The cardiovascular system - Human Anatomy and Physiology B. Pharma 1st Semester

The cardiovascular system

Objectives

At the end of this lecture, student will be able to

• Explain the location of the heart

• List the chambers, great vessels and valves of the heart

• Describe the structure and functions of the pericardium, heart wall, chambers

• Describe the structure and functions of heart chambers and great vessels

• Outline the blood flow through the chambers of the heart

• Explain the operation of heart valves

• Explain pulmonary and systemic circulation

• Explain conduction system of heart

• Explain the pressure and volume changes of cardiac cycle

• Explain cardiac output and stroke volume

• Outline the structure and function of:

– Arteries

– Arterioles

– Capillaries

– Venules

– Veins

• Explain the events of ECG

• Define blood pressure

• Describe the factors affecting BP

• Explain echocardiogram

• Explain the regulation of BP

• Point out and summarize the common disorders of cardiovascular system

Content

• Anatomy of heart

• Heart chambers

• Heart valves

• Operation of heart valves

• Pulmonary and systemic circulation

• Conduction system

• Cardiac cycle

• Innervation of heart

• Structure of blood vessels

• ECG

• Blood pressure

• Factors affecting blood pressure

• Echocardiogram

• Regulation of blood pressure

• Disorders of cardiovascular system

Introduction to Cardiovascular System

• Center of the cardiovascular system - the heart

• Connects to blood vessels that transport blood

• To accomplish this, heart beats about 100,000 times every day, (35 million beats in a year)

• Cardiology - Study of the normal heart and the diseases associated

Cardiovascular System

• Arteries

– carry blood away from the heart

– carry blood high in oxygen (except for the pulmonary arteries)

• Veins

– Veins carry blood back to the heart

– carry blood low in oxygen (except for the pulmonary veins)

• The great vessels

– Arteries and veins entering and leaving the heart

Characteristics and Functions of the Heart

• Ensures the unidirectional flow of blood

• Backflow of blood is prevented by valves within the heart

• Acts like two independent, side-by-side pumps

– One directs blood to the lungs for gas exchange

– The other directs blood to body tissues for nutrient delivery

• Develops blood pressure through alternate cycles of heart wall contraction and relaxation

Anatomy of the Heart

• Relatively small, conical organ

• Size of a person clenched fist

• Weighs about 250 to 350 grams

• Located left of the body midline

• Posterior to the sternum in the middle mediastinum

• Right side - Located anteriorly

• Left side - Located posteriorly

• Base: Formed primarily by the left atrium

• Apex - The inferior & conical end

• It projects slightly anteroinferiorly toward the left side of the body


The Heart

Pericardium

• Fibrous, serous sac

• Confines the heart

• Allows sufficient of movement for vigorous and rapid contraction

• Restricts heart movements

 • Prevents the heart from overfilling

• Between the parietal & visceral layers

- Thin film of lubricating serous fluid

• Outer Portion

– Tough, dense connective tissue

– Called the fibrous pericardium

– Attached to the sternum & diaphragm

– Prevents overstretching, provid protection

– Anchors the heart in the mediastinum

• Inner Portion

– Thin, double-layered serous membrane

– Called the serous pericardium

• Parietal layer - Fused to the fibrous pericardium

• Visceral layer (Epicardium - Adheres tightly to the surface of the heart)

Heart Wall Structure

Three distinctive layers:

– External epicardium

– Middle myocardium

– Internal endocardium

• Outer layer

• Simple squamous epithelium underlined by fat

• Age - More fat is deposited in the epicardium - thicker and fattier

• Gives slippery texture to the outmost surface of the heart

• Myocardium

– Middle layer of the heart wall

– Composed chiefly of cardiac muscle tissue

– Makes up about 95% of the heart

– Responsible for its pumping action

• Endocardium

– Thin layer of endothelium

– Provides a smooth lining for the chambers of the heart

– Covers the valves of the heart

– Minimizes surface friction as blood passes through the heart and blood vessels

Cardiac Muscle Tissue

• Fiber Characteristics

– Short, branched fibers

– One or two central nuclei

– Numerous mitochondria for ATP supply

– Striated, with extensive capillary networks

 • Intercalated discs

– Specialized cell–cell contacts

– Contain gap junctions

– Contain desmosomes

External Anatomy of the Heart

• Chambers:

