developmental anatomy of cardiovascular and respiratory system

heart

Soon after fertilisation, 3 germ layers form

Ectoderm (top)

Mesoderm (middle)

Endoderm (bottom)

The heart forms from mesoderm around 18 to 19 days after fertilization

heart

Within mesoderm, a horseshoe-shaped area develops (the cardiogenic area or plate)

The cardiogenic plate moves ventral to the pharynx as the head process grows upward

Formed from cardiac myoblasts and blood islands (forerunners of blood cells and vessels)

Within each side of the cardiogenic area, an endocardial tube forms (lined by endothelial cells)

development of the heart

The endocardial tubes fuse midway along their length, forming the tubular heart or cardiac tube

A single tube is formed with an arterial and a venous end

The tubular heart undergoes differential growth and expansion

test your previous knowlefge

Two atria and two ventricles

Atria are the blood-receiving chambers

Ventricles are the blood-pumping chambers

The auricle is blind ear-shaped pouch of the atrium

development of the heart

Truncus arteriosus (aorta and pulmonary trunk)

Bulbus cordis (right ventricle)

Primitive ventricle (left ventricle)

Primitive atrium (right and left auricles)

Sinus venosus (remains bifurcated, a paired area where veins drain

- The left sinus venosus becomes the coronary sinus;

- the right is incorporated into the wall of the right atrium

morphogenesis

Endocardial tube lengthens and loops on itself

This puts the bulbus cordis (right ventricle) beside the ventricle (left ventricle) and the atrium dorsal to the ventricle

Venous return is shifted to the right

The larger right sinus venosus becomes the right atrium (embryonic atrium becomes auricles)

The smaller left sinus venosus joins the future right atrium as the coronary sinus venosus

formation of cardiac chambers

Partitions form a 4-chambered organ. The septa that form:

1. Divide atrium and ventricle (cardiac cushions → septum intermedium)

2. Divide the atrium (septum primum and secundum)

3. Divide the ventricle (interventricular septum)

4. Divide the outflow tracts (Aortico-pulmonary septum)

dividing atrium and ventricle -1 = cardiac cushions → septum intermedium

At the atrioventricular region, two masses of cardiac mesenchymal tissue form (cardiac cushions)

They extend towards each other and fuse

The fused cushions form the septum intermedium

Separates the atrio-ventricular canal into right and left atrio-ventricular openings

dividing atrium - 2 = septum primum and secundum

A membranous fold (primary septum) grows down from the dorsal wall of the atrium towards the endocardial cushions

Divides atrium into left and right atria

Primary septum leaves a small hole near the cushions, that will eventually close (primary foramen)

Before it closes, a second hole forms in the primary septum via apoptosis (secondary foramen)

Secondary septum grows from the cranial wall of the right atrium toward the caudal wall

The septum remains incomplete, and its free edge forms the boundary of an opening called the Foramen Ovale*-left foramen ovale (oval shaped)

Asnwer to Q: Primary septum acts like a valve against the muscular secondary septum

• A shunt that allows oxygenated blood to bypass the nonfunctional fetal lungs to continue blood flow and allow oxygenated blood reaching the foetal heart

dividing ventricles (interventricular septum)

The expanded part of the bulbus cordis (right ventricle) and the ventricle form a common chamber

Externally, they are marked by a groove (the interventricular sulcus)

Internally, they are marked by a fold (primordial interventricular septum)

dividing ventricles pt 2 (interventricular septum)

At this stage:

The embryonic (primitive) ventricle = left ventricle

The embryonic bulbus cordis =right ventricle

As the ventricles expand, the interventricular septum elongates towards the endocardial cushions

separating outflows (Aortico-pulmonary septum)

The truncus arteriosus divides, to form two outflow tracts:

Aortic trunk and Pulmonary trunk

Ridges appear along the lumen wall, grow inward, and merge to create the spiral septum (aortico-pulmonary septum)

As a result, the aorta and pulmonary trunk spiral around one another

Growths from the spiral septum and endocardial cushions both contribute to the proper closure of the interventricular septum

separation of outflows

Why does it matter that the aortico-pulmonary septum spirals?

so can receive oxygenzated and deoxygenated blood from diff directions - aorta leave left ventricle and pulmonary leaves right ventricle

formation of valves

Aortic and pulmonary valves form from swellings of mesenchymal tissue

Then remodelled to form thin-walled cusps

The atrioventricular valves form from the proliferation of mesenchymal tissue at the rim of the AV opening, attached to the myocardium

• Valves remodelled, but remain anchored by muscular strands to the ventricular walls

formation of blood vessels

Blood vessel formation occurs in 2 steps: vasculogenesis and angiogenesis

Vasculogenesis -Formation of blood vessels from blood islands

Vessel formation happens when island vesicles coalesce, sprout buds and fuse to form vascular channels

Angiogenesis- Budding of new vessels from existing vessels.

