a. Urethral Sphincters. The urethral sphincters are circular muscle masses
which control the passage of the urine through the urethra. There are two urethral
sphincters--an internal urethral sphincter and an external urethral sphincter.
(1) The internal urethral sphincter is located in the floor of the urinary
bladder. It is made of smooth muscle tissue. It is controlled by nerves of the autonomic
nervous system (lesson 11).
(2) The external urethral sphincter is more inferior around the urethra in the
area of the pelvic floor. It is made up of striated muscle tissue. It is controlled by the
peripheral nervous system (lesson 11).
b. Male-Female Differences. The female urethra is short and direct. The male
urethra is much longer and has two curvatures. Whereas the female urethra serves
only a urinary function, the male urethra serves both the urinary and reproductive
Section II. INTRODUCTION TO HUMAN GENITAL (REPRODUCTIVE) SYSTEMS
8-7. SEXUAL DIMORPHISM
The human male and human female each has a system of organs specifically
designed for the production of new humans. These systems are known as reproductive
or genital systems. Since there are different systems for males and females, the genital
systems are an example of sexual dimorphism.
MORPH = form, shape
DI = two
SEXUAL = according to sex (gender)
SEXUAL DIMORPHISM = having two different forms according to sex
8-8. ADVANTAGES OF DOUBLE PARENTING
The existence of two parents for each child means that genetic materials are
recombined to produce a new type. This new type may be an improvement over
8-9. MAJOR COMPONENT CATEGORIES OF THE GENITAL SYSTEMS
Components of the genital systems may be considered in the following
a. Primary Sex Organs (Gonads). Primary sex organs produce sex cells
(gametes). A male gamete and a female gamete may be united to form the one-cell