NTA Level 4 • Semester 1 • PST04103

Structure and Functions of Cardiovascular

Human Anatomy and Physiology • Source Session/Topic 22

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Session 22: Structure and Functions of Cardiovascular

System

Total Session Time: 120 minutes

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define Circulatory and Cardiovascular System

• Explain Organization of the Cardiovascular System

• Describe Structure of the Heart

• Describe Blood Supply to the Heart

• Describe Conducting System of the Heart

• Describe Foetal Circulation

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

• Overhead Projector and Transparencies or Slide Projector/LCD and

Computer

• Handout 22.1: The Human Heart

• Handout 22.2: The Surface Anatomy of The Heart

• Handout 22.3: Blood Supply of the Heart

• Handout 22.4: Conducting System of The Heart

• Handout 22.5: Foetal Circulation

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Definition and Organization of Cardiovascular System

(15minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is circulatory system? |

|What is cardiovascular system? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

Circulatory system:

• An organ system that passes nutrients (such as amino acids and

electrolytes), gases (such as oxygen and CO2) , hormones, blood cells,

, etc. to and from cells/tissue in the body, and help stabilize body

temperature and pH to maintain homeostasis.

o The main role of the circulatory system is to transport nutrients, gases,

to/from cells/tissues of the body.

o Circulatory system is composed of the cardiovascular system, which

distributes blood and the lymphatic system, which distributes lymph.

o Humans, have a closed cardiovascular system (meaning that the blood never

leaves the network of arteries, veins and capillaries).

Cardiovascular system:

• The system that include the heart and the blood vessels.

STEP 3: Organisation of the Cardiovascular System (15 minutes)

• The main components of the cardiovascular system are the heart, the

blood, and the blood vessels

• Blood circulates within a fast, high capacity system made up of:

o The heart, which is the central pump and main motor of the system;

o Arteries, which lead away from the heart and carry the blood to the

peripheral parts of the body

o Veins which return the blood to the heart

• The heart can be thought of as a pair of following muscular pumps:

o One pump feeding a minor loop (pulmonary circulation), which serves the

lungs and oxygenates the blood,

o The other pump feeding a major loop (systemic circulation), which serves

the rest of the body

o With limited exceptions, each loop is a closed system of tubes, so that

blood by itself does not usually leave the circulation

• From the centre to the periphery, the vascular tree shows three main

modifications.

• The arteries increase in number by repeated bifurcation and by sending

out side branches, in both the systemic and the pulmonary circulation.

o The aorta, which carries blood from the heart to the systemic

circulation, gives rise to about 4 × 106 arterioles and four times as

many capillaries.

o The arteries also decrease in diameter, although not to the same extent

as their increase in number, so that a hypothetical cross-section of all

the vessels at a given distance will increase in total area with

increasing distance from the heart.

o The blood flow is faster near the heart than at the periphery.

• Venules are vessels which return blood from the periphery, converge on

each other forming a progressively smaller number of veins of

increasingly larger size.

• As with arteries, the hypothetical total cross-sectional area of all

veins at a given level reduces nearer to the heart.

• Eventually, only the two largest veins, the superior and inferior vena

cava, open into the heart from the systemic circulation.

• A similar pattern is found in the pulmonary circulation, but here the

vascular loop is shorter and has fewer branch points, and

consequently, the number of vessels is smaller than in the systemic

circulation.

STEP 4: Structure of the Human Heart (20 minutes)

|Activity: Buzzing (5 minutes) |

| |

|ASK students to pair up and buzz on the following question for 2 |

|minutes |

| |

|What is the heart? |

| |

|ALLOW few pairs to respond and let other pairs to add on points not |

|mentioned |

| |

|WRITE their response on the flip chart/board |

| |

|CLARIFY and SUMMARIZE by using the content below |

• The heart is a roughly cone-shaped hollow muscular organ

• It is about 10 cm long and it is about the size of the owner’s fist

• It weighs about 300g

Location of the Heart

• Lies in the mediastinum, behind the body of the sternum; approximately

two thirds of its mass is to the left of the midline of the body and

one third to the right

• Posteriorly the heart rests on the bodies of thoracic vertebrae five

through eight

• Apex lies on the diaphragm, pointing to the left

• Base lies just below the second rib

• Boundaries of the heart are clinically important as an aid in

diagnosing heart disorders

Covering of the Heart

• Heart is made up of three distinct layers

o Epicardium: the outer layer of heart which provides protection against

friction which is divided into

▪ Fibrous pericardium: a tough, loose – fitting inextensible sac

▪ Serous pericardium: parietal layer lies inside the fibrous

pericardium, and visceral layer (pericardium) adheres to the outside

of the heart pericardial fluid separates the two layers

o Myocardium: thick, contractile middle layer

o Endocardium: delicate inner layer of endothelial tissue

Chambers of the Heart

• The heart is divided into four chambers, the two atria and the two

ventricles

• Atria

o Two superior chambers (the atria), known as receiving chambers, since

they receive blood from veins

o Myocardial wall of each atrium is not very thick, since little pressure

is needed to move blood such a small distance

o The right atrium receives venous blood from the body through inferior and

superior vena cava, then pumps it the right ventricle

o The left atrium receive oxygenated blood from pulmonary veins and pumps

it to the left ventricle

• Ventricles

o Two lower chambers(Ventricles)are known as pumping chambers, since they

push blood into the large network of vessels

o Ventricular myocardium is thicker than the myocardium of the atria, since

great force must be generated to pump blood outside the heart

o Since the left Ventricle pumps blood via Aorta to the whole body, its

walls are thicker than those of right Ventricle (which pumps blood to the

lung)

Valves of the Heart

• These are mechanical devices that permit the flow of blood in one

direction only.

