Cardiac Embryology

Front 1

Embryologic Terminology:
What is Developmental age?
What is Gestational age?

Back 1

*Developmental age:
-Postovulatory age, fertilization age.
-Embryonic period extends to the end of the 8th week of developmental age.
-Fetal period starts on day 57 and ends with delivery.

*Gestational age: Postmenstrual age (2 weeks prior to fertilization).

Front 2

Overview of cardiac embryology:

Back 2

*First functioning system in the body!
-Begins as a primitive tube.
-Peristaltic waves of contraction start by day 22.
-Blood circulates within the embryo and to the placenta and yolk sac.

*The single heart tube is later partitioned into 4 chambers.

Front 3

Discuss Early cardiac development around Day 15:

Back 3

*The earliest cardiac precursors, located in the lateral mesoderm, move to the midline in two migratory waves and create a crescent of cells consisting of the first and second heart fields.
-FHF expresses the transcription factors TBX5 and Hand1.
-SHF expresses the transcription factor Hand2 and FGF-10.

*The multipotential cells present in both heart fields give rise to endocardium, myocardium, and smooth muscle cells.

Front 4

Diagram of Early heart development:

Back 4

The angioblastic cords appear in the cardiogenic mesoderm during the 3rd week.

Front 5

What happens to the cardiogenic tubes in the 3rd week?

Back 5

Late in the 3rd week, cephalic and lateral folding allow the cardiogenic tubes to juxtapose in the thoracic region; the three heart layers then develop.

A-B. Day 20
C. Day 21
D. Day 22

Front 6

What happens on Day 21?

Back 6

Day 21 – Cells from the second heart field migrate proximally and distally to form the RV, conotruncus (CT) and part of the atria. A series of constrictions and expansions appear in the heart tube.

Front 7

Diagram of Early vascular development:
Where all is there blood flow by the end of week 3?

Back 7

*By the end of the 3rd week, blood flow is established within the embryo and to the placenta and yolk sac.
*Note developing heart tube. Baby gets blood via UMBILICAL VEIN.

Front 8

Discuss heart development during the 4th week?

Back 8

*As the head fold develops, the tubular heart and pericardial cavity move ventral to the foregut and caudal to the oropharyngeal membrane.

*Positions of the pericardial cavity and septum transversum are reversed. The septum transversum now lies posterior to the pericardial cavity, where it will form the central tendon of the diaphragm.

*Problems in this period can result in an ectopic heart--a heart outside the thoracic cavity.

Front 9

Diagram of formation of primitive atria and ventricles:

Back 9

Front 10

Diagram of the Bulboventricular loop:

Back 10

*BV trunk must twist and loop to make room for the heart chambers.
*The D-Loop is normal.
*The L-Loop is not. You'd end up with a heart on the right side of the body!

Front 11

Diagram of developing chambers:

Back 11

Front 12

Diagrams of Formation of the atrioventricular canal:

Back 12

*Occurs in 4th-5th weeks.
*Note development of endocardial cushions.

Front 13

Discuss Partitioning of the primordial atrium:

Back 13

*The shunts are there because it's the only way to get the baby OXYGEN.
*Septum primum-->Foramen primum-->Foramen secundum (of the septum primum)-->Septum secundum-->Foramen ovale

Front 14

Discuss the development of the foramen ovale:

Back 14

*The foramen ovale allows flow from right to left. The septum primum, aka the valve of the foramen ovale, if competent and adequate, prevents flow from left to right.

*If the pressure in the left atrium is greater, there will be no flow through the foramen ovale. After birth there is physiologic closure within hours because of the changed pressure relationships.

*Anatomical closure comes later and never occurs in about one-third of individuals.

*NOTE that for a time, foramen secundum (blue) and foramen ovale (yellow) exist next to each other.

Front 15

Diagram of foramen ovale before and after birth:

Back 15

Front 16

Diagram of sinus venosus at 26 days.

Back 16

A. 26 days. Note sinus venosus with right and left horns.

Front 17

Diagram of sinus venosus at 8 weeks.

Back 17

B. 8 weeks. The right horn has been incorporated into the right atrium. This portion of the RA wall is smooth. The coronary sinus has developed from the left horn.

Front 18

Diagrams of incorporation of sinus venosus into RA and coronary sinus.

Back 18

A. 26 days. Note sinus venosus with right and left horns.

B. 8 weeks. The right horn has been incorporated into the right atrium. This portion of the RA wall is smooth. The coronary sinus has developed from the left horn.

