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The heart bulges, further develops, and begins to beat in a regular rhythm. Septum primum appears. [1] Pharyngeal arches, grooves which will form structures of the face and neck, form. The neural tube closes. The ears begin to form as otic pits. Arm buds and a tail are visible. Lung bud, the first traits of the lung appear. [1]
Heart development, also known as cardiogenesis, refers to the prenatal development of the heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube. The heart is the first functional organ in vertebrate embryos.
The first ten weeks of gestational age is the period of embryogenesis and together with the first three weeks of prenatal development make up the first trimester of pregnancy. From the 10th week of gestation (8th week of development), the developing embryo is called a fetus.
Diagram of the human fetal circulatory system. The heart and blood vessels of the circulatory system form relatively early during embryonic development, but continue to grow and develop in complexity in the growing fetus. A functional circulatory system is a biological necessity since mammalian tissues can not grow more than a few cell layers ...
The heart rate increases, but generally not above 100 beats/ minute. Total systematic vascular resistance decreases by 20% secondary to the vasodilatory effect of progesterone. Overall, the systolic and diastolic blood pressure drops 10–15 mm Hg in the first trimester and then returns to baseline in the second half of pregnancy. [6]
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The fetal circulation is composed of the placenta, umbilical blood vessels encapsulated by the umbilical cord, heart and systemic blood vessels. A major difference between the fetal circulation and postnatal circulation is that the lungs are not used during the fetal stage resulting in the presence of shunts to move oxygenated blood and ...
In the first trimester, a standard ultrasound examination typically includes: [12] Gestational sac size, location, and number; Identification of the embryo and/or yolk sac; Measurement of fetal length (known as the crown-rump length) Fetal number, including number of amnionic sacs and chorionic sacs for multiple gestations; Embryonic/fetal ...