Human Biological Science 2 · PDF fileHuman Biological Science 2 Session 3 Cardiovascular System ... Blood Circulation o Systemic circulation • left side of heart pumps blood through

© Endeavour College of Natural Health endeavour.edu.au

BIOH122Human Biological Science 2

Session 3

Cardiovascular System –

The Heart

Bioscience Department

© Endeavour College of Natural Health endeavour.edu.au 2

Session Plan

o Anatomy of the Heart• Heart Location

• Heart Orientation

• Surface Projection of the Heart

• Pericardium

• Layers of Heart Wall

• Muscle Bundles of the Myocardium

• Chambers and Sulci of the Heart

• Myocardial Thickness and Function

o Heart Valves and Circulation of the Blood• Atrioventricular Valves

• Semilunar Valves

• Blood Circulation

o Histology of Cardiac Muscle Tissue

o The Conduction System


Anatomy of the Heart


Cardiovascular system

o The cardiovascular system: consists of the blood, heart,

and blood vessels, Supply blood to whole body tissues

and maintain homeostasis

o The heart is the pump that circulates the blood through

an estimated 97,000 kilometers of blood vessels.

o Heart pumps over 10 million liters per year.


Location of the Heart

o Location: The heart is situated between the lungs in the thoracic

cavity with about two-thirds of its mass to the left of the midline .

The heart lies between two rigid structures: The vertebral column and the sternum.

External cardiac compression on the chest forces blood out of the heart and into the circulation.


Heart Orientation

o Apex - directed anteriorly, inferiorly and to the left

o Base - directed posteriorly, superiorly and to the right

o Anterior surface - deep to the sternum and ribs

o Inferior surface - rests on the diaphragm

o Right border - faces right lung

o Left border (pulmonary border) - faces left lung


Heart Orientation

Tortora, GJ & Derrickson, B 2012. Principles of Anatomy and Physiology, 13th edn, John Wiley &

Sons, New York.


Surface Projection of the Heart


Pericardium


Sons, New York.


Pericardiumo Fibrous pericardium

• dense irregular connective tissue

• protects and anchors the heart, prevents overstretching

o Serous pericardium

• thin delicate membrane

• contains

– parietal layer - outer layer

– visceral layer - inner layer

o Pericardial cavity: Space filled with pericardial fluid between the parietal

and visceral pericardium. Reduces friction between the two membranes.

– An inflammation of the pericardium is known as pericarditis. Associated

bleeding / fluid into the pericardial cavity and compresses the heart;

potentially lethal.


Layers of the Heart Wall

o Three layers: epicardium, myocardium, and

endocardium.

• The epicardium

• The myocardium composed of cardiac muscle, and

• The endocardium primarily endothelium

o Myocarditis is an inflammation of the myocardium.

o Endocarditis in an inflammation of the endocardium. It

usually involves the heart valves.


Layers of Heart Wall

o Epicardium

• visceral layer of

serous pericardium

o Myocardium

• cardiac muscle layer

is the bulk of the heart

o Endocardium

• chamber lining and

valves


Sons, New York.


Muscle Bundles of the Myocardium

o Cardiac muscle fibers swirl diagonally around the heart in interlacing bundles


Sons, New York.


Chambers of the Heart

o Four chambers:

• 2 upper atria (left and right)

• 2 lower ventricles (left and right)


Chambers of the Heart


Sons, New York.


Right Atrium

Right Atrium:

o Receives blood from 3 sources

• superior vena cava, inferior vena cava and coronary

sinus

o Interatrial septum partitions the atria

o Fossa ovalis is a remnant of the foetal foramen ovale

o Tricuspid valve

• blood flows through into right ventricle

• has three cusps composed of dense Connective

Tissue covered by endocardium


Right Ventricle

Right Ventricle:

o Forms most of anterior surface of heart

o Papillary muscles are cone shaped trabeculae carneae

(raised bundles of cardiac muscle)

o Chordae tendineae: cords between valve cusps and

papillary muscles

o Interventricular septum: partitions the ventricles

o Pulmonary semilunar valve: blood flows into pulmonary

trunk (and then pulmonary arteries)


Left Atrium

Left Atrium:

o Forms most of the base of the heart

o Receives blood from lungs - 4 pulmonary veins (2 right +

2 left)

o Bicuspid valve: blood passes through into left ventricle

• has two cusps

• to remember names of this valve, try the mnemonic

LAMB

– Left Atrioventricular, Mitral, or Bicuspid valve


Left Ventricle

Left Ventricle:

o Forms the apex of heart

o Chordae tendineae anchor bicuspid valve to papillary

muscles (also has trabeculae carneae like right ventricle)

o Aortic semilunar valve:

• blood passes through valve into the ascending aorta

• just above valve are the openings to the coronary

arteries


Sulci of the Heart

o Sulci - grooves on surface of heart containing coronary

blood vessels and fat

• coronary sulcus

– encircles heart and marks the boundary between

the atria and the ventricles

• anterior interventricular sulcus

– marks the boundary between the ventricles

anteriorly

• posterior interventricular sulcus

– marks the boundary between the ventricles

posteriorly


Chambers and Sulci

Anterior View Posterior View


Sons, New York.


