Embryology Lecture on Heart and Lungs PDF

Here's a structured markdown format of the provided text and images, focusing on clarity and organization: ### Revision Embryo, Block-ll #### Spring Semester 2023 #### Dr. Ismail Memon MBBS, PhD, Saba University School of Medicine, Dutch Caribbean This appears to be a lecture or review on embryolo...

Here's a structured markdown format of the provided text and images, focusing on clarity and organization: ### Revision Embryo, Block-ll #### Spring Semester 2023 #### Dr. Ismail Memon MBBS, PhD, Saba University School of Medicine, Dutch Caribbean This appears to be a lecture or review on embryology, specifically focusing on the heart and respiratory systems. ## Beginning of the development of Respiratory System * The respiratory system develops from the **lung bud** when the embryo is approximately **4 weeks old**. * The lung bud is a respiratory diverticulum that appears as an outgrowth from the **ventral wall of the foregut**. * A transcription factor **TBX4** induces the formation of the lung bud, which accounts for the continued growth and differentiation of the lungs. *Caption: Diagram of the developing lung bud, showing the heart, vitelline duct, allantois, and cloacal membrane.* ### Which germ layers give rise the respiratory organs? * Epithelium of the larynx, trachea, bronchi, and lungs is derived from **endoderm**. * The cartilaginous, muscular, and connective tissue components of the trachea and lungs are derived from **splanchnic (visceral) mesoderm** surrounding the foregut. *Caption: Diagram of the respiratory apparatus.* ### Development of Pleurae * The spaces for the lungs lie on each side of the foregut and are gradually filled by the expanding lung buds. * The **mesoderm**, covering the outside of the lung, develops into the **visceral pleura.** * The **somatic mesoderm layer**, covering the body wall from the inside, becomes the **parietal pleura**. * The space between the parietal and visceral pleura is the **pleural cavity**. *Caption: Diagram of the pleura.* ### Maturation of Lungs * Up to the seventh prenatal month, the bronchioles divide continuously into smaller canals, and the vascular supply increases steadily. * Terminal bronchioles divide to form **respiratory bronchioles**, which divide to form alveolar ducts and terminal sacs. * The sacs are lined by thin-walled type I alveolar cells, responsible for gas exchange. * The intimate contact between type I alveolar and endothelial cells makes up the **blood air barrier**. * The **type II alveolar epithelial** cells develop at the end of the sixth month; they produce **surfactant**, capable of lowering surface tension at the air-alveolar interface. * The amount of surfactant in the fluid increases, particularly during the last 2 weeks before birth. * Fetal breathing movements begin before birth and cause the aspiration of amniotic fluid. * These movements are important for stimulating lung development and conditioning respiratory muscles. * When respiration begins at birth, most of the lung fluid is rapidly resorbed. * The surfactant coat prevents collapse of the lung during expiration (atelectasis). * Respiratory movements after birth bring air into the lungs, which expand and fill the plural cavity. * Growth of the lungs after birth is primarily due to an increase in the number of respiratory bronchioles and alveoli and continues during the first 10 years of postnatal life. *Caption: Diagrams showing respiratory bronchioles and the alveoli.* ## Formation of the Cardiogenic Fields * By the third week of development, three germ layers form and organ formation begins. * The embryo is no longer able to satisfy its nutritional requirements by diffusion alone. * Initially, the vascular system appears in the **middle of the third week** to meet the needs. * Initially, the progenitor heart cells from the epiblast migrate into the splanchnic layer of lateral plate mesoderm. Here, they establish a horseshoe-shaped **primary heart field (PHF)** cranial to the neural plate * The primary heart field (PHF) cells form the atria, left ventricle, and part of the right ventricle. * The **secondary heart field (SHF) cells** reside in splanchnic (visceral) mesoderm ventral to thee pharynx. * The SHF cells form the remainder of the **right ventricle and outflow tract **( conus cordis and truncus arteriosus) * **Blood islands**in the cardiogenic field coalesce to form the endothelial tube (the primitive Heart by vasculogenesis * By the third week of development, three germ layers form and organ formation begins. *Caption: Diagram showing the heart development.* ## Cranial Folding Brings the Heart into the Primitive Thoracic Region * The craniocaudal folding causes the formation and progression of the head (cranial) fold to bring the heart tube into the thoracic region. * Rapid growth of the forebrain over the cardiac region is responsible for this event. *Caption: Diagrams illustrate the cranial folding process.* ## Lateral Body Folding Brings the Two Sides of the Cardiac Region Towards the Midline * Lateral folding of the body wall brings both sides of the horseshoe together. *Caption: Illustrations of lateral body folding.