Conception and Fetal Development

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Information about Conception and Fetal Development

Published on August 20, 2008

Author: claudiastoffel


Maternal & Child Nursing CareSecond Edition : Maternal & Child Nursing CareSecond Edition Lecture NotesChapter 7Conception and Fetal Development Marcia L. London Patricia W. Ladewig Jane W. Ball Ruth C. Bindler CONCEPTION ... : CONCEPTION ... Ovulation occurs approx 14 days before the start of menses Male ejaculates Each ejaculate contains 200-500 million sperm Sperm move by flagellar movement of sperm tail Viable for 2-3 days Only one sperm may enter the egg Preparation for Fertilization : Preparation for Fertilization Preparation is the first component of fertilization Ovum released into fallopian tube - viable for 24 hours Sperm deposited into vagina - viable for 48 to 72 hours (highly fertile for 24 hours) Sperm must undergo capacitation and acrosomal reaction Sperm penetration causes a chemical reaction that blocks more sperm penetration Moment of Fertilization : Moment of Fertilization Sperm penetration causes chemical reaction that blocks more sperm penetration Sperm enters ovum, chemical signal prompts secondary oocyte to complete second meiotic division True moment of fertilization occurs as nuclei unite Chromosomes pair up to produce diploid zygote Each nucleus contains haploid number of chromosomes (23) Moment of Fertilization (cont’d) : Moment of Fertilization (cont’d) Union restores diploid number (46) Zygote contains new combination of genetic material Sex of zygote determined at moment of fertilization Two chromosomes of twenty-third pair (sex chromosomes) - either XX or XY - determine sex of individual Females have two X chromosomes, males have an X and a Y chromosome FERTILIZATION : FERTILIZATION Occurs in the ampulla This is the outer third of the fallopian tube Takes 3-4 days for the fertilized ovum to move the length of the fallopian tube Cells of the ovum begin to replicate and grow to a 16 cell morula (solid ball of cells) Fluid produced-ovum separates Slide 7: FIGURE 7–3 During ovulation the ovum leaves the ovary and enters the fallopian tube. Fertilization generally occurs in the outer third of the fallopian tube. Subsequent changes in the fertilized ovum from conception to implantation are depicted. Cell Multiplication : Cell Multiplication Rapid mitotic division - cleavage Blastomeres grow to morula (solid ball of 12 to 16 cells) - solid ball of 12 to 16 cells Morula divides into solid mass (blastocyst); surrounded by outer layer of cells (trophoblast) Implantation; occurs in 7 to 10 days Cell Differentiation : Cell Differentiation 10 to 14 days (ectoderm, mesoderm, and endoderm) from which all tissues, organs, and organ systems develop Blastocyst differentiates into three primary germ layers (ectoderm, mesoderm, and endoderm) All tissues, organs, and organ systems develop from these primary germ cell layers Embryonic membranes form at implantation The chorion and the amnion Cell Differentiation : Cell Differentiation Amniotic Fluid: Created when amnion and chorion grow and connect and form amniotic sac to produce fluid Yolk sac DeveIops as part of the blastocyst Produces primitive red blood cells Soon incorporated into the umbilical cord Cell Differentiation : Cell Differentiation Ectoderm Mesoderm Endoderm - differentiation of endoderm results in formation of epithelium lining respiratory and digestive tracts Slide 12: FIGURE 7–5 Endoderm differentiates to form the epithelial lining of the digestive and respiratory tracts and associated glands. AMNIOTIC FLUID : AMNIOTIC FLUID Comes from diffusion from the maternal blood. It increases in amount weekly until there is approximately 800-1200 ml at term FUNCTIONS OF AMNIOTIC FLUID : FUNCTIONS OF AMNIOTIC FLUID Maintenance of constant body temp Source of oral fluid Collects waste Cushions the fetus Facilitates musculoskeletal development Keeps fetus from tangling with other structures Umbilical Cord : Umbilical Cord Develops from amnion Body stalk attaches embryo to yolk sac, fuses with embryonic portion of placenta Provides pathway from chorionic villi to embryo Contains two arteries and one vein; surrounded