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Chapter 16: Urinary System and Excretion

This chapter explores the urinary system's role in excretion, the removal of metabolic waste products from the body. It covers the urinary organs, kidney structure, urine production, and the functions of the urinary system, including excretion of metabolic wastes, maintenance of water-salt balance, acid-base balance, and secretion of hormones.

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Chapter 16: Urinary System and Excretion

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  1. Chapter 16: Urinary System and Excretion

  2. EXCRETION • EXCRETION – Is the removal of metabolic waste products from the body. Do NOT confuse this with the elimination of undigested wastes. • Failure to remove these metabolic wastes would result in a build up of toxins in the body, eventually leading to death. Our focus will be on the URINARY SYSTEM

  3. Urinary System • Urinary Organs • The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. • The bean-shaped kidneys are at the back of the abdominal wall beneath the peritoneum, protected by the lower rib cage. • The renal artery and renal vein along with ureters exit the kidney at the hilum.

  4. The kidneys produce urine which is conducted by two muscular tubes called ureters to the urinary bladder where it is stored before being released through the urethra. Two urethral sphincters control the release of urine. In females, the urethra is 4 cm long; in males, the urethra is 20 cm long and conveys both urine and sperm during ejaculation. • How much urine do you think your bladder could hold before you wet yourself? • 200 ml • 600 ml • 1000 ml • 1.8 liters

  5. The urinary system • About what % of the blood that leaves the left ventricle will be delivered to the kidneys? • 20% C) 50% • 75% D)3%

  6. Urination • As the bladder fills with urine, sensory impulses travel to the spinal cord where motor nerve impulses return and cause the bladder to contract and sphincters to relax. • With maturation, the brain controls this reflex and delays urination, the release of urine, until a suitable time.

  7. Urination

  8. Kidney Structure • The kidneys filter wastes from the blood, and thus the renal arteries branch extensively into smaller arteries and then arterioles inside each kidney. • Many venules unite to form small veins, which merge to become the renal vein.

  9. There are three regions to a kidney: an outer renal cortex, an inner renal medulla, and a central space called the renal pelvis. Microscopically, each contains over one million nephrons. The nephrons produce urine which flows into a collecting duct; several collecting ducts merge and drain urine into the renal pelvis.

  10. Functions of the Urinary System • Excretion refers to the elimination of metabolic wastes that were cell metabolites; this is the function of the urinary system. • Kidneys play a role in homeostasis of the blood by excreting metabolic wastes, and by maintaining the normal water-salt and acid-base balances of blood.

  11. Excretion of Metabolic Wastes • Kidneys excrete nitrogenous wastes, including urea, uric acid, and creatinine. • Urea is a by-product of amino acid metabolism. Deamination of AA’s. • The metabolic breakdown of creatine phosphate in muscles releases creatinine. • Uric acid is produced from breakdown of nucleotides. • Collection of uric acid in joints causes gout.

  12. Maintenance of Water-Salt Balance • Kidneys maintain the water-salt balance of the body which, in turn, regulates blood pressure. • Salts, such as NaCl, in the blood cause osmosis into the blood; the more salts, the greater the blood volume and also blood pressure. • Kidneys also maintain correct levels of potassium, bicarbonate, and calcium ions in blood.

  13. Maintenance of Acid-Base Balance • The kidneys regulate the acid-base balance of the blood. • Kidneys help keep the blood pH within normal limits by excreting hydrogen ions (H+) and reabsorbing bicarbonate ions (HCO3-) as needed. • Urine usually has a pH of 6 or lower because our diet often contains acidic foods. • If you are stung by a jellyfish, what have some people recommended that you should do? • But you shouldn’t do it, as the pH is helpful, but the other chemicals can cause more irritation. • So what household substance found at the beach food concession would do a better job?

  14. Secretion of Hormones • Kidneys secrete or activate several hormones: • They secrete the hormone erythropoietin to stimulate red blood cell production, • They activate vitamin D to the hormone calcitriol needed for calcium reabsorption during digestion, and • They release renin, a substance that leads to the secretion of aldosterone. • Why does it take so long to climb Mount Everest? Thin Air !

  15. PRACTICE QUIZ _____/12 • E • I • F • J • K • G • L • H

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