Cardiovascular System at Rest

Structure of the Heart

The heart is a muscular organ, roughly the size of a fist, located in the chest, between the lungs.
It is divided into four chambers: the left and right atria (upper chambers) and the left and right ventricles (lower chambers).
Valves within the heart ensure the blood flows in one direction. There are four valves: tricuspid, pulmonary, mitral (bicuspid), and aortic valves.
The septum is a wall of muscle that divides the left and right sides of the heart.

The de-oxygenated blood from the body enters the heart through the superior and inferior vena cava and flows into the right atrium.
The right atrium contracts, sending blood to the right ventricle through the tricuspid valve.
The right ventricle contracts, pumping blood to the lungs via the pulmonary artery.
In the lungs, the blood picks up oxygen becoming oxygenated, and returns to the left atrium of the heart via the pulmonary veins.
The blood then moves into the left ventricle through the mitral valve, and is pumped to the body through the aorta, the largest artery in the body.

Resting heart rate refers to the number of heartbeats per minute while the body is at rest. A normal adult resting heart rate ranges from 60 to 100 beats per minute.
Blood pressure is the pressure of blood against the walls of the arteries, and is typically lower at rest than during exercise.
Normal resting blood pressure is below 120/80 mmHg - the first number, the systolic pressure, measures the pressure in the arteries when the heart beats, while the second number, the diastolic pressure, measures the pressure in the arteries when the heart rests between beats.

Blood delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from the same cells.
Blood contains red and white blood cells, and platelets, suspended in a liquid called plasma.
Red blood cells contain haemoglobin that binds oxygen and carries it from the lungs to the tissues.
White blood cells are the cells of the immune system and function in defending the body against both infectious diseases and foreign materials.
Platelets are responsible for blood clotting which prevents excessive bleeding.

Arteries carry blood away from the heart. Most arteries carry oxygenated blood with the exception of the pulmonary and umbilical arteries.
Veins carry blood to the heart. Most veins carry deoxygenated blood from the tissues back to the heart with the exceptions being the pulmonary and umbilical veins.
Capillaries connect arteries to veins and facilitate the exchange of oxygen, carbon dioxide, and other substances between blood and tissues.