The Circulatory and Respiratory Systems
Oxygen from the atmosphere passes into the respiratory system of the animal, where it crosses cells in the lungs or gills and enters the circulatory system for transport to cell of all organs, to be utilized in nutrient metabolism.
Waste products (carbon dioxide and urea) are transported via the blood and eliminated from the lungs and the kidneys respectively.
Parts in the Thoracic Cavity
- Thymus Glands: located on each side of the neck, large in fetal pig and important in the development of the bodys immune system.
- Larynx and Trachea: expanded structure through which air passes from the mouth to the trachea, the larynx houses vocal cords.
- Thyroid Gland: covers the trachea and secretes hormones that influence metabolism.
- Esophagus: located under the trachea.
Veins vs Arteries
Veins: carry blood to heart, often carry blood low in oxygen (exception: pulmonary vein in adults).
Arteries: carry blood from heart, often carry blood rich in oxygen (exception: pulmonary arteries).
Pulmonary Circuit and Systemic Circuit
- There are two circulatory pathways in mammalian circulation.
- Pulmonary Circuit: carries blood from heart to lungs in the arteries and back to heart in veins.
- (Heart - arteries - lungs - veins - heart)
- Systemic Circuit: carries blood from the heart in arteries to all organs but the lungs and back to the heart in veins.
- (Heart - arteries - all organs, no lungs - veins - heart)
- Located in the pericardial cavity, in the pericardila sac composed of parietal pericardium and parietal pleura.
- Right Atrium (associated with cranial and caudal venae cavae) and Left Atrium (associated with pulmonary veins): heart chambers that receive blood from the venae cavae and the pulmonary veins, respectively.
- Right Ventricle and Left Ventricle: chambers that contract to pump blood.
- Coronary Artery: carries blood to heart tissue, located where the left and right ventricles share a common wall.
- Pulmonary Trunk: blood is forced from the right ventricle into this arteries, it lies on the ventral surface of the heart. It has three branches: pulmonary arteries (right and left), and ductus arteriosus. They carry blood from the right and the left lungs, the greatest volume will flow through the ductus arteriosus directly into the aorta, it will will close off after birth.
- Aorta: located dorsal to the pulmonary trunk, carry blood from the left ventricle, the small branches are coronary arteries and coronary veins that lie on surface of heart between left and right ventricles that service heart tissues..
- Atrioventricular Valves: located between the atria and the ventricles.
Venae cavae and their major branches and the Aorta.
- Blood returns to heart (right atrium) from organs of the body through two large veins, the cranial and caudal venae cavae.
- Branchiocephalic veins: unite in the cranial vena cava, the three major veins that unite to form it are: the external and internal jugulars that carry blood returning from the head, and the subclavian vein that drains blood from front leg and shoulder. The subscapular vein drains blood from shoulder region adn the axillary vein carries blood from the front leg, becoming the subclavian vein. The cephalic vein lies beneath the skin on the upper front leg.
- Aortic arch: curve of the aorta.
- Brachiocephalic trunk: larger branch that branches off first, the second is the left subclavian artery. Following in the trunk, the right subclavian artery serve the right shoulder and limb area, followed by two common carotid arteries that carry blood to the head. Other present is the subscapular artery and the axillary artery.
Branches of the dorsal Aorta (down the diaphragm) and the caudal vena cava
The first branch of the dorsla aorta is the coeliac artery carries blood to the stomach adn the spleen, next branch is the cranial mesenteric artery that carries blood to the small intestine, followed by the renal arteries leading to the kidneys. It then send branches to the hind legs (the external iliac arteries) and the the placenta (umbilical arteries). The external iliac artery divides into the femoral artery and the deep femoral artery.
From the caudal vena cava, the renal veins carries blood from the kidneys, the common iliac veins carry blood from the hind legs and the hepatic veins carry blood from the liver to the caudal vena cava.
The Portal System
- Carry blood from the capillary beds of one organ directly to the capillary beds of another organ and then blood returns to the heart. Exists in the digestive system for the absorption and processing of nutrients.
- Arteries from small intestine (mesenteric arteries) and veins leaving the small intestine (mesenteric veins) unite to form a large mesenteric vein. Veins from the stomach and spleen unite to form the larger lienogsatric vein. This two veins unite to form the hepatic portal vein which enters the liver. In the liver the hepatic portal veins branches into a second capillary bed and reunite into the hepatic veins which join the caudal vena cava.
- Bronchi: trachea branches into bronchi which leads to the lobes of the lungs.
- Bronchioles, tubes 1-2 mm in diameter lead to microscopic alveoli that are blind-ending sacs covered with capillaries where exchange of oxygen and carbon dioxide takes place.