Nursing: Fertilization and Ovulation

• Nursing care during normal pregnancy involves caring for the developing fetus

Fertilization

• Fertilization is the union of an ovum and a spermatozoon
• Usually, only one ovum matures each month in a woman
• An ovum is only capable of fertilization for about 24 hours, or up to 48 hours at most
• Mucopolysaccharide fluid (the zona pellucida) and a circle of cells (the corona radiata) surround the ovum
• These surrounding cells get propelled by fimbriae into the fallopian tube. Fimbriae are fine, hairlike structures lining the tube openings
• Peristaltic action of the tube and movement of the tube cilia help propel the ovum along the length of the tube

Ejaculation of Semen

• Semen averages 2.5 ml of fluid, containing 50 to 200 million spermatozoa per milliliter
• An average ejaculation has around 400 million sperm.

Time of Ovulation

• During ovulation, cervical mucus reduces in viscosity (thickness), making it easier for sperm to penetrate
• Sperm transport is efficient when deposited in the vagina around ovulation, reaching the cervix in 90 seconds and the fallopian tube in 5 minutes

Fertilization Process

• Sperm move through the cervix, body of the uterus, and into the fallopian tube towards the waiting ovum
• This movement is aided by the flagella (tails) and uterine contractions
• Spermatozoa cluster around the ovum's protective layer of corona cells
• Hyaluronidase, a proteolytic enzyme released by the spermatozoa, dissolves the layer of cells protecting the ovum
• Ordinarily, only one spermatozoon can penetrate the ovum's cell membrane
• After the spermatozoon penetrates the cell, the cell membrane becomes impervious to other spermatozoa

Factors Influencing Fertilization

• Equal maturation of sperm and ovum, sperm reaching the ovum, penetration of zona pellucida and cell membrane must successfully occur for fertilization

Implantation

• After penetration of the ovum, the chromosomal material of the ovum and spermatozoon fuse to form a zygote
• Spermatozoon and ovum carry 23 chromosomes each, so the fertilized ovum has 46 chromosomes
• An X-carrying spermatozoon will result in a female child (XX), and a Y-carrying spermatozoon results in a male child (XY)

Fertilization Completion

• A zygote migrates to the body of the uterus within 3 to 4 days, aided by muscular contractions of the fallopian tubes
• Mitotic cell division, or cleavage, begins with the first cleavage occurring at about 24 hours, which occurs at a rate of one every 22 hours
• The zygote consists of 16 to 50 cells when it reaches the uterus.

Blastocyst Formation

• Large cells collect at the periphery of the ball, leaving a fluid space surrounding inner cell mass over the next 3 to 4 days
• At this point the structure is referred to as a blastocyst
• Trophoblast cells form the outer ring and later the placenta and membranes
• The embryoblast cells consist of the inner cell mass, which forms the embryo

Implantation

• Contact between the growing structure and endometrium occurs ~8-10 days post-fertilization.
• ~8 days post-ovulation: blastocyst sheds corona & zona pellucida, brushes against rich uterine endometrium, and settles in soft folds
• Implantation occurs high on the posterior surface of the uterus
• Immediately after implantation, the blastocyst establishes an effective communication with the blood system of the endometrium
• When the zygote is implanted, it is called an embryo
• Implantation is an important process which around 50% of zygotes never achieve
• Occasionally, a small amount of vaginal spotting appears on the day of implantation because capillaries are ruptured by the implanting trophoblast cells
• Implantation bleeding may be confused as a scant menstrual flow, which can cause an inaccurate birth date calculation
• Birth date predicted based on the time of her last menstrual period will be calculated 4 weeks late

Embryonic and Fetal Structures

• Placenta and membranes, acting as fetal lungs, kidneys, and digestive tract, grow in coordination with embryo growth
• After fertilization, the corpus luteum in the ovary continues to function rather than atrophying
• This function is under the influence of human chorionic gonadotropin (hCG) secreted by thetrophoblast cells