– Four hollow chambers:

• Two smaller atria

• Two larger ventricles

Atria

• Thin-walled, located superiorly

    Auricle:

– Anterior part of each atrium is a wrinkled, flap like extension

– Slightly increases the capacity of an atrium

Receive blood through both circulatory circuits

• Right atrium receives blood from the systemic circuit

• Left atrium receives blood from the pulmonary circuit

• Blood that enters an atrium is passed to the ventricle on the same side of the heart

Ventricles

– The inferior chambers

– Two large arteries, the pulmonary trunk and the aorta exit the heart at the basal surface

– The pulmonary trunk carries blood from the right ventricle into the pulmonary circuit

– The aorta conducts blood from the left ventricle into the systemic circuits

• Atria are separated from the ventricles externally by coronary sulcus (or atrioventricular sulcus)

• Extends around the circumference of the heart

• The anterior interventricular sulcus and the posterior interventricular sulcus are located between the left and right ventricles

• These sulci extend inferiorly from the coronary sulcus toward the heart apex

Chambers of the Heart and Valves

Right Atrium

• The posterior wall is smooth

• The anterior wall is rough:

– Due to the presence of muscular ridges called pectinate muscles

– Extend into the auricle

• Contains fossa ovalis

• Interatrial septum

– Thin partition between the right and left atrium

Left Atrium

• Same thickness as the right atrium

• Forms most of the base of the heart

• Smooth posterior wall

• Pectinate muscles are confined to the auricle of the left atrium

Right Ventricle

• The right ventricle is about 4–5 mm in average thickness

• Interventricular septum: Separates the ventricles

• The inside of the right ventricle

– Contains a series of ridges formed by raised bundles of cardiac muscle fibers called trabeculae carneae 

• Chordae tendineae:

– Tendon like cords- connected to cone shaped trabeculae carneae called papillary muscles

– The cusps of the tricuspid valve are connected to the chordae tendineae

Left Ventricle

• Thickest chamber of the heart

• Forms the apex of the heart

• Like the right ventricle, the left ventricle contains:

– Trabeculae carneae

– Chordae tendinae - Anchor the cusps of the bicuspid valve to papillary muscles

Heart Valves

• As each chamber of the heart contracts - Pushes a volume of blood into a ventricle or into an artery

• Valves open and close in response to pressure changes as the heart contracts and relaxes

• Each of the four valves helps ensure the oneway flow of blood

 AV Valves

• Bicuspid – Left

• Tricuspid – Right

 Semilunar Valves

• Pulmonary valve

• Aortic Valve

Operation of AV Valves 

(a) AV valves open, atrial pressure greater then ventricular pressure

1. Blood returning to the heart fills atria, putting pressure against atrioventricular valves; atrioventricular valves are force to open

2. As ventricles fill, atrioventricular valves flaps hang limply into ventricles.

3. Atria contract, forcing additional blood into ventricles.

(b) AV valves closed, atrial pressure less then ventricular pressure

1. Ventricles contract, forcing blood against atrioventrcular valve cusps.

2. Atrioventrcular valve closed

3. Pipillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria

Operation of Semilunar Valves

(a) Semilunar valves open

As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open.

(b) Semilunar valves close

As ventricles relax and intraventricular pressure falls, blood flow back from arteries, falling the cusps of semilunar valves, forcing them to close.

Pulmonary and Systemic Circulation

• The heart pumps blood into two closed circuits with each beat

– Systemic circulation

– Pulmonary circulation  

• The left side of the heart

– Pump for systemic circulation

– Receives bright red, oxygen reach blood from the lungs

• The right side of the heart

– Pump for pulmonary circulation

– Receives all the dark red, deoxygenated blood returning from systemic circulation

