Circulation and heart structures
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Circulation and Heart Structures. Unit D – Human Systems. Circulatory Systems in your Body. There are two circulatory systems in your body: Pulmonary circulatory system Systemic circulatory system. 1. Pulmonary Circulatory System.

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Circulation and Heart Structures

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Circulation and Heart Structures

Unit D – Human Systems

Circulatory Systems in your Body

  • There are two circulatory systems in your body:

  • Pulmonary circulatory system

  • Systemic circulatory system

1. Pulmonary Circulatory System

  • Blood vessels that circulate blood between the heart and the lungs.

  • Carries deoxygenated blood to the lungs and brings oxygenated blood back to the heart.

2. Systemic Circulatory System

  • Blood vessels that carry blood between your heart and all other parts of the body.

  • Pumps oxygenated blood to all body tissues and returns deoxygenated blood back to the heart.

  • Watch this:

Basic Heart Anatomy

  • The heart is made up of two halves, the left and the right.

  • Each side of the heart is comprised of two chambers.

  • Upper chambers are called atria, lower chambers are called ventricles.

Starting with deoxygenated blood coming from the vena cava

  • Deoxygenated blood from your head and upper body enters the right atrium of your heart from the superior vena cava.

  • Deoxygenated blood from the lower regions of your body enters the right atrium of your heart from the inferior vena cava.

Events occurring in the right atrium

  • Blood collects in the right atrium until the pressure inside forces a set of valves called the right atrioventricular (AV)/tricuspid valves open.

  • Valves make sure that blood only travels in one direction.

  • Blood now enters the right ventricle, where it pools until the pressure inside increases, forcing the semilunar valves open.

Blood flow to the lungs

  • Semilunar valves separate the ventricles from the arteries.

  • Deoxygenated blood now flows through the left and right pulmonary arteries to the lungs.

  • In the lungs, carbon dioxide will be released, and oxygen will combine with hemoglobin.

Blood flow back to the heart

  • Oxygenated blood returns to the heart via the left and right pulmonary veins, where they will empty into the left atrium of the heart.

  • Blood will pool in the left atrium of the heart, until the pressure builds up, forcing the left AV (bicuspid) valves to open.

Blood flow to the body

  • Blood passes through the left AV valves into the left ventricle.

  • Again, blood collects until sufficient pressure builds up.

  • Blood passes through the left semilunar valves into the aorta, the largest artery in your body.

  • The aorta branches off into smaller arteries, taking blood to all parts of your body.

Heart Muscle

  • Made of myogenic muscle.

  • Myogenic muscle has the ability to contract without stimulation from the nervous system…it can beat by itself.

  • For a short time, your heart will continue to beat, even if it is removed from the body.

  • Watch this:

Heart Rate and Contractions

  • Set by the sinoatrial (SA) node, a bundle of nerves known as the “pacemaker” of the heart.

  • Heart rate is typically set at about 70 beats per minute.

  • SA node sends nerve impulses to another bundle of nerves called the atrioventricular (AV) node.

  • Watch this:

  • This nervous impulse causes the atria of the heart to contract, pushing blood into ventricles.

  • The signal is then continued to the end of the ventricles causing them to contract, pushing the blood into the arteries.


  • Relaxation of heart muscle, when the atria of the heart are filling with blood.

  • Increased blood volume and muscle contraction increase blood pressure, forcing the AV valves open.

  • Blood rushes into the ventricles of the heart, causing the AV valves to shut.

  • This causes the heavy “LUBB” sound.


  • Very quickly, increase blood volume and muscle contractions increase pressure in the ventricles.

  • This forces semilunar valves open, letting blood rush into arteries.

  • Semilunar valves close, causing the lighter “DUBB” sound.

Heart Murmur

  • Occurs when heart valves do not close properly.

  • Can be diagnosed by hearing a gurgling sound when listening with a stethoscope.

  • This means that blood can flow backwards, not in the direction it is intended to.

  • Decreases oxygen delivery to body tissues.

Student Tasks for Lesson

  • Label Heart Structures diagram given to you by your teacher and colour parts of heart accordingly: red for parts carrying oxygenated blood, blue for parts carring deoxygenated blood.

  • Complete #1-3, 7 on page 327.

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