The Circulatory System

Body Structure and Function

Chapter 25

Overview of the Circulatory System

The circulatory system consists of the heart, blood, blood vessels and the structures that make up the lymphatic system.

The heart is responsible for the blood through the arteries and veins.

The blood provides oxygen for the cells and removes carbon dioxide and waste.

The Heart

The heart is a four-chambered muscular pump lying just left of the midline of the chest.

Beneath the sternum. Consists of 3 layers:

pericarduim, myocardium and endocardium

The Heart

The human heart is about the size of a fist and weighs 9 oz.

Cone shaped. Chambers on the right

side move blood to the lungs.

Chambers on the left move blood back to the body.

Blood Flow Through the HeartRight Side (oxygen poor blood)

Blood enters the right atrium first. It is the smallest chamber and receives blood from the inferior and superior vena cava.

From the right atrium the blood passes through the tricuspid valve into the right ventricle.

Blood leaves the right ventricle through the pulmonary valve to the lungs.

In the lungs…

In the lungs we exhale releasing waste and carbon dioxide.

We inhale, enriching the blood with oxygen.

Left side of the heart (oxygen rich)

On return from the lungs, the blood enters the left atrium through the pulmonary vein.

Blood then passes from the atrium to the ventricle through the bicuspid valve.

The left ventricle is the strongest chamber, pumping blood throughout the entire body.

Blood leaves the heart through the aorta.

Valves

Valves in the heart act as doorways. Blood flows in one direction. Any damage or disease can allow a

backflow of blood. The resulting sound is a heart murmur.

Vascular System of the Heart

The heart is comprised of dense muscle and requires its own vascular system.

Coronary arteries supply the heart with blood.

Coronary veins drain the blood into the coronary sinus and back into the right atrium for oxygenation.

Myocardial infarction

When the coronary vessels are blocked, the heart muscle becomes starved for oxygen.

Resulting chest pain is called angina. If oxygen is deprived for a long time , the

heart muscle will be damaged and death may result.

Heart Facts

The heart is able to determine its own rate and rhythm.

Regulated by the autonomic nervous system

The cardiac cycle is all the events that occur in a heartbeat.

Ault rates vary from 70-110 bpm.

“LUB-DUB” is the sound of the valves closing.

Blood Vessels

Arteries

Carry blood away from the heart. Elastic tubes that expand with pressure during

contraction of the heart. We can calculate the heart rate by checking the pulse. (Pulse is checked at a site where an artery overlies a bone.)

Radial site, brachial, carotid, temporal, femoral, popliteal dorsal pedis ad anterior tibial.

Pulse Sites

Veins

The vessels that transport blood from the peripheral tissues to the heart.

Thin walls Valves that force the blood to flow towards the

heart. Elastic walls, pressure is lower than in the arteries. More superficial = blood work/phlebotomy sites or

IV sites.

Capillaries

Microscopic blood vessels. Single-celled walls. Exchange of oxygen, carbon dioxide and

waste takes place.

Veins and Arteries

Blood Pressure

Measurement of the force applied to the walls of the arteries.

The pressure is determined by the force and the amount of blood pumped and by the size and flexibility of the arteries.

Changes depending on activity, temperature, diet, emotional state, posture, physical condition and medication use.

Blood Pressure

Blood pressure is measured systolic(when the left ventricle contracts) over the diastolic pressure (when the pressure in the left ventricle relaxes).

Average BP120/80mmHg

Pulmonary Circulation versus Systemic Circulation

Pulmonary Moves blood from the

heart to the lungs and back to the heart again.

Allows for oxygenation of the blood and carbon dioxide to leave the body.

Systemic Route the blood takes

when it leave the heart, travels through the body and then returns to the heart.

Function is to delivery oxygen and nutrients to the cells and to pick up carbon dioxide and waste.

Blood

Blood is composed of red blood cells, white blood cells and plasma.

Plasma is about 55% of total volume of whole blood. Helps to maintain fluid volume an control blood pressure.

Red Blood Cells

Erythrocytes Produced in the red bone

marrow Small enough to pass

through capillaries Red pigment called

hemoglobin Hemoglobin carries

oxygen. Low RBC=anemia

White Blood Cells

Leukocytes Larger, have nucleus and

lack hemoglobin Not as many as RBC Fight infection Increased # may indicate

infection or disease.

Blood Platelets

Thrombocytes

Control bleeding by forming a clot

Functions of blood

Case Study

What are the signs and symptoms of angina?

Why was the patient given nitroglycerin?

If no relief from chest pan, what should he do next?