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Biology 3201
Ch. 15 – Reproduction and Development
15.1 – The Human Reproductive System
Male Reproductive System (see fig. 15.2, p. 487)
Testes – produce sperm and reproductive hormones. 2 parts:
1. seminiferous tubules – long coiled tubes inside the testes.
Spermatogenesis occurs here and inhibin is released from here. These tubules contain
Sertoli cells, which support, regulate and nourish developing sperm
2. interstitial cells – cells surrounding the seminiferous tubules.
They produce male hormones like testosterone.
Scrotum – sac which holds testes outside the body. Sperm develop in
temperatures slightly cooler than body temperature. However, if the environment is too
cold, the scrotum can be retracted so the testes are held closer to the body
Epididymis – the tube within the scrotum in which sperm mature and become
mobile
Vas deferens – the tube which carries sperm from the epididymis to the urethra
Prostate gland – a gland that secretes an alkaline fluid which neutralizes the
acidity within the female reproductive system
Cowper’s gland (bulbourethral gland) – same as prostate
seminal vesicles – glands that produce mucus-like fluid containing fructose as
energy for sperm
semen – fluid consisting of sperm and fluid from the prostate, seminal vesicles,
and Cowper’s gland
urethra – tube which carries sperm into female reproductive system (also used in
excretory system)
penis – transfers sperm to female reproductive system during sexual intercourse
Male Reproductive Hormones
1. Inhibin
- hormone that acts on the hypothalamus to slow down the production of
release factors that trigger FSH secretion. It is released by the seminiferous tubules.
2. Follicle-stimulating hormone (FSH) – in males, FSH increases sperm
formation (released by the anterior pituitary)
3. Lutenizing hormone (LH) – produced by the anterior pituitary; LH stimulates
interstitial cells to produce testosterone
4. Testosterone – steroid hormone produced in the testes that is responsible for
secondary sex characteristics in males, such as
- enlargement of primary sex characteristics
- enlargement of larynx (Adam’s apple)
- inhibiting fat storage and increasing muscle development
- formation of hair on chest, arms, face, genitals
The Female Reproductive System (see fig. 15.5, p. 490)
Ovary – gland that is suspended in the abdominal cavity and produces eggs (ova)
Follicles – in the female reproductive system, groups of cells held in the ovaries.
Each of these cells contain an ovum that will develop
Oviducts (Fallopian tubes) – pair of tubes in the body that transport an egg from
the ovary to the uterus. Fertilization of eggs occurs here. Oviducts are ciliated to help
eggs travel.
Fimbriae – finger-like projections that sweep eggs from where they exit the
ovaries into the oviducts
Uterus – the womb. After an egg is fertilized, it attaches to the uterine wall and
grows. Usually it is the size of a fist, but it expands to six times that size to accommodate
a fetus.
Endometrium - the mucous membrane that lines the uterus and increases in
thickness in the latter part of the menstrual cycle
Cervix – the opening/exit of the uterus
Vagina – the birth canal; an entrance for an erect penis to deposit sperm during
sexual intercourse and an exit for the fetus during childbirth.
Female Hormones
1. follicle stimulating hormone (FSH) – in females, FSH is responsible for the
follicles developing and secreting estrogen
2. lutenizing hormone (LH) – in females, LH triggers the release of an ovum
from the follicle
3. estrogen – produced by the follicles; responsible for the thickening of the
endometrium and keeps FSH secretions down (to prevent further follicles from
developing)
4. progesterone – sex hormone that is produced in females, first by the corpus
luteum and the ovary to prepare the uterus for fertilization, and later by the placenta to
maintain pregnancy
The Menstrual Cycle
Menstrual cycle – in a human female, period of 20-45 days during which
hormones stimulate the development of the uterine lining and an egg is developed and
released from an ovary. If the egg is not fertilized, the uterine lining is shed as the cycle
begins again.
