Final answer:
The human heart, located in the thoracic cavity, is about the size of a fist and consists of four chambers. It functions due to the unique properties of cardiac muscle and a specialized conduction system, with its activity recordable by electrocardiogram.
Step-by-step explanation:
Anatomy of the Heart
The human heart is located within the thoracic cavity, medially between the lungs in the space known as the mediastinum. It is encased in a protective sac called the pericardium and resides in the pericardial cavity. The heart's size is comparable to an individual's fist, with dimensions of about 12 cm in length, 8 cm in width, and 6 cm in thickness. The weight of the heart varies between genders, with female hearts weighing approximately 250-300 grams and male hearts weighing about 300-350 grams. These measurements can be significantly greater in well-trained athletes due to cardiac hypertrophy, which is an increase in muscle size without an increase in cell number.
The human heart comprises four chambers: two atria and two ventricles. The atria receive blood and the ventricles pump blood either to the lungs or to the rest of the body. Blood flows into the heart through veins to the atria, from the atria to the ventricles, and then is pumped out via the arteries. The cardiac cycle involves the contraction (systole) and relaxation (diastole) of the chambers.
Cardiac muscle is distinct from skeletal and smooth muscle. It has unique properties that enable the heart to function continuously and rhythmically. This muscle type has a specialized conduction system that initiates and coordinates contractions, ensuring efficient blood flow throughout the body. The heartbeat is controlled by electrical impulses, which are recorded by an electrocardiogram (ECG), a test used to assess heart health and function.