anatomy and physiology

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Human Anatomy
THE REPRODUCTIVE SYSTEM
Lecture Notes 11
The common purpose of the male and female reproductive
systems is to produce offspring. The role of the male in
reproduction is to produce male sex cells, called spermatozoa
(commonly called sperm), and to deliver the sperm to the
female reproductive tract, where fertilization can occur.
One reproductive role of the female is to produce female sex
cells, called ova or eggs. The gonads, which are the TESTES
in males and OVARIES in females, produce the sperm and ova.
The gonads also produce sex hormones that play vital roles in
the development and function of the reproductive organs, as
well as in sexual behavior and sexual drives.
During fertilization, a sperm and ovum fuse, forming a
fertilized egg, or zygote. The zygote divides to become the
embryo, and the embryo develops into the fetus.
The embryo is the developing individual during the first 2
months of life; the fetus is the developing individual from the
beginning of the 3rd month until birth.
The embryo and fetus develop within the female's UTERUS.
So, the female's other role in reproduction is to provide a
protective environment (the uterus) in which the embryo and
fetus develop until birth.

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ANATOMY OF THE MALE REPRODUCTIVE SYSTEM
The primary reproductive organs (gonads) of the male are called
TESTES (testis, singular) or TESTICLES, which produce sperm
and male sex hormones (androgens).
All other male reproductive organs (scrotum, ducts, glands, and
penis) are accessory reproductive structures that protect the
sperm and aid in their delivery to the female reproductive tract.
THE SCROTUM AND TESTES
The paired, oval TESTES (TESTICLES) lie suspended in the
saclike SCROTUM outside the abdominopelvic cavity. This is
important because viable sperm cannot be produced at body
temperature in humans.
The scrotum keeps the testicle temperature at about 3 degrees
Celsius lower than normal body temperature (basal body
temperature is 37 degrees Celsius).

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The SCROTUM is a pouch of skin and superficial fascia (the
subcutaneous layer consisting of fibrous connective tissue) that hangs at
the base of the penis, anterior to the anal opening. Internally, a septum
divides the scrotum into two sacs, each containing one testis.
When temperatures are cold, the scrotum becomes shorter and heavily
wrinkled as it is pulled up closer to the warmth of the body. When the
external temperature is warm, the scrotal skin is flaccid and loose, and
the testes hang lower from the body. These changes in the scrotum help
to maintain a constant internal scrotal temperature that is 3 degrees
Celsius lower than body temperature.
Two sets of muscles are responsible for these scrotal changes. The
DARTOS MUSCLE is smooth muscle in the subcutaneous layer of the
scrotum and in the scrotal septum. When the dartos muscle contracts, it
causes wrinkling of the scrotal skin.
The CREMASTER MUSCLES are bands of skeletal muscle that arise
from the INTERNAL OBLIQUE muscles of the abdomen. The cremaster
muscles elevate the testes when they are exposed to cold temperatures
and during sexual arousal. This moves the testes closer to the body to
absorb body heat. Warm temperatures cause the cremaster muscles to
relax, so the testes hang lower from the body.

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Each TESTIS is approximately 5 cm (2 inches) long and 2.5 cm (1
in.) in diameter. The testes are covered by a dense irregular
connective tissue capsule called the TUNICA ALBUGINEA.
The tunica albuginea extends inward and divides each testis into
200 to 300 wedge-shaped compartments or LOBULES. Each lobule
contains 1-3 tightly coiled SEMINIFEROUS TUBULES where
sperm are produced in a process called spermatogenesis.
In humans, spermatogenesis takes about 74 days. SPERMATOZOA
(spermatozoon, singular) are produced at the rate of about 300 million
per day. Once ejaculated, they have a life expectancy of about 48 hours
within the female reproductive tract.
Each spermatozoon consists of a head, midpiece, and tail. The HEAD
contains the NUCLEUS with its genetic material and an ACROSOME.
The acrosome contains digestive enzymes that allow the sperm to
penetrate the ovum (egg).
The MIDPIECE contains numerous mitochondria. The mitochondria
provide abundant ATP energy for sperm locomotion. The TAIL is a
flagellum that propels the sperm toward the ovum.

