Transport of Urine: Quiz on Urine Composition

Filtrate is transformed into urine before reaching the minor calyx, with no further modification.
Urine is composed of approximately 95% water and contains nitrogenous wastes (urea, uric acid, creatinine) and ions (sodium, potassium, sulphate, phosphate).
pH of urine ranges from 6.2 to 7.0 with an osmolarity of 470 mosmol/kg, potentially increasing to 2000 mosmol/kg in certain conditions.
Urine flows passively from the renal pelvis, with wall stretch initiating peristaltic contractions in the calyces, renal pelvis, and ureters.
Ureters transport urine to the bladder, where it is collected and expelled voluntarily through the urethra.

Ureter measures 25-30 cm in length and 3-4 mm in diameter, using peristaltic contractions to move urine.
Walls consist of three main subsections:
- Mucosa: Features stratified transitional epithelium that adapts to wall stretch.
- Muscularis: Contains inner longitudinal and outer circular smooth muscle layers, with an outer longitudinal layer in the lower third.
- Adventitia: Connective tissue supporting the ureter.

Lines calyces, ureters, bladder, and initial urethra, protecting underlying tissue from hypertonic urine.
TE can stretch and contract, becoming thinner to accommodate varied volumes in the urinary tract.

Bladder filling and emptying is controlled by autonomic and somatic nervous systems, as well as higher brain centers.
During the storage phase, stretch receptors in the bladder send signals to the CNS, inhibiting detrusor muscle contraction while strengthening the external urethral sphincter (EUS) contractions.
Micturition occurs when the bladder reaches about 300 ml, triggering urgency and a switch from storage to voiding in the brain's neural circuits.
Efferent nerves stimulate detrusor muscle contraction and relax the EUS during micturition; bladder wall and urethra dynamics are interdependent.

Comprised of four layers: mucosa, submucosa, muscularis, and adventitia, all lined with transitional epithelium.
Mucosa includes lamina propria, which contains connective tissue and lymphocytes.
Muscularis features three distinct layers of smooth muscle: inner longitudinal, middle circular, and outer longitudinal layers.
Adventitia consists of collagen fiber bundles, stained blue using Masson trichrome for visibility.
Incomplete muscularis mucosa may be present, separating lamina propria from submucosa in some individuals, while distinct muscle layers are typically seen near the urethral neck.