Begins in the splanchnic mesoderm of the yolk sac

formation of arteries

The aortae fuse with the cardiac tubes

Cardiac tubes fuse with the vitelline veins (1) caudally

Note paired dorsal and ventral aortae

Due to embryo folding, the dorsal aorta ends up dorsal to the cardiac tube

Paired ventral aorta receive blood from truncus arteriosus and fuse to form the adult brachiocephalic trunk

formation of aortic arches

Bilaterally, ventral & dorsal aortae are connected by up to six aortic arches

The cranial fusion between dorsal aortae and cardiac tubes becomes the 1st aortic arches

In total, 6 pairs of aortic arches will develop

formation of aortic arches continued

The aortic arches give rise to major vascular structures:

3rd arches - internal and common carotid arteries

Left 4th arch - definitive aortic arch

Right 4th arch - proximal part of right subclavian artery

6th arches - pulmonary arteries (and ductus arteriosus)

formation of veins

Three paired veins drain into the heart tube:

Vitelline veins (return poorly oxygenated blood from the yolk sac) - eventually forms plexus on duodenum and liver→portal vein system

Umbilical veins (carry well-oxygenated blood from the primordial placenta)

Common cardinal veins (return poorly oxygenated blood from the body of the embryo)

Recall that venous return is shifted to the right side, and the right sinus venosus is incorporated into the right atrium. The left sinus venosus is reduced and becomes coronary sinus

foetal shunts

Allow blood to bypass the lungs and liver:

1. Foramen ovale (fossa ovale)

(Between right and left atria - secundum septum on the primum septum)

2. Ductus arteriosus (ligamentum arteriosum)

(Between pulmonary trunk and aorta-shunts the blood from pulmonary trunk to aorta-allowing right ventricle to be exercised)

3. Ductus venosus

(Between umbilical vein and caudal vena cava-develops in the embryo as a shunt that diverts blood away from sinusoids and toward systemic veins)

development of the respiratory system

Respiratory diverticulum (the bulge) arises from foregut endoderm, and goes on to form:

• Epithelial lining of trachea

• Larynx (voice box and protects airway)

• Bronchi and alveoli

Lung buds form the left and right principal bronchi, which divide into ever-smaller branches, down to alveolar ducts and alveoli

Lungs are filled with fluid during development

Mostly glandular secretions, some amniotic fluid

foetal cardiovascular system

The foetal blood pressure is low

The foetal heart is powering it (not mum)

Lots of blood spread out in placenta

Blood is shunted right-to-left by ductus arteriosus and foramen ovale

To bypass lungs

Lungs are non-functional-collapsed

No air to breathe

Pulmonary circulation has high resistance

Vessels here are collapsed

Systemic circulation has low resistance

The placenta is a low-resistance area

Placentae must receive a large proportion of foetus's circulating blood

Two large left and right umbilical arteries

Extending from the caudal end of the abdominal aorta

Umbilical vein

After passing through the capillary bed in the placentae

This highly oxygenated blood returning from placentae to the umbilical vein bypasses liver sinusoids –ductus venosus

How does foetal heart allow blood to bypass lungs?

Foramen ovale- between the two atria

Ductus arteriosus- between the aorta and pulmonary trunk

(in foetus pressure in the right side is greater than left)

birth -3 adjustments

Contraction of umbilical arteries and veins

Prevent bleeding

Force placental blood into foetal circulation

Contraction of musculature in ductus arteriosus

Physiological shunt closure sends blood to lungs

Anatomical closure can take 2 months

May hear transient cardiac murmur in foals, calves, pigs

Reduced venous return through the umbilical vein and ductus venosus allows the latter to gradually close

Foramen ovale closes

Increased venous return from lungs to left atrium

Reduced venous flow from placenta to right atrium

Pressure in left > right, forces septum primum against

septum secundum

Anatomical closure takes up to 1 year in most species

Non-functional vessels regress, become ligaments

E.g. umbilical arteries -round ligament; ligamentum arteriosum

Compression of the thorax squeezes fluid out of the lungs

Lungs inflate

Pulmonary vascular resistance becomes lower

birth

common congenital conditions

Inter-atrial septal defects (e.g. patent foramen ovale)

Inter-ventricular septal defects

Congenital venous shunts (e.g. persistent ductus venosus)

Vascular ring anomalies (e.g. persistent or additional aortic arches) -first pic - esophagus squeezed cos aorta and pulm artery not supposed to ocnnect

Pulmonary or aortic stenosis (abnormal narrowing of a passage in the body)

Abnormal positioning of the heart (e.g. ectopic heart in the neck-Ectopia cordis) - cow

Some occur commonly together

E.g. Tetralogy of Fallot = malformation of aortico-pulmonary septum (enlarged aorta and pulmonary stenosis) + ventricular septal defect (hole), right ventricular hypertrophy

tetra = 4 so 4 things happen

But you should be able to predict what happens functionally as a result