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The adenoids (the pharyngeal tonsils)

The adenoids, also known as the pharyngeal tonsils, are a part of the lymphatic system located in the back of the throat and up into the nasal cavity. Much like the tonsils (palatine tonsils), the adenoids are made up of folded lymphatic tissue, lined with epithelial cells, house mucosal glands, and are covered in cilia and mucus. One single such fold is termed an adenoid.

The immune and lymphatic system of the head and neck

The immune and lymphatic system of the head and neck includes the tonsils, several sets of lymph nodes, countless lymphatic vessels, and red bone marrow. All of these structures work together to drain, filter and cleanse the interstitial fluids of the head and neck and destroy harmful pathogens that may infect this region.

The cardiovascular system of the leg and foot

The cardiovascular system of the leg and foot includes all of the blood vessels that provide blood flow to and from the tissues of the lower limb. These blood vessels supply vital oxygen and nutrients to support cellular metabolism in the lower limb while transporting carbon dioxide and metabolic wastes back to the trunk to be removed from the body. Large volumes of deoxygenated blood are stored in the veins of the lower limbs as a reservoir for the rest of the body. Blood flow also helps to maintain the homeostasis of body temperature by delivering hot blood from the trunk to the tissues of the extremities.

The cardiovascular system of the upper limbs

The cardiovascular system of the upper limbs plays the vital role of ensuring the adequate flow of blood to and from the shoulders, arms, hands and fingers. Adequate flow of oxygenated blood to the tissues of the upper limbs is critical to their health through the delivery of oxygen, water, and nutrients. Blood flow also helps to regulate body temperature in this region and reduces the risk of frostbite of the fingers in extreme weather conditions.

Blood filtration in the kidneys

The kidneys filter about one-quarter (750-1000 pints) of the blood that is output by the heart daily. This blood is sent to the body's filter treatment plant, where it is purified by the kidneys and circulated on to the rest of the body. Some of the blood flow becomes fluid waste (1/1000th to 2/1000th) and is sent into the bladder for storage until it can be conveniently expelled. This toxic waste is called urine.

The cardiovascular system of the lower torso

The cardiovascular system of the lower torso, including the abdomen and pelvis, features many vital blood vessels that supply blood to the many organs of this region. A vast network of blood vessels supplies essential blood to the diverse organs of the digestive, reproductive, urinary, lymphatic and endocrine system in the abdomen and pelvis. Many muscles, nerves, and bones surrounding the vital organs depend on this blood supply as well.

Oxygenated blood from the heart enters the lower torso through the descending aorta, a huge elastic artery that passes anterior to vertebral column. As the descending aorta passes through the diaphragm and enters the abdomen, it becomes known as the abdominal aorta. From the abdominal aorta, many visceral branches separate to perfuse the vital organs of the abdomen, while several parietal branches perfuse the bones, muscles, skin and tissues of the abdominal body wall. The abdominal aorta bifurcates at the pelvis to form the left and right common iliac arteries, which provide blood to the pelvis and hips before continuing into the legs as the femoral arteries.

The inferior vena cava

The inferior vena cava is the largest vein in the human body. It collects blood from veins serving the tissues inferior to the heart and returns this blood to the right atrium of the heart. Although the vena cava is very large in diameter, its walls are incredibly thin due to the low pressure exerted by venous blood.

The aorta

At about one inch in diameter and traveling almost the entire length of the trunk, the aorta is the largest artery in the human body. The aorta also has the thickest walls of any blood vessel in the body. This artery ascends superiorly from the left ventricle of the heart, arches over the heart and to the back and to the left, and descends inferiorly behind the heart just anterior to the spinal column.

Following the aorta from its origin at the left ventricle of the heart, the first section of the aorta is known as the ascending aorta. The ascending aorta branches into the left and right coronary arteries. The coronary arteries carry blood to the surface of the heart so that it has oxygen and nutrients to keep beating.

The heart

The heart is a muscular organ about the size of a closed fist that functions as the body’s circulatory pump. It takes in deoxygenated blood through the veins and delivers it to the lungs for oxygenation before pumping it into the various arteries (which provide oxygen and nutrients to body tissues by transporting the blood throughout the body). The heart is located in the thoracic cavity medial to the lungs and posterior to the sternum.

On its superior end, the base of the heart is attached to the aorta, pulmonary arteries and veins, and the vena cava. The inferior tip of the heart, known as the apex, rests just superior to the diaphragm. The base of the heart is located along the body’s midline with the apex pointing toward the left side. Because the heart points to the left, about 2/3 of the heart’s mass is found on the left side of the body and the other 1/3 is on the right.

The cardiovascular system of the upper torso

The cardiovascular system of the upper torso includes the heart and most of the major blood vessels of the circulatory system. These vital structures are critical to the process of pumping deoxygenated blood to the lungs for gas exchange as well as pumping oxygenated blood to the body’s tissues to support their metabolic functions.