WEEK 6 The Heart - Collin Collegefaculty.collin.edu/cdoumen/2402/2402/3_Cardio/2402Heart1.pdf · BIOL. 2402 Anatomy & Physiology WEEK 6 The Heart 2 A groundbreaking work in the history

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Collin College

BIOL. 2402 Anatomy & Physiology

WEEK 6

The Heart

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A groundbreaking work in the history of medicine, English physician William Harvey’s “Anatomical Essay on the Motion of the Heart and Blood in Animals” named the heart as the organ responsible for pumping blood. He also was the first one to propose that CVS is a closed circuit. Although criticized when first published in 1628, Harvey’s work was soon accepted by scientists and laid the groundwork for modern physiology.

(1578-1657)

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The heart is the pump that propels the blood through a closed circulatory system

Blood cells never leave this circulation !

Red color indicates blood that isfully oxygenated.

Blue color represents blood that is only partially oxygenated.

The Heart and the CVS

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The heart is actually a dual pump

•  Right side of the heart functions to propel blood through the pulmonary circulation

•  Left heart propels blood through the systemic circulation


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Main purpose of the heart is to generate blood flow and blood pressure

One of the key functions is to provide the distant tissues with energy so that they can function .

C6H12O6 + 6O2 6CO2 + 6H20 + 38 ATP

Exchange of nutrients and gases occurs at the capillary level.

•  5 % of total blood volume resides in the capillary beds.

•  Other 95 % of blood volume , with the heart and blood vessels, is involved in generating a pressure / flow system through the conduit.


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Heart Anatomy

Area between the two pleura is called the mediastinum

8Epicardium Parietal pericardium

Heart Anatomy

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Visceral pericardium (epicardium)

Parietal pericardium

Heart Anatomy

Pericarditis : Inflammation of the pericardium

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Heart Anatomy

Heart has two upper atria and two lower ventricles. (Expandable exterior portion of an atria is called the auricle)

Right atrium connects to right ventricle and left atrium connects to left ventricle. There is no direct connection between left side and right side.

Blood vessels leaving the heart are arteries/aorta

Blood vessels arriving at the heart are veins

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Heart Anatomy

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Heart Anatomy and Blood flow

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Major Blood Vessels at the Heart

Major blood vessels of the heart include

•  Inferior and superior vena cavae

• Pulmonary trunk (splits into pulmonary arteries)

•  Aorta•  Brachiocephalic

•  Left common carotid•  Left subclavian

• Pulmonary veins

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The heart valves make sure that blood flows only in one direction

They prevent backflow and also allow pressure to build up bt creating a closed system

Atrio-Ventricular valves are located between the atria and ventricles •  Left AV-valve or Bicuspid Valve (Mitral valve) •  Right AV - valve or Tricuspid valve •  LAB-RAT

Semi-lunar valves are located between ventricles and blood-vessel that guides blood out of the ventricle

•  Aortic semi-lunar valve between left ventricle and aorta •  Pulmonary semi-lunar valve between right ventricle and

pulmonary artery

Blood flow and Heart valves

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AV valves are connected to ventricular walls at the papillary muscles via the chordae tendineae !

They prevent the valves to flip open against the direction of the blood flow.


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The Heart wall

Components of the heart wall include

•  Epicardium = visceral pericardium

•  Myocardium = actual cardiac muscle mass

•  Endocardium= thin lining of endothelial cells that

lines inside

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The Heart wall

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Left and Right Ventricular Heart Wall

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Cardiac cells have similar arrangement as striated skeletal cells, with some obvious differences

• cells are connected via gap-junctions and desmosomes

• have sarcomeres with A-I band arrangement of actin/myosin

•  20-25 % of cell volume taken up by mitochondria (compare with 2% in skeletal muscle)

•  less T-tubules and SR

Microscopic Heart Cell Anatomy

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!  Cardiac contractile cells–  Form bulk of atrial and ventricular walls and receive

stimulus from Purkinje fibers–  Resting membrane potential

•  Of ventricular cell is about –90 mV•  Of atrial cell is about –80 mV

!  Intercalated discs–  Interconnect cardiac contractile cells–  Membranes of adjacent cells are

•  Held together by desmosomes •  Linked by gap junctions

–  Transfer force of contraction from cell to cell–  Propagate action potentials 25


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Cardiac muscle includes most of the structures seen in skeletal muscle, including the striated arrangement of actin and myosin.

Adjacent myocarial cells are connected by intercalated disks, which have desmosomes for strength, and gap junctions for the coordination of contraction during pumping.


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Blood Supply to the Heart

•  Arteries include

•  the right and left coronary arteries,

• anterior and posterior interventricular arteries,

• and the circumflex artery

•  Veins include

•  the great cardiac vein,

• anterior and posterior cardiac veins,

•  the middle cardiac vein, and the small cardiac vein

Cardiac muscle requires its own blood supply to provide the oxygen and necessary nutrients. This is done by the coronary blood vessels.

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Coronary arteries originate at the base of the aorta.

Posterior Coronary veins drain into the coronary sinus, which empties into the right atrium.