Stages:
1. Follicle Stage (10-14 days)
→ FSH secretions increase, which stimulates the follicles to
mature and release increased quantities of estrogen into the bloodstream
→ increased estrogen levels stimulate the endometrium to thicken
with blood, and stimulate LH secretion and inhibit further FSH secretion
2. Ovulation Stage (< 1 day)
→ egg is released by a follicle
→ follicle changes to become corpus luteum
corpus luteum: body that develops from a follicle that has
been emptied of its egg; produces progesterone
3. Luteal Stage (10-14 days)
→ corpus luteum begins secreting progesterone, which inhibits the
development of other follicles and inhibits LH secretion
4. Menstruation (3-5 days)
→ as LH levels drop, corpus luteum degenerates causing
progesterone levels to drop
→ the uterine lining is not maintained and the blood and
unfertilized egg are passed through the vagina
Female Hormone Treatments
Hormone replacement therapy – administration of low levels of estrogen and/or
progesterone to alleviate symptoms of menopause
Benefits:
→ relief of menopausal symptoms such as hot flashes, night sweats, and
sleep disturbance
→ prevention of bone loss (osteoporosis)
→ improved memory
→ decreased chance of urinary tract infections
→ decreased rate of macular degeneration
Potential side effects of estrogen therapy:
→ irregular vaginal bleeding
→ stomach upset
→ severe headaches
→ blood clots
→ increased risk of breast cancer
→ increased risk of uterine cancer
Potential side effects of progesterone therapy:
→ stomach upset
→ irregular vaginal bleeding
→ edema (water retention)
Potential side effects of combination therapy:
→ blood clots
→ fluctuation of blood sugar levels
→ increased risk of heart attack
→ edema
→ headaches
→ premenstrual-like syndrome
Birth Control Pills
- work by supplying excess estrogen and progesterone. This inhibits
FSH and LH secretions, so ovulation does not occur. As well, the
endometrium develops abnormally so even if ovulation occurs the egg
cannot be implanted.
- risks associated with birth control pill use same as hormone
replacement therapy (same chemicals)
Sexually Transmitted Infections (STIs)
The most common STIs are caused by either bacteria or viruses
Ex.
Bacterial – gonorrhea, syphilis
Viral – AIDS, genital herpes
AIDS and HIV
- AIDS stands for “acquired immunodeficiency syndrome” and is
caused by HIV, which attacks the immune system (helper T-cells)
- Transmitted through sexual contact (including oral, rectal, and
vaginal), sharing of needles, breast feeding, blood transfusions, etc.
- 3 stages in AIDS infection:
1) A - lasts about a year
 No visible symptoms, but can infect others
2) B - 6-8 years

T-cells reduced, lymph nodes swell and person
experiences weight loss, night sweats, fatigue, fever,
and diarrhea
3) C – full blown AIDS
 Nervous disorders occur and opportunistic diseases like
pneumonia and skin cancer. If the person does not
receive treatment, they will die in 7-9 years
Chlamydia
- bacterial infection, possibly dangerous
- burning sensation can be noticed, as well as a discharge from the penis
in males. Women may have vaginal discharges and symptoms of a
urinary tract infections
- 75% of all Chlamydia cases asymptomatic until irreversible damage is
done
- can be treated with antibiotics if caught early enough
Hepatitis
- viral infections; 3 types
1) A - contaminated drinking water
2) B – sexual contact, exchange of fluids
3) C – infected needles and syringes
- Symptoms are flu-like, and the skin turns yellowish (jaundice)
- If it spreads, can lead to liver infection, liver failure, and eventually
death
- Some people recover, others are asymptomatic carriers
- Vaccines available for hepatitis A and B
Genital Herpes
- viral infection caused by herpes simplex 2 (HSV 2); HSV 1 causes
cold sores and blisters
- symptoms occur within a month; include tingling or itching followed
by blisters that rupture. Outbreaks can occur
- no cure for genital herpes
- increased chance of AIDS, discomfort
Syphilis
-
-
bacterial infection
3 stages:
1) chancres (sores with hard edges) appear at infected sites
2) a rash that appears usually on the palms of the hands or the
soles of the feet
3) the infection affects the cardiovascular and nervous systems.
