Circulation of the Blood Nurse Continuing Education CEU Contact Hours

CIRCULATION OF THE BLOOD

Objectives
By the end of the course, students will be familiar with:
A. The various kinds and structures of blood vessels
B. The function and common disorders of blood vessels
C. Human blood circulation and blood pressure

One hundred thousand miles of blood vessels make up the elaborate transportation system that circulates materials for energy, growth and repair, and eliminates wastes for your body. These vessels called arteries, veins, and capillaries serve different functions. Arteries carry blood from the heart; veins carry blood to the heart and capillaries are exchange vessels or connecting links between the arteries and veins.

The pumping action of the heart keeps blood moving through the closed system of vessels. This closed system of circulation provides distribution of blood to the whole body (systemic circulation) and to specific organs, such as pulmonary circulation, or hepatic portal circulation. Blood pressure is the force of blood in the vessels. This force is highest in arteries and lowest in veins. Normal blood pressure varies among individuals and depends on the volume of blood in the arteries. The larger the volume of blood in the arteries, the more pressure is exerted on the walls of the arteries, and the higher the arterial pressure. Conversely, the less blood in the arteries, the lower the blood pressure.

A functional cardiovascular system is vital for survival because without circulation, tissues would lack a supply of oxygen and nutrients. Waste products would begin to accumulate and could become toxic. Your review of this system will provide you with an understanding of the complex transportation mechanism of the body necessary for survival.

Kinds of Blood Vessels

Arteries – carry blood away from the heart.
Veins – carry blood toward the heart.
Capillaries – carry blood from the arterioles to the venules.

Structure of Blood Vessels

A. Arteries

Tunica interna – inner layer of endothelial cells.
Tunica media – smooth muscle; thick in arteries.
Tunica externa – external thin layer of elastic tissue.

B. Capillaries – minute/microscopic vessels.

The only layer is the tunica interna.

C. Veins

Tunica interna – internal layer; valves prevent retrograde movement of blood.

Tunica media – smooth muscle; thin in veins.

Tunica externa – heavy layer in many veins.

Functions of Blood Vessels

A. Arteries

distribute nutrients, gases, etc. with movement of blood under high pressure; assist in maintaining the arterial blood pressure.

B. Capillaries

serve as exchange vessels for nutrients, waste and fluids.

C. Veins

collect blood for return to the heart; low pressure vessels.

Disorders of Blood Vessels

Disorders of arteries – arteries must withstand high pressure and remain free of blockage.

Arteriosclerosis – hardening of the arteries. Reduce flow of blood, possibly causing ischemia that may progress to necrosis (or gangrene).

Atherosclerosis – disorder in which lipids and other matter block arteries. May be corrected by vasodilators (vessel relaxing drugs) or angioplasty (mechanical widening of vessels) or surgical replacement.

Aneurysm – abnormal widening or ballooning of arterial wall.

a. Aneurysms promote formation of thrombi that may obstruct vital blood supply to critical organs or tissues.

b. Aneurysms may burst, resulting in life-threatening hemorrhaging.

c. Cerebrovascular accident (CVA) or stroke-ischemia of brain tissue caused by embolism or hemorrhage.

Disorders of Veins (low pressure vessels)

Varicose veins (varcies) – enlarged veins in which blood pools. Hemorrhoids are varicose veins in the rectum. Treatments include supporting affected veins and surgical removal.

Thrombophlebitis – inflammation of veins (phlebitis) accompanied by clot or thrombus formation, may result in fatal pulmonary embolism.

Circulation of the Blood

Plan of Circulation refers to the blood flow through the vessels arranged to form a circuit or circular pattern.

Types of Circulation. Systemic circulation carries blood throughout the body. Path goes to and from the heart ventricle through the aorta, smaller arteries, arterioles, capillaries, venules, the venae cava, to the right atrium of the heart.

Pulmonary circulation carries blood to and from the lungs; arteries deliver deoxygenated blood to the lungs for gas exchange. (exchange of carbon dioxide and oxygen). Path goes from right ventricle through pulmonary arteries, lungs, pulmonary veins to the left atrium of the heart.
Hepatic portal circulation is the unique blood route through the liver. Vein (hepatic portal vein) exists between two capillary beds. Assists with homeostasis of blood glucose levels.
Fetal circulation refers to circulation before birth (pre-natal circulation). Modification required for fetus to efficiently secure oxygen and nutrients from maternal blood. Unique structures include the placenta, umbilical arteries and vein (ductus venosus, ductus arteriosus, and foramen ovale).

Blood Pressure. Blood pressure is clinically measured by an instrument called a sphygmomanometer. It is highest in arteries, lowest in veins. Blood pressure gradient causes blood to circulate – liquids can flow only from the area where pressure is highest to where it is lower. Blood volume, heartbeat, and blood viscosity are main factors that produce blood pressure. Blood pressure varies within normal range from time to time. Pulse Definition – the rhythmic expansion of an artery which can be felt with a finger. Normal pulse rate is 50-100 beats per minute.

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