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Flashcards in Week 1 Content Deck (67):

Name the four somatic systems.

Skeletal system, articular system, muscular system, integumental system. (S.A.M.I)


Name the four visceral systems.

Cardiovascular & respiratory system, reproductive system, urinary system, gastrointestinal system. ((C.R.)R.U.G.)


Name the four supply systems.

Nervous system, arterial system, venous system, lymphatic system. (N.A.V.L.)


Internal rotation is also known as what kind of rotation?

Medial rotation.


External rotation is also known as what kind of rotation?

Lateral rotation.


Congenital diseases are also known as what?

Birth defects.


Birth defects are only structural. True or false?

False. Birth defects can be both structural and functional.


Congenital diseases are present at or before birth. Approximately how many babies are born with birth defects?



Congenital diseases arise from genetic factors alone. True or false?

False. Birth defects occur due to environmental, infectious, nutritional or genetic reasons.


List at least 3 examples of congenital diseases.

Any 3 of:

- Heart defects
- Orofacial clefts
- Trisomy 21 (Down Syndrome)
- Polydactyly
- Neural tube defects


List and define the three periods of human embryology.

1. "Fertilized egg"/"Conceptus" - Fertilization to the end of the 2nd week.

2. "Embryo" - Beginning of 3rd week to the end of the 8th week.

3. "Fetus" - 3rd month to birth.


Outline the early stages of embryological development.

1. Ovulation - a secondary oocyte is released from the ovary and is swept into the oviduct.
2. Fertilization - a single sperm penetrates the secondary oocyte. Eventually, the sperm and egg nuclei will fuse to form a zygote.
3. Cleavage - the zygote undergoes rapid mitotic cell division as it moves along the oviduct towards the uterus, becoming a pre-embryo consisting of 2 cells, then 4 cells, then 8 cells and so on.
4. Morula - by day 4, successive divisions produce a morula, a solid ball of cells that enters the uterus.
5. Blastocyst - by day 6, the pre-embryo becomes a blastocyst, a hollow ball of cells with a fluid-filled cavity. The blastocyst has freed itself from the zona pellucida and can increase in size.
6. Implantation - the blastocyst attaches to the uterine lining (endometrium) and begins to digest its way inwards. The cells of the inner cell mass begin to form primary germ layers.


Briefly outline the composition of a blastocyst.

A blastocyst has an outer epithelial layer known as the trophoblast. It has a bundle of cells within its cavity known as the inner cell mass.


The trophoblast forms what?

The trophoblast forms extra-embryonic structures (part of placenta).


When does a blastocyst implant into the uterine wall?

Between days 5 and 10.


A late blastocyst is a 3 germ layer stage. True or false?

False. A late blastocyst is a 2 germ layer stage. The inner cell mass splits and forms cavities and the embryonic disk.


What are the two main functions of gastrulation?

To form the primitive streak which defines all of the major body axes and to form the three primary germ layers (ectoderm, mesoderm and endoderm). These three layers give rise to distinct tissues in adults.


Briefly outline the processes of gastrulation.

During gastrulation, a line of thickened cells appear on the epiblast. This is the primitive streak. The primitive streak invaginates to form the primitive groove.

In order for the three germ layers to form, cells must migrate medially and into the primitive groove. First, cells from the epiblast move into the hypoblast to form embryonic endoderm. Next, cells migrate into the space between the endoderm and the epiblast to form embryonic mesoderm. The remaining cells of the epiblast form embryonic ectoderm. The embryo is now trilaminar.


How do body axes differ between embryos and adults?

In embryos, the cranial direction is anterior and the caudal direction is posterior. In adults, the cranial direction is superior and the caudal direction is inferior.


Which structure is vital in setting up left-right asymmetry in the body?

The node.


Which hypothesis best accounts for the formation of left-right asymmetry in the body?

(a) Morphogen hypothesis
(b) Nodal vesicular parcel hypothesis
(c) Two cilia hypothesis

(c) Two cilia hypothesis


Briefly outline the two cilia hypothesis.

Cilia within the node rotate. As there is leftward fluid flow, only cilia to the left detect the flow. This triggers a response in which left-right asymmetry is induced.


What is situs inversus and how frequently does it occur?

Situs inversus is a condition in which organs are mirrored from their regular position. Organs may only be partially mirrored, and in certain cases only some organs are mirrored. Heart defects are a problem commonly associated with situs inversus. Situs inversus occurs in approximately 1:8000.


What is the notochord?

The notochord is cartilage-like transient structure which is important for induction of the neural tube.


How does the notochord form?

There is cranial midline extension from the primitive node and a hollow tube forms. The tube grows in length as cells are added from the primitive node and the primitive streak regresses.


What complication may result if the primitive streak does not regress?

A teratoma may result if the primitive streak does not regress. This is a benign tumour that can be corrected via surgery. Teratomas are the most common tumour in new borns, occuring in 1:35000 births.


How does the neural plate form?

Formation of the neural plate is induced by the notochord. Ectodermal cells differentiate into a thick plate of pseudostratified, columnar neuroepithelial cells known as neuroectoderm. The plate extends from from the cranial end of the embryo to the primitive node.


Formation of the neural tube is also known as what?



How does the neural tube form?

The neural plate invaginates to form a neural groove. The neural folds converge to form the neural tube


Which structures does the neural crest give rise to?

- Dorsal root ganglia
- Enteric ganglia
- Sympathetic and parasympathetic ganglia
- Melanocytes
- Schwann cells
- Muscle, cartilage and bone of the face, skull, jaw and pharynx.
- Dentine


The neural tube is initially one cell layer thick. What results from segmentation of the neural tube?

