Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 The Excretory System Copyright Pearson Prentice Hall

Functions of the Excretory System Every cell produces metabolic wastes. The process by which these wastes are eliminated is called excretion - Skin excretes excess water and salts in the form of sweat. - Lungs excrete carbon dioxide - Kidneys also play a major role in excretion. Copyright Pearson Prentice Hall

Functions of the Excretory System The Kidneys What are the functions of the kidneys? remove waste products from the blood. maintain blood pH. regulate the water content of blood - therefore, blood volume Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys The Kidneys - located on either side of the spinal column - Ureter carries urine to the urinary bladder - Urinary bladder is where urine is stored Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Structure of the Kidneys Kidney Nephron Kidneys are made up of nephrons. Blood enters the nephron, where impurities are filtered out and emptied into the collecting duct. The purified blood leaves the nephron through the renal vein. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Kidney Structure  A kidney has two distinct regions: The inner part is called the renal medulla. The outer part is called the renal cortex. Blood enters the kidney through the renal artery The kidney removes urea, excess water, and other waste products and passes them to the ureter The clean, filtered blood leaves the kidney through the renal vein and returns to circulation Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Cortex Medulla Renal artery Renal vein Ureter To the bladder Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Nephrons: - functional units of the kidney - located in the renal cortex Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Capillaries Bowman’s capsule Glomerulus Kidneys are made up of nephrons. Blood enters the nephron, where impurities are filtered out and emptied into the collecting duct. The purified blood leaves the nephron through the renal vein. Collecting duct Vein Artery To the ureter Loop of Henle Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Capillaries Each nephron has its own blood supply: an arteriole (artery) a venule (vein) a network of capillaries connecting them Collecting duct Vein Artery To the ureter Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys How is Blood filtered? As blood enters a nephron, impurities are filtered out and emptied into the collecting duct The purified blood exits the nephron through the venule (vein) The mechanism of blood purification involves two distinct processes: filtration and reabsorption Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Filtration  - Passing a liquid or gas through a filter to remove wastes - mainly takes place in the glomerulus The glomerulus is a small network of capillaries encased in the top of the nephron by a hollow, cup-shaped structure called Bowman's capsule. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys Reabsorption  Most of the material removed from the blood at Bowman's capsule makes its way back into the blood. The process in which liquid is taken back into a vessel is called reabsorption Almost 99% of the water that enters Bowman’s capsule is reabsorbed into the blood. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Kidneys As the kidney works, purified blood is returned to circulation while urine is collected in the urinary bladder. Urine is stored here until it is released from the body through a tube called the urethra. Copyright Pearson Prentice Hall

Control of Kidney Function The activity of the kidneys is mostly controlled by the composition of the blood. In addition, regulatory hormones are released in response to the composition of blood. Copyright Pearson Prentice Hall

Control of Kidney Function For Example: When you drink a liquid, it is absorbed into the blood - As a result, the concentration of water in the blood increases - As the amount of water in the blood increases the rate of water reabsorption in the kidneys decreases Therefore: Less water is returned to the blood, and excess water is sent to the urinary bladder to be excreted as urine Copyright Pearson Prentice Hall

Homeostasis by Machine Humans have two kidneys, but can survive with only one. If both kidneys are damaged by disease or injury, there are two options: a kidney transplant kidney dialysis Copyright Pearson Prentice Hall

Homeostasis by Machine Kidney dialysis works as follows: Blood is removed by a tube and pumped through special tubing that acts like nephrons Tiny pores in the tubing allow salts and small molecules to pass through Wastes diffuse out of the blood into the fluid-filled chamber, allowing purified blood to be returned to the body Copyright Pearson Prentice Hall

Homeostasis by Machine Kidney Dialysis Blood in tubing flows through dialysis fluid Blood pump Vein Artery Shunt Used dialysis fluid For people with damaged kidneys, dialysis machines can perform many of the functions of the kidneys. Dialysis machine Fresh dialysis fluid Compressed air Air detector Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 A dialysis machine performs the function of which structure in the excretory system? nephron ureter urethra glomerulus Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 In the human body, the kidneys play an important role in producing digestive enzymes. circulating the blood. destroying old red blood cells. maintaining homeostasis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 In the nephron, most filtration occurs in the renal tubule. capillaries. glomerulus. loop of Henle. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 Urine leaves the body through the loop of Henle. glomerulus. urethra. bladder. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–3 Materials filtered out of the blood include all of the following EXCEPT: water. urea. amino acids. plasma proteins. Copyright Pearson Prentice Hall

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