Fertilization and embryology.pptx in reproductive health

Fertilization and embryology

1. PRESENTATION BY S E

2. FERTILIZATION AND EMBRYOLOGY General objective : At the end of the lecture/discussion the student midwives should be able to gain knowledge and an understanding of the process of fertilization and embryology.

3. Specific objectives At the end of the lecture/discussion student nurses should be able to: Define the term fertilization Describe the structure of a mature sperm and ovum. Describe process of fertilization Explain the stages of development of the fertilized ovum (brief embmbryology )

4. Introduction Following ovulation the ovum, passes into the uterine tube and is moved along towards the uterus. It during this process when it is fertilized by the spermatozoa at the uterine portion called ampulla .

5. After fertilization has taken place the fertilized ovum will continue to develop through the stages of zygote, the embryo and the fetus in utero .

6. Definition of terms Fertilization is the fusion of the sperm and the ovum to form the zygote. Zygote : is the term during the period from fertilization to the twenty first (21 st ) day (the end of the 3 rd week)

7. Embryo: is the period from the twenty second (22 nd ) day to the fifty sixth (56 th ) day after fertilization (from 3-8 weeks) Fetus: is the period from the beginning of the 9 th week after fertilization to term

8. Pregnancy: is the period of gestation in the human. Or Is the period from conception up to the time labor or childbirth is initiated.

9. Sperm structure Mature sperm is possibly the smallest cell in the body, about 65 μ m long. It is made up of the head and tail.

10. Head Size: 7 μ m long and tiny Shape: pear-shaped It is mostly made up of the nucleus containing chromosomes.

11. The front of the nucleus is covered by flattened membrane enclosed vesicle called the acrosome . Within the acrosome are hydrolytic enzymes, mainly hyaluronidase and proteolytic enzymes.

12. The neck Joining the head and tail is the neck (quite constricted), which contains a significant amount of cytoplasm

13. Tail The tail is divided into a middle piece , a principle piece and an end piece . The middle piece is 7 μ m long. Because mitochondria is concentrated in the midpiece , it thought to generate a lot of energy required for the movement of the sperm.

14. The principle piece constitutes most of the tail, and is made up of longitudinal fibrils which are responsible for the motility of the sperm. The end piece is tapered and short.

15. OVUM STRUCTURE The ovum consists of the a central nucleus , surrounded by yellowish cytoplasm known as vitellus . Perivitelline is the space surrounding vitellus .

16. The outer margin of perivitelline space, is formed by a thick membrane made from an opaque jelly-like substance known as zona pellucida .

17. The zona pellucida as a protective shield around the ovum, and is encircled by granulosa cells of the ovarian follicles, which have clumped together and appear to radiate outward from the zona pellucida .

18. This formation of granulosa cells known as corona radiata gives the ovum the appearance of a tiny, hairy ball. NB. After ovulation, the ovum must be fertilized within the first 12 to 24 hrs, after this time it begins to degenerate.

19. Fertilization process Ferlization (conception) usually takes place in the ampulla of the uterine tube soon after the ovum enters the tubes. Following ovulation, the ovum passes into the fallopian tube towards the uterus.

20. Its movement (waft) along the uterine tube is aided by the cilia and by the peristaltic muscular contraction of the uterine tube. During ovulation, the cervix, under the influence of oestrogen , secretes a flow of alkaline mucus that attracts the spermatozoa.

21. At intercourse about 300 million sperm are deposited in the posterior fornix of the vagina. Only about 1000 to 3000 sperm reach the ovum, while the rest are destroyed by the acid medium of the vagina.

22. It is during this journey that the sperm finally mature. On encountering the ovum, the sperm penetrates the corona radiata , reaches the zona pellucida ,

23. then it attaches to specialized sperm receptors on the surface of the zona pellucida which triggers the acrosome (on the sperm) to release the digestive (hydrolytic) enzymes, the hyaluronidase and proteolytic enzymes, enabling the sperm to break into the zona pellucida .

