Bladder and Micturation

Question 1

Describe the anatomy and physiology of the ureters

Answer 1

anatomy:
- retroperitoneal, muscular tubes
- 3 layers: adventitia, muscularis, mucosa

physiology:
- peristalsis occurs when urine enters the ureter
- flap of mucosa acts as a valve at the opening of each ureter preventing backflow

Question 2

Describe the anatomy and physiology of the urinary bladder

Answer 2

anatomy:
- muscular sac on the pelvic cavity floor
- 4 layers: serosa, adventitia, muscularis, mucosa
- has a trigone

physiology:
- stores urine
- detrusor muscle contracts to expel urine and the internal urethral sphincter relaxes
- max capactiy of 700-800mL

Question 3

Describe the urethra and how it is different in males and females

Answer 3

females:
- short
- solely for urine excretion
- external urethral sphincter for voluntary control

males:
- long
- passageway for urine and semen
- 3 regions: prostratic urethra, membranous urethra, spongy urethra
- internal urethral sphincter for involuntary control and external urethral sphincter for voluntary control

Question 4

Describe the flow of urine from collecting duct to release from the body

Answer 4

• urine flows from the collecting ducts into the papillary ducts
• these ducts empty into the minor calyces and then into the major calyces
• urine flows from the major calyces into the renal pelvis
• ureter transports urine to the urinary bladder and is stored until urination occurs
• during urination, urine flows from the bladder through the urethra to the outside of the body

Question 5

What are the major differences between plasma and urine?

Answer 5

plasma:
- high protein content
- contains blood cells
- contains glucose and amino acids

urine:
- higher concentration of waste

Question 6

Describe the urinary storage reflex

Answer 6

• sympathetic pathways originate in the upper lumbar spinal cord
• postganglionic fibers travel via the hypogastric nerve to the detrusor muscle causing it to relax and allow the bladder to fill
• in males, sympathetic fibers stimulate the internal urethral sphincter to contract to prevent leakage
• somatic motor fibers from the sacral spinal cord keep the external urethral sphincter constricted

Question 7

Describe the urine voiding reflex

Answer 7

• bladder fills with urine and stretches
• stretch receptors send signals to the sacral spinal cord and to the micturition center in the pons
• efferent signals from the spinal cord stimulate the detrusor muscle to contract
• when ready to urinate, the pons sends signals to relax the internal (in males) and/or external urethral sphincter
• when not ready to urinate, the cerebrum sends signals that keep the external urethral sphincter contracted