Lecture - Early Vascular Development

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Introduction

Image of mouse embryo (19 somite) vascular distribution (about Human stage 12)

This lecture has 2 parts; firstly introducing an overview of early vascular development, secondly the key events in heart development.

  • Vasculogenesis - formation of new blood vessels assemble from individual precursor cells.
  • Angiogenesis - sprouting of new vessels occurs from pre-existing vessels.

Lecture Objectives

Historic image of early human vascular development
Historic image of early human vascular development
  • Understanding of early blood vessel and blood development
    • Brief understanding of vascular growth and regression
    • Brief understanding of vascular growth factors
  • Understanding of heart development
    • Understanding of heart timeline
    • Understanding of heart septation

Lecture Resources

Movies  
Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Week3 folding icon.jpg
 ‎‎Week 3
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Heart1 looping icon.jpg
 ‎‎Heart Looping
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Heart1 realign icon.jpg
 ‎‎Heart Realign
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Heart1 atrium icon.jpg
 ‎‎Atrial Septation
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Heart1 ventricle icon.jpg
 ‎‎Outflow Septation
Page | Play
References  
UNSW Embryology logo
Hill, M.A. (2017). UNSW Embryology (17th ed.) Retrieved September 22, 2017, from https://embryology.med.unsw.edu.au
Cardiovascular Links: Introduction | Heart Tutorial | Lecture - Early Vascular | Lecture - Heart | Movies | Heart | Coronary Circulation | Heart Valve | Heart Rate | Circulation | Blood | Blood Vessel | Blood Vessel Histology | Cardiac Muscle Histology | Lymphatic | Ductus Venosus | Spleen | Stage 22 | Abnormalities | OMIM | 2012 ECHO Meeting | 2016 Cardiac Review | Category:Cardiovascular
Historic Embryology - Cardiovascular 
1902 Vena cava inferior | 1905 Brain Blood Vessels | 1909 Cervical Veins | 1912 Heart | 1912 Human Heart | 1914 Earliest Blood-Vessels | 1915 Congenital Cardiac Disease | 1915 Dura Venous Sinuses | 1916 Pars Membranacea Septi | 1919 Lower Limb Arteries | 1921 Human Brain Vascular | 1921 Spleen | 1922 Aortic-Arch System | 1922 Pig Forelimb Arteries | 1922 Chicken Pulmonary | 1923 Head Subcutaneous Plexus | 1925 Venous Development | 1928 Heart Blood Flow | 1935 Aorta | 1935 Venous valves | 1938 Pars Membranacea Septi | 1938 Foramen Ovale | 1939 Atrio-Ventricular Valves | 1940 Vena cava inferior | 1940 Early Hematopoiesis | 1942 Truncus and Conus Partitioning | Ziegler Heart Models | 1951 Heart Movie | 1954 Week 9 Heart | 1957 Cranial venous system | 1959 Brain Arterial Anastomoses | Historic Embryology Papers | 2012 ECHO Meeting | 2016 Cardiac Review | Historic Disclaimer
Textbook cover Larsen's human embryology 5th edn.
Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders.
The following chapter links only work with a UNSW connection.
Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone. The following chapter links only work with a UNSW connection.

Early Development Overview

mouse E9.5 heart (stage 10)

Stage7 mesoderm.jpg Mesoderm-cartoon4.jpgGray's Anatomy Fig. 462 Early heart tube

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 (see Heart Development later in this lecture). 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.

The Human Heart from day 10 to 25 (scanning electron micrograph)
The Human Heart from day 10 to 25 (scanning electron micrograph)


Timecourse

  • forms initially in splanchnic mesoderm of prechordal plate region - cardiogenic region
    • growth and folding of the embryo moves heart ventrally and downward into anatomical position
  • heart tube connects to blood vessels forming in splanchnic and extraembryonic mesoderm
  • Week 2-3 pair of thin-walled tubes
  • Week 3 paired heart tubes fuse, 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 until after birth, foramen ovale.
  • Week 37-38 at birth, pressure difference closes foramen ovale leaving a fossa ovals
Heart Tube Segments.jpg

Human early heart tube (Week 4, Stage 10)

Vasculogenesis and Angiogenesis

extraembryonic mesoderm
Vasculogenesis Angiogenesis
formation of new blood vessels
(endothelium from mesoderm)
formation of blood vessels from pre-existing vessels
(occurs in development and adult)


