Ch 16 Reproductive System
The reproductive system is a unique system-in fact that it isn’t
functional until puberty.
-Both male and female reproductive systems have primary
sex organs or gonads
-testes in males
-ovaries in females
-The function of the gonads is to produce gametes
-sperm in males
-ova or eggs in ovaries
-Gonads also produce sex hormones which influence
growth and development.
-Accessory reproductive organs
-Generally glands which nourish sperm in males or
nourish a fetus in
embryos
Male Reproductive System
The primary reproductive structures of the male- the testes-endocrine function
-produce testosterone
-exocrine function
-sperm production
-accessory gland secretion
Testes
-plum size
-4 cm long 2.5 cm wide
-covered by a connective tissue called tunica
albuginea which also
separates testes into lobules
-each lobule contains seminiferous tubules which are
sperm producing factories where spermatogenesis
takes place
-the interstitial cells surrounding the seminifeous
tubules are the site of
Testosterone production
-after sperm are created, they move into the rete testes
to then empty into the epididymus
-the epididymus is the beginning of the duct system
-epididymus-highly coiled tube (6m) on the exterior
superior part of the testis
-temporary storage site for immature sperm
-sperm mature and gain the ability to swim while in
the epididymus
approximately 20 days
-when sexually excited, contractions expel sperm into
the ductus deferens
-ductus deferens transports the sperm to the urethra for
expulsion from the body
-the ductus deferens runs from the testis up over the
bladder and joins with the accessory glands at the prostate
to form the ejaculatory duct and empties into the urethra
***
-The urethra carries the sperm and accessory secretions out
of the body during ejaculation
-the urethra is divided into the
-prostatic urethra
-membranous urethra
-spongy (penile) urethra
Semen- Semen is actually made up of a collection of fluids which
cleanse, nourish, activate and dilute the sperm.
- Semen is slightly alkaline with a pH of 7.2-7.6
- It neutralizes the acidic vagina, contains an antibacterial
agent and the hormone relaxin.
- The amount of semen is usually 2-5 ml and contains 50150 million sperm/mL.
- As sexual excitement increases, the bulbourethral gland
releases its secretion which cleanses the urethra and acts as
a lubricant.
- As sperm leave the epididymis, they join with the
secretions from the seminal vesicle (60%) at the
ejaculatory duct then prostate secretions are added in as the
semen is now ready for expulsion.
External Genitalia
- The testes are contained within the scrotum, which aids in
providing proper temperature for the sperm production.
o The scrotum expands and contracts to maintain a
temperature 3°c lower than body temperature.
- The penis is designed to deliver the sperm into the female
reproductive tract.
o It is divided into the shaft (made of erectile tissue) the
glans penis (enlarged tip) and the prepuce also called
foreskin.
 The foreskin is usually removed shortly after birth
called circumcision.
Production of Gametes
- males Spermatogenesis
- females Oogenesis
Spermatogenesis- begins at puberty
- Sperm production is initiated by a hormone called FSHfollicle stimulating hormone released from the anterior
pituitary gland.
- sperm are formed from stem cells called Spermatogonia
within the seminiferous tubules
- When spermatogonia divide they produce 2 cell types.
o Daughter cell A- remains in tubule to maintain stem
cell population
o Daughter cell B- pushed out to lumen to become
primary spermatocyte and go through meiosis.
- After meiosis 4 haploid spermatids are produced.
- 64-72 days later the spermatids have a tail and a helmet
like acrosome which aids in egg penetration.
Hormone Production and Secondary Sex Characteristics
Testosterone Production- also begins at puberty
- Stimulated by LH- (leutenizing hormone) from the anterior
pituitary gland.
- Testosterone causes the male secondary sex characteristics
to emerge.
o Enlarged larynx
o Increase hair growth
o Enlargement of skeletal muscles
o Increased heaviness of skeleton
Oogenesis- begins in female fetus, produces primary oocytes
within the oogonia(stem cells)
- Primary oocytes push into the ovary connective tissue-are
surrounded by layer of cells and wait until puberty
- At puberty FSH stimulates a few primary oocytes to go
through meiosis to produce a secondary oocyte and a polar
body.
- The secondary oocyte ripens into a mature vesicular
follicle stage and erupts from the ovary after about 14
days.
- This is ovulation and is in response to a release of LH.
- When/if a sperm penetrates the oocyte the cell will
undergo a second meiotic division to produce a polar body
and an ovum.
- The ovum nucleus will then unite with the sperm to form a
zygote.
Hormone Production and Secondary Sex Characteristics
- Estrogen production stimulated by the anterior pituitary
gland; begins at puberty.
- Estrogen also helps maintain low blood cholesterol and
high calcium absorption.
- Progesterone production is stimulated by the corpus
luteum after ovulation each month.
