Human Circulatory System: Structure, Function, and Components

The Human Circulatory System

The circulatory system is responsible for the distribution of nutrients and oxygen throughout the body.

The elimination of carbon dioxide is primarily handled by the respiratory system, with the circulatory system transporting CO2 to the lungs.

Functions of the Circulatory System

• Distribute the nutrients from food and oxygen throughout the entire organism.
• Collect waste substances produced by cellular metabolism and transport them to the excretory organs.

Components of the Circulatory System

Blood

Blood is a red, viscous, and saline liquid which flows within blood vessels.

Blood Vessels

Blood vessels form a network of tubes through which blood circulates. These include arteries, arterioles, capillaries, venules, and veins.

Arteries

• Walls: Thick, elastic, and designed to support high pressure.
• Circulation: Carry blood from the heart to the organs.
• Branches: Arteries branch into arterioles, which then lead to capillaries.

Veins

• Walls: Not as thick or elastic as arteries, with a larger diameter.
• Circulation: Carry blood from the organs back to the heart.
• Branches: Capillaries merge into venules, which then form veins.
• Special Feature: Contain valves in their interior to prevent the backflow of blood.

Capillaries

• Diameter: Very thin and microscopic in size.
• Circulation: They reach all body tissues.
• Function: Inside, there is the exchange of nutrients, oxygen, and waste products (like carbon dioxide) between blood and tissues.

The Heart

The heart is a muscular organ, approximately the size of a clenched fist.

Heart Location

Located in the middle of the thoracic cavity, slightly to the left side and between the lungs.

Heart Function

Its primary function is pumping blood to the entire body.

Heart Layers

1. Pericardium: The outermost layer, a double-walled sac that encloses the heart.
2. Myocardium: The middle layer, a thick layer of contractile muscle tissue whose contractions propel the blood.
3. Endocardium: The innermost layer, connective tissue that lines the inner cavities of the heart and forms the valves.

Heart Valves

The heart contains several valves to ensure unidirectional blood flow:

• Atrioventricular Valves:
  • Tricuspid Valve (Right Side): Formed by three leaflets.
  • Bicuspid or Mitral Valve (Left Side): Formed by two leaflets.

Interventricular Septum

This muscular wall prevents the mixing of oxygen-rich blood (on the left side) and oxygen-poor blood (on the right side).

Major Blood Vessels Connected to the Heart

Vessels Arriving at the Heart

• Pulmonary Veins: Four veins (two from the right lung and two from the left) that arrive at the left atrium, carrying oxygenated blood from the lungs.
• Vena Cavae: Two large veins that arrive at the right atrium, carrying deoxygenated blood from the body:
  • Superior Vena Cava: Brings blood from the superior part of the body (head, neck, arms).
  • Inferior Vena Cava: Brings blood from the inferior part of the body (trunk, legs).

Vessels Exiting the Heart

• Pulmonary Artery: Exits from the right ventricle and later divides into two branches, one for each lung, carrying deoxygenated blood to the lungs.
• Aorta: Exits from the left ventricle and carries oxygenated blood to all parts of the body. It forms the aortic arch, a curvature backwards to the left.

Coronary System

The coronary system consists of blood vessels that specifically irrigate the heart muscle itself, providing it with oxygen and nutrients.