Pulmonary and Systemic Circuits

The Systemic Circuit

• Consists of the chambers on the left side of the heart

• All the other named blood vessels

• Carries blood to all the peripheral organs of the body and tissues

The pulmonary circuit

• Consists of the chambers on the right side of the heart

• Pulmonary arteries and veins

– conveys blood to the lungs via pulmonary arteries

– To reduce CO2 and replenish O2 levels in the blood

– Blood returns to the heart in pulmonary veins

Pulmonary and Systemic Circuits

Step 1. Oxygenated blood from the left side of the heart - Pumped into the aorta

Step 2. Then into smaller systemic arteries. Gas exchange in tissues occurs from capillaries

Step 3. Systemic veins then carry deoxygenated blood and waste products

Step 4. Most veins merge and drain into the superior and inferior vena cavae

Step 5. Drain blood into the right atrium

Step 6. Blood enters the pulmonary circuit (cycle is repeated)

Coronary Circulation

• The coronary arteries

– Branch from the ascending aorta

– Encircle the heart

• While heart contracts

– Little blood flows in the coronary arteries because they are squeezed shut

• When heart relaxes

– The high pressure of blood in the aorta propels blood through the coronary arteries

– Into capillaries

– Then into coronary veins


The Conduction System

Autorhythmic fibers (Self-excitable):

– Network of specialized cardiac muscle fibers

– The source of electrical activity

• Repeatedly generate AP

• AP trigger heart contractions

• Carry out 2 important functions:

– Act as a pacemaker

– Form the conduction system

Components of the Conduction System

 • Sinoatrial (SA) node (pacemaker)

• Atrioventricular (AV) node

• Atrioventricular (AV) bundle (bundle of His)

• Bundle branches

• Purkinje fibers

Sinoatrial (SA) node (pacemaker)

• Act as the pacemaker

• Located in the posterior wall of the right atrium

• Adjacent to the entrance of the superior vena cava

Atrioventricular (AV) node

• Internodal conduction pathway

• Located in the floor of the right atrium between the right AV valve and the coronary sinus

Atrioventricular (AV) bundle (bundle of His)

• From the AV node to AV bundle

• Extends into the interventricular septum

• Then divides into one right and two left bundle branches

• Conduct the impulse to conduction fibers called Purkinje fibers in the heart apex

Purkinje fibers

• Muscle impulse conduction - Extremely rapid

• Impulse spreads immediately throughout the ventricular myocardium

Role of Conduction System

Cardiac cycle

• Series of events that occur in single heart beat

• A cardiac cycle consists of:

– Systole (contraction)

– Diastole (relaxation) of both atria & ventricles

• With an average heartbeat of 75 beats/min, a complete cardiac cycle requires 0.8 seconds


Cardiac output

• The volume of blood ejected from the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute

Cardiac reserve

• Difference between your maximum heart rate and resting heart rate

Factors regulate stroke volume

• Preload

– The degree of stretch on the heart before it contracts

• Contractility

The forcefulness of contraction of individual ventricular muscle fibers

• Afterload

– The pressure that must be exceeded before ejection of blood from the ventricles

Auscultation

• The act of listening to sounds within the body

• Done with a stethoscope

• From blood turbulence caused by the closing of the heart valves

• Smoothly filling blood is silent

Heart Sounds

• S1-lubb-closure of AV valve

• S2-dupp- closure of SL valve

• S3-rapid ventricular filling

• S4 -atrial systole

Innervation of the Heart

• Innervated by ANS

• Consists of both sympathetic and parasympathetic components

• Rich innervation to SA and AV nodes, but also to myocardial cells

• Parasympathetic innervation

– Via right and left vagus nerves

– Decreases HR & FOC

• Sympathetic innervation

– Via cardiac nerves

– Increases the rate and the FOC

Nervous Control of the Heart

Basic Structure of a Blood Vessel

Blood vessels

• Large arteries - Elastic (conducting) arteries

• Medium-sized arteries - Muscular (distributing) arteries

• Arterioles - Small arteries that deliver blood to capillaries

• Through constriction and dilation, arterioles assume a key role:

• Un-regulating blood flow

• In altering arterial blood pressure

Veins

• Venules - Small vessels that continue from capillaries

• Merge to form veins

• Veins - Consist of the same three tunics as arteries

• Valves - Prevent backflow of blood

• Systemic veins are collectively called blood reservoirs

• They hold a large volume of blood

Capillaries

• Microscopic blood vessels

• Materials are exchanged between blood and tissue cells

• Some capillaries are continuous, and others are fenestrated

• Branch to form an extensive network throughout a tissue

Anastomose

• The distal ends of two or more vessels unite

• An alternative blood route from an anastomosis - collateral circulation

• Arteries that do not anastomose are called end arteries

Electrocardiogram (ECG)

