Chapter 17 - Development Of A Human Embryo

Question 1

What is a Stem Cell?

Answer 1

Unspecialised Cells that have the ability to produce different types of body cells.

Question 2

Why are stem cells unspecialised?

Answer 2

1. NOT specialised cells for any particular use; given the right conditions they may at any time they can become specialised to a particular job.
2. Capable of repeated and continual division by Mitosis ( as needed p)
   - so there is a readily available amount of cells ready to differentiate
3. Can differentiate into Specialised cells
   - unspecialised stem cells develops the characteristics and functions of a particular types of cells
   - from the stem cells inner mass 200+ types of cells can be made
   - made to use for building up and replacement of cell for the maintence of body.

Question 3

What is Proliferation

Answer 3

When cells replicate themselves many times over; and over again for continual amount of cells

Question 4

What is Differentiation

Answer 4

Differentiation is the process by which unspecialised cells develop characteristics and functions of particular types of cells

• Eg Blood, nerve, muscle, bone intestinal cells
• 200+ types of cells that make up mature human body

Question 5

What is a tissue?

Answer 5

A tissue is a group of cells that have a similar structure and work together to perform a common function.

Question 6

How does cell differentiation occur?

Answer 6

Events of mitosis ensure daughter cell receives same genetic information contained in parent cell, therefore each cell every cell in body has same genes.

However some cells eg Stomach; secrete enzymes for digestion, Skin cells; produce pigment, Nerve cells; specialised for transmission of information

Stems cells ( found in inner mass of blastocyst) PROLIFERATE ( undergoes mitosis) - different genes become activated - resulting in differentiation into Specialised cells able to Perform particular functions.

Question 7

What causes cells to differentiate (genes)

Answer 7

Scientists beginning to understand SIGNALS INSIDE and OUTSIDE CELLS TRIGGER stem cell differentiation

INTERNAL SIGNALS are CONTROLLED BY GENES; which are interspersed across long DNA strands and carry coded instructions for all structures and functions of a cell.

EXTERNAL SIGNALS for cells diff. Include

• CHEMICALS SECRETED by other cells,
• PHYSICAL CONTACT with neighbouring cells,
• certain MOLECULES in the cell’s immediate surrounding, its MICROENVIROMENT

Question 8

Stem cells and the process of differentiation

Answer 8

1.After sperm fertilises egg = Zygote which has potential to develop into a complete embryo. At this point fertilised egg cell is a TOTIPOTENT STEM CELL.

2. In first few hours after fertilisation, the fertilised egg undergoes several cell divisions that PRODUCE IDENTICAL TOTIPOTENT CELLS.
   * * because these cells are all totipotent, any one of them has the potential to development into an entire human being.
   * * IDENTICAL TWINS formed when 2 totipotent cells separate and develop into 2 identical embryos.
3. Totipotent cells Undergoes several rounds of CELL DIVISION
4. 5 days after fertilisation they begin to specialise and form a blastocyst; a blastocyst is a ball of cells consisting of hollow outer layer of cells, within which a cluster of cells called inner cell mass.
5. OUTER LAYER OF CELLS will eventually form placenta + other tissues needed for the support and development of foetus.
6. INNER CELL MASS will form all tissues of human body; these cells develop into foetus. Cells in Inner cells mass are PLURIPOTENT STEM CELLS
7. Each pluripotent cell undergoes FURTHER SPECIALISATION into another type of stem cell; MULTIPOTENT STEM CELL
8. MULTIPOTENT gives rise to cells with a particular function.
   Exists in both the embryo and adult body Eg blood cell (RBC)

Question 9

Totipotent vs Pluripotent vs Multipotent

Answer 9

Totipotent Stem Cells
- can give rise to all cell types that make up the human body
- all cell types that make up the membranes that surround the developing embryo (including placenta)
- ability to form the embryo and membranes that will surround, support and nourish it.
Eg early embryo prior to formation of inner mass cells

Pluripotent Stem Cells

• can give rise to all the cell types that make up the body but NOT the cell types that make up embryonic membranes.
• Eg inner mass cells

Multipotent Stem Cells
- can develop into more than one of the cell types that make up the body but NOT all cell types
- produces cells with a particular function
Eg Blood Stem Cells

Question 10

List the Sources of Stem Cells for Research

Answer 10

Stem cells have the potential to be used as a form of therapy to replace damaged or degenerated tissues Eg Parkinson’s Disease, Diabetes and spinal injuries.