Front 19

Diagram of development of blood supply to the LA:

Back 19

Venous channels from the lung make contact with the wall of the atrium. Tissue comprising the common pulmonary vein and its first branches is incorporated into the wall of the left atrium.
*Only thing left from the primordial atrium is the left auricle.
*In general, "primordial" parts of the heart become "trabeculated." The mature LA is "smooth."

Front 20

Diagrams of IV septum development:

Back 20

Front 21

Role of NCCs in heart development?

Back 21

*Day 28 – Cells from the neural crest migrate into the outflow tract. They separate the right and left outflow tracts and pattern the aortic arch derivatives.

*The contribution of cells of the neural crest to the conotruncus has importance as regards conotruncal abnormalities such as tetralogy of Fallot and interrupted aortic arch. Congenital anomalies associated with this are referred to as conotruncal anomalies.

Front 22

Diagram of start of IV septum development:

Back 22

Front 23

Diagrams of IV septum development:

Back 23

Front 24

Diagrams of blood flow with and without the spiral septum.

Back 24

*Note three cell types with a role. Most common defect!

Front 25

How do the valves develop?

Back 25

*After the endocardial cushions have fused, the AV valves are formed by proliferations of tissue surrounding the AV canals.

*The valves are hollowed out from the ventricular side but tissue of the chordae tendineae is preserved.

*Not as important to know as other parts of heart development.

Front 26

RV anatomy and embryological derivatives

Back 26

*Trabeculated part came from primordial ventricle.
*Smooth part (conus) came from bulbus cordis.

Front 27

Adult derivatives of the heart tube chambers:

Back 27

*Sinus venosus
*Bulbus
*Truncus

Front 28

Contributions of FHF and SHF to the heart:

Back 28

*FHF only gives rise to LV.
*SHF does some spiraling.
*Don't forget about NCCs.

Front 29

Structures derived from the embryonic dilations of the primitive heart tube:

Back 29

Front 30

When is blood flow established within the embryo, placenta, and yolk sac?

Back 30

*By the end of the 3rd week, blood flow is established within the embryo and to the placenta and yolk sac.
*Note locations of oxygenated and deoxygenated blood (and mixed).

Front 31

Development of the Venous system:

Back 31

*Vitelline veins:
-Left regresses, right forms most of the portal system and a portion of the IVC.

*Umbilical veins:
-Right and cranial part of the left UV regress.
-The caudal part of the left UV delivers the well-oxygenated blood from the placenta to the embryo. The ductus venosus connects the UV to the IVC.

*Cardinal veins:
-Anterior – cranial, posterior – caudal circulation.
-8th week, anterior cardinal veins anastomose and form left brachiocephalic vein.
-SVC forms from the right anterior cardinal vein and the right common cardinal vein.

*Vitelline veins are most important to know about (origins of the IVC frequently asked about).
*Anterior cardinal vein and SVC may be asked about, too.

Front 32

Adult derivatives of the cardinal veins:

Back 32

A. 6 weeks B. 7 weeks C. 8 weeks D. Adult

*Posterior cardinal veins
-root of the azygos vein
-common iliac veins

*Subcardinal veins
-stem of the left renal vein
-suprarenal veins
-gonadal veins
-segment of IVC

*Supracardinal veins
-cranial part forms the azygos and hemiazygos veins
-left caudal part degenerates
-right caudal segment becomes the IVC

*Again, IVC development may be a board ?*

Front 33

Discuss Vein anomalies:

Back 33

*All 3 cardinal systems are paired veins.
*Later in development right side predominates.

*Persistence of bilateral nature results in double SVC, double IVC, or both.

*If the hepatic segment of the IVC fails to form, blood from inferior parts of the body drains into the RA through the azygos and hemiazygos veins. The hepatic veins open separately into the RA.

Front 34

Describe the Pharyngeal arch arteries:

Back 34

*Pharyngeal arch arteries are derived from the aortic sac. They terminate in the dorsal aorta of the ipsilateral side. The 6-pair of arteries are not all present at the same time.

*Major derivatives:
*Arch 1: mostly disappear but contribute to maxillary arteries
*Arch 2: mostly disappear
*Arch 3: common and internal carotid arteries
*Arch 4: Right subclavian artery and part of the arch of the aorta
*Arch 5: either rudimentary and degenerates early or doesn’t develop at all

**Arch 6: ductus arteriosus, proximal parts of pulmonary arteries.**

Front 35

Chart of embryonic blood vessel derivatives:

Back 35

Front 36

How far along?

Back 36

*8 weeks. End of embryonal life.
*All parts are in place.
*Subsequently, remodeling only.