Circulatory System - Biology

The function of the lymphatic system is to keep fluids out of the interstitium and connective tissue by returning it to the blood. Fluid leaks out of capillaries because of their thin walls. The lymphatic vessels collect this fluid and return it to the heart. When the lymphatic system is impaired, this fluid can accumulate in the tissue and cause swelling, known as edema.

Most of the lymph re-enters the venous circulation through the thoracic duct, and the volume is somewhere around a liter to a liter and a half per day.

Deoxygenated blood enters the heart through the right atrium, where it then flows into the right ventricle. The right ventricle pumps the deoxygenated blood through thepulmonary arteries to the lungs, where it becomes oxygenated. Oxygenated blood returns to the heart through the pulmonary veins, which empty into the left atrium. Blood then flows into the left ventricle, which contracts to pump the blood through the aorta and toward the rest of the body.

In the circulatory system, the heart acts as the pump, the vessels are conduits allowing blood and lymph flow, and the transport fluid is the blood, which can deliver nutrients and oxygen to tissues and cells throughout the body. Thus, the primary purpose of the circulatory system is, as the correct answer choice states, to deliver oxygen to tissues and transport blood and lymph.

The respiratory system is responsible for gas exchange, while the excretory system is responsible for maintaining fluid balance. The immune system is responsible for destroying foreign pathogens.

There can be two classes of antigens on blood cells: one can distinguish ABO blood types and the second is the Rhesus factor (Rh factor), which determines positive or negative blood type.

A person with type O blood would not carry any antigens on their cells; however this individual’s plasma would contain anti-A and anti-B antibodies. Interestingly, this is why type O blood individuals are commonly known as universal donors, as their cells do not elicit immune responses from any other blood cell types. An individual with Rh- would not carry the Rh factor antigen on the surface of their cells. Thus, O-, correctly identifies the blood type of an individual lacking any of these antigens on their blood cells.

All of the given answer options are contained in blood at some point; however the main components are red blood cells (RBC’s), platelets, plasma, and white blood cells (WBC’s). Platelets are involved in coagulation, while white blood cells are involved in immunity. Plasma refers to the fluid matrix of the blood, and contains proteins, gases, amino acids, and hormones.

Hemoglobin is a specific protein located in red blood cells. Oxygen binds to hemoglobin for transport through the boold. Neither of these are considered major components of blood.

The universal donor blood type is O-, because this blood can be transfused to any of the ABO blood types, as well as to those with Rh+ and Rh-. O-negative blood is devoid of any antigens, but carries antibodies against A, B, and Rh.

AB+ contains both A and B antigens that would elicit an immune responses against any blood containing anti-A or anti-B antibodies. However, AB blood can receive all types of blood because it contains no antibodies. Additionally, AB+ blood carries the Rh antigen and is void of Rh antibodies. This makes AB+ blood the universal acceptor.

The aorta is the largest artery in the body. Like other arteries, the aorta's walls are made up of several layers, one of the largest layers being an elastic layer, which stretches and recoils in response to high pressure blood being pumped through it. Also, recall that all arteries carry blood away from the heart. Blood from the left ventricle of the heart is pumped into the aorta through the aortic semilunar valve. The venae cavae are the largest veins in the body. Like all veins, they carry blood back to the heart. Although the pulmonary artery is quite large, it is not as large as the aorta. Recall that the left ventricle is larger than the right ventricle, and thus more blood is pumped from the left ventricle through the aorta than is pumped from the right ventricle through the pulmonary artery.

Capillaries are the smallest blood vessels. They are responsible for diffusion of gasses and other materials across their walls. For example, alveoli in the lungs are surrounded by capillaries. There, carbon dioxide from the blood diffuses through the capillary walls, into the alveoli, to be exhaled. The opposite is true for oxygen. All of these other blood vessels have walls which are too think to allow any exchange of materials.

The name of this wall is the interventricular septum. It keeps the right and left sides of the heart separate. Remember the importance of keeping these chambers separate; the circulatory system is actually two circuits: pulmonary and systemic. Pulmonary circulation involves blood traveling from the right side of the heart to the lungs to become oxygenated, then returning to the left side of the heart where it is pumped to the body, where the oxygen is taken up by cells. Lastly, the oxygen-poor blood returns from the body to the right side of the heart and the circuit starts again. Mixing blood between these two circuits would result in compromised circulatory system function.

Pulmonary arteries carry oxygen-poor blood from the heart to the lungs so that it can become oxygenated. Pulmonary veins carry oxygen-rich blood from the lungs back to the heart. The aorta carries oxygen-rich blood from the heart to the rest of the body and brain. The superior and inferior vena cavae carry oxygen-poor blood from the body back to the heart so that it can travel to the lungs and become oxygenated again.