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Between the seminiferous tubules are the INTERSTITIAL
ENDOCRINOCYTES (cells of Leydig), which are endocrine cells that
produce male sex hormones called androgens (primarily
testosterone).
Notice that each testis is both an exocrine gland (producing sperm,
which are released into ducts) and an endocrine gland (producing
androgen hormones, which are released into the bloodstream). Also
note that the sperm and hormones are produced in the testes by
completely different cells.
THE MALE DUCT SYSTEM
After the sperm are formed
in the seminiferous tubules,
they leave the testis and
enter the DUCTUS
EPIDIDYMIS. The ductus
epididymis lies within the
organ called the
EPIDIDYMIS.
The comma-shaped
epididymis is about 4 cm (1.5
in.) long and is on the
posterior side of each
testis. The ductus
epididymis is 1 mm in
diameter. The ductus
epididymis is so tightly coiled
that it would measure about
6 meters (20 ft.) long if it
were straightened out.

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The immature, nearly nonmotile sperm that leave the testis are stored
temporarily in the epididymis.
During their transport within the epididymis (a trip that takes about 10
to 14 days), the sperm become both motile and fertile (capable of
fertilizing an ovum).
Spermatozoa can be stored in the epididymis for at least a month. If
they are not ejaculated, the sperm degenerate and are reabsorbed.
When a male is sexually stimulated and ejaculates, the smooth muscle in
the walls of the epididymis contracts rhythmically, expelling sperm from
the epididymis into the next segment of the duct system, the DUCTUS
(VAS) DEFERENS.
The DUCTUS DEFERENS (VAS DEFERENS)
is about 45 cm (18 in.) long. It runs upward from the epididymis through
the INGUINAL CANAL into the pelvic cavity. {Note: The inguinal canal
is an oblique, 2 inch long passageway through the anterior abdominal wall
of the groin.
Anything that
passes between
the pelvic cavity
and scrotum must
pass through the
inguinal canal.} The
ductus deferens is
easily palpated
(felt) as it passes
anterior to the pubic
bone. It then arches
medially over the
ureter and
descends along the
posterior side of the
urinary bladder.

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Functionally, the ductus deferens stores sperm and conveys
sperm from the epididymis toward the urethra. At the moment
of ejaculation, the smooth muscle in the walls of the ductus
deferens create peristaltic waves that rapidly squeeze the
sperm forward.
The ductus deferens joins with the duct of the SEMINAL
VESICLE (a gland) to form the EJACULATORY DUCT. The
ejaculatory duct passes through the PROSTATE GLAND and
merges with the URETHRA. Each ejaculatory duct is posterior
to the urinary bladder and is about 2 cm (1 in.) long.
During ejaculation, the ejaculatory duct is where seminal fluid
from the seminal vescicle mixes with sperm from the ductus
deferens. The ejaculatory ducts then eject this mixture of
sperm and seminal fluid into the urethra during ejaculation.

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The URETHRA
measures about 20 cm (8 inches) long. The urethra passes from
the INTERNAL URETHRAL ORIFICE of the URINARY BLADDER
down through the PROSTATE GLAND and then through the
PENIS to the EXTERNAL URETHRAL ORIFICE.
The urethra conveys both urine and semen (at different times)
outside of the body. During ejaculation, the INTERNAL
URETHRAL SPINCTER (a smooth muscle sphincter) at the base
of the urinary bladder is closed, so that urine is not expelled
during ejaculation. .

