2009 Final Review: Basic Embryology

2009 Final Review Part 1: Basic Embryology

• The heart is the first organ to function within an embryo.
• The heart develops from two 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

• Week 3 development includes the formation of sinus venosus, primitive atrium, atrioventricular sulcus & primitive ventricle, interventricular sulcus, and bulbus cordis.
• The aorta sac will rise to form the aortic arch.
• The sinus venosus forms superior and inferior vena cava and posterior portions of the atria.

Heart Embryology

• The sinus venosus has a right and left sinus horn.
• The left horn forms the coronary sinus.
• The right horn is absorbed into the right atrium as the sinus venarum.
• The endocardial cushion forms the tricuspid and mitral valves, and parts of the atrial and ventricular septum.

Atrioventricular Canal Development

• The atrioventricular canal will divide into left and right sides, forming the mitral and tricuspid valves.
• The endocardial cushions are crucial for this division.

Fetal Circulation

• The placenta is responsible for the exchange of oxygen, carbon dioxide, nutrients, and waste products in the fetus.

Normal Variants:

• Chiari network is an embryologic remnant of the sinus venosus valves.
• Incomplete resorption causes this.
• Eustachian valve is an embryologic remnant of the inferior vena cava valve.
• Moderator band is a band-like structure connecting the interventricular septum to the right ventricle, transmitting the right bundle branch.
• False tendons are thin string-like structures in the left ventricle, connecting the septum to the papillary muscles.
• Sigmoid septum is an S-shaped septum that may bulge into the outflow tract.
• Lambl's excrescences are fine filamentous strands originating from the aortic valve, common in elderly patients; considered a degenerative change.

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.
• The first two branches off the ascending aorta are the coronary arteries.
• The left coronary artery (LCA) and right coronary artery (RCA) originate at the sinuses of Valsalva and travel down the outside of the heart muscle.

Order of Flow

• Oxygenated blood is pumped from the left ventricle through the aortic valve into the ascending aorta.
• The first two branches off the ascending aorta form the coronary system.
• Branches of the aortic arch provide oxygen and nutrients to the upper extremities.
• The descending thoracic aorta travels through the chest, and the descending abdominal aorta passes through the diaphragm into the abdomen, supplying oxygen and nutrients to organs and lower extremities.

Blood Vessels in the Body

• Arteries carry oxygen-rich blood from the heart to tissues.
• Arterioles regulate blood flow from arteries to capillaries.
• Metarterioles form branches into capillary beds.
• Capillaries connect arterioles to venules.
• Venules receive blood from capillaries and drain into larger vessels.
• Veins carry deoxygenated blood back to the heart.

Network of Vessels

• Arteries, arterioles, capillaries, and venules form the circulatory system.
• The system is divided into systemic and pulmonary circuits.