24. The sperm will then pass through fluid filled space, the Perivitelline . When the sperm make contact with the egg cell membrane it will fertilize the ovum.

25. After sperm attaches to the egg cell membrane, within a few minutes the outer membranes fuse and the egg pulls the sperm inside. This process causes changes in the ovum membrane that prevents over sperms from attaching to it.

26. The ovum then releases chemicals that push away other sperms away from the egg and hardening the zona pellucida , thus creating an impenetrable fertilization membrane that prevents other sperms to enter the egg.

27. On fertilization, each nucleus of the sperm and ovum containing 23 chromosomes (genetic material) will intermingle to complete the process of fertilization. This results into a new diploid cell, containing 46 chromosome, which will be the start of a complete new unique human being.

28. The fertilized ovum is now known as the zygote. The cilia and fallopian tube will then gently sweep the zygote towards the uterus where he/she will implant for grown and development for the next 9 months.

29. Embryology After fertilization, the fertilized ovum continues to move through the fallopian tube and reaches the uterus on the 3 rd or 4 th day. After fertilization, the zygote starts to divide by the process of mitosis (cell division or segmentation).

30. This mitotic division of the zygote is known as cleavage and the daughter cells are known as blatomeres . It divides into two daughter cells, then four, then eight, 16 and so on until a claster of cells known as molura .

31. On the 3 rd day following fertilization, a cluster of about 16 blastomeres has formed a solid ball looking like mulbery ( molura ). By the 4 th day, fluid from the uterine cavity has penetrated the molura and has formed a cavity (cyst), pushing the inner cell mass to one side. This changes a molura into a blastocyst .

32. Around the blastocyst there is a single layer of cells known as the trophoblast . From the 5 th day, the zona pellucida starts to degenerate and blastocyst attaches to the uterine wall.

33. On the 6 th day, the outer cells of the blastocyst become highly specialized and are known as trophoblastic cells. Trophoblastic cells secrete proteolytic enzymes that digest and liquefy the cells of the inner lining of the uterine endometrium known as compact layer of the decidua .

34. By the end of the 7 th day or after 1 week, the blastocyst is superficially implanted in the lining of the decidua . .

35. Eventually, the trophoblastic cells develop into two layers distinct layers, which together known as trophoblast / syncytiotophoblast , and this enables the blastocyst to embed into the sponge layer of the decidua and to acquire nourishment from the decidual cells

36. Trophoblast / sysncytiotrophoblast layer (2 layers) An outer syncytiotrophoblast layer ( syncytial cells): The cells continue to secrete proteolytic enzymes and so continue to invade the decidua and nourish the blastocyst .

37. 2. An inner cytotrophoblast or langhan’s layer ( cytrophic cells) These two layers of cells form the outer membrane of the trophoblast (sometimes collectively called syncytiotrohpoblast ).

38. The cells of the inner cytotrophic layer begin to secrete a hormone known as human chrionic gonadotrophin (HCG), which is very similar to the LH of the pituitary gland.

39. Development of the decidua Changes occur in the secretory endometrium of the uterus during pregnancy, which will now be known as the decidua . The basal layer of the decidua This layer is a permanent regenerative layer, which remains the same as in non-gravid state.

40. 2. The sponge layer of the decidua This layer becomes highly vascular and secretory under the influence of extra progesterone, secreted after fertilization and formation of the trophoblast , in order to provide nourishment to the blastocyst .

41. The penetrating trophoblastic villi , with their syncytial layer containing proteolytic enzymes, erode through the maternal blood vessels in the sponge layer of the decidua , causing space ( known as intervillous spaces ) between the villi to fill with maternal blood.

42. These trophoblastic villi later become known as chorionic villi ( chorion frondosum ) and will eventually develop into a placenta.

43. 3. The compact layer It consists of an outer layer of columnar epithelial cells, which forms the lining of the uterine cavity and keeps the cells of the sponge layer in place.

44. Postage-stamp layer The postage-stamp also known as the fibrinous layer of Nitabuch is a specialized layer situated between the basal and sponge layers.

