reproduction Flashcards
what are sperm cells
male gametes
sperm cell
formed in testes by meitosis to produce haploid nuclei
specailise in the testes
development under the infulence of the hormone testosterone
sperm cell features
flagellum-help sperm cell swim
haploid nucleus- only half the chromosomes (23)
mitochondria- provide energy to sperm
egg cell
to supply nutrients and energy to egg as it develops if fertilized
male reproductive system
testes- where sperm produced
penis-organ that transfers sperm to the woman
urethra- tube that carries urine or semen out of the body
scrotum- holds the testes in place
sperm duct- carries sperm from the testies to the penis
prostate gland- adds fluid to the sperm to nourish it
female reproductive system
ovary- where eggs develop
uterus-proper name for womb, where fertilized egg grows into a baby
vagina- erect penis inserted here during sex and where baby comes out at birth
cervix- a ring of muscle at the top of the vagina
what is fertilization
male nucleus fuses with female nucleus/fusion of haploid sperm nucleus and the female egg nucleus to produce a diploid zygote
fertilisation process
The sperm is deposited in the vagina, swims through the uterus and along
This occurs in the oviduct of the female the oviduct where it may fuse with an egg if one is present.
After fertilisation the zygote divides many times by MITOSIS to form a ball of cells as it travels down the oviduct to the uterus
IMPLANTATION ie this is when the ball of cells embeds in the lining of the uterus and starts to develop into a foetus (the woman is now pregnant).
After implantation in the uterus lining it then differentiates to produce a variety of tissues and organs.
implantation
After IMPLANTATION the ball of cells continues to divide further by mitosis and the cells formed start to differentiate (specialise) into different tissues and orgons.
Some of the cells develop into the PLACENTA. This is the organ of exchange between the mother’s blood and the baby’s blood Placenta exchange of dissolved nutrients, oxygen, carbon dioxide and urea
adaptions of the placenta for exchange
villi in placenta- prodives large surface area for diffusion of substances between the foetus and mother
thin wall of placenta- gives a short diffusion pathway
blood vessles in umbillical cord are close by- maintain a diffusion gradient
substances carried, direction of transport and reason for foetus
Oxygen and nutrients (e.g. glucose and amino acids)
Mother → Baby
There is a high concentration of oxygen. glucose and amino acids in the mothers blood so it diffuses across into the baby.
The baby uses oxygen and glucose for respiration and amino acids to make protein for growth
Waste materials (e.g. urea and carbon dioxide)
Baby → Mother
The baby releases carbon dioxide from respiration and it (along with urea) diffuses back into the mothers blood
umbillical cord
The UMBILICAL CORD contains the foetal blood vessels that carry these substances to and from the foetus.
amniotic sac
Pregnancy in humans lasts nine months - this is known as the GESTATION period
During this time the baby is enclosed in a membrane - the AMNION
Inside the AMNIOTIC SAC is a fluid called the AMNIOTIC FLUID
This cushions and protects the foetus during its development.ng its development.
male sex hormone
testosterone- produced in testes
female sex hormone
estrogen- produced in ovaries
what is puberty
period of development during which large physical and emotional changes take place in an individual
oestrogen functions
Oestrogen has two main functions in the menstrual cycle
(a) The initial repair and build up of the uterus wall and (b) The stimulation of ovulation.
At the start of the menstrual cycle (Day one -when bleeding starts) the level of oestrogen is low.
As the cycle progresses the level of oestrogen rises.
- It peaks in the middle of the cycle, causing the release of an egg (ovulation).
progestrone functions
The level of progesterone is also low during menstruation and peaks in the days following ovulation. The role of progesterone is to build up and maintain the thick uterine lining (and the subsequent development of the placenta and other structures associated with pregnancy) should pregnancy occur.
Note:
If pregnancy does not occur, the levels of oestrogen and progesterone drop towards the end of the cycle and this causes menstruation to occur. The cycle then begins again.
menstruation
starts during puberty in teenage girls and usually contiunes once a month until menopause when menstration stops.
generally considered as 28 day cycle
period of cycle
Day 1-5
Menstruation - blood flows out of the vagina as the lining of the womb breaks up
Day 6-10
The lining of the womb starts to grow again - becomes thick with a rich blood supply
Day 10-17
During this time it is possible for fertilisation to occur if sperm is present in the oviduct as OVULATION occurs - egg is released from the ovary
Day 13-15
Day 18 - 28
If the egg is not fertilised it dies and eventually passes out of the vagina
The cycle then repeats itself
causes of infertility
women:Failure of ovary to produce eggs (ova not released)
The oviducts may be blocked or twisted, possibly due to infection Damage to the oviducts as a result of a sexually transmitted infection
The lining of the uterus does not develop properly to enable implantation to occur ie does not allow implantation
Premature menopause
The vagina may be hostile to sperm entering, e.g. the lining may be too thick or acidic
In men:
Low sperm count.
Abnormal sperm eg poor motility
Hormone imbalances
Impotence
treatments for infertility
fertility drugs
invitro fertilisation
fertility drugs
These are given to the women to increase production of eggs. This may solve the problem if low egg production is the issue but if there are other problems such as blocked oviducts then in vitro fertilisation may be necessary.
in vitro fertilisation
IVF was developed to allow infertile couples to conceive a child. Eggs and sperm are harvested from the parents and allowed to combine in a culture dish before the fertilised embryos are placed into the mother’s uterus.
process of ivf fertilisation
The woman is given fertility hormones for a period of time before IVF - to stimulate the production of a large number or ova
to thicken the uterine lining in preparation for implantation
The ova produced are collected from the ovaries via the vagina
Sperm is donated and mixed with the eggs in a Petri dish and the nuclei allowed to fuse to fertilise the ova - in vitro
The fertilised ova are checked for healthy development by examination under a microscope
The selected fertilised ova will continue to develop for several days and are then implanted into the uterine lining.
More than one embryo (usually no more than 2-3) may be implanted -
To increase the chances of the pregnancy being successful, because
Some embryos die or do not divide or
Some embryos fail to implant successfully
risks of ivf
However multiple embryo replacements carry the risk of multiple pregnancy and birth - an increased risk of premature labor - leading to a higher risk of birth defects such a blindness, and cerebral palsy
contraception
prevention of conception by artifical or natural means
mechanical means of contraception
male:condom
female:sheath
provides physical barrier
chemical means of contraception
female: contraceptive pill
chemical implant
changes hormone levels
surgical means of contraception
male:
vasectomony- sperm ducts cut
female:
oviducts cut
advantages of mechanical means of contraception
mechanical means are reversible
do not require medical supervision
very reliable if used properly
protects against sti’s
advanages of chemical means of contraception
reliable and reversible method
disadvantages of of chemical means of contraception
side effects
requires medical supervision
doesnt protect against sti’s
disadvantages of surgical means of contraception
it is irreversible
