CARDIOVASCULARCARDIOVASCULAR SYSTEMSYSTEM

DR. ZAHOOR ALI SHAIKH

Structure of the Heart

• Structure of the Heart

Heart• Between Atria and Ventricles there is layer of dense

connective tissue known as fibrosis skeleton• Atria attach to the upper margin of fibrous Skelton• Ventricle attach to the lower margin of fibrous Skelton• Therefore Myocardium of Atria and Ventricle are

structurally and functionally separated from each other by fibrous skeleton

• Action potential from Atria to Ventricle travel via conductive tissue ( It is specialized cardiac tissue)

• Rt Atrium is separated from Left atrium by Interatrial septum

• Rt Ventricle is separated from Left Ventricle by Interventricular septum

• Myocardial cells are joined together by Intracalated disc (cell membrane) which has Gap Junctions

• In the fibrous skeleton which seperates Atria and Ventricle, there are four Valves

Heart ( Cont…)

Forms a protective inner lining of the chamber & valves

Membrane of epithelium & connective tissues, including elastic & collagenous fibers, blood vessels, & specialized muscle fibers

Endocardium

Contracts to pump blood from the heart chambers

Cardiac muscle tissue separated by connective tissues & including blood capillaries, lymph capillaries, & nerve fibers

Myocardium

Forms a protective outer coveringSecretes serous fluid

Serous membrane of connective tissue covered with epithelium and including blood capillaries, & nerve fibers

Epicardium(visceral pericardium)

FunctionCompositionLayer

LAYERS OF THE HEART

HEART VALVES1. ATRIOVENTRICULAR VALVES (AV Valves)2. SEMILUNAR VALVES1.Atrioventricular Valves:

– Rt AV Valve : Tricuspid Valve is between Rt Atrium and Rt ventricle - it has three cusps

– Lt AV Valve : Mitral valve or Bicuspid valve is between Lt atrium and Lt ventricle – it has two cusps

– AV valve are one way valve, they allow blood to flow from Atria to ventricle but they prevent backflow of blood from Ventricle to the Atria

– Opening and closing of valves occur due to pressure difference between atria and ventricle

– There are papillary muscles within the ventricles which give chordae tendineae, they are connected to AV valve cusps and prevent bulging of AV valve into Atria and keep the valve tightly closed.

2. SEMILUNAR VALVES :– Aortic valve: located at the origin of aorta. It has

three cusps– Pulmonary valve: located at the origin of pulmonary

artery. It has three cusps– When Lt Ventricle contracts blood flows to Aorta via

Aortic Valves– When Rt ventricle contracts blood flows to

Pulmonary artery via Pulmonary valve– During ventricular relaxation, when pressure in the

arteries is greater then the pressure in the ventricles, the semilunar valves close preventing the backflow of blood into the ventricles

HEART VALVES

PULMONARY AND SYSTEMIC CIRCULATION• PULMONARY CIRCULATION:

– Path of blood from Rt ventricle through the lungs and back to Lt atrium is called Pulmonary circulation

– Pulmonary circulation is low pressure circulation

• SYSTEMIC CIRCULATION:– Path of blood from Lt ventricle to the organ systems and

back to the Rt atrium is called systemic circulation– Systemic circulation is high pressure circulation.

• Left ventricular muscular valve is thicker then Rt. VentricleLt. Ventricle: 8 – 10 mm thickRt. Ventricle 2 – 3 mm thickLt Ventricle works more than the Rt. Ventricle because it

pumps blood against high pressure of systemic circulation

• The Syncytial Interconnecting Nature of Cardiac Muscle

Q: Name the atrioventricular and semilunar valves?

• AV Valves

Tricuspid (Rt AV Valve)

Mitral (Bicuspid) (Lt AV Valve)

• Semilunar Valves

Aortic Valve

Pulmonary Valve

Q: Papillary Muscles are attached to which Valve?• A: AV Valves (Mitral & Tricuspid)

Q: What are intercalated Discs and Gap junctions?How Heart Works as Syncytium?

Q: What are intercalated Discs and Gap junctions?

A: Intercalated discs are the cell membranes which connect the myocardial cells.within the intercalated disc there are Gap junctions, where the membrane offers very low resistance therefore ions can pass from one cell to another which allows the action potential to travel from one cell to another therefore heart work as a syncytium ( as one unit). We have atrial & ventricular syncytium.

What you should know from this lecture?• Functional anatomy of heart.

1. Heart : 14 cm long & 9 cm wide.

2. Base & Apex

• Layers

• The valves of heart

• Pulmonary Circulation

• Systemic Circulation

Contd……

• Conductive tissue

• Autonomic nerve supply1. Sympathetic

2. Parasympathetic

• Blood supply

• Cardiac muscle

• microscopic structure Intercalated disc – cell membrane which

connect one cell to another

Contd……

• Gap junctions allow relatively free diffusion of ions.

o Action potential travels from one cell to another easily

o Cardiac muscle works as a Syncytium Atrial syncytium Ventricular syncytium

Contd……

• Applied Physiologyo pericarditiso Pericardial effusiono Valvular lesion

Stenosis (narrowing) Incompetence

o Mitral valve prolapseo Atrial septal defect ( ASD)o Ventricular septal defect ( VSD)

