Download Human Reproduction

Human Reproduction
Testes:
Gonad: an organ that produces sex cells in animals.
Meiosis takes place at 35 degrees Celsius---------------Does not take place properly at 37
degrees Celsius.
Testes produce testosterone.
Epididymis:
Sperm mature in the epididymis and are stored for up to 6 weeks.
Sperm duct:
Carries sperm to the urthrea.
A vasectomy is an operation to cut the sperm duct (birth control).
Associated glands:
Seminal vesicles, prostate gland and Cowper’s gland produce a liquid called seminal fluid.
Seminal fluid + Sperm = Semen
Seminal fluid provides nutrients and allows the sperm to swim.
Sperm:
Sperm producing cells are diploid (46 chromosomes), however, they divide by meiosis to
produce haploid sperm cells (23 chromosomes).
Penis:
Introduces sperm into the female body
Becomes erect when more blood flows into the penis than flows out
Hormones in the male reproductive system
FSH (follicle stimulating hormone) : causes the production of sperm by meiosis.
LH (luteinising hormone): Stimulates testes to produce testosterone.
Testosterone: causes primary male sex characteristics early in life, e.g growth of penis.
Secondary male characteristics are features that distinguish males from females.
Examples: growth of pubic hair, facial hair, increased muscular and bone development,
deepening of voice.
Male infetlity (low sperm count):
Causes: smoking, alcohol, anabolic steroids, low levels of hormones.
Corrective measures: changing diet, stop smoking and drinking, reducing stress levels.
Female Reproduction system
Ovaries:
Produce eggs and female hormones
After meiosis has occurred in ovary to produce a haploid egg, it is surrounded by a Graafian
Follicle (produces oestrogen).
After ovulation (releasing of the egg) the follicle fills with yellow cells and becomes the
Corpus Luteum (produces progesterone)
Fallopian tube:
The egg is fertilised in the fallopian tube.
Egg moves in the fallopian tube by muscular peristalsis.
Uterus:
Inner lining of uterus is called the endometrium
Opening of the uterus is called the cervix
Vagina:
Allows entry of the sperm and acts as a birth canal for the baby
Menstrual cycle
Occurs every 28 days
Menopause: menstrual cycle stops
Stages of the Menstrual cycle:
Days 1 – 5:
Old lining of the uterus (endometrium) breaks down and is shed (period)
Meoisis occurs in the ovary to produce a haploid egg (egg surrounded by Graafian follicle)
Days 6 – 14:
The Graafian follicle produces the oestrogen which causes the endometrium (lining of
uterus) to thicken.
Oestrogen also prevents new eggs from developing.
Days 14:
Ovulation (realising of egg) occurs when graafian follicle bursts to release egg from ovary.
Egg is moved along the fallopian tube (egg can only be fertilised for 48 hours)
Days 14 – 28:
Remains of the graafian follicle develop into the corpus luteum (yellow body) which makes
the hormone progesterone.
Progesterone causes endometrium to thicken further.
Progesterone also prevents new eggs from developing.
IF
If fertilisation has not taken place the corpus luteum begins to break down around day 22.
The progesterone level drops which causes lining of uterus to break down on day 28.
Menstruation begins again.
Graafian follicle
Corpus Luteum
Progesterone _____
Endometrium
Hormones
Oestrogen________
5
14
28
Days
Functions of oestrogen and progesterone
Both cause the endometrium to thicken in the menstrual cycle at different stages.
Both prevent the developing of new eggs.
Both cause secondary female characteristics such as widening of pelvis, growth of pubic and
underarm hair.
Female infertility( e.g endocrine gland failure)
Cause: failure to ovulate due to hormonal disorder, stress.
Corrective measures: Hormonal disorder, reducing stress, or surgery.
Hormones in the menstrual cycle:
FSH: produced by pituitary gland-------- stimulates eggs to develop
Oestrogen: produced by the graafian follicle---------causes endometrium to develop
LH: produced by the pituitary gland---------causes ovulation to occur.
