Heart Structure and Function Answer Key

The Heart: its structure and function

1. (a) Left ventricle: To pump oxygen-rich blood into the aorta (the systemic circulation).

(b) Right ventricle: To pump oxygen-poor blood into the pulmonary arteries (the pulmonary circulation).

(c) Right atrium:To receive oxygen-poor blood from the vena cavae (from the systemic circulation).

(d) Left atrium: To receive oxygen-rich blood from the pulmonary veins (pulmonary circulation).

(e) Septum: To separate the oxygen-rich blood in the left ventricle from the oxygen-poor blood in the right ventricle.

(f) Coronary arteries: Supply oxygenated blood to the heart muscle.

(g) Coronary vein: Return deoxgenated blood from the heart muscle to the right atrium.

(h) Atrio-ventricular valves:To prevent back-flow from the ventricles into the atria when ventricles contract in systole.

Tricuspid valve. To prevent back-flow of blood from the right ventricle into the right atrium when the ventricle contracts during systole.

Bicuspid (Mitral) valve To prevent back-flow into the left atrium when the left ventricle contracts in systole.

(i) Semilunar valve: There are two semilunar valves:

Aortic valve. To prevent back flow from the aorta into the left ventricle when it relaxes (diastole).

Pulmonary valve To prevent back flow from the pulmonary arteries into the right ventricle when the ventricle relaxes (diastole).

(j) Anterior (superior) vena cava: To carry oxygen-poor blood coming from the head and neck into the right atrium.

(k) Posterior (inferior) vena cava: To carry oxygen-poor blood from the trunk and posterior parts of the body to the right atrium.

(1) Aorta: To deliver oxygen-rich blood from the left ventricle to the systemic circulation.

(m) Pulmonary arteries: To carry oxygen-poor blood from the right ventricle to the lungs for oxygenation.

(n) Pulmonary veins: To carry oxygenated blood from the lungs to the left atrium.

(o) Pulmonary trunk: To carry oxygen-poor blood from the right ventricle into the two (right left) pulmonary arteries.

(p) Chordae tendinae To attach the flaps (cusps) of the mitral and tricuspid valves (atrio-ventricular valves) to the wall of the ventricle and prevent them from inverting then the ventricles contract in systole.

2. Heart Tissue

Location

Function

(a) S-A NODE

(the pacemaker)

In wall of right atrium

To initiate and regulate the heart beat.

(b) A-V NODE

Medially at the base of the right atrium

To relay the impulse from the S-A node to the ventricular walls.

(c) PURKINJE FIBRES

In the walls of the ventricles and inter-ventricular septum

To distribute the impulses from A-V node across the ventricular walls

3. The heart has its own independenet beat and rhythm; thus an isolated (denervated) heart will continue to beat by itself until the heart muscle runs out of oxygen.

4. The S-A node.

Homeostasis: Circulation and Blood Pressure

1. (a) Working through the neurotransmitter adrenalin, sympathetic fibres will stimulate the heart pacemaker and thus increase the heart rate (and cardiac output); selective capillary vasoconstriction will cause a rise in blood pressure.

(b) The reverse of (a): Working through the neurotransmitter acetylcholine (and the vagus nerves) acting on the pacemaker, the heart rate (and cardiac output) will decrease; selective capillary vasodilation will cause a fall in the blood pressure.

(c) Nicotine causes vasoconstriction and an increase in the resistance to blood flow; nicotine also causes an increase in the heart rate; both of these factors cause a rise in blood pressure.

(d) Basically anything which increases the resistance to the blood flow will cause a rise in the blood pressure. With a high salt diet, more water will flow into the (more hypertonic) blood from the tissues (osmosis), thus inreasing the blood volume and resulting in higher blood pressure. With a high-fat diet, cholesterol deposits in the arterial walls (atherosclerosis) will cause a decrease in the size of the arterial lumen, thus raising the resistance and the pressure.

(e) With overweight (obesity) the burden on the heart is increased as it struggles to maintain blood flow through a larger and heavier body; this will increase the blood pressure.

2.(a) The velocity is highest in the arteries and lowest in the veins.

(b) The line oscillates due to the varying pressure and speed of flow during systole and diastole.

(c) The capillaries

(d) Due to the vast total cross sectional area of millions of capillaries.

3. (a) Systole The pumping phase of the cardiac cycle; both ventricles contract, the atria relax (fill).

(b) Diastole: The filling(of the ventricles) phase of the heart; both atria contract and both ventricles relax (fill).

(c) Pulse The recoil of the elastic walls of the arteries resulting from the impact of the blood forced into them by the contration of the ventricles.

(d) Hypertension: Abnormally high blood pressure.

(e) Hypotension: Abnormally low blood pressure.

4. (a)120/80= Normal blood pressure range.

(b) 200/75 = High blood pressure (hypertension).

(c) 80/40 = Low blood pressure (hypotension).

5. A sphygmomanometer is used; in a blood pressure cuff, an air bag is placed over the radial artery in the arm (at the elbow) and inflated. Listening through a stethoscope, you release the pressure on the cuff and listen for the first sound of blood flowing through the artery; the pressure (in mm/Hg) at that point is the systol* pressure. Still listening with the stethoscope and continuing to slowly deflate the cuff, you listen until the sounds of the blood flowing through the artery disappear; that is the diastolic pressure.

Sample Exam Questions

1. To ensure one-way flow of blood towards the heart in the veins and towards the thoracic duct in the lymphatics. The valves shut if the blood or lymph tries to flow backwards.

2. (a) The atria would continue to function but the ventricles would stop pumping.

(b) The heart would stop.

(c) By depriving the heart muscle of oxygen and nourishment the myocardium would cease to function causing what is known as a myocardial infarct, or a heart attack.

(d) The flow of venous blood from the right ventricle into the right atrium when the ventricle pumps (in systole); back-up and increased pressure in the pulmonary circuit.

(e) Normal function of the atrio-ventricular valves (mitral and tricuspid) would be impaired.

3. The autonomic nervous system controls the heart automatically and usually without need for conscious intervention. The sympathetic system is especially important during emergency situations and is associated with "fight or flight." It accelerates the heartbeat, The parasympathetic system, sometimes called the "housekeeper system" promotes all the internal responses we associate with a relaxed state. It retards the heartbeat.