4. Pregnancy (embryonic + fetal stage)

embryonic stage

3rd week to 8th week, includes gastrulation and organogenesis, most critical period, embryo implants, body parts form

gastrulation

early process transforms embryonic disc into primary layers, begins ~3rd week, establishes body plan

gastrula

post-gastrulation embryo contains 3 germ layers

gastrula layers

ectoderm, mesoderm, endoderm

embryo at 4 weeks

4-5 mm long, embryonic disc becomes cylindrical, neural tube forms, by end of week → head + jaws appear, heart beats pumping blood + tiny buds form → upper and lower limbs

embryo at 5-8 weeks

head grows rapidly, limbs elongate, end of 7th week → main organs establishes (8th week → 30 mm long and 5g)

8th week

embryo and chorion engage → only villi remaining in contact with endometrium endure, others degenerate, region of chorion in contact with wall is restricted to disc shaped area becoming placenta

disturbance in embryonic stage

can cause malfunctions

teratogens

agents or factors that cause abnormal developments (birth defects) in embryo or fetus (drugs, virus, radiation, etc) effects depend on timing, dose, and duration

fetal stage

8th week and on, large head, short limbs, 3rd month → lengthens, head growth slows, upper limbs reach relative length they will keep

12th weke

external organs distinguished as male or female

4th month

lower limbs lengthen, skeleton continues ossification

5th month

growth limbs, hair grows, muscles contract

6th month

fetus gains weight, skin is wrinkled

7th month

eyes open, fat deposited, skin gets smoother, organs specialize and grow, brain cells form network, digestive and respiratory systems last to mature

266 days

baby is ready to be born

fetal blood and circulation

maternal blood supplies O2 and nutrients and removes wastes, exchange occurs through the placental membrane, and umbilical vessels transport blood to and from fetus, concentration of hemoglobin is greater in fetus than in adult

pattern of fetal circulation

fetal lungs not yet in use → blood flow is routed through temporary structures that bypass the liver and lungs, reroute blood away from lungs and liver, ensuring oxygen-rich blood from placenta reaches vital organs efficiently

temporary stuctures

ductus venosus, foramen ovale, ductus arteriosus

ductus venosus

at liver, shunts oxygenated blood from umbilical vein directly to inferior vena cava, bypassing most of the liver

foramen ovale

between left and right atria of heart, allows blood to flow directly from right atrium to left atrium, bypassing lungs

ductus arteriosus

connects the pulmonary trunk to the aorta, diverts blood from pulmonary artery → aorta, avoiding the lungs

maternal changes during pregnancy

hCG is secreted by trophoblast, hCG maintains corpus luteum, corpus luteum continues to secrete estrogens and progesterones, estrogens and progesterones promote growth, development, and maintenance of uterine wall

plavenyal lactogen

stimulates breast and mammary gland development

relaxin

from corpus luteum and placenta inhibits uterine contractions and relaxes the pelvic ligaments

aldosterone

promotes sodium and water retention

parathyroid hormone

maintains calcium concentrations in the maternal blood

uterus displaces

abdominal organs, requires smaller meals, causes heartburn, leads to increased urinary frequency

as fetus grows, more ..

oxygen is needed and waste is excreted

increases while fetus grows

maternal: blood volume, cardiac output, breathing rate, urine production

food intake

smaller meals, increased supply for vitamins, minerals, and proteins for mother and fetus

parturition

end of pregnancy, involved decrease in progesterone, causing increase in prostaglandins, which causes increased uterine contractions, cervix becomes thin, and starts to open, stretching of uterus and vagina stimulates birth → positive feedback mechanism

milk production and secretion

placental sex hormones stimulate further development of mammary glands and prolactin is released by AP gland, placental lactogen promotes mammary development

initial milk secretion

begins after birth, due to inhibitory effects on placental progesterone and placental lactogen

first milk

thin, watery fluid called colostrum (rich in proteins and antibodies, lower amounts of carbohydrates and fats than milk)

milk production steps

areola is stimulated → impulses travel to hypothalamus → hypo signals posterior lobe of P gland to release oxytocin, OH causes myoepithelial cells surrounding alveolar glands to contract, milk is ejected from ductile system through nipple

postnatal period

neonatal, infancy, childhood, adolescence, adulthood, senescence

neonatal

birth to 4th week, first breath must be powerful to expand lungs, newborn uses stored fats and colostrum for energy, secretes dilute urine; temperature control mechanisms and water and electrolyte balance may not function properly for a few days

cardiovascular changes in newborn

first breath, umbilical cord clamp

first breath

expands lungs, pulmonary vessels open, increased blood flow to lungs

umbilical cord is clamped

placental circulation stops, proximal portions become vessels supplying urinary bladder, distal portions become lateral umbilical ligaments, umbilical vein becomes ligamentum teres

foramen ovale changes

closes, prevents flow between atria (becomes fossa ovalis)

ductus arteriosus changes

blood now travels to lungs for oxygenation (becomes ligamentum arteriosum)

ductus venous changes

blood flows through liver normal (becomes ligamentum venosum)