The Circulatory System

• All arteries in the adult human body branch from the aorta, with the exception of the pulmonary artery.
• Most veins that carry blood from the body organs join the inferior vena cava or the superior vena cava, which carry blood to the right atrium.
• Valves exist inside the heart between the atria and ventricles, as well as at the bases of the aorta and pulmonary arteries.
• The cardiac cycle comprises three phases:
  • Diastole (heart relaxation)
  • Atrial systole (heart contraction)
  • Ventricular systole (heart contraction)
• The sinoatrial node, also known as the pacemaker of the heart, consists of specialized self-excitatory cardiac muscle cells in the upper wall of the right atrium that control the rate or pace at which the heart beats.
• The pulse rate, which represents the heart rate, determines how fast the heart beats.
• Pulse indicates the number of heartbeats per minute (bpm).
  • It results from the expansion and relaxation of arteries as blood is pushed through them.
• Blood pressure decreases as blood moves away from the heart.
  • The aorta exhibits the highest blood pressure, while veins have the lowest.
• A sphygmomanometer is the instrument used to measure blood pressure.
• A normal blood pressure for a young adult is about 120/80 mm Hg.
• Listening to the closing of the valves with a stethoscope can assess heart activity.
  • For a more thorough examination, an electrocardiogram test can be carried out.
• The brain sends nervous impulses to the heart's pacemaker during physical activity.
  • This accelerates the heart rate to meet the rising oxygen demands of skeletal muscles and eliminate carbon dioxide buildup.

Blood Circulation

• Blood in the human body passes through the heart twice in one complete cycle, called double circulation.
• The human circulatory system involves two pathways: pulmonary and systemic circulation.
• Deoxygenated blood travels from the heart to the lungs during pulmonary circulation.
  • Systemic circulation transports oxygenated blood from the heart to the body organs.
• Fish have a single circulation system of which blood passes through the heart only once per complete cycle.
• Single circulations have lower blood pressure than double circulations.
  • Blood travels more slowly to body organs in single circulation compared to double circulation.

Blood

• Blood is a tissue composed of different types of cells suspended in plasma, a yellowish liquid.
• Blood plasma contains red blood cells, white blood cells, and platelets.
• Red blood cells, or erythrocytes, are the most prevalent cell type in human blood, and their primary role is to transport oxygen.