Development Of Blood Vessels & Fetal Circulation

Question 1

Mention the 3 sets of aortic vessels

Answer 1

Ventral aortic sac
2 dorsal aortae
6 pairs aortic arches

Question 2

Mention parts of aortic vessels which disappear

Answer 2

1. 1st and 2nd arches (almost) and 5th arch (comletely on both sides.
2. Parts of dorsal aortae:
   - the part if dorsal aorta between 3rd & 4th aortic arches (caotid duct) on both sides
   - the part of right dorsal aorta connecting the 7th intersegmental art with the junction between 2 dorsal aortae.
3. The distal part of 6th aortic arch

Question 3

What is the result of upward extension if aortici-pulmonary septum

Answer 3

Aortic sac is divided into:

1. Large upper part connected to ascending aorta which divided into right & left horns connected to 3rd & 4th arches on both sides
2. Small lowercpart connected to pulmonary trunk and to 6th pair of aortic arches.

Question 4

What is the aortic arch derived from?

Answer 4

1. Left horn of aortic sac (proximal part)
2. 4th left aortic arch (middle part)
3. Part of dorsal aorta (distal part, between 4th arch & 7th intersegmental)

Question 5

What is the innominate artery derived from?

Answer 5

Right horn of aortic sac

Question 6

Describe embryology of the carotid system?

Answer 6

On both sides the common carotid artery derived from proximal part of 3rd aortic arch, ECA grows as a bud fromend of it, ICA formed from distal part of 3rd aortic arch and cranial part of dorsal aorta.

Question 7

Describe embryology of subclavian arts

Answer 7

On the right, derived from 4th aortic arch, part of rt dorsal aorta & 7th intersegmental artery
On the left, derived from 7th intersegmantal art

Question 8

The descending aorta is derved from …&…

Answer 8

The left dorsal aorta caudal to the 7th intersegmental art & the single dorsal aorta.

Question 9

Fate of 2st & 2nd aortic arches?

Answer 9

1st, maxillary art

2nd stapedial & hyoid arts

Question 10

Describe embryology of pulmonary arts

Answer 10

Derived from proximal part of 6th aortic arches. The left pulmonary art is connected to arch of aorta by ductus arteriosus dervied from distal part of aortic arch.

Question 11

GR: Position of recurrent laryngeal nerve

Answer 11

It is the nerve of the 6th pharyngeal arch due to caudal migration of the heart the nerve is pulled down by 6th aortic arch forming a loop before it returns back to the neck.

Question 12

Comapre rt & lt recurrent laryngeal nerves positions.

Answer 12

Lt, it hooks around the ductus arteriosus in the thorax
Rt, the distal part of 6th aortic arch disappears & the 5th arch disappears entirely so it hooks around the rt subclavian art in the neck (derivative of 4th arch)

Question 13

Describe PDA & its cause

Answer 13

The ductus arteriosus does NOT close after birth

Maybe 2ry to coarctation of the aorta or may occur alone

Question 14

Describe coarctation of aorta & its cause

Answer 14

Narrowing of segment of aorta may be preductal (PDA) or post-ductal (non-PDA)
Cause is unknown may be fetal hypoxia leading to proliferation of endothelium & hypertrophy of muscle layer.

Question 15

Describe double aortic arch & its cause

Answer 15

Right & left aortic arches arise from ascending aorta, form a vascular ring around trachea & esophagus then unit forming single descending aorta
Due to persistance of part of right dorsal aorta between 7th intersegmental art and junction between 2 dorsal aortae.

Question 16

Describe right aortic arch & its cause

Answer 16

Reversal of the normal, with right ductus arteriosus

Due to reversal of the fates of 4th & 6th aortic arches & rt & lt dorsal aortae.

Question 17

Describe interrupted aortic arch & its cause

Answer 17

The ascending aorta and 2 common carotid arteries. Desecnding aorta arises from ductus arteriosus. Rt subclavian has abnormal origin.
Due to disappearance of 4th aortic arch on both sides

Question 18

2 vitelline veins drain ….&….

Answer 18

Yolk sac & gut

Question 19

Describe fate of the vitelline veins

Answer 19

Caudal to septum transversum, form shaped anastomosis by 3 transverese channels which later disappear leaving portal vein with its 2 branches + splenic vein & superior mesenteric artery.
Within septum transversum, interrupted by gowing cords of hepatocytes forming hepatic sinusoids
Between septum transversum & sinus venosus: they form right & left hepatic veins which unit into common hepatic vein the lattercopens into right atrium and gives upper part if IVC

Question 20

Define the umbilical veins

Answer 20

2 veins which carry oxygenated blood from the chorionic villi to the sinus venosus after passing through septum transversum

Question 21

Fate of umbilical veins

Answer 21

Right disappears
Left, cranial to septum transversum disappears, within septum transversum joins liver sinusoids a new channel is formed between common hepatic vein and left umbilical vein called ductus venosus. Caudal to S.T. remains & connects placenta to left branch of portal vein.