3 sources for the stem cells are:

1. Umbilical Chord and Placental Stem Cells
2. Embryonic stem cells
3. Adult Stem Cells

Question 11

Explain how to get stem cells via UMBILICAL CORD AND PLACENTA

Answer 11

Stem cells are present in the blood in the Umbilical chord and Placenta

• MULTIPOTENT stem cells
  Obtained once baby born, these cells can be extracted from the discarded tissue

Used

• benefit of children and adults suffering from bone marrow and blood diseases.(make new and ones replace them)
• Stored in case baby requires replacement tissues or organs later in life.

In Aus

• is a national network of umbilical chord blood bank called AusCord
• parents choose to donate baby’s cord blood to public cord banks
• donated blood available to any suitable recipient
• If parent wishes to have available stem cells and cord for baby later in life they can pay for the cord blood to be stored at private blood bank

Question 12

Explain how to get stem cells via Embryo

Answer 12

Embryonic stem cells are cultured from frozen embryos
Obtained from in-vitro fertilisation clinics.
- ARE PLURIPOTENT stem cells

Unused embryos from IVF may be donated to Research because couple no longer desire additional child, no longer want to continue its storage or donation to use for infertile couples

Potential advantages since stem cells are pluripotent
- can become any cell in body and therefore are more versatile than adult stem cells

disadvantages

• embryos are not derived from the patients own cells
• high chance of rejection from patients body
• ethical issues since obtaining the means destruction of an embryo; governments have strict regulations in place for controlling this type of technology

Question 13

Explain how to get stem cells via Adult Stem Cells

Answer 13

MULTIPOTENT cells = adult stem cells
- can form cells of many kinds of tissue

Most organs of body have stem cells so they can replace dead or damaged cells
Eg bone marrow contains MULTIPOTENT stem cells to give rise to all cells in blood

Potential advantage;
- adult stem cells can be used to treat disease from patients own cells in treatment; therefore body will not reject own cells

Disadvantage
- they are pre- specialised; blood stem cells can only make blood, brain stem cells make only brain cells

Question 14

What are the two types of stems Cells (Stem Cell research)

Answer 14

1. Embryonic cells
   - present in only 3-5 days embryos
   - gives rise, through differentiation to different types of specialised cells in the body; muscle, nerve, skin, bone cells and other cells that make up body tissues
2. Adult Stem cells
   - occurs in adult tissues (bone marrow, muscles and brain) to be able to produce new cells to replace those that are worn out, injured or diseased
   - gives rise to cells that are the same as the tissue in which they are located in
   - Eg. Skin differentiate into new skin cells
   - now given the right conditions they can differentiate into quote different tissues from one located in.
   Eg. Stem cells in bone marrow - heart muscle cells, stem cells from liver - pancreatic cells producing insulin.

Question 15

A source of Adult Stem cells and its use

Answer 15

Adult cells can be found in UMBILICAL CORD AND PLACENTAL BLOOD from newborn babies. = Cord Blood.

Considered Adult stems cells even though from infants because it does not come from embryos.

Cord Blood stem cells can differentiate into red blood cells and immunise system cells.
- they’re stored at birth
- used to treat conditions such as Leukaemia, anaemia, immune system diseases should the donor baby experience later in life
- if matched can be used to treat other patients
Eg for conditions like leukaemia, most suitable transplant is another persons cord blood because patients own cord blood may have potential to develop leukaemia

Question 16

Stems have ability to differentiate into cells of different types of tissue. Why are stem cells useful and subject to intense scientific research?

Answer 16

Research in stem cells is aimed particularly at (1) identifying first how stem cells are able to remain undifferentiated and self-renewing for several year and (2) the signals that stimulate stem cells to begin differentiation

1. If found a way stem cells can be used in CELL BASED THERAPIES to treat diseases.
   - stem cells could be differentiated into particular cells to PROVIDE REPLACEMENT tissues for treating conditions such as stroke, pineal chord injuries, burns, heart disease, diabetes, arthritis, Alzheimer’s and Parkinson’s diseases.
2. In stem cell cell-based therapies additionally stems cells could be used for such things as testing new drugs or toxins, and understanding causes for birth defects.
3. Identifying agents that may kill/harm developing embryo known as TERATOGENS.
   - teratogens are identified when child is exposed to them before birth are born with defects.
   - testing new drugs and other substances on human stem cells, it should be possible: possible to identify those with the potential to disrupt normal embryonic development before tragic birth abnormalities occur.