Decidua

• Human chorionic gonadotropin (hCG) causes the uterine endometrium to grow in thickness/vascularity instead of sloughing off
• The endometrium is now typically termed the decidua because it will be discarded after birth
• The decidua basalis is where the implantation takes place and the basal plate is formed, which can be zona compacta or spongiosa
• Decidua capsularis encapsulate the chorion and the decidua parietalis are on the opposite uterus wall

Chorionic Villi/Hormones

• Chorionic villi, resembling probing fingers reach out from the trophoblast cells to begin formation of the placenta between days 11-12 post fertilization
• The center core consists of connective tissues and fetal capillaries surrounded by a double layer of cells, which produce placental hormones (hCG, hPL, estrogen, progesterone)
• The middle layer of Cytotrophoblast or Langhans’ layer protects the growing embryo and fetus from certain infectious organisms such as the syphilis spirochete early in pregnancy

Placenta

• The Chorionic Villi becomes the placenta, and Latin for pancake fits its size and appearance at term
• Placenta size equals 15-20 cm in diameter and 2-3 cm in depth, growing from trophoblastic cells to half of the uterus
• Circulation begins at the 12th day of pregnancy, maternal blood collects in the intervillous spaces of the endometrium surrounding the chorionic villi
• By the third week of pregnancy O2 and other nutrients osmose from the mother to the fetus

Placental Transfer

• Placental transfer is dynamic; almost all substances except a few can cross from the mother into the fetus
• Theoretically, an exchange process dependent on osmosis prevents the direct mixing of mother and baby's blood during pregnancy
• Occasionally, fetal cells cross into the maternal bloodstream as well as fetal enzymes, such as a-fetoprotein (AFP), produced by the fetal liver

Rate of Uteroplacental Blood Flow

• To provide enough blood for exchange and the needs of the growing fetus, the rate of blood flow in pregnancy increases from ~50 ml/minutes at 10 weeks gestation to ~500-600 ml/minutes at 36/40 weeks of gestation
• No additional maternal arteries appear after the first three months of pregnancy, the arteries only increase in size

Supine Hypotension

• The weight of the uterus can compress on the Vena Cava when lying on the back, also known as vena cava syndrome
• Reduce blood circulation which results in very low maternal blood pressure and poor uterine circulation
• At term, the Placenta weighs 400-600 g (1 lb) and compromised/inadequate circulation is related to placenta size

Mom with diabetes

• Fetus may develop a larger-than-usual placenta from excess fluid collected between cells

Left side position

• Uterine perfusion and placental circulation are most efficient when the mother lies on her left side because it lifts the uterus away from the inferior vena cava
• Preventing blood from becoming trapped in the woman's lower extremities

Endocrine/hormone production

• Syncytial (outer) layer creates independent hormone-producing system serving as the source of oxygen and nutrients for the fetus
• The first placental hormone is hCG, found in maternal blood/urine
• Presence ensures the corpus luteum of the ovary continues to produce progesterone/estrogen in order to maintain uterine endometrium

Progesterone

• Hormone to maintain the pregnancy/ the uterus endometrial lining

Estrogen

• Product of the syncytial cells of the placenta, contributes to woman's mammary gland development/stimulation of intrauterine growth

Amniotic Membranes

• Serves as source of nutrients for the fetus, the syncytial layer (outer) creates independent hormone-producing system

Chorionic Villi

• Medial surface (not involved in implantation; don't touch) gradually thins out -> becomes the chorionic membrane (outermost)
• Both layers together, and appear to be a single sac by term
• Have no nerve supply, spontaneously/artificially rupture; neither pregnant woman/ fetus experiences pain when “water breaks” during both procedures

Amniotic Fluid:

• Clear/slightly yellowish, surrounds the unborn baby contained in the amniotic sac; slightly alkaline w/ pH of ~7.2, never stagnant; constantly being formed/absorbed with placental contact
• To shield fetus abasing blows, changes in temp, aids in muscular development, and protects the umbilical cord from pressure

Excessive/Deficient amount of fluid

• Can result IF for an reason the fetus cannot swallow (esophagael atresia etc.)

