LEARNING OUTCOMES

1. explain the early development of the heart from splanchnic mesoderm ahead of the neuralplate which is then folded beneath the pharynx of the head fold.

2. outline the fusion of the endocardial tubes to form the simple linear heart with atrium, ventricle

and valvular flaps pumping blood into the aortic arches.

3. define the three circulatory arcs of the heart supplying the body tissues, the yolk sac (vitelline)

and the allantois and describe their functions

4. describe the role of the yolk sac splanchnopleure in early haematopoiesis

5. Understand the developmental process by which the aortic arches and truncus arteriosis areadapted to give the aortic and pulmonary trunks and the carotids

6. Show how septum formation in the primitive linear heart allows separate pumping of blood into

the aorta and the pulmonary trunk

7. describe the congenital abnormalities of septal defects, patent ductus arteriosus, andpersistent aortic arch

DEVELOPMENT OF THE HEART AND GREAT BLOOD VESSELS

FORMATION OF THE MAMMALIAN GASTRULA - 9

ICM EPIBLAST

NOTOCHORDCHORDA-

HEAD

LATERAL

PARAXIAL SOMITES

AXIAL SKELETON

TRUNK MUSCLES

LIMB MUSCLES

INTERMEDIATE

YOLK SAC ALLANTOIS

AMNION CHORION

MESODERM

MESODERM TYPE

DERMIS

PARTS OF KIDNEY AND REPRODUCTIVE TRACT

HEAD MUSCLES, SKULL, CARTILAGE

MESODERM DERIVATIVE

INTERMEDIATE STRUCTURE

HEART BODY CAVITY DIVIDERS

LIMB SKELETON

BLOOD CELLS

PERICARDIAL CAVITY

CARDIAC PRIMORDIUM (SPLANCHNIC MESODERM)

DORSAL AORTA

ENDODERM

A

THE EARLY DEVELOPMENT OF THE HEART - 1

The cardiac tube folds under the gut tube……

The cardiac primordia are established in the early gastrula as regions of splanchnic mesoderm ahead of the embryo itself. As a result of the head fold, this region ends up beneath the pharynx.

VITELLINE VEINS

GUT TUBE

CARDIAC TUBE

B

The heart is a U-shaped tube at this stage and the forming blood vessels are initially unconnected

……and connects bilaterally with the dorsal aorta via the aortic arches

The sides of the U-tube then fuse to produce the atrial and ventricle regions with valvular flaps to prevent back flow so that the heart can function as a simple peristaltic pump.

The dorsal aorta form independently and then grow to meet the ventral output from the heart in the aortic arches

FUSED DORSAL AORTA1ST AORTIC ARCH (R)

ORAL PLATE

ATRIUMVENTRICLE

VENOUS RETURN FROM CARDINAL VEINS, VITELLINE VEIN AND ALLANTOIC (UMBILICAL) VEIN

C

The diagram shows 6 aortic arches but, in mammals, 1 and 2 are regressing while the later arches are forming and arches 5 never form

This pattern of mammalian development is a good example of recapitulation

LUNG BUD

PHARYNGEAL POUCHES

THIS STAGE RESEMBLES FISH

D

SEGMENTATION OF THE HEAD THE BRANCHIAL ARCHES AND PHARYNGEAL POUCHES

EACH BRANCHIAL ARCH CONTAINS A CRANIAL NERVE AND AN AORTIC ARCH

THE FOUR PHARYNGEAL POUCHES CORRESPOND TO THE FOUR BRANCHIAL CLEFTS LATERALLY

REMINDER:The branchial arches and clefts and the juxtaposed pharyngeal pouches are a recapitulation of the respiratory anatomy of fish

Mouse, 8 day, sagittal

Mouse, 8 day, frontal

Mouse, 9 day, frontal Mouse, 10 day, frontal

Mouse, 9 day, side

http://www.med.unc.edu/embryo_images/

The heart folds under the pharynx

The heart twists so that the atrium is rostral to the ventricle

Aortic arches

Dorsal aorta Cardinal veinsMesonephros

Chorio-allantoicplacenta

Allantoic artery

Allantoic vein

Yolk sac

Vitelline vein

Vitelline artery

Deoxygenated blood

Mixed blood

Oxygenated blood

The embryonic circulation has three circulatory arcs through which blood is pumped by a simple linear heart

