LEARNING OUTCOMES 1. explain the early development of the heart from splanchnic mesoderm ahead of...
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Transcript of LEARNING OUTCOMES 1. explain the early development of the heart from splanchnic mesoderm ahead of...
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