|
The content on or accessible through Medpedia.com is for informational purposes only. Medpedia is not a substitute for professional advice or expert medical services from a qualified health professional.
Read more
|
Development of Cardiovascular System
There are currently no Lead Editors of this article.
Originating Author
Ask a Question on This Topic
Important Resources for Development of Cardiovascular System:
Development of the heart and vessels begins in the embryonic period. The first vessels and blood cells appear in extra-embryonic tissues in the third week after fertilization, and in the embryo in the fourth week. In the fourth week, a tubular heart forms and becomes looped. During the second month, the tubular heart develops into a four-chambered heart, and the circulatory pattern of the fetal period becomes established with circulation through the placenta and shunting of blood away from the pulmonary circulation.
Contents |
Stages of cardiovascular system development
Development of the cardiovascular system, including the heart, is perhaps best understood in the context of the physiological demands at different points in the life cycle. Four stages can be recognized:
- Precirculatory stage (weeks 1 and 2)
- Vitelline stage (weeks 3 and 4)
- Placental stage (second month to birth)
- Postnatal stage (beginning at birth)
Precirculatory stage (weeks 1 and 2)
Prior to implantation embryos generate ATP largely via the uptake and metabolism of nutrients present in tubal and uterine fluids.
At implantation the endometrium is in the secretory phase, it contains active glands, large amounts of nutrients and coiled arteries. Decidualization (the decidual reaction) occurs during implantation, at about 9 days, under the influence of progesterone. Endometrial stromal fibroblasts become large and polyploid (decidual cells), accumulate glycogen and lipid, and produce prolactin and insulin-like growth factor (IGF).
Vitelline stage (weeks 3 and 4)
During embryogenesis, the embryo eventually grows too large to obtain nutrients simply via diffusion. In the vitelline ("yolk sac") stage, nutrients are transferred from maternal sources to the embryo through the trophoblast (or, later, the chorion) and umbilical vesicle ("yolk sac").
The vitelline stage is characterized by the presence of a relatively large umbilical vesicle and vasculogenesis (angioblastic vasculogenesis). In the 3rd week, vessels and blood cells appear in the umbilical vesicle. Intraembryonic vessels begin to form in the 4th week.
During the 2nd month, vitelline circulation is superceded by placental circulation and disappears by the end of the 2nd month. Parts of the vitelline vasculature survive in the portal venous system.
Important processes in the vitelline stage include formation of the tubular heart and the beginning of development of arteries and veins. The cardiovascular system begins bilaterally and symmetrically, but many components of the heart and great vessels soon fuse in the midline and/or become asymmetric.
 The cardiovascular system in the trilaminar embryonic disc prior to embryo folding (4th week). Blue: The endocardial heart tubes, and vitelline and umbilical veins. (The vitelline veins are represented as dotted blue lines, but most are not included in the illustration.) Red: The dorsal aortae and umbilical arteries. Gray's Anatomy (1918) figure 458 (originally from Eternod). Source: Wikimedia Commons |
 Lateral view of embryo in the 5th week showing the cardiovascular system. Gray's Anatomy (1918) figure 472 (originally from His). Source: Wikimedia Commons |
Placental stage (second month and fetal period)
Placental circulation develops from allantoic circulation at the end of the first month. Oxygenated blood is brought from the placenta in the umbilical vein. Mixed (deoxygenated) blood is returned to the placenta via two umbilical arteries.
The liver becomes the primary site of hematopoiesis in first trimester. Bone marrow hematopoiesis begins in 2nd trimester and takes over in 3rd trimester.
Early in the placental stage (i.e., during the second month of the embryonic period) there are important structural changes in the cardiovascular system: conversion of the tubular heart into a four-chambered heart, and development of the great arteries and veins of the systemic and pulmonary circulations.
Blood is shunted "right-to-left" around the pulmonary circulation where there is high resistance until the lungs expand at birth. Two shunts exist, the foramen ovale, which shunts blood from the right atrium to the left atrium, and the ductus arteriosis, which shunts blood from the pulmonary artery to the aorta.
A venous shunt (ductus venous) through the liver delivers oxygenated blood from the umbilical blood directly into the heart's venous return
Changes in circulation at birth
Interruption of placental circulation and the beginning of pulmonary respiration cause functional and then structural changes in the prenatal shunts. Expansion of chest and aeration of lungs reduces resistance to pulmonary circulation. Oxygenation, nutrition and waste functions formerly served by the placenta are taken over by the lungs, alimentary tract and kidneys, respectively.
- The umbilical arteries are ligated, become constricted and then become the internal iliac arteries and the medial umbilical ligaments.
- The umbilical vein is ligated, constricts and then becomes the ligamentum teres of the liver.
- The ductus venosus closes within hours of birth and becomes the ligamentum venosum.
- The ductus arteriosus usually closes 1-4 days after birth and become the ligamentum arteriosum.
- The foramen ovale is closed by increased pressure in the left atrium. Probe patency usually lasts for months, but may be found in 20-25% of adults.
Selected Malformations of the Cardiovascular System
Most major congenital anomalies of the cardiovascular system are malformations of the heart and great vessels. Congenital heart disease is relatively common. Its incidence is about 5-8/1,000 births. The list below of the most common forms (and some uncommon forms with educational value) accounts for almost 90% of all congenital heart disease. Clinically useful classifications of congenital heart disease emphasize presence or absence of blood shunting and cyanosis.
- Malformations without a shunt are typically obstructive anomalies, and clinically acyanotic
- Malformations with a left-to-right shunt are usually acyanotic, although cyanosis may develop later
- Malformations with a right-to-left shunt are associated with early cyanosis
External Links
Human Developmental Anatomy Center (HDAC) of the National Museum of Health & Medicine
- O'Rahilly R & Müller F. Developmental Stages in Humans. Carnegie Institution of Washington, 1987.
Embryology.ch - an online course in embryology for medical students
Other Resources
O'Rahilly R and Müller F. Human Embryology & Teratology, 3rd Ed. New York: Wiley-Liss, 2001.
[[Category:|Category:]]
To suggest changes to this page, you must create an account on Medpedia.