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ACCESSORY SEX GLANDS
The accessory glands include the SEMINAL VESICLES, PROSTATE
GLAND and the BULBOURETHRAL GLANDS. These glands produce the
SEMINAL FLUID, the liquid portion of semen. SEMEN consists of both
seminal fluid and sperm.
The paired SEMINAL VESICLES are located posterior to and at the
base of the urinary bladder. They are convoluted pouchlike structures
about 5 cm (2 in.) in length. They produce about 60% of the fluid volume
of semen. The duct of each seminal vesicle joins the DUCTUS
DEFERENS to form the EJACULATORY DUCT. Sperm and seminal fluid
mix in the ejaculatory duct and enter the urethra together during
ejaculation.
The PROSTATE GLAND is a single gland about the size of a walnut. It
encircles the upper part of the urethra just inferior to the bladder. The
prostate gland secretes up to 33% of the semen volume. During
ejaculation, the smooth muscle in the wall of the prostate contracts,
propelling seminal fluid into the urethra through several prostatic ducts.
Since the prostate is located immediately anterior to the rectum, its
size and texture can be palpated (felt) through the anterior wall of the
rectum.
The paired BULBOURETHRAL GLANDS (COWPER'S GLANDS) are tiny
pea-sized glands located inferior to the prostate gland, on each side of
the urethra. They produce a thick, clear mucus which is released prior to
ejaculation when a male first becomes sexually aroused. The secretion is
alkaline, so it neutralizes traces of acidic urine in the urethra. It also
serves as a lubricant during sexual intercourse.

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Semen
is seminal fluid and sperm. Seminal fluid provides a
transportation medium to the sperm. It contains fructose sugar
for the sperm's ATP energy production.
Sperm cannot survive at acidic pH levels, so semen has a
slightly alkaline pH (7.2-7.7), which neutralizes the acidic pH of
the male's urethra & female's vagina. Seminal fluid contains
enzymes that activate sperm (making them more motile and
fertile).

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THE PENIS
The PENIS is a copulatory organ, used to deliver sperm into the female
reproductive tract. The penis and scrotum make up the external
reproductive structures, or external genitalia, of the male.
The skin covering the penis is loose. Distally, a cuff of skin called the
PREPUCE or FORESKIN covers the enlarged tip, which is called the
GLANS PENIS. The foreskin is often surgically removed shortly after
birth in a procedure called circumcision.
Internally, the body of the penis contains the urethra and three columns
of erectile tissue. Erectile tissue is a spongy tissue consisting of
connective tissue and smooth muscle permeated with vascular sinuses
(spaces). During sexual arousal, the vascular sinuses fill with blood.
Expansion of these sinuses compresses the veins draining the penis so
most of the blood entering the sinuses is retained, causing the penis to
enlarge and become rigid. This results in an erection.
The slender midventral
column of erectile
tissue is the CORPUS
SPONGIOSUM. It
surrounds the urethra
and expands distally to
form the slightly
enlarged tip of the
penis called the GLANS
PENIS. The paired
dorsal and lateral
columns of erectile
tissue are called the
CORPORA
CAVERNOSA (singular:
CORPUS
CAVERNOSUM).

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ANATOMY OF THE FEMALE REPRODUCTIVE SYSTEM
The reproductive role of the female is far more complex than
that of the male. The female must produce ova, and her body
must prepare to nurture a developing embryo & fetus for a
period of about nine months. The female also provides the
infant with nourishment after the baby is born. Therefore, the
mammary glands are considered to be part of the female
reproductive system.
OVARIES are the primary reproductive organs (gonads) of a
female, and they serve a dual purpose: they produce the ova
(eggs) and female sex hormones (progesterone and estrogen).
The accessory ducts are the UTERINE TUBES, UTERUS and
VAGINA. The ovaries and duct systems of the female are
located within the pelvic cavity and are called the internal
genitalia. External organs of the female form the external
genitalia or vulva. .