• Atrioventricular (AV) valve: This prevent blood from flowing back into

the atria from the ventricles when the ventricles contract which

includes

o Tricuspid valve (right AV valve) guards the right atrioventricular

orifice

o Bicuspid or mitral, valve (left AV valve) similar in structure to

tricuspid valve except only two flaps

• Semilunar (SL) valve.

o These are half-moon-shaped flaps growing out from the lining of the

pulmonary artery and aorta; prevents blood from flowing back into the

ventricles from the aorta and pulmonary artery.

▪ Pulmonary semilunar valve, located at the entrance of the pulmonary

artery

▪ Aortic semilunar valve, located at the at entrance of the aorta

[pic]Refer students to Handout 22.1: The Human Heart

STEP 5: Blood Supply to the Heart (15 minutes)

• The heart, like all tissues in the body, requires oxygen to function

• Indeed, it is the only muscle in the body that never rests

• Thus, the heart has reserved for itself its own blood supply

• This blood flows to the heart muscle through a group of arteries that

begins less than one half inch from where the aorta begins

• These are known as the coronary arteries, the first branch to come off

the aorta they are two, the right and left coronary artery

• These arteries deliver oxygen to both the heart muscle and the nerves

of the heart

• Both ventricles receive their blood supply from branches of the right

and left coronary arteries

• Each atrium, in contrast, receives blood only from a small branch of

the corresponding coronary artery

• The most abundant blood supply goes to the myocardium of the left

ventricle, since the left ventricle does the most work and so needs

the most oxygen and nutrients delivered to it

• Anastomoses exist between the large branches of coronary arteries

• These provide detours in which arterial blood can travel if the main

route becomes obstructed i.e. they provide collateral circulation to a

part

• This phenomenon is important in cases of coronary artery diseases;

when the interruption of coronary blood flow lasts only a few minutes,

the symptoms are called angina, and there is no permanent damage to

the heart

• When the interruption lasts longer, that part of the heart muscle dies

• This is referred to as a heart attack (myocardial infarction)

• Most of the venous drainage of the heart is through the coronary

sinuses which open into the right atrium

• The remainder passes directly into heart chambers through the little

venous channels

[pic]Refer students to Handout 22.2: Blood Supply of the Heart

STEP 6: Conducting System of the Heart (20 minutes)

• Cardiac plexuses located near the arch of the aorta made up the

combination of sympathetic and parasympathetic fibres

o Fibres of the cardiac plexus accompany the right and left coronary artery

and enter the heart

o Most fibres ends in the sinoatrial node (SA), but some end in the

atrioventricular node (AV) and in the atrial myocardium

o Sympathetic nerves, accelerator nerves

o Vagus fibres, inhibitory or depressor nerves

• The heart contains special tissue that produces and sends electrical

impulses to the heart muscle. It is these impulses that trigger the

heart to contract

• Each time the heart beats, it sends out an electric-like signal

• The heart's electrical signals can be measured with a special machine

called an electrocardiogram (ECG)

• The sinoatrial node (SAN), located within the wall of the right atrium

(RA), normally generates electrical impulses that are carried by

special conducting tissue to the atrioventricular node (AVN)

• AVN is located between the atria and ventricles; the electrical

impulse from AVN is relayed down the conducting tissue (Bundle of His)

that branches into pathways that supply the right and left ventricles

• These paths are called the right bundle branch (RBB) and left bundle

branch (LBB) respectively

• Electrical impulses generated in the SAN cause the right and left

atria to contract first

• All heart cells muscle and conducting tissue are capable of generating

electrical impulses that can trigger the heart to beat

• The SAN is known as the "heart's pacemaker" because electrical

impulses are normally generated here

• At rest the SAN usually produces 60-70 signals a minute t is the SAN

that increases its' rate due to stimuli such as exercise, stimulant

drugs, or fever

• Should the SAN fail to produce impulses, the AVN can take over

• The resting rate of the AVN is slower; generating 40-60 beats a minute

• The AVN and remaining parts of the conducting system are less capable

of increasing heart rate due to stimuli previously mentioned than the

SAN

[pic]Refer students to the handout 22.3 Conducting System of the Heart

STEP6: Foetal Circulation (25 minutes)

