12. Development of the Heart

List the overall steps in the development of the heart and its vessels.

1. Formation of the heart tube

2. Cranio-caudal folding and positioning of the heart

3. Division of the heart tube

4. Bending of the bulbo-ventricular loop

5. Circulation through the primordial heart

6. Formation of the heart chambers

7. Partitioning of the heart

Formation of the heart tube; formation of endo-cardial tubes

• When _______ folding of the embryo occurs, the __________ ____ move ________ to ____ with each other. It is followed by the __________ mesoderm.

• The splanchnic mesoderm ________ in the cardiogenic area to form 2 solid _____-_______ _____.

• Both cords start __________ to form ____-_______ tubes.

• The 2 ends of the ________ (green) fuse together forming the ___.

• lateral, endodermal ends, medially, fuse, splanchnic

• thickens, angio-blastic cords

• canalizing, endo-cardial

• endoderm, gut

Formation of the heart tube

• The 2 ____-_______ tubes start approaching each other in the _______.

• At this stage, the developing heart is composed of a ____ ___________ ____ which forms the ____________ and the _________ mesoderm forms the __________.

• The ___________ cells of the ___________ ______ forms the __________.

• endo-cardial, midline

• thin, endocardial tube, endocardium, splanchnic, myocardium

• mesothelial, pericardial coelom, epicardium

Formation of the heart tube

• The 2 tubes fuse to form one ___________ tube. This tube lies _______ to the ___ (future _________ system).

• The heart tube is connected to the _________ mesoderm:

  • Anterior through _______ (blue arrow) mesocardium

  • Posteriorly through ______ (red arrow) mesocardium.

• After that, the ventral mesocardium __________ and a single __________ ______ is formed.

• The pericardial cavity is the _____-_________ ______ around the heart.

• endocardial, ventral, gut, digestive

• splanchnic, ventral, dorsal

• disappears, pericardial cavity

• intra-embryonic coelom

Describe the cranio-caudal folding and the position of the heart.

• As folding of the head region occurs, the heart and the pericardial cavity become ventral to the foregut and caudal to the oro-pharyngeal membrane

• The pericardial cavity is ventral to the heart

• (blue arrow is stomodeum)

Division of the heart tube

The tubular heart elongates and develops alternate dilations and constrictions which are arranged from above downwards. List the divisions.

1. The bulbus cordis

2. The ventricle

3. The atrium

4. The sinus venosus

Division of the heart tube

From above downwards, the bulbus cordis is consisted of 3 things. List them.

1. The truncus arteriosus

2. The conus arteriosus

3. The conus cordis

Division of the heart tube

• The arterial end of the heart is the _______ _________.

• The venous end of the heart is the _____ _______.

• truncus arteriosus

• sinus venosus

Bending of the bulbo-ventricular loop

• Because the ______ ______ (yellow) and the _________ (red) grow faster than the other regions, the heart bends (to the _____) on itself, forming a U-shaped _________________ loop.

  • Bulbus cordis moves _________, ________ and _____.

  • The _________ moves to the left.

  • The ______ (dark blue) and the _____ _______ (green) move upwards and posterior.

• As the heart tube bends, the atrium and sinus venosus become ______ and _____ to the bulbus cordis, while they become ______ and ____ to the ventricle.

• bulbus cordis, ventricle, right, bulbo-ventricular

  • downwards, forwards, right

  • ventricle

  • atrium, sinus venosus

• dorsal, right, dorsal, left

Circulation through the the primordial heart

• The heart is formed of the _____ _______ (green), common ______ (blue), common ________ (red), and _______ ______ (yellow).

• The blood moves from the _____ _______, to the _____, and then to the ________, and finally to the ______ _____.

• sinus venosus, atrium, ventricle, bulbos cordis

• sinus venosus, atrium, ventricle, bulbos cordis

Formation of the heart chambers

How is the right atrium formed?

Formed partly from the common atrium and the right horn of the sinus venosus

How is the left atrium formed?

Formed partly from common atrium absorption of the primordial pulmonary vein

How is the right ventricle formed?

Formed from the common ventricle and the conus cordis

How is the left ventricle formed?

Formed from the common ventricle and the conus cordis

How are the ascending aorta and pulmonary artery formed?

Formed by the truncus arteriosus

How are the aortic and pulmonary valves formed?

Formed by the conus arteriosus

List the partitions of the heart.

1. Atrio-ventricular (AV) canal

2. Inter-atrial septa

3. Inter-ventricular septum

4. Bulbar septum

1. Atrio-ventricular (AV) canal

• Anterior and posterior __________ _______________ ________ project from the anterior and posterior walls of the AV canal.

• They approach each other and ____ to form the AV ______, dividing the AV canal into _____ and ____ AV canals.

• endocardial atrio-ventricular cushions

• fuse, septum, right and left

2. Inter-atrial septa

The __________ atrium is divided into right and left atria by the formation and ______ of 2 septa; septum ______ and septum ________ by the ___ week.

primordial, fusion, primum, secundum, 5th

Septum primum

• Grows from the _________ ______ towards the fusing AV _______, partially dividing the atrium into right and left halves.

• This septum develops a large _______ called the _______ ______ (green arrow), between its lower free edge and the AV ___________ _________.

• This foramen _________ in size gradually until it __________ when the septum primum is completed by the ___________ _______ of the AV ______.

• Before the foramen ______ disappears, another upper opening called the _______ ________ (blue arrow) appears.

• primordial atrium, cushions

• opening, foramen primum, endocardial cushions

• decreases, disappears, endocardial cushion, septum

• primum, foramen secundum

Septum secundum

• Is a ____, ________ septum, which starts to grow to the _____ of the septum primum.

• It gradually ________ the _______ ________ in the septum primum.

• It has an ____foramen lower down (foramen _____) (light blue arrow) between the 2 _____.

• thick, muscular, right

• overlaps, foramen secundum

• oval, ovale, atria

3. Interventricular septum

Has 2 parts; muscular part and membranous part.

Muscular part

• A median _____ or fold grows from the _____ of the primordial _________, near its ____.

• It represents the ______ 2/3 of the ______.

Membranous part

It develops from 2 sources:

• Its anterior 1/3 comes from the ________ ______ ______ (yellow).

• The posterior 2/3 comes from the _________ ___ ______(green).

• ridge, floor, ventricle, apex

• lower, septum

• proximal bulbar septum

• posterior AV cushion

4. Bulbar septum

• Is ______ in shape.

• Formed of ________ part and ______ part.

• spiral

• proximal, distal

Proximal bulbar septum

• Divides the _____ ______ into:

  • Right half _____________ of the right ventricle.

  • Left half _________ of the left ventricle.

Distal bulbar septum

• Divides the _____ __________ into:

  • _________ valve (anteriorly) and ______ valve (posteriorly).

• It divides the _______ __________ into:

  • _________ artery (anteriorly) and _________ _____ (posteriorly).

• conus cordis

  • infundibulum

  • vestibule

• conus arteriosus

  • pulmonary

  • aortic

• truncus arteriosus

  • pulmonary, ascending aorta