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THE OVARIES
The paired OVARIES are lateral to the uterus and are about the size and
shape of unshelled almonds. Each ovary is held in place by the BROAD
LIGAMENT, the OVARIAN LIGAMENT and the SUSPENSORY LIGAMENT.
These ligaments are either fibromuscular connective tissue structures or
extensions of the parietal peritoneum which help hold the ovaries,
Fallopian tubes, and uterus in place.
Like the testes, the ovaries have a dense irregular connective tissue
capsule called the TUNICA ALBUGINEA. Within the ovarian capsule is a
connective tissue stroma (framework) that contains a rich blood supply.
Notice that blood vessels enter and exit the ovaries through the
hilus. Embedded in the CORTEX of the stroma are many tiny sac-like
structures called OVARIAN FOLLICLES. Each ovarian follicle consists of an
immature ovum (egg) surrounded by one or more layers of epithelial
follicular cells.
A woman is born with thousands of PRIMORDIAL FOLLICLES. Each
primordial follicle contains an immature ovum surrounded by a layer of flat,
supportive follicular cells. Only about 400 of these will mature and ovulate
(release an egg) during a woman's lifetime. The monthly cycle in which the
ovarian follicles mature and ovulate the egg is called the ovarian cycle. The
ovarian cycle is approximately 28 days. Day 1 of the ovarian cycle is the first
day of a woman's menses (menstruation or "period").

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THE OVARIES
At the beginning of a sexually mature woman's 28 day ovarian cycle,
around 20 PRIMORDIAL FOLLICLES are stimulated by follicle
stimulating hormone (which is secreted by the ANTERIOR PITUITARY
GLAND) to grow and develop into PRIMARY FOLLICLES. By about Day 6
of the ovarian cycle, all but one of these primary follicles will
degenerate. The dominant primary follicle will continue to develop and
grow.
.

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THE UTERINE TUBES
The female possesses two UTERINE (FALLOPIAN) TUBES, also
called OVIDUCTS, which are held in position by the
SUSPENSORY LIGAMENTS. The uterine tubes extend medially
from the ovaries and they receive the ovulated ovum from the
ovaries. They also provide a site where the sperm may fertilize
the ovum. Each uterine tube is about 10 cm (4 in.) long and 1 cm in
diameter.
The MUCOSA that lines the uterine tube consists of ciliated
simple columnar epithelium. The cilia help propel the ovum
toward the uterus. Secretory cells in the mucosa produce a
secretion that keeps the ovum (and sperm, if present) moist and
nourished. The middle layer of the uterine tube wall, the
MUSCULARIS, consists of circular and longitudinal layers of
smooth muscle. The ovum is moved toward the uterus by
peristalsis of the muscularis and by the rhythmic beating of the
mucosal cilia. The outer layer of the uterine tubes is the
VISCERAL PERITONEUM (SEROSA).

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The distal end of each uterine tube is called the INFUNDIBULUM, which
lies near the ovary. It is an open, funnel-shaped structure bearing ciliated,
fingerlike projections called FIMBRIAE that drape over the ovary. Unlike
the male duct system, which is continuous with the tubules of the testes,
the uterine tubes have little contact with the ovaries. One fimbria is
attached to the lateral end of the ovary. At ovulation, an ovulated ovum is
cast into the peritoneal cavity. The cilia of the fimbriae become very
active close to the time of ovulation and undulate to create currents in the
peritoneal fluid. These currents usually carry the ovum into the uterine
tube.
From the infundibulum the uterine tube extends medially to form the
AMPULLA, the longest portion of the uterine tube. Fertilization of an
ovum by a sperm cell usually occurs in the AMPULLA of the uterine tube.
Since the ovum is viable for about 24 hours, fertilization may occur up to
24 hours after ovulation. If the ovum is not fertilized, it disintegrates. If
the ovum is fertilized, the resulting zygote (fertilized egg) undergoes cell
division as it moves down the Fallopian tube. The developing embryo
continues to divide as it moves into the uterus. About six days after
fertilization has taken place, the embryo attaches to the ENDOMETRIUM
(lining) of the UTERUS in a process called implantation.

