20.6 Development of Blood Vessels and Fetal Circulation
3 min read•june 18, 2024
Blood vessels form from embryonic mesoderm, with creating the first vascular network. This process, called , is followed by , where new vessels sprout from existing ones. These processes are crucial for developing a functional circulatory system.
Fetal circulation differs greatly from adult circulation, featuring unique shunts that bypass the non-functional lungs. The , not the lungs, oxygenates fetal blood. At birth, dramatic changes occur as the newborn transitions to breathing air, closing fetal shunts and establishing adult-type circulation.
Development of Blood Vessels
Formation of blood vessels
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- Embryonic mesoderm gives rise to the cardiovascular system including blood vessels
- Mesoderm is one of the three primary germ layers formed during gastrulation (ectoderm, mesoderm, endoderm)
- are multipotent stem cells derived from mesoderm
- Differentiate into both hematopoietic stem cells which give rise to blood cells and angioblasts
- Angioblasts are endothelial cell precursors derived from
- Differentiate into lining the inner walls of blood vessels
- Form the a network of small blood vessels through migration proliferation and differentiation
- Vasculogenesis is the process of blood vessel formation from angioblasts
- Involves migration proliferation and differentiation of angioblasts to form the primitive vascular plexus
- is the process of new blood vessel formation from pre-existing vessels
- Occurs through sprouting or splitting of existing blood vessels ()
- Allows for expansion and remodeling of the primitive vascular plexus to form a mature vascular network
- Stimulated by , which is produced in response to tissue hypoxia
Regulation of blood vessel development
- plays a crucial role in vascular development
- Activated in low oxygen conditions
- Stimulates the production of VEGF and other angiogenic factors
- Promotes the formation of new blood vessels to increase oxygen delivery to tissues
- contribute to vascular development
- Can differentiate into various cell types, including those involved in blood vessel formation
- Potential source for tissue engineering and regenerative medicine approaches in vascular disorders
Fetal Circulation
Fetal circulatory shunts
- shunts oxygenated blood from the to the inferior vena cava
- Bypasses the liver allowing rapid delivery of oxygenated blood to the fetal heart and brain
- shunts oxygenated blood from the right atrium to the left atrium
- Bypasses the pulmonary circulation as fetal lungs are not functional
- Allows more oxygenated blood to reach the systemic circulation
- shunts blood from the to the
- Bypasses the lungs allowing majority of right ventricular output to enter the systemic circulation
- Helps maintain high resistance in the pulmonary circulation as fetal lungs are not functional
Fetal vs adult circulation
- Oxygenation
- In fetuses, blood is oxygenated by the placenta not the lungs
- carries oxygenated blood from placenta to fetus
- carry deoxygenated blood from fetus to placenta
- In adults, blood is oxygenated in the lungs and returns to the left atrium via
- In fetuses, blood is oxygenated by the placenta not the lungs
- Blood flow patterns
- Fetal circulation is characterized by the presence of shunts (ductus venosus, foramen ovale, )
- Shunts allow preferential distribution of oxygenated blood to brain and heart
- In adults, there are no shunts and blood flows through pulmonary and systemic circulations in series
- Fetal circulation is characterized by the presence of shunts (ductus venosus, foramen ovale, )
- Placental circulation
- Fetal circulation includes the placental circulation responsible for gas exchange and nutrient transfer
- Adults do not have a placental circulation
- Pulmonary circulation
- In fetuses, pulmonary circulation is minimal as lungs are not functional
- In adults, pulmonary circulation is fully functional and all blood from right ventricle passes through lungs for oxygenation
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- Fetal blood contains fetal hemoglobin, which has a higher oxygen affinity than adult hemoglobin
- Allows for more efficient oxygen uptake from maternal blood in the placenta
Cardiovascular transition at birth
- Dramatic changes occur in the circulatory system as the newborn transitions to extrauterine life
- Lungs inflate and pulmonary blood flow increases
- Fetal shunts close (ductus venosus, foramen ovale, ductus arteriosus)
- Placental circulation ceases as the umbilical cord is cut
- Blood flow patterns shift to establish adult-type circulation
Key Terms to Review (31)
Angioblasts: Angioblasts are precursor cells that differentiate into endothelial cells, which line the interior surface of blood vessels. They play a crucial role in the development of the vascular system during embryonic growth.
