Final answer:
The external urethral sphincter is a voluntary skeletal muscle that controls urination, while the internal urinary sphincter is an involuntary smooth muscle which relaxes when the bladder fills. Females have a shorter urethra leading to a higher incidence of UTIs. Urination is controlled by both autonomic (internal sphincter) and somatic (external sphincter) nervous systems.
Step-by-step explanation:
The external urethral sphincter is a skeletal muscle located at the junction of the bladder and urethra which plays a crucial role in continence, allowing urine to be held in the bladder until voluntary urination is decided upon. The internal urinary sphincter, made of smooth muscle, relaxes as the bladder fills, to permit urine flow into the urethra. However, the external sphincter is under somatic nervous system control and requires conscious effort to relax for urination to occur.
In females, the external urethral orifice, and by extension the sphincter, are positioned in the anterior vaginal wall. This, along with the shorter urethral length in females, is a reason for higher incidences of UTI compared to males. The male urethra, which is longer, passes through several regions including the prostate and is associated with reproductive functions as well as urinary.
The urethra's epithelium type changes along its length, from transitional near the bladder to stratified squamous near the external orifice in both genders, with pseudostratified columnar in-between in males. Urination is controlled by the autonomic nervous system which governs the internal sphincter, and the somatic nervous system which controls the external sphincter. The external sphincter is innervated by the pudendal nerve, allowing for voluntary control over urination.