  • Begins week 3 in extraembryonic mesoderm and then embryonic splanchnic mesoderm
  • Begins as the formation of blood islands
  • Earliest islands - yolk sac, connecting stalk and chorion (Area vasculosa)
  • Growth factors stimulate growth and development - Vascular Endothelial Growth Factor (VEGF) and Placental Growth Factor (PlGF, PGF)
    • Growing blood vessels follow a gradient generated by target tissues/regions of Vascular Endothelial Growth Factor (VEGF) to establish a vascular bed. Recent findings suggest that Notch signaling acts as an inhibitor for this system, preventing sprouting of blood vessels. Notch is a transmembrane receptor protein involved in regulating cell differentiation in many developing systems.
    • PIGF is also a VEGF released from the placental trophoblast cells.
  • angioblasts form clusters called "blood islands"
  • blood islands extend and fuse together to form a primordial vascular network


Blood islands

fetal blood
  • Blood islands contain cells (haemangioblasts) which are capable of differentiating into 2 populations of cells
    • Vascular precursors (angioblasts) - form endothelial cells
    • Blood cell precursors (haemocytoblasts)
  • These angioblasts migrate, coalesce into cords and form a lumen. This process of vessel formation is called vasculogenesis and is dominant in very early embryogenesis e.g. formation of the dorsal aorta
  • Sprouting from pre-existing vessels is called angiogenesis e.g. brain is an organ which is vascularized by this process
  • Note: the vascular tree undergoes constant remodeling as the embryo grows.

Blood vessel lumen formation cartoon

Blood vessel lumen formation

Blood formation

  • blood formation from stem cells occurs initially in the extraembryonic mesoderm of the yolk sac
  • later (week 5) throughout embryonic mesenchyme
  • blood stem cells then migrate into the liver
    • then spleen, bone marrow, lymph nodes
Mouse hematopoietic stem cell.gif

Mouse hematopoietic stem cell location

Red blood cells

The only cells in the blood are nearly entirely fetal red blood cells.

These cells differ from adult red blood cells in:

  1. often remaining nucleated.
  2. contain fetal haemoglobin - which has different oxygen and carbon dioxide binding characteristics.

Placenta blood.jpg

Placenta oxygen exchange levels.jpg

Fetal Oxygen levels

Haemoglobin_comparison_oxygen_saturation_curve.png

Red Blood Cell haemoglobin oxygen dissociation curves

Blood stem cells

Hematopoietic and stromal cell differentiation.jpg

Hematopoietic and stromal cell differentiation (adult)

Early vascular systems

Early vascular systems
Early vascular systems
Week 7 embryo with placenta
  • one vascular system with 3 components - vitelline, embryonic (system) and placental
    • each component has own system of artery and vein


Vitelline blood vessels

  • Angioblasts form a network of vessels over the yolk sac and connecting stalk
  • Join into two main vessels, the vitteline veins (omphalomesenteric)
  • Pass through vitello-intestinal duct (yolk sac stalk)
  • Enter caudal end of cardiac tube
  • Vitelline Arteries - arises from dorsal aorta, contribute to adult GIT arteries (fuse to become superior mesenteric artery (midgut)
  • Vitelline 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
  • Arterial blood flow - aortic sac → aortic arches → dorsal aorta →umbilical artery
    • dorsal aorta,
      • paired initially , later fuses from T4 to L4 (gives off segmental arteries)
      • connect to ventral aorta via pharyngeal arches arteries.
      • caudally, give rise to umbilical arteries
      • laterally, give rise to intersegmental arteries
  • Veins - 3 pairs of veins empty into the sinus venosus of the heart
    • vitelline, umbilical (right and left from developing placenta enter caudal cardiac tube; only left persists)
    • cardinal veins - anterior, common, posterior
Vein histology 01.jpg Blood capillary EM 04.jpg
Vein histology Blood capillary (EM)

Placental blood vessels

(Placenta development covered in next lecture)

  • form initially in the connecting stalk (then umbilical cord) and anastomose in chorion
  • extend maternally - toward the chorionic villi
  • extend embryonically - toward the sinus venosus and dorsal aorta
  • Arteries - paired and carry deoxygenated blood (from dorsal aorta) and waste products to the placental villi
  • Veins - paired initially then only left at end of embryonic period and carry oxygenated blood to the embryo (sinus venosus)

Blood flow through the embryo

High pressure pathway

Stage13 bloodflow.jpg Gray0472.jpg

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

Stage 13 image 070.jpg

Low pressure pathway

  • Head - Large veins lateral to dorsal aortae. These are the superior or anterior cardinal veins. Their function is to drain the head region.
  • Body - Large veins lateral to dorsal aortae. These are the inferior or posterior cardinal veins. Their function is to drain the lower part of the embryo.

