Chapter 19: Pregnancy Development Conception to Newborn

2. The Embryonic Phase

- During weeks through 8 an embryo develops - It undergoes cell division - After 2 months its becomes a fetus

The Ectoderm

- is on the outer surface of the embryo in contact with the amniotic fluid -from this layer emerges the epidermis, the entire nervous system, portions of the eyes and teeth, the posterior pituitary glands, the adrenal medulla, and the epithelial linings of the digestive tract.

2. Differentiation

- the cells of the developing infant begin to specialize - these cells take on different forms and function

3. Morphogenesis

- the sum of the total of the cell differentiation is morphogenesis the spectacular changes in shape and functions of the early embryo, embryo, the fetus and their organs and tissues - both differentiation and morphogenesis result in growth, increasing # of cells, size and mass

1. The Embryonic phase

-The ovulated ovum is fertilized by the sperm -the resulting zygote is quickly transformed by cell divisions into a blastocyte that is implanted into the uterus -this phases lasts roughly 2 weeks and ends with the formation of the embryo

3. The Fetal Phase

-from weeks 9 through birth the fetus undergoes yet more spectacular transformations and becomes fully human • Inside the embryo and later the fetus development needs precise control as one cell divides over and over to form the billions of different cells in the body of the infant • The timing of those divisions and the completion of major events such as the development of a heart a central nervous system

1. Cleavage

-the zygote undergoes cleavage a series of rapid cell divisions in then first four days after fertilization. -this process does not increase the size of the zygote -it divides the zygote into many cells forming a ball of cells of roughly the same size as the original undivided zygote

3 basic kinds of cellular division and development

1. Cleavage 2. Differentiation 3. Morphogenesis

Into 4 tissue types of the Body:

1. Epithelium tissue 2. Connective tissue 3. Muscular tissue 4. Nervous tissue

Development: Week 1

1. Fertilization (occurs in uterine tube 12-24 hours after ovulation) 2. Cleavage (first cleavage completed about 30 hours after fertilization) 3. Morula (3-4 days after fertilization) 4. Blastocyst (4 ½ -5 days after fertilization) 5. Implantation (occurs about 6 days after fertilization)

What do you test for during pregnancy to fin out if you are pregnant or not

HCG, the hormone tested for in early pregnancy tests

Trophoblast

In the outer layers of a cell the trophoblast surrounds the inner cell mass

3 distinct phases of prenatal development

The Embryonic phase, The Embryonic Phase and the fetal phase

Fetal Development: week 9

after conception is a stage of rapid organ growth and maturation

The amnion (Extra embryonic Membrane section)

closest to the embryo, lines the amniotic cavity, producing a diffusion area for the amniotic fluid

Ambiguous sex (HERMAPHRODITE)

determination arises out of hormonal imbalances -The spectacularly complicated timing and choreography of hormones, cell division and growth, and organ and tissue development can lead to extraordinary events including one terms ambiguous sex determination or intersexuality

The Mesoderm

develops between the endoderm and ectoderm responsible for the dermis, all connective tissues including the skeletal system, muscles, blood, kidneys, testes or ovaries and the reproductive ducts as well as the lymphatic vessels

3 Germ Layers

endoderm, ectoderm, and mesoderm

The amniotic fluid (Extra embryonic Membrane section)

fluid protects the developing embryo and fetus from outside injury allows free fetal movements so the muscular system can grow symmetrically, maintains a constant temperature and permits proper lung development

Maternal oxytocin

initiates rhythmic contractions

Second Stage of Delivery: Expulsion

is relatively short usually lasting less than an hour

The chorion (Extra embryonic Membrane section)

is the outermost layer of the extra embryonic membrane • The chorion develops fingerlike extensions that are produced into the thickened endometrial lining

Path of a sperm cell:

o Corona radiata o Zona pellucida o Plasma membrane of secondary oocyte o Cytoplasm of secondary o Sperm cell penetrating a secondary oocyte. Only one sperm cell is able to enter the oocyte membrane. This ensures a single sperm will fertilize the egg

The allantois (Extra embryonic Membrane section)

provides the starting material for the blood vessels of the umbilical chord • These vessels will transport fetus blood to and prom the placenta exchange surfaces