Secondary Sex Characteristics
- estrogens not progesterone contributes to the changes that
cause the secondary sex characteristics.
o Enlargement of accessory organs
o Breast development
o Hair growth
o Increased fat deposits
o Widening of pelvis
o Onset of mensus
Female Reproductive Anatomy
- Ovaries (gonads) produce haploid gametes
- Within the ovaries one egg is released each month growing
from a primary follicle until it ruptures from the ovary as a
secondary oocyte during a process called ovulation.
- The remaining ruptured follicle (scar tissue) is called the
corpus luteum and it releases progesterone to help regulate
the menstrual cycle.
- The egg is pulled through the waving fimbrae into the
uterine (fallopian) tubes.
- Moving from ovary to uterus takes 3-4 days.- fertilization
usually takes place in the fallopian tubes.
- The uterus about the size and shape of a pear is the site
where the fertilized egg is nourished and grows.
- The uterus is divided into 3 regions; the top known as the
fundus, the body which is the hollow chamber and the
cervix the bottom most outlet to the vagina.
- The uterus also has 3 layers; the inner endometrium is the
site of implantation- this layer is vascular soft and shed
monthly during mensus if fertilization does not occur. The
myometrium is the middle muscular layer which contracts
during delivery of a baby and the outermost perimetrium.
- The vagina is a thin walled tube 3-4 inches long which
receives the penis during intercourse.
- It is also called the birth canal.
- The vagina has a partially closed thin layer called the
hymen which usually ruptures during the first sexual
intercourse.
External Structures collectively called the vulva include the
following:
- The mons pubis which is the fully rounded area overlying
the pubic symphysis.
- The large fleshy hair covered labia majora are folds on
either side of the smaller hairless labia minora; these flank
the vagina.
- The labia majora enclose the vestibule area which contains
the vagina and urethral openings.
- Greater vestibule glands- flank the vagina and produce a
lubricating secretion.
- The clitoris hooded by a prepuce sits anterior and superior
to the vestibule- it corresponds to the male penis and is
composed of erectile tissue.
Mensus- the menstrual cycle.
-The uterus is essential for the growth of a fetus, however it is
onlya short period where conditions are right for implantation.
-The menstrual cycle keeps the uterus in perfect timing and
conditions to receive a fertilized egg in a process called
implantation.
-As a cycle mensus usually takes 28 days and is influenced by
different levels of hormones released at different times
controlled by anterior pituitary gonadotropic hormones FSH
and LH.
-Menstrual phase days 1-5
 The functional superficial layer of the endometrium
detaches from the uterus was and is accompanied my
bleeding for 3-5 days (up to 7).
 The average blood loss is only 50-150 mL.
 By day 5 growing ovarian follicles are beginning to
produce more estrogen.
-Proliferative phase days 6-14
 Rising estrogen levels from the follicles cause the
endometrial lining to regenerate and glands form within it
 It becomes thick and velvety
 Ovulation occurs within the ovary at the end of this phase
in response to a sudden rise in LH
-Secretory phase-days 15-28
 Levels of progesterone rise (produced by the corpus
luteum) adding to the increase in blood flow to the velvety
endometrial lining
 Progesterone also causes the glands in the endometrium to
secrete nutrients into the uterus which will sustain an
embryo until implantation (if fertilization occurs)
 If fertilization does NOT occur the corpus luteum begins to
degenerate as LH declines.
 The sudden decrease in hormones causes the endometrial
lining blood vessels to spasm and kink, cutting off supplies
and cells begin to die
 The cycle starts over again
Mammary Glands function is to produce milk to nourish a newborn
baby.
 stimulated to increase in size during puberty by
hormones (estrogen)
 modified sweat glands, part of the skin
 composed of fat and lobules of alveolar glands which
produce milk, milk passes out to the lactiferous ducts
and exits through the protruding nipple.
 External structures include the pigmented areola and
nipple.
Fertilization- the union of egg and sperm
 Timing is key- the oocyte is only viable for 12-24
hours after ovulation
 Sperm remain viable 24-48 hours after expulsion
 Sperm may be deposited before ovulation 48 hours
prior and up to 24 hours after ovulation for conditions
to be suitable for fertilization. This is a 3-4 day
window.
 It takes 1-2 hours for the sperm to travel up the 12 cm
uterine tube to reach the ovulated oocyte.