Blood vessel remodeling

Cervical intersomitic vessels Gray0473.jpg
Early vascular development is laterally symmetrical (paired left and right). Embryo development extensively remodelled leading to an asymmetric adult system in the body. Complex balance between Stimulators and Inhibitors of Angiogenisis.

Vascular Endothelial Growth Factor (VEGF)

  • belongs to the platelet derive growth factor (PDGF) family.
  • required for early stages of blood vessel patterning.
  • required later for endothelial cell maintenance in tissues.
  • autocrine VEGF loop from endothelial cell secretion involved in vascular growth.
  • 4 protein isoforms generated from a single gene.

VEGF protein family - VEGF (or VEGF-A), VEGF-B, VEGF-C, VEGF-D and placental growth factor (PGF),

VEGF receptors - VEGFR-1, -2 and -3.

  • Cells expressing the receptors are directed in their growth.
  • Note that there are other growth factor families (FGF, Tie, TGF-β, netrins, semaphorins) that can also influence vessel growth.
  • Some angiogenic factors also involved in organ development (liver).


Links: Blood Vessel Development | Vascular Endothelial Growth Factor

Heart Development

Septation

There are several key developmental events that divide the heart into 4 separate chambers (right atria, right ventricle, left atria, left ventricle) and also divide the outflow tract into 2 (aortic and pulmonary trunks). You should understand the sequence and timing of these septation events. The linked online tutorial is a useful supplement to your understanding of these events.

  1. atrioventricular separation
  2. atrial septation
  3. ventricular septation
  4. outflow tract division


Week 4 - Stage 10 Human Heart tube Week 5 - Stage 13 Human Heart (sagittal view)
Heart Tube Segments.jpg Stage 13 MRI S01.jpg
from a pair of heart tubes to the heart forming chambers

Heart1 atrium.gif

Intermediateicon.jpg
Begin Intermediate: Primordial Heart Tube  Heart Tube Looping  Atrial Ventricular Septation  Outflow Tract  Heart Valves  Cardiac Abnormalities  Vascular Overview
Intermediate Heart Development Timeline.jpg

The cardiovascular system is the first major system to function within the embryo, with the heart beginning to function during the fourth week. Congenital heart defects affect 8-10 of every 1000 births in the United States. Hence in both embryological and clinical contexts it is important to consider heart development.

The intermediate section of this module on cardiac embryology is directed at university level students with some previous study of embryology but minimal previous study of cardiac development specifically. This unit takes approximately 30-40 minutes to complete. The intermediate cardiac module contains 7 pages which should be worked through in order.

  1. Primordial Heart Tube
  2. Looping of the Heart Tube
  3. Atrial and Ventricular Septation
  4. Development of the Outflow Tract
  5. Development of Heart Valves
  6. Abnormalities of Cardiac Development
  7. Overview of Vascular Development


Early Heart Description  
  • Mesenchymal condensation in splanchnic mesenchyme = cardiogenic plate
  • Following bending and folding, the plate comes to lie dorsal to pericardial coelom
  • Plate undergoes bilateral canalisation to form 2 cardiac tubes:
    • cranial part of cardiac tubes = ventral aortae which will later join the existing dorsal aortae
    • Caudally the tubes will join vitelline and umbilical veins
  • Cardiac tubes fuse to form single heart tube that sinks into coelom (= future pericardial sac)
  • At this stage, the heart is an endothelial tube surrounded by visceral layer of pericardium (epicardium)
  • From the time of the fusion of cardiac tubes, the walls undergo fibrillary movements (forerunner of cardiac contraction)
  • Later, space between epicardium and cardiac endothelium fills with jelly-like material (cardiac jelly), which becomes invaded by cells of deep layer of epicardium. These are the myoblasts (future cardiac muscle)
  • Combined layer of epicardium and invaded jelly = myoepicardial mantle.
  • Epicardial layer also gives rise to blood islands which form vascular network (future coronary vessels)
  • Heart tube (now within the pericardial coelom) begins to undergo internal and external changes.

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 looping

Heart Looping Sequence.jpg

Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Heart1 looping icon.jpg
 ‎‎Heart Looping
Page | Play
Stage 13 MRI S01.jpg
 ‎‎Heart Sag MRI
Page | Play

Transverse 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...

