Human Circulatory System: Blood, Heart, and Cardiovascular Health

The Circulatory System: Blood and Its Components

Composition of Blood

Blood is a red liquid that constantly circulates through blood vessels. It transports cells, nutrients, and oxygen, while collecting carbon dioxide and other waste products that must be expelled. Blood is formed by plasma and blood cells.

• Plasma: Transports nutrients and supports the blood cells.
• Blood Cells:
  • Red Blood Cells (Erythrocytes): Responsible for oxygen transport.
  • White Blood Cells (Leukocytes): Including neutrophils, monocytes, and lymphocytes, crucial for the immune system.
  • Platelets (Thrombocytes): Essential for blood clotting.

Blood Vessels

Blood vessels form a network of channels that distributes blood throughout the body, comprising three main types:

• Arteries: Carry oxygenated blood away from the heart to all organs and tissues.
• Veins: Carry deoxygenated blood from the organs and tissues back to the heart.
• Capillaries: Microscopic vessels where the vital exchange of substances (oxygen, nutrients, waste) occurs between blood and tissue cells.

Exchange of Substances

Arteries branch into smaller vessels called arterioles, which then lead to the capillaries. It is within the capillaries that the exchange of substances between the blood and the surrounding tissue cells takes place.

The Heart and Blood Circulation

The Heart: The Body's Pump

The heart is a hollow, muscular, and slightly conical organ located in the thoracic cavity, between the lungs. It is surrounded by the pericardium, and its walls are primarily formed by the myocardium (heart muscle).

The heart is divided into four chambers: two upper chambers called atria (auricles) and two lower chambers called ventricles.

How the Heart Works

The myocardium contracts and relaxes rhythmically to pump blood. This rhythmic action defines the cardiac cycle:

• Systole: The contraction phase, when the heart chambers pump blood out.
• Diastole: The relaxation phase, when the heart chambers fill with blood.

Blood Circulation Pathways

The blood pumped by the heart during each systole circulates through arteries, capillaries, and veins in a twofold movement, involving two main circuits:

• Pulmonary Circulation: This circuit carries deoxygenated blood from the heart to the lungs to pick up oxygen, and then returns oxygenated blood to the heart.
• Systemic Circulation: This circuit carries oxygenated blood from the heart to the rest of the body's organs and tissues, delivering oxygen and nutrients, and then returns deoxygenated blood to the heart.

Common Cardiovascular Diseases

Arterial Hypertension

An increase in the pressure exerted by the blood on arterial walls. If maintained over a long period, arterial hypertension can lead to an overload on the heart and blood vessels, increasing the risk of serious health problems.

Varicose Veins

These are inflamed and enlarged veins, most commonly found in the lower limbs. They are often caused by faulty valves within the veins, which prevent efficient blood flow back to the heart. Factors like increased abdominal pressure can exacerbate them.

Stroke (Apoplexy)

A stroke occurs when there is an interruption of blood supply to a part of the brain, leading to brain cell damage. This can be caused by a blockage (ischemic stroke) or a rupture of a blood vessel (hemorrhagic stroke).

Pulmonary Embolism

This condition involves the blockage of one or more branches of the pulmonary artery, typically caused by a blood clot (embolus) that has traveled from another part of the body, often the legs.

Aneurysm

An aneurysm is a localized, sac-like dilation or ballooning in the wall of an artery. It is caused by a weakening of the arterial wall and can be dangerous if it ruptures.

Acute Myocardial Infarction (Heart Attack)

This severe condition occurs due to a partial or total obstruction of one or more coronary arteries, which supply blood to the heart muscle. This blockage deprives a portion of the heart muscle of oxygen, leading to tissue damage or death.