Gross Anatomy of the Trunk

INGLES I

TP.4

READING AND COMPREHENSION

Gross Anatomy of the trunk

The trunk is the central part of the body. The neck and head extend above the trunk and are continuous with it. The upper limbs are attached to either side of the trunk and the lower limbs extend downwards from it. The outer tissues of the trunk form the body wall.

The trunk consists of two main cavities, namely the thorax and the abdomen. These are separated by a dome-shaped muscle known as the diaphragm. The thorax lies above the diaphragm, and the abdomen lies below it.

The posterior wall of both cavities is composed of the vertebral column and its related muscles.

The thoracic cavity is bounded at the sides and front by the ribs, the sternum, and the intercostal muscles. The principal internal organs contained in the thorax are the heart and the lungs.

The abdomen is the largest cavity in the body. It consists of two parts: the abdominal cavity proper and the pelvic cavity.

The lateral and anterior walls of the abdominal cavity proper are formed mainly by three layers of muscle which run concentrically round the cavity. The organs of digestion are the principal internal organs contained in the abdomen.

The pelvic cavity, or pelvis, lies below the abdominal cavity and is continuous with it. It is bounded anteriorly and laterally by bone. The contents of the pelvis are the urinary bladder, the lower part of the large intestine, the rectum, and some of the reproductive organs.

• Decide if the following sentences are true or false according the information in the text above. If they are false justify them (in Spanish).

1. The trunk means the same as the body.
2. The neck and head form part of the trunk.
3. The abdomen is bounded superiorly by the diaphragm.
4. The abdomen is bounded posteriorly by the vertebral column and its related muscles.
5. The walls of the thoracic cavity are composed of the ribs, the sternum, and the intercostal muscles.
6. The heart and the lungs lie within the thoracic cavity.
7. The cavity above the diaphragm is larger than the cavity below the diaphragm.
8. The abdominal cavity is part of the abdominal cavity proper.
9. The pelvic cavity can be said to be part of the abdomen.
10. The organs of digestion are the only internal organs contained in the abdomen.
11. The abdominal cavity and the pelvic cavity are separated by layers of muscle.
12. The reproductive organs are found in the pelvis.

• Rewrite the following sentences replacing the underlined words, with expressions from the text, which have the same meaning.

1. The body wall is composed of the outer tissues of the trunk.
2. The muscle which separates the thorax from the abdomen is referred to as the diaphragm.
3. The vertebral column and its associated muscles form the posterior wall of the thorax.
4. The abdomen is situated below the diaphragm.
5. The organs contained within the abdomen are principally the organs of digestions.
6. The pelvic cavity is bounded laterally and anteriorly by bone.
7. Some of the organs of reproduction are found in the pelvis.

The Thoracic Cavity

The thoracic cavity is divided by fibrous partitions into three compartments. The central compartment, the mediastinum, is a mass of tissue and organs, extending from the vertebral column behind to the sternum in front. It contains the heart and great blood vessels, the oesophagus, the trachea and its bifurcation, the phrenic and the vagus nerves, and the thoracic duct. The two lateral compartments are cavities, known as the pleural cavities. These contain the lungs.

The mediastinum is commonly considered to have three divisions, lying anterior, posterior and superior to the pericardium. Both the anterior and the posterior mediastinum are continuous with the superior mediastinum, which connects freely with the neck.

The anterior mediastinum is not much more than a potential space. It lies between the sternum and the pericardium and is overlapped by the anterior edges of both lungs. It sometimes contains the lower part of the thymus gland, but usually this does not extend lower than the superior mediastinum.

The posterior mediastinum lies behind the pericardium and the diaphragm. It contains the thoracic lymph nodes and, in addition, various organs in their passage to or from the superior mediastinum. These are principally the aorta and the oesophagus, which descend from the superior mediastinum. These are principally the aorta and the esophagus, which descend from the superior mediastinum through the posterior mediastinum to the abdomen, and the thoracic duct, which leads upwards from the posterior mediastinum into the superior mediastinum.

The superior mediastinum contains the esophagus, the trachea, the apices of the lungs, the phrenic and vagus nerves, the arch of the aorta, and other major blood vessels. The superior mediastinum is remarkable for the asymmetrical relationships of its contents, mainly due to the position of the great veins and arteries, that is to say veins on the right side and arteries on the left. The trachea, for example, is in contact with the right vagus nerve and the apex of the right lung, but is separated from the left vagus and the apex of the left lung by the left common carotid and the left subclavian arteries.

The pericardium is a fibrous sac that encloses the heart. The pericardium is conical in shape, fused at its apex with the roots of the great veins and arteries and at its base with the central tendon of the diaphragm. It is attached by ligaments to the upper and lower ends of the sternum. A layer of serous membrane lines the fibrous pericardium and is reflected round the roots of the great veins and arteries to cover the surface of the heart. Thus the heart is separated from the fibrous pericardial sac by two adjacent layers of serous membrane.

The lungs and the pleural cavities are lined by the pleura, a membrane of fibrous tissue surfaced by a single layer of squamous epithelium. In each cavity the pleura lines the thoracic wall, the upper surface of the diaphragm and the mediastinal surface.

At each lung root the pleura is reflected from the mediastinum to from a layer, which covers the surface of the lung. Thus each lung lies enclosed in a pleural sac, just as the heart lies enclosed in the pericardial sac, and again two layers of serous membrane are adjacent.

The pericardium and the pleura have the same function, namely to provide two slippery surfaces so that the structures contained within can move without friction. The thoracic cavity is a very mobile area. The heart is in rhythmic pulsation and changes its position a little between systole and diastole; the lungs also are in rhythmic motion, gliding down and up; the oesophagus dilates with each bolus; and the great veins expands considerably during increased blood flow.

• Answer the following questions about the text (in Spanish):

1. How many compartments are there in the thoracic cavity?

Name them.

1. Where are the compartments located?
2. What are the anatomical structures found into each mediastinum?
3. Which is the most important division of the mediastinum according to its content?
4. What is the relation between the superior mediastinum and the neck?
5. Why is superior mediastinum “remarkable”?
6. Is the heart in contact with the pericardium? Why?
7. What is the name of the membrane that lines the lungs?
8. What is the main function of the pericardium and the pleura?
9. Why does the article say, “The thoracic cavity is a mobile area”?