3.3 Blood Vessels

CIRCULATORY SYSTEM 1. INTRODUCTION The circulatory system is also known as the cardiovascular system. This system is a double circulatory closed system which transports blood via arteries, veins and capillaries to the lungs through the pulmonary circulation and to the rest of the body tissues in the systemic circulation. Since the blood travels to varying distances around the body, the blood vessels have to be adapted to overcome different pressures. The pressure changes in the four chambers on the heart (two atria’s and two ventricles) allow the blood to continuously flow in one direction.

Materials are exchanged between the blood and cells through the thin walls of the capillaries. The inner layer of blood vessels is lined with endothelial cells that create a smooth passage for the transit of blood. This inner layer is surrounded by connective tissue and smooth muscle that enable the blood vessel to expand or contract. Arteries are thicker the veins to hold the pressure of the blood being pumped from the heart. Blood in the veins is low pressure.

Thus, the pericardial cavity allows the heart movement to be flexible. The pericardial cavity surrounds the heart totally except at the inlet and outlet of the cardiac vessels, where they form two significant tubes. One of the tubes serves as an interconnection to the inferior and superior vena cava and the pulmonary veins, whereas the other connects the aorta and the pulmonary trunk. Blood Supply and Innervation of the

It is an elongated muscle which allows for slow and regular contractions. The nuclei of the smooth muscle cells are centrally located and elongated, similarly to the shape of the cell. In pulmonary blood vessels and the bronchus, this muscle is used to maintain the shape and rigidity of the structure, which it does so involuntarily. The function of the pulmonary vein is the opposite to that of the pulmonary artery, in being that the pulmonary vein carries oxygenated blood back to the heart in order for the blood to be pumped around the body. Similarly to the pulmonary artery, the pulmonary vein has very thin walls although the vein’s walls are even thinner than those of the pulmonary artery due to the wider lumen and low pressure of the blood.

The heart, blood, and blood vessels all form the circulatory system, also known as the cardiovascular system. As one of the most important systems in the human body, the circulatory system transports oxygen, nutrients, and hormones and removes any waste products. Without the circulatory system, your organs wouldn't be able to function, causing death. With the blood vessels taking blood around the body, the heart pumps all this blood. According to Ballard, "Inside the heart there are four spaces called chambers.

The heart may have the sinoatrial node (SA node) to trigger contraction, but in order for us to breath our nervous system has to signal for us to begin the process of ventilation (breathing). Our brain stem has three parts to it, but only the pons and medulla oblongata play a key role in breathing. The medulla helps set the respiratory rhythm by receiving and sending impulses to a bundle of neurons called the ventral respiratory group to the phrenic nerve to bring about contraction in the diaphragm and external intercostal muscles. All this only happens though due to the sensors of the chemoreceptors. The chemoreceptors located in the medulla and carotid and aortic bodies detect a rise in carbon dioxide (CO2).

1. Explain the function of the heart, and the structure of the arteries veins and capillaries The heart is a key muscular organ, and is controlled by the autonomic nervous system. It transports blood to the body’s tissues via the circulatory system; blood provides the body with oxygen, nutrients and also assists in the removal of carbon dioxide and metabolic wastes, hormones are transported throughout the body by plasma. Arteries, arterioles, veins, capillaries and valves, are the blood vessels which are responsible for transporting the blood throughout the body. The arteries are thick walled muscular and elastic, three layered hollow tubes the thickness is needed to cope better with the pressure of blood flowing through the lumen of

Blood drives through the capillaries - vessels located between the veins and arteries. When the blood has been worn-out of oxygen, it makes its way back to the heart and lungs through the veins. The circulatory system might also comprise the circulation of lymph, which is basically recycled blood plasma once it has been filtered

CO2 is then expelled and O2 enters the bloodstream, from there the re-oxygenated blood flows into organs and tissues expelling CO2 from and replacing it with oxygen. The blood finally pumps back to the atrium where the process begins again. (University of Waikato) (See fig.5 ) In humans, blood enters the heart from the posterior and anterior veins vena cava which carries de-oxygenated blood from parts of the body into the right atrium. From the right atrium the blood flows into the right ventricle and through the tricuspid valve which shuts when the ventricle is full. The blood exits the heart through the pulmonic valve, into the pulmonary artery and then into the lungs where gas exchange occurs.

The primary function of the respiratory system is gas exchange, which consists of movement of oxygen into the body and removal of carbon dioxide. To achieve this goal, respiration can be divided and four major functions. First of all, we have pulmonary ventilation, which means the inflow and outflow of air between the atmosphere and the lung alveoli; second, the diffusion of oxygen and carbon dioxide occurs between the alveoli and the blood; after this, these gases are transported in the blood and body fluids to and from the tissue cells. Finally, all these steps are controlled and regulated by respiratory center and receptors. (GUYTON, A.C.; HALL, J.E.