6.6 Reproduction

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6.6 Reproduction

  1. 1. 6. Human Physiology 6.6 Reproduction
  2. 2. Female reproductive systemOvaries : egg cells areproduced. Within the ovaries,each developing egg cell iscontained inside a follicle.Oviduct (also called a fallopianor uterine tube): narrow tubeabout 10 cm long, which servesas a passageway to the uterus.It is normally the site offertilization.Uterus: a hollow, muscular organwith thick walls. If an egg isfertilized by a sperm cell, theuterus functions to contain andprotect the developing baby.Cervix: connects the uterus tothe vagina.Vagina: has several functions: itreceives the penis and sperm
  3. 3. Male reproductive systemTestes: Sperm cells begin theirdevelopmentScrotum: a sac-like structure thatcontains the testes. One function of thescrotum is to house the testes outsidethe main body cavity, a location that is1° to 3°C cooler than normal bodytemperature.Epididymis: Sperm complete theirdevelopment and are stored in a long,thin, coiled tube attached to each testis.Seminal vesicles, prostate gland, andbulbourethral glands: secrete fluids thatfunction in the transport and survival ofsperm: semen.Vas deferens: connecting ducts.Muscular contractions propel spermfrom the epididymis through the urethra.Penis: an organ consisting mainly of
  4. 4. Development of gametes
  5. 5. Development of egg cells By the time a human female reaches puberty her ovaries contain about 400,000 follicles. Each follicle contains a resting primary oocyte. Ovulation: approximately every 28 days, hormones cause one follicle and the oocyte within it to mature, commonly called ovule. When the follicle breaks open, the secondary oocyte is released. Meiosis II is not completed unless the egg is penetrated by a sperm cell. As soon as this occurs, the secondary oocyte undergoes its final meiotic division. This forms the ovum, the mature egg cell with a haploid nucleus that is capable of fusing with the sperm nucleus.
  6. 6. Development of sperm cells The development of sperm cells begins when males reach puberty. The process begins with the primary spermatocyte within the testis that undergoes meiosis and produces four haploid sperm cells. Sperm cells move from the testes to the epididymis where they complete their development. A mature sperm has a tail (flagellum) that enables it to swim within the female reproductive
  7. 7. Hormonal control in females • Sexual maturity in women is marked by the beginning of the menstrual cycles. These cycles coordinate the development and release of an egg with the conditions required in the uterus to support a pregnancy. Anterior pituitary hormones • The cycle is controlled by hormones from the brain (FSH and LH) and the ovary (estrogen and progesterone). • FSH and LH are two hormones Ovarian hormones that are active at significant phases of human development including primary and secondary sexual characteristics. They are both significant hormones in the
  8. 8. http://kidshealth.org/misc/movie/bodybasics/bodybasics_female_repro.htmlhttp://www.sumanasinc.com/webcontent/animations/content/ovarianuterine.
  9. 9. (d) (a) (e) (b) (g) (g) (c) (f) (d) (g)(a) FSH is secreted by the pituitary gland of the brain and stimulates the developmentof a primary follicle.(b) Primary follicle cells secrete estrogen which in turn increase the secretion of FSH ina positive feedback.(c) The estrogen thickens the lining of the uterus in preparation for a fertilized egg.(d) The peak of estrogen secretion at day 12 causes the pituitary to release a surge ofLH. This loosens the now mature egg which is released in ovulation(e) Progesterone and estrogen together stop any more LH and FSH being secretedfrom the pituitary. (negative feedback) – This prevents further follicle development orovulation.(f) Progesterone maintains the lining of the thickened endometrium in preparation forthe implantation of a fertilized egg.(g) If implantation does not take place then the Corpus luteum degenerates and
  10. 10. Hormonal regulation in males Roles of testosterone in males 1. Week 7 of embryonic development, testosterone initiates the development of male genitalia. 2. Puberty: testosterone initiates the development of secondary sexual characteristics: - increase in muscle mass - increase in the length of the long bones (height) - increase in the length of the vocal cords (voice deepens) - spermatogenesis - growth of the penis and testis 3. Post puberty testosterone maintains the production of sperm
  11. 11. In Vitro Fertilization (IVF) IVF is a method where the eggs are removed from the ovaries to be fertilized in the laboratory. The eggs are then cultured for approx. 2 days and nights before the fertilized egg is transferred to the uterus for normal growth. At IVF the woman’s ovaries are stimulated to produce more and bigger eggs than at a normal cycle. This means that more than one egg can be removed for the treatment. More eggs improve the probability of finding suitable eggs for fertilization. IVF treatment is recommended in those cases where the woman has tubal blockage, the man has a poor sperm quality, or the cause of infertility is unexplained. There are a number of different medications for IVF treatment, which are to be adjusted to the individual need.
  12. 12. In Vitro Fertilization (IVF)a) FSH and LH are given to stimulate multiple egg cell releasesb) Eggs are collected from the ovariesc) Eggs are fertilized with father’s sperm in a dish or tube and it’s incubated.d) After incubation, viable blastocysts are selected and developed into embryose) Usually 3 embryos are selected for implantation. Usualle one or more will be successful, hence the risk for multiple pregnancyf) After a month of rest, a woman can take a pregnancy test. If it did not succeed, she can wait a few months to try again. (a) (b) (c) (d) (e)
  13. 13. IVF Treatment with in vitro fertilization implies that: The man produces sperm cells, or has sperm cells that we in special cases can extract from the testicle or from the epididymis. If the man does not produce sperm cells, donor sperm cells can be used. The woman has ovulation, either by herself or through hormone treatment. The woman has a normal uterus. The couple has no incidence of venereal diseases or infections. You have received genetic counseling.
  14. 14. Ethical issues associated withIVF FOR  AGAINST Right to have children  Risk of mother and Provide a family for fetuses of multiple radiation, chemo pregnancy therapy cancer  Can be expensive patients.  Emotional cost of Medical advances failure can be high make it safer every  Does termination of time human embryos count Unused embryos can as ending a human be stored (frozen) for life? later use, donated for  Religious: are we research or as a playing ‘God’? source of stem cells
  15. 15. Natural fertilization Fertilization occurs when the egg and sperm cells fuse. When a sperm cell penetrates the egg, meiosis II is completed and the ovum is formed. Within the ovum, the nuclei of the sperm and ovum fuse, forming a diploid nucleus. This fertilized egg cell is called a zygote.
  16. 16. Human development, first trimester Approximately three weeks after fertilization, gastrulation takes place. It forms three cell layers: ectoderm, endoderm, and mesoderm. The ectoderm (outer layer) forms the outer part of the embryos skin and the central nervous system. The endoderm (inner layer) forms the digestive tract and lungs. The mesoderm (middle layer) forms most of the other organs.
  17. 17.  Soon after implantation, trophoblast cells and cells from the uterus form the placenta. This structure enables nutrients and waste products to be transferred between the mother and developing baby. By the end of the third month, the placenta is fully formed and functional. In the wall of the placenta, the mothers blood and babys blood remain isolated in separate circulatory systems.

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