Early Vascular Development

Introduction

This lecture will introduction to the events in early embryonic development that relate to mesoderm and early cardiovascular development. Most texts will separate heart development from vascular development in order to simplify their descriptions of cardiovascular development, though the two are functionally and embryonically connected. Note that we will be returning later to discuss the late development of the heart and vascular changes.

Lecture Objectives

Understanding of mesoderm development
Understanding of heart tube formation and early development
Understanding of early blood vessel and blood development
Brief understanding of vascular growth and regression
Brief understanding of vascular growth factors

Textbook References

Human Embryology (3rd ed.) Larson Chapter 7 p151-188 Heart, Chapter 8 p189-228 Vasculature
The Developing Human: Clinically Oriented Embryology (6th ed.) Chapter 14: p304-349

Other textbooks

Before we Are Born (5th ed.) Moore and Persaud Chapter 12; p241-254
Essentials of Human Embryology Larson Chapter 7 p97-122 Heart, Chapter 8 p123-146 Vasculature
Human Embryology Fitzgerald and Fitzgerald Chapter 13-17: p77-111

UNSW Embryology Links

Cardiovascular Slides Cardiovasular Lecture 7 2008 | Heart Lecture 2008 - 1 slide/page | Heart Lecture 2008 Slides - 4 slides/page | Heart Lecture 2008 Slides - 6 slides/page
Cardiovascular Movies
Cardiovascular Notes

Development Overview

The heart develops from cardiogenic mesoderm that originally lies above the cranial end of the developing neural tube. Enlargement of the cranial neural fold brings this region ventrally to its correct anatomical position. The original paired cardiac tubes fuse, with the "ventricular" primordia initially lying above the "atria". Growth of the cardiac tube flexes it into an "S-shape" tube, rotating the "ventricles" downward and pushing the "atria" upward. This is then followed by septation, a complex process which converts this simple tube into a four chambered heart. A key part of this process is the separation of cardiac outflow (truncus arteriosus) into a separate pulmonary and aortic arch outflow. During embryonic development there is extensive remodelling of the initially right and left symmetrical cardiovascular system and a contribution from the neural crest to some vessels.

Development Overview

Introduction
Below is a summary of development. Alternatively read these listed recent reviews.
- Moorman A, Webb S, Brown NA, Lamers W, Anderson RH. Development of the heart: (1) formation of the cardiac chambers and arterial trunks. Heart. 2003 Jul;89(7):806-14.
- Anderson RH, Webb S, Brown NA, Lamers W, Moorman A. Development of the heart: (2) Septation of the atriums and ventricles. Heart. 2003 Aug;89(8):949-58.
- Yutzey KE, Kirby ML. Wherefore heart thou? Embryonic origins of cardiogenic mesoderm. Dev Dyn. 2002 Mar;223(3):307-20. Review.
- Bruneau BG. Transcriptional regulation of vertebrate cardiac morphogenesis. Circ Res. 2002 Mar 22;90(5):509-19. Review.
Timecourse
- forms in mesenchyme of precordal plate region
- cardiogenic region
- growth and folding of the embryo moves heart ventrallly and downward into anatomical position
- week 3 begins as paired heart tubes
- fuse to form single heart tube
- begins to beat in Humans- day 22-23
- heart tube connects to blood vessels forming in
- splanchnic mesoderm
- extraembryonic mesoderm
Week 2 pair of thin-walled tubes
Week 3 tubes fused, truncus arteriosus outflow, heart contracting
Week 4 heart tube continues to elongate, curving to form S shape
Week 5 Septation starts, atrial and ventricular
Septation continues, atrial septa remains open, foramen ovale
Week 40 At birth pressure difference closes foramen ovale leaving a fossa ovalis

Angiogenesis

Introduction
- blood vessel formation
  - vasculogenesis
- also occurs in adult and disease
- begins week 3 in extraembryonic mesoderm
  - yolk sac
  - connecting stalk
  - chorion
- Growth Factors
  - Vascular endothelial growth factor (VEGF), PIGF
Angiogenesis 2
- angioblasts form clusters - blood islands
- blood islands extend and fuse together
- forms a network
- 2 populations of cells
  - peripheral- form endothelial cells
  - core- form blood cells (haemocytoblasts)
- all vessels (arteries and veins) appear initially the same
Blood formation
- blood formation occurs later (week 5)
- occurs throughout embryoic mesenchyme
- liver
- then spleen, bone marrow, lymph nodes
Vascular systems
- one vascular system with 3 components
  - vitelline
  - embryonic
  - placental
- each component has own system of artery and vein
Vitelline Blood vessels
- cover entire surface of yolk sac
- connect to embryo through yolk stalk
- Arteries
  - arises from dorsal aorta
  - contribute to adult GIT arteries
- Veins
  - empties into sinus venosus
  - contribute to the adult portal system
Embryo Blood vessels (systemic)
- will form the most of the cardiovascular system
- some vessels have neural crest contribution
- Arteries
  - aortic sac -> aortic arches -> dorsal aorta - umbilical artery
  - dorsal aorta
  - paired initially and fuses
  - gives off segmental arteries
- Veins
  - 3 pairs of veins empty into the sinus venosus of the heart
  - vitelline, umbilical (only left persists), common cardinal veins
  - cardinal veins- anterior, common, posterior
  - systemic circulation
Placental Blood vessels
- form initially in the connecting stalk (then umbilical cord)
- anastomose in chorioni
- extend maternally toward chorionic villi
- extend embryonically to the sinus venosus and dorsal aorta
- Placental Vessels
- Arteries
  - paired
  - carry deoxygenated blood (from dorsal aorta) and waste products to the placental villi
- Veins
  - paired initially then only left at end of embryonic period
  - carry oxygenated blood to the embryo (sinus venosus)

