Download Functions of Female Reproductive Organs

Chapter 41: The human
reproductive system
Leaving Certificate Biology
Higher Level
Structure of Female Reproductive Tract
Structure of Female Reproductive Tract
Structure of Male Reproductive Tract
Functions of Female Reproductive Organs:
• Ovaries:
– Where eggs develop
– Produce sex hormones: oestrogen and progesterone that
are responsible for the onset of puberty and the
maintenance of secondary sexual characteristics
• Fallopian tubes (oviducts):
– Collect the egg following ovulation and direct it towards
the womb using muscular contractions
• Uterus (womb):
– Has a delicate lining called the endometrium that is shed
once a month
– Fertilised egg develops in the uterus to become an
embryo and then a foetus
Functions of Female Reproductive Organs:
• Cervix:
– Located at the bottom of the womb and is the
region where the sperm enter following
intercourse
• Vagina:
– Muscular tube that receives the penis during
intercourse
– Serves as the birth canal during parturition
Functions of Male Reproductive Organs:
• Testes:
– Located outside the body so that the temperature
is lower as sperm require a lower temperature of
35 ˚C for proper formation
– Where sperm develop and mature before being
released
– Produce testosterone that is responsible for the
onset of puberty and the maintenance of
secondary sexual characteristics
Functions of Male Reproductive Organs:
• Epididymis:
– Located at the top of each testes and sperm are
stored until they are released – if they are not
released then they are broken down and
reabsorbed
• Sperm ducts (vas deferens):
– Where sperm are carried to the urethra and then
out of the body
Functions of Male Reproductive Organs:
• Glands:
– There are three glands associated with the male
reproductive system:
• Seminal vesicles
• Prostate
• Cowper’s gland
– They all contribute to seminal fluid that is the
medium for the sperm to swim in and contains
nutrients for the sperm that will help nourish
sperm while they are within the female
reproductive tract
Functions of Male Reproductive Organs:
• Penis:
– The penis is a muscle that is capable of swelling
with blood in order that it can be inserted into the
vagina
– It is responsible for delivering the sperm at the
cervix
Meiosis and Gamete Formation
• Meiosis has an important function:
– Meiosis halves the number of chromosomes in
the formation of 4 haploid daughter cells from
one diploid parent cell
– Halving the number of chromosomes is critically
important in propagating the species as it ensure
that the resulting offspring (the next generation)
will have the correct number of chromosomes in
every cell
Secondary Sexual Characteristics
• Secondary sexual characteristics are those
features that distinguish males from females,
apart from the sex organs themselves
Secondary Sexual Characteristics in
Males:
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Pubic hair
Underarm, body and facial hair
Enlarged pharynx
Larger muscles and bones
Wide shoulder girdle
Large body size in comparison to females
Sebum secretion
Secondary Sexual Characteristics in
Females:
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Pubic hair
Underarm and body hair
Breasts
Wide pelvic girdle
Higher body fat in comparison to males
Sebum secretion
Oestrogen
• Oestrogen is one of the female sex hormones
that is made in the ovaries and secreted into
the bloodstream
– Oestrogen affects a wide variety of tissues
throughout the body – the most common ones
including: breast, brain, adipose, and uterine
tissue
– Oestrogen has a very important role in the
menstrual cycle – see forthcoming slides
Progesterone
• Progesterone is the other sex hormone in
females that has a similar structure as
oestrogen and similar effects but the timing of
the effects is different
• Progesterone is also secreted by the ovary
Testosterone
• Testosterone is the male sex hormone that is
secreted by cells within the testes
• Testosterone:
– General growth
