Case 2- embryology

Question 1

Ovulation

Answer 1

Release of an egg

Question 2

Fertilization

Answer 2

When an egg and sperm combine to form a zygote

Question 3

Conceptus

Answer 3

The structure in the uterus during pregnancy which will develop into the baby i.e. embryo or zygote

Question 4

Cleavage

Answer 4

Cell division

Question 5

Gastrulation

Answer 5

The movement of cells to produce the three germ layer

Question 6

Bilaminar disk

Answer 6

The two layers of the cell mass which our separated by an extracellular basemen membrane

Question 7

Trilaminar disk

Answer 7

When the cell mass goes from having two distinct layers to having three

Question 8

Morula

Answer 8

When the early stage embryo consists of 16 cells

Question 9

Pre-conceptus

Answer 9

The conceptus before implantation, the cell division period between 1 and 2

Question 10

Embryo

Answer 10

The conceptus after implantation, between weeks 3-8

Question 11

Foetus

Answer 11

The conceptus between weeks 9-38

Question 12

Organogenesis

Answer 12

Development of organs

Question 13

What stages overlap in early human development

Answer 13

Neurulation and folding
Gastrulation and neurulation
Placental villus formation and implantation/gastrulation/ neurulation

Question 14

Ovulation

Answer 14

In the ovaries one of the oocytes matures fully and undergoes follicle rupture releasing an oocyte into the uterine tubules. In the ovaries a corpus luteum is formed which releases Progesterone. The oocyte moves from the infundibulum to the ampulla along the uterine tubes. Sperm moves to the ampulla through cervical contraction.

Question 15

Fertilization (day 0)

Answer 15

• Sperm penetrates the corona radiata
• The sperm head attaches to the zona pellucida
• Acrosome reaction
• Sperm penetrates the zona pellucida
• Sperm binds to the plasma membrane and then enters the oocyte.

Question 16

What happens stright after fertilization

Answer 16

Egg cell becomes impenetrable so no other sperm fertilise it. Sperm head form the pronucleus and causes the oocyte to complete its second mitotic division to form a second polar body which forms the female pronucleus

Question 17

Embryology between days 1 and 2

Answer 17

Fertilisation forms a zygote which undergoes cell division, though its total size remains the same the number of cells increase. This cell division is known as cleavage, each of the cells is known as blastomeres. It moves along the uterine tube.

Question 18

Embryology day 3-5

Answer 18

The morula forms which is when differentiation of the cell begins. Cell division continues till you get a blastocyst at day 5, it’s a ball of cell containing a blastocoel cavity. At day 5 it implants into the uterine wall of the endometrium for nutritional support

Question 19

Implantation embryology

Answer 19

Starts to implant between 5 and 6 days. The trophoblast cells on the blastocyte will form the placenta, the inner cell mast are going to form the baby. At around 9-10 days the blastocyst is almost completely embedded within the uterine wall. The uterine lining will reform and enclose the blastocyst. The syncytiotrophablast link up with the maternal blood supply to form the placenta. The cytotrophoblast are the original trophoblast cells that the syncytiotrophablast emerge from and are involved in implantation.

Question 20

Embryology- what are the three germ layers

Answer 20

Ectoderm, endoderm and mesoderm. The ectoderm is on the outside

Question 21

Embryology- what were the original two layers?

Answer 21

Hyperblast (front) and epiblast (back). Surrounded by yolk sac ventrally and amniotic cavity dorsaly

Question 22

Embryology- Gastrulation

Answer 22

Between days 13-18. In the epiblast layer there is a primitive streak which contains the primitive groove. The cells from the epiblast migrate through the groove becoming either the mesoderm or endoderm. The cells which don’t go through it become the ectoderm.

Question 23

Embryology- neural induction

Answer 23

Days 16-17. Signals are sent out from the Notochord (in the mesoderm layer) which cause part of the ectoderm (called the neural plate) to become the neuroectoderm. The neural plates edges begin to elevate forming the neural folds on either side of the neural groove. The grooves continue to elevate and move towards the midline

Question 24

Embryology- neurulation

Answer 24

The neural plate sinks below the surface, into the embryo and rolls up into a tube. The neural folds start to fuse, the fusion goes from the middle outwards. The exception is the forebrain region where a second fusion region occurs. This creates two opening, the anterior neuropore, and the posterior neuropore but they eventually close. This forms the neural tube. Crest cells form from the neural tube .

Question 25

Embryology- folding

Answer 25

Says 22-28. Due to the nervous system growing faster then the rest of the embryo. Intracellular clefts form in the lateral plate mesoderm. These spaces become bigger causing the lateral plate to split into two layers, the Parietal mesoderm layer adjacent to the ectoderm, and a visceral mesoderm layer next to the endoderm. The space between is the embryonic body cavity. As the embryo continues to grow, lateral body wall folds form and curve ventrally. This pulls the amniotic cavity towards the midline where they will fuse. The amnion then detaches to surround the embryo. The endoderm form the gut tube which is surrounded by lateral plate mesoderm.

Question 26

What does the neural ectoderm give rise to

Answer 26

Part of the ectoderm which is induced to form a neural plate by the notochord. Will form the nervous system and sensory organs

Question 27

What does the surface ectoderm give rise to?

Answer 27

Form the epidermis of the skin

Question 28

What does the neural crest give rise to

Answer 28

Derived from the neural ectoderm, form the cranial and cardiac nerve cells.

Question 29

What does the mesoderm give rise to?

Answer 29

endothelium, bone, cartilage, skeletal muscle, smooth muscle, blood, lymph, heart, kidneys, spleen, reproductive system and limbs.

