Development of the heart

Development of the heart• Heart development is first apparent at the 18-

19th day in the cardiogenic area in the mesoderm

• A paired heart cords form first and shortly each heart cord turns into heart tube

• The paired heart tubes been to migrate toward each and fuse to form a single endocrdial heart tube lying in the midline.

• The endocardial heart tube (EHT) undergoes dilations and constrictions so that five distinct regions of the heart can be identified. These are the truncus arteriosus, bulbus cordis, ventricle, atrium, and sinus venous.

• thereafter the EHT undergoes looping

HT in the cardiogenic area. Note the caudal displacement as a result cranial fold and the looping of the EHT into the pericardial cavity

Fusion of heart tubes as a result of lateral folding

Partitioning of EHT• Truncus arteriosus is divided by

aorticopulmonary septum into ascending aorta and pulmonary trunk

• The bulbus cordis is incorporated into the wall of the ventricles

• The primitive A-V canal is divided into left and right A-V opening by endocardial cushions

• The ventricles is divided into left and right ventricles by interventricular septum

• The atrium is partially partitioned by 2 septa- septum primum and septum secundum

Septation of atrium : formation of septum primum and ostium secundum. Note the position of endocardial cushion, dividing the A-V canal.

Septation of atrium : formation of septum secundum and foramen ovale. Note that the closure of foramen is by a flap of septum primum

The sinus venosus and pulmonary veins are incorporated into the walls of the right and left atria respectively

Note the fusion of endocardial cushion and its contribution to the membranous part of interventricular septum

anomalies• Abnormal position of the heart

• Dextrocardia (may be associated with situs inversus)• Ectopia cordis

• Atria septa defects (ASD) very common. There are various clinical types

• Probe patent foramen ovale• Secundum ASD• Endocardial type• Sinus venosus• Common atrium• Ventricular septa defects (VSD) most common» Membranous VSD» Muscular VSD» Absence of interventricular septum – cor triloculare

biatriatum (very rare)

Anomalies cont.

• Abnormal division of truncus arteriosus• Persistent truncus arteriosus• Aorticopulmonary septa defect (aortic window)• Transposition of the great arteries• Pulmonary stenosis/atresia• Tetralogy of Fallot• Aortic stenosis/atresia

LeftAnti clockwise

Fallot tetralogy

Persistent truncus arteriosus

Transposition of great arteries and pulmonary valve atresia

Diaphragm (Development )• The diaphragm develops from 4 sources1. Septum transversum (gives rise to the central

tendon)2. Cervical myotomes (C3,4,5)3. Mesodermal fold- pleuroperitoneal membrane4. Oesophageal mesenteryFailure of the pleuroperitoneal membrane

development is the common cause of CDH (Bochdalek’s foramen)

Others: Morgagni foramen hiatus hernia (sliding or rolling types)

Diaphragm (clinical notes)• Referred pain from the diaphragm• Hiccups (hiccoughs)• Diaphragmatic rupture

• Why it is that patients suffering from severe dyspnœa are most comfortable and least short of breath when they sit up?

Development of VASCULAR system

Circulation in ½ of the embryo

Derivatives of aortic arches• Aortic arches are the arteries of the branchial arches• Aortic arteries arise from the aortic sac and terminate at

the paired dorsal aortas• There are 6 pairs of aortic arches (but do not develop at

the same time). Remember that the 5th never developed completely

• The caudal portion of the aortic sac continuous with truncus arteriosus

• The division of the truncus arteriosus by aortic pulmonary septum, the aortic sac divides into left and right horns

• The right horn give rise to brachiocephalic trunk/artery• The left horn give rise to the proximal portion of the

aortic arch

Aortic arch derivatives cont.• The 1st aortic arches disappear (3rd week). A small portion

persist as maxillary arteries• The 2nd aortic arches also disappear. The remaining portions

give rise to hyoid and stapedial arteries• The 3rd aortic arches; the proximal portions form common

carotid arteries, distal portions join with the dorsal aorta to form the internal carotid arteries

• The 4th aortic arch: the left aortic arch forms part of the arch of the aortic arch. The proximal part of the arch of the aorta develops from the aortic sac and the distal part from the left dorsal aorta. The right 4th aortic arch become the proximal part of the right subclavian artery. The distal part of the right subclavian is formed from the right dorsal aorta and the right 7th intersegmental artery

Aortic arch derivatives cont.• The left subclavian artery is not derivative of aortic arch. Is

derived entirely from left 7th intersegmental artery• The 5th aortic arches disappear entirely• The 6th aorta arches:

– the left arch develops as follows – • Proximal part becomes the proximal part of left

pulmonary artery• The distal part which initially is attached to the dorsal

aorta persists as ductus arteriosus– The right arch develops as follows –

» The proximal persists as the proximal part of right pulmonary artery.

