Lower urinary tract Flashcards
Renal papilla
Region of the kidneys where fluid exits collecting duct into calyces.
Located at the tip of the renal pyramid.
The papilla is a site of drug-induced nephrotoxicity causing renal papilla necrosis (NSAIDs)
Urine from renal pelvis to ureter
Urine from major and minor calyces enter the renal pelvis and stretches the smooth muscle.
Distension stimulates peristaltic contractions at the hlius.
- This pushes urine bolus down in pulses into ureter.
Ureter structure
- Length
- Layers
Length: Around 30cm
Mucosal layer
- Transitional epithelium
- Impermeable to urine
3 layers of muscle:
- Inner longitudinal SM
- Outer circular/spiral SM
- Extra-oute longitudinal SM
Ureter function
Ureter is a muscular tube that transports urine to the bladder.
Dilation in ureter generates action potentials in the pacemaker cells at the hilum.
- Generates peristaltic waves[1-6/min]
When relaxed, the lumen stays folded.
Upon the presence of urine, folds dilate.
Ureter peristalsis
Longitudinal SM contract first in front of bolus of urine.
Halfway through, circular SM contracts behind bolus.
Circular SM in front contracts and relaxes behind bolus.
- LSM relaxes
Entrance of urine into the bladder
Ureters into the bladder posteriorly at an oblique angle
- Ureteral opening.
- 2-3cm into bladder
Ureteral opening is a slit that acts as a valve and prevents backflow of urine.
Bladder structure
Overall:
- Fundus
- Neck
Layers:
- Detrusor muscle: outer layer. Contains longitudinal and circular muscles.
- Mucosal layer: inner layer. Transitional epithelium with folded rugae.
Rugae is highly elastic and expands when bladder fills
Trigone:
- Triangular area with opening for ureter and exit for urethra
- Acts as a funnel to channel urine to the neck of bladder
Function of bladder
Temporary storage of urine
- Stores up to 1L
Contraction stimulated by PNS, relaxation stimulated by SNS.
Female urethra
- Length
- Sphincter
- Orifice
Much shorter that males- more susceptible to UTIs.
External sphincter is less developed that males
- Can be damaged during childbirth and cause incontinence
Opens at external urethral orifice- between clitoris and vagina
Male urethra
Much longer than females.
- Protective against UTIs
Passes through prostate gland then urogenital diaphragm.
Prostate and detrusor muscle hypertrophy after age 60
- Treated with surgery and hormone therapy
Two stages of micturition
- Filling of bladder: Urine fills the bladder and increases pressure up to a threshold.
- Micturition reflex: urge to urinate and emptying of bladder
Control of micturition reflex
- Inhibition
- Stimulation
Inhibited by the high centres in the brain:
- Contracts external urethral sphincter
Stimulated by cortical centres:
- Stimulates micturition reflex and relaxes external sphincter.
- Relaxes internal sphincter.
Filling of bladder
Rate: 1mL/min in normal hydration
Filling= increase in intravesical pressure.
At around 200mL- periodic reflex contractions occur.
- Relax after a few seconds.
When bladder is more fully= more intense, frequent and longer contractions
Guarding reflex
As bladder fills:
- Distension is detected by mechanoreceptors in the bladder wall and internal sphincter = stimulation of pelvic nerve.
- Pelvic nerve stimulates hypogastric nerve= relaxation of detrusor muscle + constriction of internal sphincter
- Pudenal nerve constricts external sphincter
Micturation reflex
Stimulated of the pelvic nerve is increased by stretch:
- Contraction of detrusor muscle
- Relaxation of internal sphincter
Volume >300mL= contractions outweigh relaxation.
When bladder is full= signal to thalamus and cerebral cortex
- Increases desire to urinate.
When appropriate:
- External sphincter relaxes voluntarily from pudendal nerve innervation.
Micturition occurs:
- Diaphragm lowers
- Abdominal muscle contracts
- Internal sphincter opens.