Angiogenesis: Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels. This process is crucial for growth, wound healing, and in the context of exercise, it improves muscle performance by increasing blood supply to tissues.
Angiogenesis: Angiogenesis is the physiological process of new blood vessel formation from pre-existing vasculature. It is a crucial process that occurs during tissue injury, disease, and development, as it allows for the delivery of oxygen and nutrients to tissues in need.
Aorta: The aorta is the largest blood vessel in the human body, originating from the left ventricle of the heart and serving as the main conduit for oxygenated blood to be distributed throughout the body. This crucial artery plays a central role in the heart's anatomy, the cardiac cycle, cardiac physiology, and the development of the cardiovascular system during fetal circulation.
Blood islands: Blood islands are clusters of developing blood cells and future blood vessels found within the embryonic yolk sac. They represent the earliest stages of blood vessel and blood cell formation during fetal development.
Cardiovascular transition at birth: Cardiovascular transition at birth refers to the series of physiological changes that occur in the circulatory system of a newborn as it shifts from fetal to postnatal life. This transition is crucial because it enables the newborn to breathe air, redirects blood flow to different parts of the body, and establishes independent circulation outside the womb. It involves the closure of specific fetal shunts, the establishment of pulmonary circulation, and the adaptation of the heart and blood vessels to support the increased demand for oxygen.
Descending aorta: The descending aorta is the portion of the aorta, the largest artery in the body, that runs down through the chest (thoracic aorta) and abdomen (abdominal aorta), delivering oxygen-rich blood to the lower parts of the body. It follows the arch of the aorta and extends to where it bifurcates into the two common iliac arteries in the lower abdomen.
Ductus arteriosus: The ductus arteriosus is a temporary blood vessel in fetal circulation that connects the pulmonary artery to the descending aorta, allowing most of the blood to bypass the lungs which are not yet in use. After birth, it normally closes and becomes the ligamentum arteriosum within a few days.
Ductus Arteriosus: The ductus arteriosus is a temporary blood vessel present in the fetus that connects the pulmonary artery to the aorta, allowing blood to bypass the lungs before birth. It is a crucial structure in the development of the fetal cardiovascular system and the transition to postnatal circulation.
Ductus venosus: The ductus venosus is a fetal blood vessel that connects the umbilical vein to the inferior vena cava, allowing oxygenated blood from the placenta to bypass the liver and flow directly into the fetal heart. This vessel plays a critical role in fetal circulation by ensuring that highly oxygenated blood reaches vital organs efficiently.
Embryonic Stem Cells: Embryonic stem cells are pluripotent cells derived from the inner cell mass of a blastocyst, an early-stage embryo. These cells have the unique ability to differentiate into virtually any cell type in the body, making them a valuable tool in the fields of cellular differentiation and fetal development.
Endothelial cells: Endothelial cells are specialized cells that line the interior surface of blood vessels, forming a barrier between the blood and the surrounding tissues. These cells play a crucial role in vascular biology, influencing blood flow, maintaining vascular homeostasis, and participating in inflammatory responses. They are essential for the development and function of blood vessels, particularly during embryonic development and fetal circulation.
Fetal hemoglobin: Fetal hemoglobin (HbF) is a special type of hemoglobin found in fetuses, characterized by its higher affinity for oxygen compared to adult hemoglobin (HbA). This adaptation is crucial during prenatal development, as it allows the fetus to effectively extract oxygen from maternal blood while in the low-oxygen environment of the uterus. The unique structure of HbF facilitates gas transport and supports the developing tissues and organs of the fetus.
Foramen Ovale: The foramen ovale is an opening in the fetal heart that allows blood to bypass the lungs and flow directly from the right atrium to the left atrium, bypassing the pulmonary circulation. It is a critical feature of fetal cardiovascular development and the transition to postnatal circulation.
Foramen ovale of the middle cranial fossa: The foramen ovale is an oval-shaped opening in the sphenoid bone of the middle cranial fossa through which the mandibular branch of the trigeminal nerve (cranial nerve V3) passes. It serves as a crucial pathway for both nerves and blood vessels connecting the cranium to other parts of the head.
