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Bekah's Embryology Assignment #6

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Bekah's Embryology Assignment #6 1 Part 1 Read pages 289 – 362 (Chapter 13 through Chapter 14) in The Developing Human For all fill in the blank questions you only need to provide the missing word or phrase. For all other questions including definitions please ensure you write in complete sentences using appropriate grammar. A question will be deemed to have been answered when the question has been restated in your answer along with all pertinent information. Ensure you do not miss any information in multi-part questions. Simply listing facts is less important than explaining the information so that we can be sure you fully grasp the content. 1. What is the first major system to function in the embryo? The first major system to function in the embryo is the cardiovascular system. 2. When do the primordial heart and vascular system appear? The primordial heart and vascular system appear in the middle of the third week of development. 3. Briefly explain the development of the heart and veins associated with the embryonic heart. The heart starts off as a pair of endothelial strands (called angioblastic cords) that are from the cardiogenic mesoderm. These appear in the third week. These cords then form a few thin heart tubes. Later, these heart tubes fuse together to form a single heart tube. This begins at the cranial end of the developing heart and it extends caudally. The heart then begins to beat at 22-23 days and blood begins to flow during the 4th week. Various cells give rise to certain parts of the heart with progenitor cells giving rise to the ventricular myocardium and the myocardial wall. Progenitor cells also help with the rapid growth and elongation of the heart tube. At 4 weeks, there are 3 paired veins that drain into the tubular heart. These veins are: vitelline veins (which return poorly oxygenated blood from the umbilical vesicle), umbilical veins (which carry well-oxygenated blood from the chorionic sac), and common cardinal veins (which return poorly oxygenated blood from the body of the embryo). As development continues, the right umbilical vein disappears at about week 7 which leaves only the left umbilical vein to carry well-oxygenated blood from the placenta to the embryo. The vitelline veins is in the mid-gut region of an embryo, 2 traveling to the heart and the liver. The cardinal veins form the main venous drainage system of the embryo. 4. Define the inferior vena cava and its function. The inferior vena cava is a vein that carries de-oxygenated blood from the lower half of the body back to the right side of the heart for oxygenation. 5. Define the superior vena cava and its function. The superior vena cava is a vein that carries de-oxygenated blood from the upper half of the body (above the diaphragm) to the right side of the heart for oxygenation. 6. Explain the anatomy and development of the fetal heart. The fetal heart continues to develop and mature. The endothelial tube develops into the internal endothelial lining of the heart, the endocardium. The primordial myocardium further develops into the muscular walls of the heart and becomes the mature myocardium. The epicardium, is derived from mesothelial cells that came from the external surface of the sinus venosus and that spread over the myocardium. Even before the early heart tube was formed, the homeobox transcription factor was expressed in the left heart that helped to form the left-right patterning of the heart tube which aids in the formation of the cardiac loop that is necessary for mature heart functions. The tubular heart continues to elongate and develop and the bulbus cordis (which is composed of the truncus arteriosus, the conus arteriosus, and the conus cordis), ventricle, atrium, and sinus venosus develops. These 4 structures develop into the 4 chambers of the heart. The arterial and venous ends of the heart are fixed due to the pharyngeal arches and the septum transversum. At about 23-28 days, the heart tube gets looped so that a U-shaped D-loop is formed with the apex of the heart pointing to the left. As the heart continues to elongate and bend, it gradually goes into the pericardial cavity. Initially, the early heart is suspended from the dorsal wall by the dorsal mesocardium, however, this soon begins to degenerate, leaving just the transverse pericardial sinus between the right and left sides of the pericardial cavity. At this point, the heart is only attached at both its cranial and caudal ends. 7. Explain tetralogy of fallot. Tetralogy of fallot is a heart defect that consists of a grouping of four cardiac defects. These defects include: pulmonary artery stenosis (which is the obstruction of the right ventricular outflow), VSD (ventricular septal defect), dextroposition of aorta (overriding or straddling aorta), and right ventricular hypertrophy. With tetralogy of fallot, the 3 pulmonary trunk is usually small and there can be varying amounts of pulmonary artery stenosis. The obvious sign for tetralogy of fallot is cyanosis, indicating a deficiency in the oxygenation of blood. Cyanosis is not typically present right away at birth but typically a bit after birth. With this, surgical intervention is typically needed almost immediately to either place a shunt for a temporary fix or to perform a full surgical repair. 