CONCEPTION AND FETAL DEVELOPMENT.pptx

ivth yr bsc nursing

1. CONCEPTION AND FETAL DEVELOPMENT Prepared by : Mrs Bemina JA Assistant Professor ESIC College of Nursing Kalaburagi

2. Conception Other terms used to describe this phenomenon are fertilization, impregnation or fecundation. PRE EMBRYONIC PERIOD Also known as ovular period or germinal period. Embryogenesis start with the fertilization of the egg cell (ovum) by a sperm cell (spermatozoon). Once fertilized, the ovum is referred to as zygote, a single diploid cell. DEFINITION Fertilization is the union of the ovum and a spermatozoa. Fertilization must occur fairly quickly after release of the ovum because it usually occurs in the outer third of a fallopian tube, the ampullar portion. The functional life span of a spermatozoa is about 48 hours / may be as long as 72 hours or longer. Therefore, sexual coitus during this time may result in fertilization /pregnancy. Conception

3. The acrosomal layer of the sperm secrete the enzyme hyaluronidase which disperse the corona radiata (outermost layer of oocyte ) allowing assess to zona pellucida . The sperm reaches to the zona pellucida and penetrates it. Upon penetration a chemical reaction known as the cortical reaction , which alters the zona pellucida making it impermiable to other sperm . The plasma membranes of the sperm and oocyte fuse , each pronucleus containing 23 chromosomes refered as haploid, and become diploid having 46 numbers of chromosomes. This new cell is called zygote .

4. During the first week the zygote travels along the uterine tube towards the uterus, the zona pellucida surrounds the zygote. It nourished by glycogen secreted by globlet cell of uterine tube and later the secretory cells of uterus . The zygote undergoes mitotic cellular replication refered as cleavage, resulting into the formation of smaller cells known as blastomeres .

5. Development of the Fertilized Ovum The zygote divides into two cells- at 1st day 4 cells –at 2 days 8 by – 2.5 days 16 cells by- 3 days. Known as morula . The cells binds together tightly in a process known as compaction. Cavitation occur whereby the outermost cells secrete fluid into the morula and form blastula comprising of 58 cells .

6. Next, fluid filled the cavity or blastocele appears in the morula which now becomes known as the blastocyst . Around the out side of the blastocyst there is a single layer of cell known as the trophoblast while the remaining cells are clumped together at one end forming the inner cell mass . The trophoblast will form the placenta and chorion , while the inner cell becomes the fetus, umbilical cord and the amnion. Embedding of the blastocyst is normally completed by the 11th day after ovulation and the endometrium closes over it completely

7. NIDATION Implantation occurs in the endometrium of the anterior or posterior wall of the body near the fundus on 6th day. The blastocyst possesses an inner cell mass or embryoblast and outer cell mass or trophoblast . Trophoblast - becomes the placenta and chorion . Embryoblast - become embryo, amnion and umbilical cord.

8. This is the name given to the endometrium during pregnancy. Three layers are found in decidua . The basal layer lies immediately above the myometrium . The functional layer consists of tortus glands which are rich in secretions. The compact layer forms the surface of the decidua and is composed of closely packed stroma cells and the neck of the glands The Decidua

9. Those trophoblastic cells differentiate into layers , The Outer Syncitiotrophoblast ( syncitium ), and Inner Cytotrophoblast and Below this, a Layer of Mesoderm or Primitive Mesenchyme . The Trophoblast

10. The syncitiotrophoblast is composed of nucleated protoplasm which is capable of breaking down tissue as in the process of embedding. The cytotrophoblast is a well defined single layer of cells which produces a hormone known as human chorinic gonadotrophin (HCG)

11. While the trophroblast is developing into the placenta , which will nourish the fetus, the inner cell mass is forming the fetus itself. The cells differentiate into three layers, each of which will form particular parts of the fetus. The inner cell mass

12. THE ECTODERM mainly forms the skin and nervous system THE MESODERM forms bones and muscles and also the heart and blood vessles , including those which are in placenta. THE ENDODERM forms mucous memberanes and glands. The inner cell mass

13. The three layers together are known as the embryonic plate. Embryoblast Develops the embryo, and differentiate into two types of cells Epiblast - epiblast have three layers, which forms the particular parts of the embryo. The first appearance of these layers, collectively known as the primitive streak is around 15 days. Hypoblast - the hypoblast cell migrate along with inner cytotrophoblastic lining secreting extracellular tissue which becomes the yolk sac .