Fetal Urine

• Added to quantity of amniotic fluid during fetal life, when the fetal kidneys become active. Disturbance of kidney can result in less amniotic fluid
• Test amniotic Fluid after membrane raptures to determine that it is not urin, which would indicate that membranes have ruptured

Umbilical cord

• Connecting fetus to the chorionic villi to deliver circulation that transfers O2 and nutrients from mother -> baby + return waste products
• A structure that is 53 cm (21 inches) long and 2cm thick during the term
• Volume controlled by gelitanous mucopolysacharide (Wharton Jelly) to give body/prevents pressure on the vessels

Umbilical Arterty/Vein:

• Contains Only one vein carrying blood from the placental villi + the two arteries carrying blood from the fetus back to the placental villi
• Abnormality: the Number of veins and arteries is assessed and recorded at birth because the condition of a single vein and artery occurs in approx 1% to 5% of infants, and 15% to 20% may possess chromosomal disorders
• Adequacy of blood flow/blood velocity through the cord, assessed with ultrasound Assessing the coils can be used to predict healthy growth
• Hypocoding: associated with maternal HTN
• Hypocoiling: related to newborn distressed

Origins of The Organs

• Early processes involves zygotes undergoing active phase, starting organ development (cephalocaudally; head-to-tail)
• Totipotent vs. Pluripotent: During the first phase is called a zygote, which begins to differentiate, so it doesn't grow into a body cell, it becomes a stem cell
• 3 germ layer that form body are the ectoderm, the endoderm, and the mesoderm

Major Organ System Development

• organ systems are essentially complete by 8 weeks of gestation, and in rudimentary form
• Organ development is highest during this time by invasion of teratogens medicines and Toxoplasmosis

Heart Structure

• At week 16- blood cell and vessels began to develop at 24th day, the single heart tube starts
• Week 6 to 7, septum and atria forms, as well as Heart Valve chambers
• Week 7: start vales and septum begin to develop
• Fetal heart is affected by O2 as well 0-160 BPM.

Blood flow:

1. Highly Oxygenated Blood enters via the umbilical cord
2. Blood enters through blood ductus venosus to the fetal liver, it connects to the venous cava to get carried out to the right side
3. Blood then goes into left atrium due to open Foremen ovals/adulthood from ventricle -> aorta bloods becomes DEoxygenated in descending and placental
4. Arteries take blood FROM fetus to placenta, where oxygen is exchanged to supply oxygenate to the cell
5. Blood will be 95-100% saturated 80–140 bpm on a baby at birth, where the O2 saturation is low to about 80% saturation 6 More: fetal Hg has higher O2 affinity, with about 53% respiration (tract) 3 wk solid to hollow to give birth

Respiratory

1. By week 3 it is the respiratory and digestive tract

• By week 4: divided into esophagus and the lungs
• By week 7: it travels to thorax w/ important respiratory developmental milestones
• Fetal Hg is more effective to transport and concentrate O2

Neural Sytem/ Brain Devlopment

• Development for the system begins at the 3rd week with three of its main parts: the ecto/endoderm and the mesoderm, the head is usually formed before any other part
• After 8 week we can measure activity as they finish construction to perform the functions

Genitary/Urination

• After week 12 Kidneys form; Kidneys help the baby to clear any wastes, however not vital during life
• Form urine which is then added to the amniotic fluid

Liver facts

• Does not prevent transfer from drugs to the baby's blood stream
• Glyocgen helps deposit certain stores (iron) which the kid lack (Vitamin K)

Fetal Development Milestones

Week 4

• Spinal Cord fuse/form; Head is ⅓ of the entire structure/ prominent heart structure/limb/eyes and nose are discernible
• Length: 0.76cm. Wt = 0.4 gram