all about urine Flashcards
urine
excreted metabolic wastes, solutes and water from the kidneys based on the body’s needs
what does the ultimate composition of urine depend on
- what is filtered at the glomerulus
- reabsorbed or secreted at the tubules
what is total body water controlled by
fluid intake and renal water exretion
kidneys excrete excess water make ____ urine
dilute
kidneys conserve excess water make ____ urine
concentrated
ADH has ultimate control over:
urine concentration
ADH secretion decreases and increases when
- decreases when there is a decrease in osmolarity
- increases when there is an increase in osmolarity
what does increased ADH lead to
insertion of aquaporins in the collecting duct
what are the two basic requirements to make concentrated urine
- high levels of ADH
- concentrated renal medulla
describe concentrated renal medulla
- medullary interstitum is hypertonic to the lumen
- when aquaporins are inserted, water is rapidly reabsorbed into the interstitum then into the vasa recta
- osmolarity increases down the length of the nephron, so longer loops of henle can create more concentrated urine
the countercurrent multiplier mechanism maintains a:
concentrated renal medulla
characteristics of the loop of henle
- thin and thick ascending limbs are impermeable to water so when solutes are pumped into the medullary interstitium water does not follow
- descending limb is permeable to water so the filtrate quickly reaches osmolarity with the renal medullary interstitum
characteristics of the distal and collecting tubules
- water reabsorption here is dependent on ADH
- most water reabsorption occurs in the cortex ratehr than the medulla, which helps preserve the renal medullary concentration
what is the vasa recta
- specialized peritubular capillaries that run along side the loop of henel in the medulla
- slow blood flow allows for reabsorption of solutes
- as it descends, water is lost into the interstitum and solutes are gained, which helps maintain hypertonicity
importance of urea
- contributes ~40-50% of the osmolarity in the renal medullary interstitium
- passively reabsorped from the tubules, large amounts in the medullary collecting duct
what areas of the nephron are impermeable to urea
- ascending loop of henle
- distal and cortical collecting tubules
(concentrated in these segments, especially with ADH - more water is reabsorbed)
high concentration of urea in the tubule leads to:
urea diffusion into the medullary interstitium from the medullary collecting duct
ADH increases presence of ____ transporters and aquaporins
urea
higher USG =
more concentrated urine (linear relationship)
what is USG
depends on both number and size of the molecules in a given volume of urine because it is a measure of weight per volume
how is osmolarity different from USC
osmolarity is based on the number of molecules per volume without regard to weight
what are the two main steps in micturition
- storage
- voiding
urine flow is ____-directional
uni
peristalsis is enhanced by:
parasympathetic activity and inhibited by sympathetic activity
what type of reflex is the micturition reflex
autonomic spinal cord reflex
describe micturition reflex
- filling of the urinary bladder activates sensory stretch receptors
- sensory messages sent via the pelvic n.
- parasympathetic signals via the pelvic n. stimulate the detrusor muscle to contract in a micturition contraction
- as the bladder fills, micturition contractions become stronger and more frequent
- sympathetic nervous system inhibits detrusor contraction and allows for the bladder to fill
the micturition reflex is one complete cycle of:
- progressive and rapid increase in pressure
- a period of sustained pressure
- return of pressure to basal tone of the bladder
what happens if the micturition reflex does not lead to urinary bladder emptying
- inhibited for minutes to hours
- as the bladder fills more, the micturition reflex occurs more frequently and more powerfully
voiding urine
- very powerful micturition reflex sends an inhibitory signal via the pudenal n. to the external urethral sphincter to allow it to relax as long as the brain is not sending conflicting signals
- the detrusor muscle contracts while the external urethral sphincter relaxes, allowing urine to exit the urinary bladder via the urethra
centers in the brainstem and cerebral cortex exert final control over micturition by:
- keeping micturition reflex partially inhibited unless urination is desired
- tonic contraction of the external urethral sphincter, even when the micturition reflex occurs
- cortical centers facilitate the sacral urination centers to initiate a micturition reflex and inhibit the external ureathral sphincter so urination can occur
which of the following favores filtration at glomerulus:
- glomular hydrostatic pressure
- glomular oncotic pressure
- bowmans capsul hydrostatic pressure
glomular hydrostatic pressure
glucose reabsorption in PCT utilizes which mechanism of transport:
* primary active transport
* secondary active transport
* osmosis
* pinocytosis
secondary active transport
which segment of nephrone is responsible for reabsorption of most of solutes:
* DCT
* CT
* PCT
* thin ascending loop of henle
PCT
which of the following is NOT required to make concentrated urine
* ADH
* Na+
* K+
* urea
K+
