Excretion

Do Now Your Body’s Filter Section 38-3 Your Body’s Filter Have you ever seen a water-purification system attached to a faucet? This system removes impurities from the water such as arsenic or other chemicals that can be harmful to people. As water passes through the filters contained in the system, the impurities are trapped on the surface of the filters. Eventually, the water that comes out of this purifier is free of the impurities. 1. Your body has its own system for filtering blood. Why might the blood in your body need to be filtered? 2. What organ(s) do you think filters your blood? 3. How do you think the filtered materials leave your body?

Checks and Balances Your body is amazingly maintaining homeostasis through an intricate system of checks and balances to satisfy your body’s needs and remove waste products that are not useful or toxic

Human Excretion Excretion = the process by which wastes are eliminated from the body The excretory system includes: Lungs: excrete gaseous carbon dioxide and water from cellular (aerobic) respiration Rectum: excrete solid undigested remains from food Skin: excretes excess water, salts, urea Kidneys and accessory organs

Protozoa and Cnidarians Since all cells are in contact with the external, aqueous environment, they excrete using simple diffusion through the cell membrane. Contractile vacuole = organelle specialized for water excretion by active transport in freshwater organisms

Annelida (Earthworm) Nephridia tubules = excrete water, mineral salts and nitrogenous wastes (urea) from each body segment Fluid from the circulatory system is also filtered out of the blood into fluid that fills the central body cavity.

Arthropods (Grasshopper) Malpighian tubules = accumulate mineral salts and uric acid forming solid uric acid crystals (conserving water) Crystals are excreted with solid waste in the intestines.

The Human Urinary System The urinary system rids the blood of wastes produced by the metabolism of nutrients and controls blood volume by removing excess water produced by body cells. The urinary system includes: Kidneys Urinary bladder Connecting tubules: Ureter Urethra

The Urinary System Section 38-3 Artery Vein Kidney (Cross Section) Cortex Medulla Ureter Urinary bladder Urethra

Kidneys Most people have 2 kidneys located on either side of the spinal column on your lower back Ureters = tubes that carry urine from each kidney to the urinary bladder Urinary bladder = saclike organ that stores urine until it can be excreted The kidneys filter blood by removing urea, excess water and other wastes collected as urine and the clean filtered blood returns to circulation

Kidney Structure Inner part = renal medulla Outer part = renal cortex Functional units of the kidney = nephrons About 1 million nephrons in each kidney Each nephron has its own arteriole (small artery), venule (small vein), and network of capillaries to filter blood

Figure 38–17 Structure of the Kidneys Section 38-3 Kidney Nephron Cortex Medulla Renal artery Renal vein Ureter To the bladder Bowman’s capsule Glomerulus Capillaries Collecting duct To the ureter Loop of Henle Artery Vein

Filtration Blood enters a nephron through the glomerulus (network of capillaries) in Bowman’s capsule (cup-shaped structure) Blood is under high pressure causing fluid to flow from the blood into Bowman’s capsule = filtration The filtrate contains water, urea, glucose, salts, amino acids, and some vitamins

Reabsorption Most of the material removed from the blood at Bowman’s capsule makes its way back into the blood = reabsorption 99% of water is reabsorbed into blood

Secretion Some materials, including hydrogen ions (H+) are transferred from the blood into the filtrate = secretion

Figure 38–18 The Nephron Reabsorption As the filtrate flows through the renal tubule, most of the water and nutrients are reabsorbed into the blood. The concentrated fluid that remains is called urine. Filtration Most filtration occurs in the glomerulus. Blood pressure forces water, salt, glucose, amino acids, and urea into Bowman’s capsule. Proteins and blood cells are too large to cross the membrane; they remain in the blood. The fluid that enters the renal tubules is called the filtrate. Secretion Substances such as hydrogen ions are transferred from the blood to the filtrate. http://www.youtube.com/watch?v=glu0dzK4dbU&feature=related

Urine The material that remains = urine containing urea, salts, water and other substances (ammonia and uric acid) The loop of Henle conserves water and minimizes the volume of urine Urine is stored in the urinary bladder until it can be released from the body through a tube = urethra

Kidney Function The kidneys maintain homeostasis by: Regulating the water content of the blood (blood volume) Maintaining blood pH Removing waste products from the blood

Dialysis Although you are born with two kidneys, you can live with only one kidney. If both kidneys malfunction, a kidney dialysis machine can artificially filter blood