• AP propagate through the heart

• Generate electrical currents

• Can be detected at the surface of the body

• An electrocardiogram (ECG or EKG):

– Recording of electrical signals of the heart

• Electrodes - Positioned on the arms and legs (limb leads) and at six positions on the chest (chest leads) to record

• Amplifies the heart’s electrical signals

• Each electrode records slightly different electrical activity

• Position relative to the heart

Significance of ECG

• By comparing these records with one another and with normal records, it is possible to determine–:

(1) If the conducting pathway is abnormal

(2) If the heart is enlarged

(3) If certain regions of the heart are damaged

(4) The cause of chest pain

Normal ECG

• Consists of:

– P wave

– QRS complex

– T wave

P wave: Atrial depolarization

QRS complex: Onset of ventricular depolarization

• T wave: Ventricular repolarization

The P-Q interval: Beginning of atrial excitation to the beginning of ventricular excitation

The S-T segment: Represents the time when ventricular contractile fibers are fully depolarized

Blood Pressure

• Hydrostatic pressure exerted by blood on the walls of a blood vessel

• Contraction of the ventricles generates blood pressure

• BP is determined by

– Cardiac output

– Blood volume

– Vascular resistance

• Systolic BP- Highest pressure attained in arteries during systole

• Diastolic BP- Lowest arterial pressure during diastole

Mean Arterial Pressure (MAP)

• The average blood pressure in arteries

• Roughly one-third of the way between the diastolic and systolic pressures

• It can be estimated as follows:

MAP = diastolic BP + 1/3 (systolic BP - diastolic BP)

Eg. Thus, in a person whose BP is 110/70 mmHg,

[70 + 1/3(110 - 70)]= MAP is about 83 mmHg

Factors Affecting BP

Vascular resistance

• Opposition to blood flow due to friction between blood and the walls of blood vessels

• It depends on

– Size of the blood vessel lumen, Blood viscosity & Total blood vessel length

• SVR or TPR: Refers to all the vascular resistances offered by systemic blood vessels

• Most resistance- In the smallest vessels

Velocity of Blood Flow

Venous Return (VR)

Blood from the Lower Body Back To the Heart

• Two pump blood from the lower body back to the heart:

(1)The respiratory pump – based on alternating compression and decompression of veins

(2) The skeletal muscle pump

Echocardiogram

• Uses ultrasound waves to examine the heart

• Non-invasive test

• To diagnose – abnormalities of the heart

Significance

• Size and shape of the heart

• Pumping efficiency of the heart

• Valve abnormalities

• Other - Detect the presence of fluid around the heart; blood clots, or masses inside the heart; and abnormal holes between heart chambers

Control of Blood Pressure

• The cardiovascular (CV) center:

– Group of neurons in the medulla oblongata

– Regulates HR, contractility, and blood vessel diameter

– Receives input from higher brain regions and sensory receptors (Baroreceptors and Chemoreceptors)

– Output from the cardiovascular center flows along sympathetic and parasympathetic axons

Neural Regulation of BP

• Sympathetic impulses

– Propagated along cardio - accelerator nerves

– Increase HR and FOC

• Parasympathetic impulses

– Propagated along vagus nerves

– Decrease HR

• Baroreceptors - Monitor blood pressure

• Chemoreceptors - Monitor blood levels of O2 &CO2 and H+ ions

• The carotid sinus reflex - Helps regulate blood pressure in the brain

• The aortic reflex regulates general systemic blood pressure

Hormonal Regulation of BP

• Hormones that help regulate blood pressure are:

• epinephrine

• nor-epinephrine

• ADH (vasopressin)

• angiotensin II

• ANP

Autoregulation

• Refers to local, automatic adjustments of blood flow in a given region to meet a particular tissue’s need