First Stage of Delivery: Dilation

the fetal head presses on the cervix

The Endoderm

the innermost layer, produces the alveoli, liver most endocrine glands (pancreas, thyroid, parathyroid, anterior pituitary gland and thymus), tonsils and portions of the inner ear

Genital development: 10 weeks

the penis forms or the clitoris forms

The final Stage of Delivery

the placenta and umbilical chord are expelled

Chronic Villus sampling-

used in this test a small bit of the chronin is removed usually between 10 and 12 weeks early enough to allow for an abortion if defect is detected • Looks for abnormalities such as trisomy, down syndrome etc

Capacitation

• A traveling sperm undergoes capacitation- changes that make it able to fertilize the egg - the flagellum moves faster - the membrane of the sperm head changes so that it can fuse with an ovum -the acrosome enzymes are primed to digest the protective layers surrounding the egg allowing the male DNA to enter the egg the process of capacitation takes 7 hours o any sperm that reaches the ovum before completing capacitation cannot fertilize the egg , the corona radiata

Prenatal Analysis

• Amniocentesis and chronic villus sampling key data information on the genetic health of the fetus

Fertilization

• Fertilization creates an entire diploid genome • New life begins as sperm fuses with egg DNA - the sperm travel up the female tract propelled by muscular contractions of the female organs as well as the sperm's flagella • Once egg and sperm fuse a zygote forms- 2n, 23 and 23 chromosomes, one set of 23 form each parent. • The corona radiata is composed of cells from the ovarian follicle still clinging to the ovum • The zone pellicuida is a clear looking layer between the corona radiate and the ovum membrane

Embryonic Development: weeks 5-8

• From weeks 5-8 week the embryo becomes increasingly human in appearance • The Tail that appeared in the first month regresses • The head enlarges • Limb buds that appeared in the first month are forming structures that look very much like arms, legs and hands feet • The gonads are formed • The nose is flat • The eyes are widely spaced and open • All of the major organs and organ systems are present

Implantation

• Implantation occurs as the blastocyst tentatively attaches to the uterine wall • As the trophoblast enzyme digest the endometrium the blastocyst trophoblast develops into the chorion • This tissue one of the fetal membranes will form the exchange membrane between fetal and maternal blood • As the embryo develops this layer surrounds the new life • Eventually the chrion becomes the main embryonic contribution to the placenta • Blastocyte placement can cause problems • If it settles lower in the uterus a life threatening condition called placenta previa may develop • The placenta grows near or over the cervical opening

Labor

• Initiates the end of pregnancy • labor begins with the hormonal triggers that are though to originate in the fetal pituitary glands • the fetal anterior pituitary gland secretes hormones that affect the placenta • the placenta increases production of estrogen and decreases production of proestrogen

The Embryonic Stage (Additional Information)

• It is estimated that the upward half of all conceptions so not result in successful implantation and pregnancy due to the myriad hazards of the early embryonic stage • Embryonic development proceeds from weeks 3- 8 • during this time the embryo undergoes rapid growth, differentiation, and morphogenesis • the rate of natural miscarriage during this time is thought to be nearly 20%

When does Gender Differentiation occur?

• Occurs in About 7 weeks • Prior to the 7th week, the male and female development is the same with two sets of reproductive tubes and no differentiation • Between male and female

Blastocyte

• The fertilized egg becomes a blastocyte -During the blastocyte stage of development some cells • During implantation and development the blastocyte's inner mass is developing

The Placenta

• The placenta is unique • It is necessary for embryonic and fetal development but is disposable • The placenta develops as the embryonic chronic villi extend into the endometrium of the uterus • The placenta works like a large diffusion filter allowing the exchange of nutrients, gases and antibodies between mother and infant • In addition to providing nutrition and oxygen the placenta also produces a range of hormones responsible for maintaining pregnancy

In the 7th week

• if the Y chromosome is present the male tubes will be stimulates, and release testosterone to the new testes will case new male characteristics to form • If no Y chromosomes form than the organs destined to become the testes degenerate and the organs primed to develop into the ovaries will mature instead

Estrogen

• increases oxytocin receptors on the placenta and increases • this combination of factors makes the uterus much more sensitive to oxytocin levels

3rd Trimester

• mother is extremely tired, rapid growth and maturation • the eyes open and close, the sucking response develops • loud noises initiate a startle reaction • heartbeat can be heard- second trimester • after week 38 the baby is ready for the world