Fertilization

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​First Lunar Month

Germ layers differentiate by 2nd week.

First Lunar Month

Amnion and chorion appear by 2nd week.

First Lunar Month

Nervous system develops rapidly by 3rd week.

First Lunar Month

Fetal heart begins forming by 16th day.

Second Lunar Month

All vital organs formed by 8th week.

Second Lunar Month

Placenta fully develops.

Second Lunar Month

Sex organs formed by 8th week.

Second Lunar Month

Meconium forms in intestines by 5th–8th week.

Third Lunar Month

Kidneys function and urine formed by 12th week.

Third Lunar Month

Milk teeth buds form.

Third Lunar Month

Bone ossification begins.

Third Lunar Month

Fetus swallows amniotic fluid.

Fourth Lunar Month

Lanugo appears.

Fourth Lunar Month

Permanent teeth buds form.

Fourth Lunar Month

Heartbeats audible via fetoscope.

Fifth Lunar Month

Vernix caseosa appears.

Fifth Lunar Month

Lanugo covers body.

Fifth Lunar Month

Quickening felt.

Fifth Lunar Month

Fetal heartbeats very audible.

Sixth Lunar Month

Skin becomes wrinkled.

Sixth Lunar Month

Fetus resembles full-term baby.

Seventh Lunar Month

Alveoli begin forming.

Seventh Lunar Month

28th week marks the lower limit of prematurity.

Eighth Lunar Month

Fetus is viable.

Eighth Lunar Month

Lanugo begins to disappear.

Eighth Lunar Month

Nails reach fingertips.

Eighth Lunar Month

Subcutaneous fat begins depositing.

Ninth Lunar Month

Lanugo and vernix disappear.

Ninth Lunar Month

Amniotic fluid volume decreases.

Tenth Lunar Month

All features of a normal newborn.

First Trimester

Focuses on organogenesis.

First Trimester

Formation of organs and structures from 0–12 weeks.

Second Trimester

Fetal growth and length increase.

Second Trimester

Rapid growth and continued organ development from 13–28 weeks.

Third Trimester

Rapid growth and fat deposition.

Third Trimester

Most rapid growth and fat deposition from 29–40 weeks.

Umbilical Vein

Carries oxygenated blood from placenta to fetus.

Umbilical Vein

Single vein within umbilical cord with approximately 80% oxygen saturation.

Umbilical Arteries

Carry deoxygenated blood from fetus to placenta.

Umbilical Arteries

Two arteries within umbilical cord with approximately 52% oxygen saturation.

Ductus Venosus

Shunts blood past the liver into inferior vena cava.

Ductus Venosus

Moderately oxygenated blood with approximately 78% oxygen saturation.

Foramen Ovale

Opening between right and left atrium.

Foramen Ovale

Shunts oxygenated blood from right atrium to left atrium to supply brain and heart.

Ductus Arteriosus

Connects pulmonary artery to aorta.

Ductus Arteriosus

Diverts blood from lungs to systemic circulation.

Amniotic Fluid

Pale and yellow in color with slightly basic pH.

Amniotic Fluid

Contains alpha-fetoprotein, distinguishing it from acidic urine.

Simple Diffusion

Primary mechanism for gases and simple molecules across the placenta.

Simple Diffusion

Substances move from higher to lower concentration, e.g., oxygen, carbon dioxide, water.

Facilitated Diffusion

Substance moves from higher to lower concentration with carrier protein assistance.

Facilitated Diffusion

Example: glucose, the primary energy source for the fetus.

Active Transport

Substance transferred against concentration gradient using carrier protein and energy.

Active Transport

Examples: amino acids, water-soluble vitamins, essential minerals like iron and calcium.

Pinocytosis

Placental membrane engulfs a substance, forming a vesicle to move it across the cell.

Pinocytosis

Example: transfer of maternal antibodies (IgG) for passive immunity.

Ectopic Pregnancy

Implantation outside the uterus, e.g., fallopian tube or ovary.

Ovarian Pregnancy

Rare ectopic pregnancy where implantation occurs in the ovary.

Placenta Previa

Placenta implants low in the uterus, possibly covering the cervix.

Corona Radiata

Outer layer of follicular cells surrounding the ovum.

Corona Radiata

Penetrated by spermatozoa during fertilization.

Zona Pellucida

Inner glycoprotein shell surrounding the ovum.

Zona Pellucida

Penetrated by spermatozoa during fertilization.

Acrosome

Enzyme cap on sperm head.

Acrosome

Releases enzymes to break through corona radiata and zona pellucida during fertilization.

Abortus

Fetus weighing less than 500g or less than 20 weeks gestation, considered not viable.

Abortion

Termination of pregnancy before the age of viability.

Gametes

Egg and sperm cells, each with 23 chromosomes (haploid).

Somatic Cells

All other body cells with 46 chromosomes (diploid).

Somatic Cells

Divide through mitosis and meiosis.

Cytokinesis

Final step of cell division where the cell splits.

Cytokinesis

Studied in cancer research.

Trisomy 21

Chromosomal abnormality causing Down syndrome due to an extra chromosome 21.

Chorionic Plate

Composed of trophoblastic lining and fibrous mesoderm.

Chorionic Plate

Forms by fusion of primary and secondary chorionic plates by 8–10 weeks.

Intervillous Space

Trophoblast-lined channels in the placenta where maternal-fetal exchange occurs.

Intervillous Space

Maternal blood bathes chorionic villi for nutrient and gas exchange.

Primary Villi

Solid projections of cytotrophoblast cells into the syncytiotrophoblast.

Primary Villi

Form before 12 days post-fertilization.

Secondary Villi

Mesenchymal cords from extraembryonic mesoderm invade primary villi by day 12.

Tertiary Villi

Formation of fetal blood vessels (angiogenesis) begins in the mesenchymal core.

Tertiary Villi

Form vascular villi for maternal-fetal exchange.

Zona Compacta

Surface or compact zone of decidua parietalis and basalis.

Zona Spongiosa

Middle portion of decidua containing remnants of glands and small blood vessels.

Zona Spongiosa

Forms part of the zona functionalis with zona compacta.

Zona Basalis

Basal zone of decidua that remains after delivery.

Zona Basalis

Gives rise to new endometrium.

Fetal Circulation

Unique blood circulation system bypassing nonfunctional fetal lungs.

Fetal Circulation

Placenta serves as the organ for gas exchange, nutrient delivery, and waste elimination.

Fertilization

The union of the sperm and the mature ovum in the outer third or outer half of the Fallopian tube.

Zygote

The first cell of a new organism formed after fertilization.

Morula

Solid ball of cells (16–50 cells) after multiple cleavage divisions, formed by day 3–4.

Blastocyst

Fluid-filled structure with inner cell mass and trophoblast, attaches to the uterus.

Blastocyst

Forms by day 3–4 with about 58 cells.

Trophoblast

Cells outside the ring that will later form the placenta.

Trophoblast

Differentiates into syncytiotrophoblast and cytotrophoblast layers vital for implantation and placenta formation.

Embryoblast

Inner cell mass that will form the embryo.

Implantation

Attachment of blastocyst to uterine lining.

Implantation

Occurs 6–7 days after fertilization.

Implantation

Involves apposition, adhesion, and invasion processes.