Sexual reproduction is the only method of reproduction in
humans Sexual reproduction involves the fusion of specialised sex
cells (gametes):- sperm (male gamete) & egg cell (female
gamete). The fusion of the nuclei male gamete and female gamete is
called fertilisation. Fertilisation results in the formation of a
zygote from which a new individual develops.
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Male reproductive system Functions of the male reproductive
system are: production of male gametes (sperms) transfer of sperm
into the female reproductive system produces male sex hormone
testosterone
Functions of parts of male reproductive system scrotum - Testes
- Sperm ducts - Prostate gland - Urethra - Penis - holds testes at
cooler temperature than core body temperature produces male gametes
(sperms) & sex hormone testosterone passage of sperms travel
from testes to urethra during intercourse secretes seminal fluid in
which sperm swim passage of semen (seminal fluid + sperm) during
ejaculation inserted into vagina during intercourse where it
deposits semen
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Female reproductive system Functions of the female reproductive
system are: to produce the egg cells (female gametes) to provide a
safe place for fertilisation to provide protection and nourishment
for a developing foetus to produce sex hormones (oestrogen &
progesterone)
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Female reproductive system oviduct ovary uterus cervix vagina
vulva
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Functions of parts of female reproductive system Ovary Oviduct
Uterus Cervix Vagina produce female gamete & sex hormones
oestrogen & progesterone site of fertilisation & movement
of egg cell and (or) embryo from ovary to uterus site of
implantation of embryo, foetus development & muscular wall
contracts to push out foetus during birth directs sperm into
uterus,mucus plug during pregnancy prevents infections &
dilates at the beginning of birth site of deposition of sperm
during intercourse & its the birth canal it stretches during
birth to allow passage of foetus out of the body
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Menstrual cycle It is characterised by changes in the uterus
and ovaries The cycle lasts 28 days and if implantation does not
occur, the cycle repeats itself The menstrual cycle is controlled
by hormones released by pituitary gland and the ovary
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Interaction of hormones in the menstrual cycle
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Follicle stimulating hormone (FSH) released by anterior lobe of
pituitary glad stimulates growth of follicles in the ovaries
stimulates secretion of oestrogen
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Oestrogen estrogen is secreted from follicle cells in the ovary
it stimulates the repair of endometrium (uterus lining) increase in
estrogen inhibit FSH & LH secretion by ve feedback rapid
increase in the middle of the cycle stimulates LH & FSH
production by +ve feedback if no fertilization, lower concentration
of estrogen allows disintegration of endometrium & menstruation
occurs
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Luteinising Hormone (LH) LH is secreted by anterior lobe of
pituitary it stimulate ovulation It causes the development of the
corpus luteum from empty follicle it stimulates secretion of
progesterone & estrogen by corpus luteum
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Progesterone progesterone is secreted from follicle cells &
corpus luteum in the ovary it stimulates final thickening of
endometrium & maintains the thickening high levels inhibits
secretion of FSH & LH through ve feedback if no fertilization
occurs, low levels of progesterone causes disintegration of
endometrium & menstruation occurs
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Roles of testosterone in males. pre-natal development of male
genitalia promotes development of primary sexual characteristics:
development of genitalia, ducts, glands Spermatogenesis promotes
development of secondary sexual characteristics: larynx growth
deepening of voice facial, body, and pubic hair muscle and bone
development male behavior pattern maintenance of sex drive
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Reasons for infertility in humans Low sperm count of the male.
This can be rectified by concentrating the male sperm before being
placed into the uterus of the female. Blockage of the cervix which
again can be overcome by simple procedures and the mechanical
introduction of sperm through this passage.
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Assisted reproductive technology In complex cases of
infertility it is necessary to fertilize the egg cell outside of
the body before introducing the embryos into the uterus for
implantation. One of the assisted reproductive technologies is
called 'In Vitro fertilisation' or IVF. First performed by Sir
Robert Winston in 1978 Oldham England. Louise Brown was the first
of millions of 'test tube babies'.
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In Vitro fertilisation ( IVF) The egg is fertilized by the
sperm outside the woman body then embryo is introduced into the
uterus for implantation IVF is a major treatment for infertility It
was first performed by Sir Robert Winston in 1978 at Oldham
England
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Process of In Vitro fertilisation ( IVF) (IVF) is fertilization
outside the female body i.e. "in glass" drugs are injected to stop
normal menstrual cycle FSH is injected to stimulate ovaries to
produce eggs HCG is injected to matures the follicles eggs are
harvested from follicles in the ovaries using a fine needle male
provides (donates) sperm washing of sperms i.e. capacitation of
sperm is done eggs are mixed with sperms and incubated for 24 hours
to allow fertilization to occur 2-3 embryos are selected and
implanted into uterus pregnancy test is done to see if implantation
& pregnancy has occurred additional embryos frozen for future
use
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Ethical Issues associated with IVF Advantages of IVF
Disadvantages of IVF chance for infertile couples to have children
of their own decision to have children is clearly a conscious one
due to difficulty of becoming pregnant genetic screening of embryos
could decrease suffering from genetic diseases spare embryos can
safely be stored for future pregnancies or for use in stem cell
research IVF is expensive and might not be equally accessible to
all infertile couples success rate is low therefore it is stressful
for the couple it is not natural, thus it faces cultural &
religious objections could lead to eugenics (i.e. improving the
qualities of the human species) & (or) gender choice could lead
to (unwanted) multiple pregnancies with associated risks production
and storage of unused embryos may raise legal issues such as stem
cell research which many consider unethical inherited forms of
infertility might be passed on to children