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THE UTERUS
The UTERUS (womb) is located in the pelvis anterior to the rectum and
superior to the urinary bladder. It is a hollow, thick-walled organ shaped
like an upside-down pear. Its functions are to receive, retain and nourish
an embryo. It is the site of menstruation, implantation of the embryo,
development of the embryo and fetus during pregnancy, as well as labor
contractions. In a woman who has never been pregnant, the uterus is about
the 7.5 cm (3 in.) long, 5 cm (2 in.) wide, and 2.5 cm (1 in.) thick, but it is
usually larger after childbirth.
The wall of the uterus is smooth muscle stretches as the developing fetus
grows in the womb.

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The FUNDUS:
of the uterus is the rounded top of the uterus. The CERVIX is
the narrow outlet of the uterus. Most of the lubrication during
sexual intercourse comes from secretions of glands of the
cervix. The VAGINA is inferior to the cervix.
Normally, the uterus is tilted anteriorly and the cervix projects
down and back, and joins the vagina at a nearly right angle. This
position is called anteflexion. Several structures called
"ligaments" maintain the anteflexed position of the uterus and
keep the uterus from dropping into the vagina (prolapsing). The
paired BROAD LIGAMENTS are double folds of parietal
peritoneum that attach the uterus to the lateral sides of the
pelvic cavity. Uterine blood vessels and nerves pass through the
broad ligament to the uterus.

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THE VAGINA
The VAGINA is a thin-walled, muscular, tubular organ, about 10
cm (4 in.) long. It is posterior to the urinary bladder and urethra
and anterior to the rectum. It extends from the cervix to the
external vaginal opening, the VAGINAL ORIFICE. The vagina is
often called the birth canal, and it provides a passageway for
delivery of an infant and for menstrual flow. Since it receives
the penis and semen during sexual intercourse, it is the female
organ of copulation.
The vagina is lined with a MUCOUS MEMBRANE (MUCOSA),
which consists of nonkeratinized stratified squamous
epithelium, which resists friction.
The vaginal mucosa has no glands. Its lubrication is provided by
cervical mucous glands and by vestibular glands located outside
the vaginal orifice. The pH of the vagina is normally quite acidic
(pH 3.5-4). This acidity helps keep the vagina healthy and free of
infection, but it is unhealthy for sperm. Alkaline seminal fluid
from the male neutralizes the acidity of the vagina so sperm can
survive.

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The MUCOSA lies in a series of transverse folds, called RUGAE.
Where else have we seen rugae? What is the function of rugae?
The tissue layer beneath the mucosa is the MUSCULARIS, which
consists of smooth muscle. The rugae and smooth muscle allow
the vagina to stretch considerably, which is important during
copulation (sexual intercourse) and childbirth.
The lower end of the vaginal opening to the outside is the
VAGINAL ORIFICE . Around the vaginal orifice, the mucosa
forms an incomplete partition called the HYMEN. The hymen is
very vascular and tends to bleed when it is ruptured during the
first coitus (sexual intercourse).
Note that in males, the urethra carries both urine and semen
through the penis. The female urinary and reproductive tracts,
however, are completely separate.

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THE EXTERNAL GENITALIA
The female reproductive structures located external to the
vagina are called the EXTERNAL GENITALIA. The VULVA or
PUDENDUM is the collective designation for the external
genitalia of the female. The following structures are part of the
vulva.
The MONS PUBIS is a fatty, rounded area overlying the pubic
symphysis. After puberty this area is covered with pubic hair. It
is anterior to the urethral and vaginal openings. Running
posteriorly from the mons pubis are two elongated folds of skin
called the LABIA MAJORA.
The labia majora contain adipose tissue, sebaceous (oil) glands
and apocrine sweat glands, and they are covered with pubic hair.
The labia majora enclose the LABIA MINORA, two thin, delicate,
hair-free skin folds that are covered with mucosa and richly
supplied with sebaceous glands.
The labia minora enclose the VESTIBULE, where the external
openings of the urethra and vagina are located. On either side of
the urethral orifice and vaginal orifice are glands that secrete
mucus, which keeps the mucosa of the labia minora moist and is
used as lubrication during sexual intercourse.

