EMBRYONIC AND FETAL GROWTH AND DEVELOPMENT

ObjectivesAt the end of 1 hour interactive lecture-

discussion and small group activity, the students will be able to1. Define related terminologies

2. Identify the different stages of human intrauterine development.

4. Identify and describe the different changes involve in each stage of embryonic development

3. Identify the 3 primary germ layers that develop into specific organ systems.

5. Identify and describe the different changes involve in each stage of fetal development

6. Integrate Christian values in the discussion of the concept of human prenatal development

Related TerminologiesPrenatal ZygoteEmbryoFetusDeciduaOrganogenesisFertilizationImplantation

STAGES OF HUMAN PRENATAL DEVELOPMENT

1. First 12-14 days = zygote2. From 15th day up to the 8th

week = embryo3. From 8th week to the time of

birth = fetus

ORIGIN AND DEVELOPMENT OF

ORGAN SYSTEM

PRIMARY GERM LAYERS

Ectoderm Mesoderm Endoderm CNS (brain and spinal cord)PNSSkin, hair and nailsSebaceous glandsSense organsMucous membranes of the anus, mouth, and noseTooth enamelMammary glands

supporting structures ofThe body (connective tissue, bones, cartilage, muscle, ligaments and tendons)dentin of teethUpper urinary system (kidneys and ureters)reproductive systemheart and circulatory systemblood vesselslymph vessels

lining of pericardial, pleura, and peritoneal cavitieslining of gastrointestinal tractrespiratory tract, tonsils, parathyroid, thyroid, thymus glandslower urinary system (bladder and urethra) lining of pericardial, pleura, and peritoneal cavitieslining of gastrointestinal tractrespiratory tract, tonsils, parathyroid, thyroid, thymus glandslower urinary system (bladder and urethra)

FETAL GROWTH AND DEVELOPMENT

First Lunar Month

Formation of Fetal Nervous system The spinal cord is formed and fused at the midpoint Lateral wings that will form the body are folded

forward to fuse at the midline. Head folds forward and becomes prominent,

representing about one third of the entire structure. Arms and legs are budllike structures Rudimentary eyes, ears, and nose are discernable Fetal heart begins to form The digestive tract exists as a single tube until the

3rd week of life Length: 0.75 to 1 cm Weight: 400 mg

Second Lunar MonthAll vital organs are formed by the 8th weekThe heart, with a septum and valves, is beating

rhythmically.Facial features are definitely discernible.Arms and legs are developedExternal genitalia are present, but sex is not

distinguishable by simple observationThe primitive tail is regressingAbdomen appears large because the fetal intestine is

growing rapidlyPlacenta develops fullySonogram shows gestational sacLength: 2.5 cm (1 inch) Weight: 20g

Third Lunar MonthKidneys are able to function – urine is formed by the

12th week.Buds of milk teeth formBeginning bone ossificationNail beds are forming on finger and toes.Spontaneous movements are possible, although they

are usually to faint to be felt by the mother.Sex is distinguishable by outward appearanceFetus swallows amniotic fluidHeartbeat is audible through doppler technologyFeto-placental circulation is established by selective

osmosis; no direct exchange between fetal and maternal blood.

Length: 7 to 8 cmWeight: 45 g

Fourth Lunar Month

Lanugo appearsBuds of permanent teeth formHeart beat maybe audible with fetoscopeLiver and pancreas are functioningFetus actively swallows amniotic fluidFetal urine is present in the amniotic fluidSex can be determined by ultrasonographyLength: 10 to 17 cmWeight: 55 to 120 g

Fifth Lunar Month

Vernix caseosa appearLanugo covers entire bodyHair forms, extending to include eyebrows and

hair on the head.Meconium is present in the upper intestineFormation of brown fatDefinite sleeping and activity patterns are

distinguisableSpontaneous fetal movements can bee sensed by

the motherLength: 25 cmWeight 223 g

Sixth Lunar MonthSkin markedly wrinkledAttains proportions of full term babyActive production of lung surfactant beginEyebrows and eyelashes are well definedPupils are capable of reacting to lightEyelids, previously fused since the 12th week,

are now openHearing can be demonstrated by response to

sudden soundMeconium is present as far as the rectumLength: 28 to 36 cmWeight: 550 g

Seventh Lunar Month

Maturation of the lung alveoliSurfactant can be demonstrated in the

amniotic fluidTestes begin to descend into the scrotal sac

from the lower abdominal cavityThe blood vessels of the retina are thin and

extremely susceptible to damage from high oxygen concentrations.

