development of human embryo

What is a stem cell?

A stem cell is an unspecialised cell that can undergo repeated mitosis (proliferation) and differentiate into specialised cell types.

What is potency?

Potency is the ability of a stem cell to differentiate into different types of cells. The greater the potency, the more cell types it can become.

What is a totipotent stem cell?

A totipotent stem cell can develop into all cell types, including the cells of the embryo and extraembryonic structures such as the placenta.

What is an example of a totipotent stem cell?

The fertilised egg (zygote) is a totipotent stem cell.

Why are totipotent cells considered the most powerful stem cells?

Because they can give rise to every cell required to form a complete organism, including both the embryo and the placenta.

How do identical twins form?

Identical twins form when early totipotent cells separate and each develops into a separate embryo.

What is a pluripotent stem cell?

A pluripotent stem cell can differentiate into all body cell types but cannot form extraembryonic membranes such as the placenta.

Where are pluripotent stem cells found?

They are found in the inner cell mass of the blastocyst.

What is the difference between totipotent and pluripotent stem cells?

Totipotent cells can form both the embryo and placenta, whereas pluripotent cells can form all body cell types but cannot form the placenta.

What is a multipotent stem cell?

A multipotent stem cell can differentiate into a limited range of related specialised cells.

Which stem cell type has the greatest potency?

Totipotent stem cells.

Arrange stem cells from greatest to lowest potency.

Totipotent → Pluripotent → Multipotent.

What is differentiation?

Differentiation is the process by which unspecialised stem cells become specialised cells with specific functions.

Do specialised cells have different DNA from stem cells?

No. The DNA remains the same; different genes are activated or deactivated.

What is proliferation?

Proliferation is repeated cell division by mitosis.

What is mitosis?

Mitosis is a form of cell division that produces genetically identical daughter cells.

What is a zygote?

A zygote is a fertilised egg cell formed when a sperm fuses with an egg.

What happens to the zygote after fertilisation?

The zygote undergoes repeated mitotic divisions to produce many cells.

What is a blastocyst?

A blastocyst is an early stage embryo consisting of an outer layer of cells and an inner cell mass.

Approximately how long does it take for a blastocyst to form?

About 6 days after fertilisation.

What forms the outer layer of the blastocyst?

The outer layer develops into structures that contribute to the placenta.

What is the inner cell mass?

A group of cells inside the blastocyst that develops into the embryo and contains pluripotent stem cells.

Which part of the blastocyst develops into the foetus?

The inner cell mass.

Which part of the blastocyst contributes to the placenta?

The outer layer of cells.

What is implantation?

Implantation is the process in which the blastocyst embeds into the endometrium of the uterus.

Why is implantation important?

It allows the developing embryo to obtain nutrients and oxygen from the mother.

What is the endometrium?

The endometrium is the inner lining of the uterus.

What is the corpus luteum?

The corpus luteum is a structure in the ovary that produces hormones after ovulation.

What is the role of the corpus luteum during early pregnancy?

It produces hormones that prevent the endometrium from breaking down until the placenta takes over.

What is gastrulation?

Gastrulation is the stage of development where the three primary germ layers form.

Why are germ layers important?

They give rise to all tissues and organs of the body.

What are the three primary germ layers?

Ectoderm, mesoderm, and endoderm.

What does the ectoderm form?

The ectoderm develops into structures such as the nervous system and skin.

What does the mesoderm form?

The mesoderm develops into muscles, bones, blood vessels, and connective tissues.

What does the endoderm form?

The endoderm develops into the digestive tract, respiratory tract, and associated organs.

What is the amnion?

The amnion is the membrane that surrounds the developing embryo.

What is amniotic fluid?

Amniotic fluid is the liquid surrounding the embryo within the amnion.

What are the functions of amniotic fluid?

It cushions the embryo, acts as a shock absorber, maintains a stable temperature, and allows movement.

What happens to the amnion during childbirth?

It ruptures, releasing the amniotic fluid.

What is the chorion?

The chorion is an outer membrane formed from the outer cells of the blastocyst and contributes to the placenta.

What is the main function of the chorion?

It forms the major foetal part of the placenta.

What are chorionic villi?

Chorionic villi are finger-like projections containing many blood vessels that grow from the chorion.

Why are chorionic villi important?

They greatly increase the surface area available for exchange between mother and foetus.

Where do chorionic villi grow?

They extend into the endometrium and become surrounded by maternal blood.

Do maternal blood and foetal blood mix?

No. Maternal and foetal blood remain separate.

How are substances exchanged between maternal and foetal blood?

By diffusion and other transport mechanisms across the placental barrier.

What is the placenta?

The placenta is an organ that facilitates exchange of substances between the mother and the developing foetus.

What is the role of the placenta in respiration?

It transports oxygen to the foetus and removes carbon dioxide.

What is the role of the placenta in nutrition?

It transfers glucose, amino acids, fatty acids, vitamins and minerals from the mother to the foetus.

What is the endocrine role of the placenta?

It produces hormones required to maintain pregnancy.

What is the excretory role of the placenta?

It removes metabolic wastes such as urea, uric acid, ammonia and creatinine from foetal blood.

What is the immune role of the placenta?

It transfers antibodies from the mother to the foetus, providing protection against some diseases.

What substances pass from the mother to the foetus through the placenta?

Oxygen, glucose, amino acids, fatty acids, vitamins, minerals and antibodies.

What substances pass from the foetus to the mother through the placenta?

Carbon dioxide, urea, uric acid, ammonia and creatinine.

What is the umbilical cord?

The umbilical cord is a structure that connects the foetus to the placenta.

How many blood vessels are in the umbilical cord?

Three vessels: two umbilical arteries and one umbilical vein.

What do the umbilical arteries carry?

The umbilical arteries carry blood from the foetus to the placenta.

What do the umbilical arteries transport to the placenta?

Carbon dioxide and metabolic wastes from the foetus.

What does the umbilical vein carry?

The umbilical vein carries blood from the placenta to the foetus.

What does the umbilical vein transport to the foetus?

Oxygen and nutrients.

What is a foetus?

A foetus is the developmental stage after the embryo stage when major organs have begun to form.

State the development sequence from fertilisation to foetus.

Fertilisation → Zygote → Mitosis → Blastocyst → Implantation → Gastrulation → Formation of amnion and chorion → Placenta development → Embryo → Foetus.

Why can't pluripotent stem cells form a complete organism?

Because they cannot develop into extraembryonic tissues such as the placenta.

What is the key fact about mother and foetal blood in the placenta?

The blood supplies remain separate and do not directly mix.

What are the five major functions of the placenta?

Respiration, nutrition, endocrine support, excretion and immunity.