Question 30

What does the endoderm give rise to ?

Answer 30

the gut tube, such as the oesophagus, stomach and the small intestine. Also gives rise to abdominal organs such as the liver, pancreas, trachea and lungs.

Question 31

What does the ectoderm give rise to?

Answer 31

Skin, nails and hair

Question 32

Formation of the cardiac crescent

Answer 32

Heart development begins at 16 days with the migration of progenitor heart cells from the epiblast through the primitive node. These cells migrate cranially to form the primary heart shield, this is in the lateral plate mesoderm, around the cranial end of the neural plate. The primary heart shield will form the left ventricle and most of the two atria. The secondary heart field adds cells to both ends of the heart tube. This will form the cardiac crescent, which is the start of heart development.

Question 33

Formation of the heart tube

Answer 33

The cardiac crescent comes together to form a horseshoe shaped tube. This happens when the embryo is undergoing lateral body wall folding. The tube then connects so that the open ends are adjacent to each other, this forms the heart tube. The closed end forms the outflow tract which sprouts the aortic arches. The heart tube forms on day 20

Question 34

Differentiation of the heart tube

Answer 34

Between 20-25 days connections are made as arteries and veins form. At 21 days, further differentiation of the heart tube results in the inflow tract forming the sinus venosus. The outflow tract differentiates into the conus cordis (bulbus cordis), truncus arteriosus and aortic sac. This means blood can now go in and out of the heart. Overgrowth of the head region and the cranial folding position the heart in the thorax. The heart tube also differentiates into a common atrium and common ventricle.

Question 35

Looping of the heart tube

Answer 35

Looping begins in the 4th week, the aortic arch vessels form from the outflow tract. The heart tube folds over on itself to give it its shape. The heart tube gets bigger due to the addition of secondary heart field cells, to form the right ventricle and outflow tract. The venous pole is formed from the opened ends of the tube. Growth of the primitive heart chambers position it to the left of the thoracic chamber. The ventricle, atrium and outflow tracts have been formed but there is no separation.

Question 36

Embryology- separation of the heart summary

Answer 36

The atrioventricular septum of the heart forms at the 4th week of development, in the 5th week the atrial septum, ventricular and aorticpulmonary septum are formed as well

Question 37

Embryology- formation of the atrioventricular septum

Answer 37

The endocardial cushion forms from the side of the heart tube in the AV (atrioventricular) canal. There are 4 cushions. The ventral and dorsal cushions reproduce rapidly and grow towards each other, fusing to separate the common AV canal. These channels separate the atrium from the ventricle. Blood flows via right and left atrioventricular canals. Atrioventricular valves prevent backflow.

Question 38

Formation of the atrial septum

Answer 38

The primary septum at the top of the common atrium. It grows downwards to fuse with the endocardial cushion in the AV canal. Programmed cell death occurs in the upper part of the primary septum and the lower part of the secondary septum, creating the foreman ovale, the primary septum forms a valve over this opening

Question 39

Formation of ventricular septum

Answer 39

The ventricles septum has a muscular portion formed from the expansion of the cardiac crescent in lateral plate mesoderm and division of muscular tissue. It also has a membrane portion made from the neural crest tissue which grow downwards and fuse with the ventricular septum. The neural crest tissue becomes fibrous forming the tricuspid valve on the right and the mitral valve on the left

Question 40

Foreman ovale

Answer 40

A gap between the two septum. The foramen ovale is a cardiac shunt and blood can move from the right to left atrium and bypass the lungs which are non-functional for a foetus. Both atrial septum fuse at birth to form the fossa ovalis.

Question 41

Formation of aorticpulmonary septum

Answer 41

Septation of the outflow tract is due to division and fusion of neural crest tissue, which form on each side of the outflow tract. This is a continuation of the ventricular septum. As it forms it twists 180 degrees so that they are in the right position

Question 42

What do the different cardiac progenitor cells contribute to

Answer 42

Cells that contribute to heart development. In the lateral plate mesoderm you have the cardiac crescent which is made of two types of cardiac progenitor cells, the primary heart field (PHF) and secondary heart field (SHF). The ectoderm forms the cardiac neural crest (CNCC) which is migratory. The PHF forms the heart tube, the SHF migrate in and add to the heart. The CNCC’s contribute to the septa and vessels.

Question 43

ASD

Answer 43

When the patent foramen ovale does not fuse at birth, this is known as the patent foramen ovale or atrial septal defects (ASD)

Question 44

VSD

Answer 44

An opening which allows blood to move from the left to right ventricle. This is due to the membranous ventricular septum and aorticpulmonary septum being shifted to the right. This is due to a genetic abnormality in the cardiac neural crest cells, which leads to impaired migration and adhesion, causing an asymmetric septum. Genetic defect

Question 45

Transposition of the great arteries

Answer 45

Genetic defect which causes the pulmonary trunk and aorta to be swapped. The aorta now goes from the right ventricle, pulmonary trunk from the left

Question 46

Tetralogy of fallot

Answer 46

A neural crest congenital heart abnormality causing CSD, an overriding aorta, pulmonary stenosis and ventricular hypertrophy

Question 47

Patent ductus arteriosus

Answer 47

No blood can go through the ductus arteriosis

Question 48

What are fetal cardiac shunts

Answer 48

Openings/vessels which allow blood to bypass the non-functioning foetal lungs, they close after birth

Question 49

Ductus arteriosus

Answer 49

Connects the pulmonary trunk and the aorta, in adults this fuses and forms the ligamentum arteriosum.