The Heart

Location: the heart is located centrally, but 2/3 of the heart lies left of the midline. The lungs protect the heart, because the heart in enveloped by them. The sternum protects the heart as well and the heart lies against it.

The Heart's Coverings:

• Fibrous Pericardium-helps restrict the heart's movement.
• Serous Pericardium-is the ballon-like covering that the heart rests in. It it made up of two layers, the visceral pericardium and the parietal pericardium..
• Fluid between the visceral and parietal pericardium provides lubrication and prevents friction of the heart as its beating its 37 million beats/year.

Pericardial Layers of the Heart: Okay, so you know the order the layers go for muscle and bone coverings right? Well, it's the same order for these as well.

1. Epicardium-visceral layer of the pericardium.
2. Myocardium-the actual cardiac muscle.
3. Endocardium-lining of the chambers of the heart.

*The heart also has some fibrous connective tissue, which give the heart its "skeleton."

Blood Flow

1. Blood flows into the right (R) atrium from the superior vena cava (top of the body), inferior vena cava (bottom of the body), and the coronary sinus (from the coronary veins).
2. Blood flows through the tricuspid valve into the right ventricle.
3. As the R-ventricle contracts, the chordae tendinae and papillary muscles keep the tricuspid valve closed.
4. Blood flows from the R-ventricle, through the pulmonary semilunar valve, and out through the pulmonary trunk.
5. The pulmonary trunk splits into the pulmonary arteries, which take the blood to the lungs.
6. Oxygenated blood comes back from the lungs via the pulmonary veins, and into the left (L) atrium.
7. Blood flows from the L-atrium through the biscuspid/mitral/L-AV valve, and into the L-ventricle.
8. Blood flows from the L-ventricle out through the aortic semilunar valve and enters the ascending aorta.
9. The ascending aorta has three branches at the top: brachiocephalic (which branches into the R-common carotid and r-subclavian), L-common carotid, and L-subclavian. The aorta then curves downward, and any blood going to the lower portion of the body enters the descending aorta.

Okay, that might seem kinda wordy, so I'll put the blood flow through the heart like this as well. Hopefully this makes sense to some people too. We'll start with blood coming from the body into the heart.

Superior Vena Cava, Inferior Vena Cava, Coronary Sinus --> R. Atrium --> Tricuspid Valve --> R. Ventricle --> Pulmonary Semilunar Valve --> Pulmonary Trunk --> Pulmonary Arteries --> Lungs --> Pulmonary Veins --> L. Atrium --> Bicuspid Valve --> L. Ventricle --> Aortic Semilunar Valve --> Aorta

Fetal Structures: there are a couple of structures that are found in the fetus that are not found or have changed in the adult.

• Foramen ovale-this is a hole that shunts blood from the R-atrium to the L-atrium. In the adult, it is called the fossa ovalis.
• Ductus arteriosis-this is an arteric shunt that bypasses the lungs. In the adult, it is the ligamentum arteriosum, which connects the pulmonary trunk to the aorta.
• Ductus Venosus-shunts blood past the liver (past the hepatic portal vein.
• Umbilical arteries-take deoxygenated blood from the baby to the placenta.
• Umbilical veins-take oxygenated blood from the placenta to the baby.

Electrical Pattern of Stimulation

1. Sinoatrial (SA) Node starts an action potential to both atria. Result: atria contract. The SA node is the pacemaker of the heart, which beats about 75 bpm in an average adult.
2. Atrioventricular (AV) Node slows the signal from the SA node just a little bit.
3. AV node passes the signal to the AV Bundle (Bundle of HIS), which takes the signal to the interventricular septum.
4. Once in the interventricular septum, the signal passes to the L and R bundle branches, which wrap around each ventricle.
5. The signal is then passed to the Purkinje fibers, and the ventricles contract.

Website Links

Heart and Blood Flow Quizzes

• http://www.gen.umn.edu/faculty_staff/jensen/1135/webanatomy/wa_cvs/default.htm

Pig Heart Dissection

• http://www.delta.edu/dmknox/Systempages/web.circ/lPigpicsalbum/index.htm

Heart Anatomy Review

• http://www.wisc-online.com/objects/index.asp?objID=NUR1403