The patient can develop mental illness, bleeding, and/or heart
disease
can be treated with antibiotics
Gonorrhea
- bacterial infection
- can cause infection of the urethra, cervix, rectum and throat
- often characterized by pain on urination and a thick green-yellowish
discharge from the urethra
- can spread to other parts of the body
- can be treated with antibiotics
15.2 – Reproductive Control
Infertility
Sterile – incapable of becoming pregnant or of inducing pregnancy
Infertile – physically incapable of conceiving children
Reasons for Infertility:
Men
→ blocked vas deferens or epididymis
→ low sperm count
→ high proportion of abnormal sperm
Women
→ blocked oviducts
→ failure to ovulate – hormonal imbalance
→ endometriosis: a painful condition in which the endometrium goes
outside the uterus
→ damaged eggs
Technologies to Combat Infertility
1) Artificial Insemination (AI)
- sperm placed in the vagina
- used when sperm count is low (taken and concentrated) or a woman
wants a child without a partner
2) In-Vitro Fertilization (IVF)
- eggs taken outside of the body, fertilized, then re-inserted in the uterus
- used when a woman has blocked or damaged oviducts
3) In-Vitro Maturation (IVM)
- oocytes taken out of woman, matured, and then used for IVF
4) Superovulation
- uses FSH injections to produce multiple eggs
- used when a woman does not ovulate regularly or frequently
5) Surrogate Motherhood
- fertilized egg is placed in a fertile surrogate mother who carries the baby
to term
6) Cryopreservation
- oocytes, semen and/or zygotes are preserved by freezing
- used in situations where people may become sterile later in life but still
want children
Contraceptive Methods
Contraception – a way of avoiding pregnancy, using either artificial methods such
as condoms and birth control pills or natural methods such as avoiding sexual intercourse
during the woman’s known fertile periods
(see table 15.2, p. 502 Contraceptive Methods)
15.3 – Development and Differentiation
fertilization – first stage of embryonic development, when a sperm and egg
interact successfully to form a zygote (reproductive cell)
Implantation – the embryo’s attachment of itself to the endometrium, occurs
within the first week after fertilization in humans
Pathway to Fertilization
Sperm develop in testes → epididymis → vas deferens→ urethra → vagina → cervix →
uterus → oviduct (fertilization)
After fertilization, the zygote travels down the oviduct to the uterus to implant.
As it does, it undergoes cell divisions called cleavage
(see fig 15.12, p. 507)
(see fig 15.12, p. 507)
zygote – a young reproductive cell in humans formed from sperm and egg
embryo – a human offspring in the early stages of development where it
undergoes cleavage up until it forms bone cells
fetus – an unborn vertebrate at a stage where all the structural features of the adult
are recognizable and the first bone cells form, especially an unborn human after 8 weeks
of development
cleavage – the process of cell division without cell growth
morula – an early stage in the development of an animal’s embryo, consisting of a
solid ball of cells derived by the cleavage of a fertilized egg.
Blastocyst – a mammalian embryo which is implanted in the wall of the uterus
and consists of a nearly hollow ball of cells
Trophoblast – the outer layer (ectoderm) of a blastocyst; attaches the fertilized
ovum to the wall of the uterus and absorbs nutrients. The trophoblast develops into
membranes that will protect and nourish the fetus through its gestation
During the blastocyst stage, all the cells of the blastocyst are similar. In the
second week of development, these cells begin to specialize
Gastrula – stage in embryonic development after the blastocyst during which the
embryo develops distinct layers called germ layers
Germ layers – three cellular layers in the gastrula from which the organs and
tissues of an animal’s body develop
3 germ layers:
1) Ectoderm – outside, forms skin and nervous system
2) Mesoderm – middle, forms the kidneys, skeleton, muscles,
blood vessels, and gonads
3) Endoderm – inside, forms lungs and lining of digestive tract
In the third week of human development, the nervous system begins to form.
