Urinary System, Lecture 4

Question 1

Balances and Intake - sodium

Answer 1

sodium balance:
- intake (liquid, foods - have that sodium molecule in them)
◦ gains of that substance (increase)
- output (sweat, feces, urine)
◦ losing
◦ urinary losses have a certain value, there are
other areas we can lose sodium such as sweat,
feces and GI tract
salt intake “appetite”
- regulatory - minimal in humans (sodium level is dropping so regulatory would kick in to increase it up back up, replenish)
- hedonistic - generally consume well in excess of body needs (see this more in humans)
◦ consumption is already 10 times what we need
from a physiological point of view
◦ we do not regulate anything by nutritional status
(deficiency in some nutrient) - our regulation is l
largely based on the volume of consumption and
composition that triggers certain mechanisms

Question 2

Balance and Intake - water

Answer 2

water balance:
- intake (liquids, food (that have water volume in them), metabolic) - gains
◦ metabolic - water generated in metabolic
reactions (reaction that produces water - did not
come with intake, instead generated within body) -
does not make huge contribution

• output (insensible, sweat, feces, urine) - losing
  ◦ insensible - skin epithelial and breathing losses
  (evaporating from surface of skin, not sweat l
  losses, “evaporation”)
  ◦ sweat comes from sweat glands and would be
  aware of the evaporation
  ◦ not aware of the skin epithelial as it just happens
• water intake: “thirst”
  ◦ kidneys minimize losses but really need intake to
  replace losses
  ◦ replace water loss only mainly through intake (can
  turn up reabsorption to help us, but mainly need
  intake)

Question 3

Signals that stimulate thirst centre in hypothalamus

Answer 3

• mechanoreceptors (stretch) - blood volume changes (easy one to remember with AMP)
• baroreceptors - blood pressure changes (venous, arterial, etc.) -> vasopressin
• osmoreceptors - blood osmolarity (most important)
• dry mouth (stimulus being sent to thirst centre) - send thirst signal
• also psychological and conditioned response for thirst

Question 4

Urinary Bladder

Answer 4

• urine flow through to the bladder is propelled by contractions of the ureter wall smooth muscle
  when there is fluid in the ureter, pushed along by smooth muscle contraction
• urine is stored in the bladder and intermittently ejected during urination and micturition
• bladder structures are innervated by parasympathetic and somatic motor neurons to control filling and micturition
• initial role of bladder is filling and storage

Question 5

Urinary Bladder

Answer 5

• urine flow through to the bladder is propelled by contractions of the ureter wall smooth muscle
  - when there is fluid in the ureter, pushed along by
  smooth muscle contraction
• urine is stored in the bladder and intermittently ejected during urination and micturition
• bladder structures are innervated by parasympathetic and somatic motor neurons to control filling and micturition
• initial role of bladder is filling and storage

Question 6

Urinary Bladder - Filling

Answer 6

• bladder distends (stretches) with filling - pretty elastic
• capacity ~700 - 800 mL
• at a certain point in filling “sensation of fullness” signal sent to brain (~200 - 400 mL)
  ◦ conscious awareness of desire to urinate
  ◦ get to certain level of stretch and then the signal is
  sent to the brain that it is reaching some capacity
• detrusor - layers that surrounds the bladder (relaxation as it is being filled at this time)
• the other two control the exit so they contract

Question 7

Urinary Bladder - filling (muscle and innervation (during filling)) -> table

Answer 7

detrusor (smooth muscle) -> parasympathetic inhibited (relax)
internal urethral sphincter (smooth muscle) -> sympathetic stimulated (contract)
external urethral sphincter (skeletal muscle) -> somatic motor stimulated (contract)

Question 8

Urinary Bladder - micturition reflex

Answer 8

signal sent to spinal cord
- 1st part of micturition reflex - initiation

signal comes back from spinal cord
- 2nd part of micturition reflex – detrusor contracts, both sphincters relax
- complete micturition reflex and urinary excretion (voiding) occurs

• learn to initiate and stop micturition reflex (voluntary) by maintaining stimulation and contraction of external urethral sphincter
• signal from cerebrum can over ride micturition reflex for limited time

Question 9

Urinary Bladder - micturition reflex (muscle and innervation (during micturition))

Answer 9

detrusor (smooth muscle) -> parasympathetic inhibited (contract)
internal urethral sphincter (smooth muscle) -> sympathetic stimulated (relax)
external urethral sphincter (skeletal muscle) -> somatic motor stimulated (relax)
-> opposite of filling
-> two sphincters relax while detrusor contracts