|Activity: Buzzing (5 minutes) |

| |

|ASK students to pair up and buzz on the following question for 2 |

|minutes |

| |

|What is the importance of foetal circulation? |

| |

|ALLOW few pairs to respond and let other pairs to add on points not |

|mentioned |

| |

|WRITE their response on the flip chart/board |

| |

|CLARIFY and SUMMARIZE by using the content below |

• Foetal circulation in the body before birth differs from circulation

after birth for one main reason

• Foetal blood secures oxygen and food from maternal blood instead of

from foetal lungs and digestive organs

• Foetal blood reaches the placenta via two umbilical arteries and

returns by one umbilical vein

• Blood from the placenta is carried to the foetus by the umbilical vein

o About half of blood enters the foetal ductus venosus

(the ductus venosus, arises and ascends posterior to the liver to join

the left hepatic vein near its termination in the inferior vena cava)

and is carried to the inferior vena cava)

o Other half of blood enters the liver proper from the inferior border

of the liver

• The branch of the umbilical vein that supplies the right lobe of the

liver first joins with the portal vein

• The blood then moves to the right atrium of the heart

• In the foetus, there is an opening between the right and left atrium

(the foramen ovale),

• Most of the blood flows through this hole directly into the left

atrium from the right atrium, thus bypassing pulmonary circulation

• The continuation of this blood flow is into the left ventricle, and

from there it is pumped through the aorta into the body

• Some of the blood moves from the aorta through the internal iliac

arteries to the umbilical arteries,

• and re-enters the placenta, where carbon dioxide and other waste

products from the foetus are taken up and enter the woman's

circulation

• Some of the blood entering the right atrium does not pass directly to

the left atrium through the foramen ovale but enters the right

ventricle and is pumped into the pulmonary artery

• In the foetus, there is a special connection between the pulmonary

artery and the aorta, called the ductus arteriosus, which directs most

of this blood away from the lungs (which aren't being used for

respiration at this point as the foetus is suspended in amniotic

fluid).

• At birth, when the infant breathes for the first time, there is a

decrease in the resistance in the pulmonary vasculature, which causes

the pressure in the left atrium to increase relative to the pressure

in the right atrium.

• This leads to the closure of the foramen ovale, which is hence

referred to as the fossa ovalis.

• Additionally, the increase in the concentration of oxygen in the blood

leads to a decrease in prostaglandins, causing closure of the ductus

arteriosus.

• These closures prevent blood from bypassing pulmonary circulation, and

therefore allow the neonate's blood to become oxygenated in the newly

operational lungs.

• After closure, the duct becomes the ligamentum arteriosum, which

connects the left pulmonary artery (near its origin) with the aortic

arch.

• The ductus venosus shuts down by an unknown mechanism, its fibrous

remnant is the ligamentum venosum.

• If these opening persist after birth may lead to a serious conditions

known as congenital heart diseases

[pic]Refer students to the Handout 22.4: Foetal Circulation

STEP 7: Key Points (5 minutes)

• The cardiovascular system consists of the heart, blood vessels, blood,

and lymph

• The heart is a hollow muscular organ consisting of the myocardium,

pericardium, and endocardium.

• Four valves control blood flow into and out of the heart

• Coronary arteries provide blood flow and nutrients to the heart muscle

itself

• The largest of the blood vessels are the arteries, which carry

oxygenated blood away from the heart to the capillaries.

• The pulmonary arteries are the exceptions; they carry deoxygenated

blood from the heart to the lungs.

STEP 8: Evaluation (5 minutes)

• What is circulatory system?

• What is cardiovascular system?

• What are the components of cardiovascular system?

• What is foetal circulation?

References

Seeley, R. R., Stephens, T. D., &Tate, P. (2003). Anatomy and Physiology.

New York:

McGraw-Hill.

Shier, A., Butler, J., & Lewis, R. (2004). Hole’s Human Anatomy &

Physiology. New York:

McGraw-Hill.

Standring, S. (2008). Grays’s Anatomy The anatomical basis of clinical

practice. United

Kingdom: Churchill Livingstone Elservier.

Thibodeau, G. A., & Patton, K. T. (1999). Anatomy & Physiology. Saint

Louis: Mosby, Von

Hoffman Press, Inc.

Waugh, A., & Grant, A. (2006). Ross and Willson Anatomy and physiology in

Health and

illness. United Kingdom: Churchill Livingstone Elservier.

|[pic] |Handout 22.1: The Human Heart |

| | |

[pic]

The Anterior View

Moore, K. L., & Agur, A. M. R. (2007)

[pic]

Posterior View

Moore, K. L., & Agur, A. M. R. (2007)

[pic]

Front View

Moore, K. L., & Agur, A. M. R. (2007)

|[pic] |Handout 22.2: Blood Supply of the Heart |

Arterial supply to the heart

[pic][pic]

Venous return to the heart

Source: Moore, K. L., & Agur, A. M. R. (2007)

|[pic] |Handout 22.3: Conducting System of The Heart |

[pic]

Source: Moore, K. L., & Agur, A. M. R. (2007)

|[pic] | |

| |Handout 22.4: Foetal Circulation |

| | |

[pic]

Source: Standring, S., 2008.

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