14. The amniotic cavity- lies on the side of the ectoderm; The yolk sac lies on the side of the endoderm and provides Nourishment for the embryo until the trophoblast is deficiently developed to take over The amniotic cavity

15. 1 . Pre embryonic period Week 1-2 – no developments occurs since fertilization hasn’t actually occurred. Week 3 - from 15-21 days, embryonic 5-7 days. Fertilization occur and form zygote. The embryo hatches from its protein shell and perform implantation (5-6 days). CHANGES OR DEVELOPMENT BY WEEKS OF GESTATION

16. Week 4th – days 22-28 from LMP embryonic age 2 weeks- Events Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into uterine lining. Eventually form placenta and embryonic membrane. Formation of yolk sac. Primitive streak develop at 13 days. Primary stem villi appears at 13 days

17. Week 5 Gestational age: 4 weeks Embryonic age: Week no. 3 A notochord forms in the center of the embryonic disk. (day 16 of fert gastrulation commences. A neural groove (future spinal cord)forms over the notochord with a brain bulge at one end. Neuromeres appear . (day 18 of fert .) Somites , the divisions of the future vertebra , form. (day 20 of fert .) Primitive heart tube is forming. Vasculature begins to develop in embryonic disc.

18. Week 6 Gestational age-5 week Embryonic age 4 weeks Events Embryo measures 4 mm The heart bulge , and begins to beat in a regular rhythm. The neural tube closes . Arm buds and tail are visible. Pulmonary primordium appear Hepatic plate appear Buccopharyngeal membrane ruptures. This form the future mouth. Anterior and posterior horns differentiate in the spinal cord.

19.  Week 7- Embryonic age 5 week Events- Length is 9 mm Lens pits and optic cups develops Nasal pits form Brain divides into 5 vessicles including the early telencephalon . Leg buds form. The metanephros , precursor of kidney start to develop. Stomach differentiation begins.

20. Week 8 The embryo measures 13 mm (1/2 inch) in length. Lungs begin to form. The brain continues to develop . Arms and legs have lengthened with foot and hand areas distinguishable. The hands and feet have digits , but may still be webbed. The gonadal ridge begins to be perceptible. UROGENITAL The lymphatic system begins to develop. Main development of external genitalia starts .

21. Week 9 The embryo measures 18 mm (3/4 inch) in length. Fetal heart tone (the sound of the heart beat) can be heard using doppler Nipples and hair follicles begin to form. Location of the elbows and toes are visible. Spontaneous limb movements may be detected by ultrasound. All essential organs have at least begun. The vitelline duct normally closes connects the yolk sac to the small intestine.

22. From the 10 weeks of gestation (8th week of embryogenic ) the developing organism is called FETUS . All the major structures are already formed in the fetus but they continue to grow.   Fetal development

23. Week 10 -12 Embryo measures 30–80 mm (1.2–3.2 inches) in length. Intestines rotate . Facial features continue to develop. The eyelids are more developed . The external features of the ear begin to take their final shape. The head comprises nearly half of the fetus' size. The face is well formed The eyelids close and will not reopen until about the 28th week. Tooth buds appear . The fetus can make a fist with its fingers. Genitals appear well differentiated. Red blood cells are produced in the liver

24.   Week 13-16 The fetus reaches a length of about 15 cm (6 inches). A fine hair called lanugo develops on the head. Fetal skin is almost transparent . More muscle tissue and bones have developed, and the bones become harder. Sucking motions are made with the mouth. Meconium is made in the intestinal tract . The liver and pancreas produce fluid secretions . From week 13, sex prediction At week 15, main development of external genitalia is finished Abdominal wall closes.

25. Week 17-21 The fetus reaches a length of 20 cm (8 inches). Lanugo covers the entire body . Eyebrows and eyelashes appear . Nails appear on fingers and toes. The fetus is more active with increased muscle development. "Quickening" usually occurs (the mother and others can feel the fetus moving). The fetal heartbeat can be heard with a stethoscope.

26. Week 23 The fetus reaches a length of 28 cm (11.2 inches). The fetus weighs about 925g . Eyebrows and eyelashes are well formed. All of the eye components are developed. The fetus has a hand and startle reflex. Footprints and fingerprints continue forming. Alveoli (air sacs) are forming in lungs.

27. Week 27 The fetus reaches a length of 38 cm (15 inches). The fetus weighs about 1.2 kg . The brain develops rapidly. The nervous system develops enough to control some body functions. The eyelids open and close. The respiratory system , while immature, has developed to the point where gas exchange is possible.