» The distal part degenerates

Note the derivatives of the aortic arches

The course of recurrent laryngeal nerve• The differences in the transformation of the 6th aortic arches

has resulted in the asymmetry in the course of the recurrent laryngeal branch of vagus nerve (nerve for the 6th brachial arch). The nerve hook around the 6th aortic arches on the way to the larynx

• On the right: • The distal part of 6th arch has denerated• The 5th has degenerated entirely• Prompting the right recurrent laryngeal nerve to move

superiorly to hook the right subclavian artery derive from the 4th arch

• On the left:» The left recurrent laryngeal nerve hook ductus

arteriosus - the persisted distal part of the 6th aortic arch

Anomalies • Patent ductus arteriosus• Coarctation of the aorta (preductal and

postductal)• Double aortic arch• Right arch of aorta (with or without

retroesophageal component)• Abnormal origin of right subclavian

Abnormal origin of right subclavian artery

Pre and post ductal coarctation of aorta. note the expansion of the alternate pathways

double aorta

Vitelline, umbilical and intersegmental arteries• Vitelline arteries supply the york sac. They paired

numerous arteries. As the york sac is being incorporated into the body cavity to form the primitive gut, the arteries fuse and in adult form celiac trunk, SMA and IMA that supply the derivatives of foregut, midgut and hindgut.

• Umbilical arteries initially paired ventral branch of dorsal aorta; latter acquires secondary connection with CIA. After birth, the proximal portion persist as the IIA and superior vesical artery. The distal portion become obliterated to form medial umbilical ligaments.

• Intersegmental arteries are initially, pair branches of the dorsal aortal supplying the somites and their derivatives– In the neck the intersegental arteries fuse longitudinally

to form the vertebral arteries– In the thorax they form the intercostal arteries– In the lumbar region they form the lumbar arteries and

CIA (the CIA is formed by fusion of number of lumbar arteries.

– In the sacral region, the form lateral sacral arteries and median sacral artery.

Development of venous system:• The adult venous system develops from 3

primitive veins (or venous systems)– Vitelline or omphalomesenteric veins; this carries

blood from the york sac to the sinus venosus– Umbilical veins; from the chorionic vili carrying

oxygenated blood to the sinus venosus– Cardinal veins form the main venous draining

system of the body of the embryo. Initially consists of

• Anterior and superior cardinal veins• Common cardinal veins

Derivatives of sinus venosum• The sinus venosum separate into left and right sinus

horns• Each horn receives venous blood from the following

• Common cardinal vein• Umbilical vein• Vitelline vein• The left umbilical and vitelline veins (cranial to

septum transversum) disappear resulting in L to R shift of venous blood flow to the atrium

• At the same time the posterior cardinal veins become obliterated. The left common cardinal vein also becomes obliterated

Derivatives of sinus venosum cont.

• Most parts of the right sinus horn become incorporated into right atrial wall (sinus part of right atrium)

• Consequently:– The remains of the left sinus horn is oblique vein

of the left atrium and coronary sinus– The distal portion of ACV becomes the SVC– The IVC (intrahepatic portion) is derived from

right vitelline vein (see changes during liver developments)

Venous system cont.• Derivatives of the vitelline veins.

– Form plexus around the developing duodenum and passes through the septum transversum to enter the sinus venosum

– The liver bud growing into the septum transversum interrupt the course of the vitelline and umbilical veins, forming extensive vascular network called hepatic sinusoids

– The right vitelline vein enlarges (hepatocardiac channel) following disappearance of the left sinus horn and proximal portion of left vitelline

– The hepatocardiac channel become the hepatocardiac portion of the IVC

– The hepatic veins are derived from the remaining right vitelline veins of developing liver.

Venous system cont.

• Umbilical vein– Initially the L $ R umbilical veins both side of the

expanding liver, but some become connected into the hepatic sinusoids

– The right umbilical vein and part of the left between the liver and sinus venosum disappear

– The persisted portion of the left umbilical veins therefore carries all the blood from the placenta to the faetal heart

– Ductus venosus is a large shunt passes through the liver connecting the umbilical vein and IVC directly.

– After birth the umbilical vein and ductus venosum become ligamentum teres and ligamentum venosum respectively

Venous system cont.

• Cardinal veins– Initially there are 3 cardinal veins :- anterior,

posterior and common. They empty into the sinus venosum. Later additional veins develops

• The anterior cardinals become connected by oblique anatomoses which becomes the left brachiocephalic veins. The caudal part of the left anterior cardinal vein degenerates

• The lower part of the right anterior cardinal vein and the right common cardinal vein become SVC

• Posterior cardinal veins (initially for the mesonephros and the body wall) thus degenerate completely excepts the root of azygos and common iliac veins

Venous system cont.

• Subcardinal vein – replaces part the posterior cardinal vein and drains the

kidneys. – They are connected to each other by subcardinal

anastomosis. – The anastomoses between the subcardinal veins become

the left renal vein– Most upper of left subcardinal veins disappears– The caudal portion of subcardinal vein remains as the left

gonadal vein– The right subcardinal vein thus become the main drainage

channel that form the renal segment of IVC

Venous system cont.

• Supracardinal vein– Develops when the posterior cardinal veins disappear– drains the body wall via intersegmental veins– The are disrupted by the developing kidneys– Cranial to the kidneys the L $ R are connected by anatomosis

that represents azygos and hemi-azygos veins– The 4th – 11th right intercostal vein drains into right

supracardinal vein which togather with remains of posterior cardinal vein formed the azygos vein

– On the left, the 4th – 7th intercostal veins drain into left supracardinal vein the represents the hamiazygos vein

– The hemiazygos vein empty into the zygos vein via the anastomosis.

Venous system cont.

• Sacrocardinal vein– The anastomosis between L $ R sacrocardinal

form the left common iliac vein– The right sacrocardinal becomes the lower part of

IVC

anomalies

• Double IVC• Absence of IVC• Left SVC• Double SVC