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•  Coronary artery disease– Usual cause is formation of a fatty deposit, or

atherosclerotic plaque, in wall of coronary vessel – The plaque, or an associated thrombus (clot),

narrows passageway and reduces blood flow– Spasms in smooth muscles of vessel wall can

further decrease or stop blood flow

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Normal Artery

Tunica externa

Narrowing of Artery

Atherosclerotic plaque

Tunica media

Cross section Cross section

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Occluded coronary artery

Damaged heart muscle

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CAD = coronary artery disease Ischemia = reduced circulatory supply

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Angina pectoris : •  temporary ischemia develops during increased

workload on the heart ( such as exercise)

Medication : •  sympathetic blockers (propranolol) •  Vasodilators ( nitroglycerin) •  Calcium blockers

Myocardial infarction (MI), or heart attack •  Part of coronary circulation becomes blocked •  Cardiac muscle cells die from lack of oxygen •  Death of affected tissue creates a nonfunctional

area known as an infarct •  Most commonly results from severe CAD

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The Heart has the property of being able to contract without impulses from the nervous system.

This auto-rhythmic property is due to the presence of specialized cell that fire action potentials at a certain rhythm.

•  Main pacemaker center is called the Sino Atrial (SA) node, located in the upper part of the right atria

•  Electrical impulses are picked up by the AtrioVentricular Node and conducted via the Bundle of His (AtrioVentricular bundle) down the intraventricular septum and the left and right bundle branches.

•  Finally, electrical impulses are conducted up the walls of the ventricles via the Purkinje fibers.

Autorhythmic Activity of the Heart

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The heart’s pacemaker and conducting system are shown in bright yellow.


Sinoatrial (SA) node

Internodal pathways

Atrioventricular (AV) node

AV bundle

Bundle branches

Purkinje fibers

Impulse conduction through the heart

1. SA node activity and atrial activation begin

2. Stimulus spreads across atria through the internodal pathways and reaches AV node

3.  Impulse is delayed for 100 msec at AV node

Atrial contraction begins


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Sinoatrial (SA) node

Internodal pathways

Atrioventricular (AV) node

AV bundle

Bundle branches

Purkinje fibers

Impulse conduction through the heart

4.  Impulse travels in AV bundle to left and right bundle branches in interventricular septum •  To Purkinje fibers •  And to papillary

muscles via moderator band

5.  Purkinje fibers distribute impulse to ventricular myocardium

Atrial contraction is completed Ventricular contraction begins


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The sinoatrial node is the heart’s pacemaker because it initiates each wave of excitation with atrial contraction.

The Bundle of His and other parts of the conducting system deliver the excitation to the apex of the heart so that ventricular contraction occurs in an upward sweep.


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This electrical discharge by the autorhythmic cells provides a neat coordinated process with the contractile activity of the cardiomyocytes, which in turn provides the heart beat, blood flow and blood pressure.

This sweep of electrical activity across the heart is at the basis of the electrocardiogram (ECG or EKG).

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The Heart Beat

Two types of cells are involved in a normal heart beat.

•  the autorhythmic cells (depolarize with a certain rhythm)

•  the cardiomyocytes

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The Heart Beat and action potentials

What ionic events occur during a normal action potential in a nerve or skeletal muscle cell ?

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The Heart Beat: AP’s in the pacemaker cells

The action potential of an autorhythmic cardiac cell.

The rhythmic aspect is due to an unstable resting membrane potential called the pacemaker potential or pre-potential.

When it reaches threshold it result in an action potential.

What causes this pre-potential to drift ?

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Unstable prepotential is due to closure of K+ channels and brief opening of “funny” channels that slowly let more Na+ in.

At threshold, L-type Calcium open, resulting in depolarization.

L-type Calcium channels close and K+ channels open, resulting in re-polarization.

Funny channels close and T-calcium briefly open and close.

The Heart Beat: AP’s in the pacemaker cells

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The Heart Beat: the conducting cells

•  Heart is stimulated by the sympathetic cardioacceleratory center

•  Heart is inhibited by the parasympathetic cardioinhibitory center

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The Heart Beat: the conducting cells

Sympathetic activity :

•  NE binds to beta-1 receptors and opens Ca-channels

•  This increases the rate of depolarization during the prepotential phase; HR increases !

ParaSympathetic activity :

•  ACh increases K+ permeability during the prepotential drift.

•  Prolongs the time to reach threshold ; HR slows down

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The Heart Beat: AP’s in the contracting cells

The action potential of a myocardial pumping cell.

The top graph shows the action potential.

The lower graph shows what happens to the ion permeability of the membrane during the same time.

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The quick opening of voltage-gated sodium channels is responsible for the rapid depolarization phase.

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The quick opening of voltage-gated sodium channels is responsible for the rapid depolarization phase.

The prolonged “plateau” of depolarization is due to • Fast closing of Na channels • Closure of potassium channels • Slow but prolonged opening of voltage-gated calcium channels

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Opening of potassium channels and closure of the calcium channels results in the repolarization phase.


Documents

WEEK 6 The Heart - Collin Collegefaculty.collin.edu/cdoumen/2402/2402/3_Cardio/2402Heart1.pdf · BIOL. 2402 Anatomy & Physiology WEEK 6 The Heart 2 A groundbreaking work in the history