28. Week 31 The fetus reaches a length of about 38–43 cm (15– 17 inches). The fetus weighs about 1.5 kg (3lb 0 oz). The amount of body fat rapidly increases . Rhythmic breathing movements occur, but lungs are not fully mature. Thalamic brain connections , which mediate sensory input, form. Bones are fully developed , but are still soft and pliable. The fetus begins storing a lot of iron, calcium and phosphorus

29. Week 35 The fetus reaches a length of about 40–48 cm (16– 19 inches). The fetus weighs about 2.5 to 3 kg (5 lb 12 oz to 6 lb 12 oz). Lanugo begins to disappear . Body fat increases . Fingernails reach the end of the fingertips. A baby born at 36 weeks has a high chance of survival, but may require medical interventions

30. Week 36-40 The fetus is considered full-term at the end of the 39th week of gestational age. It may be 48 to 53 cm (19 to 21 inches) in length. The lanugo is gone except on the upper arms and shoulders. Fingernails extend beyond fingertips. Small breast buds are present on both sexes. Head hair is now coarse and thickest

31. Respiration - As pulmonary exchange of gases does not take place in the uterus the fetus must obtain oxygen and excrete carbon dioxide through the placenta Nutrition - Food for the fetus derives from the mother’s diet and has already been broken down into forms by the time reachs the placenta site. The placenta is able to select those substances required by the fetus, even depleting the mother’s own supply in some instances. Storage - The placent metabolises glucose and can also stores it in the form of glycogen and reconverts it to glucose as required. The placenta store iron and the fat soluble vitamins. Excretion - The main substance excerted from the fetus is carbondioxide ; bilrubin will also be excreted as red blood cells are released relatively frequently. Protection - It provides a limited barrier to infection with the exception of the treponeona of syphilis and, few bacteria can penetrate. Viruses, however, can cross freely and may cause congenital abnormalities as in the case the rubella virus and HIV virus. Endocrine - Human chorinnic gondotroghin (HCG) is produced by the cytotrophoblastic layer of the chorinonic villi . ƒ Oestrogens as the activity of the corpus luteum declines, the placenta takes over the production of oestrogen , which are secreted in large amounts through out pregnancy. ƒ Human placental lactogen ( HpL ) has a role in glucose metabolism in pregnancy. ƒ Progestrone Functions of Placenta

32. The placenta is completely formed and functioning from 10weeks after fertilization . Between 12 and 20 weeks gestation the placenta weighs more than the fetus. Fetal blood, low in oxygen , is pumped by the fetal heart towards the placenta along the umblical arteries. Having absorbed oxygen the blood is returned to the fetus via the umblical vein. The Placental Circulation

33. Appearance of the Placenta at Term   discoid- shape   The placenta measures about 20 cm in diameter and 2.5cm thick from its center. It weighs 500 to 600 gm approximately one sixth of the baby’s weight at term. It has two surfaces. 1. The maternal surface maternal blood gives this surface a dark red colour and part of the basal decidua will have been separated with it. The surface is arranged in about 20 lobes which are separated by sulci 2. The fetal surface . The amnion covering the fetal surface of the placenta gives it a whitish, shiny appearance . Branches of the umbilical veins and arteries are visible and spreading out from the insertion of the umbilical cord which is normally in the center. Appearance of the Placenta

34. THE AMINOTIC SAC consists of a double memberane . Chorion – Outer layer adher to the uterine wall. Amnion.- The inner layer of the aminotic sac containing an aminotic fluid and cover the fetal surface of the placenta and are what give the placenta its typical shiny appearance. Protects the fetus from any infection and the amniontic fluid is a clear, pale straw in colour . It secreted by the amnion and fetal urine also contributes to the volume from the 10th weeks of the gestation on wards.

35. The total amount of amniotic fluid is about 1 litter and diminished to 800ml at 38 weeks of gestation (term). If the total amount exceeds 1500 ml, the condition is known as polyhdramnous and if less than 300ml it is known as oligohydraminous . It constitutes 99% water and the remaining 1% is dissolved organic maters including substances and waste products . FUNCTION - Allows for free movement of the fetus - Protects the fetus from injury - Maintains a constant temperature for the fetus - During labour it protects the placenta and umblical cord from the pressure of uterine contraction - Aids effeciement of the cervix and dilation of the uterine os