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The CLITORIS is a small, protruding structure, composed mostly
of erectile tissue. It is located at the anterior junction of the
labia minora. The clitoris is richly innervated with sensory nerve
endings sensitive to touch, and it becomes swollen with blood
during tactile stimulation, contributing to the female's sexual
arousal.
The PERINEUM is the diamond-shaped region between the
thighs and buttocks of both FEMALES and MALES. It is located
between the pubic symphysis and coccyx (tailbone).

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The mammary glands are modified sudoriferous (sweat) glands
and are present in both sexes, but are functional only in females
of reproductive age. The biological role of the mammary glands is
to produce milk to nourish the newborn baby. Milk secretion and
ejection is called lactation. Lactation is controlled by hormones
from the pituitary gland.
Each mammary gland is contained within a rounded skin-covered
breast that is attached to the underlying pectoralis major
muscles of the chest by connective tissue structures called
SUSPENSORY LIGAMENTS OF THE BREAST.
Slightly below the center of each breast is a pigmented area, the
AREOLA, which surrounds a central protruding NIPPLE.
Numerous large sebaceous glands in the areola produce sebum
(oil) that lubricates the areola and nipple during nursing. A hint
for those women who plan to breastfeed their infants: Make sure
the baby's mouth is around the areola and the nipple, not just
the nipple. This will prevent nipple soreness and cracking during
nursing.
Figure or final
only

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Internally, each mammary gland consists of 15 to 20 LOBES
that radiate around the nipple. The lobes are padded and
separated from each other by adipose tissue. Within the lobes
are ALVEOLAR GLANDS or ALVEOLI (No! These are not air
sacs!), which secrete milk when a woman is lactating. The alveoli
are arranged in clusters like grapes. Milk passes from the
alveoli into ducts, which expand as they approach the nipple to
form LACTIFEROUS SINUSES, where milk is stored during
lactation. The lactiferous sinuses continue as LACTIFEROUS
DUCTS, which open to the outside at the nipple.
A few words regarding breastfeeding: Breast milk is the best
food that you can give to your infant. It has nutrients that are
more easily digestible for the infant, and iron that is in a highly
absorbable form, so that you normally do not need to give
breastfed infants a vitamin and iron supplement. The nutrients
in infant formula are harder for the infant to digest. This
means that the baby's tummy feels fuller longer (which is why
formula fed infants can go longer between meals than
breastfed infants), but the baby is not getting the nutrients in
the form that nature intended. Also, the unique fats in breast
milk are necessary for proper central nervous system
development.

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Breast milk contains some of the mother's antibodies, which
helps the baby resist infections. As a result, breastfed babies
usually have fewer instances of diarrhea, colds, and ear
infections.
Breastfeeding is also a plus for the mom. Breastfeeding helps
the uterus shrink back to its normal size much faster. You can
breastfeed instead of endure the painful ordeal of "drying up"
when your milk comes in. Breastfeeding is much more convenient
and much less expensive than bottle feeding. Breast milk doesn't
stain the baby's (or your) clothes like formula does (due to the
iron supplement in formula). And breastfeeding can create a
closeness between mother and infant that bottle feeding can't
simulate.
Many people think that when the baby is nursing every hour or
two, the baby is not getting enough milk. Nursing every couple of
hours in the beginning is the normal course of breastfeeding.
Formula makes the baby feel full longer, because the nutrients
are not as easily digested. The more you nurse, the more milk you
will produce - milk production is by supply and demand. If you cut
back your nursing to give your baby bottles of formula, you'll cut
back your milk production. As the baby gets older, more time will
pass between breastfeedings.

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