* ### Formation of the Heart (cardiac) Tube * The heart first appears in the form of two endothelial heart tubes that fuse to form a single endothelial heart tube. * The heart tube has a cranial (arterial/outflow) end and a caudal (venous/inflow) end. * Initially, the heart tube is cephalic to the buccopharyngeal (oropharyngeal) membrane and neural plate. * Later on, due to the growth of the brain and cephalic folding of the embryo, the heart and pericardial cavity move ventrally, first to the cervical region and finally to the thorax. * heart tube * oropharyngeal membrane * pericardial 1. cavity * septum Transversum *Caption: Diagram showing the heart. ### Formation of the Cardiac Loop * Initially, the heart tube is straight; later, it bends. * Cardiac looping is the process whereby the heart tube folds on itself to create the typical heart shape and location. * Even though it is just a tube, it is beating, and the different regions have begun to differentiate into: primitive atria, primitive ventricle (left), bulbus cordis(right ventricle), and outflow tract. * During looping, the ventricular region grows forward, downward, and to the right. * The atrial portion grows backward, upward, and to the left. * This places the atria superiorly and posteriorly, the ventricles anteriorly and inferiorly, and the heart itself to the left side of the body. * If looping occurs in the opposite direction, then dextrocardia occurs, and the heart is on the right side. * Cardiac looping establishes the Basic Morphology of the heart art 28 Days *Caption: Diagrams showing the folding heart.* Note that in addition to situating the heart in the correct location, looping establishes the basic shape of the heart. Thus, atrial and ventricular regions are recognizable due to creases resulting from looping. ### External and Internal Characteristics of the Heart after Looping at the End of 4 Weeks * Despite the external appearance, no septation of the chambers has yet occurred. * Although primitive atria appear to be well demarcated, many changes will occur in these regions prior to the completion of their development. *Caption: Graphic, showing the developing heart.* ### Adult Structures Derived from Dilatation of Primitive Heart Tube | Embryonic Dilatation | Adult Structure | | :------------------- | :----------------------------------------------------------------------------------------------------------------- | | Truncus arteriosus | Aorta, Pulmonary trunk | | Bulbus cordis | Smooth part of right ventricle (conus arteriosus), Smooth part of left ventricle (aortic vestibule) | | Primitive ventricle | Trabeculated part of right ventricle, Trabeculated part of left ventricle | | Primitive atrium | Trabeculated part of right atrium, Trabeculated part of the left atrium | | Sinus venosus | Right horn - Smooth part of the right atrium (sinus venarum) Left horn - Coronary sinus, oblique vein of the left atrium | ### Transposition of Great Arteries * Caused by abnormal neural crest cell migration, resulting in the non the non-spiral spiral development of the spiral septum. * The aorta arises from RV, and the pulmonary trunk arises from LV. * Associated with cyanosis (**R-L** shunting). * Incompatible with life unless an accompanying shunt like VSD, patent ductus arteriosus (PDA), or patent foramen ovale, is present. *Caption: Diagram.* ### Tetralogy of Fallot * Caused by abnormal neural crest cell migration. * Associated with cyanosis (**R-L** shunting * Characterized by: 1. Pulmonary stenosis 2. Right ventricular hypertrophy 3. Ventricular septal defect 4. Overriding of aorta *Caption: Diagram.* ## Regression Patterns of the Aortic Arches * In forming the definitive pattern of arteries in this region, some parts of the arches and dorsal aorta undergo programmed cell death as the vessels regress. * Major vessels are formed by the: * Third arch (**carotid system**) * Fourth arch (Subclavian (right) arch of Aorta (left)) * Sixth arch (Pulmonary Arteries and Ductus Arteriosus). *Caption: Diagram.* ## Summary of the Aortic Arch Derivatives | | Ventral View Right Left Week 5 | | :------------------------- | :------------------------------------------------------------------------------------- | | 1 | Maxillary Arteries | | 2 | Stapedial, hyoid Arteries. | | 3 | Carotid system | | 4L | Arch of aorta | | 4R | Subclavian Arteries | | 5 | Disappears | | 6 | Pulmonary Arteries and Ductus Arteriosus(l) | *Caption: Diagram to show the process of the aortic arch* ## The Venous Pole of the Heart is anchored in the Septum Transversum * The Caudal ( Venous pool ) of the Heart is anchored to the Septum Transversum,will form the centrral tendon and Diaphragm * The Venous pole receives three different sets of Veins: * Common Cardinal veins( from body) * Vitelline or Yolk Sac Veins * Umbilical Veins . all these Veins are paired at this time * All Three viens empty in the common Cardinal Veins on each side from here into the Right and Left Horns. * the horns Contininue the expanded region called the Sinus Venous, which drains intiative the primitive. *Caption: Graphic, showing heart development.* ### Vascular pattern * Vitelline Veins From a yolk Sac, Ubmilical Viens an anterior * anterier and posterisior cordinal Veins from the body of the embryo inter the Sinous Venus *Caption: Cardiac graphic.* ## Pattern of the Left Horn * the incorpation og the Right simus, the Venous to the sight Aurim 1. the Trabeculated and primisideatnum. *Caption: cardiac view and structures.* ### Remnants of left horn * As Venom is full Shits to the right where the Vena cata area form. The right so you're seeing has expend to accomde the increased blood flow it is opening into the right Atrim expands * As it Expands is incorporrated into the right Aurin which the opening from the left sun is diminished . * Eventually all they're remains of the horn this will be the cornory Sinus and Olique vein of left Atrim.