Question 17

Explain the EMBRYONIC STEM CELL RESEARCH (early) And where obtained

Answer 17

• 1981 scientists 1st succeeded in obtaining stem cells from ear,h mouse embryos and culturing in lab.
• 1998 stem cells were isolated from human embryos and grown in laboratory
• obtained from embryos produced by IVF; embryos produced to assist an infertile couple but no longer needed for possible implantation into female’s uterus. Are available, for research with informed consent of donors.

Question 18

The Process Of using embryonic stem cells for research

Answer 18

1. Embryonic stem cells are obtained from 4-5 days old embryos at the blastocyst stage of development.
2. The inner mass cells of about 30 cells is transferred into a culture dish containing nutrient solution.
3. Over a few days the cells divide, spread over the surface of the culture medium and begin to fill the dish. At this stage they are removed and placed into several fresh culture dishes.
4. This SUBCULTURING can be repeated many times over a number of months, developing a STEM CELL LINE.
5. In 6mnths the 30 cells from original cell mass can develop into cultures containing millions of embryonic stem cells.
6. Cultures are frozen and made available for research in other labs for THERAPEUTIC CLONING.

Question 19

The procedure of therapeutic cloning and why it is a controversial method of obtaining stem cells.

Answer 19

Clones are two or more cells, tissues or organisms that are genetically identical.

Eg Dolly a sheep born in 1997, was the first animal produced that was a clone of its mother.

In therapeutic cloning, a nucleus from a patient’s body cell is inserted into a donors egg from which the egg nucleus has been removed.
1. resulting cell develops into a blastocyst from stem cells from which the stem cell is harvested.

2. Those stem cells are genetically identical cells of the patient’s from whom the nucleus came.
3. A tissue developed from the stem cells and transplanted into the patient will not be rejected. (Big advantage)

The procedure is controversial because the cloned embryo, if allowed to develop could potentially develop into a person who would be a clone of the patient.

Question 20

Explain the ADULT STEM CELL RESEARCH (early) And where obtained

Answer 20

• research began in 1960s when it was discovered that bone marrow contains 2 different types of cells; those that give rise to blood cells and those that differentiate into bone, cartilage and fat storage tissues.
• most research is centred around bone marrow cells; bone marrow stem cells that differentiate into blood cells have been used in transplant for over 30 years.

Question 21

Discoveries and why ADULT stem cells for research

- (recent discoveries)

Answer 21

Recently discovered; Stem cells probably exist in all body tissues although there are only a small number in each tissue.

Scientists are now trying to find ways growing cultures of adult stem cells and inducing them to differentiate into particular cell types for use in treatment of injury or disease.

If patient’s own stem cells could be cultured and then reintroduced into the body, the introduced cells would not be rejected by the patient’s immune system.

Recent discovered that adult stem cells may be able to differentiate into tissues different from the one in which they are located have given much impetus to adult stem cell research.

Question 22

Ethical considerations of STEM CELL RESEARCH

Answer 22

Most promising lines of research involve the use of human embryos
- stem cells cultured in lab are able to differentiate into any type of cell.

It is controversial due to peoples conflict ethical values

PRO- therapies from embryonic stem cells have potential to ALLEVIATE much of HUMAN SUFFERING.
- PREVENTION OF HUMAN SUFFERING is an important moral principle in human societies.

CON - another moral principle is RESPECT for THE VALUE OF HUMAN LIFE

To achieve goal of developing new and potent therapies, that will help human suffering, we destroy human embryos which are potential human life.

Question 23

List of arguments for embryonic stem cell Research need to be considered before arriving a conclusion.
What are they?

Answer 23

1. Production of replacement tissues and organs for transplant will be of great benefit because organs for transplant are always short in supply.
2. Adult stem cells can be used for research, thus avoiding destruction of human embryo.
3. Tissues developed from a person’s own stem cells would not provoke an immune stem response when transplanted into the person’s body.
4. At parents, embryonic stem cell research uses surplus embryos from IVF programs. These embryos would have eventually been destroyed anyway.
5. Embryos used in stem cell research are PRE-IMPLANTATION BLASTOCYSTS that would not be able to develop into a human unless implanted into a females uterus.
6. There is no difference between the prevention of implantation of an embryo using an IUD or the morning after pill and the destruction of an embryo for research purposes.
7. Compared with embryonic stem cells, therapies from adult stem cells will take many more years to develop because adult stem cells cannot yet be easily harvested and cultured in the lab.

