Urinary part 2

• What activates the micturition reflex?


  Stretching of the urinary bladder wall
• What is the normal response of the bladder when the micturition reflex is activated?


  It produces a series of contractions
• At what age does inhibition of micturition typically develop?


  By age 2–3 years
• What influences the spinal micturition reflex after the age of 2–3 years?


  The influence of the pons and cerebrum predominates
• How does internal pressure in the bladder relate to the urge to urinate?


  Little urge when less than 300 mL, rapidly increases at 400 mL
• What can initiate the urge to urinate even if the bladder is nearly empty?

  Irritation of the urinary bladder or urethra
• What determines the amount of water that the kidneys excrete?


  The body's state of hydration
• What is the normal daily urine output range?


  1200 to 1500 mL
• What is oliguria?


  A decrease in urine output
• When is oliguria commonly seen?


  During dehydration from excessive water loss
• What is the definition of anuria?


  Cessation of urine flow
• What is polyuria?


  An increase in daily urine volume
• What conditions are often associated with polyuria?


  Diabetes mellitus and diabetes insipidus
• What is the threshold for polyuria in adults?


  Greater than 2.5 L/day
• What is nocturia?


  An increase in nocturnal urine excretion
• How does urine excretion during the day compare to night?

  Kidneys excrete 2-3 times more urine during the day
• What percentage of body weight is water in infants?


  75%
• What percentage of body weight is water in adults?

  50%
• How does the amount of adipose tissue affect water levels in the body?


  More adipose tissue results in lower water levels
• What are the two major fluid compartments in the body?

  • Intracellular Fluid Compartment
  • Extracellular Fluid Compartment
• What are the subcompartments of extracellular fluid?


  • Interstitial Fluid (outside blood vessels)
  • Plasma (inside blood vessels)
  • Lymph, CSF, Synovial fluid, etc.
• What is edema?


  Water leaves plasma and enters interstitial fluid
• What is the total volume of water entering the body per day?


  1500-3000 mL
• How is water absorbed in the digestive tract?

  By osmosis
• What are the sources of water intake and routes of water loss?

  Sources of Water Intake:

  • Ingestion (90%)
  • Cellular Metabolism (10%)

  
  

  Routes of Water Loss:

  • Urine (61%)
  • Evaporation (35%)
  • Feces (4%)
• What is the greatest influence on the sensation of thirst?

  Increased solute concentration in extracellular fluid and low blood pressure
• What are the three mechanisms that influence thirst sensation?

  Arterial baroreceptors, juxtaglomerular apparatus, hypothalamic osmoreceptors
• What temporarily reduces the thirst sensation?

  Drinking a small amount of liquid or wetting dry oral mucosa
• What is the regulated range for extracellular fluid osmolality?


  285 – 300 mOsm/kg
• How does altering the water content of a solution affect its concentration?

  It changes the osmolality
• What are the effects of increased and decreased osmolality on thirst and ADH?


  Increased Osmolality:

  • ↑ Thirst
  • ↑ ADH

  
  

  Decreased Osmolality:

  • ↓ Thirst
  • ↓ ADH
• What is the primary route of water loss in the body?

  Urine (61%)
• What happens to body fluid volume when a large volume of sweat is lost?


  It decreases body fluid volume and increases solute concentration
• What is the significance of the sweat test in diagnosing cystic fibrosis?


  It measures chloride levels in sweat
• What are the primary organs for regulating body fluid composition and volume?

  The kidneys
• How does blood pressure affect the conduction of action potentials in the neural mechanism of blood volume regulation?


  Increased BP decreases action potentials in afferent arterioles
• What happens to GFR and urine volume when blood pressure decreases?


  GFR and urine volume decrease
• What is the role of the juxtaglomerular apparatus in blood volume regulation?


  It detects blood pressure changes
• How does the renin-angiotensin-aldosterone mechanism respond to decreased blood pressure?


  It increases renin secretion
• What effect does atrial natriuretic hormone have on sodium reabsorption?


  It decreases sodium reabsorption