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Fertilization
When the sperm and egg (called the gametes) come togeather (fertilization) to form zygote then they start to divide. In all animals except sponges the zygote (ferilized egg cell) undergoes cell division to form a hollow ball of cells called blastula. The egg and the sperm were haoploid cells meaning they only had half the number or normal chromosomes. When they combined the zygot has a complete set it is called diploid. -
implantation
A rapidly dividing ball of cells develops called the blastocyst. It burrows into the uterine wall. That process is called implantation. -
Embryonic Period Begins
The baby's brain, spinal cord, heart and other organs begin to form. it is the size of the tip of a pen. It has 3 layers the inner layer is called the endoderm. the middle layer is the mesoderm and the outer layer is the ectoderm. The ectoderm will become the skin, central and peripheral nervous systems, eyes, inner ear, and many connective tissues. The mesoderm will become the bones, muscles, kidneys, and reproductive system. The endoderm will become the lungs, intestines, and bladder. -
The Neural Tube Closes
the neural tube along the back is closing and the heart is pumping blood. Things will begin to appear and make up the inner ear and arches e body begins to take on a C-shaped curvature. Small buds will soon become arms and legs. A passage way for the ear opens up. The jaw begins to form. -
the head develops
the brain and face develope inclouding nostrils and the lense of the eye begins to appear. Arm buds have become paddles. The baby is a little bigger than the top of a pencil eraser. -
week 6
arms and legs are growing longer. Fingers are forming, as well as the shell shaped part of thhe ear, the nose and the upper lip the baby is one half inch long. -
week 7
Arms grow, develop bones, and bend at the elbow. Toes form. Eyelids and ears continue to grow. The baby is 3/4 inches long. -
week 8
The head becomes rounder. The neck begins to form. The eye lids begin to close. -
week 9
The baby is now a fetus and its genatelia and red blood cells are forming. -
Week 10
The baby is 2 1/2 inces long. It is developing finger nails. -
Week 11-facial expression
The fetus can make facial expressions, grasp, urinate, and suck his thumb, 3 1/2 incehes -
week 12 forming taste buds
legs are growing longer than arms and the baby is moving amniotic fluid through the lungs. -
week 14 skeleton turning into bone
soft cartilidge is turning into bone. The baby is about 5 inches long from head to bottom. -
week 16 sensory development is exploding
th brain is developing special areas for smell, taste, hearing, vision, and touch. The baby may be able to hear. The baby is 6 inches from head to bottom. -
week 18 the baby is very active
eye brows and lids are present. The baby is 10 1/2 inches long from head to heel. -
week 21 brain growing rapidly
Baby is skinny but begins to put on weight his lungs are developing branches. The baby is almost a foot long. -
week 24 brain is very active now
The baby is 14 1/2 inches long. Baby sleeps and wakes at regular intervols. The baby opens and closes eyes. More brain tissue is developing. This is the last week of the second tri mester the baby weighs 2 ponds.
