2009 Final Review Part 1: Basic Embryology

2009 Final Review Part 1: Basic Embryology

• The heart is the first organ to function within an embryo.
• The heart develops from a pair of heart tubes.
• These heart tubes are composed of two layers of cells.
• The outer layer forms the myocardium.
• The inner layer forms the endocardium.

Week 3 Heart Development

• Sinus venosus develops into the superior vena cava (SVC), inferior vena cava (IVC), and pulmonary veins.
• Primitive atrium divides into right and left atria.
• Atrioventricular sulcus divides the primitive atrium.
• Primitive ventricle develops into the apical portion of the left ventricle (LV) and inlet portion of the right ventricle (RV).
• Interventricular sulcus divides the primitive ventricle and bulbus cordis.
• Bulbus cordis develops into the apical portion of the RV, RV outflow tract (RVOT), LV outflow tract (LVOT), aorta (AO), and pulmonary artery (PA).
• The aorta begins to form the aortic arch.

Heart Embryology: Sinus Venosus

• The sinus venosus has a right and left sinus horn.
• The left horn forms the coronary sinus.
• The right horn becomes absorbed into the right atrium.

Endocardial Cushion

• Endocardial cushions form the tricuspid valve, mitral valve, and parts of the atrial and ventricular septa.

Questions about Heart Development

• The heart is the first organ to function during embryonic development: TRUE
• The sinus venosus develops into the superior and inferior vena cava and pulmonary veins: TRUE
• The structure responsible for oxygen, carbon dioxide, nutrient, and waste exchange in the fetus is the placenta.
• The right sinus horn becomes absorbed into the right atrium as the sinus venarum.
• The left sinus horn forms the coronary sinus.
• The growth of the atrioventricular canal separates into left and right sides, forming the mitral and tricuspid valves. This is accomplished by the endocardial cushions.

Normal Variants

• Chiari network is an embryologic remnant of the sinus venosus valves.
• Eustachian valve is an embryologic remnant of the inferior vena cava valve.
• Moderator band is a band-like structure in the right ventricle.
• False tendons are thin, string-like structures in the left ventricle.
• Sigmoid septum is an S-shaped septum.
• Lambl's excrescences are fine filamentous strands originating from the aortic valve in elderly patients, commonly considered a degenerative change.

Questions Regarding Normal Variants

• The Chiari network is an embryologic remnant related to the valves forming the sinus venosus. (Correct answer: c)
• The Eustachian valve is an embryologic remnant of the inferior vena cava valve. (Correct answer: a)

Moderator Band

• The moderator band is a structure in the right ventricle that transmits the right bundle branch from the bundle of His to the right ventricle.

False Tendons

• False tendons are thin string-like structures located in the left ventricle, connecting the interventricular septum to the papillary muscles.

Sigmoid Septum

• The shape of the interventricular septum (IVS) and left ventricular outflow tract can change with age, sometimes becoming S-shaped (sigmoid).

Aortic Valve Mass: Lambl's Excrescences

• Lambl's excrescences are fine filamentous strands that can be seen originating from the aortic valve in elderly patients.
• They are considered a degenerative change.
• Multiple can fuse to form giant excrescences.

Coronary Arteries

• The left main coronary artery arises from the superior aspect of the left coronary sinus of Valsalva.
• The right coronary artery arises from the superior aspect of the right coronary sinus of Valsalva,.

Order of Blood Flow Through the Heart and Aorta

• Oxygenated blood is pumped from the left ventricle through the aortic valve into the ascending aorta.
• The first two branches of the ascending aorta form the coronary system.
• The left and right coronary arteries arise from the sinuses of Valsalva and travel downward along the outside of the heart muscle.

Order of Blood Flow Through the Aortic Arch

• Branches off the aortic arch include: the brachiocephalic (innominate) artery, the right common carotid artery, the right subclavian artery, the left common carotid artery, and the left subclavian artery.
• The aortic isthmus connects the left subclavian artery and the ligamentum arteriosum.

Blood Vessels in the Body: Arteries, Arterioles, Capillaries, Venules, Veins

• Arteries carry oxygen-rich blood away from the heart to the tissues. They are muscular tubes with three layers.
• Arterioles regulate blood flow from arteries to capillaries.
• Capillaries connect arterioles to venules and exchange nutrients and waste between blood and interstitial fluid. Capillary walls are composed of a single layer of cells.
• Venules drain blood from capillaries to veins.
• Veins return blood to the heart, carrying low-pressure blood. They have thinner walls than arteries.

Network of Blood Vessels

• The network of vessels includes arteries, arterioles, capillaries, venules, and veins.