THE CIRCULATORY ARCS OF THE EMBRYONIC BLOOD SUPPLY

1. BODY CIRCULATION TRANSPORT OF O2 /FOOD MATERIALS TO TISSUES TRANSPORT OF WASTE MATERIALS AWAY

2. VITELLINE CIRCULATION CARRIES MOBILISED FOOD MATERIALS FROM THE YOLK SAC LOST FUNCTION IN MAMMALS BECAUSE SAC EMPTY CARRIES FIRST BLOOD CELLS FROM YOLK SAC

SPLANCHNOPLEURE

3. ALLANTOIC CIRCULATION

IN MAMMALS TAKES OVER THE FUNCTIONS OF THE VITELLINE ARC IN BIRDS

SUPPLIES FOOD MATERIALS FROM MATERNAL CIRCULATION

RETAINS AVIAN FUNCTION OF REMOVAL OF WASTE AND GAS EXCHANGE

MESENCHYME IN SPLANCHNOPLEURE OF YOLK SAC

CELL CLUSTERS

ENDOTHELIAL CELLS

HAEMATOPOIETIC CELLS

FORMATION OF BLOOD VESSEL

AGGREGATION OF FURTHER MESENCHYME TO FORM MUSCULAR AND CONNECTIVE TISSUE WALL

ENDOTHELIUM

BLOOD ISLAND

From Noden and La Hunta p 211

Haematopoiesis begins in the splanchnopleure of the yolk sac before transferring to the embryo itself later in development

The simple tubular heart twists to prepare for septum formation and the creation of a four-chambered organ. The aortic arches are selectively modifed to give rise to the great arteries

THE HEART AND THE AORTIC ARCHES - FORMATION OF THE GREAT BLOOD VESSELS

NOTES: 1. View from ventral surface 2. RA - Right atrium, LA - Left atrium, RV - right ventricle, LV - left ventricle, TA = truncus arteriosus

A

V

IIIIIIIVVVI

VENOUS RETURN

V

A

IIIIV

VI

TA

After birth venous return is from vena cava (blue arrows) and pulmonary veins (red arrows)

LARA

LVRV

CAROTIDS(from L and RIII)

AORTA (from LIV)

DUCTUSARTERIOSUS

(LVI to LIV)

SEPTA

RIGHT SUBCLAVIAN(from RIV)

PULMONARY TRUNK

(from LVI)

V

A

PRIOR TO SEPTATION (SURFACE VIEW)

INCOMPLETE SEPTATION (SECTION)

Pulmonary veins

Vena cava

Vena cava

Foramen ovale

LVRV

ATRIAL SEPTATION

VENTRICULAR SEPTATION

ATRIO-VENTRICULAR

SEPTATION

SEPTUM FORMATION

The separation between atria and between ventricles and between atria and ventricles occurs by means of septum formation

Mouse, 10 days, frontal section

Mouse, 12 days, section of truncus arteriosus

A

Blood from the atrium passes to the ventricle by means of a channel. The beginnings of interatrial septum formation can be seen (A)

Cushions form within the truncus arteriosus and will fuse to form the aortico-pulmonary septum separating the aortic and pulmonary flows

http://www.med.unc.edu/embryo_images/

DA

FO

Trunk

HindlimbPlacenta

Liver

From lungs

To lungs

Brachycephalic vessels

14

30

14

25

25

25

22

19

19

FOETAL CIRCULATIONThere is a split between deoxygenated blood returning from the rostral end of the foetus and oxygenated blood returning from the placenta. This spit is achieved by directed flow through the foramen ovale

CHANGES IN THE CIRCULATION AT BIRTH

• Contraction of allantoic artery and veins to force placental blood into main circulation. Rupture of umbilical cord

• Contraction of Ductus arteriosus and closure of Foramen ovale so that right side blood is directed to lungs

DEFECTIVE SEPTUM FORMATION

INTER-ATRIAL SEPTAL DEFECT (persistent Foramen ovale)

INTER-VENTRICULAR SEPTAL DEFECT (Tetralogy of Fallot is variation on this)

PATENT DUCTUS ARTERIOSUS

PERSISTENCE OF AORTIC ARCHES AND VASCULAR RING ANOMALIES

PERSISTENT RIGHT AORTIC ARCH IV

Right 4Left 6

Oesophagus

Carlson BM (2003) Patten's Foundations of Embryology

Noden DM, de Lahunta (1985) A Embryology of domestic animals

McGeady TA, Quinn PJ, Fitzpatrick ES, Ryan MT (2006) Veterinary embryology

University of North Carolina web site: http://www.med.unc.edu/embryo_images/

REFERENCES