Biology 12-3.3A Anatomy of the Heart

Overview
Your heart weighs less than half a kilogram. An elephant’s heart weighs 20 kilograms. A blue whale has a heart the size of a Volkswagen beetle and an adult human could crawl into its aorta.It has been estimated that your heart beats over 100 000 times a day. If you live to be 70 years old, your heart will pump over 250 million litres of blood through your body. This lesson introduces the structures of the heart and the functions of its various parts.

Heart Anatomy
The heart is a cone-shaped, fist-sized, muscular organ found within the thoracic cavity beneath the sternum and between the lungs. It is a double pump that pushes blood through the pulmonary and systemic circuits at the same time. The heart has four chambers: two atria and two ventricles. The right side of the heart pumps blood to the lungs via the pulmonary trunk, and the thicker walled left side of the heart pumps blood to the body via the aorta.

Contractions of the heart are synchronized so both atria contract to load the ventricles and then both ventricles contract to push blood into the pulmonary and systemic circuits. (Note: the septum dividing the two sides of the heart is muscle shared by both ventricles. During contraction, it provides force for both ventricles at the same time.)

Heart Valves
The valves inside the heart are crucial to its pumping action and ensure that blood moves in only one direction. As each chamber contracts, blood is forced backwards against the flaps of the valve, closing it and preventing backflow of blood.

The valves between each atrium and ventricle are called atrioventricular (AV) valves. Stringy fibres called chordae tendineae prevent the flaps of the AV valves from inverting. The AV valve on the right side of the heart has three flaps and is called the tricuspid valve. The AV valve on the left side of the heart has two flaps and is called the bicuspid or mitral valve. The valves that allow blood to pass from the ventricles to the pulmonary trunk (pulmonic valve) and the aorta (aortic valve) are called semilunar valves.

The cardiac muscle fibres that make up the heart are unique. The heartbeat (called a cardiac cycle) is initiated and synchronized by special nodal tissue that is part muscle and part nerve, and the heart beat does not depend on the nervous system. The heartbeat and its control is the topic of the next lesson.

Pathway of blood through the heart
Blood flows through the heart structures in the following sequence:

deoxygenated blood is returned to the right atrium from the body

the right atrium pumps the blood through the atrioventricular valve into the right ventricle

the right ventricle pumps blood through the semilunar (pulmonic) valve into the pulmonary truck and into the pulmonary arteries to both lungs

oxygenated blood is returned to the left atri via the pulmonary veins

the left atrium pumps the blood through the atrioventricular valve into the left ventricle

the left ventricle pumps the blood under high pressure through the semilunar (aortic) valve to the body

Note that the contraction of both sides of the heart occurs together. Both atria contract and then both ventricles contract. The pathway of blood through the heart is something you will need to be able to describe.

anterior vena cava

aorta, pulmonary

arteries

atrioventricular valves

chordae tendineae

coronary arteries

coronary veins

heart

left atrium

left ventricle

posterior vena cava

pulmonary trunk

pulmonary veins

right atrium

right ventricle

semilunar valves

septum

To which heart chamber does blood from the body (but not the lungs) return?
right atrium

Veins usually carry blood that is low in which substance? Which veins defy this rule?
Veins carry blood that is low in oxygen, except the pulmonary veins that carry oxygenated blood from the lungs to the left side of the heart. Recall that umbilical veins in fetal circulation also carry oxygenated blood from the placenta to the fetus.

Name the valves through which blood leaves the ventricles.
semilunar valves—the pulmonic valve to the lungs and the aortic valve to the body

Describe the pathway of blood through the heart.
Blood flows through the heart structures in the following sequence. Deoxygenated blood is returned to the right atrium from the body; the right atrium pumps blood through the atrioventricular (AV) valve into the right ventricle; the right ventricle pumps blood through the semilunar (pulmonic) valve into the pulmonary truck and into the pulmonary arteries to both lungs; oxygenated blood is returned to the left atrium; the left atrium pumps the blood through the atrioventricular (AV) valve into the left ventricle; the left ventricle pumps the blood under high pressure through the semilunar (aortic) valve to the body.

Summary
identify the structures of the heart in a diagram

name a function of each structure of the heart identified in the lesson

describe the path of blood through the heart, including the valves it passes through

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Cardiac Output is – the amount of blood pumped out of each ventricle in one minute. – the number of impulses fired by the SA node in one minute. – the amount of blood pumped out of the heart during …

Heart the pump in the cardiovascular system that distributes blood for all functions and to all tissues in the body Cardiology the study of the heart and the diseases associated with it WE WILL WRITE A CUSTOM ESSAY SAMPLE ON …

Artery carry blood away from heart to capillaries Vein return blood from capillaries to heart WE WILL WRITE A CUSTOM ESSAY SAMPLE ON ANY TOPIC SPECIFICALLY FOR YOU FOR ONLY $13.90/PAGE Write my sample capillaries join arterioles to venules; permit …

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