8. Explain the fetal and neonatal circulation/9. Explain transitional neonatal circulation. Fetal circulation: Fetal circulation before birth is vastly different than adult circulation. The main source of oxygen is the placenta, not the lungs. In fact, the lungs are largely bypassed in fetal circulation (before birth). There are several additional structures in the circulatory system that are present. These include: umbilical vein, umbilical arteries, ductus venosus, ductus arteriosis and the foramen ovale. Oxygenated blood is taken from the placenta through the umbilical vein into the baby’s abdominal wall where it travels through the ductus venosus and into the inferior vena cava where it then travels throughout the body going to the heart and traveling through the foramen ovale (which allows blood to move from the right atrium to the left atrium) before then going into the umbilical arteries where it returns to the placenta to pick up oxygen and nutrients and then repeat its path in the baby’s body. Transitional Neonatal circulation: After birth, the fetal circulation changes quite rapidly to become like an adult’s circulatory system. This change starts immediately after the baby is born and may continue for a few weeks. Instead of relying on the placenta for oxygen, the baby must not breathe and rely on its lungs. One of the big changes is that pulmonary circulation changes from high-resistance to low-resistance. Vasoconstriction also occurs which helps to decrease placental circulation which prevents blood flow from going from the baby back to the placenta. Many of the structures that were needed for fetal circulation are no longer needed in mature human circulation after birth. For instance, the foramen ovale gets pushed closed due to decreased umbilical flow and pressure. The ductus venosus and ductus arteriosus constrict and close shortly after birth as these are no longer needed, instead other veins and arteries become the primaries (vena cava, aorta, etc.). Some of these changes begin as a newborn takes its first breath. However, other changes occur over hours and days. During this transitional stage, there may be some right-to-left blood flow through the foramen ovale. Also, while initially the closure of the fetal vessels and foramen ovale is a functional change, later the anatomic closure results due to a proliferation of endothelial and fibrous tissues that close off these vessels/structure. 10. What is associated with aeration of the lungs? Aeration of the lungs is associated with: 4 • Dramatic decrease in pulmonary vascular resistance • Marked increase in pulmonary blood flow • Progressive thinning of the pulmonary arteries 11. Explain the development of the lymphatic system. The development of the lymphatic system starts at the end of the 6th week of development, about 2 weeks after the primordia of the cardiovascular system are present and recognizable. The development of lymphatic vessels is very similar to that of the development of blood vessels. The lymphatic system functions closely with the circulatory system as the lymph vessels make connections with the venous system. Early capillaries of the lymphatic system join together to form a network of lymphatics. At the end of the embryonic stage, there are 6 primary lymph sacs that are present. These include: 2 jugular lymph sacs, 2 iliac lymph sacs, 1 retroperitoneal lymph sac, and 1 cisterna chyli. Lymphatic vessels connect to these lymph sacs as they pass along near the main veins of the body. Most parts of the lymph sacs (except a small superior part of the cisterna chyli) will develop into groups of lymph nodes during the early fetal period. Part 2 For this assignment you will become familiar with ultrasounds. They are a tool often used in fetal development and it can be confusing to know exactly how they work, even if you have been pregnant and had ultrasounds yourself. Watch these two films and take notes. You will be learning the specifics of ultrasound generally and then obstetrically. Once you have your information from the two videos you can write a 2-3 paragraph synopsis of what you learned. Video 1 Video 2 The unaided human ear can hear sounds that are between 20Hz - 20,000Hz. Above this range is called ultrasound (above sound). In an ultrasound, a transducer sends out multiple, fast pulses and will reflect off of certain items and note any difference there is in time.
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