Chapter 28

Coitus

Actual sexual union

Pregnancy

The events from fertalization until birth

Coitus

Actual sexual union

Pregnancy

The events from fertalization until birth

Conceptus

Developing of offspring

Zygote

When there is a new fertalized ovum

embryo

Period from fertalization until the 8th week

Fetus

Period from the ninth week until birth:

1. Leaking from vagina

2. Acidic environment of vagina

3. Inability to apss through cervical mucous

4. Destruction of sperm itself by defensive properties of uterus

Barriers for the sperm to get to egg: [4]

Capacitation

the set of natural physical changes that a spermatozoon undergoes in order to be able to fertilise the ovum

1. Corona radiata

2. Zona pellucida

What two layers of the oocyte does the sper have to rbeach first?

Binds to receptors on zona pellucida. Calcium channels open. and sperm cell releases acrosomal enxymes, sperm is engulphed into cell.

What layer of the oocte does the sperm bind to?

The oocyte puts up a block to polyspermy. It sheds all receptors on the outside.

Forms ovum pronucleus and second polar body (meiosis 1)

Is now zygote

What happens once the sperm is able to penetrate the oocyte? [3]

Cleavage

Period of rapid cell division

Morula

Ball of cells (16+) at 72 hours

Blastocyst

About 100 cells. Has traveled to the uterus, is a fluid filled ball. Flattened trophoblast cells and rounded inner mass cells. (days 3-4)

Forms the embryonic side of placenta. Protects the zygote from immune response from mother.

What do trophoblast cells of trophoblast become?

Become embryonic disc and three embryonic membranes.

What do inner mass cells of trophoblast become?

6-7 days past ovulation, or 12th day of cycle

When does implantation happen?

Huan chorionic gonadotropin (hCG)

Hormone secreted by the trophoblast cells that prompts corpus luteum to continue secretion of progesterone and estrogen. Prevents menstruation and promotes placental development.

3rd month of pregnancy

When is the placenta full formed?

Placenta

Temporary organ that arises from embryonic and maternal tissues. Functions include nutrients, ecretory, endocrine etc

Chorion.

Outermost membrane of the embryo. Develops finger-like villi that become richly vascularized.

Amnion

Layer of embryo that is filled with amniotic fluid

Allantois

Layer of embryo that forms the umbilical cord

Yolk sac

Layer of the embryo that forms the gut and is imortant for circulatory development:

1. Ectoderm

2. Mesoderm

3. Endoderm

Three germ layers of embryo:

8 weeks

When are organs formed?

week 9

When is embryo called a fetus?

27-28 weeks

Age of viability:

Lung maturity is still a concern and surfactant available may not be adequate to supply fetal lungs. Not enough volume to keep lungs open until last 2 months ov development

why wouldn’t a newborn beforer 27 weeks be viable, even if all organs are there?

Yolk sac, by the end of the third week of developmet.

Where do first blood cells arise?

2.5 weeks

When does heart start beating?

System of paired vessels, heart is tubular bent into S shape

Embryonic “heart”:

1. Foramen ovale: mixing of oxygenated and deoxyenated blood

2. Ductus venosus: bipasses liver

3. Ductus arteriosus: bipasses pulmonary circulation

Three vascular shunts in newborns. Organs are bipassed because organs are not functional

Parturition

Process of giving birth

Placenta secretes more estrogen. Causes production of oxytocin receptors. Antagonises calming effects of progesterone, leads to Braxton hicks.

Fetal secretion of cortisol in last weeks of pregnancy stimulates what?

Softening of the cervix. Sends message to mother that it is developed

Surfactant in baby’s lungs causes what to happen?

More strong, frequent contractions

Oxytocin triggers what?

1. STIs

2. POS

3. Cancer

4. Endometriosis

5. PID

Causes of infertility (Some):