1. 17 -1 Chapter 17 Urinary System

2. 17 -2  Introduction A.The urinary system consists of two kidneys that filter the blood, two ureters, a urinary bladder, and a urethra to convey waste substances to the outside. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3. 17 -3  Kidneys A.The kidney is a reddish brown, bean-shaped organ 12 centimeters long; it is enclosed in a tough, fibrous capsule. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

4. 17 -4 B.Location of the Kidneys 1.The kidneys are positioned retroperitoneally on either side of the vertebral column between the twelfth thoracic and third lumbar vertebrae, with the left kidney slightly higher than the right. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. 17 -5 C.Kidney Structure 1.A medial depression in the kidney leads to a hollow renal sinus into which blood vessels, nerves, lymphatic vessels, and the ureter enter. 2.Inside the renal sinus lies a renal pelvis that is subdivided into major and minor calyces; small renal papillae project into each minor calyx. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6. 17 -6 3.Two distinct regions are found within the kidney: a renal medulla and a renal cortex. a.The renal medulla houses tubes leading to the papillae. b.The renal cortex contains the nephrons, the functional units of the kidney. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

7. 17 -7 D.Kidney Functions 1.The kidneys function to regulate the volume, composition, and pH of body fluids and remove metabolic wastes from the blood in the process. 2.The kidneys also help control the rate of red blood cell formation by secreting erythropoietin, and regulate blood pressure by secreting renin. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

8. 17 -8  Urine Formation A.Urine formation involves glomerular filtration, tubular reabsorption, and tubular secretion. B.Glomerular Filtration 1.Urine formation begins when the fluid portion of the blood is filtered by the glomerulus and enters the glomerular capsule as glomerular filtrate. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. 17 -9 C.Filtration Pressure 1.The main force responsible for moving substances by filtration through the glomerular capillary wall is the hydrostatic pressure of the blood inside. 2.Due to plasma proteins, osmotic pressure of the blood resists filtration, as does hydrostatic pressure inside the glomerular capsule. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

10. 17 -10 D.Filtration Rate 1.The factors that affect the filtration rate are filtration pressure, glomerular plasma osmotic pressure, and hydrostatic pressure in the glomerular capsule. 2.When the afferent arteriole constricts in response to sympathetic stimulation, filtration pressure, and thus filtration rate, declines. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

11. 17 -11 3.When the efferent arteriole constricts, filtration pressure increases, increasing the rate of filtration. 4.When osmotic pressure of the glomerular plasma is high, filtration rate decreases. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

12. 17 -12 5.When hydrostatic pressure inside the glomerular capsule is high, filtration rate declines. 6.On average, filtration rate is 125 milliliters per minute or 180 liters in 24 hours, most of which is reabsorbed farther down the nephron. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

13. 17 -13 E.Regulation of Filtration Rate 1.Glomerular filtration rate is relatively constant, although sympathetic impulses may decrease the rate of filtration. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

14. 17 -14 2.Another control over filtration rate is the renin-angiotensin system, which regulates sodium excretion. a.When the sodium chloride concentration in the tubular fluid decreases, the macula densa senses these changes and causes the juxtaglomerular cells to secrete renin. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

15. 17 -15 b.Secretion of renin triggers a series of reactions leading to the production of angiotensin II, which acts as a vasoconstrictor; this may, in turn, affect filtration rate. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16. 17 -16 c.Presence of angiotensin II also increases the secretion of aldosterone, which stimulates reabsorption of sodium. d.The heart can also increase filtration rate when blood volume is high. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17. 17 -17 F.Tubular Reabsorption 1.Changes in the fluid composition from the time glomerular filtrate is formed to when urine arrives at the collecting duct are largely the result of tubular reabsorption of selected substances. 2.Most of the reabsorption occurs in the proximal convoluted tubule, where cells possess microvilli with carrier proteins. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18. 17 -18 3.Carrier proteins have a limited transport capacity, so excessive amounts of a substance will be excreted into the urine. 4.Glucose and amino acids are reabsorbed by active transport, water by osmosis, and proteins by pinocytosis. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

