birth and pregnancy 12.1, 12.2, 12.4

What is insemination? 

When the male ejaculates, the spermatozoa are released into the vagina at the entrance to the uterus. This is known as insemination.

Once insemination has occurred where do the spermatozoa travel and what helps with their travel? 

Spermatozoa then travel through the cervix, into the body of the uterus and into the fallopian/uterine tubes. the muscular contractions of the uterus and uterine tube that help to transport the sperm.

Where does fertilization usually occur? 

Fertilisation typically occurs ~ 1/3 of the way down the fallopian tube.

Describe what the secondary oocyte consist of? 

Corona radiata: follicle cells held together by cementing materials that contain acid.

Zona pellucida: A glycoprotein matrix surrounding the plasma membrane.

How can the corona radiate be broken through? 

The acrosome of the spermatozoa contains enzymes that are capable of breaking the cementing material between the corona radiata.

When the spermatozoa encounter the zona pellucida what happens? 

When the spermatozoa encounter the zona pellucida, the acrosomal reaction is initiated.

What happens when a secondary oocyte and spermatozoon fuse? 

This triggers the secondary oocyte to form a fertilisation membrane around the oocyte which prevents the entry of additional spermatozoa.

Once the sperm enters the secondary oocyte enters, what happens to the head of the spermatozoon? 

Once the sperm enters the secondary oocyte, the head of the spermatozoon moves through the cytoplasm and enlarges to form the male pronucleus (haploid).

One the secondary oocyte completes meiosis II after fertilization, what happens to the ova that forms the zygote. 

The nucleus of the ova develops into the female pronucleus (haploid).

The pronuclei fuse to form a single nucleus which is diploid.

The cell is now fertilised and is known as a zygote (diploid).

Once the zygote divides by mitosis, what does it form by day 6. 

By ~ day 6, the original zygote has reached the uterus and has formed a structure known as a blastocyst.

A blastocyst is comprised of ~ 84 cells by day 6.

Describe the blastocysts and what it contains. 

The blastocyst is a hollow ball which is filled with fluid.

At one side of the blastocyst is a group of ~ 30 cells known as the inner cell mass (embryoblast).

The cells of the inner cell mass are pluripotent and will differentiate into the body cells of the embryo.

What is implantation? 

The blastocyst remains in the uterus for 2 – 3 days before sinking into the endometrium and firmly attaching to the wall of the uterus.

What happens when the blastocyst is implanted and what does this provide for the blastocyst? 

Implantation of the blastocyst puts the blastocyst into close contact with glands and capillaries in the uterine lining.

This nourishes the blastocyst by providing it with nutrients necessary for growth and development.

What is vital for the development of the blastocyst?

 the endometrium

How does the corpus luteum maintain the endometrium? 

The corpus luteum maintains the endometrium by producing oestrogen and progesterone. This prevents menstruation.

What are the first 2 months of pregnancy known as and what is the individual called as it develops? 

embryonic period, after the second month, the developing individual is called a foetus.

Once the oocyte is fertilized what type of stem cell is it and what does this mean? 

totipotent stem cell, necessary for embryonic development.

Describe the cells that will develop into the foetus. 

pluripotent stem cells, The inner cell mass will form all the tissues of the human body; therefore, these are the cells that develop into the foetus.

What do pluripotent cells specialized further into?

Multipotent stem cell.

Multipotent cells of the inner cell mass differentiate into 3 layers during the third week of embryonic development. What are they? 

• Ectoderm

• Mesoderm

• Endoderm

Describe what is the ectoderm and what they differentiate into? 

Ectoderm – The outermost germ layer. These cells will differentiate into the cells of the nervous system and skin.

Describe what is the mesoderm and what does it differentiate into? 

Mesoderm – The middle germ layer. These cells will differentiate into the skeleton, muscles, connective tissue, cardiac system, blood, intestines and more.

Describe the endoderm and what it differentiates into? 

Endoderm – The innermost germ layer. These cells will differentiate into the epithelial linings of multiple systems.

Four embryonic membranes form. What do they do for the embryo and foetus and what are they? 

