Chapter 20: The Heart

Systemic circuit

Carries oxygenated blood from the heart to body tissues and returns deoxygenated blood with wastes such as CO₂ to the heart.

Blood-flow pathway of the systemic circuit

Left ventricle → aorta → arteries → arterioles → capillaries → veins → right atrium.

Blood pressure change in systemic circuit

Greatly reduced as arteries branch into arterioles and capillaries.

Pulmonary circuit

Carries blood to and from the gas-exchange surfaces of the lungs.

Pulmonary circulation pathway

Right atrium → right ventricle → pulmonary artery → lung capillaries → pulmonary veins → left atrium.

Pulmonary capillaries function

O₂ enters the blood and CO₂ leaves the blood.

3 types of blood vessels

Arteries (carry blood away from heart), Veins (carry blood to heart), Capillaries (connect arteries and veins).

Why capillaries are called exchange vessels

They exchange gases, nutrients, and wastes between blood and tissues.

Left atrium function

Collects blood from the pulmonary circuit.

Left ventricle function

Pumps blood into the systemic circuit.

Right atrium function

Collects blood from the systemic circuit.

Right ventricle function

Pumps blood into the pulmonary circuit.

Heart location

Directly behind the sternum, in the mediastinum, between the two pleural cavities.

Apex of the heart

The pointed tip of the heart.

What surrounds the heart

The pericardial sac.

Parietal pericardium

The outer layer of the pericardium; forms the inner layer of the pericardial sac.

Visceral pericardium

The inner pericardial layer, also called the epicardium.

Pericardial cavity

Space between the parietal and visceral pericardium containing pericardial fluid.

Pericardial fluid function

Lubricates and reduces friction between heartbeats.

Pericardial sac function

Fibrous collagen tissue that surrounds and stabilizes the heart.

Pericarditis

Infection/inflammation of the pericardium, causing rubbing/scratching sound and possible fluid accumulation.

Atria structural characteristics

Thin-walled chambers with expandable auricles.

Coronary sulcus separates

Atria from ventricles.

Interventricular sulci separate

Left and right ventricles.

Structures in interventricular sulci

Blood vessels supplying the cardiac muscle.

3 layers of the heart wall

Epicardium, myocardium, and endocardium.

Epicardium

The outer layer of the heart; also the visceral pericardium.

Myocardium

The muscular middle layer responsible for heart contraction.

Myocardium contents

Cardiac muscle tissue, blood vessels, and nerves.

2 divisions of ventricular myocardium

Superficial muscles (surround ventricles) and deep muscles (spiral around and between ventricles).

Endocardium

The inner layer of the heart wall.

Intercalated discs

Structures that connect cardiac muscle cells.

Structures in intercalated discs

Desmosomes and gap junctions.

Desmosomes function

Secure cardiac muscle cells and help convey contraction force.

Gap junctions function

Allow action potentials to propagate between cells.

Cardiac muscle cell characteristics

Small, one central nucleus, branching connections, and intercalated discs.

Interatrial septum separates

The right and left atria.

Interventricular septum separates

The right and left ventricles.

Vena cava delivers

Systemic venous blood to the right atrium.

Superior vena cava drains

Head, neck, upper limbs, and chest.

Inferior vena cava drains

Trunk, viscera, and lower limbs.

Coronary sinus

A vessel receiving blood from cardiac veins and emptying into the right atrium.

Foramen ovale

A fetal opening through the interatrial septum connecting the two atria.

Foramen ovale after birth

It closes and forms the fossa ovalis.

Pectinate muscles

Prominent muscular ridges on the anterior atrial wall and inner surface of the right auricle.

Cusps

Fibrous flaps forming the bicuspid and tricuspid valves.

Connects valve cusps to papillary muscles

Chordae tendineae.

Chordae tendineae and papillary muscles function

Prevent AV valves from swinging backward into the atria.

Right AV valve

Tricuspid valve, located between right atrium and right ventricle.

Tricuspid valve cusps count

3 cusps.

Main function of AV valves

Prevent backflow into the atria during ventricular contraction.

AV valves location

Between the atria and ventricles.

Trabeculae carneae

Muscular ridges on the inner surface of the ventricles.

Moderator band

A ridge containing part of the conducting system, helping coordinate ventricular contraction.

Thicker ventricular wall

Left ventricle.

Right ventricular wall is thinner because

It develops less pressure than the left ventricle.

Shape of the ventricles

Right ventricle is pouch-shaped; left ventricle is round.

Semilunar valves

Pulmonary and aortic valves.

Semilunar valves prevent

Backflow from the pulmonary trunk and aorta into the ventricles.

Semilunar valves cusps count

3 cusps.

Semilunar valves muscular support

None.

Aortic sinuses

Spaces at the base of the ascending aorta that keep valve cusps from sticking to the aorta.

Arteries from aortic sinuses

Right and left coronary arteries.

Carditis

Inflammation of the heart.

Condition causing valvular heart disease after strep

Rheumatic fever.

Rheumatic fever symptoms

High fever, joint pain, and rash.

Heart valves after rheumatic carditis

Scar tissue, thickening, and calcification.

Damaged valves and dentist antibiotics

Prevent bacterial infection causing endocarditis.

Coronary circulation

The coronary arteries and cardiac veins that supply the heart muscle itself.

Coronary arteries origin

At the aortic sinuses.

Blood forced into coronary arteries

Mainly between contractions, due to high pressure and elastic rebound.

Right coronary artery supplies

Right atrium, portions of both ventricles, and SA and AV nodes.

Major branches of right coronary artery

Marginal artery and posterior interventricular artery.

Left coronary artery supplies

Left ventricle, left atrium, and interventricular septum.

Two main branches of left coronary artery

Circumflex artery and anterior interventricular artery.

Great cardiac vein drains

Area supplied by the anterior interventricular artery, draining into coronary sinus.

Anterior cardiac vein empties

Directly into the right atrium.

Posterior, middle, and small cardiac veins empty

Into the great cardiac vein or coronary sinus.

Heartbeat

A single contraction sequence: atria first, then ventricles.

2 types of cardiac muscle cells

Conducting cells (coordinate heartbeat) and contractile cells (produce contractions).

Cardiac cycle electrical start

At the sinoatrial (SA) node.

Conducting system

Specialized cardiac muscle cells that initiate and distribute electrical impulses.

Automaticity

Ability of cardiac muscle tissue to contract automatically.

Main structures of the conducting system

SA node, AV node, and conducting cells.

SA node location

Posterior wall of the right atrium.

Pacemaker cells location

In the SA node.

SA node initiates

Atrial activation.

SA node to AV node connection

By internodal pathways.

AV node location

In the floor of the right atrium.

AV node function

Receives the SA-node impulse and delays it while atrial contraction begins.

AV bundle location

In the septum.

AV bundle pathway

Left and right bundle branches → Purkinje fibers.

Moderator band conducts impulses to

Papillary muscles.

Purkinje fibers function

Distribute impulses throughout the ventricles.

Purkinje fibers activating ventricles results in

Atrial contraction finishes and ventricular contraction begins.

Conduction order of the heart

SA node → AV node → AV bundle → bundle branches → Purkinje fibers.

Cardiac cycle

Time between the start of one heartbeat and the beginning of the next.

Systole vs Diastole

Systole = contraction; Diastole = relaxation.

Chamber pressure during systole

Increases.

Chamber pressure during diastole

Decreases.