Gonadal and Placental Hormones: Gonadal hormones are steroid hormones produced by the gonads (ovaries in females and testes in males) that regulate reproductive functions and secondary sexual characteristics. Placental hormones are produced by the placenta during pregnancy, supporting fetal development and modifying maternal physiology to sustain the pregnancy.
Hemangioblasts: Hemangioblasts are stem cells that serve as common precursors to both blood cells and the cells lining blood vessels (endothelial cells) during embryonic development. They play a critical role in the formation of the vascular system and blood components in the fetus.
Hemangioblasts: Hemangioblasts are bipotential progenitor cells that give rise to both the hematopoietic (blood) and endothelial (blood vessel) lineages during embryonic development. These cells are crucial for the development of blood vessels and fetal circulation.
Hypoxia-Inducible Factor (HIF): Hypoxia-inducible factor (HIF) is a transcription factor that plays a crucial role in the body's response to low oxygen levels (hypoxia). HIF is a key regulator of cellular adaptation and survival under hypoxic conditions, and is closely linked to the development of blood vessels and fetal circulation.
Intussusceptive Angiogenesis: Intussusceptive angiogenesis is a process of blood vessel formation where existing vessels expand by splitting into two, rather than through the formation of new capillaries. This method of angiogenesis allows for a more rapid increase in vascular network density and is critical during development and growth, particularly in the context of blood vessel development and fetal circulation.
Placenta: The placenta is a temporary organ that develops during pregnancy, connecting the developing fetus to the uterine wall of the mother. It serves as a vital interface for the exchange of nutrients, waste, and gases between the maternal and fetal circulatory systems, enabling the growth and development of the fetus.
Primitive Vascular Plexus: The primitive vascular plexus is an early network of blood vessels that forms during embryonic development, serving as the foundation for the body's circulatory system. This initial vascular structure is essential for the development and growth of the fetus, as it facilitates the transport of oxygen, nutrients, and waste products throughout the developing organism.
Pulmonary artery: The pulmonary artery is a large blood vessel that transports deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. Unlike other arteries, it carries blood low in oxygen content.
Pulmonary Artery: The pulmonary artery is a major blood vessel that carries deoxygenated blood from the right ventricle of the heart to the lungs, where the blood becomes oxygenated. It is a crucial component in the circulatory system, playing a vital role in the cardiac cycle and fetal circulation.
Pulmonary veins: Pulmonary veins are blood vessels that carry oxygenated blood from the lungs back to the left atrium of the heart. Unlike most veins, which carry deoxygenated blood, pulmonary veins are unique because they transport blood rich in oxygen.
Pulmonary Veins: The pulmonary veins are blood vessels that carry oxygenated blood from the lungs to the heart's left atrium. They play a crucial role in the cardiovascular and respiratory systems, facilitating the exchange of gases and the circulation of blood throughout the body.
Umbilical arteries: Umbilical arteries are two blood vessels that carry deoxygenated blood and waste products from the fetus to the placenta during pregnancy. They play a crucial role in fetal circulation by ensuring that waste is efficiently removed to be processed by the maternal system.
Umbilical vein: The umbilical vein is a blood vessel present during fetal development that carries oxygen-rich blood from the placenta to the fetus. It plays a crucial role in providing the fetus with oxygen and nutrients necessary for growth and development.
Umbilical Vein: The umbilical vein is a blood vessel that carries oxygen-rich blood from the placenta to the developing fetus during pregnancy. It plays a crucial role in the fetal circulation and development of the blood vessels.
Vascular Endothelial Growth Factor (VEGF): Vascular Endothelial Growth Factor (VEGF) is a potent signaling protein that stimulates the growth and development of blood vessels. It is a crucial factor in the processes of angiogenesis and vasculogenesis, which are essential for the formation and maintenance of the circulatory system.
Vasculogenesis: Vasculogenesis is the process by which new blood vessels form from undifferentiated precursor cells, known as angioblasts or endothelial progenitor cells. This process is crucial for the development of the circulatory system and the formation of the first primitive blood vessels during embryonic development.