These membranes serve to protect and nourish the embryo and later foetus as it develops.

They are the:

• Amnion

• Chorion

• Yolk sac

• Allantois

What is the amnion and what do the cells in the amnion secrete? 

Amnion – A membrane that surround the embryo.

The cells of the amnion secrete the amniotic fluid which surround the embryo.

What does the amniotic fluid do? 

The amniotic fluid protects the embryo by acting as a shock absorber.

It also helps to maintain a constant temperature and enables the foetus to move freely within it.

What happens to the amnion before childbirth? 

It usually ruptures just before childbirth, releasing amniotic fluid ‘water broke’.

What is the chorion and what does it form? 

Chorion – The outermost membrane, it forms from the trophoblasts.

The chorion forms the main part of the foetal region of the placenta.

What does the inner chorion fuse with and what does the chorion form? 

The inner chorion fuses with the amnion as the amnion enlarges.

The chorion forms the main part of the foetal region of the placenta.

What is the role of the yolk sac? 

The yolk sac is important for the early embryonic blood supply. The Yolk sac provides nutrients and gas exchange between mother and embryo before the placenta takes over this function.

What are the 2 main roles of the allantois? 

Allantois – Serves a role in gas exchange in addition to collecting and storing liquid waste from the embryo.

The allantois also forms part of the umbilical cord.

What does the placenta form from? 

The placenta forms from both foetal and maternal tissues during the first three months of gestation

What is the role/function of the placenta? 

The placenta facilitates nutrient, gas and waste exchange between the physically separated maternal and foetal blood circulations.

The placenta is also an endocrine organ, producing hormones necessary to maintain pregnancy.

What does the placenta contain? 

Small, branching, finger-like projections called chorionic villi develop from the chorion and contain blood vessels.

What do chorionic villi grow into and why? 

The chorionic villi grow into the endometrium. As this occurs, maternal blood pools around the chorionic villi.

Why does foetal and maternal blood not directly mix? 

Foetal and maternal blood does not directly mix due to a few layers of cells separating the blood supplies.

What processes occur for nutrient, has and waste exchange? 

Nutrient, gas and waste exchange takes place via diffusion and active transport between the two blood supplies.

The placenta is attached to the umbilical cord, what is inside it that allows for exchange of nutrients and wastes? 

1. The placenta is attached to the foetus by the umbilical cord.

2. Inside the umbilical cord are two umbilical arteries which carries blood from the foetus to the chorionic villi.

3. A single umbilical vein carries blood from the chorionic villi to the foetus.

What is parturition? 

Parturition is preceded by a sequence of events known as labour.

Prior (before) to labour, what do hormonal changes do? 

Hormonal changes cause the ligaments of the pelvis to soften in preparation for parturition.

Hormones also increase the strength of the uterine contractions.

What 3 processes occur during labour? 

1.Dilation of the Cervix– First Stage

2.Foetal expulsion – Second Stage

3.Placenta delivery – Third Stage

What happens during the last 3 months of gestations(pregnancy) to the uterus? 

During the last 3 months of gestation, the uterus undergoes, weak, irregular contractions which gradually grow stronger and more frequent in the last weeks of pregnancy.

Once labour begins what happens to these contractions? 

They start occurring about every 30 minutes, this begins the birth process and the contractions are now known as labour pains.

What occurs during dilation? 

Dilation lasts ~ 8 – 9 hours for a woman’s first child birth.

During this time, uterine muscle contractions cause the cervix to shorten and widen.

Dilation of the cervix allows the foetus to move deeper into the pelvis.

What happens as the contractions become stronger and more frequent? 

As contractions become stronger and more frequent, the head of the foetus is forced against the cervix.

What happens to the cervix during dilation? 

cervix dilates to ~ 10 cm and forms a single curved passage with the vagina known as the birth canal where the foetus will pass aided by contractions of the uterus and voluntary contractions of the abdominal muscles of the mother.

When does the first stage of labour end? 

Complete dilation of the cervix marks the end of the first stage of labour.

 How does foetal expulsion frequently begin with? 

Foetal expulsion begins when the cervix is fully dilated and ends with the baby is born.