Question 22

Define & their fate common common cardinal veins

Answer 22

2 veins which drain body walls & end in sinus venosus
They are formed by union on ant & post cardinal veins
Fate, rt, lower part of SVC below azygos. Lt, oblique vein of lt atrium

Question 23

Define ant cardinal veins & their fate

Answer 23

2 veins which drain cephalic part of body, become connected by oblique anastomotic channel which carries blood from left to right side.
Fate, rt, right bracheocephqlic vein & rt IJV & part of SVC. Lt, lt IJV & lt superior intercostal vein.
Oblique anastomotic channel, left bracheocephalic vein.

Question 24

Define post cardinal veins & their fate

Answer 24

2 veins which drain caudal part of embryo become connected by iliac anastomotic channel
They disappear & become replaced by sub & supracardinal veins.
Remnants of rt, root of azygos & rt common iliac vein. Lt, left common iliac vein completed by iliac anastomosis.

Question 25

Sub or supracardinal veins appear first?

Answer 25

Subcardinal

Question 26

Mention derivatives of subcardinal veins

Answer 26

On both sides, cranial gives suprarenal veins & caudal gives gonadal veins. On right side most of the cranial part becomes segment of IVC

Question 27

Mention derivatives of supracardinal veins

Answer 27

Become disrupted in region of kidneys
Cranial part: on right, azygos vein. On left, hemiazygos vein.
Caudal part: Rt, segment of IVC, rt, disappears.

Question 28

Mention derivatives of transverse anastomsis

Answer 28

Between rt & lt supracardinal veins, connection of azygos with hemiazygos
Between rt & lf subcardinal, lt renal vein
Between supra & subcardinal, parts of both reanl veins & segment of IVC

Question 29

Mentio sources of IVC

Answer 29

1. Hepatic segment:continuation of common hepatic vein which opens into right atrium from terminal part of Rt. Vitelline vein.
2. Hepatic-Subcardinalsegment:
   a connection that develops between the common hepatic v. and the right subcardinal v.
3. Subcardinal segment: from the right subcardinal v.
4. Subcardinal- supracardinal segment: from the right subcardinal- supracardinal anastomosis.
5. Supracardinal segment: from the caudal part of the right supracardinal v. (Right sacro-cardinal)

Question 30

Describe the double SVC & its cause

Answer 30

An additional left SVC which opens in rt atrium via coronary sinus that is enlarged.
Due to failure of formation of cranial anastomosis

Question 31

Describe the right SVC & its cause

Answer 31

Opens into right atrium via coronary sinus that is enlarged

Due to reversal of the shunt

Question 32

Describe the double IVC & its cause

Answer 32

The lt common iliac vein doesn’t join the right but continues as lt IVC which ends in left renal vein
Due to disappearnce of iliac anastomosis & persistance of caudal part of left supracardinal vein.

Question 33

Describe the absent IVC & its cause

Answer 33

The IVC doesn’t drain into the rt atrium but drains via azygos v (which is enlarged) then to SVC.
Due failure of anastomosis between subcardinal v & common hepatic vein instead anastomses with suoracardinal v.

Question 34

Most blood from left umbilical vein passes through

Answer 34

Ductus venosus

Question 35

What happens to fetal circulation during uterine contraction?

Answer 35

Physiological sphincters in ductus venosus divert blood to hepatic sinusoids, in case of high umbilical vein blood flow to prevent overloading of the heart

Question 36

Most of blood of IVC, passes to …..through….

Answer 36

Left atrium

Foramen ovale

Question 37

GR, Most blood passes through foramen ovale

Answer 37

The inferior border of septum secondum guides it
The foramen ovale lies opposite the opening of IVC
Pressure in left atrium is lower than right

Question 38

Mention the highly oxygenated fetal organs

Answer 38

Heart, head and neck, upper limb.

Question 39

Describe the path of completely deoxygenated blood

Answer 39

Enters via SVC, to right ventricle where it is mixed with oxygenated blood then pumped to pulmonary trunk then to ductus artriosus and the aortic arch after its 3 branches.

Question 40

Mention functions of mixed blood

Answer 40

Supply abdomen and lower limbs
Pass in common iliac then intetnal iliac arteries then to umbilical arteries then to placenta where gas exchange occurs and the cycle repeats

Question 41

GR, Pressure of atria equalize at birth & what is the resuly

Answer 41

1. Respiration begins on exposure to cold tempreture, leading to return of blood to left atrium from functioning lungs
2. The umbilical cord is ligated so no blood returns via occluded umbilical vein
   Thus, septum primum and secondum fuse amd foramen ovale is closed.

Question 42

Umbilical vein gives….

Bilical arteries give….

Answer 42

Ligamentum teres of the liver

Medial umbilical ligaments

Question 43

Occluded ductus venosus gives…

Occluded ductus arteriosus gives…

Answer 43

Ligmentum venosus

Ligamentum arteriosus