Fetal Circulation

Fetal circulation involves three shunts: ductus venous, ductus arteriosus, and foramen ovale (Figure III-2-10). After birth, a number of changes occur in the circulatory system because of the cessation of placental blood flow and start of lung respiration (Table III-2-3).

Table III-2-3. Adult Vestiges Derived From the Fetal Circulatory System

Changes After Birth

Remnant in Adult

Closure of right and left umbilical arteries

Medial umbilical ligaments

Closure of left umbilical vein

Ligamentum teres

Closure of ductus venosus

Ligamentum venosum

Closure of foramen ovale

Fossa ovale

Closure of ductus arteriosus

Ligamentum arteriƶs um

Vasculogenesis starts in the mesoderm surrounding the yolk sac.

Hematopoiesis occurs initially in the mesoderm surrounding the yolk sac and later in the fetal liver, spleen, thymus, and bone marrow.

Tetralogy of Fallot occurs when the AP septum fails to align properly and results in (1) pulmonary stenosis, (2) overriding aorta, (3) interventricular septal defect, and (4) right ventricular hypertrophy. This causes right-to-left shunting of blood with resultant cyanosis.

Persistent truncus arteriosus occurs when there is only partial development of the AP septum. This results in a condition in which only one large vessel leaves the heart and it receives blood from both the right and left ventricles. This causes right-to-left shunting of blood with resultant cyanosis. This defect is always accompanied by membranous ventricular septal defect

Overriding Aorta Anatomy

140 medical

Figure IN-2-11. Divisions of the Mediastinum

Middle Mediastinum

This section contains the pericardium, phrenic nerves, and heart.

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Pregnancy Diet Plan

Pregnancy Diet Plan

The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.

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