Heart Structure and Function

[The heart is a cone-shaped, muscular organ about the size of a fist. It is located in between the lungs directly behind the sternum. The major portion of the heart is the myocardium (cardiac muscle) The heart lies within the pericardium, a sac which contains a small quantity of lubricating liquid. The heart has 4 chambers: 2 upper, thin walled atria and 2 lower thick walled ventricles.

Identify and give functions for each of the following:

- left and right atria - The left atrium sends blood through an atrioventricular valve to the left ventricle. The right atrium atrium sends blood through an atrioventricular valve to the right ventricle.

- left and right ventricles - the left ventricle sends blood throught the aortic semilunar valve into the aorta to the body. The right ventricle sends blood throught the pulmonary semilunar valve into the pulmonary trunk and the pulmonary arteries to the lungs.

- coronary arteries and veins - Important part of the systemic circuit they serve the heart muscle itself. The coronary areteries are the first branches off the aorta. The coronary capillary beds on the exterior of the heart join to form venules. The venules converge to form cardiac veins which empty into the right atrium.

- anterior (superior) and posterior (inferior) vena cave - both carry deoxygenated blood (low O2 high CO2) to the right atrium. Superior collects from the head chest and arms. Inferior collects from the lower body regions.

- aorta - The path of the systemic blood to any organ in the body begins in the left ventricle, which pumps blood into the aorta.

- pulmonary arteries and veins - Pulmonary arteries carry deoxygenated to the lungs from the heart. Pulmonary veins carry oxygenated blood to the heart from the lungs.

- pulmonary trunk - Blood from all regions of the body first collects in the right atrium and then passes into the right ventricle, which pumps it into the pulmonary trunk. The pulmonary trunk divides into the pulmonary arteries to each lung.

- atrioventricular valves - The valves between the atria and ventricles. Supported by strong fibrous strings called chordae tendineae that prevent the valves from inverting. Prevent the backflow of blood into the atria after it has entered the ventricle.

- chordae tendineae - that prevent the atrioventricular valves from inverting

- semi-lunar valves - between the ventricles and their attached vessels. The pulmonary semilunar valve lies between the right ventricle and the pulmonary trunk. The aortic semilunar valve lies between the left ventricle and the aorta.

- septum - A wall that seperates the heart into a right side and a left side



Describe the location and functions of the SA node, AV node, and Purkinje fibres

The SA (sinoatrial) node is found in the upper dorsal wall of the right atrium. The AV atrioventricular) node is found in the base of the right atrium very near the septum. The purkinji fibres are small and numerous and extend from two large fibres that carry a signal from the AV node through the walls of the ventricles. The SA node initiates the heartbeat and automatically sends out an excitation impulse every 0.85 seconds causing the atria to contract. When the impulse reaches the AV node, the AV node signals the ventricles to contract by sending the signals to the purkinje fibres. Because the SA node keeps the heartbeat regular it is called the pacemaker

Describe the autonomic regulation of the heartbeat by the nervous system

The autonomic nervous system, a part of the peripheral nervous system, is made up of motor neurons that control the internal organs automatically and usually without need for conscious intervention.

There are two divisions of the autonomic nervous system: the sympathetic system and the parasympathetic system.

The sympathetic system is especially important during emergency situations and is associated with "fight or flight." It inhibits the digestive tract, but it dilates the pupil, accelerates the heartbeat, and increases the breathing rate.

The parasympathetic system, sometimes called the "housekeeper system" promotes all the internal responses we associate with a relaxed state. It promotes digestion of food, causes the pupil of the eye to contract and retards the heartbeat.

Distinguish between systolic and diastolic pressures

Systole refers to the contraction of the heart muscle and diastole refers to relaxation of the heart muscle. The heart contracts (or beats) about 70 times per minute each beat lasting about 0.85 sec. Normally the pulse rate indicates the heart rate because the arterial walls swell with the surge of blood every time the left ventricle contracts and then immediately contract.

Systolic pressure (the highest arterial pressure) is reached during ejection of blood from the heart.

Diastolic pressure (the lowest arterial pressure) is ocurs while the heart ventricles are relaxing.

Normal resting blood pressure for a young adult is said to be 120/80. The higher number is the systolic pressure in mm Hg the lower number is diastolic pressure.

Demonstrate the measurement of blood pressure

Blood pressure is the pressure of blood against the wall of a blood vessel. A sphygmomanometer is used to measure blood pressure. To read someones blood pressure place the cuff two finger widths above the bend in the elbow. The brachial artery (which you want to listen for is just to the inside of center above the bend in the elbow. Find it by using your fingers to find a pulse. You should then position the stethoscope before inflating the cuff. Inflate the cuff with to about 160 mm Hg. Remember to close the air valve before pumping the bulb. Listetning in the stethoscope you will hear no sound because the artery is closed by the pressure of the cuff. Listen as you gradually release the pressure by opening the valve on the inflation bulb. Record the pressure reading the instant you begin to here a sound. This is the systolic pressure. The sound is the artery opening and closing. Keep releasing the pressure gradually and record the pressure reading the instant there is again no sound. This is the diastolic pressure. No sound is heard because the artery is open. Normal resting blood pressure for a young adult is said to be 120/80. The higher number is the systolic pressure in mm Hg the lower number is diastolic pressure.

Relate factors that affect and regulate blood pressure to hypertension and hypotension

Hypertension - high blood pressure. 160/95 or above in women

130/90 or above in men under age 45

140/95 or above in men beyond age 45

Diastolic pressure is emphasized when medical treatment is being considered.

Two controllable behaviors contribute to hypertension. Smoking cigarettes and obesity.

Hypertension is also seen in individuals who have artherosclerosis. Artherosclerosis is an accumulatation of soft masses, particularly cholesterol, beneath the inner linings of the arteries. These deposits called plaque tend to protrude into the vessel and interfere with blood flow. To prevent the onset and development of artherosclerosis doctors recommend a diet low in saturated fat and cholesterol.

A stroke occurs when a portion of the brain dies due to a lack of oxygen.

A heart attack occurs when a portion of the heart muscle dies because of a lack of oxygen.

[Check out figure 12.18 on page 216 if you have ever wondered what a coronary bypass operation entails.]