19. 17 -19 G.Sodium and Water Reabsorption 1.Sodium ions are reabsorbed by active transport, and negatively charged ions follow passively. 2.As sodium is reabsorbed, water follows by osmosis. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20. 17 -20 H.Regulation of Urine Concentration and Volume 1.Most of the sodium ions are reabsorbed before the urine is excreted, and sodium is concentrated in the renal medulla by the countercurrent mechanism. 2.Normally the distal convoluted tubule and collecting duct are impermeable to water unless the hormone ADH is present. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21. 17 -21 I.Urea and Uric Acid Excretion 1.Urea is a by-product of amino acid metabolism; uric acid is a by- product of nucleic acid metabolism. 2.Urea is passively reabsorbed by diffusion but about 50% of urea is excreted in the urine. 3.Most uric acid is reabsorbed by active transport and a small amount is secreted into the renal tubule. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22. 17 -22 J.Tubular Secretion 1.Tubular secretion transports certain substances from the plasma into the renal tubule. 2.Active transport mechanisms move excess hydrogen ions into the renal tubule along with various organic compounds. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23. 17 -23 3.Potassium ions are secreted both actively and passively into the distal convoluted tubule and the collecting duct. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

24. 17 -24 K.Urine Composition 1.Urine composition varies from time to time and reflects the amounts of water and solutes that the kidneys eliminate to maintain homeostasis. 2.Urine is 95% water, and also contains urea, uric acid, a trace of amino acids, and electrolytes. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

25. 17 -25  Urine Elimination A.After forming in the nephrons, urine passes from the collecting ducts to the renal papillae, then to the minor and major calyces, and out the renal pelvis to the ureters, urinary bladder, and finally to the urethra, which conveys urine to the outside. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

26. 17 -26 B.Ureters 1.The ureters are muscular tubes extending from the kidneys to the base of the urinary bladder. 2.The wall of the ureter is composed of three layers: mucous coat, muscular coat, and outer fibrous coat. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

27. 17 -27 3.Muscular peristaltic waves convey urine to the urinary bladder where it passes through a flaplike valve in the mucous membrane of the urinary bladder. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28. 17 -28 C.Urinary Bladder 1.The urinary bladder is a hollow, distensible, muscular organ lying in the pelvic cavity. 2.The internal floor of the bladder includes the trigone, which is composed of the openings of the two ureters and the urethra. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29. 17 -29 3.The wall of the urinary bladder is made up of four coats: inner mucous coat, submucous coat, muscular coat made up of detrusor muscle, and outer serous coat. a.The portion of the detrusor muscle that surrounds the neck of the bladder forms an internal sphincter muscle. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30. 17 -30 Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

31. 17 -31 D.Micturition 1.Urine leaves the bladder by the micturition reflex. 2.The detrusor muscle contracts and the external urethral sphincter (in the urogenital diaphragm) must also relax. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

32. 17 -32 3.Stretching of the urinary bladder triggers the micturition reflex center located in the sacral portion of the spinal cord. 4.Return parasympathetic impulses cause the detrusor muscle to contract in waves, and an urge to urinate is sensed. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

33. 17 -33 5.When these contractions become strong enough, the internal urethral sphincter is forced open. 6.The external urethral sphincter is composed of skeletal muscle and is under conscious control. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

34. 17 -34 E.Urethra 1.The urethra is a tube that conveys urine from the urinary bladder to the outside. 2.It is a muscular tube with urethral glands that secrete mucus into the urethral canal. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

35. Kidney Stones A kidney stone is a solid mass made up of tiny crystals. One or more stones can be in the kidney or ureter at the same time. 17 -35

36. Symptoms The main symptom is severe pain that starts suddenly and may go away suddenly: Pain may be felt in the belly area or side of the back Pain may move to groin area (groin pain) or testicles (testicle pain) Other symptoms can include: Abnormal urine color Blood in the urine Chills Fever Nausea Vomiting 17 -36

37. Treatment The goal of treatment is to relieve symptoms and prevent further symptoms. (Kidney stones that are small enough usually pass on their own.) Treatment varies depending on the type of stone and how severe the symptoms are. People with severe symptoms might need to be hospitalized. 17 -37

