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The Urinary System

The Urinary System. Kidneys. Kidneys. The paired kidneys are retroperitoneal in the superior lumbar region Each kidney has a medial indentation (hilus), where the renal artery, renal vein, and ureter are seen. Kidneys. Each kidney is enclosed in a tough fibrous capsule

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The Urinary System

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  1. The Urinary System

  2. Kidneys

  3. Kidneys • The paired kidneys are retroperitoneal in the superior lumbar region • Each kidney has a medial indentation (hilus), where the renal artery, renal vein, and ureter are seen

  4. Kidneys • Each kidney is enclosed in a tough fibrous capsule • A fatty cushion holds the kidneys against the body trunk wall

  5. A longitudinal section of a kidney reveals an outer cortex, deeper medulla, and medial pelvis. • Extensions of the pelvis (calyces) surround the tips of medullary pyramids and collect urine draining from them

  6. The renal artery, which enters the kidney, breaks into segmental, lobar, and then interlobar arteries that travel outward through the medulla • Interlobar arteries split into arcuate arteries, which branch to produce interlobular arteries, which serve the cortex

  7. Nephrons are structural and functional units of the kidneys • Each consists of a glomerulus and a renal tubule

  8. Subdivisions of the renal tubule (from the glomerulus onward) are: • glomerular capsule • proximal convoluted tubule • loop of Henle • distal convoluted tubule

  9. A second (pertubular) capillary bed is also associated with each nephron

  10. Nephron functions include: • Filtration • Reabsorption • Secretion

  11. Filtrate formation is the roles of the high-pressure glomerulus • Filtrate is essentially plasma without blood proteins

  12. In reabsorption, done by tubule cells, needed substances are removed from filtrate (amino acids, glucose, water, and some ions) and returned to blood

  13. The tubule cells also secrete additional substances into filtrate • Secretion is important to rid the body of drugs and excess ions and to maintain acid-base balance of blood

  14. Urine is clear, yellow, and usually slightly acidic • pH values vary widely • Substances normally found in urine are; • Nitrogenous wastes • Water • Various ions (sodium and potassium) • Substances normally absent • Glucose • Blood proteins • Blood • Pus (WBCs) • Bile

  15. Ureters, Urinary Bladder, and Urethra

  16. The ureters are slender tubes running from kidney to the bladder • They conduct urine by peristalsis from kidney to bladder

  17. The bladder is a muscular sac posterior to the pubic symphysis • It has two inlets (ureters) and one outlet (urethra) • In males, the prostate gland surrounds its outlet • The function of the bladder is to store urine

  18. The urethra is a tube that leads urine from the bladder to the body exterior • In females, it is 3 to 4cm long and conducts only urine • In males, it is 20cm long and conducts both urine and sperm

  19. The internal sphincter of smooth muscle is at the bladder urethra junction • The external sphincter of skeletal muscle is located more inferiorly

  20. Micturition is emptying of the bladder • The micturition reflex causes the involuntary internal sphincter to open when stretch receptors in the bladder wall are stimulated • Since the external sphincter is voluntarily controlled, micturition can ordinarily be temporarily delayed • Incontinence is the inability to control micturition

  21. Fluid, Electrolyte, and Acid-Base Balance

  22. Blood composition depends on diet, cellular metabolism, and urinary output • To maintain blood composition, the kidney must: • 1. Allow nitrogen-containing wastes (urea, ammonia, creatinine, uric acid) to leave the body in the urine

  23. 2. Maintain water and electrolyte balance by absorbing more or less water and reclaiming ions in response to hormonal signals. • ADH increases water reabsorption and conserves body water • Aldosterone increases reabsorption of sodium and water and decreases potassium reabsorption

  24. 3. Maintain acid-base balance by actively secreting bicarbonate ions (and retaining H+) and by absorbing bicarbonate ions (and secreting H+) • Chemical buffers tie up excess H+ or bases temporarily; respiratory centers modify blood pH by retaining carbon dioxide (decreases pH) or by eliminating more carbon dioxide from the blood (increases blood pH) • Only the kidney can remove metabolic acids and excess bases from the body

  25. Developmental Aspects of the Urinary System

  26. The kidneys begin to develop in the first few weeks of embryonic life and are excreting urine by the third month

  27. Common congenital abnormalities include polycystic kidney (cyst form on kidneys; genetic) and hypospadias (urethra develops on underside)

  28. Common urinary system problems in children and young to middle-aged adults are infections caused by fecal microorganisms, sexually transmitted disease causing microorganisms, and Streptococcus

  29. Renal failure is an uncommon, but extremely serious, problem in which kidneys are unable to concentrate urine, and dialysis must be done to maintain chemical homeostasis of blood

  30. With, age filtrate rate decreases and tubule cells become less efficient at concentrating urine, leading to urgency, frequency, and incontinence (can not hold urine) • In males urinary retention (unable to release urine) is another common problem

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