Cardiovascular System

This chapter describes the structure of blood and how it is pumped by the heart around the body in the circulatory system. The many important functions of the cardiovascular system are also explained.

This chapter is divided into three sections:

The Blood

The Heart

The Blood Circulation

Objectives | Blood

After completing this section, you should know:

• the main functions of blood
• what the term haematocrit or packed cell volume (PCV) means
• what is in blood
• what plasma is and what is in it
• the appearance and function of red blood cells (RBCs)
• the appearance and function of white blood cells particularly granulocytes, lymphocytes and monocytes
• the function of platelets and fibrinogen in blood clotting
• how oxygen and carbon dioxide are transported in the blood
• the names of some anticoagulants and their function in the body and in the vet clinic

Summary | Blood

• The main functions of blood are transport of oxygen, food, waste products etc., the maintenance of homeostasis and defending the body from disease.
• Blood consists of fluid, plasma, in which red and white blood cells are suspended. The blood cells typically make up 30-45% of the blood volume.
• Plasma consists of water containing dissolved substances like proteins, nutrients and carbon dioxide.
• Red Blood Cells contain haemoglobin to transport oxygen.
• White Blood Cells defend the body from invasion. There are 2 kinds:
• Granular white cells include neutrophils, basophils and eosinophils. Neutrophils which destroy bacteria are the most numerous. Eosinophils are involved with allergies and parasitic infections.
• Non-granular white cells include lymphocytes that produce antibodies to attach bacteria and viruses and monocytes that engulf and destroy bacteria and viruses.
• Platelets are involved in blood clotting.

Learning Activities

Library of Resources

Presentations and Blackboard quizzes can be accessed by students of Otago Polytechnic.

Objectives | The Heart

After completing this section, you should know:

• where the heart is located in the body
• the structure of the heart
• the structure and function of the heart valves and their role in producing the heart sounds
• the stages of the heart beat and the route the blood takes through the heart
• that the coronary arteries supply the heart muscle

Summary | The Heart

• The heart is situated in the thorax between the lungs
• The heart is a hollow bag made of cardiac muscle. It is divided into four chambers (right and left atria and right and left ventricles).
• Valves stop blood flowing backwards. The right and left atrio-ventricular valves prevent blood in the ventricles from flowing back into the atria. The semilunar valves at the entrance of the pulmonary artery and aorta prevent blood flowing back into the ventricles. The closing of the valves produces the heart sounds heard with a stethoscope.
• There are 4 stages to the heart beat. 1. blood flows into the right and left atria. 2. The atria contract and blood flows into the ventricles. 3. The ventricles contract and the closing of the atrio-ventricular valves produces the first heart sound. 4. Blood flows to the lungs and body and when the ventricles stop contracting the closing of the semilunar valves produces the second heart sound.
• The coronary arteries supply the heart muscle with oxygenated blood.

Learning Activities

Library of Resources

Presentations and Blackboard quizzes can be accessed by students of Otago Polytechnic.

Objectives | Blood Circulation

After completing this section, you should know:

• that the circulatory system is double consisting of pulmonary and systemic circuits with the blood :passing through the heart twice;
• the differences in the structure and function of arteries, capillaries and veins;
• how the pulse is produced and where it can be felt;
• what tissue fluid and lymph are and how they are formed;
• the names of the main arteries and veins.

Summary | Blood Circulation

• The circulatory system is double with the blood passing through the heart twice.
• Arteries carry blood away from the heart. They have thick elastic walls that stretch and can withstand the high pressure of the pulse.
• Capillaries are small, thin walled vessels that form a network between the cells of the tissues.
• Veins return low pressure blood to the heart. They have thinner walls than arteries.
• The pulse is the spurt of high pressure blood that passes along the arteries when the left ventricle contracts. It can be felt where arteries pass close to the body surface.
• Tissue fluid is the clear fluid that leaks from the capillaries and surrounds the cells of the tissues. Lymph forms when tissue fluid enters lymphatics.
• Important blood vessels include the vena cava, aorta, pulmonary artery, carotid artery, jugular vein, renal artery and vein and hepatic portal vessel.

Learning Activities

Library of Resources

Presentations and Blackboard quizzes can be accessed by students of Otago Polytechnic.