Excretion

Waste products build up as an organism carries out its life processes If metabolic wastes are not removed, the organism would die Excretion is the process by which wastes and excess substances are removed from the organism

Excretion also removes heat from the body or helps to maintain the organism’s internal temperature constant Excretion is often confused with elimination or the removal of unabsorbed and undigested foods in the form of feces

In complex animals, such as humans, the organs involved in the excretion process are the lungs, kidneys, liver and skin These organs work with the circulatory, nervous and endocrine systems to maintain homeostasis

CO2 (formed during cellular respiration) various nitrogen compounds (formed from the breakdown of amino acids) mineral salts (formed during metabolism) are important metabolic wastes

Earthworms Special excretory organs must remove the metabolic wastes from organisms whose cells are not in constant contact with the environment Nephridia are the excretory organs of the earthworm These structures are found in pairs in most of the earthworms segments

Some cellular wastes diffuse directly into the fluid in the body cavity The body fluid enters the nephridium at the nephrostome, the funnel shaped opening of each nephridium Cilia then moves the fluid through a tubule to the major part of the nephridium in the next segment

Tubules loop into a large bladder which drains to the outside of the body through an external opening called the nephridiopore The nephridiopores are surrounded by capillaries Wastes past from the bloodstream through capillaries into the nephridium

Conversely, glucose and water pass from the body fluid in the nephridium into the bloodstream The remaining wastes in the nephridium leave the body through the nephridiopore as urine (made up of water, mineral salts, ammonia and dioxide)

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Grasshoppers The excretory organs of grasshoppers and other insects are the Malpighian tubules The open circulatory system of the grasshopper allow the excretory tubules to be bathed by the blood

Wastes and other substances from the blood enter the tubules by diffusion and active transport, and then move onto the intestines Water, nutrient and other useful substances are reabsorbed from the tubules and the digestive tract and are returned to the body fluids

The dry nitrogenous waste product, uric acid, passes out of the body with the feces through the anus

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Assignment Draw and label the excretory system of the earthworm and grasshopper Page 239, 240

The Human Excretory System The organs involved in the excretory system are: Liver Kidneys Lungs Skin http://www.web-books.com/eLibrary/Medicine/Physiology/Urinary/urinary_system.jpg

http://en.wikipedia.org/wiki/Liver

Liver Detoxifies or removes harmful substances from blood (i.e. bacteria, drugs, hormones) The liver turns poisons into less poisonous forms and returned into the bloodstream and eventually excreted from the body through the kidneys

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Bile is produced by the liver and aids in digesting fat However, bile contains bile salts (aka bile acids), cholesterol and hemoglobin from worn out blood cells and is considered a metabolic waste Bile collects in the gall bladder and passes through bile duct to the small intestine where it is reabsorbed into the blood and returned to the liver

From the liver, they pass through the small intestine again and are re-used The remaining bile passes onto the large intestine and eliminated as feces Jaundice is when bile is not excreted properly and the metabolic wastes are reabsorbed into the blood This causes the bloodstream to look yellow

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a.a. changes into different substances Proteins are broken down into amino acids; a.a. cannot be stored in the body and are broken down in the liver a.a. changes into different substances NH2 is changed into NH3 the remaining amino acids molecule is changed into pyruvic acid and used as an energy source in cellular respiration or changed into fat (glycogen) for storage

Ammonia is poisonous and is changed into urea which is then diffused from the liver into the bloodstream, then to the kidneys The kidneys filter the urea from the body and excreted in urine

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The Urinary System Made up of the kidneys Ureters Bladder Urethra Kidneys produce urine and pass through a tube called a ureter to the bladder where it is stored

During urination, urine goes from the bladder through the urethra to the outside of the body The kidneys are important in that they remove wastes from the blood and the regulate the concentrations of the substances found in the body fluids If the body cannot do these 2 functions, you can die

Structure of the Kidneys 3 parts: Cortex (the outer part) Medulla (the middle: made up of tubes called collecting ducts which carries filtrates to the pelvis) Pelvis (the inner region: cavity connected to the ureter)

http://www.ivy-rose.co.uk/Topics/Urinary_System_Kidney_Diagram.htm

Urine Formation Urine is made in the nephrons in 2 stages: Filtration Reabsorption Filtration takes place in the glomeruli and Bowman’s capsules

If all the filtrate was excreted, the body would lose too much water Kidneys form 180 liters of filtrate in 24 hours but only about 1 – 1.5 liters of urine If all the filtrate was excreted, the body would lose too much water Reabsorption occurs in the renal tube and reduces the volume of filtrate and return some important substances to the blood

The Urinary System Questions- Biology 30S Why must metabolic wastes be removed from an organism? Explain the relationship between the nephridium and the capillaries of the earthworm. What is the function of bile? What are the 2 main functions of the kidneys? Compare the process of filtration in the kidneys with the process of reabsorption. (explain in full) What does the kidney threshold level mean?

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The Lungs Lungs are the gas exchange organ in air breathing vertebrate The lungs rid the body of CO2 and water vapour, both end products of cellular respiration Internal respiration is the exchange of oxygen and carbon dioxide between the blood in the capillaries and the body cells.

Oxygen diffuses from the blood through the intercellular fluid in the body cells CO2 diffuses from the cells through the intercellular fluid into the blood

The Skin Made up of many different kinds of tissues and perform various functions such as excretion

The skin has 2 layers: epidermis (outer layer) and dermis (inner layer) The epidermis is formed of layers of tightly packed, dead, epithelial cells

The deepest layer of the epidermis is constantly producing new skin cells, pushing the older dead cells up; this part always wears away The epidermis produces keratin before it dies; this is a weatherproofing protein that protects the dermis

The dermis lies below the epidermis and is made of elastic connective tissue The dermis supports the skin and binds it to muscle and bone The dermis contains blood vessels, lymph vessels, nerves, sense receptors, sebaceous glands, sweat glands and hair follicles

Beneath the dermis contains a layer of adipose (fat) tissue The sebaceous glands produce oily secretions that provide a protective coating to the skin and hair to keep it soft and flexible Sweat glands are tiny coiled tubes that open to the surface of the skin through holes called pores

The skin has many functions: Keeps microorganisms and foreign materials from entering the body Keeps body from drying out Removes excess heat from the body and keeps heat when the body is too cool