Blood flow through the Embryo

Maternal Blood | -> umbilical vein -> liver -> anastomosis -> sinus venosus -> atria ventricles-> truncus arteriosus -> aortic sac -> aortic arches-> dorsal aorta-> pair of umbilical arteries | Maternal Blood

This is shown on the stage 13/14 pig G6 section.

Cartoon Heart Development

File:Heart1.gifTransverse section- Heart is 2 tubes that fuse in the midline anterior to pharynx.

The pericardial cavity can be imagined as the top of the "horseshoe" of the intraembryonic coelom. (where the arms become the pleural cavity and the ends fuse anteriorly to form a single peritoneal cavity).

This view shows the initial positioning of the ventricles above the atria. The ventricles are rotated into their correct anatomical position by the growth of the heart tube, bending into an "S" shape.

Initially...

Cardiac inflow- at the bottom (sinus venosus)

Cardiac outflow- at the top (truncus arteriosus)

Heart Layers

pericardium - covers the heart. Formed by 3 layers consisting of a fibrous pericardium and a double layered serous pericardium (parietal layer and visceral epicardium layer).

myocardium - muscular wall of the heart. Thickest layer formed by spirally arranged cardiac muscle cells.

endocardium - lines the heart. Epithelial tissue lining the inner surface of heart chambers and valves.

Heart Volume

Week*	Heart Volume (ml)	Lung Volume (ml)
10	0.6	1.6
18	4.3	10.9
30	26.6	49.3

*Table data is "embryonic age" while original reference used "gestational age" (from LMP)(Data: Peralta CF, Cavoretto P, Csapo B, Falcon O, Nicolaides KH. Lung and heart volumes by three-dimensional ultrasound in normal fetuses at 12-32 weeks' gestation. Ultrasound Obstet Gynecol. 2006 Feb;27(2):128-33.)

Stroke Volume

Week*	Left Stroke Volume (ml)	Right Stroke Volume (ml)	Cardiac Output L/R (ml/min)
10	0.02	0.01	2.39 / 1.8
18	0.32	0.30	43.46 / 46.72
32	2.07	2.67	284.71 / 365.99

*Table data is "embryonic age" while original reference used "gestational age" (from LMP). The stroke volume (SV) can be calculated from ultrasound measurement of end diastole volume (EDV) minus end systole volume (ESV); (SV = EDV - ESV).(Data: Molina FS, Faro C, Sotiriadis A, Dagklis T, Nicolaides KH. Heart stroke volume and cardiac output by four-dimensional ultrasound in normal fetuses. Ultrasound Obstet Gynecol. 2008 Aug;32(2):181-7.

UNSW Embryology Links

Terms

angioblast - the embryonic precursor cell which will form the walls of both arteries and veins. (More? Blood Vessel)

bulbus cordis -common outflow tract region of the early developing heart tube. Blood Pathway: sinus venosus - atrium - ventricle - bulbus cordis (outflow tract) (More? Heart Notes)

cardinal vein - name given to the initial early vessels that will form the systemic venous system. System, like most vessels are initially bilaterally symmetrical. (More? Blood Vessel Notes | Cardiovascular Notes)

cardiocyte - cardiac muscle cell.

coarctation of the aorta - (Latin coartare = to press together) Term used to describe a developmental abnormality of narrowing (stricture, constriction) of the aortic arch. (More? Coarctation of Aorta)

splanchnic mesoderm - Embryonic origin of the gastrointestinal tract connective tissue, smooth muscle,, cardiac tissue and blood vessels. In the trilaminar embryo, the portion of the lateral plate mesoderm closest to the endoderm when this mesoderm is divided by formation of the intraembryonic coelom.

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Next Lecture

Lecture 8 | Course Timetable

Cite this page: Hill, M.A. (2024, May 4) Embryology 2009 Lecture 7. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_7

What Links Here?