequent urge to urinate, bloody or brown urine
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Treatment: antibiotics, but without treatment can cause kidney infection and lead to kidney failure
Kidney Stones
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More common in men than women
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Causes : reoccurring UTI’s, lack of water, too much vitamin C &
D, low activity levels
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Symptoms include severe pain of the abdomen and lower back,
blood in urine, nausea
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Treatments: passing through the urine on their own,
medications to break down, or shockwave treatment
Renal Failure
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When a person’s kidneys stop functioning, wastes begin to accumulate in the bloodstream. This can result in serious
damage to vital organs (liver, heart) and may result in death.
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Often a kidney transplant is required but while the patient is waiting for a suitable donor, dialysis may be used.