484 Chapter 19
- Also in the vestibule are two openings, the vaginal
orifice and the urethral orifice.^
- On each side of the urethral orifice are the two
openings of the ducts of the lesser vestibular or
Skene’s glands, which secrete mucus.^
- On each side of the vaginal orifice are the two
openings of the greater vestibular or Bartholin’s
glands that also secrete mucus for lubrication
during sexual intercourse.
The Perineum
- The perineum is a diamond-shaped area between the
buttocks and thighs of males and females.^
- It is divided into an anterior urogenital triangle that
contains the external genitalia and a posterior anal
triangle that contains the anus.
The Anatomy an d Function
of the Mammary Glands
- Mammary glands, found in both males and fe-males,
are functional to produce milk only in the female.
They increase in size during puberty due to estrogen. - Each gland consists of 15 to 20 lobes separated by
adipose tissue.^
- Each lobe contains smaller compartments called
lobules, which contain the milk-secreting cells or
alveoli arranged like a cluster of grapes.^
- The alveoli convey the milk into secondary tubules,
which join into mammary ducts.^
- As the ducts approach the nipple, they expand into
milk storage sinuses called ampullae.^
- Ampullae continue as lactiferous ducts that termi-
nate in the nipple.^
- The circular pigmented area around each nipple is
called the areola and contains modified sebaceous
glands.^
- The function of the mammary glands is to produce
milk and to eject it out the nipple, a process called
lactation.
Pregnancy and Embryonic
Development
- An egg cell must be fertilized within 12 to 24 hours
after ovulation; sperm remains viable for 12 to 48
hours in the female reproductive tract.
2. It takes the egg 24 hours to move down one-third of
the uterine tube. Fertilization will occur in the up-per
two-thirds of the tube.^ - A fertilized egg is called a zygote. As it moves down
the uterine tube, it divides by mitosis to form a hol-
low sphere of cells called the blastocyst or blastula.^
By the time it reaches the uterine cavity, it is called a
chorionic vesicle.^ - It secretes chorionic gonadotropin, which stimu-lates
the corpus luteum to maintain the uterine lin-ing via
its hormones. It embeds in the endometrial lining by
the 7th day.^ - The three primary germ layers are now being devel-
oped. The ectoderm will develop into skin and the
nervous system; the endoderm will form the linings of
internal organs; and the mesoderm will form muscles,
bones, and other tissues. These tissues come from the
blastocyst’s inner cell mass.^ - The blastocyst’s fluid-filled sphere, the trophoblast,
forms projections called chorionic villi, which will
interact with uterine tissue to form the placenta.^ - Once the placenta is formed, the three-layered
embryo becomes surrounded by a fluid-filled sac
called the amnion.^ - The embryo becomes attached by a connecting
stalk called the umbilical cord.^ - The placenta exchanges nutrients, oxygen, and wastes
between the embryo and the mother. By the 9th week
of development, the embryo is called a fetus. Later in
development, the umbilical cord will become the ma-
jor exchange structure between fetus and mother.^ - As pregnancy continues, the uterus expands into the
abdominal cavity to accommodate the growing fetus. - Childbirth is called parturition and begins with con-
tractions of the smooth muscles of the uterus, called
labor.^ - Labor is divided into three stages: the dilation stage,
the expulsion stage, and the placental stage.^ - During the dilation stage, the cervix is fully dilated
by the head of the fetus and the amnion ruptures
releasing amniotic fluid.^ - During the expulsion stage, the child moves through
the cervix and vagina, usually head first into the out-
side world.^ - During the placental stage, the placenta detaches
from the uterus within 15 minutes following birth,
called the afterbirth.