What is embryonic development?

-The sequence of events that gradually changes a Zygote into a functional organism

Zygote- Fertilized egg

Embryo- an organism in the early stages of development (up to week 8)

Fertilized Egg Stage:

Fertilization

After fertilization, zygote begins A series of cell divisions called CLEAVAGE (mitosis)

Fertilized egg divides by MITOSIS

-Zygote DOES NOT grow in size

Solid Ball Stage (Morula):

-Result of cleavage

-About 100 tiny cells. All identical

Blastula Stage:

-Solid ball rearranges. All cells pushed To the outside creating a hollow ball (1 cell thick and filled with fluid)

Stem cells are taken at this point. 5 days After fertilization

-Specialized changes that transform embryonic cells Into specialized cells, tissues and organs

Gastrula Stage:

Gastrulation occurs:

Cells push in on one side of blastula, forming a two layered embryo

3 Primary Germ Layers form giving rise to organs and tissues

Primary Germ Layer Structures Give Rise To

Ectoderm

(Outer Layer)

-Nervous System, skin, hair, nails

Mesoderm (middle layer)

-Muscles, Circulatory, and Skeletal Systems Sex organs (testes and ovaries)

Endoderm

(Inner Layer)

-Lining of digestive and respiratory Tracts, parts of liver and pancreas

Bird Embryo:

Chorion & Allantois (Chorioallantoic Membrane):

-Combine to help embryo exchange Gases and remove wastes

Yolk Sac: -Surrounds the yolk which is the food source for The embryo

Amnion:

-Surrounds embryo, protects it, and holds it in a Solution of salt water (similar to the ocean)

Human embryo:

The following extraembryonic membranes develop AFTER Implantation (embryo burrows in uterine lining):

Chorion: Connects to uterine wall

Amnion: Contains amniotic fluid which surrounds and Protects the embryo (shock absorbency)

Placenta: Combination of fetal and maternal tissue that Nourishes the embryo by providing it with Oxygen and nutrients and removes wastes

*** The blood of the fetus and mother NEVER mix. They are close enough for DIFFUSION to occur.

Umbilical Cord: Connects the placenta to the fetus (at Belly button). Transports oxygen, nutrients, And wastes between fetus and mother (placenta)

How do the placenta and the umbilical cord work together?

-Nutrients, oxygen, and wastes diffuse across the Placenta. The umbilical cord transports these materials between the fetus and the placenta.

Identical Twins: 1 egg + 1 sperm (egg splits giving rise to 2 separate zygotes with Identical DNA)

Fraternal Twins:

(2 eggs released and each fertilized with a different sperm cell)

2 eggs and 2 sperm cells

Involves 3 Processes that ALL begin with fertilization:

1. Growth- Increase in # of cells by MITOTIC CELL DIVISION (no increase in size)

2. Development- As cells develop they move within the embryos body and arrange themselves into specific layers

3. Differentiation- Each cell becomes specialized to Perform specific tasks (heart cells, brain cells, skin cells given their identity)

Meiosis Fertilization Mitosis Differentiation Birth (Creates gametes) (zygote) (growth/development)

How long does human pregnancy last?

-About 266 days of development (fertilization to birth) called the GESTATION PERIOD

1st Trimester:

-All organ systems begin to form

-Most critical time; most Sensitive to outside influences

6 Weeks

-1st detectable brain waves

8 weeks

-Now called a FETUS (living organism in the later stages of development. Week 8 and on)

-Eyes well developed and fingers lengthen

12 Weeks

-End of 1st trimester

-Fetus able to move (mother unable to sense)

14 Weeks

2nd Trimester:

-Rapid body growth

-Fetus more flexible with movement

18 Weeks

-Phases of sleep and awakening

At 20 weeks (5 months):

-May suck thumb

-Rapid brain development

21 Weeks

-Fetus begins to kick

- 8” in length

24 Weeks

-Response to light and sound from outside the uterus

-End of 2nd trimester

32 Weeks (8 months)

3rd trimester:

-Mass more than triples

-During 8th month Eyes open/close

-Fully mature at 35 Weeks (20”)

-Perfect hearing

What are some of the first signs of birth?

-”water breaks” (Amniotic sac breaks and fluid is released Into the vagina)

-Muscular contractions cause cervix to widen (dilate)

-Baby moves further from the uterus towards the vagina

What is afterbirth? -The placenta separates from the uterus and exits through the vaginal canal

What are some dangers facing a fetus?

-Radiation (X-rays)- may stop cell division

-Genetic mutations (chromosome #)

-Infectious Illness (can lead to brain damage, miscarriage)

-Inadequate Diet

-Harmful Lifestyle- (smoking, drugs, alcohol, std’s) may lead to still birth, brain damage, low birth weight, mental retardation, learning disabilities

Artificial Insemination-

-Donor sperm is inserted into vaginal canal of female during ovulation and internally fertilizes the egg in the oviduct

-Baby contains ½ of mother’s DNA and ½ from the donor

In Vitro Fertilization-

-Sperm and egg are combined EXTERNALLY

-Embryo implanted into female’s uterus for development

Amniocentesis- -Technique used to extract fetal cells and examine DNA for possible genetic defects (can be risky)

Cloning-

-Technique in which the nucleus is removed from a Normal body cell and used to replace the nucleus of An egg cell -Egg is implanted into female’s uterus for development

-Offspring is IDENTICAL to parent (no variation)

-Offspring ages faster than normal

-Not successful in humans as to date (moral and ethical issues involved)

Stem Cell Research-

-UNDIFFERENTIATED embryonic cells are removed (around day 5) and treated with chemicals to develop into specific tissues and organs

-Moral and ethical debates

-Belief is that this technique can be used to cure many diseases and disorders