The cranial end of the neural tube starts to swell and form vesicles. These vesicles give rise to the brain. The remainder of the neural tube gives rise to the spinal cord.


List three ectoderm derived structures.

- The central nervous system
- The epidermis of the skin
- The neural crest


List the layers of skin.

Dermis and Epidermis.


Which primary germ layer is the epidermis derived from? What type of cells colonize the epidermis?

The epidermis is derived from ectoderm. Melanocytes (produced by the neural crest) and Langerhans cells (made from the immune cells of bone marrow) colonize the epidermis.


Which primary germ layer is the dermis derived from?

The dermis of the face is derived from the neural crest. The dermis of the body is derived from mesoderm.


At the end of the third week, the embryo has a flat, ovoid trilaminar disc. In the forth week, body folding commences. What is the main driving force of body folding?

A differing growth rate of the various tissues. The embryonic disk and the amnion have a high growth rate whereas the yolk sac experiences almost no growth.


Which developing structures stiffen the dorsal axis?

The developing notochord, neural tube and somites stiffen the dorsal axis.


What is folded during body folding?

Cranial, caudal and lateral body folds.


Mesoderm is divided into what 3 types of mesoderm?

- Paraxial/somitic mesoderm
- Intermediate mesoderm
- Lateral mesoderm


What does paraxial mesoderm give rise to?

­- Dermis of skin
-­ Axial skeleton
-­ Axial and limb muscles


What does intermediate mesoderm give rise to?

The urogenital system (kidney and gonads).


What does lateral mesoderm give rise to?

Somatic lateral mesoderm gives rise to the body cavity, the pelvis and the limb bones.

Splanchnic lateral mesoderm gives rise to the circulatory system (heart and vasculature).


Paraxial mesoderm in the head region forms what?

Head mesoderm (together with the neural crest) forms the skeleton, muscles and connective tissue of the face and skull.


In the trunk region, paraxial mesoderm forms what?

Somites, which will produce muscle, bone, and dermis.


Which structure gives rise to the kidney?

The metanephros.


Which structures form along the mesonephric duct?

The pronephros, mesonephros and metanephros.


Where do the gonads develop?

The ventro-medial surface of the mesonephros.


Do neural crest cells undergo EMT or MET?

EMT. Epithelial to mesenchymal transition.


Mesenchymal cells are usually ...?

Irregular and migratory.


Does EMT or MET occur with the formation of somites?

MET. Mesenchymal to epithelial transition.


Somitogenesis occurs in which direction?

Cranial to caudal.


Somites re-organise into what?

- Epithelial dermamyotome
- Mesenchymal sclerotome

The epithelial dermamyotome then further differentiates into the dermatome and the myotome.


What does the dermatome give rise to?

The dermis of that section of the body.


What does the myotome give rise to?

Certain muscles in that section of the body.


What does the sclerotome give rise to?

The axial skeleton in that area of the body.


What are the other terms for the mesonephric duct?

The Nephric duct or the Wolffian duct.


Which structure can act as the embryonic kidney?

The mesonephros.


Does a Wolffian duct AND a Mullerian duct form in both females and males?

Yes. However, if the undifferentiated gonads/genital ridge turns into a testis, and the testis produces AMH (Anti Mullerian Hormone), then the Mullerian duct disappears. The testis also produces testosterone which causes the Wolffian duct to differentiate into the epididymus, vas deferens and seminal vesicle. (SRY gene present on Y chromosome).

If the undifferentiated gonads turn into the ovary, no AMH or testoterone is present and therefore the Mullerian duct is the only remaining duct. The Mullerian duct differeniates into the oviduct, the uterus and the upper part of the vagina. (No SRY).


In which sex is there an opening to the peritoneal cavity?



There are two processes in the development of the cardiovasculature system. What are they?

Vasculogenesis and Angiogenesis


Briefly outline Vasculogenesis.

1. Endoderm gives signal to mesoderm cells.
2. Haemangioblast cells form (from mesoderm) and cluster together.
3. Haemangioblast cells differentiate into Haematopoietic cells and angioblast cells.
4. Haematopoietic cells give rise to blood cells; angioblast cells give rise to endothelial cells.
5. First blood vessels form.


Define angiogenesis.

Blood vessel formation from pre-existing vasculature.


Define vasculogenesis.

De novo formation of vasculature.


What is tumour Angiogenesis?

Tumours in hypoxic areas can reactivate angiogenesis (a process in embryonic development) to vascularize, grow and metastasize to other parts of the body.


Briefly outline the development of the heart.

Vasculogenesis gives rise to two endocardial tubes. The endocardial tubes fuse to form one primitive heart tube. with two inlets and two outlets. The tube bulbs out and forms vesicles, looping and forming septa. Ultimately forming a four-chambered heart with two inlets and two outlets.


Briefly outline Lymphangiogenesis.

Shortly after the first blood vessels form, lymphatic endothelial cells develop from the pre-existing Cardinal vein. VEGF-C is produced from an unknown place and cells migrate from the Cardinal vein to form a primary lymph sac. The lymph sac then matures and forms lymph vessels to form the entire lymphatic system.


Briefly outline angiogenesis.

Near a pre-existing blood vessel, in a hypoxic area, cells produce VEGF-A (growth factor). The growth factor binds to receptors on the blood vessel, inducing the formation of extensions which branch out to create new vessels. The new blood vessels grow toward the hypoxic area to deliver needed oxygen.