36. • The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium . • Placenta grows throughout pregnancy. • Development of the maternal blood supply to the placenta is complete by the end of the first trimester of pregnancy (approximately 12–13 weeks). Fertilization - Zygote The cleavage starts in the zygote immediately after fertilization and on 4th day morula has formed. The morula consists of two groups of cells: • Inner Cell Mass (Central Cells) • Outer Cell Mass (Peripheral Cells) Within one day morula is converted into blastocyst consisting of same two groups of cells, now with different names: – Embryoblast derived from Inner Cell Mass – Trophoblast derived from Outer Cell Mass • Embryoblast forms the embryo proper • Trophoblast forms the placenta and associated membranes. Development of placenta starts as soon as blastocyst is attached to the endometrium . Trophoblasts start proliferating rapidly and differentiate into two layers : • Cytotrophoblast or cellular trophoblast • Syncytial trophoblast ( syncytiotrophoblast ) DEVELOPMENT OF PLACENTA

37.   3 weeks after fertilisation -Small projections appear on the trophoblastic layer of the blastocyst , proliferate to form chorionic villi • Abundant in decidua basalis called chorionic frontosum & develops into placenta • The villi under decidua capsularis are less abundant and atrophy to form chorionic leave which later form chorion Placental Development • Chorionic villi erode the walls of maternal blood vessels and opens up to form a pool of maternal blood(sinuses) • Few villi attach deeply into decidua (anchoring villi ) • Placental circulation establishes by 17th day • Placenta completely develops and functions by 10th week after gestation

38. SUCCENTURIATE LOBE OF PLACNETA: A small extra lobe is present , separate from the main placenta and joined to it by blood vessles which ran through the memebrane to reach it. The danger is that this small lobe may be retained in utro after delivery, and if it is not removed it may lead to haemorrhage and infection. Identification On inspection, the placenta will appear torn at the edge, or torn blood vessles may extend beyond the edge of the placenta. ANATOMICAL VARATIONS OF THE PLACENTA AND THE CORD

39. SUCCENTURIATE LOBE OF PLACNETA:

40. Circum vallate placenta In this situation an opaque ring is seen on the fetal surface. It is formed by a doubling back of the chorion and amnion. Danger May result in the membranes leaving the placenta nearer the center instead of at the edges as usually..

41. Circum vallate placenta

42. Battledore inseration of the cord The cord in this case is attached at the very edge of the placenta in the manner of the table tennis bat. Danger Likely it is detached up on applying traction during active management of the third stage of labour .

43. Velamentous insertion of the cord It is inserted into the memberans some distance from the edge of the placenta. The umblical vessles run through the memberanous frorm the cord to the placneta . Danger The vessles may tear with cervical dilatation and would result in sudden blood loss. Velamentous insertion

44. Two complete and separate lobes are present, each with a cord leaving it. The bipartite cord joins a short distance from the two parts of the placenta. Danger - The extra lobe may retained during delivery A tripartite Placenta is similar but with three distinct lobes. Bipartite Placenta

45. Bipartite Placenta

46. PLACENTAL VARIATIONS

47. Placental infarction occurs when the blood supply to an area of the placenta is blocked and tissue necrosis results. It appears most commonly on the maternal surfaces and most often associated with vascular disease of the utero - placental unit secondary to maternal hypertension. As the infarct at area becomes necrotic, fetal circulation is reduced because blood flow through the placenta will decrease. However, if the circulation through the rest of the organ is sufficient, a fetus may survive when as much as 20% to 30% of the placenta is infracted. Placental infractions can be treated. Placenta infarction

48. Placental tumors ( Haemongiomata of the Placenta) These tumors are relatively common, being found in approximately 1 percent of all placentas. Most tumors are small and without clinical significance but a few are large and associated with hydraminious , antepartum hemorrhage and premature labour . Placental tumors

49. The umblical cord or funis extends from the fetus to the placenta and transmits the umblical blood vessles , two arteries and one vein. These are enclosed and protected by Wharton’s jelly, (a gelatious substance formed from mesoderm). The whole cord is covered in a layer of amnion continuous with that covering the placenta. The length of the average cord is about 50cm. A cord is considered to be short when it measures less than 40cm The Umblical Cord

50. INTRODUCTION Fetal circulation  is the term used to describe how blood flows from the placenta through the developing fetus. Fetal circulation is very fascinating and has several unique components. In addition, fetal circulation is different from the circulation in newborn babies . For one, before a baby is born the placenta is the sole source of oxygen whereas in a newborn baby, the lungs are the sole site of oxygen exchange. Fetal circulation

51. The fetal heart also has a connection called the  foramen ovale  that allow blood flow from the right atrium to the left atrium of the heart bypassing the lungs since they are not needed for oxygen at this point. Once the baby is born , the increase pressure in the left atrium and increased oxygenation in the fetal blood causes the foramen ovale to close . This causes blood to flow through the lungs for oxygenation postdelivery .

