Embryology- Circulatory System

Because the rapidly growing embryo can no longer satisfy its nutritional oxygen requirements by diffusion alone.

1. Splanchnic mesoderm, which forms the primordum of the heart.
2. Paraxial and lateral mesoderm near the otic placodes from which the internal ears develop.
3. Neural crest cells from the region between the otic vesicles and the caudal limits of the third pair of somites

Angioblastic cords--> heart tubes
-->> Folding==>> Fusion of heart tubes,

22-23 days. Blood flow can be detected by sonography

1. Viteline veins (return poorly oxygenated blood from the umbilical vesicle)

2. Umbilical veins (carry well oxygenated blood from the chorion)

3. Common cardinal veins (return poorly oxygenated blood from the body of the embryo)

Regress

Forms most of hepatic portal system and a portion of vena cava

On each side of the liver, deliver oxygenated blood from placenta to inf. vena cava.

7th week: right umbilical vein disappears. Left carry blood to first sinus venosus, then to liver

Develop in the liver and connect umbulical vein with inf. vena cava (bypass liver)

Primordal placenta

Yolk sac

Main venous drainage system of the embryo

Drain cranial part of embryo, join with posterior cardinal veins to common cardinal veins--> enter sinus venosus.

8th week: anastomose==> Left brachiocephalic vein

Right anterior cardinal vein and right common cardinal vein

Stem of left renal vein, the suprarenal veins and the gonadal veins + part of vena cava

Azygos and hemiazygos veins

Developmental circulatory system providing nourishment before the internal circulatory system takes over in the 5th week.

1. Hepatic segment derived from hepatic vein (right vitelline vein) and hepatic sinusoids

2. A prerenal segment derived from the right subcardinal vein

3. A renal segment derived from the subcardinal anastomosis

4. A postrenal segment derived from the right supracardinal vein

Interrupted abdominal course==> blood drains from lower limbs, abdomen and pelvis to the heart through the azygous system of veins

Persistence of left anterior cardinal vein results in persistent left superior vena cava= double vena cava

Usually common cardinal vein becomes SVC, but in this case it degenerates and left anterior cardinal vein and common cardinal vein develop SVC.
---> blood from the right side is carried by the brachiocephalic vein to the left SVC which empties into coronary sinus.

Fusing of caudal portions of dorsal aorta. The right dorsal aorta regress and the left becomes primordal aorta

Intersegmental arteries in the neck

Thorax intersegmental arteries

Intersegmental arteries in the abdomen

Fifth pair of lumbar intersegmental arteries

Sacral intersegmental arteries

1. Celiac trunk
2. Sup. mesenteric a.
3. Inf. mesenteric a.

Internal iliac arteries
Superior vesical arteries

Medial umbilical ligaments

Gelatinous connective tissue separating thick primordal myocardium from the thin endothelial tube of the heart

Splanchnic mesoderm surrounding pericardial coelom

Gelantinous connective tissue separating primordal myocardium from the thin endothelial tube of the heart

Mesothelial cells that arise from the external surface of the sinus venosus and spread over the myocardium.

Primordal ventricle of the heart

A structure that form when other structures of the heart bends upon itself forming a U- shaped loop because the bulbus cordis and ventricle grow faster then other regions of the heart

Sinus venosus

By the end of fourth week

(Common cardinal vv., umbilical vv., vitelline vv.)--> sinus venosus---> Primordal atrium (SA- valves)---> atrioventricular canal---> primordal ventricle---> bulbus cordis + truncus arteriosus---> aortic sac==> Pharyngeal arch arteries + dorsal aorta

Divide AV canal into right and left AV canal and which partially separate the primordial atrium from the primordial ventricle and also functions as AV valves

Grow from the endocardial cushions--> foramen primum

Becomes progressively smaller and disappears as the septum primum fuses with the fused endocardial cushions---> primordial AV septum

Arise from perforations through the septum primum

Grows in 5-6yh week and overlap foramen secundum

Cranial part disappears. The remaining part form the flaplike valve of the oval foramen

After 3 months of age the valve of oval foramen fuses with septum secundum forming oval fossa

Communicating shunts from left to right anterior cardinal vein.

