Sexual Reproduction in Humans
Insemination – semen being released into the vagina just outside the cervix
Ejaculation – the release of sperm from the penis
Acrosome – digestive enzymes in head of the sperm which digest an opening
through membrane of the egg
Androgens – male hormones that cause the primary and secondary male sex
characteristics
Fertilisation – nucleus of the egg fusing with the nucleus of the sperm
Gestation – the amount of time the foetus spends in the uterus
Birth control – deliberate prevention of pregnancy
Male reproductive system
Testes – Makes the sperm
Epididymis – Matures the sperm
Sperm ducts – Carries sperm from testes to urethra
Seminal vesicle – Forms seminal fluid
Prostate gland – Forms seminal fluid
Cowpers gland – Neutralises urethra for passage of sperm
Penis – Organ of copulation
Scrotum sac – Responsible for holding sperm at 35 degrees for meiosis to occur
Hormones in the male reproductive system:
1. F.S.H. (follicle stimulating hormone) causes the sperm producing cells in
the testes to produce sperm
2. L.H. (lutenising hormone) stimulates the testes to produce testosterone
Primary male sex characteristics
 Growth of penis and descent into scrotum
 Development of other male reproductive parts
Secondary male sex characteristics
 Growth of underarm, face, and body hair
 Widening of shoulders
 Growth spurt
Male infertility
Definition –Inability to produce offspring
Cause – low sperm count, possibly due to alcohol, cigarettes or drug abuse
Corrective measures – Change in lifestyle and diet
Female reproductive system
Ovary- produces and matures eggs
Ovary ligament- holds ovary in place
Funnel- collects egg after ovulation
Fallopian tube- site of fertilisation
Uterus- site of pregnancy
Lining of uterus- maintains pregnancy
Cervix- opening to uterus
Vagina- birth canal
Menstrual cycle 1-28 day
Days 1-5
menstruation occurs
Lining of womb breaks down
Meiosis occurs in ovary to produce a new egg surrounded by
graafian follicle
Day’s 6-14 graafian follicle produces oestrogen
Endomentrium thickens
No further eggs mature in ovary
High levels cause pituitary to release L.H.
Day 14
ovulation occurs (L.H. produced by pituitary)
Passes into fallopian tube (if sperm is present fertilisation may
occur, egg is only viable for 48 hours
Causes graafian follicle to become corpus leutum
Days 14- 28 corpus leutum produces progesterone
Prevents contractions of the uterine lining
Thickens and maintains the lining
Prevents further L.H. and F.S.H. being secreted
Hormones in the female reproductive system:
1. F.S.H. (follicle stimulating hormone) causes meiosis in ovary and
production of the graafian follicle
2. Oestrogen causes maturing of follicle/ thickens lining & inhibits F.S.H
3. L.H. causes ovulation/ triggers production of corpus leutum/ causes
progesterone production
4. Progesterone maintains endometrium/ prevents uterine contractions/
inhibits L.H. & F.S.H
Female infertility
Definition inability to produce offspring
Causes failure to ovulate e.g. maybe a hormonal disorder, stress or a tumour
Corrective measures hormonal treatment or surgery on the ovary
Foetal growth
Events from fertilisation to implantation of embryo
Takes up to 6-9 days
Fertilised egg contains 46 chromosomes. The zygote divides rapidly by mitosis
– 16 cells produces morula (2/3 days)
At day 5/6 the morula keeps dividing to produce a large hollow ball called the
blastocyst. It is moved down the fallopian tube (wafted by cilia and
contractions of uterus)
When it reaches the endometrium the outer layer of cells of blastocyst forms
the trophoblast
It later forms membranes around the embryo
Implantation occurs, trophoblast cells & endometrium cells begin to form
placenta (trophoblast forms tiny extentions that grow into the prepared wall)
Early development of the embryo
After implantation the blastocyst obtains its nutrition by absorption through
the trophoblast cells from endometrium
Development of the embryo cell sees the formation of the 3 germ layers
Ectoderm- skin, nails, nervous system
Mesoderm- bone, blood vessels & kidneys
Endoderm- inner lining of intestines, lungs, & liver
By week 8 all the major organs are formed (now called a foetus)
By week 12 the eyes are low & widely spaced, cartilage is replaced by bone,
sex organs are distinguishable, baby teeth begin to grow
By week 12 the baby is fully formed and no new organs will develop. All
features will be defined & the baby continues to grow
The placenta
Development:
It develops from the embryonic & uterine tissues
The trophoblast forms villi which embed into the lining of the endometrium
By week 12 the placenta is fully formed & takes over production of oestrogen
& progesterone
The umbilical cord connects the placenta to the embryo
Functions:
Transfer of food, gases, and excretory products between embryo and mother
Prevents the transfer of pathogens, blood cells, and hormones
Secretes the hormones progesterone and oestrogen
Keeps the 2 bloods separate as their blood groups could be different and the
mother’s blood pressure is too strong for the baby
Stages of birth
Stage 1:
Foetus rotates towards the cervix
Oxytocin stimulates contractions of the uterus and the cervix dilates
Amniotic fluid bursts
Contractions begin
Stage 2:
Frequent contractions
Foetus is pushed out head first
Stage 3:
The placenta and the foetal membrane are expelled
Lactation
Secretion of milk by mammary glands
Stimulated by prolactin from the pituitary gland
Biological benefits- correct nutrients, antibodies, bonding and helps the
mother regain shape
I.V.F
Fertilisation outside the body
Female is given fertility drugs to stimulate eggs to develop
Eggs are removed from the ovary and mixed with sperm in a glass dish
A number of the fertilised eggs are replaced back in the uterus for implantation
Birth control/ contraception
Deliberate prevention of pregnancy
Four methods - Natural (rythm method)
- Mechanical (condom/ diaphragm
- Chemical (birth control pill/ spermicides)
- Surgical 9tube ligation/ vasectomy)