Blood flows back to the heart through the pulmonary veins after being oxygenated in the lungs and re-enters the heart through the left atrium. The blood then passes into the left ventricle, which pumps an enormous volume of blood via the aorta to the rest of the body. This chamber of the heart is under a lot of pressure since the heart must pump blood through the many miles of vessels and arteries; therefore, the left ventricle wall must be thicker to withstand the force of these contractions.

The left ventricle pumps blood into the aorta, through which oxygen-rich blood circulates throughout the body.

The sympathetic nervous system is a branch of the autonomic nervous system and provides the "fight or flight" response. For this, muscles will need an increased amount of blood, so the heart increases its force of contraction and rate of contraction (heart rate). Additionally, more oxygen needs to be supplied to the muscles, so the respiratory rate also increases. The increase in cardiac output leads to an increase in blood pressure in the sympathetic response.

During the sympathetic response, blood flow is shunted from other organs and sent to the heart and muscles instead. Therefore, digestion and urine production is decreased. Less blood to the kidneys means less urine gets produced.

Deoxygenated blood returning from the body is carried in the vena cava, which empties into the right atrium. Blood passes through the tricuspid valve and enters the right ventricle. Then, the deoxygenated blood is carried to the lungs by the pulmonary arteries. Once in the lungs, the blood becomes oxygenated.

The oxygenated blood is carried back to the heart by the pulmonary veins. The blood enters the left atrium and passes through the bicuspid (mitral) valve to enter the left ventricle. From the left ventricle it is pumped out of the heart and into the aorta to be circulated through the body and deliver oxygen to the tissues

Always remember that the pulmonary arteries carry DEOXYGENATED blood and the pulmonary veins carry OXYGENATED blood. This is the exception to the rule that states that veins carry deoxygenated blood and arteries carry oxygenated blood.

Arteries are responsible for carrying blood to organs, traveling away from the heart, while veins are responsible for transporting blood back toward the heart. Arteries generally carry oxygenated blood to deliver oxygen to organs, and veins generally carry deoxygenated blood back to the heart for re-oxygenation. The singular exceptions are the pulmonary arteries and pulmonary veins. The pulmonary arteries still travel away from the heart, but carry deoxygenated blood from the right atrium to the lungs. The pulmonary veins still travel toward the heart, but carry oxygenated blood from the lungs to the left atrium.

A common misconception is that veins always carry deoxygenated blood. Veins always return blood to the heart, but the pulmonary veins are bringing oxygenated blood back to the heart so that it may be pumped to the body's tissues. Deoxygenated blood travels through the right ventricle to the pulmonary arteries. In the lungs it is reoxygenated, then returned to the heart in the pulmonary veins.

Blood is able to flow through the blood vessels due to pressure caused by the pumping of the heart. The pressure is the greatest in vessels just leaving the heart (arteries), and decreases as the blood vessels get further away from the heart. Veins have the lowest pressures out of all the blood vessels.

Arterial walls have three distinct layers: an inner smooth endothelium, a heavy coat of smooth muscle cells and elastic fibers, and a looser outer layer of connective tissue. Arteries are uniformly recognizable as robust, thick-walled structures compared with nearby veins.

Although some veins have muscular fibers in their walls (for example, those in the legs), this layer of cells is thin and often incomplete. Instead of muscle to counteract gravity, veins usually use valves to prevent blood from flowing backward. Arteries, veins, capillaries, and the heart chambers all have an endothelial layer.

In fetal mammals, oxygenated blood returns to the fetus via the umbilical veins. It then drains into the right side of the heart. There would be no use in sending oxygenated blood into non-aerated lungs, so it is diverted through a channel, the ductus arteriosus, into the aorta of the fetus.

At birth, this structure closes rapidly, allowing blood to pass the lungs of the newborn. A residual band of connective tissue, the ligamentum arteriosum, marks the site of the original structure. The foramen ovale is a developmental aperture between the atria, and it usually closes spontaneously as the heart develops.

The circulatory system of the body is composed of blood vessels. There are three main types of blood vessels: the arteries, the capillaries, and the veins.

Arteries always carry blood away from the heart. Usually the blood is oxygenated; the exceptions are the pulmonary arteries, which carry blood away from the heart to the lungs to become oxygenated. Veins carry deoxygenated blood towards to heart from tissue, with the exception of the pulmonary veins, which carry oxygenated blood from the lungs to the heart. Capillaries allow for exchange between blood and tissue.