Length: 35 to 38 cmWeight: 1,200 g

Eight Lunar Month

Birth position may be assumedFetus is viableNails extend to ends of fingersSubcutaneous fat deposition beginsLength: 38 to 43 cmWeight: 1, 600 g

Ninth Lunar Month

Amount of lanugo begins to diminishMost babies turn into a vertex position (head-

down presentation during this month.Sole of the foot has only one or two crisscross

creasesLength: 42 to 48 cmWeight: 1, 800 to 2,700 g (5 to 6 lb)

Tenth Lunar Month

All characteristics of the normal newborn Creases on the soles of the feet cover at least 2/3 of

the surface Vernix caseosa is fully formed Length: 48 to 52 cm Weight: 3, 000 g

FOCUS OF FETAL DEVELOPMENT

1ST TRIMESTER – PERIOD OF ORGANOGENESIS

2ND TRIMESTER – Period of continued growth and development; rapid increase in fetal length

3rd TRIMESTER – period of most rapid growth and development due to deposition of subcutaneous fat.

Formation and development of the

Embryonic and Fetal Structures

1. Formation of fetal membrances

1. Chorion – outside embryonic membrane that develops from the trophoblast; contains the chorionic villi at the surface.

2. Amnion – innermost membrane that develops from the interior cells of the blastocysts.

Structure arising from amnion

Amniotic fluid/ Bag of Water (BOW) Clear albuminous fluid in which the baby floats. Begins to form at 11-15 weeks gestation. Alkaline in nature (pH 1.0-1.25) with specific gravity of

(1.007-1.025) Near term is clear, colorless, containing little white

specks of vernix caseossa and other solid particles. Average amount of 500ml-1000ml up to maximum of

1200ml Sources of are: amniotic cells, fetal urine, and maternal

serum. Functions include:

Cushions the fetus against danger.Equalize pressure Prevents adhesion in the sticky skin and umbilical

cord compressionfetal movementthermoregulationOral source of fluid for fetus.

Structure arising from amnion

Umbilical Cord/ Funis 21-23 inches or 50-53cm long with 2 ¾” thick. Has 1 vein (carrying blood from the placental villi to

the fetus) and 2 arteries (carrying blood from the fetus back to placental villi). AVA

Approximately 350ml/min blood flow rate. Covered with gelatinous mucopolysaccharide

substance called wharton’s jelly that gives body to the cord and prevents pressure on the vein and arteries.

Structure arising from Chorion

Chorionic Villi – projections of the trophoblast that produce human chorionic gonadotropin and begin osmosis of nutrients to the embryo.

Parts of Chorionic Villi Central core – loose connective tissue that contains

the fetal capillaries.

Syncytiotrophoblast/ syncytial layer – outer layer of chorionic villi where production or various placental hormones (HCG, somatomammotropin, human placentak lactogen, estrogen, progesterone) during the first 2 months of gestation happen.

Cytotrophoblast or Langerhan’s layer – inner layer of the chorionic villi.

present as early as 12 days of gestation. Protects the growing fetus from certain infectious

organisms such as spirochete of syphilis. Disappears between 20th and 24th week of

gestation.

Structure arising from ChorionPlacenta – rose from chorion together with

decidua basalis.Begins to function by the 4th week of

gestation.Completely independently functioning

organ by 14th weekTransmit nutrients and oxygen to the fetus

and removes waste and carbon dioxide by diffusion.

The endocrine organ of pregnancyEstrogenProgesteroneHuman Chorionic GonadotropinHuman Placental Lactogen/ Human

Chorionic Somatomammotropin

Functions of Placenta

Diffusion – movement of molecule from the area of higher concentration to the area of lower concentration. (oxygen, carbon dioxide, sodium, chloride, fat soluble vitamins, liquids including narcotics, anesthetics and barbiturates cross the placenta by simple diffusion.

Facilitated Diffusion - placental crossing of some substances that is more rapid and more easily that requires less energy. (glucose)

Active Transport – a process that requires energy and action of enzyme to facilitate transport. (essential amino acids and water soluble vitamins)

Pinocytosis – absorption by the cellular membrane of microdroplets of plasma and dissolve substances. (Gamma globulin, lipoproteins, phospholipids, and other molecular structures that are too large for diffusion and that cannot participate in active transport cross in this manner.