Circulation, Blood Vessels, and the Lymphatic System

Circulation and Blood Vessels

Blood vessels, along with the heart, make up the blood circulatory system. This system can be divided into several smaller subsystems:

Arterial Circulation

The part of the circulatory system that involves the arteries makes up the arterial circulation. Arteries include blood vessels such as the aorta and pulmonary arteries. Arteries are strong, elastic blood vessels that carry blood away from the heart. Most arteries carry oxygenated blood with the exception of the pulmonary artery. Arteries branch into smaller blood vessels called arterioles. Arteries and arterioles have strong, flexible walls that allow them to adjust the amount and rate of blood flowing to parts of the body.

The structure of an artery

Venous Circulation

The part of the circulatory system that involves veins makes up the venous circulation. Veins include blood vessels such as the vena cavae and pulmonary veins. Veins have thinner walls than arteries and carry blood to the heart. Most veins carry deoxygenated blood to the heart with the exception of the pulmonary vein. These vessels branch into smaller blood vessels called venules. Veins are less muscular than arteries, closer to the skin, and contain valves (in most cases) to prevent backflow.

The structure of a vein.

Capillary Circulation

Capillaries are very small blood vessels that connect the arterial and venous circulatory subsystems. Oxygen, nutrients, and waste pass between your blood and parts of your body through their very thin walls. These thin walls also allow waste products like carbon dioxide to pass from the organs and tissue into the blood where it is transported to places like the lungs to be released.

The structure of a capillary.

Blood Pressure

Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels (typically arterial pressure in the systemic circulation). It is usually measured at a person's upper arm and is expressed in terms of the systolic (maximum) pressure over diastolic (minimum) pressure. Normal resting blood pressure in an adult is approximately 120/80 mm Hg.

Blood pressure is regulated by the nervous and endocrine systems and can vary depending on the situation, activity, and state of a person's body. Blood pressure that is low is called hypotension, and pressure that is consistently high is hypertension. Long-term hypertension is a risk factor for many diseases, including kidney failure, heart disease, and stroke.

The main complications of persistent high blood pressure are listed, full description linked below

See description of diagram

Watch the video below to review this lesson.

Lymphatic System

The lymphatic system is part of the circulatory system and a vital part of the immune system. The lymphatic system is composed of a network of lymphatic vessels that carry a clear fluid called lymph. Lymph is a fluid that leaks out of capillaries into spaces between cells. As the lymph accumulates between cells, it diffuses into tiny lymphatic vessels. The lymph then moves through the lymphatic system from smaller to larger vessels. It finally drains back into the bloodstream in the chest. As lymph passes through the lymphatic vessels, pathogens are filtered out at small structures called lymph nodes. The filtered pathogens are destroyed by lymphocytes.

The human body has as many as two trillion lymphocytes. These cells make up about 25% of all leukocytes. The majority of lymphocytes are found in the lymphatic system, where they are most likely to encounter pathogens. The rest are found in the blood. There are two major types of lymphocytes, called B cells and T cells. These cells get their names from the organs in which they mature. B cells mature in bone marrow, and T cells mature in the thymus. Both B and T cells recognize and respond to particular pathogens.

Structures of the Lymphatic System

The structures of the lymphatic system include: Organs, lymph vessels, lymph, and lymph nodes

Organs of the lymphatic system include:

Lymphatic System
Organ	Location	Function
Bone marrow	Inside many bones	Produces lymphocytes
Thymus	In the upper chest, behind the sternum	Stores and matures lymphocytes
Spleen	In the upper abdomen	Filters pathogens and worn-out red blood cells from the blood; lymphocytes in the spleen destroy them
Tonsils	On either side of the pharynx	Trap pathogens, which are destroyed by lymphocytes in the tonsils

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