6.3 Sexual reproduction

Copulation

sexual union facilitating reception of sperm by the female

offspring inherits half its genome from one parent and half from the other

Diploid cells

human cells throughout the body contain 46 chromosomes

Haploid cells

Gamete cells in males and females contain 23 chromosomes

Zygote

gametes combine to form a fertilized egg

grows and divides by mitosis into an embryo and then a fetus

Amnion

forms a fluid sac to cushion and protect fetus

Placenta

tempoarary organ

carries out nutritive, respiratory, excretory and endocrine functions until delivery

Umbilical cord

attaches the embryo to the placenta

Ectoderm

Outer layer of the embryo

Becomes the skin and nervous tissue

Endoderm

inner layer of the embryo

Forms glands

Forms solid organs

Forms lining of the hollow organs of digestive and respiratory system .

Mesoderm

middle layer, forms all other tissues

cardiovascular system

red blood cells

muscle tissue

Trimesters

development of a fetus is divided into three trimesters

First trimester: months 1-3

Second trimester: month 4-6

Third trimester: 7-9

First trimester

Body systems begin to develop

• nervous and cardiovascular system

Week 3: heart begins to beat

Week 6: fetal heartbeat can be detected on ultrasound

Head shape is formed during this trimester but disproportionately large

Neurulation

Formation of the neural tube from the outer folds of ectoderm

Neural fold becomes the neural crest

Spina Bifida

Occurs if neurulation does not completely close the neural tube