52. The fetal circulation is the circulatory system of a human fetus, often encompassing the entire fetoplacental circulation which includes the umbilical cord and the blood vessels within the placenta that carry fetal blood. Umbilical Cord 2umbilical arteries: return non-oxygenated blood, fecal waste, CO2 to placenta 1umbilical vein: brings oxygenated blood and nutrients to the fetus The Fetal Circulation

53. It has a branch which joins the portal vein and supplies the liver. The ductus vensous (from a vein to a vein) connects the umblica vein to the inferior venacava . At this point the blood mixes with deoxygenated blood returning from the lower parts of the body. Thus the blood throughout the body is at best partially oxygenated.

54. 1. Ductus venosus : connects the umbilical vein to the inferior vena cava 2. Ductus arteriosus : connects the main pulmonary artery to the aorta 3. Foramen ovale : anatomic opening between the right and left atrium. Three shunts are present in fetal life:

55. The foramen ovale (oval opening) is a temporary opening between the atria which allows the majority of blood entering from the inferior vencava to pass across into the left atrium. The reason for this diversion is that the blood does not need to pass through the lungs since it is already oxygenated. The foramen ovale

56. The ductus arteriosus (from an artery to an artery) leads from the bifuraction of the pulmonary artery to the descending aorta, entering it just beyond the point where the subclavian and carotid arteries leave. The ductus arteriosus

57. The hypogastric arteries branch off from the internal iliac arteries and become umbilical arteries when they enter the umblical cord. They return blood to the placenta. This is the only vessel in the fetus which carries unmixed blood. The hypogastric arteries

58. Starting from the red blood cells that make up blood, fetal red blood cells and maternal red blood cells are different . Blood cells are made of a key protein called  hemoglobin , which is responsible for binding and transporting oxygen to tissues. Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin This difference facilitates the offloading of oxygen from mom to fetus. Fetal circulation starts after oxygen rich maternal blood is delivered to the placenta. FETAL CIRCULATION

59. The placenta is connected to the fetus via the  umbilical cord . The umbilical cord contains a single  umbilical vein  and two  umbilical arteries . The umbilical vein carries oxygenated blood from the placenta to the fetus and the umbilical arteries carry deoxygenated blood from the fetus to the placenta and ultimately to maternal circulation . This is another unique feature of fetal circulation as veins typically carry deoxygenated blood and arteries carry oxygenated blood . Some blood from the umbilical vein flows through an opening called the  ductus venosus  bypassing the liver and going directly into the  inferior vena cava (IVC) .

60. The IVC is large blood vessel that takes blood from the lower half of the body to the heart. The blood from the umbilical vein that does not flow through the ductus venosus enters the fetal liver via the  portal vein . The blood from the IVC enters the heart via the right atrium. The foramen ovale is an opening between the right and left atria allowing most of the blood bypass the fetal lungs which are unable to provide oxygen until the baby is born. A small amount of blood will ultimately enter the right ventricle and exit via the pulmonary artery heading for the lungs.

61. However, to maximize the amount of oxygenated blood reaching the rest of the fetus another bypass exists called the  ductus arteriosus . The ductus arteriosus connects the pulmonary artery to the aorta. The  aorta  is the largest artery in the body . It carries blood from the heart to the rest of the body. The blood from the left atrium then flows into the left ventricle and out of the heart to the body via the aorta. Once the blood has supplied most of its oxygen content to the body, it picks up carbon dioxide and returns it to the placenta via the umbilical arteries.

62. At birth the baby takes a breath and blood is drawn to the lungs through the pulmonary arteries . It is then collected and returned to the left a sudden inflow of blood. The placental circulation ceases soon after birth and so less blood returns to the right side of the heart . In this way the pressure in the left side of the heart is greater while that in the right side of the heart becomes less. Adaptation to extra Uterine life

63. This results in the closure of a flop over the formaen ovale which separated the two sides of the heart and stops the blood flowing from right to left. The cessation of the placenta circulation results in the collapse of the umbilical vein, the ductus venosus and the hypogastric arteries.

64. These vessels after collapse change to the following structure. The umbilical vein → the ligamentaum teres The ductus venosus → the ligamentum venosum The ductus arteriosus → the ligamentum arteriousm The foramen ovale → the Fossa ovalis The hypogastric arteries → the obliterated hypogastic arteries atrium via the pulmonary veins