38. Treatment When the stone passes, the urine should be strained and the stone saved and tested to determine the type. Drink at least 6 - 8 glasses of water per day to produce a large amount of urine. Some people might need to get fluids through a vein (intravenous). Pain relievers can help control the pain of passing the stones (renal colic). For severe pain, you may need to take narcotic pain killers or nonsteroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen. Depending on the type of stone, your doctor may prescribe medicine to decrease stone formation or help break down and remove the material that is causing the stone. Medications can include: Allopurinol (for uric acid stones) Antibiotics (for struvite stones) Diuretics Phosphate solutions 17 -38

39. Treatment Surgery is usually needed if: The stone is too large to pass on its own The stone is growing The stone is blocking urine flow and cuasing an infection or kidney damage Today, most treatments are much less invasive than in the past. Extracorporeal shock-wave lithotripsy is used to remove stones slightly smaller than a half an inch that are located near the kidney. This method uses ultrasonic waves or shock waves to break up stones. Then, the stones leave the body in the urine. Percutaneous nephrolithotomy is used for large stones in or near the kidney, or when the kidneys or surrounding areas are incorrectly formed. The stone is removed with an endoscope that is inserted into the kidney through a small opening. Ureteroscopy may be used for stones in the lower urinary tract. Standard open surgery (nephrolithotomy) may be needed if other methods do not work or are not 17 -39

40. Urinary Tract Infections Urinary tract infections are a serious health problem affecting millions of people each year. Infections of the urinary tract are the second most common type of infection in the body. Urinary tract infections (UTIs) account for about 8.3 million doctor visits each year.* Women are especially prone to UTIs for reasons that are not yet well understood. One woman in five develops a UTI during her lifetime. UTIs in men are not as common as in women but can be very serious when they do occur. 17 -40

41. What are the causes of UTI? Normally, urine is sterile. It is usually free of bacteria, viruses, and fungi but does contain fluids, salts, and waste products. An infection occurs when tiny organisms, usually bacteria from the digestive tract, cling to the opening of the urethra and begin to multiply. The urethra is the tube that carries urine from the bladder to outside the body. Most infections arise from one type of bacteria, Escherichia coli (E. coli), which normally lives in the colon. In many cases, bacteria first travel to the urethra. When bacteria multiply, an infection can occur. An infection limited to the urethra is called urethritis. If bacteria move to the bladder and multiply, a bladder infection, called cystitis, results. If the infection is not treated promptly, bacteria may then travel further up the ureters to multiply and infect the kidneys. A kidney infection is called pyelonephritis. 17 -41

42. What are the causes of UTI? Microorganisms called Chlamydia and Mycoplasma may also cause UTIs in both men and women, but these infections tend to remain limited to the urethra and reproductive system. Unlike E. coli, Chlamydia and Mycoplasma may be sexually transmitted, and infections require treatment of both partners. The urinary system is structured in a way that helps ward off infection. The ureters and bladder normally prevent urine from backing up toward the kidneys, and the flow of urine from the bladder helps wash bacteria out of the body. In men, the prostate gland produces secretions that slow bacterial growth. In both sexes, immune defenses also prevent infection. But despite these safeguards, infections still occur. 17 -42

43. How is UTI diagnosed? To find out whether you have a UTI, your doctor will test a sample of urine for pus and bacteria. You will be asked to give a "clean catch" urine sample by washing the genital area and collecting a "midstream" sample of urine in a sterile container. This method of collecting urine helps prevent bacteria around the genital area from getting into the sample and confusing the test results. Usually, the sample is sent to a laboratory, although some doctors' offices are equipped to do the testing. In the urinalysis test, the urine is examined for white and red blood cells and bacteria. Then the bacteria are grown in a culture and tested against different antibiotics to see which drug best destroys the bacteria. 17 -43

44. How is UTI treated? UTIs are treated with antibacterial drugs. The choice of drug and length of treatment depend on the patient's history and the urine tests that identify the offending bacteria. The sensitivity test is especially useful in helping the doctor select the most effective drug. 17 -44