• O2 level is the principal stimulus for autoregulations

Arrhythmia or dysrhythmia

• Refers to an abnormal rhythm as a result of a defect in the conduction system of the heart

• The heart may beat irregularly, too quickly, or too slowly

• Symptoms include

– Chest pain

– Shortness of breath

– Lightheadedness

– Dizziness and fainting

Hypertension

• Persistently high blood pressure

• Most common disorder affecting the heart and blood vessels

• Major cause of heart failure, kidney disease, and stroke

Hypotension

• Low blood pressure

• Commonly used to describe an acute drop in BP - excessive blood loss

• Symptoms include

– Dizziness

Weakness

Lightheadedness

Syncope

Nausea

Transient ischemic attacks

Disturbed speech

Vision change

Angina pectoris

Arteriosclerosis

– Group of diseases

– Thickening of the walls of arteries

– Loss of elasticity

Atherosclerosis

– One form of arteriosclerosis

– A progressive disease

– Characterized by the formation of lesions - atherosclerotic plaques

Myocardial infarction (Heart attack)

• Happens when blood stops flowing properly to part of the heart

• The heart muscle is injured due to not receiving enough oxygen

Angina Pectoris

• Chest pain often due to ischemia of the heart muscle

• Due to obstruction or spasm of the coronary arteries

• Main cause improper contractility of the heart muscles

Congestive Heart Failure

• Congestive cardiac failure or chronic heart failure

• Unable to pump sufficiently to maintain blood flow to meet the needs of the body

• Most common: Shortness of breath, excessive tiredness & leg swelling

Summary

• Cardiovascular system consists of the blood, the heart, and blood vessels

• Heart - Relatively small, conical organ, located in the mediastinum

• Heart ensures the unidirectional flow of blood through the blood vessels

• Backflow of blood is prevented by valves within the heart

• Blood that enters an atrium is passed to the ventricle on the same side of the heart

• Heart chambers and relaxation – Undergo alternate periods of contraction

• Fossa ovalis: Oval depression (remnant of the foramen ovale)

• Chordae tendineae: Tendon like cords- connected to cone shaped trabeculae carneae called papillary muscles

• As each chamber of the heart contracts - Pushes a volume of blood into a ventricle or into an artery

• Valves open and close in response to pressure changes as the heart contracts and relaxes

• The left side of the heart

– Pump for systemic circulation

– Receives bright red, oxygen rich blood from the lungs

• The right side of the heart

– Pump for pulmonary circulation

– Receives all the dark red, deoxygenated blood returning from systemic circulation

• Components of conduction system: Sinoatrial (SA) node (pacemaker), Atrioventricular (AV) node, Atrioventricular (AV) bundle (bundle of His), Bundle branches, Purkinje fibers

• Cardiac cycle phases: Atrial systole, ventricular systole, relaxation

• Systole - Contraction of a heart chamber

• Diastole - Relaxation of a heart chamber

• Auscultation- Act of listening to heart sounds

• Blood vessels: Arteries, arterioles, capillaries, venules and veins

• Three layers of blood vessel: Tunica interna, tunica media, and tunica externa

• Sympathetic innervation - Increases the HR and FOC

• Parasympathetic innervation - Decreases HR, but tends to have no effect on the FOC, except in special circumstances

• An electrocardiogram (ECG or EKG): Recording of electrical signals in the heart

• Blood pressure: Hydrostatic pressure exerted by blood on the walls of a blood vessel

• Factors affecting BP:  Vascular resistance, VR & velocity of blood flow

• Two pump blood from the lower body back to the heart:  The respiratory pump and the skeletal muscle pump

• Echocardiogram: Uses ultrasound waves to examine the heart

• Regulation of BP: Neural, hormonal and autoregulation

• The cardiovascular (CV) center: Group of neurons in the medulla oblongata which regulates HR, contractility, and blood vessel diameter

• Baroreceptors - Monitor blood pressure

• Chemoreceptors - Monitor blood levels of O2 &CO2 and H+ ions

 • Sympathetic impulses: Propagated along cardioaccelerator nerves, increase HR and FOC

• Parasympathetic impulses: Propagated along vagus nerves, decrease HR

• Disorders: MI, AP, CHF, arrythmia, hypertension, hypotension

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