The HeartCirculatory System

A closed system of the heart and blood vessels◦The heart pumps blood◦Blood vessels allow blood to circulate to all parts of the body

The function of the cardiovascular system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products

The Cardiovascular System

What does it mean to be a “closed system?”

Closed system?

Location:◦In the thorax◦Between the lungs◦Pointed apex directed toward left hip

About the size of your fist◦Less than 1 lb.

The Heart

The Heart

Figure 11.1

Pericardium – tissue like sac surrounding the heart

A double membrane made of:◦A. Visceral pericardium – thin layer of

tissue that hugs the heart◦B. Parietal pericardium – fibrous outer

layer to protect heart Fluid fills the space between the

layers of pericardium and allows the heart to beat without friction

The Heart: Coverings

3 layers of heart tissue◦Epicardium

Outside layer of connective tissue◦Myocardium

Middle layer made mostly of cardiac muscle This is the layer that actually contracts

◦Endocardium Thin inner layer that lines heart chambers

The Heart: Heart Wall

External Heart Anatomy

The Heart: Chambers· Right and left side act as separate pumps· 4 chambers:

· Atria (2) - Receiving chambers· Right atrium· Left atrium

· Ventricles (2) - discharging chambers· Right ventricle· Left ventricle

Vena cava – deoxygenated blood enters right atrium◦ Superior and Inferior

Pulmonary arteries – deoxygenated blood leaves right ventricle

Pulmonary veins (four) – oxygenated blood enters left atrium

Aorta – oxygenated blood leaves left ventricle

The Heart: Associated Great Vessels

Blood C

irculation

Each of the hearts 4 chambers has its own valve Valves allow blood to flow in only one direction

A. Atrioventricular (AV) valves – located between atria and ventricles

1. Bicuspid or mitral valve (left side) – made of two flaps of endocardium 2. Tricuspid valve (right side) – made of three flaps

B. Semilunar valves – located at the base of two large arteries leaving the ventricles

3. Pulmonary semilunar valve – made of 3 leaflets 4. Aortic semilunar valve – made of 3 leaflets

The Heart: Valves

AV valves are open when the heart is relaxed and blood is passively filling into the ventricles

◦ Held in place by tendon-like cords As the ventricles contract, they press on the

blood in their chambers which closes the AV flaps◦ This prevents backflow into the atria

The semilunar valves then open during ventricle contraction

How they work…

So, does the heart need its own blood for nutrients and oxygen? We know that the heart pumps blood, but

does the heart need blood for itself too? YES! Of course it does

BUT…. Blood in the heart chambers DOES NOT

nourish the myocardium (heart muscle cells)

So where does the heart get blood?

The heart has its own nourishing circulatory system

The blood supply that oxygenates and nourishes the heart is provided by:◦Coronary arteries◦Cardiac veins

Waste products in the blood are then emptied into the right atrium via the coronary sinus

Cardiac Circulation

Intrinsic Conduction System - Heart muscle cells contract, without action potentials, in a regular, continuous way· 1. Sinoatrial node (SA): group

of myocytes in the right atirum that conduct AP’s · Also called the “Pacemaker” –

generator of heart rhythm· 2. Atrioventricular node (AV) –

myocytes located at the junction between the atria and ventricle

The Heart: Conduction System

Heart Contractions

Figure 11.5

3. Bundle of His - a collection of heart muscle cells that transmits AP’s from the AV node to the bundle branches

4. Bundle branches – long muscle fibers that travel down the inner ventricular walls

5. Purkinje fibers – muscle fibers located on the lower ventricular walls that allow the ventricles to contract

The Heart: Conduction System

Heart Contractions

Figure 11.5

Electrocardiograms (EKG/ECG) An interpretation of the electrical activity of the

heart captured and recorded by skin electrodes Three formations:

◦ P wave: impulse across SA node (P)◦ QRS complex: spread of impulse down AV

node (Q), towards Bundle of His (R), down bundle branches, and around ventricles in Purkinje fibers (S)

◦ T wave: end of electrical activity in ventricles

Electrocardiograms (EKG/ECG) (cont.)