Neurula – vertebrate embryo in an early stage where the nervous system begins to
develop
In the gastrula, the mesoderm cells that lie along what will be the back of the
vertebrate come together to form a rod called the notochord (develops into spinal
column). The nervous system develops from ectoderm that is located just above the
notochord. First, cells above the surface of the notochord begin to thicken. Folds
develop on each side of the groove along the surface. The folds become a tube when they
fuse. The anterior, or “head” end, of the neural tube becomes a brain.
Primary Membranes
Primary membranes – in mammals, reptiles, and birds thin flexible sheets of
tissue that are not part of the embryo but that support, nourish, and protect it
Primary membranes in humans (see fig 15.15, p. 509)
1) Chorion – outer membrane enclosing the embryo of mammals, reptiles, and
birds. It has a dense concentration of blood vessels and aids in the formation of the
placenta in mammals
2) Amnion – inner of the two membranes enclosing the embryo of a mammal,
bird or reptile and its amniotic fluid; provides cushioning
3) allantois – membranous sac that grows from the lower gut in an embryo of a
mammal, reptile, or bird. In mammals, it help builds the umbilical cord and placenta
4) yolk sac – in humans, a structure which is the site of the first red blood cell
formation
5) placenta – in most pregnant mammals, a blood-vessel rich organ that develops
inside the uterus to supply food and oxygen to the fetus through the umbilical cord
6) umbilical cord – flexible, often spirally twisted tube that connects the abdomen
of a fetus to the mother’s placenta in the uterus, and through which nutrients are derived
and wastes are expelled
Factors that Affect Development
Teratogen – any agent that causes a structural abnormality of the developing fetus
due to fetal exposure during pregnancy
Examples of teratogens:
→ cigarette smoke: causes fetal blood vessels to constrict, which cuts off oxygen.
Babies are born underweight
→ alcohol: affects the brain, nervous system, and overall development. Fetal
Alcohol Syndrome (FAS) babies have decreased weight, height, head size, and may show
mental retardation
→ prescription drugs: Thalidomide was a drug prescribed for morning sickness.
However, it was linked to babies being born with deformed or missing limbs.
Twins
Identical twins – form when one sperm fertilizes one egg, but the zygote or
blastocyst splits into two separate bodies. They have the same genetic material.
Fraternal twins – form when more than one egg is released at a time by the ovary
or ovaries and more than one egg becomes fertilized. Fraternal twins are as different as
normal siblings.
The Process of Birth
Birth goes through 3 stages:
1) Dilation stage
- uterine contractions and oxytocin cause the cervix to open up or dilate
- during this stage, the amnion breaks and the amniotic fluid is released
through the vagina
- lasts 2-20 hours
2) Expulsion stage
- forceful contractions push the baby through the cervix to the birth canal
- as the baby moves through the canal the head rotates, making it easier
for the body to pass through the canal
- lasts 0.5-2 hours
3) Placental stage
- about 10-15 minutes after the baby is born, the placenta and umbilical
cord are expelled from the uterus
prolactin – non steroid protein hormone produced by the anterior pituitary gland
that stimulates mammary gland tissue growth and milk production.
Monitoring Fetal Development
There are various methods to monitor how well the fetus is developing inside the
female:
1) ultrasound – a procedure where sound waves are used to take a picture of the
developing fetus
2) amniocentesis – medical procedure in which a sample of cells from the
amniotic fluid is tested for abnormalities in a fetus
3) fetoscopy – medical procedure that involves direct observation of the fetus with
an endoscope
4) CVS (chrorionic villi sampling) – sampling of cells from the chorion to test for
genetic conditions in a fetus.