conception and fetal development revised fall 2012

CONCEPTION AND FETAL DEVELOPMENT

Revised Fall 2012

HOW DOES THE FEMALE BODY PREPARE FOR CONCEPTION?Describe the process of maturation of an ovum

Menstrual Cycle

Varies every 28 - 35 days

The time between ovulation and menstruation is relatively constant (14 days). Luteal phase.

The variable is from menses to ovulation. It can not be predicted, the Follicular phase.

Affected by various physical and emotional factors

Maturation of the OvumOvarian Cycle

Follicular Phase- Development of the graafian follicle (ovum)

Ovulatory Phase- about 2 days before ovulation

Luteal Phase- Formation of corpus luteum

HOW WILL THE PATIENT KNOW THAT SHE IS OVULATING?

Signs and Symptoms of Ovulation

1. Body temperature increase 2. Mittelshmerz 3. Cervical mucus changes

Increase in amount Becomes thin, watery, and clear Ferning Stretchable: spinnbarkheit Alkaline

WHAT HAPPENS TO THE CORPUS LETEUM OF I DO NOT GET PREGNANT?

WHAT HAPPENS TO THE CORPUS LUTEUM IF I BECOME PREGNANT?

Endometrial Cycle

The uterine endometrium repsonds to ovarian hormones and goes through the phases in building up the lining of the uterus in preparation for implantation Proliferative Secretory Menstural

Hormonal Cycle

FSH- Follicle stimulating hormone Begins growth and maturation of the graafian

follicle LH- Luteinizing hormone

Assists in continued growth of the graafian follicle Estrogen

Responsible for proliferation of endometrium Progesterone

“Pro gestation”. The corpus luteum produces progesterone so the endometrium won’t slough off

Conception

Maturation of ovum and sperm cells Pregnancy comes about from the union of a

female germ cell, ovum with a male germ cell, the spermatozoon

Conception

One ovum per month is discharged from the ovary. It is transported into the fallopian tube where it begins its journey through the tube in search of the sperm. Viable for 12-24 hours

Fertalization

When intercourse occurs, millions of sperm travel in search of an ova. During travel through the female reproductive system, capacitation occurs

Fertilization

As the sperm swarm around the ova, the Acromosome caps of sperm release zona digesting enzymes

WHY IS THE NUMBER OF SPERM SO IMPORTANT IF ONLY ONE SPERM ENTERS THE EGG?

Fertilization

Distal portion of the fallopian tube

Only one sperm penetrates ova

Each contributes 23 chromosomes

Sex of baby determined at this time

PRE-EMBRYONIC DEVELOPMENT

Fertilized ovum begins its travel to the uterus

Cellular Multiplication

Morula eventually forms a fluid filled cavity within the cell mass. Inner solid cell

mass is called the blastocyst

Outer cell mass that surrounds the cavity is called the trophobast

TrophoblastOuter layer of cells

BlastocystInner cell mass

PlacentaChorion

FetusAmnion

Implantation

Germ Layers

Ectoderm Mesoderm Endoderm

Development Periods

Stage 1 – pre-embryonic weeks 1 - 2

Stage 2 -- embryonic weeks 3 - 8 period of ORGANOGENESIS

Stage 3 -- fetal weeks 9 - 40

Embryonic PeriodWeeks 4-8

Week 4 anterior end of neural tube closes to form

the brain and the posterior end closes to form the spinal cord

Heart begins to beat Eyes appear Limb Buds for arms and legs CR = 4 mm

Week 5 Head grows larger Hand and feet plates develop Facial features begin to develop CR = 8 mm.

Week 6 Fetal circulation is established Chambers form in the heart Upper lip and palate start fusing Eyes move to front of face Fingers are webbed External ear develops

Week 7 Eyelids start to form Fingers develop; elbows visible Diaphragm separates abdomen from chest Bronchi develop Arms and legs move

Week 8 Fingers and toes distinct Skeletal ossification begins Testes and ovaries are distinguishable Heart has four chambers Circulation through umbilical cord occurs

*** ALL essential external and internal structures are present and now will continue to grow

The patient tells the nurse that she is worried that the baby may have some defect because she was on antibiotics and other cold medication during the

first week after intercourse/conception

What is happening during the first week after conception that would assist the

nurse in answering her question?

Fetal PeriodWeeks 9-40

Weeks 9-12

Head size increases Face is well formed Nails appear Eyelids appear and close and fuse shut Kidneys excrete urine Intestines are forming; peristalsis begins Heartbeat can be heard via ultrasound Tooth buds appear for the baby teeth

Weeks 13-16

Lips form, facial contour develops Ossification of bone begins Meconium begins to form in the

intestines Hair present on scalp Sex can be determined visually

Weeks 17-20

Hair abundant on head Lanugo covers the body Vernix begins to form Myelination of spinal cord begins Suck and swallow begin Quickening occurs ~ 18 weeks

Weeks 21-24

Respiratory movement with air sacs formed

Surfactant production begins ~ 24 weeks

Brain appears mature Eyebrows and eyelashes can be seen Reacts to sudden noise with active movement

Weeks 25-28

Eyelids open and close Capillaries proliferate around the lungs’

alveoli making gas exchange possible Skin has wrinkled red appearance Rapid brain development

Weeks 29-32

Subcutaneous fat forms Testes start descending Fingernails and toenails are complete Bones are fully developed, but still soft

and pliable

Weeks 33-40

Limbs start to flex Muscle tone is developed Lanugo disappears Body begins to store fat Maternal antibodies transfer to the fetus Exhibits sleep and awake patterns

Answer this……

The fetal nervous system is formed by the germ layer known as the:a. ectoderm

b. mesoderm c. entoderm d. endoderm

AUXILLARY STRUCTURESPlacenta

Fetal Membranes

Functions of the Placenta

Fetal Respirations

Fetal Nutrition

Endocrine Functions

Elimination of Wastes

Barrier against certain substances

Amnion

Smooth, glistening membrane known as the Amnion is the lining of a fluid filled space that develops around the embryo

Functions of Amniotic Fluid

Keeps the fetus at an even temperature

Cushions the fetus against possible injury

Provides place for the fetus to move easily and grow symmetrically

Fetus drinks the fluid

Chorion

Thick membrane with finger-like projections called chorionic villi.

Chorionic villi contain blood vessels that are main connection with mother.

Chorionic villi produce human chorionic gonadotropin (HCG)

Merges with the decidua basalis to form the PLACENTA.

Umbilical Cord

Body stalk that attaches the embryo to the yolk sac

Contains blood vessels that extend into the chorionic villi

Protected by wharton’s jelly

Teratogens

Risk factors such as environmental substances Smoking Alcohol Drugs Viruses Occupational hazards

During what period of time is the baby most susceptible to damage from teratogens?

Review

Describe the components of the process of fertilization.

Ovum released into fallopian tube—viable for 24 hr. Sperm deposited into vagina—viable for 48 to 72 hr

(highly fertile for 24 hr). Sperm must undergo capacitation and acrosomal

reaction. Sperm penetration causes a chemical reaction that

blocks more sperm penetration. Fertilization occurs in the distal end of the fallopian

tube. Sperm enters ovum. The nuclei of the ovum and

sperm unite and become a diploid zygote.

Review

How can knowledge of the normal fertilization process assist in helping couples conceive?

Review

How can knowing the gestational age of the fetus help in assessment for the

potential effects of a teratogen?