Embryology

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Fertilisation

Ovum released from ovary to ampulla of fallopian tube

Acrosomal cap of sperm cell breaks down and allows release of protealytic enzyme to allow sperm to penetrate ovum membrane.

The zygote has 14 days to embed itself in endometrium of uterus

Hormonal mechanisms are turned on = menstruation is stopped

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First 2 weeks of life

Day 1 - sperm penetrates ovum and loses tail

12 hours after penetration nuclei fuse forms gene

12 hours later Zygote divides

Days 2-14 - cell division and differentiation

division occurs every 12 - 15 hours

cells still enclose by zona pellucida and nutrient cells

This prevents polyspermy

Day 4 - first signs of differentiation

inner cell mass will form embryo, trophoblasts forming the wall

Blastocyst is swept into the uterine cavity

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Implantation

Trophoblast cells contacts uterine wall and differentiate into layers

The Sycytiotrophoblast and Cytotrophoblast

Sycytiotrophoblast cells implant blastocyst

Completly embedded by day 14

Digest through endometrial tissue surrounded by a nourishing environment

Spaces appear and are filled with blood

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Embryonic life

Ectoderm - brain, CNS, skin

Mesoderm  - muscle and connective tissue

Endoderm - gut, lungs, digestive organs

Flat Plate forms = tiny embryo

beginnings of nervous system - developing limbs

8 weeks = embryo looks human.

yolk sac forms digestive tract outpouchings 

Embryo suspended in a fluid filled cavity and linked by a stalk(umbilical cord) to Placenta

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Foetal Life

Week 9 - FOETAL PERIOD considerable growth

6 months - Independant existance

Last three months - build up of fat stores

9-12 weeks kidneys produce urine, foetus is active and bones and Nervous system developed

5-6 months - Lanugo (soft hair), brown fat

6 months - produce surfactant

7-9 months - continued maturation, nervous sytem develops, head of hair forms, fat is laid down, birth body fat will equal 15 percent of total body weight

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