Question

1. what cavities exist between the thoracic and cavities? what folds close these cavities? 2. what folds separate the thoracic cavity? 3. Discuss how the foregut separates to form the trachea ventrally and the oesophagus dorsally? 4. list the components of the heart tube and the adult derivative of each.

no figure is needed.

Answer 1

1.

The two pleural cavities are situated on both sides of the body, anterior to the spine and lateral to the breastbone. The superior mediastinum is a wedge-shaped cavity located between the superior regions of the two thoracic cavities. ... The pericardial cavity roughly outlines the shape of the heart.

The Mammalian coelum is made up of 4 main parts; The Abdominal Cavity, Pericardial Cavity, and two Pleural Cavities. The Pericardial and Pleural Cavities along with the Mediastinum make up the Thoracic Cavity. The boundaries of the Thoracic Cavity are the Ribs (and Sternum), Vertebral Column, and the Diaphragm.

✓Pleura, plural pleurae, or pleuras, membrane lining the thoracic cavity (parietal pleura) and covering the lungs (visceral pleura). The parietal pleura folds back on itself at the root of the lung to become the visceral pleura.

2. The diaphragm is a C-shaped structure of muscle and fibrous tissue that separates the thoracic cavity from the abdomen. The dome curves upwards. The superior surface of the dome forms the floor of the thoracic cavity, and the inferior surface the roof of the abdominal cavity.

3.Embryologists have long recognised that clarifi-

cation of the processes that surround normal tra-
cheoesophageal separation was critical to a better
. understanding of the abnormal separation of the
- trachea from the oesophagus that leads to EA/TEF. Many theories of the pathophysiology of

EA/TEF have been proposed but even the two
theories that have held most sway have recently
been challenged . One theory, the “tap water”
theory states that the respiratory bud
forms from the primitive pharyngeal wall and
descends in a way similar to that of a tap being
turned on: first the trachea develops after which
the bronchi appear and develop. The second the-
ory, the “tracheoesophageal septum” theory, describes how fusion of two lateral tracheo-
esophageal ridges separates the trachea from the
oesophagus. These ridges form a septum that
ascends to the pharynx to complete the process of
separation, leaving the trachea ventrally and
oesophagus dorsally.

4. The ectodermal cells migrate into the mesoderm as cardiogenic cells which condense to form a pair of primordial heart tubes. The pharyngeal area mesoderm contributes further cells which form a secondary heart forming region around the primordial heart tubes. Further cells are contributed by the splanchnic mesoderm which form the myocardium around the primordial heart tubes. This newly formed myocardium will start secreting hyaluronic acid and other connective tissue components which are termed together and called as Cardiac Jelly. Cardiac jelly in future becomes the connective tissue of the heart. These newly formed primordial heart tubes are surrounded by pericardial cavity which provides the outer Parietal layer of the Pericardium which is adherent to the Fibrous pericardium in the adult heart. The Caudal or Inflow part of the Heart tube that is Sinus Venosus provides the cells which form the visceral or inner layer of pericardium, also called EPICARDIUM.

By the 21st day the two primordial heart tubes fuse under the influence of VEGF into a single endocardial or Heart tube. On 22nd day the embryonic heart starts beating.

DILATATIONS & DERIVATIVES OF THE HEART TUBE

The Primordial heart tube now orients itself into a cephalic INFLOW (Venous region) and a cranial OUTFLOW (Arterial Region) ends. At this point the primitive heart tube has five dilatations which are as following:

1. Truncus Arteriosus (arterial outflow region): Forms adult aorta, pulmonary trunk and their respective semi-lunar valves.
2. Bulbus Cordis: Forms smooth parts of adult right ventricle (conus arteriosus) and left ventricle (aortic vestibule).
3. Primitive Ventricle: Forms trabeculated (rough) parts of right and left ventricles.
4. Primitive Atrium: Forms trabeculated (rough) parts of right and left atria i.e., the pectinate muscles.
5. Sinus Venosus: On the right side it forms Sinus Venarum (smooth part of right Atrium), superior vena cava and the inferior vena cava. On the left side it forms coronary sinus and oblique vein of left atrium.