Why does the bladder have rugae

The external urethral sphincter is voluntary. It must be relaxed for urine to flow through the urethra and outside the body. The bladder expands as urine flows in from the ureters, but there is a limit to the volume it can contain. At about ml of urine, the detrusor muscle begins to contract and the internal urethral sphincter muscle begins to relax.

If this urge is ignored, continence may be threatened. At about ml, detrusor muscle contractions begin to force open the internal urethral sphincter. Unless the external urethral sphincter is powerful enough to prevent it, micturition urination will occur involuntarily.

Smooth muscle stretch initiates the micturition reflex by activating stretch receptors in the bladder wall. This autonomic reflex causes the detrusor muscle to contract and the internal urethral sphincter muscle to relax, allowing urine to flow into the urethra.

The stretch receptors also send a message to the thalamus and the cerebral cortex, giving voluntary control over the external urethral sphincter. We usually gain this control of urination between the ages of 2 and 3, as our brains develop. Download Urinary System Lab Manual.

See more from our free eBook library. A description of the urinary bladder from the edition of Gray's Anatomy of the Human Body. Using bladder ultrasound to detect urinary retention in patients from Nursing Times. Urinary System Structures. Are you sure you want to remove bookConfirmation and any corresponding bookmarks?

My Preferences My Reading List. Anatomy and Physiology. Urinary Bladder. Quiz: What is Anatomy and Physiology? It is one of the most elastic organs of the body and is able to increase its volume greatly to accommodate between to ml of urine at maximum capacity.

Transitional epithelium, elastic fibers, and visceral muscle tissue in the walls of the urinary bladder contribute to its distensibility and elasticity, allowing it to easily stretch and return to its original size several times each day.

It also helps to expel urine from the body during urination by contraction of the detrusor muscle and the relaxation of the internal urethral sphincter. Another separate muscle, the external urethral sphincter, surrounds the urethra just inferior to the bladder and helps to control and delay urination through its contraction.

The external urethral sphincter is a skeletal muscle and therefore allows for the voluntary control of the urination reflex. By: Tim Taylor. Last Updated: Apr 29,