Myocardial Thickness and Function

o The thickness of the myocardium of the four chambers

varies according to the function of each chamber.

• The atria walls are thin because they only deliver

blood to the ventricles

• The ventricle walls are thicker pumping blood further.

• The right ventricle walls are thinner than the left

because they pump blood into the lungs, which are

nearby and offer very little resistance to blood flow.

– The left ventricle walls are thicker because they pump blood

through the body where the resistance to blood flow is

greater.


Myocardial Thickness and Function


Sons, New York.


Heart Valves


Heart Valves and Circulation of Blood

o Heart Valves: open and close in response to pressure

changes as the heart contracts and relaxes.

o Fibrous Skeleton of Heart: Dense Connective Tissue

rings surround the valves of the heart, fuse and merge

with the interventricular septum

• Support structure for heart valves

• Insertion point for cardiac muscle bundles

• Electrical insulator between atria and ventricles

– prevents direct propagation of Action Potential to

ventricles


Fibrous Skeleton of Heart


Sons, New York.


Atrioventricular Valves Open

o Atrioventricular (A-V) Valves open and allow blood to flow from atria into ventricles when ventricular pressure is lower than atrial pressure

• occurs when ventricles are relaxed, chordae tendineae are slack and papillary muscles are relaxed


Sons, New York.


Atrioventricular Valves Close

o A-V valves close preventing backflow of blood into atria

• occurs when ventricles contract, pushing valve cusps closed, chordae tendinae are pulled taut and papillary muscles contract to pull cords and prevent cusps from everting


Sons, New York.


(c) Tricuspid valve open

Cusp of

tricuspid

valve

Chordae

tendineae

Papillary

muscle


Semilunar Valves Open


Sons, New York.

(e) Superior view with atria removed: pulmonary and aortic valves open, bicuspid and tricuspid valves closed

Pulmonary valve (open)

POSTERIOR

Aortic valve

(open)

Tricuspid valve

(closed)

o Semilunar (SL) valves open with ventricular contraction

• allow blood to flow into pulmonary trunk and aorta

Bicuspid valve

(closed)


Semilunar Valves Close

o SL valves close with ventricular relaxation

• prevents blood from returning to ventricles, blood fills valve cusps, tightly closing the SL valves


Sons, New York.


Semilunar cusp of

aortic valve

(g) Superior view of aortic valve


Heart Valve Disorders

o Stenosis is a narrowing of a heart valve which restricts

blood flow.

o Insufficiency or incompetence is a failure of a valve to

close completely. Causes regurgitation / back flow

o Stenosed valves may be repaired by balloon

valvuloplasty, surgical repair, or valve replacement.


Blood Circulation

o Circulation of the

blood: divided into

two closed circuits

• Systemic circulation

(includes coronary

circulation)

• Pulmonary circulation

Blood flow

Blue = deoxygenated

Red = oxygenated


Sons, New York.


Blood Circulation

o Systemic circulation

• left side of heart pumps blood through body

• left ventricle pumps oxygenated blood into aorta

• aorta branches into many arteries that travel to

organs

• arteries branch into many arterioles in tissues

• arterioles branch into thin-walled capillaries for

exchange of gases and nutrients

• deoxygenated blood begins its return in venules

• venules merge into veins and return to right atrium


Blood Circulation

o Pulmonary circulation

• right side of heart pumps deoxygenated blood to

lungs

• right ventricle pumps blood to pulmonary trunk

• pulmonary trunk branches into pulmonary arteries

• pulmonary arteries carry blood to lungs for exchange

of gases

• oxygenated blood returns to heart in pulmonary veins

to left atria


Coronary Circulation

o Coronary Circulation:

• The flow of blood through the many vessels that flow

through the myocardium of the heart is called the

coronary (cardiac) circulation

• It delivers oxygenated blood and nutrients to and

removes carbon dioxide and wastes from the

myocardium.

• Many anastomoses provide alternate routes if one

artery becomes occluded.


Coronary Arteries

Coronary Arteries:

o Branches off aorta above aortic semilunar valve

o Left coronary artery

• supplies left atrium and left ventricle

o Right coronary artery

• supplies right atria

• supplies both ventricles


Coronary Arteries


Sons, New York.


Coronary Veins

Coronary Veins:

o Collects wastes from cardiac muscle

o Drains into a large sinus on posterior surface of heart called the coronary sinus

o Coronary sinus empties into right atrium


Myocardial Ischemia and Infarction

o Myocardial Ischemia: Reduced blood flow through

coronary arteries may cause ischemia. Ischemia causes

hypoxia and may weaken the myocardial cells. Ischemia

is often manifested through angina pectoris.

o Myocardial infarction: A complete obstruction of flow in a

coronary artery may cause myocardial infarction (heart

attack).

