Thyroid Gland

Thyroid Gland: the oval shaped gland is found in the neck ventral to the trachea and just below the larynx.

Bronchi

The trachea branches into each lung. These two tubes are called bronchial tubes. Inside the lungs these branch into smaller bronchioles that end with a grape-like cluster of air sacs or alveoli where oxygen and carbon dioxide are exchanged with capillaries.

Diaphragm

Since the pig is already open from the digestive system dissection, examine the diaphragm, a sheet of muscle that stretches across the abdominal cavity and separates it from the thoracic cavity where the lungs are located and in the center is the heart. It can be found right above the stomach and liver and under the lungs and heart. Once you locate this, the respiratory and circulatory is right on top. You may need to cut through the pig's sternum and expose the chest cavity (thoracic cavity) to view. You will need to cut up under the pig's throat and neck and make two more lateral incisions in order to fold back the flaps of shin covering the throat to expose the thoracic.

Pulmonary Veins

Pulmonary Veins: Consists of four vessels that return form lungs to the left atrium of the heart.

Pulmonary Arteries

Pulmonary Arteries: The pulmonary arteries carry deoxygenated blood from the heart to the lungs. These are the only arteries that carry deoxygenated blood. It begins at the base of the right ventricle then branches into two pulmonary arteries (left and right), which deliver de-oxygenated blood to the corresponding lung.

On the ventral surface of the heart passing dorsally and to the left is the large pulmonary artery. It originates in the right ventricle. Try tracing it its two branches to the lungs.

Pulmonary Trunk

Pulmonary Trunk: Is the artery that goes from the right ventricles to the lungs. It has two main branches (right and left pulmonary arteries).

Aorta

Locate the aorta, the largest systemic artery of the body. It leaves the left ventricle, curves to the left, dorsal to the pulmonary artery, and continues dorsally in a posterior direction along the left side of the vertebral column. The proximal curved portion of the aorta is called the aortic arch, while the next segment of the aorta within the thorax is known as he thoracic aorta.

Caroited Arteries

Carotid Arteries: Supplies blood to the neck and face from the top of the heart. Can be found in the neck and behind the larynx.

Pericardium

Pericardium: is a membrane like the pleura. The pericardium consists of two parts; the visceral pericardium is the thin and shiny membrane that is on the surface of the heart, and the parietal pericardium is the thicker membrane.

Vena Cava

Anterior vena cava: locate the trunk of this systemic vein above the heart. In the pig the term anterior vena cava is more correct and therefore preferred to superior vena cava. All anterior veins lead into it.

Posterior vena cava: This is the major vein returning blood from the lower extremities and from the abdominal area. Again, this designation in the pig is preferred to inferior vena cava. It can clearly be seen rising from the diaphragm, which it has penetrated, to enter the heart at the right atrium together with the superior vena cave.

Anterior to the heart, you can locate a large vein that enters the right atrium. This vein is the anterior vena cava, which brings blood to the right atrium from the anterior part of the body. Now lift the heart to view its dorsal surface. To do this you must use your scissors to carefully cute through all the major arteries attaching the heart to the mediastinum and then removing the heart with your hands to observe the posterior vena cava that carries blood from the posterior part of the body and empties it into the right atrium.

Mediastinum

Mediastinum: The mediastinum is a structure in the thorax, surrounded by loose connective tissue. It is the central compartment of the thoracic cavity. It contains the heart, the great vessels of the heart, esophagus, trachea, phrenic nerve, cardiac nerve, thoracic duct, thymus, and lymph nodes of the central chest. The mediastinum lies between the right and left pleura in and near the median sagittal plane of the chest. It extends from the sternum in front to the vertebral column behind.

Coronary Vessels

Coronary Vessels: The vessels on the heart that supply blood to the heart muscle. The vessels are found in the interventricular groove and this groove shows the split between the right and left ventricle.

Ventricles and Atria

Remove the pericardium, which is a thin membrane that surrounds the heart, with a blunt probe to expose the structure of the heart more closely. The right side of the heart pumps blood to the lungs, while the left side of the heart pumps blood to all other parts of the body. Locate the right and left sides of the heart. The structures visible on the heart are the two atria, the ventricle which have two chambers. Each side of the heart has an upper and a lower chamber. Upper chambers are called atria and receive blood, while lower chambers are called ventricles and pump blood out of the heart. You can easily locate the right and left atria and ventricle by looking at the heart.

Atria

Atria: The heart is divided into four chambers that are connected by heart valves. The upper two heart chambers are called atria. Atria are separated by an interatrial septum into the left atrium and the right atrium. The lower two chambers of the heart are called ventricles. Atria receive blood returning to the heart from the body and ventricles pump blood from the heart to the body. The heart is located between the lungs an under the sternum and is protected by the rib cage.

Visceral Pleura

Visceral Pleura: the thin, shiny membrane on the surface of the lung. The pleura cavity is the space located between the visceral and parietal pleura.

Parietal Pleura

Parietal Pleura: This is the serous membrane found within the thorax. The parietal pleura lines the inner walls and can easily be found by locating where the lungs are and the rib cage, and then looking at the filmy thin layer of tissue laying on top.

Lungs

Lungs: is the essential respiration organ. The two lungs are located near the backbone on either side of the heart in the chest cavity. Their main function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. This exchange of gases is accomplished in the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs called alveoli.

In the thoracic cavity, carefully separate the pericardium or sac surrounding the heart and the diaphragm from the body wall. Locate the two, spongy lungs that surround the heart. The tissue that covers and protects the lungs is called pleura.

Trachea

Trachea: A tube-like portion of the respiratory tract that connects the larynx with the bronchi. Also known as the windpipe, the trachea is located in the chest cavity and in the neck. This allows air to be transported down into the lungs where it is cycled into the bloodstream.

Find the trachea: a large air tube that lies anterior to the lungs. The trachea is easy to identify because of the cartilaginous rings that help keep it form collapsing as the animal inhales and exhales.

Larynx

Larynx: At the anterior (toward head) of the trachea, you can find the hard light colored larynx (or voice box). The larynx allows sounds to be produced. Once you cut up into the throat with scissors and remove the two flaps to expose what is under, the larynx is easily identifiable due its width compared to the small ringed trachea and light pinkish color. Its uppermost segment is the triangular flap of tissue, the epiglottis, which protects the opening to the trachea.

Thymus

Thymus: The thymus is a pinkish-gray color, soft, and lobulated on its surfaces. The thymus is made up of two identical lobes and is located anatomically in the anterior superior mediastinum, in front of the heart and behind the sternum. The thymus provides an inductive environment for development of T-lymphocytes from hematopoietic progenitor cells. In addition, thymic stromal cells allow for the selection of a functional and self-tolerant T-cell repertoire. Therefore, one of the most important roles of the thymus is the induction of central tolerance.

The Respiratory System

The Respiratory System: The organ system that carries out gas exchange and supplies the body with oxygen and disposes it of carbon dioxide.