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6.6 Reproduction

6.6 Reproduction. 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 ).

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6.6 Reproduction

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  1. 6.6 Reproduction

  2. 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 gameteand female gameteis called fertilisation. • Fertilisation results in the formation of a zygotefrom which a new individual develops.

  3. 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

  4. ureter urinary bladder sperm duct Seminal Vesicle Prostrate gland cowper’s gland urethra penis testiss scrotum

  5. 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

  6. 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)

  7. Female reproductive system oviduct ovary uterus cervix vagina vulva

  8. 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 & it’s the birth canal – it stretches during birth to allow passage of foetus out of the body

  9. 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

  10. Interaction of hormones in the menstrual cycle

  11. Follicle stimulating hormone (FSH) • released by anterior lobe of pituitary glad • stimulates growth of follicles in the ovaries • stimulates secretion of oestrogen

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.

  17. 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'.

  18. 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

  19. 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

  20. 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

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