  • Heat tube develops a series of constrictions:
    • Truncus arteriosus – ventral aortae meet - OUTFLOW
    • Bulbus cordis
    • Ventricle
    • Atrium
    • Sinus venosus – caudal end of tube, receiving 4 veins - INFLOW
  • Rapid growth – ‘buckling’ and ‘twisting’
  • Heart tube bends ventrally into pericardial coelom
  • Ventricle enlargens, absorbs lower part of bulbus cordis (bulboventricular loop)
  • Ventricle also twists to left- atrium and sinus venosus come to lie dorsal to bulbus cordis and lower part of truncus arteriosus
  • Venous inflow comes to lie directly dorsal to the arterial outflow.
  • Possible abnormality – dextro-rotation, the heart bends or twists to the right. Maybe associated by other abnormalities.
  • Later, sinus venosus becomes absorbed into atrium

Heart neural crest

  • The mouse model shows that the heart also has contributions from neural crest E8.5 mouse neural crest
    • between the levels of post-otic hindbrain to somite 4, with the most contribution from somite 2 level.
  • 7 somite stage - Migration of cardiac neural crest from the neural tube begins. (level post-otic hindbrain and somite 4)
    • Pathways dorsolateral, medial, and between somites.
    • Then through peri-aortic mesenchyme (lateral to pharynx), through pharyngeal arches (3, 4, 6) into the aortic sac.
  • 32 somite stage: Colonisation of the outflow tract mesenchyme.

Data from: Chan WY, Cheung CS, Yung KM, Copp AJ. Chan WY, Cheung CS, Yung KM, Copp AJ. Cardiac neural crest of the mouse embryo: axial level of origin, migratory pathway and cell autonomy of the splotch (Sp2H) mutant effect. Development. 2004 Jul;131(14):3367-79. PMID: 15226254


Embryonic heart rate

  • Ultrasonographic measurement of embryonic heart rate (EHR) shows a steady increase from Stage 9-10 (75 beats/minute) to Stage 18 (130 beats/minute) and on to Stage 20, following which a gradual decrease in EHR occurs
  • Maximal EHR is reached when morphological development of the embryonic heart is completed.


Links: Embryonic Heart Rate

Internet Links

Embryo Images Unit: Embryo Images Online Early Cell Populations (cardiogenic section) | Cardiovascular Development | Week 3 Development | Week 4 Development | Heart Chambers and Outflow Tract | Atrioventricular Septation | Outflow Tract Septation | Ventricular Septation | Atrial Septation | Atrial Walls Aortic Arch Vessels | Changes at Birth