– Growth of the male reproductive system early in
life
– Development of secondary sexual characteristics
– Maintenance of secondary sexual characteristics
– Sperm production
The Menstrual Cycle
• The menstrual cycle biorhythm in females that takes
approximately 28 days
• The menstrual cycle begins at puberty (ages 11 to 16) and
usually lasts until menopause (ages 45 to 55)
• The menstrual cycle is controlled by four hormones:
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Follicle-stimulating hormone (FSH)
Oestrogen
Luteinising hormone (LH)
Progesterone
• The menstrual cycle can be divided up into three main
stages or events:
1. Menses and follicular phase
2. Ovulation
3. Luteal phase
1. Menses and the follicular phase
• Menses: occurs between days 1 and 5:
– Involves the shedding of the lining of the uterus
• Follicular phase: FSH secretion from the
pituitary increases and causes a number of
Graafian follicles to form
– Only one of these follicles normally survives and a
new egg develops within the Graafian follicle
• The Graafian follicle secretes oestrogen
• As the Graafian follicle enlarges the amount of oestrogen
secreted increases
• Only one Graafian follicle normally develops so that only
one egg will be produced each month
1. Menses and the follicular phase
(continued)
• Repair of the endometrium occurs over days 6
to 13 where the developing Graafian follicle is
secreting oestrogen which causes the
endometrial cells to start dividing again
• As oestrogen levels are increasing it inhibits
FSH secretion by negative feedback – ensuring
no more Graafian follicles develop
2. Ovulation
• Oestrogen levels keep increasing until they
reach a critical concentration
• When this concentration is reached it
stimulates the release of a hormone from the
pituitary called luteinising hormone (LH)
• LH causes ovulation
• Ovulation occurs on day 14 and involves the
release of the egg from the ovary into the
funnel and onto the oviduct
3. Luteal phase
• When the egg is released from the ovary the
Graafian follicle turns into a yellow structure called
the corpus luteum
• Oestrogen levels drop
• The corpus luteum secretes progesterone which
maintains the endometrium in preparation for
fertilisation
• In addition progesterone maintains the inhibition
on FSH and LH ensuring no further eggs develop
• If fertilisation does not occur then the corpus
luteum dies and progesterone levels drop causing
the beginning of menstruation
Menstrual Disorder
• Fibroids:
– Fibroids are benign tumours within that develop within
the uterus as the female gets older
– Most are very small but some can grow large enough to
cause symptoms
– Symptoms of large fibroids are pain, prolonged
menstrual bleeding, infertility and anaemia (through
loss of blood)
– Their cause is thought to be due to abnormal responses
to oestrogen
– Most fibroids do not need any medical treatment,
however, large fibroids may require surgery
(hysterectomy may be carried out)
Stages of Copulation
• Sexual arousal:
– Males: blood flows into the penis and the penis
becomes erect
– Females: blood flow to vagina increases causing it
to becomes longer and mucous secreting cells
ensure the vagina is lubricated
• Copulation:
– Penis is inserted into the vagina
Orgasm and Insemination
• Copulations causes physical and mental
sensations in both the female and male
• These sensations are collectively called
orgasm
• During orgasm in the male, semen is released
into the female at the site of the cervix
• The release of sperm at the cervix is called
insemination
Survival Time for Sperm and Ova
• Sperm can survive for up to 3 days within the
female reproductive tract
• The egg cell survives for 2 days following
ovulation
Fertilisation
• Fertilisation is the fusion of an egg cell and a
sperm cell to produce a diploid zygote
• Fertilisation normally occurs in the fallopian
tube
Sequence of Development of Zygote
• After fertilisation the diploid zygote divides by
mitosis into 2 cells, 4 cells, 8 cells etc.
