abnormalities of human development

Question 1

What causes mal-development

Answer 1

30% genetic
Environmental – 15%
Multifactorial – 55%

Question 2

How are identical twins formed

Answer 2

Identical twins / triplets: one conceptus forms 2 / 3 inner cells masses to form 2 / 3 genetically identical individuals

Question 3

How is a chimera formed

Answer 3

Chimerism: 2 genetically distinct conceptuses combine to form one individual

Question 4

What is mosaicisim

Answer 4

Mosaicism (non disjunction) – differences between cells within one individual

Question 5

Give an example of mosaicism

Answer 5

Type of Down’s syndrome or heterochromia

Question 6

Which chomoasome is eye colour on?

Answer 6

15

Question 7

When does differentiation of eye colour occur

Answer 7

day 22 pf

Question 8

What does mutation in the KITr gene cause

Answer 8

Piebaldism

Question 9

What is the manifestation of Holt-Oram syndrome

Answer 9

Heart defects and triphalengeal thumb

Question 10

What causes achondroaplasia

Answer 10

Chr 3 gain in FGFR3 function

Question 11

After how many weeks is the conceptus a foetus

Answer 11

8

Question 12

when does pre-implantation take place

Answer 12

over 6 days

Question 13

what is a morula

Answer 13

ball of undifferentiated cells

Question 14

whats a blastocyst

Answer 14

structure that has an outer layer of trophectoderm, an inner cell mass, and a fluid-filled cavity.

Question 15

when does implantation occur

Answer 15

10 days post fertilisation

Question 16

what does the inner cell mass become

Answer 16

bilayer disk, composed of hypoblast and epiblast cells

Question 17

what is gastrulation

Answer 17

converts the bilayer of hypoblast and epiblast cells into a trilaminar embryo, containing the three layers of Germ Cells (Ectoderm, Mesoderm and Endoderm), occurring during days 14-18 postfertilisation.

Question 18

what does the ectoderm give rise to

Answer 18

skin and the central nervous system

Question 19

What does the mesoderm give rise to

Answer 19

muscles, blood, skeleton, heart and kidney

Question 20

What does the endoderm give rise to

Answer 20

gut, lungs and liver

Question 21

when have precursors for all internal tissues been laid down

Answer 21

week 4

Question 22

what develops in weeks 5-8

Answer 22

mostly the elaboration of the tissues generated during the early weeks

Question 23

How does thalidomide cause birth defects

Answer 23

affects growth of blood vessels, depriving cells of nutrients, and ability to grow. 8 weeks = arm deformation

Question 24

name the stages of kidney development

Answer 24

Pronephros is the most immature form of kidney
Mesonephros, an intermediate phase
Metanephros is most developed and persists as the definitive adult kidney.

Question 25

When do gonads show sign of differentiation

Answer 25

7 weeks

Question 26

What gives rise to male genital ducts

Answer 26

mesonephric ducts

Question 27

What gives rise to female genital ducts

Answer 27

paramesonephric ducts

Question 28

Describe relationship of developing kidney with ureters and arteries

Answer 28

ureters change length, and grow with kidney, arteries break down and re-form during this process.

Question 29

Name some kidney mal-developments

Answer 29

Pelvic kidney, horseshoe kidney, enlarged renal pelvis

Question 30

when are meso and paramesonephric pathways developed

Answer 30

week 5

Question 31

where does gonadal precursor develop

Answer 31

mesonephric mesoderm

Question 32

What is the role of the primordial germ cell in gondal development

Answer 32

give rise to the gametes within the gonads

Question 33

What is the pathway of the primordial germ cell

Answer 33

hey originate in the epiblast, but then migrate to the caudal part of the yolk sac (Figure 5.4.5A). Once the main caudal structures of the embryo proper have developed, the PGC migrate through the hind-gut and dorsal mesentery to the mesonephros and thence to the developing gonads.

Question 34

What is a key regulator of male devlopment

Answer 34

testosterone from lyedig cells under regulation of maternal Hcg

Question 35

What causes regression of paramesonephric ducts in males

Answer 35

sertoli cells produce anti-Mullerian hormone,

Question 36

What is a common cause of male mal-development

Answer 36

inability to produce the appropriate hormones (testosterone and anti-Mullerian hormone (AMH) or (b) the inability of target tissues to respond to these hormones, normally the result of defects in the cognate receptors

Question 37

What is Androgen Insensitvity syndrome

Answer 37

mutant androgen receptor. There is no or limited virilisation of external genitalia (which show relatively normal female structures). No mesonephric ducts, non descended testis, but no Mullerian duct because sertoli and AMH is normal.

Question 38

What is CAH

Answer 38

21-hydroxylase enzyme (CYP 21A2), so cortisol production from the fetal adrenal is very limited as this enzyme is key in cortisol synthesis. High ACTH leads to androgen production, virilisation of female

Question 39

Describe heart development

Answer 39

cardiogenic cells develop in a U (or horseshoe) pattern outside the embryo proper. These form a pair of heart tubes, which fuse to form a single heart tube by ~21 days post-fertilisation. This tube is already able to pump blood unidirectionally. Looping of the heart and septation give rise to the 4-chambered structure of the normal human heart. During this process the vascular connections are maintained, so that the major veins are connected to the atria, and major arteries to the ventricles. Valves develop, to ensure that blood flows unidirectionally within the heart.

Question 40

Describe foetal heart differences

Answer 40

formamen ovale and ductus arteriousus

Question 41

Describe implications of the RV Aorta, LV PA issue

Answer 41

The aorta is connected to the right ventricle, and the pulmonary artery to the left ventricle. This generates two separate blood flows; oxygenated blood is cycled through the left side of the heart via the lungs; de-oxygenated blood through the right side of the heart to the rest of the body. Before birth, this does not matter, as the foreman ovale and ductus arteriosus allow mixing of the blood flows sufficiently to sustain fetal growth and development. The closure of these connections after delivery separates the blood flows, so the infant becomes cyanotic (‘blue baby syndrome’). Immediate treatment may involve administering prostaglandins to keep the ductus arteriosus open, and perhaps opening of a link between the atria. Definitive treatment would usually involve the switching of the two arteries, to restore the normal blood flows.

Question 42

How is spina bifida prevented

Answer 42

3 months pre-conception folate

Question 43

Describe the process of lung developmetn

Answer 43

``` embryonic 3-8 weeks pseudoglandular 5-18 week cannalicular 16-20 weeks saccular 24-36 weeks alveolar 36-> ```

Question 44

When is surfactant produced

Answer 44

3rd trimester

Question 45

what is an issue with pre-term babies

Answer 45

(Respiratory Distress Syndrome, RDS)