References

Online Textbooks

Terms

Cardiovascular Terms  
Cardiovascular System Development See also Heart terms
  • angioblast - the stem cells in blood islands generating endothelial cells which will form the walls of both arteries and veins. (More? Blood Vessel)
  • angiogenesis - the formation of new blood vessels from pre-existing vessels following from vasculogenesis in the embryo. (More? Blood Vessel)
  • anlage (German, anlage = primordium) structure or cells which will form a future more developed or differentiated adult structure.
  • blood islands - earliest sites of blood vessel and blood cell formation, seen mainly on yolk sac chorion.
  • cardinal veins - paired main systemic veins of early embryo, anterior, common, posterior.
  • cardiogenic region - region above prechordal plate in mesoderm where heart tube initially forms.
  • ectoderm - the layer (of the 3 germ cell layers) which form the nervous system from the neural tube and neural crest and also generates the epithelia covering the embryo.
  • endoderm - the layer (of the 3 germ cell layers) which form the epithelial lining of the gastrointestinal tract (GIT) and accessory organs of GIT in the embryo.
  • endocardium - lines the heart. Epithelial tissue lining the inner surface of heart chambers and valves.
  • endothelial cells - single layer of cells closest to lumen that line blood vessels.
  • extraembryonic mesoderm - mesoderm lying outside the trilaminar embryonic disc covering the yolk sac, lining the chorionic sac and forming the connecting stalk. Contributes to placental villi development.
  • haemocytoblasts - stem cells for embryonic blood cell formation.
  • anastomose - to connect or join by a connection (anastomosis) between tubular structures.
  • chorionic villi - the finger-like extensions which are the functional region of the placental barrier and maternal/fetal exchange. Develop from week 2 onward as: primary, secondary, tertiary villi.
  • estrogens - support the maternal endometrium.
  • growth factor - usually a protein or peptide that will bind a cell membrane receptor and then activates an intracellular signaling pathway. The function of the pathway will be to alter the cell directly or indirectly by changing gene expression. (eg VEGF, shh)
  • maternal decidua - region of uterine endometrium where blastocyst implants. undergoes modification following implantation, decidual reaction.
  • maternal sinusoids - placental spaces around chorionic villi that are filled with maternal blood. Closest maternal/fetal exchange site.
  • mesoderm - the middle layer of the 3 germ cell layers of the embryo. Mesoderm outside the embryo and covering the amnion, yolk and chorion sacs is extraembryonic mesoderm.
  • myocardium - muscular wall of the heart. Thickest layer formed by spirally arranged cardiac muscle cells.
  • 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).
  • pericytes - (Rouget cells) cells located at the abluminal surface of microvessels close to endothelial cells, mainly found associated with CNS vessels and involved in vessel formation, remodeling and stabilization.
  • pharyngeal arches (=branchial arches, Gk. gill) series of cranial folds that form most structures of the head and neck. Six arches form but only 4 form any structures. Each arch has a pouch, membrane and groove.
  • placenta - (Greek, plakuos = flat cake) refers to the discoid shape of the placenta, embryonic (villous chorion)/maternal organ (decidua basalis)
  • placental veins - paired initially then only left at end of embryonic period, carry oxygenated blood to the embryo (sinus venosus).
  • protein hormone - usually a protein distributed in the blood that binds to membrane receptors on target cells in different tissues. Do not easliy cross placental barrier.
  • sinus venosus - cavity into which all major embryonic paired veins supply (vitelline, placental, cardinal).
* splanchnic mesoderm - portion of lateral plate mesoderm closest to the endoderm when coelom forms. 
  • steroid hormone - lipid soluble hormone that easily crosses membranes to bind receptors in cytoplasm or nucleus of target cells. Hormone+Receptor then binds DNA activating or suppressing gene transcription. Easliy cross placental barrier.
  • syncitiotrophoblast extraembryonic cells of trophoblastic shell surrounding embryo, outside the cytotrophoblast layer, involved with implantation of the blastocyst by eroding extracellular matrix surrounding maternal endometrial cells at site of implantation, also contribute to villi. (dark staining, multinucleated).
  • truncus arteriosus - an embryological heart outflow structure, that forms in early cardiac development and will later divides into the pulmonary artery and aorta. Term is also used clinically to describe the malformation where only one artery arises from the heart and forms the aorta and pulmonary artery.
  • vascular endothelial growth factor - (VEGF) A secreted protein growth factor family, which stimulates the proliferation of vasular endotheial cells and therefore blood vessel growth. VEGF's have several roles in embryonic development. The VEGF family has 7 members (VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, VEGF-F, and PlGF) that have a common VEGF homology domain. PIGF is the placental growth factor. They act through 3 VEGF tyrosine kinase membrane receptors (VEGFR-1 to 3) with seven immunoglobulin-like domains in the extracellular domain, a single transmembrane region, and an intracellular tyrosine kinase sequence.
  • vasculogenesis - the formation of new blood vessels from mesoderm forming the endothelium. Compared to angiogenesis that is the process of blood vessel formation from pre-existing vessels.
  • vitelline blood vessels - blood vessels associated with the yolk sac.
  • waste products - products of cellular metabolism and cellular debris, e.g.- urea, uric acid, bilirubin.
Other Terms Lists  
Terms Lists: ART | Birth | Bone | Cardiovascular | Cell Division | Gastrointestinal | Genetic | Hearing | Heart | Immune | Integumentary | Neural | Oocyte | Palate | Placenta | Renal | Respiratory | Spermatozoa | Ultrasound | Vision | Historic | Glossary



 2017 ANAT2341 - Timetable | Course Outline | Group Projects | Moodle | Tutorial 1 | Tutorial 2 | Tutorial 3

Labs: 1 Fertility and IVF | 2 ES Cells to Genome Editing | 3 Preimplantation and Early Implantation | 4 Reproductive Technology Revolution | 5 Cardiac and Vascular Development | 6 CRISPR-Cas9 | 7 Somitogenesis and Vertebral Malformation | 8 Organogenesis | 9 | 10 | 11

Lectures: 1 Introduction | 2 Fertilization | 3 Week 1/2 | 4 Week 3 | 5 Ectoderm | 6 Placenta | 7 Mesoderm | 8 Endoderm | 9 Research Technology | 10 Cardiovascular | 11 Respiratory | 12 Neural crest | 13 Head | 14 Musculoskeletal | 15 Limb | 16 Renal | 17 Genital | 18 Endocrine

 Student Projects: 1 Cortex | 2 Kidney | 3 Heart | 4 Eye | 5 Lung | 6 Cerebellum