Chapter 23 The Circulatory, Respiratory, Digestive, and Excretory ...

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Figure 23.34: The kidneys are the chief organs of the urinary system. Figure 23.35: Each kidney is supplied by a renal artery and renal vein. www.ck12.org 722
The kidney and nephron are discussed at http://www.youtube.com/user/khanacademy#p/c/7A9646BC5110CF64/ 57/cc8sUv2SuaY (18:38). Figure 23.36: (Watch Youtube Video) http://www.ck12.org/flexbook/embed/view/228 Additional information about the nephron is shown at http://www.youtube.com/user/khanacademy#p/ c/7A9646BC5110CF64/58/czY5nyvZ7cU. Figure 23.37: (Watch Youtube Video) http://www.ck12.org/flexbook/embed/view/229 Filtering Blood and Forming Urine As shown in Figure 23.38, each nephron is like a tiny filtering plant. It filters blood and forms urine in the following steps: 1. Blood enters the kidney through the renal artery, which branches into capillaries. When blood passes through capillaries of the glomerulus of a nephron, blood pressure forces some of the water and dissolved substances in the blood to cross the capillary walls into Bowman’s capsule. 2. The filtered substances pass to the renal tubule of the nephron. In the renal tubule, some of the filtered substances are reabsorbed and returned to the bloodstream. Other substances are secreted into the fluid. 3. The fluid passes to a collecting duct, which reabsorbs some of the water and returns it to the bloodstream. The fluid that remains in the collecting duct is urine. Excretion of Urine From the collecting ducts of the kidneys, urine enters the ureters, two muscular tubes that move the urine by peristalsis to the bladder (see Figure 23.34). The bladder is a hollow, sac-like organ that stores urine. When the bladder is about half full, it sends a nerve impulse to a sphincter to relax and let urine flow out of the bladder and into the urethra. The urethra is a muscular tube that carries urine out of the 723 www.ck12.org
Page 1 and 2: Chapter 23 The Circulatory, Respira
Page 3 and 4: Figure 23.1: The function of the ci
Page 5 and 6: • Arteries are muscular blood ves
Page 7 and 8: Figure 23.6: The systemic circulati
Page 9 and 10: Blood Blood is a fluid connective t
Page 11 and 12: • Blood is a fluid connective tis
Page 13 and 14: Figure 23.12: (Watch Youtube Video)
Page 15 and 16: Figure 23.14: Alveoli are tiny sacs
Page 17 and 18: • Pneumonia is a disease in which
Page 19 and 20: Apply Concepts 6. Sometimes people
Page 21 and 22: Figure 23.18: The digestive system
Page 23 and 24: The following interactive animation
Page 25 and 26: Table 23.1: (continued) Enzyme What
Page 27 and 28: • Food allergies occur when the i
Page 29 and 30: Table 23.3: (continued) Vitamin Fun
Page 32 and 33: Figure 23.30: Nutrition facts label
Page 34 and 35: Lesson Review Questions Recall 1. W
Page 38 and 39: Figure 23.38: The parts of a nephro
Page 40 and 41: 2. List organs of the excretory sys

Chapter 23 The Circulatory, Respiratory, Digestive, and Excretory ...

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