• After approximately 3 days a clump of cells
between 32 and 128 cells is formed – this is
called the morula
• After 1 week a hollow structure of a few
hundred cells (inner cell mass) has formed and
this is called the blastocyst
• The outer layer of cells is called the trophoblast
and it is this structure that will enable
implantation to occur
Early Sequence of
Zygote Development
Implantation
• Implantation is the embedding of the blastocyst
into the lining of the uterus
– Implantation occurs approximately 1 week following
fertilisation
– Once implanted the blastocyst continues to grow and
the trophoblast extends projections into the uterine
tissue
– The interaction between the uterine tissue and the
trophoblast will eventually give rise to the placenta
– The implanted embryo continues to grow and the
placenta begins to form
– The embryo is recognisably human after about 8 weeks
post-fertilisation – at this stage it is called a foetus
Placenta
• The placenta is an organ made of two tissues: mother’s
uterine tissue and foetal tissue
• The bloodstream of the foetus and mother DO NOT mix,
but come into close contact so that materials can be
exchanged
• The placenta is only fully formed and fully functional
after about 3 months
• The placenta is the foetus’ life support
• The foetus gains its nourishment from the mother via
the placenta
• Examples of materials that pass from mother to foetus
are: oxygen, water, glucose, amino acids, hormones,
antibodies
• Examples of materials that pass from foetus to mother
are: carbon dioxide and urea
Embryo Development – Germ Layers
• Ten days following fertilisation the inner cell
mass give rise to an embryonic disc
• The embryonic disc gives rise to three layers of
cells called:
– Endoderm:
gives rise to liver and pancreas and
to inner lining of digestive,
respiratory and excretory systems
– Mesoderm: gives rise to internal organs such as
heart, lungs, kidneys, muscles,
skeleton
– Ectoderm: gives rise to skin, hair, nails, nervous
system
Embryo Development – First 8 Weeks
• First 4 weeks: heart forms and begins to beat
and brain develops as well as the umbilical cord
• Week 5: limbs begin to form
• Week 6: eyes are visible and face is forming
• Week 7: tail begins to disappear and all the
internal organs are now formed
• Week 8: ossification starts to occur
Embryo Development – First 8 Weeks
• Week 8 onwards: the embryo rapidly increases
in size
• By week 12: eyes are low in the face and bone
continues to replace cartilage; nerves become
coordinated and the embryo begins to move
• For the rest of pregnancy, the foetal organs
increase in size, become stronger and mature so
that they will be able to function independently
following birth
Birth
• During pregnancy, oestrogen and progesterone
are produced in high amounts by the placenta –
inhibiting the release of FSH and also inhibiting
contractions of the uterus
• However, these hormones stop being secreted
towards the end of pregnancy and then the walls
of the uterus begin to contract
• Pituitary gland then begins to secrete oxytocin
which causes further stronger contractions of the
uterus
Birth (continued)
• Birth is subdivided into three parts:
– Labour: lasts approx 12 hours:
• Waters break and baby moves down towards the cervix
– Parturition: lasts 20 minutes to 1 hour:
• Cervix dilates
• Baby is pushed out through cervix and vagina head first
• Umbilical cord is clamped and cut
– Afterbirth: 30 minutes:
• Continuing uterine contractions expel the placenta
from the uterus
Lactation
• Lactation is the production and secretion of
milk by the mammary glands of the female
– Following birth the pituitary begins to secrete
prolactin
– Prolactin stimulates the breasts to secrete milk
– For the first few days of the baby’s life the mother
produces a thick yellow fluid called colostrum
– For as long as the baby suckles prolactin will
continue to be produced and milk will continue to
be secreted
Benefits of Breast-Feeding
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Ideal balance of nutrients
Contains antibodies – helps baby’s immunity
Helps mother bond with the baby
Helps the mother’s body recover from
pregnancy
• Evidence suggests it may reduce the risk of
developing breast cancer later in life
Birth Control
• Birth control is any mechanism whereby
pregnancy is prevented
• Birth control can be carried out by the use of
contraception or by carrying out an abortion
after fertilisation has occurred
• Both methods of birth control are disallowed
by the Catholic Church and abortion is illegal
in many countries
Birth Control (continued)
• There are four main types of contraception:
1. Natural: involves not having intercourse or by
using the rhythm of the menstrual cycle to predict
when ovulation is likely to occur
2. Mechanical: use of a condom or diaphragm to
prevent entry of the sperm through the cervix
3. Chemical: use of the contraceptive pill (contains
oestrogen and progesterone) prevents ovulation
4. Surgical: involves usually irreversible sterilisation
of the male or female whereby the vas deferens or
the fallopian tubes are cut or tied to prevent the
sperm and the egg reaching each other