Question 24

List of arguments AGAINST embryonic stem cell Research need to be considered before arriving a conclusion.
What are they?

Answer 24

1. The begins of stem cell research as only POTENTIAL BENEFITS. The outcomes of scientific research are unpredictable and the goals may prove to be unattainable or many decade away.
2. In the future, embryos may be produced just for research purposes. This could ultimately lead to a trade in human embryos.
3. Allowing human embryos to be routinely destroyed may mean that society will become desensitised to the destruction of human life.

Question 25

2 Acts in Parliament govern stem cell research in Australia.

Answer 25

1. ‘THE RESEARCH INVOLVING HUMAN EMBRYOS ACT 2002’
   - permits research on surplus embryos from IVF programs.
   - researchers have to apply for a licence to do the research,
   - is carefully regulated to make sure that ethical standards are observed
   - WRITTEN PERMISSION must be obtained from the female (and partner where appropriate) for whom the embryo the embryo was created.
2. THE PROHIBITION OF HUMAN CLONING ACT 2002 banned human cloning, including cloning for therapeutic purposes.
   - only purpose for which human embryos could be created in AUS was to achieve pregnancy.

Question 26

New laws and Acts in Australia

Answer 26

Written in both Acts in Australia was a PROVISION FOR REVIEW AFTER THREE YEARS.

REVIEW BEGAN - second half of 2005

• RECOMMENDED that the PRESENT REGULATORY FRAMEWORKS be MAINTAINED
• THERAPEUTIC CLONING be allowed UNDER STRICT ethical regulations.

In 2007 - australian parliament passed an Act that allow cloning of human embryos for therapeutic purposes be allowed.

Question 27

Acts and laws for embryonic stem cell research in other countries

Answer 27

Since 2002; scientists in the UK have be able to obtain licences to create therapeutic human clones

In the US, Government funding is now available for research on stem cells from human embryos.
- no laws against therapeutic cloning although attempts have been made to pass these legislations.

Question 28

When does human life begin?

Answer 28

A new life begins when an egg is fertilised by a sperm. But when to regard new life as human?

Question with huge disagreement in society.

These arguments have particular relevance to rye questions of Abortion, harvesting stem cells from embryos, disposal of surplus embryos produced by IVF.

Science cannot answer such questions; each must consider the evidence that scientific evidence has produced and make up own minds about the stance on the issue.

1. Many argue that human life begins at the movement of fertilisation; fertilised egg or zygote has a unique set of DNA and all requirements necessary to develop into a human person.
2. Others argue; embryo cannot Be regarded as human until it is implanted into the lining of the mother’s uterus.
   - unless implantation occurs, the embryo cannot develop any further.
3. Another view; developing child becomes a Human when it looks like a miniature human being.
   - occurs at the end of the second month of pregnancy, and from that time on embryo - referred to as foetus.
4. Another argument; foetus becomes human during the 5th month of pregnancy.
   - when activity begins in the cerebral cortex of the developing brain
   - we cannot know whether foetus is aware of its surroundings or feel pain, but during 5th month the brain develops to the point where such processes could be possible.

Question 29

What is a zygote?

Answer 29

A single cell that results from the fertilisation of an egg by a sperm and has potential to grow into a new individual human.

Question 30

What is a blastocyst?

Answer 30

The word ‘blastocyst’ refers to the stage that the human embryo reaches approximately five to six days after fertilisation

Has reached uterus.

Question 31

Explain Early embryonic development and implantation

Answer 31

1. After fertilisation the zygote travels down the Fallopian tube and begins to Divide by MITOSIS
2. Process of Mitosis results in the formation of 2 cells exactly the same as the original parent cell. Then 2 cells divide again by mitosis into 4,8 then 16 and so on.
3. By day 6 after fertilisation, the original zygote has REACHED the UTERUS and developed into a BLASTOCYST.
4. Blastocyst; hollow ball of cells that surround a cavity filled with fluid
   - at one side is a group of 30 cells called INNER CELL MASS (aka EMBRYOBLAST)
5. The INNER CELL MASS WILL DEVELOP INTO THE EMBRYO, and cells that compose it are TERMED STEM CELLS; able to produce any of the different types of body cells.
6. The process called IMPLANTATION; Blastocyst remains Free for 2-3 days, then sinks into soft endometrium (uterine lining) to become firmly attached to the wall of the uterus NATURALLY,
   * This allows blastocyst to gain NOURISHMENT for GROWTH and DEVELOPMENT by ABSORBING NUTRIENTS FROM THE GLANDS AND BLOOD VESSELS OF UTERINE LINING.