 Millions of sperm reach the oocyte, enzymes break
down the corona radiate surrounding the oocyte
 The acrosome of the sperm makes contact with the
oocyte membrane receptors
 The sperm is pulled into the cytoplasm and the oocyte
completes its second meiotic division forming an
Ovum and a polar body then changes occur in the egg
to keep other sperm from entering
 LOOK diagram fertilization.pdf
 Finally the genetic material of the sperm and the egg
unite in fertilization to form a zygote-the first cell of a
new individual
Embryonic and Fetal Development
 Zygote undergoes cell division to become an embryo
 The developing embryo reaches the uterus about 3 days
after ovulation and is a tiny ball of cells (about 16)
 Embryo floats in uterus and continues to divide into about
100 cells in a hollow sphere called a blastocyst
 The blastocyst secretes an LH-like hormone called human
chorionic gonatoropin-stimulates the corpus luteum to
produce progesterone which continues the blood supply to
the endometrial lining
 By 7 days after ovulation the blasocyst has implanted into
the endometrial lining
 Development is continuing and the primary germ layers
(ectoderm, mesoderm, endoderm) are formed
 Placenta is formed
 By 3rd week placenta is functioning
 By the second month the placenta is producing all
hormones to maintain pregnancy
 By the 8th week all organ systems have been laid down and
groundwork is complete
 At 9th week now referred to as fetus
 During fetal stage grows from 3 cm to about 36 cm
 About 270 days after fertilization pregnancy is considered
to be full term
Childbirth- also called parturition expels the infant from the
uterus during labor.
 During the last few weeks of pregnancy estrogen levels
peak causing the myometrium to form oxytocin receptorsit also interferes with progesterone which acts to calm
uterine muscles during pregnancy
 Now the uterine muscle begins to quiver these “practice”
contractions are called Braxton Hicks contractions
 The fetus starts to release oxytocin which stimulates
prostoglandins-combined these initiate more frequent and
powerful contractions
 Now true labor begins
 Labor is often divided into 3 stages
-Dilation Stage
 From initial contractions to 10 cm dialation and
infants head pressing against cervix
 Longest stage usually 6-12 hours
-Expulsion Stage
 Period of full dialation to delivery of the
infant
 Accompanied by the urge to push
 Takes as long as 2 hours (avg 50 min 1st
child)
 Infants usally are born head first facing down
 After birth the umbilical cord is clamped and
cut
 Breech (but first) deliveries are much more
difficult and the use of forceps or vacuum
extractor are often necessary
-Placental Stage
 Actually the delivery of the placenta, usually
happens within 15 min of birth
 Often called the afterbirth
Effects of pregnancy on the mother
 Uterus enlarges slowly to consume the majority of space
within the abdominopelvic cavity
 Fundus reaches the xiphoid process
 Ribs flare to help accommodate space
 Center of gravity changes
 Accentuated lumbar curvature
 Nearing birth placenta releases the hormone relaxin
causing pelvic ligaments and pubic symphasis to soften
and increase in motility
 Good nutrition is important through pregnancy as building
materials for tissues and organs
o If this does not occur the fetus will “steal” nutrients
from the mothers body to make up for the lack of
building materials
 Pregnancy requires about 300 additional calories for fetal
growth keeping nutrition in mind
 Morning sickness is often a symptom of nausea in
response to elevated levels of progesterone
o *this occurs until the woman adjusts to the increased
levels-and some women never adjust
 Heartburn is often a symptom as the stomach and
esophagus are pushed upward causing the pyloric sphincter
to open more easily
 Constipation often occurs because of decreased motility of
the digestive tract due to overcrowding
 Kidneys have increased duty as they cleanse the blood of
the fetus too, causing more frequent urination
o NOTE the blood of the fetus does not mix –see FAQ’s
 Nasal mucosa respond to estrogen becoming swollen and
congested –this symptom usually occurs later in pregnancy
and can in some cases cause noticeable physical swelling
in and around the nose
 Blood volume rises 25-45% much of which is water
 Increase in blood pressure and pulse as cardiac output must
increase to propel more blood
 Venous return is poor especially in lower limbs-sometimes
resulting in varicose veins
Developmental Aspects and Homeostatic Imbalances
 Sex of an individual IS determined at the time of
conception-but gonad formation does not begin until the
8th week this is sometimes called the indifferent stage
 After gonads are formed it testosterone is present
(produced by the fetal testes) the male duct system will
result, if absent in significant quantities the female duct
system will arise
 Puberty- usually between 10-15yrs is the time when
reproductive accessory organs grow and mature
o Boys- puberty begins with growth of the testes
followed by increased hair growth in pubic, auxillary
and facial regions then the penis enlarges for the next
2 years
o Girls- puberty begins with the budding of the breasts
often apparent by age 11, increased hair growth
follows then about two years after puberty has begun
the 1st menstrual cycle (menache) occurs. It takes
about 2 more years until regular ovulation and fertility
are accomplished
 Even though these steps remain the same sequence the age of
onset varies greatly among individuals
FAQ’s
1. What are hormones?
a. Hormones are chemicals secreted in one tissue which
travel via body fluids to other parts of the body. Its
like a chemical messenger that affects growth and
behavior.
2. Do women have testosterone?
a. Yes. Usually small amounts, increased levels are
associated with weight gain (apple shaped body),
acne, menstrual irregularities, high cholesterol and
more.
3. Do mother’s and baby’s blood mix?
a. No. Not in normal situations. Diffusion allows for the
transfer of nutrients and wastes.
See link Fetal Anatomy: Understanding Placenta
Anatomy | BabyZone