Study guide chl 18 Heart

Preload:

is the degree of stretch, or tension, on the muscle fibers when they begin to contract.

6. Describe the sequence of excitation throughout the heart. What happens when there are defects in this sequence?

Action potentials that originate in the SA node spread to the myocardial cells of the atria through gap junctions between cells. Depolarization of the atria stimulates contraction of the atrial myocardium. Action potentials cannot directly spread from the atrial myocardium to the ventricular myocardium due to the presence of the non-conducting fibrous skeleton that separates them. Rather, the impulse travels to the ventricles through a system of specialized cells called the conduction system.

9. What is cardiac output?

Cardiac output is the amount of blood the left ventricle pumps into the aorta per minute. This is a systolic event. The stroke volume times the number of cardiac cycles per minute (heart rate) equals the cardiac output.

What two things affect cardiac output?

Cardiac output varies directly with Stroke Volume and HR. CO increases when the stroke volume increases or the heart beats faster or both, and it decreases when either or both of these factors decrease.

12. What happens when any of these mechanisms are imbalanced?

Congestive heart failure occurs when the pumping ability of the heart cannot provide adequate circulation to meet body needs. Right Heart failure leads to systemic edema; left heart failure results in pulmonary edema.

Blood pathway Superior Vena cava to the pulmonary veins

Deoxygenated blood enters the right atrium through the superior vena. From the right atrium through the tricuspid valve to the right ventricle. Through the pulmonary semilunar valve to the pulmonary trunk then to the pulmonary arteries to the lungs; in the lungs the blood pass through the pulmonary capillaries, and is oxygenated. It returns to the heart via the four pulmonary veins.

Diastole?

Diastole is relaxation of the muscle. 1. Ventricles relax 2. pulmonary and aortic valves close 3. AV valves open 4. ventricles fill (about 80% of capacity) 5. atria contract (ventricles fill another 20%

5. What is the coronary circulation?

Is the shortest circulation in the body. It provides blood supply of the heart. The coronary arteries originate from the left side of the heart at the beginning of the aorta, immediately above the aortic valve. Coronary arteries run both along the surface of the heart and deep within the myocardium. Epicardial coronary arteries, which run along on the surface of the heart, are capable of autoregulation to maintain coronary blood flow at appropriate levels to fit the needs of the heart muscle.

blood pathway From the pulmonary veins to systemic capillaries

Oxygenated blood returns to the heart via the pulmonary veins to the left atrium. From the left atrium through bicuspid valve to the Left ventricle. Through the aortic semilunar valve to the aorta. The aorta branches into other arteries, which then branch into smaller arterioles. The arterioles meet up with capillaries (in the body tissue= systemic circuit), which are the blood vessels where oxygen is exchanged for carbon dioxide. Poor oxygenated blood returns from the body tissue back to the heart.

10. What are three things that affect cardiac stroke volume?

Preload: Afterload: Contractility:

3. What are the valves that separate the atria and the ventricles?

Sheets of tough connective tissue that act like flaps. They ensure a one-way flow of blood through the heart. When pressure is greater behind the valve, the leaflets are blown open and the blood flows through the valve. However, when pressure is greater in front of the valve, the leaflets snap shut and blood flow is stopped.

What is the coronary circulation?

Subendocardial coronary arteries run deep within the myocardium to provide oxygen throughout the thickness of the cardiac wall. In systole, the ventricular myocardium contracts, generating high intraventricular pressure and compressing the subendocardial coronary vessels, but allows the epicardial coronary vessels to remain patent. With the subendocardial coronary vessels compressed, blood flow essentially stops below the surface of the myocardium. In diastole, the ventricular myocardium contracts, lowering the intraventricular pressure and allowing the subendocardial vessels to regain patency. Due to the high pressures generated in the ventricular myocardium during systole, most myocardial perfusion occurs during diastole.

11. Describe the three ways that the heart rate can be regulated

Sympathetic Nervous System: when activated increase HR and contractility. Parasympathetic Nervous System: Decreases HR; has little effect on contractility. Chemical regulation: is affected by hormones (epinephrine and thyroxine) and ions (particularly potassium and calcium). Ion imbalances severely impair heart activity. Other factors: age,sex, exercises, and body temperature.

. What is systole?

Systole is contraction of the muscle. The contraction and relaxation of the ventricles are normally described with the terms systole and diastole. Contraction of heart. 1. ventricles contract 2. AV valves close 3. aortic and pulmonary valves open 4. blood is ejected 5. atria relax and fill with blood

What is the left side of the heart responsible for?

The Left side pump the oxygenated blood out to the rest of the body supplying the fuel that the body cells need to function.

1. What is the right side of the heart responsible for?

The right side of the heart (RA and RV) receive poor oxygenated blood from the body and pump it to the lungs, where the blood cells pick up fresh oxygen. This oxygenated blood is then returned to the left side of the heart (LA and LV).

What are the semilunar valves?

The semilunar valves (pulmonary valve and aortic valve) are one-way valves that separate the ventricles from major arteries. The aortic valve separates the left ventricle from the aorta, while the pulmonary valve separates the right ventricle from the pulmonary artery.

The epicardium

is a thin layer of connective tissue and fat, and serves as an additional layer of protection for the heart, under the pericardium.

The endocardium

is composed of endothelial cells which provide a smooth, non-adherent surface for blood collection and pumping and may help regulate contractility.

Afterload:

is the load or amount of pressure the left ventricle must work against to eject blood during systole and corresponds to the systolic pressure. The greater the resistance is, the greater the heart's workload. Afterload is sometimes called systemic vascular resistance.

The myocardium

is the middle layer of the heart, composed of cardiac muscle cells called cardiomyocytes, which contract like other muscle cells, but also conduct electricity to coordinate contraction. Myocardium makes up the majority of the thickness and mass of the heart wall and is the part of the heart responsible for pumping blood.

Contractility:

is the ventricles' ability to contract, which is determined by the degree of muscle fiber stretch at the end of diastole. The more the muscle fibers stretch during ventricular filling, up to an optimal length, the more forceful the contraction.

Be able to describe the pathway of the blood through the heart and the pulmonary and systemic circuit.

pag.675 text book: The left side of the heart is the systemic circuit pump. The right side is the pulmonary circuit pump. Right atrium to right ventricle to pulmonary arteries to lungs (pulmonary circuit pump); pulmonary veins to left atrium to left ventricle to aorta to body tissues to venae cavae (systemic circuit pump).