Question 32

After Implantation- Continued Embryonic development

Answer 32

7. Continued development depends on the endometrium being maintained
   - HIGH LEVELS of HORMONES in blood STOP the ENDOMETRIUM BREAKDOWN, and the MENSTRUAL CYCLE CEASES
8. During nearly stages of pregnancy the CORPUS LUTEUM produces these hormones until developing placenta can take over the role of maintaining the endometrium.
9. The first 2 months of pregnancy are referred to as the embryonic period; after second month the developing individual is called a FOETUS.

Question 33

Primary GERM LAYERS

Answer 33

While the blastocyst is IMPLANTING in the lining of the UTERUS, the inner cell mass undergoes changes resulting in the formation of the THREE LAYERS OF CELLS = PRIMARY GERM LAYERS

called the

• ECTODERM
• MESODERM
• ENDOERM

Question 34

What are the structures formed by the the 3 PRIMARY GERM LAYERS

Answer 34

• ENDODERM
  1. Epithelium of alimentary canal and its glands (liver and pancreas)
  2. Epithelium of urinary bladder, urethra and fall bladder
  3. Epithelium of tonsils, thyroid, parathyroid and thymus glands
  4. Epithelium of Pharynx, auditory canal, larynx, trachea, bronchi and lungs
  5. Epithelium of vagina and associated glands

MESODERM

1. Skeletal, smooth and cardiac muscles
2. Cartilage, bone, blood and other connective tissue
3. Lymphoid tissue
4. Endothelium of blood vessels and lymphatics
5. Epithelium of the body and joint activities
6. Epithelium of Kidneys and ureters
7. Epithelium of Ovaries, testes and reproductive tracts
8. Epithelium of adrenal cortex
9. Dermis of Skin

ECTODERM

1. Epidermis if skin
2. Hair, nails, glands of skin
3. Lens, cornea and muscles of the eye
4. Receptor cells of the sense organs
5. Epithelium of mouth, nostrils, sinuses, glands of mouth and anal canal
6. Enable of teeth
7. Entire nervous system
8. Anterior lobe of the pituitary gland
9. Adrenal medulla

Question 35

What are the 4 EMBRYONIC MEMBRANEs

Answer 35

During early embryonic period, 4 membranes form.

Lies outside the embryos and serve to PROTECT AND NOURISH IT AS IT DEVELOPS

The AMNION, AND CHORION

THE other 2 membranes not as important in humans as they are in other animals.
- BECOMES PART OF THE UMBILICAL CORD

Question 36

Amnion and Chorion.

Answer 36

Amnion

• amnion is the first embryonic membrane to develop
• by 8th day after fertilisation it surrounds the embryo, enclosing a cavity into which it SECRETES AMNIOTIC FLIUD.
• the fluid serves to PROTECT the embryo against physical injury by acting as a SHOCK ABSORBER
• helps MAINTAIN A CONSTANT TEMPERATURE AND ALLOWS THE DEVELOPING EMBRYO - later foetus - To MOVE FREELY
• usually RUPTURES just before CHILDBIRTH, releasing the amniotic fluid - called ‘breaking of fluid’

CHORION

• formed from the outer cells of the blastocyst together with layer of MESODERMAL CELLS
• the chorion surrounds the embryo and the 3 EMBRYONIC membranes
• as the AMNION ENLARGES, IT FUSES WITH the inner layer of the Chorion
• Eventually becomes the main part of the foetal portion of the Placenta

Question 37

What is a placenta? Explain the Development of the PLACENTA

Answer 37

The placenta is an ORGAN that supplies nutrients to, and removes wastes from, the FOETUS

1. IT IS A COMBINATION OF FOETAL AND MATERNAL TISSUES
   - develops from the part of the chorion
   By the end of the 3rd month, the placenta is completely formed
2. Also serves as an ENDOCRINE ORGAN, producing a number of the hormones necessary to Maintain pregnancy
3. The foetal part of the placenta begins to DEVELOP as the BLASTOCYST is IMPLANTED IN THE ENDOMETRIUM
4. CHORIONIC VILI; Small finger-like projections develop the OUTER LAYER OF CELLS.
   - with numerous blood vessels
   - grows into endometrium (like tree root projects in soil)
5. A fully developed PLACENTA has an ESTIMATED SURFACE AREA OF 16m^2

Question 38

How Can exchange of wastes and nutrients be transferred between the and foetal blood and mother’s blood with them mixing?