Progesterone: produced by the corpus luteum---------maintains structure of endometrium
Menstrual disorder:
Example: Fibroids------benign tumours of the uterus
Cause: may be due to responses to oestrogen
Prevention: surgery or a hysterectomy.
Events leading to fertilisation:
Fertilisation is when the nucleus of the sperm fuses with the nucleus of the egg forming a
diploid zygote.
Acrosomes: acrososmes at the front of the sperm contain enzymes which digest an opening
on the membrane of an egg.
Birth control:
1) Abortion
2) Contraception
Contraception:
Natural contraception----------times of past menstrual cycles
Mechanical contraception: condoms, diaphragms, caps
Chemical contraception: Spermicides-----used to kill sperm
Surgical contraception: vasectomy for males and sterilisation for females.
Implantation:
Is the embedding of a fertilised egg into the lining of the uterus.
It occurs between 6 – 9 days after fertilisation in which the zygote has grown into an
embryo.
An amnion membrane develops around the embryo which secretes amniotic fluid which
acts as a shock.
In-vitro fertilisation
Treats infertility
Removes eggs from ovary and fertilises them outside the body
IVF literally means fertilisation in a glass.
Placenta
The Placenta
Placenta
Chorion
Embryo
Mother’s blood
Wastes, Carbon Dioxide, Water
Nutrients, Oxygen, antibodies
Mother
Amnion
Amniotic fluid
Umbilical cord
Embryo’s blood
Embryo
After implantation the embryo forms an outer membrane called a chorion.
The chorion develops villi along with the blood vessels of the mother in endometrium to
form placenta.
Function:
Allows nutrients, wastes, gases, antibodies and hormones to be exchanged between the
blood of the mother and the embryo
Note: the blood supply of the mother and the embryo do not mix (reason: blood pressure
of mothers system would damage the embryo).
Early stages of zygote
It divides rapidly by mitosis to produce 2 cells,
then 4, then 8, 16 etc. and continues to divide
After 3 days, a solid clump of cells form called morula.
Around 5 days a hollow ball of a few hundred cells form called blastocyst.
 The outer layer of
the blastocyst forms
the trophoblast. This
will later develop
into the layer of
membranes that
surround the
embryo (placenta
and amnion)
Trophoblast
NOTE: stem cells are found in the blastocyst. They can be used to form many different types
of tissue.
Embryonic development
10 days after fertilisation the inner cell mass of the blastocyst forms an embryonic disc
consisting of three germ layers.
Ectoderm – skin, nervous system
Coelom – heart, lungs
Mesoderm – muscles, skeleton
Endoderm – inner lining of
digestive system
The mesoderm is split by the coelom which allows space for the heart and lungs.
4 - 5 weeks
Heart starts to beat.
Brain, umbilical cord and limbs form
6th week
Eyes, mouth, ears nose begin to form
8th week
Major body organs begin have formed
Sex glands develop into testes and ovary
Embryo is now recognised as a foetus.
12th week
Eyes are low on the face
Bones replace the cartilage
Nerves and muscle become coordinated
Gender of foetus can be seen
Gestation: the length of time in the uterus from fertilisation to birth.
Stages of Birth
Immediately before birth the placenta stops producing progesterone which causes the
walls of the uterus to contract.
The pituitary gland also secretes oxytocin which causes contractions of the uterine muscle
which results in labour.
3 stages of labour:
Stage 1) Normally lasts 12 hours which pushes the foetus down towards the cervix.
The membranes around the foetus break which releases fluid out of the vagina
(water breaking).
Stage 2) Normally lasts 20 minutes to an hour. The cervix dilates (opens) enough to
allow baby to be born. The umbilical cord is clamped and cut.
Stage 3) Within 5 to 30 minutes the uterine contractions expel the placenta and
foetal membranes called the afterbirth.
Lactation:
Secretion of milk by the mammary glands.
A thick yellow fluid called colostrum is produced in first few days as it is higher in minerals,
proteins and antibodies.
Prolactin hormone stimulates milk production.