The Excretory System

The Excretory System

• Function: – Removal of metabolic wastes and excess substances from cellular activities that build up in bodily fluids

• This is not egestion which is the removal of undigested food or feces

Major Metabolic Wastes • Carbon Dioxide – produced from cellular respiration

• Nitrogen Compounds – produced by the breakdown of amino acids – Ammonia, urea, uric acid

• Mineral Salts • Water

Disposed of in urine and sweat

Organs of Excretion • • • •

Kidney Liver Lungs Skin

• These organs work with the circulatory, nervous and endocrine systems to help keep the body’s internal environment constant and maintain homeostasis

The Kidneys and the Urinary System • Composed of: – Kidneys – Ureters – Bladder – Urethra

• Summary: – Kidneys produce urine which passes to a tube called a ureter – Urine flows to the urinary bladder where it is stored.

– During urination the stored urine travels from the bladder to the outside of the body through the urethra – Helps to maintain a proper fluid balance in the body

Structure of the Kidney – Cortex: outer part where blood is filtered – Medulla: middle part made up of tubes called collecting ducts that carry filtrate to pelvis – Pelvis: inner region connected to ureter

Kidney Function Filters the blood Primary organ of “Osmoregulation” (regulating water balance)

The Nephron

• Part of the kidney where filtering of the blood happens – Each kidney has over a million nephrons – Part of nephron lies in cortex, part in the medulla

Filtration and Reabsorption in the Nephron Renal vein Renal Artery Glomerulus

Bowman’s Capsule

Loop of Henle

Collecting duct for urine

Parts of the Nephron • Glomerulus: – group of capillaries in a tight ball at end of nephron – Where substances filter out of blood and enter nephron as “filtrate”

• Bowman’s Capsule: – cup shaped structure that surrounds the glomerulus and receives filtrate from blood

• Loop of Henle (Renal Tubule) – Long loop of the nephron – Surrounded by capillaries – Reabsorption of certain parts of filtrate back into the bloodstream takes place here. Materials reabsorbed from filtrate

How is Urine Formed? • Process of filtration and reabsorption – Filtration of materials from blood – Reabsorption of certain useful substances

• Filtration: – Blood enters kidney under pressure forcing filtrate through thin walls of glomerulus into Bowman’s Capsule – Filtrate: • Composed of water, urea, glucose, amino acids, various salts

• But: – We need a lot of this fluid back! – Otherwise we lose too much water, glucose and salts

– On average about 180 liters of filtrate is formed in 24 hours but only 1 to 1.5 liters of urine is produced!

• Reabsorption: – takes place in renal tubule (Loop of Henle) – Returns 99% of filtrate back to the blood • Most of the water – By passive transport

• Glucose, amino acids and most of the salts – Mostly by active transport

– Way to conserve water

– Way to keep nutrients like glucose and amino acids – Filtrate becomes very concentrated as urine

• Urine: made of urea, water and excess salts

• Interactive showing Nephron Function and what is filtered and reabsorbed: • http://www.biologymad.com/resources/kidn ey.swf

• The Excretory System and The Nephron • http://www.youtube.com/watch?v=ROHOn PUu0aA&safe=active

Regulation of Urine Output • Hypothalamus (small area of brain) – Secretes hormone called ADH (antidiuretic hormone)

• Fluid intake low = ADH secreted – Stimulates reabsorption of water in nephron. – Urine output decreases and is more concentrated

• Fluid intake high: ADH not secreted – Less reabsorption of water in nephron – Urine output increases and is relatively dilute

Kidney Disorders • Kidney Stones: – found when substances crystalize out of urine – may may block kidney, ureters, bladder •

http://www.youtube.com/watch?v=16ewFJiQtw&safe=active

• Uremia: – urine and other wastes are not filtered out of blood, poisoning cells

• Kidney Dialysis: – when the kidneys fail, excess fluids and wastes accumulate in blood. – use artificial kidney to filter blood

http://www.youtube.com/watch?v=t QzqGHKkdE8&safe=active

• Gout: – uric acid crystals are produced and accumulate in joints – Similar to arthritis

http://www.youtube.com/watch? v=9nB0JD9Lpq0&safe=active

• Crash Course on the Excretory System • http://www.youtube.com/watch?v=WtrYotj YvtU&safe=active • Tutorials on Kidney and Nephron Function: • http://wps.aw.com/bc_martini_eap_4/40/10 469/2680237.cw/content/index.html

The Liver • Helps to filter the blood and regulate the makeup of body fluids

• Detoxifies Blood – Removes substances such as drugs, alcohol and certain toxins from the blood – Changes them to an inactive form which is excreted from the body by kidneys

• Breaks Down Worn Out Red Blood Cells – RBCs don’t have nuclei and don’t live very long – Part of the hemoglobin molecule is found in bile.

• Excretes Bile: – the liver synthesizes and excretes bile into gall bladder to add in fat digestion

• Forms Urea – Excess amino acids from protein digestion are broken down in the liver by deamination.

– Deamination: • “amino group” is removed from amino acid • changed to ammonia NH3 • ammonia is toxic to the body and is changed into urea in the liver

– Kidneys filter out urea in the nephron and excrete it from the body in urine.

Diseases of the Liver • Cirrhosis: – disease caused by overloading liver with harmful materials such as alcohol – Liver becomes enlarged and overgrown with excess tissue

• Jaundice: – Bile is not secreted properly – Reabsorbed hemoglobin fragments form bilirubin in the blood and make the skin look jaundiced or yellow

Lungs • An excretory organ • Give off carbon dioxide, and excess water both metabolic wastes.

Skin • Gives off sweat or perspiration to help regulate body temperature. • Sweat is composed of 99% water, salts and some urea.

• Also capillaries close to skin surface help to eliminate or conserve heat.

Skin • Skin is the largest organ of the human body. • It protects the inner organs and tissues of the body, and has sensory cells to help us detect changes in our environment. • It also has sebaceous glands that produce oil that help protect skin and keep it soft and pliable.

Comparative Excretory Systems in Animals

Excretion in Protists and Hydra • Direct contact with cell membrane and environment. • Wastes diffuse out of cell membranes or are excreted through active transport • Metabolic wastes include: carbon dioxide, ammonia and mineral salts • Ammonia is the chief nitrogenous wastes of protists

• Freshwater protists use contractile vacuoles and active transport to remove excess water that is constantly entering the cell by osmosis. • Concentration of water greater outside cell than inside so it moves across membrane by diffusion into cell.

• Salt water protists don’t have this problem.

Excretion in Earthworms • Pairs of nephridia found in almost every segment – Surrounded by capillaries and filter wastes from blood – Wastes form a dilute urine which passes through a bladder and out through the nephridiopore.

• Urine is water, mineral salts, ammonia and urea.

Don’t Forget! • Thin outer skin is the respiratory surface – Below skin are capillaries carrying blood with hemoglobin

• Live in moist soil and constantly secretes mucus to keep skin moist – If exposed to air and dries out it will suffocate

Excretion in Grasshoppers • Malpighian tubules are bathed by blood from open circulatory system – Wastes enter tubules and pass into intestine – Water and other useful substances are reabsorbed and returned to body fluid

• Dry nitrogenous waste product: uric acid – Helps conserve water

Don’t Forget! • System of tracheal tubes for gas exchange – Branching air tubes carry air directly to cells – Muscle contractions pump air in and out of tubes

• Spiracles: outside openings that lead to tracheal tubes