Answer 38

As the Chorionic vili penetrate the endometrium they become SURROUNDED BY POOLS OF MOTHER’s blood.
*which is collected in spaces within the endometrium.

In this way the VILI ARE BATHED IN MOTHER’s Blood ; HOWEVER THE FOETAL AND MATERNAL BLOOD DO NOT NORMALLY MIX BECAUSE A FEW LAYERS OF CELLS SEPARATE THE 2 Blood supplies.

• the exchange of materials takes place by DIFFUSION AND ACTIVE TRANSPORT.
• Oxygen and nutrients from the mother’s blood diffuse into the foetal blood and wastes leave the foetus by diffusing into the maternal blood.
• the large number of vili that form provides an extensive surface area across which substances can pass.

Question 39

What is the UMBILICAL CORD and its function?

Answer 39

The Placenta is Attached to the Foetus via the Umbilical Cord.

The cord is sometimes called the baby’s “supply line” because it carries the baby’s blood back and forth, between the baby and the placenta.
**It delivers nutrients and oxygen to the baby and removes the baby’s waste products.

Question 40

What is inside the umbilical cord?

Answer 40

2 UMBILICAL ARTERIES - carries blood to the capillaries of the chorionic vili.

A SINGLE Umbilical Vein; carries blood FROM the PLACENTA - through umbilical cord - to foetus

On maternal side - blood from the mother enters the placenta through the uterine arteries, flows through the blood spaces where the exchange of substances occur and leaves again through the uterine vein.

Question 41

Feature of an embryo at 1 month

Answer 41

After 1 month of growth

1. human embryo is under 4mm long
2. obvious feature is DEVELOPMENT of MUSCLE SEGMENTS on either side of the tube that is to become the BRAIN and SPINAL CORD
3. 30 pairs of blocks of mesodermal tissue; representing the beginnings of the muscles and the vertebrae of spinal column
4. brain is beginning to form
5. tail is evident
6. heart and liver beginning to develop.
7. THROAT region contains a number of PHARYNGEAL ARCHES WITH CLEFTS between them. —> development —> ARCHES will FORM the STRUCTURAL ELEMENTS OF THE FACE and THROAT and POUCHES that DEVELOP IN the CLEFTS will give rise to the EPITHELIAL LININGS and GLANDS ASSOCIATED with the THROAT.

Question 42

Embryo to foetus from 5 weeks - 2months. Basic plan of Organ systems in place; from this stage foetus - developing individual.

Answer 42

Week 5

• ARM and LEG BUDS APPEAR
• arm buds are slightly more advanced, but BOTH ELONGATE RAPIDLY from this time on

Week 8

• END of EMBRYONIC STAGE
• recognisably HUMAN FORM
• ALL ORGANS PRESENT but not MANY are NOT FULLY FUNCTIONAL.
• UNDERGONE considerable GROWTH from MICROSCOPIC cell to 3cm from top of enlarged head to buttocks,
• WEIGHS 1g approx
• HEAD HALF SIZE of EMBRYO
• EYES appear as SLITS having moved from SIDES of head to DIRECTED FORWARD
• JAWS and NOSE are almost FULLY DEVELOPED
• SMALL EARLOBES formed
• ARMS and LEGS are WELL PROPORTIONED
• hands and legs are formed with DISTINCTLY HUMAN FINGERS and TOES
• EXTERNAL SEXUAL ORGANS are EVIDENT

Question 43

Functions of the Placenta

Answer 43

1. Endocrine; secretes a number of hormones necessary for maintaining pregnancy
2. Excretory; transports nitrogenous wastes Eg Urea, uric acid, ammonia, creatinine from the foetal blood to the mother’s blood to mother’s blood supply for excretion by mother’s kidneys
3. Immune; transports antibodies from the mother into the foetal blood supply so that foetus has immunity to infectious disease
4. Nutritional; transport nutrients such as glucose, amino acids, fatty acids, vitamins and minerals from the mother’s blood to the foetal blood; stores some essential nutrients early in pregnancy and releases them later when demand is greater
5. Respiratory; transports oxygen from the mother to the foetus, and carbon dioxide from the foetus to the mother