• Tissue distal to the obstruction dies and is replaced by scar

tissue.

• Treatment may involve injection of thrombolytic agents, coronary

angioplasty, or coronary artery bypass grafts.


Histology of Cardiac Muscle Tissue


https://www.youtube.com/watch?v=rUDqP

hzKzZM

Cardiac muscle fibers:

Shorter in length

Larger in diameter

compared to skeletal muscle fibers.

They also exhibit branching.

Fibers within the networks are connected

by intercalated discs, which consist of

desmosomes and gap junctions.

Gap junctions important for electrical

connectivity

https://www.youtube.com/watch?v=rUDqPhzKzZM


Cardiac Muscle Histology

o Branching, intercalated discs with gap junctions, involuntary,

striated, single central nucleus per cell


Sons, New York.


Cardiac Myofibril


Sons, New York.

Have actin and myosin

Arranged in

Lines

Zones

Bands

Z discs

Have less sarcoplasmic

reticulum and require

Ca2+ from extracellular

fluid for contraction.


Conduction System of Heart



o The conduction system in the heart is unique with

autorhythmic cells derived from cardiac muscle.

• Autorhythmic cells are cardiac muscle cells that are self-

excitable. They repeatedly generate spontaneous action

potentials that then trigger heart muscle contractions.

• These cells act as a pacemaker to set the rhythm for the entire

heart.

• They form the conduction system, the route for propagating

action potentials through the heart muscle

o This co-ordinates contraction of heart muscle.



o Components of Conduction system:

• Sinoatrial (SA) node (pacemaker),

• Atrioventricular (AV) node,

• Atrioventricular bundle (bundle of His),

• Right and left bundle branches,

• The conduction myofibers (Purkinje fibers)

o Signals from the autonomic nervous system and

hormones, such as adrenaline can modify the heartbeat

(in terms of rate and strength of contraction)





o SA node

• cluster of cells in wall of right atria

• begins heart activity that spreads to both atria

• sets the rhythm for contraction of the heart—the

natural pacemaker.

• excitation spreads to AV node

o AV node

• in atrial septum, transmits signal to bundle of His



o Bundle of His

• the connection between atria and ventricles

• divides into the left and right bundle branches

o Purkinje fibers

• large diameter fibers that conduct signals quickly


Rhythm of Conduction System

o SA node fires spontaneously 90-100 times per minute

o AV node fires at 40-50 times per minute

o If both nodes are suppressed then the fibers in the

ventricles by themselves fire only 20-40 times per minute

o Artificial pacemaker needed if pace is too slow

o Extra beats forming at other sites are called ectopic

pacemakers

• caffeine and nicotine increase activity


Timing of Atrial and

Ventricular Excitation

o SA node sets the pace since it is the fastest

o Spreads through both atria and down to AV node

o 100 msec delay at AV node. This allows atria to fully

contract so ventricles are full before ventricles contract

o Excitation spreads through both ventricles

simultaneously


Abnormal Conduction

o Sick sinus syndrome: An abnormally functioning SA node

that initiates irregular heart beats.

o When abnormal pacing of the heart develops, heart

rhythm can be restored by implanting an artificial

pacemaker, a device that sends out small, regular

currents to stimulate myocardial contraction.


Readings and Resources

o Tortora, GJ & Derrickson, B 2014. Principles of Anatomy and Physiology, 14th edn, Wiley.

o Harris, P, Nagy, S & Vardaxis, N 2010, Mosby’s Dictionary of Medicine, Nursing and Health Professions, 2nd edn, Mosby Elsevier.

o Guyton, AC & Hall, JE 2011, Textbook of Medical Physiology, 12th edn, Saunders Elsevier.

o Marieb, EN & Hoehn, K 2010, Human Anatomy and Physiology, 8th edn, Benjamin Cummings Pearson.

o Moore, KL, Dalley, AF & Agur, AMR 2010, Clinically Orientated Anatomy, 6th edn, Lippincott, Williams & Wilkins.


Copyright

COMMONWEALTH OF AUSTRALIA

Copyright Regulations 1969

WARNING

This material has been reproduced and

communicated to you by or on behalf of

the Endeavour College of Natural Health pursuant to

Part VB of the Copyright Act 1968 (the Act).

The material in this communication may

be subject to copyright under the Act.

Any further reproduction or

communication of this material by you

may be the subject of copyright

protection under the Act.

Do not remove this notice.

Documents

Human Biological Science 2 · PDF fileHuman Biological Science 2 Session 3 Cardiovascular System ... Blood Circulation o Systemic circulation • left side of heart pumps blood through