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)