The major contractile muscle of the bladder is the detrusor. Urination involves either sustained contractions or short intermittent contractions of the detrusor along with contraction of the muscles in the urethra, the duct from the urinary bladder that conducts urine from the body.
Mitochondria is the site of cellular respiration which produces energy. A cell with few energy needs would therefore contain a small number of this organelle.