45. This collagen or postage-stamp layer becomes highly specialized and forms a barrier to the invading trophoblastic villi , preventing them from penetrating into the basal layer of the decidua and into the myometrium .

46. NB, detachment of the placenta at this area allows a uniform separation of the placenta from the decidua during the third stage of labour , hence the name postage-stamp layer.

47. Implantation sites Implantation of the zygote happens during the second week after fertilization. The normal site of implantation is in the posterior, an anterior or a lateral wall of the uterus, just below the entry of the uterine tube.

48. The trophoblast will form the placenta and chorion , while the inner cell mass will become the fetus, amnion and umbilical cord.

49. The cells of the inner cell mass will then differentiate into three layers, each of which will form particular parts of the body. The three layers together are known as the embryonic plate or disc .

50. These three layers include: The ectoderm : this layer mainly forms: The nervous system: the brain, spinal cord, nerves, the eyes, ears, the nose and the pituitary gland.

51. The skin and appendages and the mammary gland. The medulla of the adrenal gland.

52. 2. The mesoderm : this layer forms The skeletal system: bones, cartilage and connective tissue Muscle tisssue Cardiovascular and lymphatic system The spleen

53. The urogenital system: kidneys and the gonads Serous membranes lining the body cavities The cortex of the adrenal gland.

54. 3. The endoderm : this layer forms the epithelial lining of: The gastro-intestinal tract The respiratory tract The liver

55. The thyroid, parathyroid and the thymus glands The pancrease The urinary bladder and urethra The ear.

56. During the embryonic period all the organs and systems of the body are laid down in rudimentary form.

57. Summary of development 0-4 weeks after conception Rapid growth Formation of the embryonic plate Primitive CNS forms Heart develops and begin to beat Limb buds form.

58. 4-8 weeks Very rapid cell division Head and facial features develop All major organs laid down in primitive form

59. External genitalia present, but sex not distinguishable Early movements Visible on ultrasound from 6 weeks

60. 8-12 weeks Eye lids fuse Kidneys begin to function and fetus passes urine from 10 weeks Fetal circulation function properly

61. Sucking and swallowing begin Sex distiguishable Moves freely (not felt by mother) Some primitive reflexes present

62. 12-16 weeks Rapid skeletal movements- visible on X-ray Meconium present in gut Lanugo appears Nasal septum and palate fuse

63. 16-20 weeks Quickening Fetal heart heard on auscultation Vernix caseosa appears Fingernails can be seen Skin cells begin to be renewed

64. 20-24 weeks Most organs become capable of functioning Periods of activity and sleep Responds to sound Skin red and wrinkled

65. 24-28 weeks Survival may be expected if born Eyelids reopen Respiratory movements

66. 28-32 weeks Begins store fat and iron Testes descend into scrotum Lanugo disappears from face Skin becomes paler and less wrinkled

67. 32-36 weeks Increased fat makes the body more rounded Lanugo disappears from body Head hair lengthens Nails reach tip of fingers Ear cartilage soft Plantar creases visible

68. 36-40 weeks or 38-42 weeks Term reached Contour rounded Skull firm

69. PLACENTA Introduction The placenta originate from the trophoblastic layer of the fertilized ovum. It provides a link between the fetus and mother, and aids in carrying out functions that the fetus is unable to perform for itself during intrauterine life.

70. The survival of the fetus depends on the placenta’s integrity and efficiency. The fetus, together with the placenta, the umbilical cord, the membranes, and liqour , are referred to as the feto -placental unit .

71. Objectives General objective By the end of the lecture/ discussion, student midwives should able to gain knowledge and understanding of placenta.

72. Specific objectives Describe the development of the placenta Identify the structure of the mature placenta. State the functions of the placenta

73. Describe the parts that makes up the feto -placental unit, other than the fetus.

74. Assignment Explain the development of the placenta Describe the parts of the mature placenta, together with the cord, membranes, and liqour . Outline the functions of the placenta.

75. Describe the abnormalities of the placenta, membranes and cord.