Smooth part of the wall of the right atrium is called sinus venarum because it is derived from sinus venosus

By the end of 7th week

Incorporated in the ventricles and become conus arteriosus (infundibulum) of the right ventricle and the aortic vestibule of left ventricle

Neural crest mesenchyme

Originate by 180- degree spiraling of the bulbar and truncal ridges.

It divides bulbus cordis and truncus arteriosus into the ascending aorta and pulmonary trunk.

Three swellings of subendocardial tissue around the orifices of the aorta and pulmonary trunk.

5th week

Account for 50 % of infant death during the first year. There are several hypothesis for this, i.e; brain stem developmental abnormality or maturational delay in relation with regulation of cardiorespiratory control.

6-8 per 1000 births

The heart bends to left instead of right and there is a transposition where the heart and its vessels are reversed left to right as in a mirror image.

Faulty development of the sternum and pericardium because of failure of complete fusion of the lateral folds in the formation of the thoracic wall during fourth week.

More frequent in females then in males. Most common ASD is patent oval foramen.

1. Ostium secundum defect
2. Endocardial cushion defect with ostium primum defect
3. Sinus venosus defect
4. Common atrium

Ventricular septal defects (25 % of CHD)- membraneous is most common

Failure of aorticopulmonary septum to develop. VSD is always also present in TA.

Most common cause of cyanotic heart disease in newborns. Often associated with ASD and VSD. Usually patent ductus arteriosus.

Separation of truncuas arteriousus superior to the valve is unequal!
--> small pulmonary trunk (pulmonary stenosis) and large aorta + hypertrohpy of right ventricle and patent ductus arteriosus

Characterized by 4 heart defects:
1. Pulmonary stenosis
2. VSD
3. Dextroposition of aorta
4. Right ventricular hypertrophy

Cyanosis, but not often present at birth

Maxillary arteries, and may contribute to the formation of external carotid arteries

Stems of Stapedial arteries

Common carotid arteries

Left: Arch of aorta
Proximal part: Aortic sac
Distal part: Left dorsal aorta

Proximal part of right subclavian artery

Left 7th intersegmental a.

50 % become rudimentary aa. that regress, and 50 % don`t develop at all

Proximal part of left pulmonary a.
The distal part of the a. form the ductus arteriosus

Proximal right pulmonary a.
Distal part of the a. regenerates

In 10 % of people with congenital heart disease. Most occur distal to origin of left subclavian a. and opening of ductus arteriosus.
Twice more common in males. Postductal coarctation usually leads to poor circulation to lower limbs.

Vascular ring around trachea and esophagus---> respiratory wheezing. Results from failure of the distal part of the right dorsal aorta to disappear

Sphincter mechanism close to the umbilical vein. When the sphincter contracts, more blood is diverted to the portal vein and hepatic sinusoids and less to the ductus venosus.

Crista dividens (inferior border of septum secundum)

About 10 % (the rest bypass lungs by ductus arteriosus and goes to the descending aorta

65 %. 35 % supply the viscera and inferior part of the body

Sphincter in ductus venosus constricts, decreasing pressure in DV and right atrium.

First breaths decrease resistance in pulmonary circulation and increase blood flow, which increase return to the left ventricle which makes pressure in left ventricle higher then pressure in right ventricle---> closing of foramen ovale

96 hours

Oxygen (PO2 > 50mmHg ---> bradykinin released from lungs==> contraction of smooth mm.

Prostaglandins which relax smooth mm.

Hypoxia leads to local production of prostaglandins which keeps DA open

Administer "Indomethacin" which inhibits prostaglandin synthesis

Ligamentum venosum

Blood transfusions

The round ligament of liver (l. teres)

Medial umbilical ligaments, and the proximal part become superior vesical a.

12th postnatal week

Patent ductus arteriosus

A patent ductus arteriosus in the first 24 hours of postnatal life.

At the end of 6th week

From stem cells in the umbilical vesicle (yolk sac) mesenchyme and later from the liver and spleen. They move to bone marrow where they become lymphoblasts.

Day 20 to day 50 after fertilization.