DR. ZAHOOR ALI SHAIKH

CARDIOVASCULAR SYSTEMLECTURE - II

• EXCITABILITY

• RHYTHMICITY

• CONDUCTIVITY

• CONTRACTILITY

PROPERTIES OF CARDIAC MUSCLE

EXCITABILITY

Action Potential From a Purkinje Fiber and Ventricular Muscle Fiber

Myocardial Action Potential ( Excitability )

• Once myocardial cells are stimulated by action potential originating in SA node, it produces its own action potential

Action Potential From Ventricular Muscle Fiber

Action Potential in Myocardial cell

• Resting membrane potential is about -90mv

• Rapid depolarization (Phase 0) – due to Na+ influx

• Rapid repolarization (Phase 1) - Due to closure of Na+ channels

• Slow depolarization (Phase 2) - this is called Plateau phase and is maintained for 200 – 300 ms – due to Ca++ influx

• Repolarization (Phase 3) – due to K+ efflux

• Resting Membrane Potential (Phase 4)

• Action Potential From Ventricular Muscle Fiber.• Contractile Response from Ventricular Muscle Fiber.

VENTRICULAR ACTION POTENTIAL

• Ventricles have long Action Potential up to 300 ms due to plateau phase

• During Action Potential there is absolute refractory period and relative refractory period

• Ventricle contraction occurs during absolute refractory period therefore two contraction cannot be summated therefore heart muscle can not be Tetanised

• Note: Absolute refractory period is that period during which if we apply second stimulus, there will be no response • Action Potential From Ventricular Muscle Fiber.

•Contractile Response from Ventricular Muscle Fiber.

Q: What is the difference between. SA Node Actionpotential. Atrial Actionpotential. Ventricular Actionpotential

• Q: Name the phases of Ventricular Action potential and give the cause of each phase

Q: Show absolute refractory period and relative refractory period during Ventricular Action potential and Ventricular contraction?

WHAT YOU SHOULD KNOW FROM THIS LECTURE?

• EXCITABILITY ( Action potential in cardiac muscle cell)

1. Action potential in ventricular muscle fiber. (Draw the diagram & show the phases 0,1,2,3,4.

2. Give the cause of each phase.

3. Show refractory periods (Absolute & Relative on the diagram)

Contd..

1. Show the cardiac muscle contraction on the diagram.

2. Draw action potential & contraction of skeletal muscle & compare it with action potential & contraction of cardiac muscle.

3. Draw action potential in purkinje fiber & Atrial muscle fiber.

DR. ZAHOOR ALI SHAIKH

CARDIOVASCULAR SYSTEMLECTURE - III

• EXCITABILITY

• RHYTHMICITY

• CONDUCTIVITY

• CONTRACTILITY

PROPERTIES OF CARDIAC MUSCLE

RHYTHMICITY

Pacemaker Potential( Rhythemicity )

• SA node is pacemaker of normal heart

• SA node has a spontaneous depolarization called as pacemaker potential or pre potential

• Membrane potential begins at -60mv and slowly depolarizes to -40mv, which is threshold for producing Action Potential

Cause of Prepotential

• Na+ going inside

• Ca++ going inside

• ↓ K+ going outside

• After Prepotential we get Depolarization and Repolarization

Cause of Depolarization - Ca++ going inside

Cause of Repolarization - K+ going outside

• Rhythmical Discharge of Sinus nodal Fiber.• SA Node Action Potential compared with

Ventricular Muscle Fiber

Phase 4

Phase 0 Phase 3

Effect 0f Sympathetic and parasypathetic Stimulation on Prepotential (Pace Maker Potential)

Effect 0f Sympathetic and parasypathetic Stimulation on Prepotential

(Pace Maker Potential)

• Epinephrine & Norepinephrine

(Adrenaline and Noradrenaline) causes prepotential to occur faster therefore increase the heart rate

• Acetylcholine causes prepotential to occur at slow rate therefore decrease the heart rate

Difference between Myocardial AP & Pacemaker Potential

Myocardial AP• Resting Memb. Potential is

about -90mv• It is stable• Needs stimulus• No Prepotential• Phases 0,1,2,3 & 4• Rapid depolarization due to

Na+ influx

Pacemaker Potential• Memb. Potential is about

-60mv• It is unstable• Automatic• Prepotential • Phase 0,3 ,4.(no phase 1 & 2).• slow depolarization due to ca+

+ influx

Q: Why SA Node is pacemaker?

• Because of Pacemaker Potentials or Prepotentials

What is the cause of Prepotentials in SA Node?

• Decrease Potassium efflux

• Increase Sodium Influx and Calcium influx

• This brings the resting membrane potential from -55 mv to -40 mv which is the firing level, therefore it causes self excitation

WHAT YOU SHOULD KNOW FROM THIS LECTURE?

• Rhythmicity ( Prepotential & Action potential in S-A node.)

1. Spontaneous generation of action potential in S-A node without neural input.

2. Draw the diagram of action potential in S-A node & show the phases 4,0,3.

3. Cause of prepotential.

4. Cause of action potential

5. Why S-A node is PACE MAKER of heart.

Contd…..

• Effect of sympathetic & parasympathetic stimulation on prepotential.

• Compare S-A node & ventricle muscle fiber action potential.