HHD - prenatal development stages

Fertilisation

1. During equal intercourse, sperm is deposited in the vagina & swim towards fallopian tubes

2. Sperm will reach the ovum & break the membrane to enter the cell

3. Genetic material fuse together to begin germination

—> forms a zygote - has 46 chromosomes → determines the gender, sex, hair & eye colour

The germinal stage - 1st day after fertilization

• the new cell (zygote) divides as it travels down the fallopian tubes

The germinal stage - 4th day after fertilization

• the zygote contains around 6 cells, it turns into a morula

The germinal stage - 5th day after fertilization

• morula has 64 cels & turns into blastocyst, the inner mass of it will become the embryo and the outer cell will become the placenta

The germinal stage - 7-12 days after fertilization

• when it reaches the uterus the blastocyst plants itself in the endometrium and becomes known as an embryo

The embryonic stage -

• begins at imaplantation & ends at 8 wks

1. Most internal & eternal organs and systems are formed and brain & spinal cord are almost complete by the end

2. Following the proximodistal pattern of development → limbs start out as buds emerging from the torso & continue to grow and develop during this stage

3. By the 8th week, the embryo becomes distinctly human looking

4. Although the head & neck still account for half of the embryo’s total length & the brain makes up almost half of it’s body weight

The foetal stage (part 1)

1. The period is a time of extensive growth (in size & mass) as well as the development of organs & systems that were established in the embryonic period

2. By the beginning of the foetal stage, all of the muscles, organs & nerves re beginning to function

The foetal stage (part 2)

3. The lungs of the foetus are filled with amniotic fluid not air

4. Babies are considered premature if they’re born 3 wks before their due date

Germinal stage - week 1

• 30hrs after fertilisation → cell division begins & will continue for life

• 3 days later, zygote consists of 16 cells

• Zygote travels down fallopian tube into uterus

Germinal stage - week 2

• the ball of cells (blastocyst) implants into the endometrium→ takes a week

• The formation of placenta begins

Embryonic stage - week 3

• begins at implantation & ends at 8 weeks

• Marked by cell differentiation - cells form specialised roles

• Implantation is complete → is now an embryo

Embryonic stage - week 4

• brain & spine develop

Embryonic stage - week 5

• Buds starts to appear on each side of embryo → will become limbs

• Heart begins to beat

• It’ll be several weeks until placenta is fully functional it access oxygen and nutrients from mothers bloodstream

Embryonic stage - week 6

• embryo is approximately 1.3cm long

Embryonic stage - week 7

• blood cells are made in liver

• Facial features (eye + mouth) forming

• Tiny muscles have formed → allow embryo to move

Embryonic stage - week 8

• embryo = approximately 2.5cm

• Fingers & toes forming

• Brain = active & makes up half of the body weight

—> embryo => distinctly human-looking

Foetal stage - week 9-13

• all body organs are formed but aren’t functioning

• Foetus = 7cm in week 11

Foetal stage - week 14-18

• foetus = 14cm in week 14

• Sex can be distinguished via ultrasound

• Ears are fully functional

Foetal stage - week 19-23

• foetus = 33cm in week 22

• Eyelids seperate into upper & lower lids → foetus can open/shut eyes

• Foetus will swallow regularly → but only takes amniotic fluid

Foetal stage - week 24-28

• foetus = 37cm & approx 1 kg

• Finger & toes grow nails

• Production of surfactant begins → breathing preparation

Foetal stage - week 29-33

• eyebrows & eyelashes grow

• Fat is laid down under the skin to assist with adjusting to life outside uterus

Foetal stage - week 34-38

• the foetus assumes the head down position in prep for birth

• Lungs develop at a rapid rate

• Foetus = 50 cm