During foetal expulsion the foetus moves through the dilated cervix into the vagina, what does this movement signal? 

The movement of the foetus signals the mother to contract her abdominal muscles.

The skull of the foetus can change change as it passes through the birth canal – why is this not an issue? 

Because the skull/bones of the foetus is still soft and will form to become stronger as foetus ages.

Why does the body of the foetus turn sideways again once the head has emerged? 

The rotation allows the shoulders and the rest of the body to move more easily through the birth canal.

What happens during placenta delivery? 

The uterus continues to contract following foetal expulsion and ~ 5 minutes following birth, the placenta, remains of the umbilical cord and other membranes are expelled – luckily not much blood is lost in this stage.

What does the foetal blood circulation contain to allow it to function efficiently when in the womb? 

The foetal blood circulation has many adaptations that enable it to efficiently carry out its function.

They include the:

• Umbilical vein

• Umbilical arteries

• Ductus venosus

• Foramen ovale

• Ductus arteriosus

Where are the umbilical vessels located within? 

located within the umbilical cord.

Where does the umbilical arteries carry blood from? 

foetus to the placenta.

Where does the umbilical vein carry blood from? 

placenta to the foetus.

Where does 30% of the blood from the umbilical vein go to? 

30% bypasses the liver via the ductus venosus.

Why does the foetal blood not have to all pass through the liver at this stage? 

The mother’s liver is serving the needs of the foetus and so it is not necessary for all of the blood to pass through the liver at this stage.

What are the 2 paths that blood returning from the foetal heart can follow? 

Right ventricle flows through the ductus arteriosus to the aorta.

The ductus arteriosus is a vessel that bypasses the lung, allowing blood in the pulmonary artery to flow directly into the aorta, or it can pass through the foramen ovale into the left atrium.

What does the ductus arteriosus do? 

The ductus arteriosus is a vessel that bypasses the lung, allowing blood in the pulmonary artery to flow directly into the aorta.

Where is the foramen ovale located and what is the benefit of it? 

It is located so that most of the blood entering the right atrium goes through it – this is benefical as the blood coming from the placenta is highly oxygenated and can flow to the developing foetal tissues via the aorta very quickly.

Why does blood not need to enter the pulmonary circulation and where is it directed to instead? 

Therefore, the majority of the blood does not need to enter the pulmonary circulation and so is directed towards the systemic circulation via the foramen ovale.

As only minimal blood is required to enter the pulmonary circulation, what does the ductus arteriosus do? 

As only minimal blood is required to enter the pulmonary circulation, the ductus arteriosus diverts blood from the pulmonary arteries directly into the systemic circulation via the aorta.

Once the baby is born and takes their first breath, what happens to some of the components of foetal circulation? 

The baby’s lungs expand following the first breath which starts a series of events which close off the ductus venosus, ductus arteriosus and foramen ovale.

What happens to the ductus arteriosus as the lungs expand and why is this the case? 

• As the lungs expand, they no longer offer the same resistance to blood flow and so blood flow through the ductus arteriosus decreases.

• Within three weeks the ductus arteriosus completely degenerates into fibrous tissue.

What happens to foramen ovale once the baby is born and how does this occur? 

• Pressure in the left atrium increases as more blood returns from the heart from the lungs.

• This forces the flap of the foramen ovale against the wall of the atrium, closing it off.

• Eventually foramen ovale becomes permanently closed.

What does the foramen ovale fuse with eventually following birth? 

• The flap closes immediately following birth and eventually fuses with the septa.

What happens to the ductus venosus once the umbilical cord is cut? 

• With the cutting of the umbilical cord, blood no longer flows from through the umbilical vessels or ductus venosus.

• The ductus venosus constricts, clots and closes off as no blood is being carried through it.

• Functionally, the ductus venosus closes within minutes of birth.

• Structurally, the vessel forms into fibrous tissue within a week.

What happens to the umbilical vein and artery once the umbilical cord is cut? 

• Similarly, the umbilical vein is obliterated and replaced by fibrous tissue.

• The umbilical arteries are mostly obliterated, however, a portion remains open and integrates into the system circulation.