PHYSIOLOGY OF THE HEART
1. The cardiovascular system
2. Structure and function of cardiac muscle
3. Conducting system of the heart
4. Cardiac contraction
5. The cardiac cycle
6. Regulation of heart rate
7. Vascular functions and characteristics
9. Neurohumoral regulation of the vascular system
10. Regional blood flow
11. Lymphatic system
1. The cardiovascular system
The cardiovascular system consists of the heart, blood vessels, and blood. Its primary function is to transport materials to and from all parts of the body. The heart pressurizes blood and provides the driving force for its circulation through the blood vessels. Blood is propelled away from the heart in the arteries and returns to the heart in the veins.
The heart has four chambers. The two atria serve as reservoirs for blood returning to the heart. The two ventricles are pumps that propel blood through the circulation. A septum divides the heart into right and left sides.
The right atrium is the reservoir serving the right ventricle, which pumps blood to the pulmonary circulation via the pulmonary artery. Blood returns from the lungs to the left atrium via the pulmonary veins. The left ventricle propels blood, via the aorta, to all other organs in the body through the systemic circulation.
The right side of the heart propels deoxygenated blood to the lungs, and the left side of the heart propels oxygenated blood to the tissues.
MEDIUM LAYER (MYOCARDIUM)
Output from the left ventricle is distributed at higher pressure through organ systems arranged in parallel.
In the pulmonary circulation, blood normally flows at low pressure and receives the entire output of the right ventricle.
One-way valves between the atria and the ventricles, between the ventricles and their receiving arteries, and within the systemic veins ensure that blood flows in one direction around the circulation.
2. Structure and function of cardiac muscle
Atria and ventricles are composed of cardiac muscle cells, together with supporting connective tissue.
Cardiac muscle is striated and has an intracellular sarcomere structure that is very similar to that of skeletal muscle. Сardiac muscle cells (myocytes) form a highly branched network.
Myocyte connections occur at structures called intercalated disks.
The presence of gap junctions in intercalated disks accounts for high electrical conductance (low resistance) between myocytes.
A single adequate stimulus for action potential in one myocyte results in the rapid spread of excitation to all myocytes via gap junctions.
This is known as the all-or-none electrical response of the heart.
The all-or-none electrical response of the heart
