Emybryonic and Foetal Periods

Question 1

When is the embryo’s 3D structure created?

Answer 1

At end of gastrulation, flattened disc of 3 layers from embryo proper. Around the oval disc, attached to the yolk sac, an anchoring point, is where the embryo fold around

Question 2

Types of folding?

Answer 2

Lateral folding - converts the open coelum into a closed cavity, creating thoracic and abdominal cavities and closing fore and hid gut; mid-gut is the last to close. Pulls edges of endoderm towards anterior aspect and unites to gives the gut tube
Cranial folding - forms the foregut and defines the thoracic cavity; developing heart tube is displaced into thw thoracic cavity
Caudal folding - cloacal membrane and connecting stalk are displaced ventrally alongside the neck of the yolk sac, forming the hindgut, anus and umbilical cord

Question 3

Characteristics of months in foetal development?

Answer 3

3rd month - face more human-looking (position of eyes and ears), limbs lengthen, 1 O ossification centres in long bones and skull and sex can be determined by external genitalia

4th and 5th months - rapid increase in length

6th month - rapid increase in weight

Question 4

Describe head vs body development

Answer 4

When head develops, during 3rd month, it is disproportionately large; in later stages, the rest of the foetus begins to lengthen so proportionality is achieved

Question 5

Why does weight gain occur before birth

Answer 5

In preparation for life outside the womb

Question 6

Causes of birth defects?

Answer 6

40-60% unknown
15% genetic factors
10% environmental:
Infectious agent
Radiation
Chemical agents %  pharmaceutical drugs
Nutritional deficiencies
Maternal disease

20-25% multifactorial - may be genetic and environmental causes, etc. E.g: spinal bifida (prevention includes folic acid but there are other factors like a genetic predisposition, etc)

Question 7

Importance of the heart and development?

Answer 7

Begins to develop at week 4 and is essential for continued growth of the embryo

Question 8

Defects during system development?

Answer 8

For each organ system development, earlier critical parts are more prone to serious defects; later parts tend to be minor
Neural system develops longer, so defects can occur throughout

Abnormalities during 1st two weeks results in miscarriage or embryo completely compensating

Question 9

Describe development of the heart

Answer 9

Develops around week 4; first step:
Single heart tube that has an inflow and outflow connects to dorsal ?
As soon as cardiac myocytes differentiate, pumping occurs causing unilateral flow

Heart undergoes looping/folding to put future atria superior and posterior to ventricles

In other words, U-shaped to S-shaped structure

Question 10

Describe normal atrial septation

Answer 10

Growth of 2 septa:
Septum primum (flexible)
Septum secundum (more rigid)
Communication between right and left atria continues (to bypass lungs) until birth -foramen ovale

Question 11

Describe atrial septation 1

Answer 11

30 days
Ultimately, communication between right and left atria is lost but small areas of cell death form new communication openings in upper part

Question 12

Describe atrial septation 2

Answer 12

33 days

Question 13

Describe atrial septation 3

Answer 13

37 days

Important for changes at birth to get rid of communication almost instantly at birth

Question 14

Function of foramen ovale

Answer 14

ADD PICTURE

Question 15

Describe normal ventricular septation

Answer 15

Septation of outflow tract

Muscular portion - grown upwards from wall of expanding ventricle
Membranous portion - growth of tissue from endocardial cushions

Ventricular septation closely linked to septation of the outflow tract

Question 16

Types of congenital heart defects?

Answer 16

Most common birth defect
Wide range of defect types inc.:
Atrial septal defects
Ventricular septal defects
Outflow of tract defects, e.g: transposition of the great vessels
Combination of defects

Question 17

What are atrial septal defects?

Answer 17

ASDs - defects of one or both of the atrial septae

Inc:
Excessive resorption of septum primum
Absent septum secundum
Probe patent foramen ovale - septum primum and septum secundum fail to fuse; mixing of blood prevented due to pressure difference

Question 18

What are ventricular septal defects?

Answer 18

Muscular defect - most common and least severe
Membranous defect - relatively uncommon and very severe
Failure of full septum formation
Transposition of great vessels - aorta exits right ventricle and pulmonary trunk exits left ventricle so deoxygenated blood is pumped around the body

Question 19

4 components of tetralogy of fallot?

Answer 19

Pulmonary stenosis - narrowing; entrance into pulmonary trunk is narrow
Hypertrophy of right ventricle - can occur in response to pulmonary trunk stenosis
VSD - Ventricular Septal Defect
Over-riding aorta