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Understanding the Urinary System: Organs and Functions

This chapter provides an overview of the urinary system, including the major organs (kidneys, ureters, urinary bladder, and urethra) and their functions. It explains how urine is formed, the processes of filtration, reabsorption, and secretion, and the role of the kidneys in maintaining blood composition. It also discusses the excretion of nitrogen-containing waste, water and electrolyte balance, and the regulation of blood pH. Additional topics include the characteristics of urine, substances found and not found in urine, and the process of micturition.

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Understanding the Urinary System: Organs and Functions

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  1. Do Now • What are the major organs of the urinary system? • What are the major functions of the urinary system?

  2. Chapter 15 The Urinary System

  3. Major Organ – Kidneys • Major Function – filter the blood allowing waste and excess ions to leave as urine and returning the needed substances to the blood in the right proportions

  4. Other Functions – regulate blood’s volume and chemical make-up

  5. Other Regulatory Functions • Enzyme renin regulates blood pressure • Hormones from kidneys stimulate RBC production in bone marrow • Kidneys convert Vitamin D to its useable form

  6. Organs of the Urinary System • Kidney • Ureters • Urinary bladder • Urethra

  7. The Kidneys • Located near the elbow, posterior in the body cavity • 5 in and 2.5 in wide (size of a fist, large bar of soap) • Right kidney lower than the left because of the liver

  8. Figure 15.1b

  9. Adrenal Gland – produces hormones • Hilus - indent

  10. Structure of the Kidneys • Renal artery – blood from the heart with oxygen • Renal Vein – Blood to heart – no oxygen • Ureter – urine to bladder • Renal cortex – outer region

  11. Renal Pelvis – area superior to the ureter • Wastes drain to this area • Renal pyramid – pyramid shape – made of nephrons • Nephrons – structural and functional units of the kidney • Millions in each kidney • Form urine

  12. Renal Medulla – space between cortex and pelvis

  13. Figure 15.2b

  14. Structure of a Nephron Two Parts • Glomerulus • Renal Tubule (leads to collecting duct)

  15. Blood comes from the renal artery, into the glomerulus where it is filtered. • It then passes through the capillary bed and leaves through the renal vein.

  16. Urine Formation Results from 3 processes • Filtration • Reabsoprtion • Secretion

  17. Filtration • Passive process • Blood plasma with small molecules goes through • Proteins and RBC are too big and stay in the blood stream

  18. Reabsorption • Occurs in the beginning of the tubule • Filtrate contains waste and good things (water, glucose, amino acids and ions) • Reabsorption – takes back the good things by selective active transport • This part of the tubule has lots of mitochondria and microvilli

  19. Secretion • Occurs in the capillary net • Removes “bad” stuff from the blood (H+, K+, drugs and creatine) • Regulates blood pH (H+) • This is added to the tubule and secreted

  20. The filtrate made of wastes leaves through the collecting duct to the renal pelvis to the ureter, then the bladder and the out through the urethra

  21. Control of Blood Composition by the Kidneys

  22. Blood composition depends on: • Diet • Cellular metabolism • Urine output In 24 hours 150-180L of blood is filtered 1-1.8 L of urine is produced

  23. The 4 Roles Kidneys play in keeping blood composition constant

  24. Excretion of nitrogen-containing waste • Water balance in the blood • Electrolyte balance in the blood • Ensuring proper blood pH

  25. Nitrogen Waste • Urea – comes from AA when used for energy • Uric Acid – comes from the metabolism of nucleic acids • Creatinine – associated with creatine metabolism in muscle tissue

  26. Water/Electrolyte Balance • Males – 60% water • Females – 50% water (fat less water)

  27. Electrolyte – charged particle that conducts electric currents • Water is essential for the functioning of the body and its cells • Hormones control the reabsorption of water and electrolytes

  28. Maintaining Acid-Base Balance of blood • pH of blood – 7.35-7.45 • Kidneys do most of the regulation • Blood buffers and respiratory controls do the rest

  29. Characteristics of Urine

  30. Color • Clear and pale to yellow • Yellow due to urochrome (pigment from the destruction of hemoglobin) • Deeper yellow – more concentrated • Sterile when exits the body – then begins to grow bacteria

  31. pH • About 6

  32. Density • Greater that distilled water • Specific gravity – about 1.001 – 1.035

  33. Solutes in Urine • Na+ • K+ • Urea • Uric acid • Creatinine • Ammonia – NH4 • Bicarbonate ions

  34. Substances NOT found in Urine • Glucose – Diabetes • Blood proteins (albumin) • RBC or Erthyrocytes • Hemoglobin • WBC or Leukocytes (pus) • Bile • Crystals – kidney stones • Table 15.1

  35. Organs of the Urinary System

  36. Ureters • Long slender tubes 10-12 in • From hilus to bladder • Urine moves by peristalsis • Pain from kidney stones occurs here

  37. Urinary Bladder • Smooth collapsible temporary storage tank

  38. Urethra • Carries urine by peristalsis from bladder to the outside • Females – 1.5” – carries urine • Males – 8” – carries urine/sperm

  39. Micturition (Voiding) • Emptying the bladder • 2 sphincters control the release of urine • 200 mL – stretch receptors activated – contractions occur – urine moves to the first sphincters • Person feels the urge to void

  40. Person can wait or go • Another 200-300 mL – person has to go again • Eventually voiding will happen whether a person wants it or not

  41. Incontinence • Unable to control the external sphincter • Small children • Emotional, pressure or nervous system problems

  42. Urinary Retention • Bladder is unable to expel urine • After surgery before anesthesia wears off • Enlargement of the prostate

  43. The End

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