by Wharton’s jelly to protect vessels Wharton’s jelly: Specialized connective tissue Protects blood vessels Function of umbilical cord: Provides circulatory pathway to embryo FUNCTIONS OF PLACENTA : FUNCTIONS OF PLACENTA Produces 4 hormones necessary to maintain pregnancy and support fetus Respiration Nutrition Excretion Storage of carbs, proteins, calcium and iron Placenta : Placenta Placental development Begins at third week of embryonic development Develops at site where embryo attaches to uterine wall Function: Metabolic and nutrient exchange between embryonic and maternal circulations Placenta has two parts Maternal Fetal Placenta : Placenta Maternal portion Consists of deciduas basalis and its circulation Surface appears red and flesh-like Fetal portion Consists of the chorionic villi and their circulation The fetal surface of the placenta is covered by the amnion Appears shiny and gray Slide 19: FIGURE 7–8 Maternal side of placenta (Dirty Duncan). Slide 20: FIGURE 7–9 Fetal side of placenta (Shiny Shultz). FETAL CIRCULATION : FETAL CIRCULATION Placenta assumes function of the fetal lungs by supplying oxygen and allowing the fetus to excrete carbon dioxide into the maternal bloodstream Blood enters the placenta and flows through the umbilical vein FETAL CIRCULATION : FETAL CIRCULATION Umbilical vein divides into 2 branches One circulates a small amount of blood through the fetal liver and empties into the inferior vena cava Second (also larger) is called the ductus venosus and empties directly into the fetal vena cava See Figure 7-11 (page 171) FETAL CIRCULATION : FETAL CIRCULATION Blood then enters the right atrium Passes through the foramen ovale Then into the aorta Some blood returning from the head and upper extremities by way of the superior vena cava is emptied into the right atrium FETAL CIRCULATION : FETAL CIRCULATION Then passes through the tricuspid valve into the pulmonary artery Small amount of blood passes to the lungs for nourishment only Larger amount of blood passes from the pulmonary artery through the ductus arteriosus into the descending aorta FETAL CIRCULATION : FETAL CIRCULATION This bypasses the lungs Blood then returns to the placenta through the placenta through the 2 umbilical arteries Fetus Growth and Development : Fetus Growth and Development 4 weeks: 4–6 mm, brain formed from anterior neural tube, limb buds seen, heart beats, GI system begins 6 weeks: 12 mm, primitive skeletal shape, chambers in heart, respiratory system begins, ear formation begins Fetus Growth and Development (cont’d) : Fetus Growth and Development (cont’d) 12 weeks: 8 cm, ossification of skeleton begins, liver produces red cells, palate complete in mouth, skin pink, thyroid hormone present, insulin present in pancreas 16 weeks: 13.5 cm, teeth begin to form, meconium begins to collect in intestines, kidneys assume shape, hair present on scalp Fetus Growth and Development : Fetus Growth and Development 20 weeks: 19 cm, myelination of spinal cord begins, suck and swallow begins, lanugo covers body, vernix begins to protect the body 24 weeks: 23 cm, respiration and surfactant production begins, brain appears mature 28 weeks: 27 cm, nervous system begins regulation of some functions, adipose tissue accumulates; nails, eyebrows, and eyelids are present; eyes are open 36 weeks: 35 cm, earlobes soft with little cartilage, few sole creases Fetus Growth and Development : Fetus Growth and Development 40 weeks : 40 cm, adequate surfactant, vernix in skin folds and lanugo on shoulders, earlobes firm, sex apparent Weight about 3,000 to 3,600 g (6 lb., 10 oz. to 7 lb., 15 oz.) Varies in different ethnic groups Skin has a smooth, polished look Hair on head is coarse and about 1 inch long Body and extremities are plump Slide 30: FIGURE 7–12 The actual size of a human conceptus from fertilization to the early fetal stage. The embryonic stage begins in the third week after fertilization; the fetal stage begins in the ninth week. Fetal Development: What Parents Want to Know : Fetal Development: What Parents Want to Know Fetal Development: What Parents Want to Know (cont’d) : Fetal Development: What Parents Want to Know (cont’d)

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